Field and Analytical Studies of the First Folded Plate Girder Bridge

An innovative Folded Plate Girder (FPG) system bridge was constructed in Uxbridge, Massachusetts. The University of Massachusetts at Amherst collaborated with the Massachusetts Department of Transportation (MassDOT) Accelerated Bridge Construction Program to instrument the bridge with a total of 93 gages (strain gages, pressure cells, tiltmeters, displacement transducers, and convergence gages). Data was collected during construction, static live load testing, and long-term for twenty months. This paper presents data and comparisons to analysis (3-D bridge and girder modeling in SAP-2000 and ANSYS and 2-D hand calculations) to present an independent evaluation of the performance of this innovative bridge. Stresses in concrete and steel components are well below allowable design values through construction, long term data collection and truck load testing. Live-load test data indicate that the elastic neutral axis of the girders is higher than calculated, with measured strains being much lower than estimated from hand calculations and finite element (FE) results. This was partially explained by non-linearity of strains in the bottom flanges of the FPG due to shear lag when truck axles were positioned near instrumented locations, as confirmed through analysis. Through the first two years of service no signs of distress have been noted and readings are within the expected range of bridge behavior. Based on this study the FPG is an effective system for accelerated construction of short span bridges.