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Seismic Performance Evaluation of Base-isolated Structures Equipped With Shape Memory Alloys

Ahmadi Soleimani, Saleh | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47897 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khalu, Alireza
  7. Abstract:
  8. Design methods and technologies for the implementation of earthquake-resistant buildings in recent years has made remarkable progress. The control and energy dissipation systems such as seismic isolation systems in buildings, according to their history hands-on experience in the world, have shown good performance against seismic hazards, hence they have been considered by scientists and engineers. Most of the energy dissipation systems have limitations such as service life,durability, maintenance , need to change and modifying the structure geometry after the earthquake. In recent years the use of shape memory alloys to improve the behavior of base isolation is considered. Shape memory alloys as a shape memory material with unique and simultaneous characteristics of energy dissipation, high return, high resistance to fatigue and corroison, no need for maintenance to reduce earthquake damage on structures, can be used in various forms and can solve typically Isolation restrictions.With regard to the issues raised ,a comprehensive study of these alloy performances in combination with base isolations in improving their features, as well as controlling structural damages in higher performance levels is needed.In the present study evaluating the above isolation systems based on probabilistic concepts within the framework of the performance based evaluation is examined. In this study, 3, 6 and 9 story moment frame structures with elastomeric isolator system is designed. Following the assessment, elastomeric isolator with a shape memory alloy, is introduced. Isolators, introduced in combination with shape memory alloys for energy dissipation properties and complete restoration is designed. The shape memory alloy participation rate sensitivity analysis in the effective stiffness of isolator system was performed and is found that in almost all performance indexes using shape memory alloy leads to better performance and participation beyond the limit, causes a negative impact on some indexes. Then, each of the structures isolated with optimal isolator equipped with this alloy and with elastomeric isolators equipped with lead core and also structures with fixed base, by running incremental nonlinear dynamic analysis under a series of far-field records introduced by FEMA P-695, at various performance levels have been studied in the form of fragility curves. The fragility curves for damages on structural components sensitive to drift, non-structural components sensitive to acceleration and the level of damage to the isolation system, on 4 failure levels of slight, moderate, extensive and collapse (corresponding to levels 1, 2, 3 and 4) have been distinguished and studied. In comparing the performance of Elastomeric isolators equipped with optimal Alloy mentioned, with Lead Rubber Bearing isolators, it was observed that new isolator, operating at lower levels, in reduction the seismic risk of superstructure failure, including structural and non- structural, has better performance, but at higher damage states especially in structural components, slightly weaker than the conventional isolator.But also due to the full reversion of this type of isolator and also compared to fixed structures, have defensive performance. In all isolated structures, levels of destruction that, superstructures experienced, in most earthquake records, remained limited to levels 2 and 3. And superstructure, was less on the verge of collapse. The Lead Rubber Bearing isolators, in controlling isolator damage level, has been slightly better than the isolator equipped with shape memory alloy, but at higher performance levels are very close together. The performance of the isolated structures showed that the impact of the isolator in comparison to the structures with fixed base,in reducing seismic risk of failure states, further in structural components, has shown itself.And Isolator impact on non-structural damages, compared with structural damages, is lower.Also all isolators, in reducing seismic risk of occurring structural damages in their superstructures, compared with fixed structures equivalent,had better performance at higher states. But in the failure of non-structural components at all levels, have almost the same performance improvements
  9. Keywords:
  10. Seismic Isolation ; Shape Memory Alloy ; Fragility Curve ; Incremental Dynamic Analysis ; Performance-Based Earthquake Assessment

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