AISC Steel Bridge Competition Team 2 – Keep it Civil

Acknowledgements

We would like to acknowledge our clients Brenna Svoboda and Marcus Duren from Kiewit as well as our Project Advisors Jeffrey Holley and David Grimm for helping us during the design process. We would also like to acknowledge Dave Genova and the rest of Zimkor LLC. for donating our steel and helping us fabricate our bridge. Finally we would like to acknowledge Kiewit for donating to our project.

Elevator Pitch

Design Approach

Design Solution

Each year, AISC provides specifications for design, rules, and standards that all bridges competing within the AISC Student Steel Bridge Competition must abide by. In brief, there are requirements for dimensions, assembly, and strength that must be adhered to within the competition. Accordingly, our bridge complies with these standards (for more information, visit aisc.org). AISC provides seven different loading cases (in addition to six partial loading cases derived from these) that are equal in magnitude but different in location. These load cases serve two purposes: one, to analyze the strength of the bridge against vertical collapse and deflection, and two, to analyze the bridge’s capacity to resist lateral deflection. In order to model these variations, a consistent structural system was developed using Risa 3D in order to evaluate a single structure using multiple load cases. The results of a single unity test (from AISC Steel Construction Manual, 15th Edition) is given below.

The analysis provides an overview of the functionality of the bridge when facing simultaneous compression and bending, and is one of the 65 analysis tests that the bridge required. The blue signifies a sufficient capacity while the red shows a failing member. For this analysis, all loads are assumed to behave in perfectly elastic members, and so, loads are transferred through members regardless of capacity. The red members in question were modelled as placeholders and serve no structural purpose. The failing placeholder members in question were modelled separately in Solidworks as described in the Design Approach Step 5.

Additional analysis was performed on the shear tab connections in accordance with AISC Steel Manual Chapter J; however, due to COVID-19, the files themselves are saved in an inaccessible location. The analysis was performed by collecting the forces of every connection member and compiling them in a table. From here, the maximum values were obtained, and a conservative edge distance was determined. Unfortunately, COVID-19 also prevented the field-testing of the bridge at both Springfest and Regionals. Because of this, the bridge was never tested beyond the models.

The results of the analysis were positive. The overall weight of the bridge was under 300 LBs (most likely around 275 LBs with the modified members, but the final bridge was never actually weighed given the circumstances), and the maximum aggregate deflection in all of the load cases was approximately 0.5 inches in total (added at two locations). The maximum deformation before disqualification was 4 inches at a single location, and therefore, the bridge function was satisfactory.

The chosen design of the bridge was one that was supposed to be both unique as well as functioning. Since this competition is one that includes numerous schools with somewhat standardized ideas, it is difficult to really stretch engineering knowledge and practice. Therefore, our team selected unconventional designs for stringers, connections, and an over truss as the overarching structural system. The stringer was incredibly difficult to work around due to the constraints of the project; however, it provided an incredibly beautiful design that also adhered to the project requirements. This required unique connections to both be efficient in construction in addition to providing strength (as shown above). The final feature of design, the over truss, was difficult to fabricate; however, it provided aesthetic appeals in addition to vertical stability. Being an over truss, the bridge is naturally more difficult to construct; however, this is offset by the stiffness it provides. The overarching design philosophy of the bridge was to create something unique that was capable of performance.

Next Steps

In an announcement to educators and students, the American Institute of Steel Construction decided to cancel the 2019-2020 Student Steel Bridge Competition. This was in reaction to the COVID-19 pandemic. As a result, the constructed bridge was not officially judged and tested. The first recommendation for this project moving forward is to complete this judging, as to complete the analysis of this bridge with regards to the original problem statement. The purpose of the AISC Regional Competition was to have a performance rating that was given as a hypothetical “construction cost.” Taking into consideration aesthetics, construction speed, lightness, and stiffness, this final judging would best reflect how well the team created a viable solution. It is important to note that, while calculations for the behavior of the bridge under load conditions were modeled, no physical loading was ever done. This leaves a heavy degree of uncertainty, and begs the question as to how the bridge would truly react under actual test conditions.

Further recommendations are focused on structural design and modeling, in which the client or a following team could lead. The connections between members had proved to be a challenge, especially in terms of physical fabrication. The design of this bridge could be improved by creating full models of connections and interfaces, so that structural analyses derived from those models will be more accurate. During fabrication, these interface-points between members were constantly adjusted, and it is strongly advocated to fine-tune with those areas in mind. Overall, improvements to the solution can always be made in every judging category, especially lightness. Again, areas of improvement could be seen more clearly if a proper evaluation occurred.

Meet the Team