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Collapse Capacity Assessment of Irregular Tall Buildings Considering the Effect of Pulse-Like Forward Directivity Ground Motions

Saffar, Ali | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 47107 (57)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Rahimzadeh Rofooei, Fayyaz
  7. Abstract:
  8. Structural response to near fault ground motions has received significant attention in recent years. Such ground motions are different from ordinary ones and are characterized by a large, long period, velocity pulse caused by the forward directivity. These velocity pulses could potentially impose sever demands on structures and increase their risk of seismic collapse. The situation could even be worse for tall buildings with fundamental periods close to the period of the velocity pulses, and requires special consideration in design process. Prediction of seismic-induced collapse potential of structures has been among the main concerns in Performance Based Earthquake Engineering (PBEE). The results could be used as an important measure in designing new structures, or evaluating the seismic performance of existing ones. Not surprisingly, much effort has been made in accurate prediction of collapse capacity of structures due to its importance in estimation of the human and monetary losses during and after an earthquake episode. In this study the collapse capacity of irregular tall buildings under near-field ground motions with directivity effect will be investigated. A number of building models with different number of stories, i.e. 15, 20, 25 stories, is considered. Using 14 near field ground motions from PEER NGA database, the effect of near fault ground motion on the models will be evaluated. In order to recognize the strong pulse in velocity time history all of the pulse like ground motion in database have been rotated to the fault normal direction. Seismic collapse risk of each archetype is evaluated using incremental dynamic analysis (IDA). The hypothetical site of the buildings located in down town Los Angeles, California, USA with the longitude = -118.25 and latitude= 34.05 that is near to several known faults. This site selected in order to design the structure for the near-fault site according to the ASCE7-10 to better evaluation of the behaviour of structures designed for the near field site. In order to evaluate the collapse risk of the structure this study utilize the λc, mean annual frequency of collapse, which is then used to compute the probability of collapse of the buildings in 50 years to estimate the potential collapse of the buildings fulfils the ASCE7-10 target design collapse level which is 1% in the50 years. Seismic hazard curve and collapse fragility curve of buildings are two main component to compute the λc. Finally, based on the consideration of this study it is concluded that the new risk-targeted hazard maps do not explicitly consider the effect of the collapse in near-field area. Besides, ground motion intensities in the lower half of collapse fragility curve typically dominate the collapse risk for the both the base and corresponding irregularities cases
  9. Keywords:
  10. Near-Field Earthquake ; Forward Directivity ; Collapse Analysis ; High Structures ; Collapse Capacity

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