Dôme des Invalides

Figure 1: Les Invalides aerial view

Structure Information

Les Invalides, is the complex that houses the Dôme des Invalides. It was proposed by King Louis XIV on November 24th, 1670 as a home and hospital for elderly and sick war veterans. Before the King’s preposition, an establishment that served to accommodate elderly and disabled solders did not exist. The French Parliament funded this project under the King’s command and handed it over to War Minister Louvois, who appointed Libéral Bruant as the architecture of the project. During the completion of Les Invalides in 1676, the complex had fifteen courtyards and was largest court of honor for military parades.

A couple years later construction began on a chapel where the King and the solders could hear the mass in communal.  Due to protocol and decorum issues, the chapel was never completed as planned. As a result, the Minister of War appointed Jules Hardouin-Mansart to take over the architecture of the project. He decided to divide the church into two sections, one section purely solders and the other the royal church. The section of royal church incorporated a marvelous dome, the Dôme des Invalides, which is now the one of the major features of the complex. Jules Hardouin-Mansart completed the chapel in 1679 with the assistance of the notable Libéral Bruant in his last years. The gold-plated dome, which rises above the entire complex was completed in 1706.

By the end of the 17thcentury more than 4000 residents lived in the Les Invalides ruled in the same way as monasteries and barracks, with the solders being divided into companies where they were given tasks. The severely injured and disabled were taken care of in the hospital which was located in the South East section of Les Invalides. This hospital is actually still active today acting as hospital and retirement home for war veterans. This is amazing because the building still serves its original purpose.

Historical Significance

This building was built during the late 1600’s before the construction of Christopher Wren’s noteworthy St. Paul’s Cathedral. Domes during this time faced issues with load transfer from the dome to the walls of the structure supporting the dome. The walls could not support the tremendous load applied by the dome, resulting in the deformation of the entire structure. As a result, Jules Hardouin-Mansart with the assistance of Libéral Bruant incorporated double column buttresses in their design to resolve this issue. This idea was used in the structural design of many future domed structures after Dôme des Invalides. The idea of a three-part dome, as a solution to the tremendous load applied by the dome onto the walls of the structure was not until Christopher Wren’s St. Paul’s Cathedral in the early 1700’s.

The building that Dôme des Invalides rests on is elegant and symmetrical. The curve of the dome is offset by a straight angle of the building its supported by. As a result, the dome appears sits on the building like a crown. Besides the lantern on top the dome, the façade of Dôme des Invalides appears to be entirely symmetrical, evenly distributing the load path of the dome onto the buttresses.

Cultural Significance

Because Les Invalides was largest court of honor for military parades during its time, it was also a target during the French Revolution. On July 14th, 1789 Les Invalides was invaded by Parisian rioters who seized cannons and muskets stored in its cellars. The same cannons and muskets were used against the Bastille, which was a fortress in Paris known for its important role in internal affairs and a state prison, later the same day.

The First Consul of Paris ordered the installation Turenne’s tomb, under the Dôme in 1800 and dedicated a funeral monument to Vauban in 1808 opposite from Turenne’s tomb. Henri de La Tour d’Auvergne Viscount of Turenne better known as Turenne was a French Marshal General and one of the greatest generals in history. Sébastien Le Prestre de Vauban was French military engineer who served the King and was commissioned as a Marshal of France. During his time, he was a leading engineer because of his skills and innovation.

In 1846, the crypt of Les Invalides, which is located directly under the Dômewas prepared to receive Napoleon I’s tomb. On May 5th, 1821 Napoleon I died on the island of St. Helena, where he was exiled since 1815. He was buried near a spring on the island until 1840, when King Louis-Philippe decided to transfer his body. Napoleon was entombed with an honorable ceremony during his transfer. Napoleon Bonaparte was a French statesman and military leader who become notably prominent during the French Revolution. He dominated European and global affairs while leading France against a series of confederacies in the Napoleonic War.

The vault of the church is decorated with flags and trophies that were taken from French enemies. These flags and trophies were originally hung from the vault at the Norte Dame Cathedral until the French revolution. After the French revolution, the items that survived were transferred to Les Invalides in 1793. Today showcasing of these flags and trophies are positioned on the cornice of the church, showing the military history of France from 1805 up until the 20thcentury.

Today Les Invalides is a historic museum that exhibits the tombs of the many important people to France. It also serves as a hospital for injured and disabled war veterans. This is remarking because it still serves its original purpose from so many year ago. In 1989 the dome went under construction. Major renovations were done with the efforts of embellishment. These renovations ended up using 12kg of gold and restoring paint on the underside of the dome. Although the costs of these renovations seemed a lot, the people of France did not mind. They adore this building for its rich history, and culture, along with the beauty and elegance its brings the to the skyline of Paris.

Figure 2: Napoleon I’s tomb

Structural Art

The evaluation of structural art depends on the equal use of the three E’s according to Billington: efficiency, economy, and elegance. The goal of efficiency and economy is to design a structure that uses the least amount of material, and money. The efficiency of the structure has to carry on even after the construction of structure is completed. This means that any repairs the structure may need as a result of initial design goes against efficiency in the terms how long the structure successfully performed its function without the adding of new material. It would also go against economy in terms of the money spent in structural repairs. As for elegance, the structure must be aesthetically pleasing, while defining its engineered structures and creativity.

The Dôme des Invalides seems to be efficient in the aspect of longevity. It has not needed a lot of repairs other than for embellishment. The materials used to create the structure were efficient for its time period. Although now structures made from masonry, where reinforced concrete can be used are not considered to be efficient. Likewise, the Dôme des Invalides seems to be economic because money did not have to be put into construction of structural repairs, and overall the building is socially accepted, attracting many Paris tourists. The Dôme des Invalides is extravagantly beautiful and aesthetically pleasing. The Dôme is wrapped in gold leaf and towers over much of Paris’s skyline. It also showcases its engineering creativity with its symmetry. Therefore, according to Billington the Dôme des Invalides exemplifies structural art.

Figure 3: Exterior view of Les Invalides

 

Structural Analysis

Basic design principles and assumptions of arch analysis were applicable to the analysis of masonry domes during this time period. Different methods, like equilibrium and elastic methods, were developed to analysis masonry domes. Equilibrium methods rely on the domes geometry and self-weight to determine its stability, while elastic methods use material strength to determine force. Both methods determine the primary internal forces of the dome, meridional force and hoop force. The Dôme des Invalides is made of brick, and the exterior is wrapped in gold leaf. Domes during this time faced issues with the transfer of the tremendous weight from the dome onto the walls of the structure. As a result, such as double-columned buttress was employed in order to be able to support the entire load of the dome. The golden dome itself is topped with a lantern that measures 107 meters in height making it one of the tallest structures in Paris.

Load Path

The lantern of the structure transfers its self-weight down to the gallery which then transfers its load to the hemisphere of the dome. The dome distributes this load into the walls of the structure which are supported by buttresses. These double-columned buttress take the entire load of the dome and transfer is down into the ground of the structure.

Analysis

Diameter of dome: 114 ft (assumption) => Radius of dome: 57 ft (assumption)

Density of Brick: 115 lb/ft3(researched)

Thickness of dome: 18 inches or 1.5ft (researched)

Surface area of the dome: 20414.07 ft2

I assumed the measurement of the diameter of the dome based on the ratio of the entire height of the building, which was given from my research, to the measured length of the diameter on google maps. I used to google maps to establish this ratio by measuring the height and comparing it to the diameter forming a ratio. I assumed the dome to be a perfect hemisphere. I based this assumption on my research which stated the to be dome be symmetrical. Also just by looking at it, it looked symmetrical. As a result the radius of the dome is half the diameter throughout the dome, making the height of the dome equal to the radius.

Both the Meridional Forces and the Hoop force are in compression because meridional forces are like arches and are always in compression and we can assume the angle for the hoop force is less than 51.8 degrees, so it is also in compression.

As far presentation to stakeholders for the construction of this structure, there were none. The construction of this structure was a command from the King. As far the design, it did not have to be negotiated either because the architect was appointed so whatever he design was relatively what was going to be built. The only thing that may be changed was the appointment for a new architect, during the construction of the church which supports the Dome. This was a result of the original architects old age.

Personal Response

I spotted this structure from the second level of the Eiffel Tower during the Tour. It was so beautiful amongst the skyline of Paris. I asked around to see if anyone know what the structure was, but nobody seemed to know. Not too long after the tour guide started talking about the structure. I immediately listened in to find out it was the Dôme des Invalides. I was astonished with its history and the fact that it still fulfills its original purpose. Honestly if I had just read about this structure, I probably wouldn’t have been as interested. The gold glistening in the skyline is what really caught my attention.

References

http://www.eutouring.com/history_of_les_invalides_paris.html

https://www.britannica.com/place/Hotel-des-Invalides

http://www.musee-armee.fr/en/collections/museum-spaces/dome-des-invalides-tomb-of-napoleon-i.html

 

Westminster Bridge

Structure Information

The current Westminster Bridge was constructed from 1854 to 1862 to replace the old Westminster Bridge after the old bridge started showing signs of decay. The bridge spans the River Thames to connect Westminster and Lambeth, and it directly connects to the Houses of Parliament. Thomas Page designed the bridge with consulting from Sir Charles Barry, costing £400,000 for the Westminster Bridge Commissioners and a parliamentary grant. 

Figure 1 – Picture by Me

 

Historical Significance

There were a couple of features of the bridge that were significant in the world of bridge engineering. First, the construction process was very significant, as the technique of using caissons was used for the first time on a large scale. Also, at the time it opened, the bridge was one of the first to use Robert Mallet’s buckled plates as decking material. The plates had just been patented in 1852, and at the time they were the best combination of maximum strength and minimum weight. Later on, the plates were replaced by the more efficient reinforced concrete. Besides moving the caisson technique forward for bridge building, the bridge itself did not have much impact on future bridges, as its design did not necessarily push the boundaries of engineering.

Cultural Significance

The bridge was created during the Victoria Era and officially opened on May 24th, 1862 at four in the morning—Queen Victoria’s birthday and time off birth. Since the Brits are so into their royalty, this is probably a big deal to them, but I couldn’t care less. Moving on to actually important things, the biggest cultural impact of the bridge is that it connects the South Bank area of London to the political center of the city—Westminster. The city of London was rapidly expanding at the time, so the South Bank area was becoming more populated, and the city desperately needed a connection between these two areas. Even though this problem was solved by the original bridge, the current bridge continues to symbolize the unity and integration of these two important cultural centers. I think of the importance of the bridge the same way as I see the function of the bridges that cross I 75/85 in Atlanta. There is already a big contrast in the two “halves” of the city with the bridges in place. Without those bridges, the city would suffer in the areas of cultural unity, transportation, and business.

