Behavior of Reinforced Concrete Masonry Walls Subjected to Combined Axial Loading and Out-of-Plane Bending

Abstract

An experimental program was designed and conducted to study the strength and behavior of masonry load-bearing walls. Ten reinforced large-scale wall specimens with pinned support conditions were tested under eccentric compressive loading. The load eccentricities at two ends of the specimen were applied in a manner which resulted in various specimen bending patterns. Four of these specimens were tested under symmetrical single curvature loading, three of them were tested under asymmetrical single curvature bending, and the remaining three were tested under reverse curvature bending. Wall specimens were 2390 mm high by 790 mm long by 140 mm thick, which resulted in a slenderness ratio of 17.1. Ultimate load and corresponding applied moment, and lateral deflections at critical cross-sections were obtained and presented in either table or graph format. Moment vs. curvature curves were established and used to determine effective flexural rigidities, El(eff), at the time of failure of walls under various loading conditions. Results of large-scale tests showed that for a constant end eccentricity ratio, e1le2, the ultimate load and the associated El(eff) decreased as the end eccentricity ratio, elt, increased. The ultimate load and the El(eff) values increase as the end eccentricity ratio, e1le2, varied from 1.0 to 0.0 and to -1.0. This increase in the strength and flexural rigidity was attributed to a change of the failure mode from tension-controlled failure to compression-controlled failure associated with the change of e1le2. A comparison study revealed that similar effects of elt and e Jie2 on the capacity and El(eff) of the walls was noted in other relevant research. Through the comparison, an increase of El(eff) with the increased slenderness ratio, hit, was also believed to occur. While test results obtained by others supported the findings in this research with regard to the effects of elt and e1le2 on the capacity of the wall, the effect of hit on the El(eff) values remained inconclusive due to limited test data.

The measured ultimate loads and flexural rigidities were also compared with the predicted code values. The results showed that the current Canadian masonry design code, S304.1-M04, tends to underestimate the capacity and effective flexural rigidity of masonry walls and thus leads to a conservative design over a range of parameters. This underestimation is most significant in compression-controlled failure regions. In the regions of tension-controlled failure, the code appears to agree reasonably well with the available data. Several existing equations for determining El(eff) were also evaluated with regard to their accuracy and validity for application based on the available tested data.