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Name: James R. K.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: December 2002


Question:
Why do equilateral truss bridges hold the most weight?



Replies:
I am not sure they do, if you mean what kind of bridge holds the most weight for the smallest amount of material in the bridge. I would have thought that a suspension bridge would win that contest.

It is true, however, that three beams connected in a triangular shape must keep that shape or break. If you connect four beams in a quadrilateral shape, the quadrilateral can be deformed quite easily, as you can quickly convince yourself with a little model, if you are not already convinced.

Best, Dick Plano


I do not think you can say that any one truss type carries the most weight. Since the mid-19th century, when the basic principles of modern structural engineering were developed, a multitude of truss designs have been developed. Each of the successful ones have some advantage depending on the type of load expected, the span required, and the limitations of materials and construction available at the time.

That said, the symmetry of an equilateral triangle corresponds to a symmetry in the forces developed in the truss members. Consequently, this shape has the potential to spread the load applied to the structure in an even fashion.

Andy Johnson, Ph.D., P.E.



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