Verification of shear failures of cantilever bridge deck slabs subjected to concentrated loads

Shear design and verification of bridge deck slabs subjected to concentrated loads (as those of wheels from traffic) is a topic subjected to scientific and engineering debate, where several questions remain open. Several design procedures have been proposed in the past to determine suitable values of the internal forces for design, such as the so-called load-spreading rule or considering a smoothing length for redistribution of the internal forces calculated based on linear elastic approaches. Despite these previous efforts, several instrumental aspects governing the response of bridge deck slabs still need to be clarified and subjected to scientific discussion. An important one relates to the location of the governing control section. Typically, for the case of cantilever bridge deck slabs, two control sections are checked: one close to the webs (acting as linear support) and another near the concentrated loads. While there is no debate about the shear check performed at the section close to the linear support (similar to a one-way slab response), how the check has to be done at the section close to the load introduction zone remains unclear (which can be interpreted as punching or as a one-way shear phenomenon). Another aspect under discussion is the determination of the internal forces considering the redistributions related to the non-linear behavior of the slab, avoiding too simplistic and overly conservative rules. To better understand the phenomenon and to lead to more comprehensive and consistent design approaches, the behavior of cantilever bridge deck slabs subjected to concentrated loads is thoroughly investigated in this paper. The study starts with several phenomenological observations on shear failures in cantilever bridge deck slabs obtained from previous experimental programs. Then, a refined analysis is presented considering a realistic out-of-plane shear response of reinforced concrete slabs. From these analyses, the internal forces can be evaluated in a sound manner accounting for a gradual reduction of the out-of-plane shear stiffness as a function of bending moments and shear forces. This new feature allows tracking the location of the potential shear-critical regions and examining the forces redistributions related to non-linear behavior. Unlike traditional approaches (like the "loadspreading rule" or smoothing lengths), the presented numerical analyses can consider shear failures at any location. The main findings from the physical observations and refined analysis are eventually used to propose a simple but phenomenologically consistent design methodology aimed at practical applications.