| The design philosophy of current building codes for reinforced concrete structural walls under seismic load is to assure inelastic behavior through flexural yielding, and to prevent brittle failure modes such as shear failure. However, in actual earthquakes and in prototype wall experiments, low to mid rise walls have experienced premature shear failure. The primary reason for this premature shear failure is a lack of knowledge of shear stress distribution along wall sections.;The axial stress distribution along a wall section is well established from flexural theory. Current building codes assume uniform shear stress distribution, under which there would be no critical axial and shear stress combinations that would result in a principal tensile strength great enough to initiate diagonal tension failure. This assumption is only correct as long as the wall section is uncracked. When the wall section is cracked, portions under compressive stress will attract a greater percentage of shear force than portions under tensile stress. Thus, a critical combination of axial and shear stress (depending on the moment-to-shear ratio) may exist to initiate diagonal tension failure. An accurate assessment of shear stress distribution is the key to preventing shear failure modes. Once an accurate shear stress distribution is determined, the critical axial and shear stress combination can be identified and the section can be design to prevent shear-related failures.;The objective of the study presented here was to experimentally establish the shear stress distribution along a wall section under combined flexure and shear. For this purpose a closed-loop experimental apparatus was developed for testing wall portions. The pre-cracked wall portions representing the boundary member of a prototype wall were subjected to cyclic axial force to simulate the effect of overturning moment and simultaneous cyclic shear to determine the relationship between the shear stiffness and axial stress.;A multilinear-segment approximation of the experimental shear stress-shear strain was developed. Based on this approximation, a behavior model for describing the shear stiffness along a wall cross section as a function of axial stress is presented.;The behavior model was used to determine the shear stress distribution along prototype wall sections. The shear stress obtained for these walls provides significant insight into the premature shear failure of low to moderate rise structural walls. Based on this study, preliminary recommendations are presented concerning the design of wall boundary members to prevent premature shear failure. |