Structural Art

If I’m being honest here, the bridge is really just okay. There’s not really anything special about it structurally or visually, but it does have some elements of structural art. In terms of efficiency, the bridge has been used for over 150 years, so it is doing its job well. Though it has been standing for so long, I believe there could have been a more efficient design. There are seven spans for only 820 feet of length, so if a more intelligent design was applied the bridge could have performed equally well with less structural members. This observation also affects economy, which would have also improved if less materials were used. A positive note on economy is that money was saved when the first half of the new bridge was built upstream and put into use before the second half was built on the site of the old bridge. This construction technique was a great creative solution to cut cost. When analyzing elegance, it is fairly easy to visualize the load path in the design. The arches and piers are all very visible, and load can be traced from the deck to the foundations of the piers. There is some decoration between the arches and deck, which looks like convoluted spandrels, but it really just serves aesthetic appeal. Billington would believe that the elegance of the bridge is compromised by this design choice, but he would most likely applaud the overall simplicity. Overall, the design is really not innovative or creative enough to be considered elegant, and the bridge does not excel enough in economy or efficiency to be considered structural art.

Structural Analysis

Many of the construction processes used for the bridge were very creative. The foundations were laid in caissons, cavities were dug in the bed of the river for the reception of the caissons, and the piers were built directly on to the soil and not on piles. As mentioned before, this was the first time caissons had been used on a project of this scale, so it took a lot of creativity on the part of Page and Barry. The construction of the bridge itself included building half of the bridge upstream, putting it to use, and building the second half on the site of the old bridge. This process was used to save money by not building a temporary bridge. Money was also saved by using Portland stone from the remains of the old bridge.

The bridge has seven semi-elliptical spans—the central is 130 feet wide, the next two spans are 125 and 115 feet, and the ones adjacent to the abutments are 100 feet wide. The roadway is 58 feet wide and 13 foot footpaths run along each side. The abutments provide the horizontal reactions that counteract the thrust of the outer arches. Speaking of thrust, the bridge uses a repeated arch design, which allows all the thrust forces in each arch to be canceled by the adjacent arch, except for the arches interacting with the abutments. This feature of thrust cancellation can be visualized in the load path of the bridge (Figure 2), and the vertical forces of the bridge are transferred through the piers and into the foundations in the river.

Figure 2 – Load Path

 

To calculate the reactions from the piers and the abutments I had to come up with a model load. If an average car is assumed to be 4,000 lbs and a car takes up an area of 5×10 feet, then I assumed this load is distributed across the entire bridge at 80 lb/ft2. Using this distributed load, I calculated the reactions in the piers and abutments (Figure 3).

Figure 3 – Calculations

 

What was most interesting to me was the comparison of the horizontal reactions to the vertical reactions. While the vertical forces are distributed across eight reactions instead of two, it is still surprising to see how much force must be provided by the abutments.

Personal Response

I like this bridge more for what it symbolizes than for the structure itself. The first time I visited London, my senior year in high school, my hotel was just behind the bridge and across the river from the Houses of Parliament. The bridge allowed us direct access to Big Ben and Westminster Abbey from the hotel, and I loved being able to view these buildings from across the bridge. When you actually visit the bridge, it is surprising how long it actually is, and the walk across takes longer than expected. What’s also surprising is how much use it gets from pedestrians, as the bridge is almost always crowed. Vendors and street performers line the bridge and add to its exciting atmosphere. While I was never blown away by the structural features of Westminster Bridge, I love the overall experience and symbolism of this famous structure. 

References

[1] http://www.british-history.ac.uk/survey-london/vol23/pp66-68

[2] http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=703

Mercedes-Benz Stadium

Here is someone else talking about the Mercedes-Benz Stadium, AGAIN! What can I do?! It is one of the newer and more iconic structures located in my home city of Atlanta and hence, I couldn’t stop myself from researching it. Although I have yet to visit the stadium for a game, I’m in constant awe of the structure for good reasons!

Structural Information

Figure 1: Mercedes-Benz Stadium exterior view

The Mercedes-Benz Stadium is located in the heart of downtown Atlanta, Georgia; it sits adjacent to what stood before, the Georgia Dome. Construction of the projected started in April 2014 and it finished in 2017. The first game was played in this stadium as early as September 2017. This stadium was built to replace the Georgia Dome and become the new home for the Atlanta Falcons National Football League team as well as for the new Atlanta United soccer team. Its purpose is not limited to just this; it will serve many other purposes for other teams and events.

The team responsible for this iconic design is BuroHappold Engineering and architect, HOK. The team at Birdair was chosen as the specialty contractor to construct the roof pillow system and the facade while a general contractor team consisting of differing firms worked on the stadium. The main member of the structure, the retractable roof, was designed by HOK and TVSDesign and put into place by Birdair. The funding to construct this project was a mixture of both public and private funds. The total cost to build it was about $1.5 billion and the Falcons partnered up with the Georgia World Congress Center Authority (GWCCA) to build it (GWCCA owns it while the Falcons operate it).

The stadium is set to be an optimal location for sporting events with big future plans for holding events like the Super Bowl and College Football Playoff Championship game.

Historical Significance

The stadium was designed to be as unique and iconic as efficient. Not seen in other stadium, the whole of the structure has something new and futuristic to offer. Starting at the top, the retractable roof acts like a camera lens and is made of three layered ETFE,ethylene tetrafluoroethylene, roof pillows resting on eight petals. This particular roofing material was chosen for 3 main reasons: aesthetics, performance and sustainability. It is inspired by the Roman Pantheon and when in action, behaves like a falcon’s wings. This facade can open within 10 minutes giving an outdoor feel to the indoors when pleasant weather allows.

A 360 degree Halo scoreboard lines the upper interior of the stadium to ensure that each spectator has the best experience possible.

Figure 2: Retractable roof and interior view of screens

The Mercedes-Benz Stadium has set the standard for stadiums across the U.S. It is the first LEED Platinum professional sports stadium achieving its goal of sustainability. Some of the features include reusing rainwater, use of solar panels, efficient lighting and encouragement of alternative transportation. It has achieved 88 LEED points–the most any sports venue has achieved in the world. The characteristics described above make the Mercedes-Benz stadium a model for future buildings particularly sports arenas as it shows that efficiency, sustainability and technology can all be achieved for a structure.

Cultural Significance

Although recently built with the newest technologies, there has been one injury reported in which a worker was injured while trying to move a metal tower. This individual is suing the general contractor and other companies for permanent and continuing injuries. Other than this particular case, no injuries or deaths have been reported during and post-construction of the stadium.

 

Figure 3: Construction of the stadium

One of the historical event concerns is the impact on poor neighborhoods near the stadium: English Avenue and Vine City. Arthur Blank has suggested that millions of dollars will go to improve these neighborhoods but it seems the opposite. The money in the form of either investments or revenues is not directed towards these neighborhoods at all. In fact, these areas are seen as blotted out neighborhoods and little to no money is spent on local businesses to generate their economy. Nonetheless, Blank is persistent on changing the quality of life of the people living in these areas through donations. As can be seen, the stadium is loved by the spectators of sports and disliked by residents of surrounding neighborhoods due to each of their interests either being upheld or tossed to the side.

As it is a recently-constructed system, the human cost in building it is seen to have low statistical values and it is still used today for the purpose it was built.

Structural Art

The structure, in my opinion, does not demonstrate structural art no matter how beautiful, pleasing and futuristic it looks to my eye. This can be explained through the 3 E’s: efficiency, economy and elegance. As previously described, the structure is efficient in its purpose as it is sustainable and environmentally friendly (LEEDs too!). In terms of economy however, the stadium is quite costly as it ended up costing $1.5 billion to build and twice the material was used for construction compared to the Georgia Dome. Elegance could be seen as either aesthetically pleasing and environmentally-friendly but all 3 of the E’s are not satisfied.

Figure 4: Mercedes-Benz Stadium

Structural Analysis

Starting with the iconic roof, it is designed to be retractable and its functions are explained above. Specifically, eight cantilevered petals move to create the effect of a camera. Resting on these petals are ETFE cushion that are light-weight and allow smooth movement through the use of a cable net system. The eastern side of the structure has an a facade made of lightweight steel to allow openness and views of the city to be seen. Deep foundations and shallow foundations were put into place for the precast inner bowl. There are also 19 mega columns that support the roof and 8 other columns that support the mega columns. The foundational structures were made of thick high-strength concrete and longitudinal and shear reinforcements were used. Then, the precast seats were made of columns, vomitory walls, raker beams, and seats and placed in the inner bowl. The concrete bowl consisting of different sections such as top of seating, upper mezz and etc. was placed. A total of 150,00 cubic yards of concrete and 27,000 tons of structural steel was used to construct the stadium.

Figure 5: Depiction of the Mega Columns in place
Figure 6: Depiction of Seating

 

A detailed analysis of each of the sections was done through graphics and software such as SAFE software and designing of individual components was possible due to software like Enercalc. The design drawings generated from these softwares made it possible to communicate to the entire team what would be built and how it would be built. Manipulations and changes could easily be made to these models to make the structure’s design as best as possible.

Figure 6: Stadium Breakdown

A even more detailed analysis can be presented upon the stadium for which a whole powerpoint would not be enough due to the extensive detailing and design.

The loads on this structure include the dead load (weight of the stadium which increases as you go down since the lower parts have to hold the weight of the higher portions). The live loads can be considered to be the moving population of the spectators. No usually large dynamic loads are present as it is a very still and static structure. The total of these loads moves from the top to the bottom as following: the weight of the roof structure and the components inside moves to the triangular facade then which the increase in weight due to the facade will then move to the columns put into place. The columns then take the load of the weight and the people and transfer it to the ground through the closest column from the bowl structure. Although the system seems complicated from the outside due to the interconnectedness of the facades, the loads simple move from the top to the bottom through the closest structural member. Although stadiums and buildings weren’t covered for load paths, the idea works the same way.

Figure 7: External View of Load Path in One portion of stadium

Let’s look at a specific example. From figure 6, the blue foundation can be seen to upheld by many different columns. The load on this foundational slab will flow through/into the columns geometrically if the columns are spaced equally apart or portions of this force will go to the closest foundation columns. Then, these columns will transmit the loads to the ground. Of course, it should be noted that the force or load is the greatest at the bottom for which the columns handle a large load and must made be designed to handle the appropriate load.

Figure 8: Internal View of Load Path from slab to column

Note: Many simplifications were made due to the complexity of the stadium.

