Thesis
Time domain probabilistic seismic demand analysis of self centering bridges under near fault ground motions
Washington State University
Master of Science (MS), Washington State University
2010
Handle:
https://hdl.handle.net/2376/101290
Abstract
Ground motions at sites close to a fault are sometimes affected by forward directivity. Forward directivity is a phenomenon by which most of the energy from an earthquake rupture arrives at the site in a very short duration pulse. It is known that these pulses impose a heavy demand on structures located in the vicinity of the fault. However these effects have not been addressed clearly in the building codes and no specific guidelines exist on how to account for them when determining the seismic hazard for a structure. In this research we have done a Probabilistic Seismic Demand Analysis (PSDA) for a self centering bridge. Four different methodologies namely Traditional, Broadband, Enhanced Broadband and Time Domain methodology were used (Sehhati 2008). For the analysis, the maximum column drift was chosen as the engineering demand parameter (EDP) and the spectral acceleration at the bridge's fundamental period was chosen as the ground motion intensity measure (IM). A bridge model was built and non-linear time history analysis was performed on the model using SAP2000 (v.12.0.2), in the weak direction. The analysis was done using both pulse-like and non pulse-like ground motion. Least squares regression was used to fit power-law relationship between the EDP and the intensity measure for both pulse-like and non pulse-like ground motions. For the time domain PSDA approach, which is done using simplified pulses, the analysis discussed above was run on the structure using simplified Gabor pulses for a range of pulse period and amplitude and the bridge's response was recorded for each. A surface for bridge response was then fit using genetic algorithm software, Eureqa. Before the PSDA analysis, the range of values of pulse period where simplified pulse represents the actual forward directivity ground motions was determined. The surface was then used for this range of period, to perform the PSDA, using the algorithm from Sehhati 2008. Results of the PSDA showed that pulses impose heavy demands in near fault regions. It highlighted the importance of considering small magnitude earthquakes in near fault hazard calculation. It also showed that time domain approach is better than other traditional approaches for near fault hazard calculations, as it is able to capture resonance in the structure in a better way.
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Details
- Title
- Time domain probabilistic seismic demand analysis of self centering bridges under near fault ground motions
- Creators
- Manisha Rai
- Contributors
- Mohamed ElGawady (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Civil and Environmental Engineering, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525297601842
- Language
- English
- Resource Type
- Thesis