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Thin lightly-reinforced concrete walls in concrete shear wall buildings Fenton, Robert Kyle

Abstract

This thesis focuses on the behaviour of thin and lightly-reinforced concrete walls subjected to axial and lateral in-plane force and displacement demands within high-rise cantilever and coupled shear wall type buildings. Many older and some new high-rise buildings employ thin wall elements of this type as a part of the main gravity system. A brief case study of a fictitious sample building is used to identify some shortcomings of these elements in design practice. Current North American design codes employ two main design methods to determine the in-plane, uni-axial capacity of thin bearing walls. Results of past wall tests are aggregated and compared to the empirical method and rational "moment magnifier" method of slender wall design. Comparisons of the design methods show that significantly different design axial load capacities are possible within the same design code. The results of this comparison are used to derive a new empirical bearing wall design formula which better corresponds with the results and design input parameters of the rational "moment magnifier" design method. Recent seismic events have also shown that these thin walls are subject to sudden compression failures when subjected large in plane lateral displacements. A database analysis of past wall tests is used to identify parameters which influence the drift capacity of these elements, and a new empirical relationship of overall wall drift capacity based on shear height and compression zone slenderness is derived. The database results are used to identify several low drift capacity elements for further analysis. An analysis of several previous wall tests and non-linear finite element models is used to determine the sectional and global response characteristics of these members. The results of this test specimen analysis shows that thin and lightly-reinforced wall elements show very little vertical spread of plasticity resulting in smaller than anticipated plastic hinge lengths, however sectional analysis methods produce good estimates of overall sectional properties. Finally, a model of in-plane shear displacements based on measured average vertical strains in the plastic hinge zone is validated for these types of elements.

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