- Publication no: ABC2017-112-17
- Published: 26 April 2017
Prestressed concrete I girder bridges constructed in the 1960s and 70s have the potential to restrict transport productivity because their AS 5100.7 assessments can be poor despite satisfactory inservice performance. The primary issue is the shear strength of the girders, especially those with low levels of shear reinforcement – an issue also identified in Germany and the USA, for example. The shear strength of prestressed concrete I girders has been investigated using Australian and International assessment practice to understand the plausibility gap between observed performance and the theoretical assessments. Hypotheses for closing the plausibility gap include the shear strength model, the strength of the concrete in aged prestressed concrete girders, the dynamic response to traffic, refined analysis, heavy vehicle drive lines, live load factors, accompanying vehicle effects and capacity reduction factors.
A case study compared assessment outcomes for a range of parameters on a family of prestressed concrete I girder bridges featuring low theoretical girder shear assessment ratios despite satisfactory past performance and advanced analysis methods. The validity of these operational parameters was assessed via in-service monitoring of the bridge’s response to traffic and known road trains, weigh in motion data analysis, non-destructive and core testing of concrete strength and a calibration case study. These investigations concluded that inventory / design based parameters are conservative for bridge assessments and that the operational assessment approach is more consistent with the performance of the network. This leads to a transparent framework for making risk-informed management decisions for prestressed concrete girder bridges that will extend the lives of these structures.