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Nguyên nhân: -Nội sinh: liên quan đến vận động phun trào núi lửa, vận động kiến tạo ở các đới hút chìm, các hoạt động đứt gãy. -Ngoại sinh: Thiên thạch va chạm vào Trái Đất, các vụ trượt lở đất đá với khối lượng lớn. | 1 18 Basic Geotechnical Earthquake Engineering For compliance with the serviceability limit state performance provisions the simple linear stress strain relationships of materials are needed. These are the conventional parameters used to assess the structural resistance to other loads. Assuming that the structural system remains predominantly elastic damage avoidance can reasonably be expected and compliance can be assured. Simple elastic engineering models can be used to ascertain building response in these conditions. Consequently for concrete and masonry structures the cracked sectional properties are appropriate for the serviceability limit state although significant yield of the reinforcing steel and the subsequent retention of wide residual cracks is to be avoided. For compliance with the ultimate limit state performance provisions the post-elastic response of the structure needs to be considered. This includes large post-elastic member deformation Fig. 11.1 . Often traditional engineering models break down at this stage. There is thus little to be gained by using highly sophisticated engineering modeling techniques to demonstrate compliance with the ultimate limit states criteria unless there is a high degree of confidence that the relationship between the elastic and inelastic structural response is realistic. The simple elastic stress strain relationships and the elastic engineering models used to ascertain the load distribution between members within the structural system no longer apply. It is to address this particular post-elastic response condition being the primary objective of good earthquake engineering design that the principles of capacity design of structures were developed and subsequently introduced. 11.4 EARTHQUAKE DESIGN LEVEL GROUND MOTION A fundamental parameter contained within all earthquake loading standards is the earthquake induced ground motion. This has to be used for design. This is generally prepared by seismologists and .
