Effective shear design of reinforced masonry beams

Ensuring reinforced concrete masonry (RCM) has adequate shear strength is an important aspect of structural design. This is particularly true for masonry beams without stirrups as shear failures in these elements can be brittle, occurring with little to no warning. As such, the design provisions used to determine shear strength must be accurate, safe, and rational. The objective of this paper is to analyze shear design provisions of current design codes to assess their reliability and predictive capabilities. A database of 104 shear tests reported in the literature on RCM beams without stirrups was assembled, and the failure shear stresses of these beams were predicted using four different masonry design codes. The codes analyzed include CSA S304.1-04 (Canada), ACI 530-08 (US), AS 3700-2001 (Australia), and BS 5628-2:2005 (UK). A fifth set of shear design provisions was chosen as well -the General Method of shear design from the CSA A23.3-04 code for reinforced concrete. The study showed that the average Vexp/Vpred ratios for the masonry codes ranged from 1.06 to 1.53, with the lowest value associated with the BS 5628-2:2005 code. However, high coefficients of variation for all four masonry codes indicated that low material strength reduction factors are required in order to apply the design codes with appropriate levels of safety. Interestingly, the CSA A23.3 general method had the lowest coefficient of variation of all five codes, and the third lowest average ratio of tested to predicted strength. Further analysis indicated that the general method can account accurately for the effects of both longitudinal strain (due to variations in steel area and MA/ ratio) and size (due to changes in effective depth). It is concluded that RCM beams exhibit similar behaviour in shear as reinforced concrete beams, and that their shear strengths can be more accurately predicted using the CSA A23.3 code for concrete than current masonry codes

The behaviour of recycled aggregate concrete at elevated temperatures

Recycled concrete aggregate (RCA) obtained from crushed concrete has different properties than those of natural aggregate. A considerable number of investigations have been conducted on the physical and mechanical properties of RCA concrete. However, little attention has been directed at studying the performance of

The prediction of compressive strength of ungrouted hollow concrete block masonry

The objective of this paper is to develop a simple and accurate empirical formula to predict the compressive strength of ungrouted hollow concrete block masonry fm′. A large database of compressive test results on masonry prisms reported in the literature was assembled and analyzed for this purpose. The collected database was also utilized to evaluate the predictive capability of the proposed model compared to those of major international masonry design codes. The study showed that the masonry codes underestimate the compressive strength of ungrouted masonry with high coefficients of variation, whereas the proposed formula gives the most accurate prediction of compressive strength with the least variation. The research also highlights the necessity for improving the prediction of compressive strength of concrete masonry by masonry design codes

Does the size effect exist in reinforced masonry?

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

Residual mechanical response of recycled aggregate concrete after exposure to elevated temperatures

A considerable number of investigations have been conducted on the mechanical and material properties of concrete made with recycled concrete aggregate (RCA), as these properties can often be different than those of conventional concrete. However, relatively little attention has been directed at studying the performance of concrete made with RCA at elevated temperatures. This is despite the fact that coarse aggregates play an important role in the behavior of concrete under fire exposure. To address the lack of knowledge, an experimental program was conducted in which six different concrete mixes were prepared with different combinations of coarse aggregates made from recycled concrete aggregate, river gravel, and crushed limestone aggregates. A total of 204 concrete cylinders (100 × 200 mm) were cast and heated under four different temperatures: 20°C (ambient temperature), 250, 500, and 750°C. The residual compressive and tensile strengths, moduli of elasticity, and damage and failure patterns of the concretes were observed and analyzed. The results indicate that concrete with aggregate both fully and partially replaced with RCA exhibits good performance under elevated temperatures and it can be considered comparable to conventional concrete. No concrete disintegration was observed when RCA concrete was heated up to 750°C. The results of tests of residual mechanical properties show some variation among concretes made with different replacement percentages of RCA