Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Equilateral Truss Bridges
Name: James R. K.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: December 2002

Why do equilateral truss bridges hold the most weight?

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.

Click here to return to the Engineering Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory