Behaviour of Partially Grouted Nominally Reinforced Masonry Shear Walls under Dynamic Loading

Abstract

<p>The current Canadian masonry standard CSA S304.1 (2004) deals with the design of unreinforced and reinforced concrete masonry shear walls. The use of one or the other type of wall construction is limited to a particular seismic activity zone based on the seismic hazard index. The code does not provide any provisions for partially grouted shear walls in regions with moderate seismic demand. The experimental program described in the thesis focuses on the dynamic performance of partially grouted nominally reinforced concrete masonry shear walls having less steel and larger spacing than specified by the Canadian masonry standard for the minimum seismic requirements.</p> <p>A total of six reduced scale shear walls were designed and constructed to fail in flexure. A constant axial load was present throughout the test, which represented a single story building. The walls were grouped into three categories, Type I, II and III. Type I and III walls had reinforcement present only at the ends of the wall with vertical reinforcement ratios of 0.12% and 0.20%, respectively. Type II walls had an additional reinforcement located mid-length of the wall with a reinforcement ratio of 0.17%. Two identical walls were tested for each type with the exception of the Type III, where only one wall was tested. The walls were subject to dynamic loading of a scaled 1940 EI-Centro earthquake N-S component. The experimental results were evaluated and discussed pertaining to behaviour, lateral load capacity, stiffness, period, displacement ductility and load reduction factors.</p> <p>The general behaviour of the tested shear walls was dominated by rocking motion where a full length mortar joint crack developed, along with the yielding of reinforcement. The rocking motion was able to dissipate energy instead of the more common diagonal cracking and crushing of masonry. Type I and II walls had yields close the predicted values, while Type III wall had a lower yield point than predicted. All walls had similar trends of stiffuess degradation. The period increased by a factor of 2 or more during the course of testing. An idealized bilinear envelope was used to calculate the displacement ductility. It was found to be greater than 2 with load reduction factors ranging from 1.9 to 2.6.</p> <p>It was concluded that nominally reinforced partially grouted walls are potentially viable to be used in seismic zones where the seismic hazard index exceeds 0.35.</p>