Abstract
The behaviour of unreinforced masonry walls under seismic loading is considered, with particular emphasis being given to face-load response. It is shown that traditional methods of assessing seismic performance based on elastic stress calculations result in excessively conservative results when compared with more realistic methods of assessment. In particular, an assessment procedure based on energy considerations is developed at some length, and is illustrated by a worked sample.
Highlights
It would initially appear that ductility considerations are inappropriate, since ductility is normally provided in structures primarily by inelastic straining of steelf either in the form of reinforcing bars or structural steel sections
The concept of ductility is based on energy considerations, and it can be shown that if these considerations are applied to the analysis of unreinforced masonry, the level of seismic loading required to cause failure, for face-loaded walls, tends to greatly exceed that predicted by simple ultimate strength calculations
Examination of working stress and ultimate strength methods for assessing unreinforced masonry strength under seismic loading indicated that neither method could give an adequate representation of the dynamic response
Summary
Ultimate strength methods of design and analysis are accepted in New Zealand as necessary for assessing performance of reinforced masonry structures under seismic loading ^ * ( 1 ) and are required by. An example of the use of the methodology for a five-storey unreinforced masonry building with perimeter walls is given in an Appendix to this paper The results of this example indicate that, as expected , the top floor is the most critical, but that equivalent accelerations to induce failure are suprisingly high, given the conservative nature of the assumptions made. If the uplift displacements are too large, failure may occur gradually by shedding bricks from the tension end of the wall Many unreinforced concrete structures subjected to seismic loading have shown signs of relative displacements at one or more levels This can be attributed to rocking response with simultaneous accelerations in the face load direction. This aspect can be incorporated in the methodology developed above
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More From: Bulletin of the New Zealand Society for Earthquake Engineering
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