This study investigates seismic response of the Moment-Resisting-Steel Frames (MRSF) with the architectural setbacks. The main objective of the study is to understand the variation of the elastic and inelastic, static and dynamic behavior with changes in the geometric dimensions of the tower portion. A second objective of the study is to determine the adequacy of the analysis procedures of various rigors, specified in current seismic design provision, in predicting those behaviors for MRSF with various size of setback. The analytical study is conducted using a regular and 16 irregular models to capture all possible combinations of configuration of setback in five-story, five-bay MRSFs. An irregular model is developed by gradually changing the horizontal and vertical dimensions of the tower portion of the regular base 2D frame-model. All models were designed for (a) equal global displacement and uniform distribution of inter-story drift under First-Mode (FM) lateral force distribution pattern at first significant yield, and (b) equal period of vibration at the first mode, using Nonlinear Static Seismic analysis procedure. Among the conclusions derived from the research is that the variation of (a) the elastic and inelastic inter-story drift, the ductility demand for the top three stories, and (b) the elastic and inelastic global displacement exhibited a pattern similar to the variation of the FM participation factor at the roof, PF1Φr,1. The square-root-of-sum-of-square (SRSS) distribution provided accurate estimates of elastic story shear and inter-story drift demand as well as the story yield strength and drift.

The buildings that are designed according to the building codes generally perform well at severe performance objectives (like life safety) under high earthquake hazard levels. However, the building performance at low performance objectives (like immediate occupancy) under low earthquake hazards is uncertain. The motivation of this research is to modify the design and detailing rules to make the traditional systems perform better at multi-level hazards. This research introduces two new structural steel systems: hybrid Buckling Restrained Braced Frames (BRBF) and hybrid steel Moment Frames (MF). The "hybrid" term for the BRBF system comes from the use of different steel material including carbon steel (A36), high-performance steel (HPS) and low yield point (LYP) steel. The hybridity of the moment frames is related to the sequence in the plastification of the system which is provided by using weaker and stronger girder sections. Alternative moment frame connections incorporating the use of LYP steel plates are also investigated. The hybrid BRBF approach was evaluated on seventeen regular (standard) frames with different story heights, seismic design categories and building plans. By varying the steel areas and materials in the BRB cores, three hybrid BRBFs were developed for each regular (standard) frame and their behavior was compared against each other through pushover and incremental dynamic analyses. The benefits of the hybridity were presented using different damage measures such as story accelerations, interstory drifts, and residual displacements. Collapse performance evaluation was also provided. The performance of hybrid moment frames was investigated on a design space including forty-two moment frame archetypes. Two different hybrid combinations were implemented in the designs with different column sections and different strong column-weak beam (SC/WB) ratios. The efficiency of the hybrid moment frame in which only the girder sizes were changed to control the plastification was compared with regular moment frame designs with higher SC/WB ratios. As side studies, the effect of shallow and deep column sections and SC/WB ratios on the moment frame behavior were also investigated.   In order to provide adequate ductility in the reduced capacity bays with special detailing, alternative hybrid moment frame connections adapting the use of low strength steel were also studied. / PhD

The Central and Eastern United States (CEUS) is a region that is characterized by low frequency-high consequence seismic events such as the New Madrid sequence of 18111812. The infrequent nature of earthquakes in the region has led to a perception that the seismic risk in the area is low, and the current building stock reflects this perception. The majority of steel-framed buildings in the CEUS were designed without regard to seismic loads. Such frames possess limited seismic resistance, and may pose an unacceptable risk if a large earthquake were to occur in the region. A key ingredient of building performance and seismic risk assessment is the fragility, a term that describes the probability of failure to meet a performance objective as a function of demand on the system. The effects of uncertainties on building seismic performance can be displayed by a seismic fragility relationship. This fragility can be used in a conditional scenario-based seismic risk assessment or can be integrated with seismic hazard to obtain an estimate of annual or lifetime risk. The seismic fragility analyses in this study focus on steel frames that are typical of building construction in regions of infrequent seismicity; such frames have received little attention to date in building seismic risk assessment. Current steel building stock in Shelby Co., TN has been represented by five code-compliant model frames with different lateral force-resisting systems, i.e., braced-frames, partially-restrained moment frames and a rigid moment frame. The performance of model frames under certain hazard levels was assessed using fragility curves. Different rehabilitation methods were discussed and applied. Results indicate that PR frames behave better than expected and rehabilitated frames perform quite well even under severe earthquakes.