Dead Load Evaluation through Truss Bridge Deconstruction Monitoring

Abstract

A unique research study was performed on a steel truss bridge over 80 years old that was being taken out of service. The primary objective of the study was to evaluate the accuracy of dead load estimation for an existing truss bridge. The approach taken was to monitor the deconstruction process and identify the locked-in dead load forces within the primary truss members. This novel experiment utilized vibrating-wire strain gauges and distributed data-acquisition equipment to measure the strain release within the examined truss members. Once these measurements were obtained, a comparative study was performed with an independently developed three-dimensional (3D) finite-element model. The comparison quantitatively illustrates the uncertainty of dead load distribution within in-service steel truss bridges. This uncertainty may indicate a wider distribution of dead load than was originally utilized in the derivation of the dead load factors per code standards. The study presented is only from one bridge; however, the findings illustrate a potential misconception about the accuracy of dead load estimates for older in-service truss bridges.