Archives for May 2018

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

 

Holy S…!

Holy structure! Yeah, structure. Don’t let your mind suggest something else!

 

Figure 1: The Basilica of The Sacred Heart of Jesus[1]

Structure Information

During one of my rare errands on Peachtree Street in Atlanta, I’ve came across this beauty and convinced myself that it might be a good time to be religious. Formerly known as Saints Peter and Paul, the Basilica of the Sacred Heart of Jesus is a church founded in 1880 that

Figure 2: Location[2]

was initially located a few blocks away westward. The needs for relocation occurred in response to the congregation’s increasing number and the commercialization of the area. A new denomination “The sacred Heart of Jesus” came along with the French Romanesque design of the architect W.T. Downing in 1897. The impressive creation won a place in the National Register of Historic Places in 1976 and was later consecrated as The Basilica of the Sacred Heart of Jesus by His Holiness Pope Benedict XVI himself! Funding came from diverse unrevealed sources. During my short tour guide, I came to understand that the facility is projecting important repairs and only fifty percent of the $1.25M needed is met. I’m not preaching here…your donation…lol!

 

Historical Significance

Figure 3 : Inside toward the tabernacle

Figure 4: Inside, toward main exit/entrance

 

 

 

 

 

 

 

 

 

 

 

 

 

The engineering design for this structure was not entirely new. As expressed earlier, the Architectural style was inspired from the Roman French with a final product that demonstrated a particular touch from Downing and his engineering team. Both the exterior and interior are predominantly consisted of arches and decorative columns which are literally Roman’s footprints/signature . The idea of improving pre-existing designs in order to obtain enhanced products could not be condemned, is it? The humanity has been long relying on old patterns to define new ones.

 

Cultural Significance

While it was still Sacred Heart, Mother Theresa of Calcutta, an important figure of the Roman Catholic church, was there for a Mass in June 1995.  She came at the Basilica for the blessing of the Sisters of Charity AIDS hospice. The renowned Father Michael A. (Tony) Morris led the congregation during its growth and revitalization. The “artistically significant architecture” is said to have influenced the recognition to the National Register of Historic Places. All sort of religious education are provided on the premises in both English and Spanish.

 

Structural Art

The walls of the First Catholic Church of Atlanta are essentially made of masonry, pressed brick and terra cotta. Two twin towers with octagonal shape along with arches of various span were heavily represented. Columns are symmetrically placed, creating an aesthetic touch that follows the “function follows form” of David P. Billington [3]. Architect Downing used eyebrow windows to enhance the building’s aesthetic expression. The conic element on the top of the one-hundred and thirty-seven feet towers is visibly made from lighter material but stiff enough to resist wind loads; revealing the combination of what qualify, in my opinion, the building as a structure art.

 

Structural Analysis

The design principles were those associated with resistance to wind loads, dead weight. From the interior pictures -little dark by the way- we could perceive how the high ceiling in the shape of a dome -above the tabernacle, specifically- transmits its load to the symmetrically and strategically positioned columns. Considering the relatively small section of the columns and the thickness of the outside walls, I’m tempted to say that most of them were bearing-walls. However, the columns were collecting loads from the tributary areas of the roof and of the beams between the spans of the high-rise building. The base of the towers consists of cubic blocks containing tall, round-headed windows incorporated in recessed walls framed by strip buttresses. Depending on the cases, the arches were submitted to a triangularly distributed load which, in return are transmitted to the columns. For example, the Triple-arched doorway at the entrance displayed at the right present how the loads are applied. The reaction at the base of each column should withstand the weight of the associated tributary area. In this case, it’s clearly predictable that the pair of columns in the middle would more likely have the same design and a more consistent load compared to the others two.

Figure 4: Load below the beam on arches

Figure 5: Tributary area, load distribution

Figure 6: Collection of tributary load into the column

 

 

 

 

 

 

 

 

Due to symmetry, there’s a high likelihood to have multiples structural elements with the same sections; making the engineering duty less complex unless geotechnical conditions differ.

It was recorded that the building was built for $28,000 on a land initially acquired for $12,000[4]. I was not able to collect any technical information. I’ve resolute to focus on the design of the high ceiling with the following assumptions:

Figure 7: Load on arches

-Dead load for concrete = 145 lbs/ft3  [5]

-Live Load (snow) = 5 lbs/ft2 [6]

-Hmax = 25 ft (pure estimation)

-Slab thickness = 8 in (previous experiences input)

-Tributary Area A = 180 ft2 (pure estimation)

-Span L = 150 ft (pure estimation)

 

Figure 8: Determination of loads

 

With these information, I was able to compute the reactions on the buttresses and the load on the columns as displayed in the following figure.

