Bridge (Part III) : Examination

The Problem
The problem is to predict the behavior of the free-standing horizontal load-bearing structure as it is loaded with a concentrated tensile point load applied at midspan.

The Objectives
The objective is to deepen the understanding of the roles of intuition and form in structural design through the oberservation of the behavior and falure of a built object while under load. The goal is to design and build the most EFFICIENT bridge.

The Process
Each bridge will be weighed by the "Bridge Busting Officials." This is recorded on the public information display system in the second of four columns of information: the name of the bridge, the weight, the maximum load that the bridge carried and the ratio of the load/weight. The bridge designers then places their bridge on the abutments of the testing plaform. The "officials" first attach a five pound weight to the loading point. The bridge should be able to withstand this load. After the intial static load test, a meat hook is attached to the loading ring and a load is applied. The hook is attached to a cord that is in turn connected to a tensometer that allows the magnitude of the load to be continuously read. The rate of loading is determined by the individual team by cranking a ratchet handle. This continues until the bridge reaches it's failure load.

The Documentation
The Bridge III final lab report should contain:

• drawings of the elevations and two principle sections of the final version of the bridge
• measured sizes and prperties of the structural elements
• complete written verbal description of the design and construction process
• color identification of which elements are in tension or compression on the cross-sections
• a written verbal description of the mode of failure
• proposals as to how the load bearing capacity could be improved
• description of what was the greatest suprise during the entire bridge busting presentation
• the contents of the Bridge I and II lab reports.

The Evaluation
The evaluation for grades will be based upon the clarity and degree of completion of the lab report. It will also depend upon:

• the accruacy of the modeling techniques
• the lucid description of each of the models limitations
• the final load/weight ratio of the bridge
• the craft of construction of the physical model
• the understanding of the constructed structural system as demonstrated in the lab report