Methodology for Load Rating of Damaged Double-Tee Girder Bridges

Abstract

The most common type of bridge on South Dakota local roads is a precast prestressed double-tee (DT) girder bridge. For old and/or deteriorated bridges, the estimation of the bridge safe live load is necessary to ensure the safety of the traveling public and to prevent excessive bridge damage and collapse. Nevertheless, load rating of damaged bridges is challenging mainly because of a lack of information regarding the capacity and distribution of the live load between damaged components. The main goal of the present work is to propose a systematic analytical load rating methodology for precast bridges, specifically those with DT girders when girders are damaged with different damage levels. First, quantitative definitions in-line with those from AASHTO were modified and proposed to identify all damage types and condition states specific to DT girders. Subsequently, a statistical analysis was performed on the South Dakota DT bridge inventory to comment on the most frequent observed damages. Then, two DT bridges, which had a significant girder-to-girder joint damage, were field tested, and the measured data was used to recommend girder distribution factors and dynamic load allowance specific to DT bridges with deteriorated longitudinal joints. Furthermore, two 45-year-old DT girders, each with significant damage, were used in a strength test, and the measured data from these tests and others collected from the literature was used to validate the capacity estimation method for old and/or damaged DT girders. The verified methods were then utilized to calculate the shear and moment capacities of 23 different DT sections, which have been used in South Dakota. Based on the statistical, experimental, and analytical studies, a new methodology was proposed for load rating of typical damaged DT bridges.