Stairs serve as an essential nonstructural system within buildings, providing a safe means of egress as well as much needed access for emergency responders following an earthquake. Unfortunately, the state of knowledge regarding the seismic behavior of these critical systems is limited, despite the fact that past earthquakes repeatedly reveal that stair systems are highly vulnerable to damage even in low- or moderate-intensity earthquakes. As a result, disruptions to building functionality, delayed rescue operations, and life safety hazards ensue.

To this end, this dissertation presents a first-of-its-kind experimental investigation of the seismic behavior of a prefabricated steel stair system incorporated in a full-scale five-story building shake table test program. These system-level tests allowed investigation of the seismic behavior of these systems under realistic installation and dynamic loading conditions. In this work, the modal characteristics of the stair system identified using white noise base excitation test data as well as the physical observations of the stair system during earthquake tests of increasing intensities are presented. Analysis of the earthquake response of the stair system particularly focuses on associating their behavior with the seismic demands of the test building and the associated implications on seismic design. These shake table tests highlight the seismic vulnerability of modern designed stair systems and in particular the importance of improving the deformability of flight-to-building connections.

The second part of this work involves a comprehensive computational study to capture at first the salient seismic response characteristics of prefabricated steel stairs in isolated configurations and subsequently the key response characteristics of building-stair systems. Detailed three-dimensional finite element models of a pair of prefabricated steel stairs are developed and their efficacy evaluated through extensive comparison with experimental data. The validated modeling approach is then used in a parametric assessment of the seismic behavior of stair systems using a broader range of design variables commonly found in practice. Subsequently, a system-level numerical study is conducted to investigate the interaction between buildings and stair systems and the associated impacts on building response characteristics as well as estimated stair loss using a probabilistic seismic analysis framework. Simulation results indicate that although the presence of stairs does not significantly modify the seismic response of buildings, enhancing the stair deformability can effectively mitigate the severity of seismic damage and loss of these critical nonstructural systems.

Cold-formed steel (CFS) framing offers many benefits to buildings in seismically active regions. Amongst the most notable CFS attributes include its low fabrication and maintenance costs, noncombustible and corrosion resistant nature, high durability and ductility. These benefits have made CFS framing a popular choice for construction of low-rise and mid-rise structures. From a seismic performance perspective, the light weight and ductility offered by a CFS-framed structure aligns with system resiliency needs in moderate to high seismic zones. Although experimental data exists documenting the performance of isolated CFS-framed shear walls, the structural lateral force resisting systems (LFRS) in CFS-framed buildings are constructed and integrally attached to non-designated systems, such as gravity walls as well as various nonstructural components. The contribution of the non-designated systems and the nonstructural components towards the response of wall-lines within the building system under high intensity earthquake shaking is not well understood. Moreover, experimental data to support code guidelines in current North American standards for design of CFS-framed shear walls, which meet the seismic demands for mid-rise buildings (>6 stories) are lacking. Indeed, the paucity of full-scale test data documenting the behavior of wall-line systems detailed for mid-rise buildings has been a barrier to bringing the potential benefits of CFS framing to the community.

To address these limitations, a two-phased experimental program was undertaken in this dissertation to advance the understanding of CFS-framed steel sheet sheathed shear walls placed in-line with gravity walls. Referred to herein as “wall-lines”, these test specimens were detailed to support the lateral load demands anticipated of mid-rise buildings in high seismic zones. In the first phase, wall-line assemblies were tested at full-scale on a shake table, first under a sequence of increasing amplitude (in-plane) earthquake input motions, and subsequently under slow monotonic pull conditions (for select specimens). In the second phase, wall-line assemblies were tested under quasi-static reverse cyclic displacement-controlled loading using a simulated floor-load imposed via hydraulic actuators. Steel sheet sheathed shear walls offered energy dissipation primarily through structural member-to-sheathing connections and yielding of the steel sheet. All specimens demonstrated a tension field that spread across the entirety of the steel sheet at failure. The impact of different test variables governing the structural and nonstructural detailing on the seismic performance of the CFS-framed wall-line specimens is quantified by careful systematic comparison between different configurations. Wall-line assemblies with interior and exterior finish demonstrated substantially increased strength and stiffness without any decrease in drift capacity or change in failure mode. Specimens with hold-downs offered a larger lateral strength compared to specimens with tension tie-rods. However, hold-downs reached their capacity at higher drift demands whereas tension tie-rods remained linear elastic, even though both wall-lines with the different tie-down systems were designed for same overstrength force levels.

