Performance-based seismic retrofit (PBSR) methodology for multi-story buildings with full-scale experimental validation
Date
2015
Authors
Bahmani, Pouria, author
van de Lindt, John W., advisor
Heyliger, Paul R., committee member
Mahmoud, Hussam N., committee member
Radford, Donald W., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Recent earthquakes such as Loma Prieta (1989) and Northridge (1994) in California have highlighted the poor performance of one class of existing buildings. Many older buildings were designed prior to the implementation of modern seismic design codes. Although building codes have clearly evolved, the problem is still unresolved for older buildings that are code-deficient such as soft-story wood-frame buildings. Many retrofit procedures have been proposed by the research and structural engineering communities including force-based and performance-based retrofit methodologies. A performance-based seismic retrofit (PBSR) methodology is developed and validated in this dissertation and is a method that seeks to meet or exceed minimum performance criteria specified by building stakeholders when the building is subjected to a predefined seismic intensity level. Unlike traditional force-based design methods, the PBSR method enables engineers to design and retrofit buildings based on the performance level expected by the stakeholders; and eventually, results in a more comprehensive method of retrofitting multi-story buildings. The objective of this study was twofold. The first objective was to develop a new displacement-based design (DBD) method with the ability to account for torsion (DBDT), thereby, generalizing the displacement-based design to be applied to linear and non-linear structures with vertical and torsional (horizontal) irregularities without the need for time-history analysis. This first objective involves the decoupling of translational and torsional mode shapes of the structure, standardizing the global stiffness and mass matrices, and finally combining the decoupled translational and torsional mode shapes to meet the designated performance criteria. The second objective was to develop a new performance-based seismic retrofit (PBSR) methodology for retrofitting existing multi-story buildings with torsional (horizontal) and vertical irregularities. The PBSR method was developed using the proposed DBDT method and was validated numerically to retrofit a three-story soft-story building with excessive torsion at all stories. The PBSR method was then modified to eliminate the torsion in the building and satisfy the designated performance criteria. This enables the design to use only the dominant translational mode shape (i.e., first mode shape) for the retrofit. This also eliminates the need for modal analysis and the decoupling of translational and torsional mode shapes makes it more straightforward for practice. The new simplified PBSR method for retrofitting multi-story buildings was then applied to a four-story soft-story wood-frame building with torsional irregularities at all stories and assessed numerically using non-linear time-history (NLTH) analysis. The method developed in this dissertation was validated experimentally by conducting a series of full-scale tests on a four-story 370 m² (4,000 ft²) soft-story wood-frame building at the outdoor uni-axial shake table at the University of California - San Diego's Network for Earthquake Engineering Simulation (NEES) laboratory. The test provided the first-of-its-kind (landmark) dataset for use by researchers and practitioners for retrofitting soft-story wood-frame buildings. The experimental test results showed that the retrofitted building met the designated performance criteria and essentially validated the PBSR method developed in this dissertation. It should be noted that although the PBSR method was only validated experimentally for the asymmetric soft-story wood-frame building, the method can be used for any type of structure provided the necessary details of design and material properties are addressed. Finally, in order to investigate the collapse mechanism of soft-story wood-frame buildings the un-retrofitted building was subjected to series of ground motion with increasing intensities until it collapsed. These series of tests are the first full-scale collapse tests of a full-size building.
Description
Rights Access
Subject
performance-based seismic design
shake table test
wood-frame buildings
performance-based seismic retrofit
multi-story retrofit design
soft-story buildings