Personal Response

Although I have yet to visit the inside of the stadium, standing outside made me realized the innovations in Atlanta that have allowed such a futuristic building to be built in a still developing city! It put me in awe because of its size and the capability of the retractable roof.

References:

[1] https://www.burohappold.com/projects/mercedes-benz-stadium/

[2] http://mercedesbenzstadium.com/stadium-fast-facts/

[3] http://www.birdair.com/projects/mercedes-benz-stadium

[4] https://www.stadiumsofprofootball.com/stadiums/mercedes-benz-stadium/

[5] https://www.constructiondive.com/news/injured-worker-sues-gc-on-14b-falcons-stadium/422265/

[6] https://www.nytimes.com/2017/01/12/sports/football/atlanta-falcons-stadium-arthur-blank-neighborhood.html

[7] http://www.seaog.org/Presentations/MBS/MBS%20Presentation_SEAOG.pdf

 

The Granada Bridge

Structure Information

The Rockefeller Memorial Bridge, known by locals as The Granada Bridge, spans the Halifax River or Intracoastal Waterway. The bridge links the peninsula and mainland parts of Ormond Beach, Florida, USA. The current standing bridge was built in 1983, however, the current bridge is the fourth bridge to exist in this approximate location since 1887. The Granada Bridge is shown in Figure 1 below.

Figure 1: The Granada Bridge [1]

The purpose of the bridge is to carry highway, pedestrian, and cycling traffic over the Intercoastal Waterway. The bridge was funded and is currently maintained by the Florida Department of Transportation. The designer of the bridge is unknown due to the lack historical construction plans and records accessible to the public through the Florida Department of Transportation.

Historical Significance

The structural engineering design of the Granada Bridge is not an innovative design in a historical context. The Granada Bridge is a stringer or multi-beam bridge [2]. The beams making up each span are supported at each end by a box girder which sits atop the vertically supportive piers. There are large abutments at each end of the bridge. The structural principle of this bridge design has been used for millennia, and the most common type of highway bridges  in Florida have this same structural design. Additionally, the bridge was built using foundation and general construction technology that had been used before. The foundations for the piers were built using cofferdams installed where the piers exist in the river. The foundations, columns, and girders are cast-in-place concrete, the beams are pre-stressed concrete and the deck is cast-place concrete. The best existing example of this type of structural design is the Lake Pontchartrain Causeway over Lake Pontchartrain in Southern Louisiana, USA. The Lake Pontchartrain Causeway spans a total of 23.83 miles. It consists of four traffic lanes and has the same structural design principles as the Granada Bridge, but is 65 times longer. Figure 2 below shows an abbreviated view of the causeway.

Figure 2: Lake Pontchartrain Causeway [3]

Since the Granada Bridge is such a standard highway bridge, the actual structural design should not be considered a model for any future bridges. However, its function as a connection between the peninsula and mainland parts of Ormond Beach since 1887 has inspired the construction of multiple bridges in the greater Daytona and Ormond Beach area.

Cultural Significance

The history surrounding the Granada Bridge is fascinating. The progress and construction of the series of bridges leading to the existing bridge is reflective of the progress of industrialization and influx of population to the area. The first bridge built in the location where the existing bridge stands was the result of a competition between builders in Daytona Beach and Ormond Beach to see who could cross the Halifax River the fastest. It was a wooden bridge with a drawbridge device finished in 1887. In 1890, Henry Flagler, owner of Florida East Coast Railway bought out all shares of the Ormond Hotel, and in 1905 built a second bridge near the first that could support rail and carry passengers directly to the hotel. Figure 3 below shows the Hotel with the wooden bridge in the bottom right hand corner. Flagler later redesigned the bridge for automobiles to be able to drive to the hotel, and the first wooden bridge was demolished shortly after [4].

Figure 3: Vintage Ormond Hotel postcard with bridge in lower right-hand corner [5].

Henry Flagler was not the only notable man to leave his mark on Ormond Beach. The man known as the richest in modern history, John D. Rockefeller made his summer and retirement home at the southeast corner of the bridge. After Flagler’s redesigned railroad bridge became too old to be maintained, a new two-lane wooden bascule bridge was built in its place and named the John D. Rockefeller Memorial Bridge opening in 1952 [4]. Eventually the bridge had to be rebuilt to accommodate the widening of the connecting roads. This new bridge was constructed in 1983 and stands as the Granada Bridge today.

The first bridge built made it possible for the world’s first automobile race to take place on Ormond Beach in 1903. People loved the bridge because it allowed them to indulge in the luxury of the Ormond Hotel and the excitment of industrialization and the recreation that it made possible. Since then, the bridge has remained a north star for residents and tourists in Ormond Beach. Although there are only minor historical events surrounding the Granada Bridge, it means a lot to the residents of Ormond Beach, myself included. I was born and raised in Ormond Beach, and I know that I am home every time I reach the apex of the bridge looking towards the Atlantic Ocean. The combination of the Intracoastal Waterway and the succeeding vast ocean in front of it reminds me of watching fireworks sitting on the sloped bridge abutments on the 4th of July, or running up the steepest side during high school cross country practice.

The building of a bridge that has done so much for Ormond Beach did not come without hardships. During the construction of the existing bridge in the 1980’s, three workers fell from a scaffolded platform on to a barge below. One of the workers lost his life [6]. In addition, there have been multiple fatalities associated with normal traffic usage of the bridge. Traffic accidents are common in highly trafficked areas, and with an ever-increasing daily vehicle count using the bridge to cross the Halifax River, this is unfortunately expected. In addition to vehicular traffic, the bridge has pedestrian pathways on each side of the deck which connect four different recreational parks on each corner of the bridge.

Structural Art

By David Billington’s definition, The Granada Bridge does demonstrate some degree of structural art. The load path from the deck to the foundations is discernable. This is representative of some degree of efficiency. In addition, the bridge is owned and maintained by the Florida Department of Transportation, which indicates that the structural design was performed under certain economic constraints. Designing for a publicly funded piece of infrastructure means that the design that is sufficient at the lowest cost will be built. According to Billington, structural art only flourishes under the constraint of economy. This pillar of structural art is present in this bridge. I may be biased because the bridge is so central to my adolescence, but I think that the Granada Bridge is an elegant one. I think its elegance comes from the transition you experience when you cross it. The columns and deck are thin and intentional when compared to the vast, chaotic ocean that comes in to view as you cross over the high point of the bridge. Although you cannot do the actual experience justice, Figure 4 below shows the view of the ocean as you descend the bridge.

Figure 4: View of the Atlantic Ocean descending the Granada Bridge [6]

Even though the bridge does demonstrate some degree of structural art, I think that it generally cannot be considered structural art by the criteria provided by David Billington. I think this is mainly because of the nature of materials used and the form of the bridge deck. I think that structures made from prestressed concrete are inherently not structural art. Because the concrete is in compression before it is under service load, the true load path in final form is never actually realized. In addition, the curvature of the deck is asymmetrical relative to each land mass, meaning the apex of the bridge is closer to one end. If the bridge was symmetrical I think it would be more elegant, thus, closer to the ideal for structural art. Figure 5 below shows the asymmetry in form of the granada bridge.

Figure 5: Asymmetry of apex of Granada Bridge [6]

Structural Analysis

The Granada Bridge is a stringer/multi-beam or girder bridge. The superstructure consists of 19 spans of average length of 101 ft [2]. Each span consists of thirteen prestressed concrete I-beams. Atop of these I-beams is a cast-in-place concrete deck reinforced by steel. The ends of each beam sits atop a bearing pad which are flush with the corrugated top of a modified cast-in-place reinforced concrete box girder. The girder is the start of the substructure. The girders are supported by two cast-in-place reinforced concrete columns which are round in cross-section. The columns located closer to the center of the bridge are taller than those at the bridge ends, so they are laterally braced together at their midspan to prevent buckling. The columns are supported by cast-in-place reinforced concrete foundations located in the water only. The foundations are rectangular in cross-section. At each end of the bridge there are massive abutments. The abutments are covered in grass, but it is assumed that they are constructed using mass concrete or reinforced concrete. The construction method used to build this bridge is typical of girder bridges. The foundation for one bridge bent is built using a cofferdam. Cofferdams are watertight structures constructed using metal sheet piling or similar material which are pumped dry to permit construction below the waterline [2]. The reinforcing cage for each column is then set on the foundation and concrete is poured. The reinforcing cage for the modified box girder is then set on top of the two columns and concrete is poured. This process is a completed bent. A bearing pad is set on the girder at the location of each beam. The beams are prestressed and constructed off-site then transported to the site. The beams are set and tied to each other and to each bent that they are set on. One span consists of thirteen beams connected at each end by a bent. The bridge was built one span at a time. It is assumed that the first span would start at one end abutment and connect to the first bent. A reinforced concrete deck is then poured in sections, usually a span at a time.

The structural systems employed in this structure begin at the bridge deck. The reinforced concrete deck is statically loaded by primarily vehicular traffic. Additional load comes from the self weight of the deck. The deck transmits a compressive uniform line load on to each beam based on the tributary area of each beam. Each beam is modeled as a simply supported beam because there is no moment transmitted at supports. The beam transfers the load from the deck as well as its own self weight as point loads to each bearing pad that it sits atop of, and the bearing pad transmits that point load to the girder. The girder transmits that load  as well the load of its own self weight as two point loads, one going to each supporting column. The columns then transfers that load and the load of its own self weight to the foundations which distribute the total load to the ground. It should be noted that the abutments carry the axial force transmitted by the beams at each end of the bridge. The structural system of one bent is shown in Figure 6 below.

Figure 6: Load path on structural system

The structural system can be broken down in to structural elements with load path applied to analyze the structure. The Granada Bridge is 1923 feet in length with 19 main spans, indicating an average span length of 101 ft. The edge-to-out width is 94.5 ft. Therefore the tributary area with beams shown can be modeled as shown in Figure 7 below.

Figure 7: Model of tributary area for one span

The tributary area for Beam 1 and Beam 13 is the same are found using the calculations below

The tributary area from the remainder of the beams is the same and can be found using the calculations below.

The design load used for this bridge was AASHTO Specification HS 20 [2] which assumes an axle load of 32,000 lbs and a tire load of 16,000 lbs with a tire contact area of 200 square inches. Combined with the load of the self weight of the concrete having density assumed to be 150 pcf, the total surface load transmitted by the deck to the beams is as shown below.

