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This activity develops the skills used in TSA’s Structural Engineering event.
Structural Engineering
Activity Overview
In this activity, you will create a balsa-wood bridge and determine its failure weight
(the load at which the bridge breaks).
Materials
Grid paper.
20′ of 1/8″ × 1/8″ balsa wood.
A 3″ × 5″ note card.
Glue.
Background Information
General. There are several types of bridges: beam, truss, cantilever, suspension, and
cable stayed. The length of the span and available materials generally determine
the type of bridge used in a particular situation. For this activity, a truss design is
considered the most efficient.
Truss bridges. The truss bridge design is based on the assumption that the
structural members carry loads along their axes in compression or tension. The
members along the bottom of the bridge carry a tensile load. Those along the top
of the truss carry a compressive load. The members connecting the top and bottom
chords (members) can be in tension or compression.
Gussets. Gussets are plates connected to members at joints to add strength. They
are normally used in steel construction. The structural steel members are welded or
bolted to the gusset. When designing your bridge, include a gusset at each joint, if
possible.
Wood properties. Due to its molecular structure, wood can normally carry a larger
load in tension than it can in compression. Also, a shorter member can carry a
greater compressive load than a longer member.
TSA Modular Activity