ASCE Pacific Regional Conference – Steel Bridge Design

Client name: Dr. Joshua Hewes (joshua.hewes@nau.edu)

Team Name: Steel Bridge Team

Names of Members: James Newhall, Austin Kelley, Minghong Chen, Joey Gimbut, Xiaolei Hui, Randy Brooke

Contact information: James Newhall, jpn9@nau.edu and joey.gimbut@gmail.com

Steel bridge team. Back row, left to right: James Newhall, Joey Gimbut, Austin Kelley; front row, left to right: Randy Brooke, Minghong Chen, Xiaolei Hui.

Problem Description

The purpose of this project is to compete in the 2012 Student Steel Bridge Competition hosted by American Institute of Steel Construction (AISC) and American Society of Civil Engineers (ASCE).  Student chapters of ASCE compete by designing and building model steel bridges.  These model bridges are judged for their constructability, weight, and stiffness, among other scoring criteria.

This year’s scenario for the bridge states that Broken Paddle Resort, Inc. has expressed interest in building a bridge to permit vehicular access to a proposed lodge. The passageway bridge will be constructed over a fast moving river that is popular with local rafters and kayakers. The Broken Paddle construction manager (CM) has requested design/build proposals for the new bridge. In addition, the CM also requires the submittal of a 1:10 scale model capable of demonstrating the full-scale bridge properties. The bridge must support utilities under the deck and meet standards for durability, constructability, usability, stiffness, construction speed, efficiency, economy and display as stated by the ASCE and the AISC in the 2012 rules for the student steel bridge competition. Additionally, the bridge must compete at the ASCE Pacific Southwest Regional Conference (PSWRC) in March of 2012 at California State Polytechnic University, Pomona and participate in the 2012 Northern Arizona University (NAU) Undergraduate Research and Design Symposium (UGRADS) in April of 2012.

Site conditions place many constraints on the design and construction methods that may be used for the bridge. A temporary cofferdam is placed in the middle of the river to aid in bridge construction because Phantom River is too fast for barges. Flash flooding can occur in the river so the bridge will need clearance under it to prevent damage.  Due to undesirable geotechnical conditions on one side of the river, the bridge will need to incorporate a cantilever. Additionally, materials and tools must be stored some distance away from the edge of the river to prevent instability of the river banks.

Description of Final Product

Each competing school is requested to submit a 1:10 scale model. These models will be constructed under simulated field conditions and then load tested at the competition. A panel of judges will evaluate each bridge with the criteria of durability, constructability, usability, stiffness, construction speed, efficiency economy, and display. The bridge that is best judged to meet these criteria will win the competition. Please see www.aisc.org/steelbridge for more information.

Scope of Work

This year NAU has divided the capstone group into 2 teams for the Steel Bridge Project. The 2 groups will compete on the design on the overall bridge. The best bridge design will be chosen by Dr. Hewes. The following is Steel bridge Team 2 Scope of Services:

Task List

1. Project Management

2. Read and understand bridge rules

3. Develop Analysis Plan

1.

2.

3.

3.1Develop Moment Diagram

3.2 Analyze Multiple Truss Layouts

4. Finalize Truss Layout

5. Report for Final Bridge Design

6. Manufacture bridge members

7. Practice bridge building

8. Compete in ASCE conference

1) Project Management

Any project needs management in order to be organized and professional in its approach to design. The tasks included in project management for this bridge design are: 1) staff meetings, 2) scheduling tasks, 3) assign tasks for project members, and 4) maintaining schedule. Often engineering projects fail in its own management more so than in its design.

2) Interpret Competition Rules

The first task is to review the steel bridge rules (http://www.aisc.org/content.aspx?id=780) and commit them to memory. The team will then develop a design matrix that uses the competition’s scoring to generate a list of priorities to be used in the design of the bridge. Using the competition’s rules the team will determine which criteria in the competition is weighted the greatest and focus on those requirements. The design matrix will give greater weight to the priorities with the greater scoring value, thus, insuring the design will give the highest score possible in the competition.

Deliverables: 1) Design Matrix weighing designs against criteria

3) Develop Analysis Plan

The third task is to develop a plan to design the bridge, keeping in mind the list of priorities (generated in the design matrix), along with technical advisor’s advice. The following two sub-tasks were developed for the analysis plan.

Deliverables: None

3.1) Moment Diagram

The first part in the analysis is to use RISA to generate a moment envelope diagram that overlays all possible loading conditions’ moments on top of each other. Trusses are designed by mimicking the shape of the moment that is expected to be applied to them. Since the load applied to the bridge is randomly determined, the team is using a method like super positioning. First, the team will generate the moment diagram for each loading case given in the competition rules. Second, the moment diagrams will then be overlaid onto each other. By using this enveloped diagram, the team will have a good idea what the shape of the truss should be. Below (in figure 3.1.1 and 3.1.2) are examples of the moment envelope.

Deliverables: 1) Moment Envelope Diagrams

Figure 3.1.1

Figure 3.1.2

3.2) Analyze Multiple Truss Layouts

The second part of the analysis plan is to generate multiple truss layouts on paper that mimic the moment envelope diagram. With these truss diagrams the team will perform an analysis (in Risa3D) on each layout to see which one best meets the design criteria. Ideally, the diagonal members (the longest members) will be in tension. To make this possible the team may rearrange the internal members as they perform the analysis. The truss layout that best accomplishes the listed design priorities will be chosen as the layout of the overall bridge truss. Below (figure 3.2.1) is an example of a truss analyzed in Risa3D for its defections.

Deliverables: 1) Reports detailing deflection for all truss layouts

Figure 3.2.1

4) Finalizing Bridge Design

At this point the team will make the final detail decisions on the bridge design. These decisions are: 1) how to deal with any members that are over the competition’s allowed length; 2) what each pin connection should be; and 3) to see if any member in tension should be steel wire rather than a normal beam.

Deliverables: 1) Details on the Final Bridge Design

5) Report for Final Bridge Design

The next step is to prepare a detailed report that covers the different designs and the final design chosen. The report will include all the analysis used for each design, all the steps taken to obtain the final design, the decisions taken, and the reasons for taking them.

Deliverables: 1) Report of Truss Design

2) Report for Deflection

3) Report for Approximated Cost

6) Manufacture bridge members

This task will be at the start of next semester. Here the team will have further details on what our options for steel will be. Otherwise, this task is to have the teams start manufacturing the bridge members according to the chosen design. The team may have to make changes at this point in time, depending on what steel is available for actual use.

Deliverables: 1) Members and Member Connections

7) Practice bridge building

After the bridge members have been made the team will practice assembling the bridge. This will be done in order to make sure all members fit together, time how long the construction will take, and to try different construction methods to lower construction time. This will also determine how many people will be used to construct the bridge at the competition. Total cost for weight, construction time, and deflection will be determined.

Deliverables: 1) Report for Total Cost of Bridge

8) Compete in ASCE conference

Finally the bridge will then be taken to the ASCE conference where the team’s steel bridge will compete against bridges from competing schools. Bridges at the conference will be judged against each other on: 1) construction time; 2) weight; 3) deflection; 4) appearance; and 5) overall performance. Overall performance is based on construction time, weight, and deflection.

Deliverables: 1) Report on Performance at the ASCE Conference