Traffic Load: (32,000+16,000) lb/(200 in^2/144 in^2) = 34560 lb/ft^2

Assuming deck thickness of 1 ft,

Self-weight load: (150 pcf)*(1 ft) = 150 lb/ft^2

Total Area Load = (34560+150) lb/ft^2 = 34710 lb/ft^2

To find distributed load on Beams 1 and 13,

w=(34710 lb/ft^2)*(1/2)*(93.4 ft/13) = 124689 lb/ft

To find distributed load on remainder of Beams (2-12),

w=(34710 lb/ft^2)*(93.4 ft/13)=249378 lb/ft

Using the distributed load on Beams 1 and 13, the beam can be modeled as being simply supported as shown in Figure 9 below.

Figure 9: Beams 1 and 13 modeled as a simply supported beam

Using structural analysis and symmetry, the reactions, Ra = Rb = 629694.5 lb

Using the distributed load on Beams 2-12, the beam can be modeled as being simply supported as shown in Figure 10 below.

Figure 10: Beams 1-12 modeled as simply supported beam

Using structural analysis and symmetry, the reactions, Rc = Rd = 12593589 lb

These reastions exist as point loads on the girder as shown in Figure 11 below.

Figure 11: Girder modeled as beam

The self weight of the girder can be modeled as density of concrete time area of cross section assuming a width of 2 ft,

Self Weight = 150 pcf*(93.5 ft * 2 ft)=28050 lb/ft

Using Mastan, the reactions are found to be, C1 = 1.046E8 lb, C2 = -3.026E7 lb, and C3 = 1.046E8 lb. Assuming that the columns are not fixed to the girder, the reaction at C2 can be considered negligible, and the load will not be used in further analysis.

Using the reactions, the axial load in the columns are equal to C1, and C3. Assuming column diameter as 5 ft, the stress in the columns can therefore be defined as

stress1, stress 3 = F/A = 1.046E8 lb/2827.4 in^2=36994.7 psi

To find the load on the foundation and therefore the load transmitted to the ground, the self weight of the column can be calculated assuming an average column height of 65 ft (clearance requirement)

Self-weight = 150 pcf (pi/4)*(5 ft)^2*(65 ft) = 191440.8 lb

Therefore total load on outer foundations = (1.046E8+191440.8) lb = 1.048E8 lb.

Assuming a square cross-section of dimension 8 ft x 8 ft, the stress in the outer foundations is found using the following calculations,

stress = F/A = 1.048E8 lb/9216 in^2 = 11370.6 psi

Therefore, the strength of the soil has to be greater than or equal to 11370.6 psi.

Deformation in the columns can be found using the formula:

deflection = (PL)/(EA) = 5.7 in

5.7 inches is 0.73% of the total column height, making this deflection acceptable.

The tallest columns exist at the center of the bridge and maximum height is equal to 65 ft, therefore these columns are laterally braced for buckling. The critical buckling load can be found using the following equation,

Pcr = (pi^2*E*I)/L^2 = 7.54E9 psi

Therefore it seems that lateral bracing is not needed for stability in this analysis.

Since this bridge was constructed in the 1980’s, it is assumed that construction and design plans which follow the specifications of the Florida Department of Transportation were used to communicate the design principles used.

Personal Reaction

For years I have run, walked and driven over this bridge. To me it has always symbolized my homecoming. Looking at it from a structural engineering perspective gave me insights that I never would have gained about the history of the Granada bridge and its true significance to the growth and development of my hometown.

References

[1] https://rosebone.deviantart.com/art/Granada-Bridge-210251435

[2] http://www.city-data.com/bridges/bridges-Ormond-Beach-Florida.html#790132

[3] https://carynschulenberg.com/2015/08/lake-pontchartrain-causeway/

[4] https://ormondhistory.org/a-brief-history-of-ormond-beach-2/

[5] https://www.florida-backroads-travel.com/ormond-beach-florida.html

[6] https://www.redbubble.com/people/dbenoit/works/6631477-ormond-beach-bridge

 

Canopy Bridge at the Botanical Gardens

Canopy Bridge at the Botanical Gardens

The Canopy Bridge in the Atlanta Botanical Gardens is a structure that has always held a special place in my heart. I have been to the Botanical Gardens and walked across this bridge several times over my years at Tech, one of the most memorable times being when my girlfriend and I talked about our thoughts on the load paths of the bridge. And that conversation happened before this class started! So if you weren’t sure a nerdy Tech student was writing this blog you can now put any doubts you had to rest.

Structure Information

Canopy Bridge [1]

This bridge was constructed as part of an expansion of the Botanical Gardens that was completed in 2010 [2]. The purpose of this bridge is to provide guests with a way to see the gardens and flowers from a different perspective than they might get while on the ground. It also allows you to get from one part of the gardens to the other more quickly than walking on the ground. Jova/Daniels/Busby Architects of Atlanta were the architects that designed the bridge [2]. Halvorson and Partners (now a part of WSP) were the structural engineers that ran the analysis of the bridge design [3]. The design was inspired by the works of Spanish architect Santiago Calatrava. The bridge was part of a $55 million expansion project funded by a variety of private donors, the Kendeda fund, and the Botanical Garden itself [4].

Historical Significance

The design of the structure itself is not innovative, as the architects designing it were specifically modeling it after Santiago Calatrava’s works. Santiago’s bridge designs all featured cable stays. Instead of the bridge being supported from above by cables (such as the Golden Gate Bridge), the cables are anchored into the ground. In the figures below, you can see the comparison between the two styles.

Golden Gate Bridge, Suspension Bridge [5]

Canopy Bridge, Reverse Suspension Bridge [6]

The best existing example of Santiago’s work that influenced the design can be shown in the figure below. The style of using an anchored member with cables attached to it support the main structure is a signature style of Santiago Calatrava. That style can also be seen throughout the Canopy Bridge in the Botanical Gardens.

Reverse Suspension Structure at Quadracci Pavilion [7]

There was no special construction technique that was used for this bridge, but there was an incident regarding its construction that will be mentioned later.

Cultural Significance

This bridge was built as part of a large expansion of the Botanical Gardens in 2003 and finished in 2010 [2]. The expansion was able to take place because of a special and unique addition to the garden. In 2002, the Chihuly exhibit was presented for the first time in the gardens, and its impact was dramatic [8]. Numbers of attending people more than doubled from 200,000 to 425,000 [8]. Memberships to the garden increased from 12,000 to 19,000 [8]. Mary Pat Matheson, executive director for the gardens, said ‘The Chihuly exhibit was our coming out party. It was very deliberate. I knew what the impact would be: tremendous’ [8]. Matheson was purposely trying to make people want to visit the gardens, for more than economic reasons. She wanted people to see the garden as ‘more than just a pretty place. I want the people of Atlanta to see it as a cultural asset’ [8]. The spike in interest for the gardens made investments easier to come by when the expansion was announced in 2003.

Chihuly Exhibit [9]

Part of that expansion was making use of the previously undeveloped Storza woods, which included the Canopy Bridge. However, the building of the bridge did not come without cost. During construction of the bridge, a section collapsed killing one worker and injuring several others [3]. The metal frame of the bridge had been constructed with the shoring beneath the bridge, each column spaced out 30’ each [3]. When concrete was being poured into the top of the bridge for people to walk on, the bridge collapsed. The shoring contractor made several mistakes (or cut certain corners) which led to the collapse. The column was spaced at a distance greater than 30’ from another column, the steel beams in some towers were discovered to be W10x12 instead of W10x19, and the contractor failed to provide required lateral bracing between anchors, which were embedded at insufficient depths (anchor embedment distances on seven different towers ranged anywhere form 43” to 17”) [3]. This accident was a black mark on the expansion, but the overall public opinion of the opened section was overwhelmingly positive. Visiting numbers increased further and the gardens now featured a ‘Monet piece’ in the canopy bridge as Matheson describes it [8]. It is used today as it always has been as both a way to transport people across the gardens, or to be viewed and admired with everything else the gardens have to offer.

Structural Art

Structural art can be defined using three principles: efficiency, economy, and elegance. Efficiency describes a structure’s ability to carry the maximum amount of load with the smallest amount of material. Economy describes a structure’s cost versus utility. Ideally, a structure has minimal cost and maximum utility. Elegance is the aesthetic choices that a designer makes.

In terms of efficiency, this structure seemingly fits that role. The bridge is cantilevered at the ends and suspended by thin metal rods along the span. With its unique shape that curves around the Storza Woods, the design allows the bridge to withstand loads while keeping materials to a minimum. Solid rectangular supports could have been used as well, but it would have used much more material and not increased the capacity of the bridge. The horizontal profile of the bridge is also very small, so the bridge as a whole uses minimum materials considering its shape and carries the necessary capacities.

Speaking to its economy is a bit more difficult. The bridge costs were included in the total expansion which was $55 million [2]. The expansion was mostly privately funded by organizations and people that were interested in making the Botanical Gardens a more beautiful place. The money came in quickly so there was a high public interest in this project being undertaken [2]. The expansion brought in an increase in visitors and was beloved by all. Considering the quick funding that came in and was quickly repaid by the increase in visitors and acclaim of the gardens, I would say this structure fulfills the economy portion of structural art.

The elegance of this structure is undisputed. The bridge as a whole is very thin and and does not obstruct views in the garden, but rather becomes a part of it. The inspiration for the design came from Santiago Calatrava, but pop culture had an influence on the design as well. The bridge had a connection to the performers Fred Astaire and Ginger Rogers. The cable stay design looks like the two dancing. This attention to the appearance of the bridge checks the elegance box for me.

Figure 6, Canopy Walk Concept Art

Canopy Walk Concept Art [10]

Overall, I would definitely qualify this bridge as structural art. The design itself is not innovative but the way it is implemented shows off its beauty and strength.

Structural Analysis

The Canopy Bridge has a fairly simplistic design to it despite looking complex. The main member that carries the deck is the HSS30″ diameter by .25″ thickness tube that is cantilevered into concrete abutments at each end [3]. In the middle of the bridge is a straight span that is 70′ long and 11′ wide that is supported by two sloping HSS 16″ diameter by .625″ tubes in a V-form [3]. There are four HSS 24″ diameter by .5″ thickness pipes that have cables attached to them that support the deck of the bridge in various locations along it [3]. The framing of the bridge mainly consisted of HSS 8″x8″ members that were welded slightly above the center of the main HSS pipe [3]. These pipes were spaced at a 10′ interval from each other [3]. These pipes were diagonally braced with 6″ diameter pipes [3].

The construction of this bridge started with the concrete abutments being poured and the main HSS tube being installed [3]. The rest of the framework was constructed after that. Shoring towers were constructed to support the bridge while the concrete was being poured. As mentioned prior, the shoring towers were not constructed properly and the bridge collapsed during the first attempted construction effort [3].

