Live-Load Testing of Flat Precast Slab Bridge to Determine Joint Efficiency and Distribution Factors for Moment

Abstract

A live-load test was conducted on an in-service bridge containing flat precast concrete slabs. The purpose of the test was to evaluate transverse load distribution and efficiency of the longitudinal slab-to-slab joints. The precast slabs spanned 4.6 m (15 ft) and were 1.7 m (5.5 ft) wide. Slab-to-slab joints consisted of V-shaped interlocking shear keys. The live-load test measured vertical displacement of the slabs at several critical locations under a crawling (<5 mi/h) loaded dump truck. From the deflection data, joint efficiency and experimental distribution factors for moments (DFMs) were calculated. The test results demonstrated that the joints were no longer capable of distributing loads transversely, and each slab acted independently. Based on the test results, it is recommended that 0.55 should be the minimum distribution factor used when calculating moment demand.