The main objective of this investigation is to examine how various material properties, governed by code specification, affect the seismic response of a twelve- story reinforced concrete building. This study incorporates the pushover and response history analysis to examine how varying steel yield strength (Fy), 28 day nominal compressive concrete strength (f’c), modes, and ground motions may affect the base shear capacity and displacements of a reinforced concrete structure. Different steel and concrete strengths were found to have minimal impact on the initial stiffness of the structure. However, during the post-yielding phase, higher steel and concrete compressive strengths resulted in larger base shear capacities of up to 22%. The base shear capacity geometric median increased as f’c or Fy increased, and the base shear capacity dispersion measure decreased as f’c or Fy increased. Higher mode results were neglected in this study due to non-convergent pushover analyses results. According to the response history analysis, larger yield and concrete compressive strengths result in lower roof displacement. The difference in roof displacement was less than 12% throughout. This displays the robustness of both analysis methods because material properties have insignificant impact on seismic response. Therefore, acceptable yield and compressive strengths governed by seismic code will result in acceptable building performance.

In the past two decades, there have been significant advances in the development of self-centering (SC) seismic force resisting systems. However, examples of SC systems used in practice are limited due to unusual field construction practices, high initial cost premiums and deformation incompatibility with the gravity framing. A self-centering beam moment frame (SCB-MF) has been developed that virtually eliminates residual drifts and concentrates the majority of structural damage in replaceable fuse elements. The SCB consists of a I-shaped steel beam augmented with a restoring force mechanism attached to the bottom flange and can be shop fabricated. Additionally, the SCB has been designed to eliminate the deformation incompatibility associated with the self-centering mechanism. The SCB-MF system is investigated and developed through analytical, computational, and experimental means. The first phase of the work involves the development of the SCB concepts and the experimental program on five two-thirds scale SCB specimens. Key parameters were varied to investigate their effect on global system hysteretic response and their effect on system components. These large-scale experiments validated the performance of the system, allowed the investigation of detailing and construction methods, provided information on the behavior of the individual components of the system. The experimental results also provided data to confirm and calibrate computational models that can capable of capturing the salient features of the SCB-MF response on global and component level. As a part of the second phase, a set of archetype buildings was designed using the self-centering beam moment frame (SCB-MF) to conduct a non-linear response history study. The study was conducted on a set of 9 archetype buildings. Four, twelve and twenty story frames, each with three levels of self-centering ratios representing partial and fully self-centering systems, were subjected to 44 ground motions scaled to two hazard levels. This study evaluated the performance of SCB-MFs in multi-story structures and investigated the probabilities of reaching limit states for earthquake events with varying recurrence period. The experimental and computational studies described in this dissertation demonstrate that the SCB-MF for steel-framed buildings can satisfy the performance goals of virtually eliminating residual drift and concentrating structural damage in replaceable fuses even during large earthquakes. / Ph. D.

A novel shear wall system for building structures has been developed that improves upon the performance of conventional steel plate shear walls by mitigating buckling. The new structural system, called the Ring Shaped - Steel Plate Shear Wall, was investigated and developed through experimental and computational methods. First, the plastic mechanism of the system was numerically derived and then analytically validated with finite element analyses. Next, five large-scale, quasi-static, cyclic experimental tests were conducted in the Thomas M. Murray Structures Laboratory at Virginia Tech. The large-scale experiments validated the system performance and provided data on the boundary frame forces, infill panel shear deformation modes, buckling mode shapes, and buckling magnitudes. Multiple computational modeling techniques were employed to reproduce different facets of the system behavior. First, detailed finite element models were constructed to accurately reproduce the cyclic performance, yielding pattern, and buckling mode shapes. The refined finite element models were utilized to further study the boundary element forces and ultra-low cycle fatigue behavior of the system. Second, reduced-order computational models were constructed that can accurately reproduce the hysteretic performance of the web plates. The reduced-order models were then utilized to study the nonlinear response history behavior of four prototype building structures using Ring Shaped - Steel Plate Shear Walls and conventional steel plate shear walls. The nonlinear response history analyses investigated the application of the system to a short period and a long period building configuration. In total 176 nonlinear response history analyses were conducted and statistically analyzed. Lastly, a practical design methodology for the Ring Shaped - Steel Plate Shear Wall web plates was presented. The experimental tests and computational simulations reported in this dissertation demonstrate that Ring Shaped - Steel Plate Shear Walls are capable of improving seismic performance of buildings by drastically reducing buckling and improving cyclic energy dissipation. / Ph. D.