The next step was to evaluate the bearing stress on the columns. With the diameter of the column estimated to be around 18 feet, the area of the column is estimated to be in the order of 36,643.54 in2. The bearing stress being equal to the force over the area, the bearing stress of the columns is evaluated at 80.41 psi. With a supposed Factor of safety of 11, I was able to conclude that the allowable stress should be 884.5 psi in order to prevent any eventual buckling. Furthermore, it’s imperative to appreciate the responsiveness of the columns to stress and since the maximum occurs at the center, that would be the center of our focus.

 

Personal Response

The physical presence inside an historic building of this type is more than insightful. Anyone else could have also suspected the building for being a little old but just not as much as a century. Its powerful in some ways to get so close of one of the oldest structures built in Atlanta which is still functional. Now I understand, how incertitude has influenced a relatively greater factor of safety for ancient structures; leading for massive sections not necessarily cost-efficient. Especially, in this case of a religious building, I just hope for my visit to have occasioned my sins to be washed away!

 

References

[1] http://www.sacredheartatlanta.org/directionsparking.html

[2] https://screenshots.firefox.com/UKHW08xvzEaflSA7/www.google.com

[3] David P. Billington  The Tower and the Bridge: The New Art of Structural Engineering

[4]http://www.sacredheartatlanta.org/about-sacred-heart.html

[5] https://www.atlantaga.gov/government/departments/city-planning/office-of-design/urban-design-commission/church-of-the-sacred-heart-of-jesus

[6] https://www.atlantaga.gov/home/showdocument?id=33495

 

 

The Lincoln Memorial

Lincoln Memorial

As I was watching Elle Woods (in the movie Legally Blonde) fiercely climb the stairs of the Lincoln Memorial and find the courage to pursue her dreams while gazing into the strong stare of Lincoln on his throne, I knew at that moment that I too wanted to live out a dramatic scene on those stairs and experience the majestic strength that emanated from that structure.

The statue itself is magnificent but what really grabs attention and allows the structure to truly shine is the house where the structure sites. Its high columns give Lincoln a regal, majestic almost celestial feel. The large scale of the memorial, the height, the thickness of the columns and the stark white of the marble give me the impression that it is almost sitting on clouds. It is, in my opinion, a piece of architectural art; but is it structural art? Keep reading to find the answer. 

I did not grow up in the United States and all I ever knew about Lincoln was from the embarrassing amount of television dramas that my mom (me really) watches. Through this blog post, I had the opportunity to learn more about this great man as well as the structure used to remember him. Lincoln was a man of honor who served his country like no other and died in a most tragic way. It only seemed right that he may be remembered in a structure as grand as he was.

Related image

Figure 1: The Lincoln Memorial looking as though it sits on clouds [2]

Structure Information

Ever since Lincoln’s death in 1865, Congress had been toying with the idea of having built a monument in his honor. It was not until 1911 though that Congress gathered enough funds to commission the memorial. They approved, $2 million dollars (3) bill (in today’s money) and created a commission that was headed by President Taft to oversee the project. Construction started on February 12th, 1914, (Lincoln’s birthday) and the memorial was dedicated on May 30th, 1922. It is located at West Potomac Park at the western end on the national mall in Washington DC The Lincoln memorial is actually across from the Washington Monument for those who have never been (shame on you!).

The memorial ended costing $2,957,000 and the statue $88,400 for a total cost of $3,045,400. The structure includes 3 chambers with the statue resting in the central one. The purpose of this building is to commemorate the 16th president of the united states, Abraham Lincoln who was tragically assassinated in 1865. It is a historical site and a tourist attraction.

Three people contributed to the design, each acting in different part. The architect of the memorial was famous French architect of the time Henry Bacon (3). The murals feature intricate artwork done by Jules Guerin and the statue itself was carved by artist, Daniel Chester French.

Image result for lincoln memorial structure

Figure 2: Lincoln Memorial [4]

  1. Historical Significance 

Nothing about the Lincoln memorial ‘s structural design is particularly innovative. It was built to be reminiscent of old Greek temples, but with a modern twist. I doubt that this will be a model for future buildings due to its symbolic nature and its use of old structural themes.

