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Connecting Railway, Schuylkill River Bridge

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