Comparison of Load Managing and Structural Integrity between Beam Bridges and Suspension Bridges
The Tacoma Bridge Incidents
City College of New York
Project Dates: March 5th, 2024 – March 19th, 2024
Budget: $1075.00
Abstract
Bridges are critical infrastructures that facilitate transportation over obstacles such as rivers and highways. Suspension bridges and beam bridges are two distinct types of bridges that use different structural designs. Suspension bridges use cables attached to support pillars to transfer load, whereas beam bridges depend on supports beneath the bridge surface. Both are needed in specific conditions, however, it is important to know which one is more reliable, stronger, and overall better to provide a safe path to travel. The purpose of this research is to compare side by side the structural virtue of suspension and beam bridges under load scenarios to determine which design is superior. The study is carried out by simulating both bridge types with rudimentary models and testing them by increasing loads till failure. The experiment is conducted at a smaller scale however, it has the fundamentals needed to make strong affirmations. The experiment establishes which bridge style can withstand the most weight before collapsing, providing important insights into bridge engineering. The research technique entails building models of each bridge type, performing load testing, collecting data, and assessing the results. As expected, the suspension bridges had a greater load-bearing capability than beam bridges due to their design characteristics.
Introduction
Bridges are structures built to traverse over obstacles, such as rivers and highways. Of the variety of bridge designs, this study compares the different weight tolerances between the suspension bridge and the beam bridge. A beam bridge is designed to offload the stress onto the vertical pylons holding the bridge deck up. On the other hand, this compression is only a part of the function of the suspension bridge. A suspension bridge uses vertical pylons that stretch further above the bridge deck in which suspension wires are directly connected. These wires span the entire structure’s length and hold up the bridge deck while compressing the pylons. These bridges are built for different circumstances and must be able to withstand the traffic and stress passing over them.
This research was conducted to clarify these different circumstances by collecting experimental data on their respective weight loads and structural limits. Through these experiments, the data signified that the suspension bridge had a higher weight load than the beam bridge and collapsed at a much slower rate.
Project Narrative (Methods)
The experiment is conducted with built miniature replicas, where the maximum weight load is tested by placing coins, specifically pennies, into a load tester. This experiment was repeated a total of three times and the average number of pennies required for structural failure was recorded.
The initial setup required for the beam bridge was as follows:
To build the pylons, two straight, non-bendable straws were taped directly together on one end, with a shorter cut piece of straw put in between the straws on the other end, also taped together. Two pylons are constructed and taped to the same height on two opposing chairs. A full-length straw is then placed into the opening of the pylons on each end above the shorter straw piece to act as the bridge deck.
Once this is done, a lightweight cup is hung at the center of the bridge deck to act as the load tester. To construct the load tester, one paperclip is shaped into a v and poked into opposite sides of the cup to hold it. Another paperclip is shaped into a hook and suspends the cup from the bridge deck.
To construct the suspension bridge, the following steps are taken:
In addition to the already constructed beam bridge, two equal-length strings are drawn over the pylons and taped to the bridge deck and chairs, acting as the suspension wires. Three trials are taken for the respective bridges and the individual coin count, as well as the average required for collapse, is recorded.
Results
Suspension Bridge After Beam Bridge After
Figure 1 represents the collected data during the three trials where pennies were placed in the load tester until the bridges collapsed, said data is then illustrated in graph 1. The more pennies that the bridge can hold, the it’s more suitable for a larger load. According to the data collected, the suspension bridge is more suitable to carry more weight than a beam bridge. It is speculated that the cables on the suspension bridge allow less pressure on the weight of the actual bridge which allows it to carry more. The more trials ran, the less the beam bridge was able to hold which shows its durability over time after every attempt. The suspension bridge was able to hold much more weight as well as hold it for a longer period. The suspension bridge data was also more spread out over time and was not decreasing after every attempt. The beam bridge took most of the weight towards the middle of the bridge which led to the collapse.
Bridge Design | Trials | Number of Pennies | Average Number of Pennies |
|---|---|---|---|
Suspension Bridge | 1 | 136 | 142 |
| 2 | 150 | ||
| 3 | 140 | ||
Beam Bridge | 1 | 76 | 67 |
| 2 | 69 | ||
| 3 | 56 |
Figure 1
Graph 1
Discussion
As expected, the suspension bridge was able to hold more weight than the beam bridge. The cables seem to take some of the weight off of the bridge itself making it last longer overall. For more populated areas, the more suitable bridge would be the suspension bridge due to it being able to handle heavy loads of traffic. This is the reason why there are such long suspension bridges like the George Washington Bridge in New York City or the Golden Gate Bridge in San Francisco.
