midspan

Midspan is a term used in civil and structural engineering to describe the portion of a structural span between its supports, often near the center of the span. The exact location is usually defined in project drawings, but it generally refers to the segment of a beam, girder, or bridge deck midway along its length.

In analytical terms, the midspan is frequently the point of maximum bending moment and maximum vertical deflection for a simply supported beam under uniform or symmetric loading. For continuous or statically indeterminate spans, the maximum moment may shift toward supports, but the midspan remains a critical region for serviceability design and reinforcement detailing. Designers use midspan references when placing loads, fabricating joints, and selecting reinforcement or stiffeners.

Practically, midspan is a common reference for monitoring and testing. Instrumentation such as strain gauges, fiber optic sensors, or deflection measurements are often located at midspan to characterize overall behavior under load, temperature, or dynamic excitation. In construction specifications, midspan can denote the location for fatigue tests, cross-frames, or expansion joints relevant to the central portion of a span.

See also: bending moment, span, beam, bridge engineering.