The second part of this work involved a comprehensive numerical modeling effort, using prior experimental findings, both of the wall-line experiments discussed herein as well as a previous mid-rise six-story building specimen tested at full-scale using a suite of earthquake excitations. The developed finite element model takes into consideration the major assemblies, beyond just the isolated shear walls, which influence the dynamic response of the system, such as the strength and stiffness contribution from gravity walls as well as nonstructural components such as exterior and interior finishes installed over the shear wall and gravity wall segments. In this phase, as is common in west coast practice in the United States, a continuous tie-rod system is also modeled to capture the cumulative floor displacements caused by the axial elongation in the steel rods. The effect of built-up stud packs on strength, stiffness and drift parameters of a shear wall is also considered in the nonlinear hysteretic material model of shear walls. Very good agreement between numerical predictions and available experimental seismic response data of the six-story test building demonstrates that the proposed numerical model scheme can be employed to predict the seismic response of mid-rise CFS-framed buildings. Development of such a numerical model is an essential tool for enabling performance-based seismic design of cold-formed steel structures in this rapidly growing industry.

Architectural precast concrete (APC) cladding is a type of building façade composed by concrete panels separated from each other by joints and attached to the building structure with steel connections. Seismic damage to this component has been observed in past earthquakes, it is costly and time consuming to repair, and, importantly, it can be life threatening. APC cladding is unique among nonstructural components, since its heavy concrete panels span from floor to floor. As a result, this system is uniquely sensitive to both interstory drifts and floor accelerations. However, only few experimental or analytical programs have specifically focused on this type of façade. Since knowledge regarding the seismic behavior of APC façades is limited, design code prescriptions are relatively qualitative and do not accurately consider the many features of the system.

The first part of this dissertation aims to provide guidance to practitioners to improve the drift-compatible design of APC cladding. Results are based on three experiments: one system level experiment in which sixteen panels were installed on a full-scale building and two component tests on tieback connections. The combination of the results from these tests provided information on the how to improve the detailing of tieback connections to create the optimal compromise between good seismic performance and constructability. In addition, this part of the dissertation includes a one-of-a-kind study of a new type of corner system allowing for smaller corner joints thanks to a ductile fuse.

The second part of this dissertation presents an analysis of the accelerations developed in the APC cladding during seismic motions. This analysis is based on numerical models validated using data from the system level experiment. Initially, the dynamic characteristics of the APC cladding are analyzed using models of the panels and connections. Subsequently, the APC cladding is included in a building model, with the goal of determining the amplification of accelerations in the panels during service and design level motions. The study revealed issues in the way the panels are currently designed to resist seismic forces.

Reinforced concrete shear walls are commonly used to provide lateral strength and stiffness to concrete buildings in seismic regions. Typically installed in the wall face, mechanical anchors are responsible for connecting various nonstructural systems to the main structure. During an earthquake, anchors in reinforced concrete structural elements need to retain their strength and stiffness, despite the inevitable presence of cracks and damage in the concrete, developed as a consequence of the lateral cyclic loading. Anticipating damage to the concrete, which will naturally influence anchor response, current guidelines to qualify anchors for seismic applications require adequate performance in cracked concrete to assure minimal anchor load loss. However, these guidelines are based on anchor performance in pure flexural cracks, as this is the typical damage condition occurring in reinforced concrete frame elements, which has been studied for decades. The response of anchors to a mix of flexure and shear cracks, i.e., the complex situation realized in shear-flexure structural components such as shear walls, however, has largely not been studied.