The type of structural system employed for this system was a cable stay bridge [8]. The dead load of the bridge is supported by the cantilevered ends and the four HSS members with cables attached to the deck. Each HSS member had three cables connected to the deck and two cables attached behind them as backstays [3]. The pipes beneath the deck take a linear dead load but their main purpose is to provide an area for the deck to sit on. The cables in the HSS members are what keeps the entire bridge suspended.

Canopy Bridge Components [11]

Cable Tension Load Paths [12]

An analysis can be done on the bridge itself to see how much capacity is needed in the cables to support the structure. We can simplify the bridge into a straight segment to analyze a part of it via methods we have learned in class. We can take an 80′ span of the bridge and one of the sets of the cable connections to determine the strength needed in the cables. I am assuming a density of 145lb/ft^3 for the concrete and ignoring all but the main HSS member that has a density of .284lb/in^3 for the self-weight of the bridge. The calculation and analysis of the bridge is as shown below.

Simplified problem set up

The cables are assumed to be at 45 degree angles from the deck. All other assumptions that were made in the problem are listed in the calculations.

Cable tension forces and deformation

The tension in the second cable resulted in an almost zero force because of its orientation in this simplified example. In reality, the curvature of the bridge would result in non-zero tensions in each cable.

The design drawings successfully communicated the idea of the beauty of the bridge to stakeholders as many people were very eager to invest in the building of this bridge and the gardens. The technical drawings were less successful in communicating ideas between different parts of the job. The shoring consultant left out details regarding the type of steel that should be used and the shoring contractor ignored parts of the instructions from the structural engineers. Communication breakdowns between the companies ultimately led to its collapse during construction.

Personal Response

I have always admired the Canopy Bridge from my visits to the Botanical Gardens in the past, but it has taken on a whole new meaning now that my civil engineering background keeps developing. The first time I noticed that change was that first conversation I had about its function as a structure.

Researching this project and seeing the passion behind the bridge’s design process and construction has made this an even more special part of the gardens to me. I am definitely going back to the gardens in the future and dragging along any friends that will listen to me talk about its bridge.

References

1. Shell, B. (2018). Atlanta Botanical Garden Canopy Walk Images. [email].

2. https://www.myajc.com/blog/arts-culture/atlanta-botanical-grows-support-for-nourish-and-flourish-enhancements/xknBqvbdeSFd1AvTSj8HoK/

3. https://www.osha.gov/doc/engineering/2008_12_19.html

4. https://kendedafund.org/grantee/inspiring-the-public-through-beauty/

5. https://wall.alphacoders.com/by_sub_category.php?id=160347&name=Golden+Gate+Wallpapers

6. Shell, B. (2018). Atlanta Botanical Garden Canopy Walk Images. [email].

7. https://www.bluffton.edu/homepages/facstaff/sullivanm/wisconsin/milwaukee/calatrava/calatrava.html

8. https://www.accessatlanta.com/entertainment/calendar/atlanta-botanical-garden-grows-phase-opens-saturday/HGedrkVTonq00qRMImLbIN/

9. https://www.pinterest.com/pin/182958803590374050/

10. Shell, B. (2018). Atlanta Botanical Garden Canopy Walk Images. [email].

11. Shell, B. (2018). Atlanta Botanical Garden Canopy Walk Images. [email].

12. Shell, B. (2018). Atlanta Botanical Garden Canopy Walk Images. [email].

 

Spanish Arch in Galway

Structure Information

The Spanish Arch is in fact two arches in the Irish city of Galway, so the name can be a little misleading in my opinion. The Arch is on the left bank of the Corrid River, where the river meets Galway Bay. [1] It was constructed in 1594 by Wylliam Martin, who was the 34th mayor of Galway. The name of the arch was originally Ceann an Bhalla (“the head of the wall”) and it did not become known as the Spanish Arch until much later. It was called “The Head of the Wall” because it marked the start of the city walls, which were designed to protect docked ships from thefts. The city walls also included a bastion, which allowed the soldiers stationed on the walls to fire cannons from them. [4]

 

Figure 1: The Spanish Arch in Galway, Ireland [3]

Historical Significance

The Spanish Arch extends from the wall which was built in the 12th century during Norman times. Arches have been around since ancient times so the structure is not any innovative structural engineering design, nor was a new certain construction technique used. The wall itself does not have as much significance throughout history, but currently the area around Galway Bay is used for eating, drinking, and playing music. [3]

Cultural Significance

Soldiers lived in the town wall and manned cannons on the roof. [1]The fact that the structure is called the Spanish Arch in a small city on the Irish west coast showcases the historical links between Ireland and Spain. The reason for the name is believed to be due to the merchant trade of the region of Galway to Spain, and Spanish ships would often stop at the docks in Galway. In fact, Christopher Columbus is believed to have visited the city in 1477. There is a “Latin Quarter” of the city so the influence of Spanish culture is still apparent. However, there is not a proven link between the Spanish people in Galway and the building of the Arch. [4] Today the Spanish Arch is used as a part of the Galway City Museum, which is located next to the Arch.

Structural Art

I would not call this piece structural art according to David Billington’s requirements for structural art: efficiency, economy, and elegance. There is a well-known sculpture on the top of the Arch called Madonna of the Quays designed by the artist Claire Sheridan. [4] The area around the Arch is a part of the lively Latin Quarter of the city, so the symbolism behind the Arch reminds me of the public’s reaction to the Brooklyn Bridge, but on a much smaller scale.

Structural Analysis

The medieval city walls in Galway were constructed using stone since the stone arches were a method perfected throughout Roman times. The load on the arch would be a distributed load since the only applied load is the self-weight of the stone. If there is a person or a cannon on the city walls (as there was in medieval times), a point load would be applied to the free body diagram. However, for this case the only load is the self-weight.

Figure 2: Load Paths in Spanish Arch [5]

Figure 3: Free Body Diagram of loads on arch

 

Figure 4: Calculating max force in arch

In order to calculate the max forces in the arch, cut the arch at the point where it is the tallest (in the middle of the length in this case). Take the sum of the forces in the y- direction and the sum of the forces in the x-direction to obtain the max force at the pinned ends. The max force occurs at the ends of the arch.

Personal Response

I knew that the concepts behind arches have been understood for thousands of years, but it was actually pretty cool to be able to walk under an arch that has been standing around for close to 500 years. While the arch itself is not that impressive, knowing the load paths behind the arch is interesting and I think it’s fascinating that people were able to understand this in order to successfully build them. Also I was able to witness the area around the Bay being used as a social setting during a nice and sunny day in Galway.

References

  1. https://www.galwaytourism.ie/pThe-Spanish-Arch.html
  2. https://www.historyireland.com/volume-9/ireland-spain/
  3. http://snoozleshostelgalway.ie/spanish-archcladdagh/
  4. http://galwaycity.galway-ireland.ie/spanish-arch.htm
  5. https://pbs.twimg.com/profile_images/935815544053358592/zmC63ql-_400x400.jpg

Peachtree Street North Bridge

At the beginning of my sophomore year at Georgia Tech (end of 2016), I started making the weekly drive on I-85 from campus to Buckhead and back on Fridays. For those of you who don’t know, rush hour in Atlanta on Friday afternoons can be a slow journey, leaving lots of time to look at the scenery. I started realizing towards April and then in the following months that the bridge by the Peachtree St. exit kept catching my eye. There hadn’t been any major construction, so I was positive the bridge wasn’t new, however, a bridge that had never crossed my mind started stealing my attention every Friday. At first, the only difference was the signage, where Peachtree Street was written in large letter signs over the bridge, which I started to use to mark how much further I had. I eventually grew used to the sign and it slept out of my mind again until the first semester of my junior year, many arches appeared above me as I drove past the bridge. In the blink of an eye, the unmemorable bridge became the lasting impression of my Friday afternoon drives.

Figure 1: Finished – Gateway to Atlanta [1]

Structure Information

Figure 2: Rendering of Bridge [1]

Name: Peachtree Street North Bridge

Location: Peachtree Street exit, I-85, Atlanta, Georgia, USA

Date finished: November 2017

Owner: Midtown Alliance

Implementation Partners: Midtown Alliance, Central Atlanta Progress, Silverman Construction Program Management, Kimley Horn, CW Matthews, and Henry Incorporated

Funded by: Midtown Improvement District, Atlanta Downtown Improvement District, Georgia Department of Transportation, the State Roadway and Tollway Authority, and the Woodruff Foundation [1]

The Peachtree Street North Bridge was a renovation of the already existing utilitarian bridge that functioned as a path over I-85 for pedestrians and vehicles. The new additions serve a more symbolic purpose as the gateway to metropolitan Atlanta.

 

Historical Significance

Historically, in building connector bridges, Atlanta has always leaned towards a fully utilitarian approach in design. When looking at the three E’s, economy, efficiency, and elegance, Atlanta designers and public agencies completely ignored elegance in the formation of the metropolitan area. This renovation signals not only the massive beautification of Atlanta for its travelers, but also a significant shift in mindset from function to global effect of structures in all capacities of serving society.

In terms of the structure itself, the design does not employ any new or innovative techniques. At its most bare essence, this structure is still a simple highway connector bridge, just with added dead weight from the arches and signs. Moving forward though, this bridge renovation may trigger a brand-new approach to design for Atlanta that integrates the symbolic purpose into the structural design. If this happens, this bridge project will become historically significant as the catalyst for this change despite not being all that technologically innovative in its own design when compared to other historically significant structures. I am very excited to see if designers and structural engineers start using the Peachtree Street North Bridge as inspiration. I mean, as a New Yorker, adding arches to a highway connector doesn’t seem all that special. But, as a civil engineer in training whose main prospect for life after college is in Atlanta, I can’t help but be my dorky, typical Georgia Tech self, and get giddy at the idea of participating in the beautification of Atlanta.

 

Cultural Significance

While this bridge didn’t have anybody die or have some massive political proclamation made upon it to add drama to this post, the Peachtree Street North Bridge does reflect a larger cultural shift in attitude towards the infrastructure of our city. While I am the typical New Yorker who brags about being from a “real city,” – and yes, you should imagine me doing the obnoxious air quotes when I say that because, unfortunately, I do – I still can’t help but look at Atlanta when I flyover it and feel slightly dissatisfied, and I think this is more universal than my bias. So, I am excited to report to you all that this bridge renovation is not a unique exception to the utilitarian approach that I mentioned earlier. In fact, this bridge is one of two for this specific Midtown Alliance project to “beautify the city” and make everyone aware when they are entering Atlanta.