Nonlinear structures, when subjected to multiple ground motion records that are scaled to consistent ground motion intensity show significant variation in their response. This effect of ground motion randomness on the variation of structural response is defined as Record-to-Record (RTR) Variability. Ground motion characteristics that contribute to this variability in response includes the variation of signal composition (frequency content) with time (spectral nonstationarity).The phenomenon of moving resonance which occurs when the frequency content of the ground motion shifts in a similar manner as the natural frequencies of the structural response, is likely a contributor to variability. This brings the need to further understand the sources of variability due to moving resonance. The present study was carried out to develop a method to analyze the time-frequency content of a ground motion to assess the occurrence of moving resonance and to quantify its potential in effecting the structural systems. Bilinear elastic and elastoplastic hysteretic behavior was considered. Detailed analysis is done to quantify the effect of moving resonance on structural systems due to 22 far field ground motion records. The wavelet coefficient plots gave very good detail of the characteristics of the ground motions that were not clear from the acceleration time histories and response spectra plots. Instances of moving resonance were found out to be significant. Amplification due to moving resonance was found to be quite large. One instance studied in detail (accelerogram of Northridge earthquake at Beverly Hills) had peak displacement amplified by 6 times compared to the amount of peak displacement expected if the system did not exhibit moving resonance. Based on the analyses results, the characteristics of the ground motion records that don't cause significant moving resonance effect on structural systems were observed. Similarly, the characteristics of the ground motions that do cause moving resonance effect on structural systems were examined. / Master of Science

No description available.

Traditional seismic load resisting systems in buildings are designed to undergo inelastic deformations in order to dissipate energy, resulting in residual displacements. This work explores an approach to eliminate these residual displacements. The systems investigated have low initial stiffness which increases at a predefined displacement, and are therefore called stiffening elastic systems. This thesis begins with an examination of single-degree-of-freedom stiffening elastic systems. A case study is presented which suggests that the benefits from stiffening elastic behavior may be limited to systems which would have long periods if designed traditionally. A thorough parameter study is also presented which indicates the benefit of stiffening elastic behavior for SDOF systems with periods greater than four seconds. A final case study is presented that compares the response of a twelve-story stiffening elastic system to a ductile system and an elastic system. The stiffening elastic system was able to eliminate the residual displacements inherent in a ductile system while lowering the base shear experienced by the elastic system, but is not clearly better than the ductile system because the base shear force was much higher.

This research evaluates the seismic demands for a three-span curved bridge crossing fault-rupture zones. Two approximate procedures which have been proved adequate for ordinary straight bridges crossing fault-rupture zones, i.e., the fault-rupture response spectrum analysis (FR-RSA) procedure and the fault-rupture linear static analysis (FR-LSA) procedure, were considered in this investigation. These two procedures estimate the seismic demands by superposing the peak values of quasi-static and dynamic bridge responses. The peak quasi-static response in both methods is computed by nonlinear static analysis of the bridge under the ground displacement offset associated with fault-rupture. In FR-RSA and FR-LSA, the peak dynamic responses are respectively estimated from combination of the peak modal responses using the complete-quadratic-combination rule and the linear static analysis of the bridge under appropriate equivalent seismic forces. The results from the two approximate procedures were compared to those obtained from the nonlinear response history analysis (RHA) which is more rigorous but may be too onerous for seismic demand evaluation. It is shown that the FR-RSA and FR-LSA procedures which require less modeling and analysis efforts provide reasonable seismic demand estimates for practical applications.