Beam bridges hold less weight for a shorter amount of time which is why they are used in less populated places to connect places over a shorter distance. For the experiment, the types of chairs that were used didn’t have a solid surface which made it difficult for the bridges to stand. The issue was solved by tapping the base of the bridge to books and then putting the books on the chair. Another possible issue could’ve been that the thread wasn’t thick enough for the weight of the pennies. In the Article Gregor P. Wollman, a Doctor and Professor in structural engineering, mentioned that live loads can affect the cables. In the case of the experiment, the Suspension bridge was only able to handle a load of around 142 pennies before dropping meaning that if the bridge wanted to last more than 142 pennies, the bridge would need to have more cables or stronger cables. In the article by Osamu Yoshida, Motoi Okuda, and Takeo Moriya, it is explained that the rigidity in the center of a suspension bridge generally causes deformation in the bridge. With this in mind, maybe the fact that the suspension bridge had a rigid center was the reason why the suspension bridge in the experiment couldn’t hold more than about 142 pennies. In the last image in the results section, the bridge fell and the sides of the bridge are bent towards the chair due to the weight of the pennies but the middle remained in good condition.
Bibliography
Choi, Dongho, et al. “Simplified Analysis for Preliminary Design of Towers in Suspension Bridges.” *Journal of Bridge Engineering*, vol. 19, no. 3, Mar. 2014, https://doi.org/10.1061/(asce)be.1943-5592.0000551.
Ma, Lin, et al. “The Theoretical Impact Factor Spectrum for Highway Beam Bridges.” *Journal of Bridge Engineering*, vol. 26, no. 12, Dec. 2021, https://ascelibrary.org/doi/10.1061/%28ASCE%29BE.1943-5592.0001800.
Rahimi, Arash, et al. “A Simplified Beam Model for the Numerical Analysis of Masonry Arch Bridges –A Case Study of the Veresk Railway Bridge.” *Structures*, vol. 45, Nov. 2022, pp. 1253–66. https://doi.org/10.1016/j.istruc.2022.09.087.
Wollmann, Gregor P. “Preliminary Analysis of Suspension Bridges.” *Journal of Bridge Engineering*, Aug. 2001, https://ascelibrary.org/doi/10.1061/%28ASCE%291084-0702%282001%296%3A4%28227%29.
Xia, Qing, and Yaojun Ge. “Robustness Evaluation of Aerodynamic Flutter Stability and Aerostatic Torsional Stability of Long-Span Suspension Bridges.” *Applied Sciences (2076-3417)*, vol. 13, no. 24, Dec. 2023, p. 13136. EBSCOhost, https://doi-org.ccny-proxy1.libr.ccny.cuny.edu/10.3390/app132413136.
Yoshida, Osamu, et al. “Structural Characteristics and Applicability of Four-Span Suspension Bridge.” *Journal of Bridge Engineering*, Sept. 2004, https://ascelibrary.org/doi/abs/10.1061/(ASCE)1084-0702(2004)9:5(453)?casa_token=mb1GiePdCoIAAAAA:JJjCTDx2GwM5J9NzRhAyCeI6JTSaA4rOpKVTZ18n5wXxYh6wAIBaG75KnlIf4IKnPW-n1MJxSQ.
Work Cited
Choi, Dongho, et al. “Simplified Analysis for Preliminary Design of Towers in Suspension Bridges.” Journal of Bridge Engineering, vol. 19, no. 3, Mar. 2014, https://doi.org/10.1061/(asce)be.1943-5592.0000551.
Ma, Lin, et al. “The Theoretical Impact Factor Spectrum for Highway Beam Bridges.” Journal of Bridge Engineering, vol. 26, no. 12, Dec. 2021, https://ascelibrary.org/doi/10.1061/%28ASCE%29BE.1943-5592.0001800.
Rahimi, Arash, et al. “A Simplified Beam Model for the Numerical Analysis of Masonry Arch Bridges –A Case Study of the Veresk Railway Bridge.” Structures, vol. 45, Nov. 2022, pp. 1253–66. https://doi.org/10.1016/j.istruc.2022.09.087.
Wollmann, Gregor P. “Preliminary Analysis of Suspension Bridges.” Journal of Bridge Engineering, Aug. 2001,
Xia, Qing, and Yaojun Ge. “Robustness Evaluation of Aerodynamic Flutter Stability and
Aerostatic Torsional Stability of Long-Span Suspension Bridges.” Applied Sciences ( 2076-3417), vol. 13, no. 24, Dec. 2023, p. 13136. EBSCOhost, https://doi-org.ccny-proxy1.libr.ccny.cuny.edu/10.3390/app132413136.
Yoshida, Osamu, et al. “Structural Characteristics and Applicability of Four-Span Suspension Bridge.” Journal of Bridge Engineering, Sept. 2004, https://ascelibrary.org/doi/abs/10.1061/(ASCE)1084-0702(2004)9:5(453)?casa_token=mb1GiePdCoIAAAAA:JJjCTDx2GwM5J9NzRhAyCeI6JTSaA4rOpKVTZ18n5wXxYh6wAIBaG75KnlIf4IKnPW-n1MJxSQ.