Here are some quick notes to briefly sum up how the Peachtree Street North Bridge is part of a larger cultural mission:

  • Midtown Alliance (the driving force behind this project) has embarked upon a $6 million beautification project for Metro Atlanta – this bridge is the first step.
  • This massive endeavor included the cooperation of multiple public and private agencies, signaling its cultural importance to everyone, not just one sector of society.
  • While currently Peachtree Street North Bridge is one of only two bridges either in construction or completed, this project has garnered enough interest that Midtown Alliance is already in the process of procuring more.
  • Like many of the famous bridges that signified new eras in structural design, the designs for all the bridges encompassed within this the confines of this project were procured through a competition demonstrating this bridge’s cultural relevance.

 

Just to demonstrate how much value Midtown Alliance is placing upon the addition of these arches to the city landscape, here is a slightly dramatic or theatrical quote from the organization itself describing it as a “sweeping, 35-foot tall gateway arches and illuminated ‘Peachtree’ signage, providing bold visual impact from the interstate that creates a sense of arrival into Atlanta’s urban core” [2]. I don’t know if I would put it exactly that way, but nevertheless, this bridge is supposed to make an impact, and to those who pay attention, I believe it does.

After painting this bridge in such a beautiful light, I must remind all readers that this was in fact a construction project in the middle of I-85, and as Oscar Wilde put it so delicately, “No good deed goes unpunished.” Okay, I might be overstating the level of issues faced in construction, but, as I’m sure many Atlantans remember not-so-fondly, the construction of this project mid-way through during the I-85 bridge collapse. While it was not this specific bridge that collapsed, Atlantans do tend to value something over the sightseeing on their ways to work: getting to work in a timely manner. Traveling on I-85 after the bridge collapse was a nightmare. My usual 20-minute drive to Buckhead, if that, turned into at least a 45-minute one. And in my experience, Atlanta drivers are not known for their patience and sound judgements in traffic-heavy circumstances. Just to add onto all of the chaos, and right when it seemed like the project was getting back on track, Hurricane Irma hit. Construction, which was originally set to end in April 2017, did not finish until November of 2017. Yikes! So, while the appearance of these arches and signage did convey a message, it was somewhat muddled by the not-so-great circumstances. I just hope people moving forward will still put in the effort to read between the lines of chaos and through to the potential beauty that could put Atlanta on the map in a new way.

 

Structural Art

Okay, evaluating the bridge in its entirety as a piece of structural art is difficult. The original bridge built in the 1980s and pictured below in Figure 3, was purely utilitarian and is not a sight I want to set my eyes on all that much.

Figure 3: Peachtree Street Connector Before Renovations [1]

At best, it fits into the landscape of the highway and doesn’t really catch my eye; at worst, I might call it ugly. However, when looking at the three E’s, it does seem to cover at least one of them: efficiency and even possibly economy although not much information on the original bridge is available given that it was supposed to be monotonous and fit in with the surrounding concrete. At the bare minimum it succeeded in its purpose of getting people from point A to point B. However, it is most definitely not elegant, in fact its appearance was very consciously dismissed or ignored in its design.

On the other hand, the renovations, mainly the added 22 arches pictured in Figure 4, had very little if any structural purpose in terms of helping the bridge resist the natural forces acting upon it, mainly gravity as well as a live load of the foot and vehicular traffic.

Figure 4: First Arches Added on Southbound Side [1]

Really, it is using extra, unnecessary material to add dead weight to the already existing structure. So, the arches, which function as the key part of the renovations, have a large symbolic purpose which would achieve elegance, but most definitely on its own did not endeavor for good economy and efficiency. I would say that they serve an architectural purpose, but the arches don’t actually add to people’s use of it, which is key in architecture.

And at the core of Billington’s category of structural art is intention during the design. To truly be an exhibit of structural art, the designer had to design with the three E’s in mind. No matter whether we look at the renovations themselves, or the original bridge design, the designer in each case definitely did not endeavor to achieve in its entirety elegance, economy, and efficiency. The first designer didn’t care about elegance at all, and the second had no need for achieving economy and efficiency because he/she was limited to the constraint of adding on to the existing bridge. Therefore, I conclude that while this bridge may function as a catalyst for future structural art in Atlanta, it is not structural art itself.

 

Okay, now onto the fun part (hopefully?)… the structural analysis.

Structural Analysis

The design for the Peachtree Street North Bridge was completed as part of a bridge competition for all the bridges Midtown Alliance hoped to construct as part of its $6 million beautification project. The criteria given to the competitors were symbolic, not structural other than the existing bridge had to be able to sustain and integrate the arches into its existing system. The symbolic goals were as previously stated, to make a statement to everyone approaching Metro Atlanta that the city is worth recognizing and noting.

The construction was more complex. As an I-85 connector bridge, traffic is heavy. 42,000 cars travel on the bridge each day, not including pedestrians and bikers, and 300,000 cars pass under the bridge EACH. DAY. Interrupting traffic was not an option. So the 22 arches, consisting of 2,200 linear feet of steel tubing, were assembled off site. The reason for this was two-fold: the contractor needed limit disruption of regular traffic flow on and around the bridge, and the arch assembly required more space than available on the bridge had it been assembled on site. The arches were painted off site. Then, first on the southbound side, the 10 minor arches were erected and bolted in place. Only once southbound major arch was completed did construction proceed on with the northbound side. Notably uneconomical and inefficient, each segment, angle, joint and weld was assembled uniquely and individually. While somewhat small-scale when compared to the Eiffel Tower or even the Bank of America plaza (or more properly known to Georgia Tech students the Pencil Building), Midtown Alliance has stated that this is “one of the most sophisticated structural engineering projects [they] have ever undertaken” [1]. To show the progress made, here are monthly taken photographs of the construction of the Peachtree Street North Bridge as provided on the Midtown Alliance web page.

Figure 5: Offsite Arch Assembly [1]

Figure 6: Beginning of Onsite Minor Arch Assembly on Southbound Side [1]

Figure 7: Southbound Arch Assembly cont’d [1]

Figure 8: Southbound Arch Assembly cont’d [1]

Figure 9: End of Minor Arch Southbound Assembly [1]

Figure 10: Completed Minor Arch Construction [1]

Figure 11: Southbound Major Arch Construction [1]

Figure 12: Beginning of Northbound Major Arch Construction [1]

Figure 13: Completed Bridge Construction [1]

Structural Systems:

  • Footings
  • Columns supports
  • Concrete beams

Figure 13: Footings, Columns, and Concrete Beam [3]

  • Rectangular steel girders
  • Deck
  • Steel tube arches

Figure 14: Steel Girders, Deck, and Steel Tube arches [1]

Load Path:

Steel Tube Arches (uniform weight load) –> Deck (point loads + self weight + LL) –> Steel Girders (Line Load) –> Concrete Beams (Point Loads) –> Columns (compressive point loads) –> Footings (line load) –> Ground (surface load)

 

Mechanics of Load Distribution:

**Many assumptions were made on the dimensions of all elements except for the steel tube arches as those are the only new structures so the information is readily available. Simplifications were also made to the shapes to make calculations more straight forward. Also, based on the simplifications to basic beams and such, I found that the bridge only experienced axial forces, and bending is not an issue when modeling the dynamic load of the cars and pedestrians as a uniform load and ignoring weather conditions. The bridge is also not high enough to warrant wind force analysis.

Figure 15: Steel Tubed Arch Calculations and Models

Figure 16: Deck, Girder, and Beam Calculations

Figure 17: Footing Calculations

CAD drawings were absolutely instrumental in the successful design and implementation of the steel tubed arches. According to the Midtown Alliance, 1 million data points were used to model the BIM and CAD drawings effectively for the arches. Due to the massive public participation in this project, the drawings needed to be as accurate and easy to read as possible to get as many people on board to fund and politically support the project.

Personal Response

Overall, my drive was definitely improved by the addition of these arches to my trip. While the bridge might not hold up to my New York standards of bridges (the George Washington Bridge is the ultimate structure), my dorky-ness couldn’t help but shine through

References

  1. https://www.midtownatl.com/about/programs-and-projects/capital-improvements/peachtree-street-north-bridge
  2. https://atlanta.curbed.com/2016/5/6/11605204/atlanta-bridge-architecture-fancy
  3. https://www.ajc.com/news/local-govt–politics/peachtree-bridge-sign-put-premier-street-lights/1RxpKqHukolDoQTUJvWoeO/
  4. https://atlanta.curbed.com/2017/3/23/15031664/peachtree-street-bridge-midtown-arches
  5. https://www.midtownatl.com/about/programs-and-projects/capital-improvements/peachtree-street-north-bridge
  6. https://en.wikipedia.org/wiki/Sydney_Harbour_Bridgehttps://atlanta.curbed.com/2013/7/10/10221698/peachtree-street-bridges-to-be-beautified
  7. https://atlanta.curbed.com/2015/11/24/9897018/midtown-peachtree-bridge-upgrade-aims-make-statement

Canopy Walk at the Atlanta Botanical Gardens

The Canopy Walk makes itself known by crossing over one of the roadways entering Piedmont Park, bridging (literally) two areas of the Atlanta Botanical Gardens. The bridge makes a striking first impression to those visiting the park and the Gardens, and is even more interesting to me as an engineer for its unique shape.   

Figure 1: The Canopy Walk [1]

Structural Information

The Canopy Walk is a steel pedestrian bridge that snakes through the trees at the Atlanta Botanical Gardens in Piedmont Park. The bridge was designed by architects Jova/Daniels/Busby and structural engineers Halvorson and Partners, P.C. [2]. The bridge began construction under Hardin Construction Company during 2008, and was opened to the public in May 2010. The project was ordered and developed by the Atlanta Botanical Gardens.

Historical Significance

Just by looking at this bridge, one can tell it is unique – it’s sweeping pathway form and unconventional support structure make it stand out as different and intriguing. Its form speaks true – the Canopy Walk is the only winding tree canopy walkway of its kind in the United States [2]. The form is inspired by the Spanish architect and structural engineer Santiago Calatrava, who is known for sweeping, dynamic forms and bridges supported by single pylons. This bridge is a graceful imitation of his style, snaking between trees while appearing light and open through its suspensions. The bridge is the sole example of this suspended type bridge through tree canopies, and could serve as an example for future bridges to take inspiration from.