 

Image result for greek parthenon

Figure 3: Ruins of Parthenon in Acropolis, Athens, Greece [6]

  1. Cultural Significance 

The Lincoln memorial today stands as an iconic symbol of America. Its representation can be found on the back of 5-dollar bill (I have provided a picture for those who forgot what money looks like). It was also found at the back of pennies. As Lincoln abolished slavery, his memorial played an important role in the civil rights movement. It served as a place of protest, it was a part of the March on Washington in 1963 and the place that Martin Luther King Jr. gave his famous “I have a dream” speech. It hosted the Easter Sunday Concert (9) a major event for the civil rights movement too.

Figure 4: penny [11]

 

Figure 5: 5 dollar bill showing memorial [12]

As stated previously, the design was based on Greek Parthenian temple. You might wonder what Greece has to do with the United States.  Don’t worry you are not the first to ask such a question. When the design was first released it received great criticism for architects all over the United States. Many detested the designed and the fact that it was based on old Greek architecture. A certain architect, Lewis Mumford, went as far as to say it reminded him of the “mortuary air of archeology” (5). Bacon justified his choice saying he saw Greece as a symbol of democracy, which is what Lincoln embodied to him (3).

  1. Structural Art 

When first looking at this building and seeing the strong columns one may confuse certain elements with structural art. Though the load path on the columns may seem clear, there are many more columns then needed to support the weight of the roof- the number was a purely aesthetic choice. This structure was not designed by an engineer but by an architect, its sole purpose was to carry its own weight and the weight of its statue. Although it has a beautiful historic significance in most of its design features, none of the elements designed for the memorial were chosen based on economy or efficiency, two key components to structural art.  Throughout the construction process, reinforcements were added as needed, almost on a trail error basis. There is very little correlation between design and efficiency or even economy.  There are too many decorations and superfluous elements for this to be considered structural art.

For the structural analysis I will only be analyzing the outside structure which houses the statue and not the statue.

The materials used were to emulate the unity of the country. The chose materials from all over the 36 states: granite from Massachusetts for the terrace, marble form Colorado for the upper steps and outside facade, pink marble from Tennessee for the floor of the chambers, limestone form Indiana on interior walls and columns of the chamber, marble from Alabama for ceiling tiles and the statue itself was carved from Georgia marble (1). The structure also has 36 columns to represent the 36 existing states of the time.

 

Most of the load of the system is carried through its foundation. The foundation is very deep and constitutes about 40% of the structure. The foundation is made of concrete and is 44 to 66 (1) feet deep. The foundation needed to be very deep to support the weight of the memorial and that of the marble structure. It is enclosed by granite retaining walls.

For this analysis we will assume that the entirety of the weight of the exterior roof is supported by all 36 columns and the walls. In reality, most of the columns support zero to few loads. The columns are in compression and transfer 36 point loads to the foundations.  For the interior structure, the weight is supported by the 5 walls. The interior structures transfer a uniform surface load onto the foundation. The foundation receives the 36 points loads as well as the uniformly distributed surface loads. It is important to note that the foundation bears the entirety of the load.

 

 

Figure 6: Wall Load Paths

Figure 7: Column Load Paths

 

Given information(1)

Foundation of building: 44 to 65 feet from original grade to bedrock.

Total width of building north to south: 201 feet 10 inches at widest point.

Total depth of building east to west: 132 feet at widest point.

Memorial weight: 76,000,000 pounds.

Given that the total weight of the memorial is known, we will treat it as a surface load onto the foundation.

Given a height of 44’, a length of 201’10” and width of 132’, the dead weight load is 64.8lb/ft^3.

Figure 9: Simplified drawing of foundation

 

Figure 9: Tributary area and load

 

Solving for R1 and R2

W = 64.8lb/ft^3 * 132ft * 44ft =376.42k/ft

Sum of Forces in Y:

R1+ R2 = 376.42k/lb * 201ft 10in = 76 000 k

Sum of Moment about A

R2 (201’10”)-76000k(201’10”/2)=0

R2= 38 000k

R1 = 38 000k

 

Figure 8: Shear and Bending Moment Diagrams

The max shear is 38 000k

The max moment is  15,344,400k ft.

 

Now that we have analyzed the system let us look at why congress found thiss design appealing.

One of the reasons this design was kept is because it aligned with the aesthetic conservatism (3) ideas of congress. President  Taft was largely conservative. Congress wanted to commemorate Lincoln but did not want an overly complicated design. The design by Bacon displayed a Greek like structure  with large central court and flanking sanctuaries that would contain “ a statue of heroic size expressing Lincoln’s humane personally and memorials of his two speeches” (7). One of the rejected designs had taken inspiration from the pyramids and was seen as overly complicated. Initially there was more interest in the statue, the building was actually built with a plaster model of the statue in it to make sure it would fit. Upon realizing the unusually large scale of the memorial, a larger statue had to be ordered.

