A portable self-monitoring instrument for load history studies

Development and operation of a portable instrument for recording strain events in bridges under field service conditions are described. The instrument consists of a transducer, which is clamped to the flange of a bridge by four allen screws, a set of mechanical counters driven by electronic logic circuitry, a battery pack, and a tamper-proof enclosure. Each counter is incremented every time the strain reaches the triggering level selected for that counter. For the usual case where the triggering levels are all in the elastic range, a simple hand calculation will produce a stress histogram from the counter readings.