Institute for Transportation

The dynamic response of three stress-laminated wood bridges was determined from field test results using a heavily loaded truck. Deflections at the bridge midspan were measured at various vehicle speeds using a high-speed data acquisition system, and a dynamic amplification factor (DAF) was computed. These tests represent only a portion of the field testing, which is part of a larger research study that also includes analytical research. Experimental data described will be used to validate analytical models. The objective of the larger study is to determine the dynamic behavior of stress-laminated wood bridges so that reliable design specifications can be developed. The three bridges represent contrasting approach conditions at the bridge entrance, asphalt and gravel roadways and bridge surfaces, and different natural frequencies. Results show that for smooth in situ conditions at the bridge entrance and an asphalt roadway surface, maximum DAF is 1.08 for a bridge with a relatively high calculated natural frequency (10.6 Hz). For rough conditions at the bridge entrance approach and an asphalt roadway surface, maximum DAF is 1.34 for a bridge with a high calculated natural frequency (10.6 Hz) and 1.20 for a bridge with a low calculated natural frequency (3.2 Hz). The DAF was found to be very high (1.50) at high vehicle speeds for the bridge with gravel surface approach conditions and a calculated frequency of 7.8 Hz.