Loading...

Probabilistic Evaluation of Nonlinear Behavior of Fixed- and Flexible-Base Shear Buildings

Abtahi, Shaghayegh | 2016

823 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49632 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannad, Mohammad Ali; Mahsoli, Mojtaba
  7. Abstract:
  8. This thesis revisits the effect of dynamic soil-structure interaction (SSI) on multistory buildings with a probabilistic approach. For this purpose, the relationship between the strength demands of fixed- and flexible-base multi-degree-of-freedom (MDOF) systems, or strength reduction factor thereof, with that of fixed- and flexible-base equivalent single-degree-of-freedom (eSDOF) systems is investigated considering prevailing uncertainties. To this end, Monte Carlo sampling analysis is employed in which a suite of nearly 2000 records are utilized to properly quantify the ground motion uncertainty. The soil-structure system is modeled by the sub-structure method. The uncertainty in the properties of the soil and the structure is described by random variables that are input to this model. This thesis comprises two major studies that respectively address fixed-base and flexible-base MDOF systems, as follows:The fixed-base study starts with quantifying the probability distribution of the well-known MDOF modification factor, defined as the ratio of the strength demands of an MDOF system to that of the eSDOF system. The number of stories and the level of nonlinearity are found to be the most influential parameters on this factor. The second part of the study probabilistically quantifies the effect of this factor on the seismic performance of the structure. The results indicate a very high probability that a multistory building endures more than a twofold increase in the ductility demand when designed based on SDOF assumptions with no modification. The final part proposes a novel relationship to predict the modification factor using 1,200,000 data points, and examines past relationships in light of the new results.The flexible-base study, too, starts with quantifying the probability distribution of the modification factor defined before for soil-structure systems. Despite several past studies, it is concluded that SSI only insignificantly affects the modification factor. The next part of the flexible-base study investigates why past studies have concluded that SSI significantly affects the performance of MDOF systems. It is concluded that most of this influence is caused by the effect of SSI on the performance of eSDOF systems and the share of MDOF aspects of the system in this effect is insignificant. As a result, the modification factor of fixed-base systems adequately represents that of flexible-base systems. This forms the basis of the final part of the study. In particular, the relationship that was proposed to predict the modification factor for fixed-base systems is employed to correct the strength demand of flexible-base systems. The results show that the ensuing ductility demands for the latter systems coincide with the target ductility demand of the flexible-base eSDOF systems
  9. Keywords:
  10. Strength Demand ; Uncertainty ; Soil-Structure Interaction ; Multi-Degree of Freedom Structures ; Equivalent Single Layer Theory ; Probability Analysis ; Inelastic Behavior ; Shear Structures

 Digital Object List

 Bookmark