 

Figure 9: One of the originals plans of the Lincoln Memorial [10]

Figure 10: Floor Plan [10]

 

6. Personal Response

In April 2016, I finally had the honor to visit this structure and experience its magic with my two eyes. My first impression that there was a whole lot of people! In fact, there were so many people that I could not see Lincoln properly. All my pictures were photo bombed by random people, I got hit, pushed, yelled at and tousled like a bag of potatoes. The structure itself was much bigger than I had imagined and as impressive.

 

References

[1]https://www.nps.gov/linc/learn/historyculture/lincoln-memorial-building-statistics.htm

[2]https://www.southeasterntraveler.com/blog/2014/09/national-mall-monuments-the-lincoln-memorial/

[3] https://traveldigg.com/lincoln-memorial/

[4]http://mentalfloss.com/article/66932/15-monumental-facts-about-lincoln-memorial

[5]http://lincoln-memorial.org/history-culture/

[6] https://www.pinterest.com/pin/166422148706667374/

[7]https://www.washingtonpost.com/archive/lifestyle/1984/02/13/building-lincolns-memorial/ebd18616-7319-4cc7-815e-b6d0cdbfc01a/?utm_term=.6d6deee107c0

[8]https://www.nps.gov/linc/learn/historyculture/lincoln-memorial-design-individuals.htm

[9]http://livinglincoln.web.unc.edu/2015/04/12/the-creation-of-the-lincoln-memorial/

[10]http://www.flickriver.com/photos/neefer/4633736533/

[11]https://www.usacoinbook.com/coins/small-cents/lincoln-memorial-cent/

[12]http://funnypictures.co.uk/art/5-dollar-lincoln-memorial/

 

Connecting Railway, Schuylkill River Bridge

Structure Information

The Connecting Railway, Schuylkill River Bridge is in Philadelphia, PA, and it crosses the Schuylkill River. Construction began in 1866 and was completed in 1867. The bridge has seen modifications, which took place in 1873, 1897, and 1912-1915. The main purpose of the bridge was to help create a more direct route in the railroad system from Philadelphia to New York City. It was designed by the Chief Engineer of the project, John A. Wilson. The Pennsylvania Railroad (PRR) helped fund the Connecting Railway. The bridge in Figure 1 came from reconstruction in 1912, which was designed by Alexander C. Shand at the discretion of PRR. [3]

Figure 1. View of the bridge across the Schuylkill. [1]

Historical Significance

Initially, the bridge had a cast and wrought iron, double-intersection Whipple truss in the center of stone arches. When this type of truss couldn’t carry the increasing railway loads, the Whipple truss was replaced by a Pratt truss. They switched the trusses in under two and a half minutes, which paved the way for fast construction techniques. When traffic began to pick up in the twentieth century, the PRR wanted to widen the bridge. This new bridge did not use any innovative structural engineering designs because it was made of stone. Some marked how unusual it was because reinforced concrete was already available. During this time, city authorities like the Fairmount Park Commission most likely influenced the use of stone. It made the bridge quicker to construct and less expensive. Even though the construction techniques weren’t new, it was the first bridge to eliminate the detour between West Philadelphia and the waterfront across from New York City. [3]

 

Cultural Significance

What was interesting about the initial construction of the bridge was that Wilson wasn’t in charge during construction. He took a job with the Philadelphia & Reading Railroad, so George B. Roberts oversaw construction. In both major construction periods, the designer didn’t do much. Roberts oversaw construction in the first bridge and the builders made decisions about how to construct the 1912 bridge. Many appreciated this bridge when it was first built because it made the commute time by rail between Philadelphia and New York City less. This bridge was used as inspiration for many artists, including Thomas Eakins and Edmund Darch Lewis. This part of the Schuylkill River is also used by many rowing teams. I found the bridge when I was at the Dad Vail Regatta recently. Many people row under the arches of it and can see the design. In Figure 2, you can see a painting by Eakins that portrays a man in a single, rowing. Today, Amtrak and Pennsylvania Transportation Authority’s passenger trains use the bridge. [3] Even through all of the reconstruction phases, the bridge is still used for the reason it was created.

