Bridge Design Project (Statics I)

Objective

Design a bridge using MATLAB and SOLIDWORKS to span a certain distance a sustain a load of some specific amount.

Statics I covers the basics of statics and strength of materials. Forces, stress, and strain were a few of the topics covered. The final project in the course was to design and analyze a bridge using MATLAB, SolidWorks, and the Finite Element Analysis package within SolidWorks. The course was taken during Covid so no physical testing was completed. The requirements for the bridge design were as follows:

        - The bridge must support 100 lbf

        - The bridge must span across 18"

        - The main beams must use 3/8" x 3/4" balsa wood

        - The truss sections must be 3/8" x 3/8" balsa wood

        - The truss connection must use 8-32UNC bolts with nuts and washers

Beyond the minimum requirements of the bridge design, our grade was based on the performance of the bridge using a metric that accounted for the failure load, the weight of the bridge, and the projected cost of the bridge. The formulation for the performance index (PI) was the failure load divided by the product of the weight and the cost of the bridge.

(1) PI = F/WC

The project was completed in groups of three: Project Manager, Engineering Manager, and the Engineer. My role was the engineer. As the engineer, I was responsible for producing a design, modeling the design in Solidworks, and conducting technical analysis on the design through the use of Matlab and Solidworks FEA.

Initial research on bridges left Howe and Pratt trusses as possible options. In turn, I constructed a set of linear equations using the method of joints and then solved for the forces, axial stress, and bearing stress in the members. Theses preliminary tests allowed us to remove the zero-force members (green color in the second figure) to make the bridge lighter. The group decided to move forward with the Pratt truss as there was no significant difference in the performance of the truss types. I modeled the Pratt truss in SolidWorks and subjected the truss and the cross-members of the bridge to failure loads. Using six cross-members loaded at 43 lbf each (258 lbf total), the axial stress in the truss members exceeded the strength of the Balsa wood.