Pratt truss—a type of truss bridge where the upper and lower chords are connected by vertical posts and diagonals angled toward the center of the span.
Working Principle: • The load from the roadway is transferred to the trusses and distributed across the triangles, and the triangle is the stiffest shape—it does not change its form. • The diagonals work in tension, and the vertical posts work in compression. The upper chord is in compression, and the lower chord is in tension. • Stretched elements can be made thinner (they used to be steel rods), and short vertical posts are less susceptible to longitudinal bending. Therefore, the structure is material-efficient. • Supports: one is fixed (Pin), and the other is movable (Roller). This allows the bridge to expand and contract with temperature changes.
Pratt Truss Bridge
Bridge Mockup