To address the paucity of data regarding anchor behavior in cracked concrete, the behavior of anchors installed horizontally in three full-scale reinforced concrete shear walls with different aspect ratios (wall height/length) is studied in this dissertation. Notably, two types of post-installed anchors were investigated in these tests, namely: i) expansion anchors and ii) bonded anchors. One slender and two identical low-aspect ratio walls were designed according to current U.S. design codes. Simulated seismic loading was imposed at the top of the wall using an equivalent cyclic displacement history, while uniform compression was applied on the slender and one of the two identical low-aspect ratio shear walls. One of the low aspect ratio walls was tested without axial compression to investigate its effect on the anchor response. Anchors were continuously loaded to their design tension while the walls were cycled. The slender full-scale wall failed in a predominantly flexural mode, precipitated by buckling and fracture of the boundary reinforcement. The two identical full-scale low-aspect ratio walls failed in a mixed flexure-shear response, with severe web concrete crushing and buckling and rupture of the boundary reinforcement. Anchor axial load and displacement data, continually measured during the wall cyclic tests, confirmed the sensitivity of the performance of anchors amidst the presence of a variety of cracked concrete conditions, especially in walls prone to develop large shear stress and shear induced damage when subjected to lateral cyclic loads. Following the wall cyclic tests, tension failure tests performed on the anchors indicated that their residual tension load capacity was significantly compromised by concrete damage. Such damage was concentrated in specific wall regions, such as the boundary elements and the plastic hinge region in slender walls, or along the diagonal struts, the boundary elements and near the base of low-aspect ratio walls. Of the two types of anchors tested, expansion anchors observed the most significant load loss (and consequentially axial displacement) in the presence of both the wall cyclic loading and the residual tests on the anchors themselves.

Following the experimental program, a multiple vertical line finite element model was used to predict the response of each of the tested full-scale shear walls. Numerical analyses cross-comparison with test results demonstrated a high level of accuracy of the selected modeling approach. As such, an expanded parametric study was conducted to understand the extent of severe concrete strains on the crack distribution and width, using a smeared crack approach. Wall models designed for the parametric study were intended to explore different geometry, reinforcement and axial compression to study the damage distribution within the wall elevation. Crack pattern distribution plots developed using the parametric study results were used to identify regions where anchors would be vulnerable to load loss upon achievement of service, design and severe seismic damage. Ultimately, the findings from this dissertation shed light on the vulnerability of anchors placed in reinforced concrete shear walls, where damage in the form of mixed mode cracking and spalling can be expected. Future design guidelines would benefit from precluding crack sensitive anchors in the most highly damaged regions of these essential lateral force resisting components of the structural system.

