Experimental evaluation of in-span hinge details in reinforced concrete box-girder bridges

Abstract

During the past three decades, considerable research efforts have sought to improve the seismic design of California highway bridges. However, the in-span hinge (ISH) regions of concrete box girders have not been studied adequately. ISHs are classified as disturbed regions caused by the concentrated bearing loads and the possible existence of utility and maintenance openings, which induce a complicated three-dimensional stress state. Nevertheless, ISHs are commonly designed as two-dimensional short cantilevers following standard procedures. These designs typically lead to congested reinforcement causing constructability concerns from practical and economical aspects. The behavior and the strength of ISHs were assessed with five one-third–scale specimens that were tested at the University of California, Berkeley. The first two specimens represent the as-built conditions of typical ISHs of California box girder bridges. These specimens were detailed identically, but with one, utility openings were considered to study their influence on the behavior and strength of ISHs. The typical ISH characteristics were obtained from a survey of eight projects in California. The other three specimens represent new ISH designs, aimed at reducing the steel congestion and improving the structural performance of ISHs. Findings from the experimental results revealed that as-built ISHs fail with a combination of three failure modes: (a) beam shear, (b) two-dimensional strut and tie, and (c) punching shear. On the basis of the observed failure modes, it was concluded that the current ISH design could be optimized to reduce steel congestion and improve constructability.