Recent advancements in earthquake engineering have caused a movement toward a probabilistic quantification of the behavior of structural systems. Analysis characteristics, such as ground motion records, material properties, and structural component behavior are defined by probabilistic distributions. The response is also characterized probabilistically, with distributions fitted to analysis results at intensity levels ranging from the maximum considered earthquake ground motion to collapse. Despite the progress toward a probabilistic framework, the variability in structural analysis results due to modeling techniques has not been considered. This work investigates the uncertainty associated with modeling geometric nonlinearities and Rayleigh damping models on the response of planar frames at multiple ground motion intensity levels. First, an investigation is presented on geometric nonlinearity approaches for planar frames, followed by a critical review of current damping models. Three frames, a four-story buckling restrained braced frame, a four-story steel moment resisting frame, and an eight-story steel moment resisting frame, are compared using two geometric nonlinearity approaches and five Rayleigh damping models. Static pushover analyses are performed on the models in the geometric nonlinearities study, and incremental dynamic analyses are performed on all models to compare the response at the design based earthquake ground motion (DBE), maximum considered earthquake ground motion (MCE), and collapse intensity levels. The results indicate noticeable differences in the responses at the DBE and MCE levels and significant differences in the responses at the collapse level. Analysis of the sidesway collapse mechanisms indicates a shift in the behavior corresponding to the different modeling assumptions, though the effects were specific to each frame. The FEMA P-695 Methodology provided a framework that defined the static and dynamic analyses performed during the modeling uncertainties studies. However, the Methodology is complex and the analyses are computationally expensive. To expedite the analyses and manage the results, a toolkit was created that streamlines the process using a set of interconnected modules. The toolkit provides a program that organizes data and reduces mistakes for those familiar with the process while providing an educational tool for novices of the Methodology by stepping new users through the intricacies of the process. The collapse margin ratio (CMR), calculated in the Methodology, was used to compare the collapse behavior of the models in the modeling uncertainties study. Though it provides a simple scalar quantity for comparison, calculation of the CMR typically requires determination of the full set of incremental dynamic analysis curves, which require prohibitively large analysis time for complex models. To reduce the computational cost of calculating the CMR, a new parallel computing method, referred to as the fragility search method, was devised that uses approximate collapse fragility curves to quickly converge on the median collapse intensity value. The new method is shown to have favorable attributes compared to other parallel computing methods for determining the CMR. / Ph. D.

This work stems from two different studies related to this performance assessment of seismic resistant systems. The first study compares the performance of newly developed and traditional seismic resisting systems, and the second study investigates many of the assumptions made within provisions for nonlinear response history analyses. In the first study, two innovative systems, which are hybrid buckling restrained braces and collapse prevention systems, are compared to their traditional counterparts using a combination of the FEMA P-695 and FEMA P-58 methodologies. Additionally, an innovative modeling assumption is investigated, where moment frames are evaluated with and without the lateral influence of the gravity system. Each system has a unique purpose from the perspective of performance-based earthquake engineering, and analyses focus on the all intensity levels of interest. The comparisons are presented in terms consequences, including repair costs, repair duration, number of casualties, and probability of receiving an unsafe placard, which are more meaningful to owners and other decision makers than traditional structural response parameters. The results show that these systems can significantly reduce the consequences, particularly the average repair costs, at the important intensity levels. The second study focuses on the assumptions made during proposed updates to provisions for nonlinear response history analyses. The first assumption investigated is the modeling of the gravity system's lateral influence, which can have significant effect on the system behavior and should be modeled if a more accurate representation of the behavior is needed. The influence of residual drifts on the proximity to collapse is determined, and this work concludes that a residual drift check is unnecessary if the only limit state of interest is collapse prevention. This study also finds that spectrally matched ground motions should cautiously be used for near-field structures. The effects of nonlinear accidental torsion are also examined in detail and are determined to have a significant effect on the inelastic behavior of the analyzed structure. The final investigation in this study shows that even if a structure is designed per ASCE 7, it may not have the assumed probability of collapse under the maximum considered earthquake when analyzed using FEMA P-695. / Ph. D.

This thesis is divided into two topics: the development of a procedure for wind serviceability design of steel buildings and the development of a simple linear response history analysis for building codes. In the United States the building codes are generally silent on the issue of serviceability. This has led to a wide variation in design practices related to service level wind loads. Chapter 2 of this thesis contains a literature review which discusses pertinent aspects of wind drift serviceability, including selecting the mean recurrence interval (MRI), mathematical modeling of the structure, and establishment of rational deformation limits. Chapter 3 contains a journal article submitted to Engineering Journal which describes the recommended procedure for damage based wind serviceability design of steel structures. The procedure uses a broad range of MRIs, bases damage measurement on shear strains, includes all sources of deformation in the model, and bases deformation limits on fragility curves. Chapter 4 of this thesis contains a literature review which examines issues related to performing linear response history analysis. Chapter 5 contains a conference paper submitted to the Tenth U.S. National Conference on Earthquake Engineering which serves as a position paper promoting the inclusion of a linear response history analysis procedure in future editions of the NEHRP Recommended Seismic Provisions and ASCE 7. The procedure address the following issues: selection and scaling of ground motions, the use of spectral matched ground motions, design for dependent actions, and the scaling of responses with the response modification coefficient (R) and the deflection amplification factor (Cd). / Master of Science