Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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2. DUCTILITY AND SEISMIC RESPONSE OF STRUCTURES against injury or death. Criteria for structure checking to minor or moderate earthquakes that may occur relatively frequently in the life of the building are not specified explicitly. A review of 41 codes elaborated all over the world shows that 38 are based on just one level, the principal design being concentrated on strength requirements (Bertero, 1997). So, the first step in the performance basic design philosophy is to define an acceptable level of damage due to an earthquake, and this is the purpose of the design code. Performance-based seismic engineering, elaborated by the Vision 2000 Committee of SEAOC (1995) and ATC (1995), consists of a selection of appropriate systems, layout and detailing of a structure, and of non-structural components and contents so that, at specified levels of ground motion and defined levels of reliability, the structure will not be damaged, beyond certain limit states. The performance levels have been defined for four levels as a combination of damage to structure and to non-structural elements, building facilities and required repairs. 1. Near collapse level: collapse prevention is directly related to the prevention of casualties and of damage to the contents of buildings. The structure can undergo serious damage during the major earthquakes, but it must be standing after the ground motion. 2. Life safe level: the casualties in a building are usually caused by the collapse of the building components during an earthquake. The evaluation of the number of casualties as an economic damage in an optimisation process, as suggested in some studies, poses very difficult ethical problems. 3. Operational level: a distinction is made between structural damage which cannot be repaired and damage which can be repaired. Irreparable damage is a specific subject for individual engineering judgement of experts. The damage refers both to structure and to non-structural elements. 4. Fully operational level: in some cases the value of the business is more important than the value of the buildings themselves and the interruption of this activity is intolerable. If the owner of a building wishes to avoid the cost of interruptions, it is necessary to fulfil more than the minimum requirement of design codes. By using stronger and stiffer designs, it is possible to reduce or even eliminate, the interruption of the building function after a strong earthquake, but this results in a more expensive structure. These limit states are presented in Figure 2.4, as a function both of the structure and of non-structural elements. In the seismic load-top sway displacement curve, 17
2. DUCTILITY AND SEISMIC RESPONSE OF STRUCTURES there are three very significant points: the limit of elastic behaviour without any damage, the limit of damage with major damage and, finally, the limit of collapse, for which the structure is at the threshold of breakdown. By taking different limit states for the structure and for non-structural elements, some multi-level approaches are possible. 18 Figure 2.4. Performance levels A verification at three performance levels has been proposed by different researchers (Gioncu and Mazzolani, 2002): 1. Serviceability limit state (SLS) for frequent earthquakes; the corresponding design earthquake is called a service earthquake. This limit state imposes that the structure, together with non-structural elements, should suffer minimum damage and the discomfort for inhabitants should be reduced to a minimum. Therefore, the structure must remain within the elastic range or it can suffer unimportant plastic deformations; 2. Damageability limit state (DLS) for occasional earthquakes: this limit state considers an earthquake intensity which produces damage in non- structural elements and moderate damage in a structure, which can be repaired without great technical difficulties;
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3. SEISMIC BEHAVIOUR OF BOLTED END
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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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6. SUMMARY, CONCLUSIONS AND FUTURE
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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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