Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Civil Engineering

First Adviser

Ricles, James M.

Other advisers/committee members

Wilson, John L.; Pakzad, Shamim N.; Garlock, Maria

Abstract

The design method used for conventional steel special moment resisting frame (SMRF) with welded beam-to-column connections leads to significant inelastic deformations and formation of plastic hinges in the beams under the design earthquake for seismic resistant steel frame buildings. This may cause significant damage. A self-centering (SC) moment resisting frame (SC-MRF) is a viable alternative to a conventional SMRF. The beams in an SC-MRF are post-tensioned to the columns by high strength post-tensioning (PT) strands oriented horizontally to provide SC forces when gap opening occurs. An SC-MRF is characterized by gap opening and closing at the beam-column interface under earthquake loading. The SC-MRF is typically designed to meet several seismic performance objectives, including no structural damage under the DBE in order to perform in a resilient manner. Recent analytical and experimental research has shown that an SC-MRF can achieve this performance objective. Since an SC-MRF system is a new concept little is known about its collapse resistance under extreme seismic ground motions. For an SC-MRF to be accepted in practice, the collapse resistance of this type of structural system under extreme ground motions must be established to assess whether it is adequate. Incremental Dynamic Analysis (IDA) are performed using an ensemble of 44 far-field ground motions to determine the probability of collapse of a 4-story low-rise building with perimeter SC-MRFs. A model of the SC-MRF was developed that included both stress-resultant and continuum finite elements to enable the important limit states, including local buckling in the beams, to be accounted for in the IDA. In order to compare the collapse performance of an SC-MRF with an SMRF a 4-story SMRF was designed and IDA performed to determine the collapse resistance of the SMRF. The results show that the collapse resistance of an SC-MRF system can exceed that of a conventional steel SMRF. In addition, the design of the SC-MRF is modified to investigate the collapse resistance sensitivity to the PT strand detailing, by varying the number of PT strands and level of PT force. The results show that collapse resistance is affected by the level of PT force, where an increased number of strands lead to a higher post-gap opening stiffness resulting in larger axial forces and local buckling developing in the beams. This leads to a higher probability of collapse than the original design and comparable with the collapse resistance of SMRF.Structures are built where active faults may be in close proximity. The probability of collapse of a 4-story low-rise building with perimeter SC-MRFs subjected to near-field ground motions was studied and compared to the results for far-field ground motions. IDA are performed using an ensemble of 56 near-field ground motions. The results show that the SC-MRF built close to active faults has less collapse resistance in contrast to the one built in seismic zones away from active faults. The structure has larger spectral acceleration for near-field ground motions than far-field ground motions at the fundamental period, leading to excessive inelastic deformations that cause structure collapse earlier. The results obtained, however, show that an acceptable margin against collapse is still achieved and therefore indicate a potential for an SC-MRF to be used in seismic zones with active near-field faults.

Available for download on Saturday, October 28, 2017

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