Lab 4: Bridge I : Brainstorming
The Problem
The problem is to design and build a free-standing horizontal load-bearing structure (a bridge) that can carry a concentrated tensile point load applied at midspan that achieves the greatest load to self-weight ratio.
The Objectives
The objective is to design and construct a structural system that will provide a vehicle for the investigation of materiality and the appropriateness of material choices as well as for the comparison of modeling techniques. This horizontal load-bearing structural system (bridge) should also help one to understand the role of intuition, flow of forces, attention to detail and the role of form in structural design.
In order to facilitate the objective of the Lab, the structural system will be built both in the virtual and physical worlds. Multi-Frame will be used to help predict the behavior of the physical model.
The Parameters
The parameters for the design and construction of this structural system are as follows:
- it can only be made from cellulose based materials (wood, paper, cardboard, etc.), non-metallic thread or twine, and any type of glue.
(Ask the instructor if you are unsure of a material!!!)
- it must stand without addition support (such as hands or fingers propping up an element)
- it must freely span 31.5 inches (80 cm)
- a ring which has a diameter which will allow the pentration of a 3/8" meat hook must be inlcuded below or within the structure at midspan so that the load can be applied (this can/should be metallic)
- it must carry the minimum of a single 5 pound weight, applied, all at once, as a concentrated load to the loading ring
- it must weigh no more than 6 oz. (about the weight of a chocholate bar)(use a postal scale)
- it must be elegantly and well built
- it cannot have any part of its structure protruding below the plane of the top of the supports at any time (the loading ring is the only exception to this)
- it cannot be fixed to the supports in any way
- it must not be toxic
The Documentation
This is a multi-part project. Thus, it is very important that all phases are well documented. The Bridge I lab report should contain:
- freehand sketches of the bridge's structural concept
- a diagram of the assumed structural behavior in which the type (C or T) and relative magnitude of the internal forces are indicated
- a proposal for the materials, with sizes, to be used
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 accuracy of the sketches
- the understanding of the structural system as demonstrated in the lab report
Copyright © 1995, 1996, 1997 by Chris H. Luebkeman