Does the Size Effect Exist in Reinforced Masonry?

Abstract

The research described in this paper studies the effect of the effective depth, d, on the shear behavior of large reinforced masonry beams. Five fully grouted shear critical reinforced masonry beams ranging in effective depth from 300 mm to 1400 mm were tested to failure under three point loading to investigate their cracking behavior and ultimate shear strengths. The experimental shear strengths were compared with the failure shear stresses predicted using three different design codes: the TMS 402 code, the CS A S304.1-2004 code and the CS A A23.3-14 code for reinforced concrete. The test results show that the size effect in reinforced masonry is real and very significant, in that failure shear stresses decreased as the effective depth increased. It is shown that as the effective depth increases, the longitudinal crack width and spacing at mid-depth increase as well. These wider cracks initiate shear failure at a lower shear stress due to reduced aggregate interlock capacity. It is shown that the TMS masonry design code gives non-conservative predictions of the shear strength of large masonry beams. The most accurate prediction of the size effect in masonry is given by the CSA A23.3-2014 code which is based on the General Method of shear design used extensively to design reinforced concrete. The paper highlights the necessity to revise masonry design codes to address the size effect.