Figure 2. Max Schmitt in a single scull. [2]

Structural Art

By using the stone, the PRR was able to save money, which fulfills the economic portion of structural art. However, even though the old bridge had a truss, the new one has stone arches. The truss would have been lighter and more open, but you can’t see through the stone arch. This makes the bridge not aesthetically appealing. Also, the new bridge wasn’t trying to conserve material. They built it out of stone instead of concrete even though concrete or another material would have been stronger. Since large span stone bridges can’t support trains, multiple arch spans had to be used for this bridge. The builders for reconstruction were more focused on making the new bridge look like the old bridge instead of trying to create structural art.

 

Structural Analysis

At first design, stone arches were placed on both sides of a cast and wrought iron, double-intersection Whipple truss. The arch spans were 60’ stone-faced brick, and they were separated by 7’ piers to support the arches. In the 1873 reconstruction, builders increased the thickness of the stone piers at both ends. Then, a Pratt truss replaced the Whipple truss in 1897 to support increased railway loads. When the Pennsylvania Railroad wanted to increase the number of tracks going across, Shand initially designed two 103’ spans and a pier in the middle of the river which would go underneath the existing truss. Eyre Shoemaker, Inc., the construction company, was not able to build on the old arches because they were damaged. Instead, Shoemaker tore down the arches and rebuilt it trying to resemble the preexisting bridge as much as possible. Today you can see what Shoemaker built. There is a 22’ pier in the center of the river that supports the two main arch spans of 103’. On the outside of these arches are two more piers that are slightly larger resembling the 1873 reconstruction. Next to these two piers lay more stone arches that have only a 60’ span. [3] The arches were slightly corbeled so that the bridge could take more load as well. The bridge involves a dead load from the stone, which can be very heavy, and a live load from the trains. As seen in Figure 4, the load is transferred down the arch and to the pier.

Figure 4. Load distribution of the arch.

Next, I analyzed the different parts of the arch. As seen in Figure 2, I assumed that the depth of the bridge was about 90 feet since there are five train tracks, that the height of the load was 10 feet, and the weight of sandstone is 150 lb/ft^3.

Figure 5. Calculation of weight of sandstone.

Once I got a number for the load distribution, I decided to calculate the live load at different parts of the main span since the train is a live load. I assumed the train load as a uniform load, and I also assumed the passenger train weighs 1.08 million pounds and with 6 cars and a locomotive, is around 600 feet in length. This came to a uniform load of about 1800 lb/ft existing on top of the dead load of the sandstone. Using this information, I was able to calculate the vertical reaction forces, as seen in Figure 6.

Figure 6. Finding vertical reaction forces.

Once I did this, I made a cut in the middle of the arch. I was then able to solve for the horizontal reaction force and the maximum force at point A, as seen in Figure 7.

Figure 7. Calculation of the maximum force.

Since the train is moving, I decided to treat the train as a uniform load only in the first quarter of the arch, which can be seen in Figure 8.

Figure 8. Live load on part of the arch.

Using the entire beam, I was able to calculate the reaction forces at A and then the maximum force at A. All the calculations can be found in Figure 9.

Figure 9. Calculations to find the reaction and maximum forces.

Since these calculations were for the main span, I also included one analysis of a bridge with the smaller, 60-foot span. Again, I made all of the assumptions I previously made for the 103-foot span arch. As shown in Figure 10, the span is 60 feet, but everything else is the same.

Figure 10. Loads on the 60′ span arch.

I was then able to calculate all of the forces, which can be seen in Figure 11.

Figure 11. Calculations for 60′ span arch.

Engineers like Shand and others would have made calculations like I did (and more complicated ones since I only know so much structural engineering) to figure out how much load a pier could take through combining the maximum loads of two arches. It was especially important for this bridge that the engineer make the piers large enough to support the weight of the stone and of the trains moving across. When Shand’s design didn’t work initially, Shoemaker took his own initiative to make sure that the bridge was stable and would hold the railway load.

 

Personal Response

You see old railway bridges in books and movies from the past, but you never realize how different a stone arch bridge across the Schuylkill is from the surrounding area. Philadelphia houses many types of bridges, and surrounding this bridge are many up-to-date bridges that make this bridge seem out of place. I really enjoy looking at historic structures, but it is a little odd to see this kind of bridge still used among all the newer bridges. I’m sure it sticks out like a sore thumb to many who see it visiting Philadelphia.

 

References

[1] https://en.wikipedia.org/wiki/Pennsylvania_Railroad,_Connecting_Railway_Bridge

[2] https://www.metmuseum.org/toah/works-of-art/34.92/

[3] http://cdn.loc.gov/master/pnp/habshaer/pa/pa1600/pa1646/data/pa1646data.pdf