Fatigue Testing and Performance of Welded Single-Support Bar Modular Bridge Joints

Single-support bar modular joints are widely used in large-span bridges because of their competitiveness and their ability to accommodate larger movements than conventional multiple-support bar joints can accommodate. Despite their general acceptance and use, detailed fatigue testing and design guidelines well suited for these joints are still not well documented. This has been the main impetus for carrying out this experimental and analytical investigation on the fatigue performance of a single-support bar modular bridge expansion joint with welded stirrups. Three identical subassemblies were tested in fatigue to establish the experimental fatigue S-N curve for the main critical details. In addition, a few variants of stirrup specimens were separately tested under static and fatigue loadings to investigate failure modes and the effects of important geometric parameters such as bottom-plate thickness on the stress range and fatigue resistance of the stirrups. The tested joint subassemblies and stirrup specimens developed characteristic fatigue cracks in and around the stirrups and their welded connections. These cracks are classified into three distinct categories, and expressions for computing their associated stress ranges and fatigue resistance are presented. This study reveals that secondary bending moments within the stirrup make a major contribution to the stress range at critical sections of the stirrup. This contribution should be included for adequate prediction of the fatigue life of single-support bar modular joints and can be reasonably determined with basic models using one-dimensional (1D) beam elements for the center beam and for the stirrup. The importance of secondary bending moments within the stirrup is strongly related to the relative stirrup bottom plate-to-vertical leg bending stiffness and to the relative stirrup vertical leg-to-center beam bending stiffness. DOI: 10.1061/(ASCE)BE.1943-5592.0000661. (C) 2014 American Society of Civil Engineers.