Figure 2: Canopy Walk under construction, prior to collapse. [3]

Cultural Significance

This bridge was added as a part of a large expansion project by the Atlanta Botanical Gardens that nearly doubled the size of the Gardens. Given the scope of this expansion, the bridge was inevitably going to be a gateway for heightened attention for the Gardens, and attention it brought – although, not in the best of ways at first. At the end of 2008, the park hosted a news event to commemorate concrete being poured into the deck to excite the public about the upcoming bridge. Unfortunately, during the pouring, the Canopy Walk collapsed due to failure in its shoring systems during construction, leading to the injury of 18 construction worker and the death of one more [4]. The failure led to the opening to be delayed until 2010, when structural issues were fixed and it was finally opened to the public. Despite the rough start, the Canopy Walk has become a beloved addition to the Atlanta Botanical Gardens, leading the park to expand to further attractions and allowing guests to gain an unparalleled view of the forests and Gardens from above. To this day, it remains a popular attraction.

Structural Art

Now that the Canopy Walk is staying up, it can definitely be seen as an example of structural art in its lightness of form and its open design. Structural art, according to Professor David Billington’s works, is characterized by three dimensions: scientific, social, and symbolic.

Scientifically, this bridge succeeded, eventually. The pedestrian walkway is a cable-stayed bridge supported by 4 masts nearby the bridge, but also includes two inclined columns at a fixed span halfway through the bridge. The bridge is composed of steel, supporting a concrete walkway for foot traffic only. Since its opening, it has remained steady.

Socially, this bridge exists as the first of its kind in the United States. As a canopy bridge, it allowed the Atlanta Botanical Gardens to expand over roadways and improve the experiences of visiting guests. Since opening it has been popular with the public, drawing in more visitors with its clear presence. [5] Additionally, the cable-stayed structure uses minimal materials to keep the bridge up, increasing its economy through efficiency of materials.

Symbolically, this bridge rises over the ground giving visitors a bird’s eye view of the park and its expanded grounds with its unobtrusive cable suspension. However, aside from that flavor text, it isn’t really considered widely impactful outside of the Gardens themselves.

Billington was clear in another aspect of structural art that is apparent with the Canopy Walk: openness of form. The bridge is without much ornament, with the main visual impact coming from the walkway itself and the steel cables and towers supporting it. The structural pathways and reasons for each part of the bridge are clear and make sense. From all these factors, I would consider this first-of-its-kind bridge structural art.

Structural Analysis

The Canopy Walk uses two different methods of support along its 575-foot length to suspend the walkway above the ground. The more prominent and impactful support structure is in its cable-stayed supports, with four masts connecting support cables to the structure of the bridge. These cables hold the bridge in place through tension with the 24”, ½” thick structural pipe columns off to the side. The second support structure is in two columns simply supporting a 70-foot fixed span near the center.

The support systems carried a 30” diameter, ¾” thick structural pipe supporting cantilevered framing members holding up the steel and concrete deck. Three support cables per column connected via gusset plates to this main pipe – one connecting perpendicularly, two at angles. These cables connected at the top of the mast and then connected angled back to be anchored in the ground below the columns. The cantilevered steel tube framing members were welded above the structural pipe. The deck above consisted 2” steel and 6” concrete. During construction, the steel pipe frame was supported using 21 temporary shoring towers used until the masts and cables were set in place. It was structural failure in these showing towers that resulted in the bridge collapse during 2008.

Figure 3: Underside of the bridge [6]

The three cables act in tension to suspend the bridge in the air from the angled support columns. The cables typically are connected to the bridge 25’ from the top of the support columns. The bridge is also designed to take 85 psf live load. After this however, information gets more tricky: the incident occurred before the cables and columns seemed to be installed, so I cannot find information on cable thickness or column height or exact figures on dead load. It is given that the average bridge load over each of the 21 temporary shores was 22 tons, so by that figure, the dead load can be calculated to 803 psf, resulting in a total load of 888 psf.

Figure 4: Detail of cables [7]

As stated, the cables serve to both hold the bridge in its curvy form and to keep the bridge raised. The total distributed load over the bridge from dead load and live load is 510.875 kips. The ends of the bridge connect to the ground via concrete abutments. Each cable supports its own tributary area, meaning that cable supports on the ends carry greater load than the central cable supports. The bridge can be simplified to a 2-dimensional system to determine cable reactions carrying the load.

Tributary areas are assumed to be split between support structures. For cable supports at the ends of the first and last structures, it is assumed they take the entire load of the bridge ends without aid from the concrete abutments. From there, vertical load requirements can be simply calculated using the load per foot over each tributary area. The loads of the deck then travel up the cables which are attached to the offset masts, which then transfer the load from each cable down to the ground.

OSHA documentation from after the accident show architectural and engineering details of walk. The detail sheets point out cross sections of the bridge, along with locations of the support systems. Since this project was completed, both the architecture and construction firm have been disbanded or absorbed, so finding more drawings and models was difficult beyond those provided to the accident report.

 Fig. 5: Engineering details of the Canopy Walk, prior to collapse in 2008. [3]

 

Personal Response

This bridge was one of the first moments of awe I felt when visiting the Atlanta Botanical Gardens, as I had never seen a bridge quite like it before. Looking at it a second time, now through the armed with a stronger knowledge of structural engineering, I can better appreciate the cable towers and their purpose in keeping up the bridge. Before, the bridge caught my eye because it was interesting to look at. I now know more about the history of its construction, and how the bridge succeeds now in carrying these wondering guests through the air.

References

[1] http://journeyleaf.typepad.com/journeyleaf/2014/07/atlanta-botanical-garden.html

[2] http://atlantabg.org/about-us/news-blogs/canopy-walk

[3] https://www.osha.gov/doc/engineering/2008_12_19.html

[4] https://www.nytimes.com/2008/12/20/us/20collapse.html

[5] https://www.myajc.com/entertainment/atlanta-botanical-garden-expands-into-woods/ClIsngYS4p5lApfzKvGS6O/

[6] http://www.wanderlustatlanta.com/2010/08/atlanta-botanical-garden-oasis-in-city.html

[7] http://www.wanderlustatlanta.com/2011/01/atlantapix-600-foot-canopy-walk.html

Coda Building

Structure Information

The new Coda Building began construction in 2016 and is expected to be completed in the 4th quarter of 2018 [1]. It is located in Midtown, Atlanta, just one block from Tech Square. Georgia Tech and John Portman & Associates announced their plan for the 750,000 square foot collaborative building and high performance computing center. 620,000 sq.ft. of the building will be office space, half of which will be available for companies and the other half will be occupied by Georgia Tech. There will also be 40,000 sq.ft. of retail space, which includes the historic Crum and Forster building, labelled as 1 in Figure 1 and in the foreground of Figure 2. and 80,000 sq.ft. of a data center, labelled as 2 in Figure 1 [1]. The building plans to offer an “unparalleled collaboration between research and industry” by giving major companies associated with Georgia Tech the opportunity to work closely with Georgia Tech and with each other with access to a high performance computing center and interactive community space. FS2 was commissioned for designing John Portman & Associates’ 21-story building [3].

Figure 1. Overall Picture [1]

Figure 2: The Historic Crum and Forster Building

Historical Significance

The Coda building itself embodies many state of the art design aspects.There are 5 stories of parking located below the building. The parking deck was put in place using a boring machine and soil nailing. Laser scanning has been used in every phase of construction and by plotting exact points, the scanner was able to catch that one wall was leaning a few inches. The soil nails were redone and this was taken care of thanks to the newly practiced laser scanning technology. The building is also the first ever in America to have TWIN elevators. The TWIN design has two elevators running at the same time in one shaft [3]. Because companies may have multiple floors, this permits someone who is going from floor 17 to 15 to hail the top elevator, instead of sharing with the lower floors. There is a holding place for the elevator at the top and bottom of the shaft so the elevator can go from the top floor to the bottom floor without being blocked by the other elevator in the shaft. The elevators can work with varying floor heights (i.e. a taller lobby) and go to any floor, without separating even or odd floors [3].  The difference is, passengers enter their desired destination upon hairling the elevator, so the paths and elevator can be selected in advance[4]. Initially, the building design had a low rise/ high rise solution, which required a physical barrier separating the lower and upper floors. This solution fit the requirements, but not the collaborative goal of the building. With the TWIN elevator system, the building can remain one part and keep the connection between the upper and lower floors [3]. More than 200 buildings around the world have implemented this elevator made by Thyssenkrupp, including their headquarters in Essen, Germany [1]. There have been many other collaborative spaces constructed and loads of research done on the topic, but the Coda building combines many different practices from floor plan to structural design. Other complete examples include Oregon’s Collaborative Life Sciences Building, the Bacardi headquarters, and the Hyundai Campus. Many of these buildings embody similar approaches to collaboration including open, connected spaces with natural lighting and open floor-plans. They strive to inspire with their spaces and promote the Green initiative [5]. A key difference is a few companies find that being in a suburb increases motivation and productivity compared to urban campuses [5]. The Coda building will definitely inspire future buildings. It is the newest example of a collaborative building, with innovations that are appearing for the first time in the US. Once complete, the Coda building will be the “thing to beat” as others aspire to create collaborative, innovation driven spaces. From design to furniture selection, Coda will have state of the art technology and research in every detail.

Cultural Significance

The Coda building will house both industry professionals and GT research and extend Tech Square. Over the past few years, Tech Square has become the innovation hub of the southeast and, with Coda, it will have three million square feet of commercial space attributed to it [3]. The use of new technologies in the building and collaboration spaces with researchers and professionals in the Coda building will add fuel to the innovation fire currently in Tech Square. The building will also have public spaces, an interactive media wall, and retail spaces for the public. The historic Crum and Forster building will be updated and accessible to the public as a gathering place and outdoor living room [1]. President Bud Peterson discussed how the collaborative building will also have a positive impact on Midtown by bringing people together in “a mixed-use community of innovation, education, and intelligent exchange.”

Structural Art

In regard to the basis of structural art, economy, efficiency, and elegance, the Coda building is very lacking in the first. There were no major monetary constraints, which violates the basic principle structural art, that creativity is fueled by the monetary constraints (economy). The historic building has features pre-dating the era of structural art and is not tall enough to be considered structural art. The Coda addition does embody some features of structural art including clear load path because it is a glass building and the beams are visible. Only necessary supports were used, but they were not always the most cost effective options (efficiency). The single beam support of the staircase and pop-out section of the building are examples of this. Also, by omitting beams through the walkway and having the large open space below, large expensive supports were needed to hold the structure up during construction, until it was tall enough to be stable. See Figure 3, Figure 4, and Figure 5 for the temporary supports and after removal.

Figure 3: Base of Temporary Support

Figure 4: Top of Temporary Support

Figure 5: Remanence of Temporary Support

Elegance is satisfied in the engineering sense as the supports and load paths used are visible and the engineering systems are innovative and impressive, although not affected by monetary constraints. The main focus of this building is aesthetics and that is it’s fault in structural art. In regards to scientific, social, and symbolic aspects of the building, Coda does a better job than compared to the E’s. Scientific is where the building is lacking, as the design and materials are not constrained by money, although the structural design is creative, clear, and safe. Socially, as I described in the cultural and historical sections, Coda will have a major impact on the innovation world, the workplace, Midtown, and future buildings. There are not many long term costs to society, and, as a privately funded building, there are not short term monetary costs. There are, however, short term costs in the noise and road closures. Symbolically, the building creativity and public gathering spaces embody the aspirations of the building, collaboration and innovation. Even the research and innovation being done within often does not have monetary constraints, so the building symbolizes the uses perfectly. Overall, Coda cannot be considered structural art because of the basis of creativity with economic constraints. The building cannot be compared to other examples of structural art or explained with the E’s and S’s other than economic because they all have a basis of monetary constraints.

 

Structural Analysis

The Coda building was designed to embody collaboration and innovation in every aspect. The staircase and pop-out side of the building are examples of structural innovation and the glass shows the connection and openness within the building. The speed and precision of construction shows how innovation and collaboration are being applied. Boring down five levels and using soil nailing while pumping out and lowering the water level below is almost unheard of. Forms and concrete pump trucks are adding floors constantly with a crane on site 24/7 to move the forms once the concrete has solidified. While concrete is forming floors, other sections of the building are getting the steel frame put in. The two sides of the building joined at the staircase are going up simultaneously with the crane in the elevator shaft because from there it can work with and reach both. These are just a few examples of how every aspect of the building embodies collaboration and innovation.

The systems I will be analyzing are the staircase and the pop-out section of the building. The design load of an office building is 50 pounds per square foot per floor, although the measured load is only 10.9 pounds per square foot. The staircase goes from a line load from the roof through the walls, to a surface load of the floor, to a line load in the walls below and so on down the building until the surface load on the bottom floor is distributed into a point load in the single column to the ground as seen in Figure 6, Figure 7, and Figure 8. The glass panels around the staircase are shortened to account for the curvature. Assuming the windows are a foot wide, the diameter would be 12 feet. The stress would be the force over area. Force equals the number of floors (7) times the area (pi*6^2) times the force per square foot per floor (50) divided by the area (pi*6^2). The stress calculation for the floor above the column gives a stress of 350 lb/sq.ft. (1). The stress in column is the force (same as above) over the area of the column (pi*2^2). The stress calculation gives a stress of 3150 lb/sq.ft. (2). I am neglecting the self weight of the pole in this calculation because it is negligible. I found the diameter by comparing to the people standing by the pole and the windows. The critical buckling is (pi^2*E*I)/L^2. Assuming E is 7250 ksi (that of strong concrete, have to x12x12 to get feet), I is ¼ (pi*R^4), the height is 25 feet,  the critical buckling point is 207,171 lb, which is much greater than the P of (3150*A) which is 39,584lb. The change in shape (delta) is (P*L)/(E*A). In this case, delta is .075 feet. This could be explained in drawings by showing how the force over the whole area of the staircase/ room is initially distributed then all on one point, the column, therefore it is very large and requires such a thick column. The drawings would show the detailed supports that transfer the load to the column and how they connect.

Figure 6: Stairwell Load Path [1]

Figure 7: Process of Stairwell

Figure 8: Future Completed Pedestrian Walkway

The pop-out section of the building is a cantilever with 18 floors. The load goes from the roof, down as a line load to the floor below for each of the 18 floors above the overhang. From the bottom of the overhang, the load is transferred through a fixed connection, like a cantilever, to the main structure of the building. Refer to Figure 9 to see the load path.  Assuming each window is 3 feet wide, the side length is 25.5 feet and the width is ¼ of that so 6.375 feet. Therefore, the force on the cantilever is 50 pounds per square foot per floor *18 floors * 25.5feet * 6.4 feet, which equals 146,310 lb. Assuming there is one beam supporting each side and even distribution, each will hold 73155 lb total, which results in a w of 5852 lb/ft (73155 lb/25ft/2). Assuming the beam is 2×1 with the long side on top, the deflection is (wL^4)/(8EI). Assuming L is equal to the side length of 6.4, E of steel 29007*12*12, and I is of a 2ftx3ft beam (as observed in Figure 10), the deflection would be 0.14 feet. Fx at the base would be 0, Fy would be w*l 33650lb upward, and M would be 3.2ft*33650lb (107700 ft.lb.) clockwise. With this information you could explain the design by showing that a thicker beam will not break and that a heavier base will ensure the cantilever does not tip (i.e. a toothpick will break trying to hold a weight but a pencil would not, the pencil in an eraser would tip over but in a wall pencil holder will not) and explain how the force requires a thick beam and the building can hold the rotation caused by the force. The drawings could show exactly how to attach the beam and it’s dimensions.

Figure 9: Cantilever Load Path

Figure 10: Cantilever Process

Personal Response

Having been in the building, I learned a lot about how much more complex the construction activities are and that you never know what is going to happen. Very often on sites, unexpected bumps in the road are hit, causing delays. In the Coda case, the water continuously had to be pumped out to bore the parking, 24/7 for weeks. I also had never realized what it took to have large gaps and how expensive adding a truss instead of columns is. Material wise, it seems the truss is equal, if not better. However, on the construction side you see the semi-permanent, expensive to get and install, time consuming supports and scaffolding needed to hold the load until the truss is complete. In design classes and in final presentations or books on buildings, details like this are often omitted.

Resources

[1]http://www.news.gatech.edu/2016/04/20/georgia-tech-portman-announce-coda-tech-square

[2]https://archpaper.com/2018/01/georgia-tech-atlanta-coda-technology-jobs/#gallery-0-slide-0

[3]https://www.fs2ec.com/coda-in-tech-square

[4]https://www.wired.com/2016/05/thyssenkrup-twin-elevator/

[5] https://www.gensler.com/design-forecast-2015-the-future-of-workplace

 

Gardiner Building’s Chart House

 

Structure Information

[Figure 1: Gardiner Building’s Chart House]   

Chart House, once known as Gardiner Building, is located on Boston’s historic pier Long Wharf, at 60 Long Wharf, Boston, MA 02110, USA. Gardiner Building was built in 1763 after the 1710 to 1721 construction of Long Wharf.

The Gardiner Building was once used as office space and cargo storage. Captain Oliver Noyes constructed Long Wharf and the buildings that occupy it, including the Gardiner Building. The historic pier, Long Wharf, once served as the heart of Boston’s maritime trade and was leased to the government for customs work.

Historical Significance

The entire pier was built from a 2,200-foot-long barricade composed of a wharf of stone and wood piles. Gardiner Building House was built with large cellars that would store cargo, then later sell the same cargo at its doors. There was nothing really structurally innovative or new about this building. It is a basic three-story brick and concrete, routinely shaped house.

Cultural Significance

Chart House is Long Wharf’s oldest surviving structure and was once home to the offices of John Hancock, also known as John Hancock’s Counting House. The historic restaurant attracts many different people from your fascinated Boston tourist, to your everyday Bostonian who just loves the food, and the experience of Gardiner Building’s Chart House. I do not know of any backlash or outright love for the construction of Gardiner Building, as well as the human cost in the building it, but I can imagine a relatively low human cost for this uncomplicated, three-story building. Today the structure serves as delicious, historic waterfront restaurant, and a great place for date with your significant other, or maybe even a lonely happy hour.

Structural Art

In my opinion the Gardiner Building does not demonstrate structural art. According to David P. Billington, structural art gives equal weight to the three E’s of a structure: efficiency, economy, and elegance. Although the structure may exhibit efficiency and economy, it does not showcase elegance, therefore it cannot be referred to as structural art. In regard to efficiency the structure was built on a historic pier with the use of old materials, while money and time seemed to be used successfully, and without waste. As for economy, the structure was used offices and storage space during Boston’s colonial era. Nevertheless, the structure is an uninteresting three-story house, therefore is does not present structural art.

Structural Analysis

The Gardiner building is the great grandfather of all buildings on Boston’s waterfront, so engineers had been watching it closely. In 2001 Gardiner started showing its age, and monitoring indicated that the structure was in danger of crumbling. As a result, PAF architects worked with a team of engineers and construction mangers to save little old Gardiner. They used low overhead drilling equipment when repairing the exterior walls, in an effort to protect the original structure. Reinforced concrete was used as rebar for new subgrade beams as the support for the exterior walls. During the repair, temporary corner bracing was also added in order to save the integrity of Mr. Gardiner. This work was completed on a fast track schedule and took only about six months to accomplish. I guess the people of Boston were eager to see Mr. Gardiner up a running again.

 

[Figure 2: Load path of the Gardiner Building]

Load Path Analysis

Red : Surface load

Green : Point load

Blue : Uniform load

The roof of the structure has a uniform surface load, from its own weight, and any wind, snow, or birds it may encounter. The chimney applies a point load on the section of the roof that supports it. The roof is then supported by beams that receive and uniform line load from the roof. The beams are then supported by trusses that receive point loads from the points of intersection. There are numerous arches throughout the building that all receive uniform loads from beams they support. The arches are also subject to point loads in the downwards direction from their columns. The concrete beams collect a uniform load from the beams they support and transfer the specific load back to the columns of the structure. Lastly, the columns of the structure transfer a point load to the concrete base that supports them.

[Figure 3 : 3D load path of the top portion of the structure]

[Figure 4: Structural analysis calculations]

Calculations

Dead load for concrete: 145 lbs/ft^3

Approximated tributary area: 180 lbs/ft^2

Approximate base length of arch: 10 ft

Approximate height of arch: 6 ft

W = (Dead load)(Tributary Area)

Selected arch supports a uniform load

 Fmax is the maximum force applied to the arch as well as the maximum force the arch applies to the beam that supports it.

 

[Figure 5: Me wishing I could afford to eat at Chart House]

 

 

 

Personal Response

You all may be wondering why I would pick such a random structure, and I can honestly say I did not plan this. The cheapest way to London, resulted in a seven-hour layover in Boston. I am always one to make the best out of any situation, so I decided to explore the city. Initially I was just looking for a good, unique, cheap place to eat, but in my journey, I stumbled upon an exquisite, historic waterfront. I did not end up eating at Chart House because my funds are a bit rocking at the moment and it did not meet my criteria of a cheap place to eat, but I did get a great blog post idea from it. If I would have just seen this structure in a book or a video I would not have been able to appreciate the beauty of the location of the structure and its rich history. The entire waterfront has an inimitable exquisiteness that captures the historic aroma Boston.

References 

https://www.nps.gov/nr/travel/maritime/lon.htm

http://www.pafaa.com/Adaptive%20Reuse%20&%20Historic.html#chart