Characterizing the performance of retrofitted and unretrofitted single-family wood frame houses has become increasingly important in California due to the high seismicity of the state and the often-poor seismic resiliency of some portions of the housing stock. From field observations following earthquakes, inadequate lateral bracing of cripple walls and sill bolting are primary reasons for significant failures of residential homes, even in the event of moderate intensity earthquakes. Cripple walls are the short-elevated wall segments supporting the first-floor framing and upper stories of a dwelling. These important components were common in construction practices in older, particularly pre-1970s homes, as they provided a crawl space for ventilation and placement of utilities. Often, they lack adequate bracing and load transfer to carry seismic inertial loads generated during an earthquake from the superstructure to the foundation. While methods to retrofit weak cripple walls and improve sill anchorage have been developed, the improvement in performance with retrofit has not been adequately quantified. In addition, little knowledge is available to quantify the performance of houses with unretrofitted cripple walls and sill anchorages. To address the paucity of experimental data to characterize the seismic performance of cripple walls and sill anchorage, a series of 28 cripple wall-only assemblies were tested. Details representative of era-specific construction, specifically the most vulnerable pre-1970s construction, are of predominant focus in the present effort. Parameters examined include cripple wall height, exterior finish materials, retrofit condition, boundary conditions, anchorage type, gravity load, and loading protocol. Of the 28 assemblies, all but one was tested using a newly developed quasi-static reversed cyclically displacement-controlled protocol intended to simulate seismic demands from the upper story of a dwelling. The remaining assembly was monotonically loaded. Each specimen was nominally 12 feet in length and either 2 feet or 6 feet in height. Exterior finish materials were either wet (stucco) or dry (non-stucco) application types. The experimental program was designed to elicit the effect of a single parameter on the seismic behavior of the cripple wall by changing one parameter between each specimen and controlling the remaining. For each specimen, key measurements pertaining to the hysteretic response as well as documentation of the damage evolution were collected. Results from these experiments provided an experimental basis to validate a numerical modeling tool, and ultimately to develop loss models, which are intended to quantify the reduction of loss achieved by applying state-of-practice retrofit methods as identified in modern retrofit design guidance (FEMA P-1100, 2019). Findings from the experimental program revealed that the implementation of the FEMA P-1100 prescriptive retrofit dramatically improved the strength, stiffness, and energy dissipation of cripple walls, and in many cases, it also increased the drift capacity. In addition, it was found that horizontal siding was the weakest finish material tested regardless of the cripple wall height, while diagonal sheathing was found to be the strongest finish material. Following the experimental program, finite element connection-level numerical models were developed to predict the response of dry finished cripple walls tested in the experimental program. Subsequently, phenomenological numerical models were developed to capture the global response of wet finished cripple walls. A cross-comparison of the numerical models demonstrates a high level of accuracy of the connection-level modeling approach, while the phenomenological models did well in capturing the pre-peak response of wet finished cripple walls but lost accuracy when tasked with capturing well beyond post-peak response, due to the disengagement of the stucco finish. The validated connection-level models were used to conduct a parametric study on horizontal siding finished cripple walls in an effort to investigate equivalent, simple detailing methods as an alternative to modern retrofit guidelines, which prescribe installation of full or partial sheathing within the interior space. Detailing alternatives investigated included, siding board size, vertical nail spacing, cut-in diagonal blocking, and diagonal strap bracing. Parametric study results indicate that a strong linear correlation between the vertical nail pair spacing and lateral strength and hysteretic energy dissipation of horizontal siding finished cripple walls is realized. Furthermore, it was demonstrated that the implementation of diagonal cut-in blocking elements provided the largest increases in strength and stiffness for shorter, low aspect ratio 2-ft-tall cripple walls, while diagonal strap bracing provided significant increases for taller, high aspect ratio 6-ft-tall cripple walls. Ultimately, the findings of this dissertation fill prominent gaps in the testing database of cripple walls and sill anchorage, including both the hysteretic response as well as the damage evolution. Moreover, experimental findings demonstrate the substantial benefits of implementing modern retrofit design guidelines, while numerical simulations offer promising alternative details, each geared towards improving the seismic performance of cripple walls.

Systems of unattached, or freestanding, structures are highly vulnerable to sliding and/or overturning when subject to seismic excitation. This class of structures includes many rigid and heavy systems such as classical multi-drum columns, statue-pedestal systems, and various building contents. Damage to these structures can result in loss of irreplaceable heritage, limited functionality of critical facilities, and even loss of life. As a result, accurate predictions of their response are essential. However, traditional analytical methods cannot be feasibly extended to account for the multiple modes engaged during the excitation, the three dimensional nature of the body, and (if present) additional blocks in a system. All of which may be necessary to model realistic structures.

In an effort to develop robust predictive tools for freestanding structural systems, three research objectives are addressed in this dissertation. The first is to understand the general geometric and mass characteristics of freestanding structural systems. This was accomplished through a field survey targeting the geometrically complex statue-pedestal system. The geometry of these structures was captured using light detection and ranging scanning and computer vision techniques. The resulting range of geometry guided the design of two phases of shake table testing addressing the second objective, which is to generate a comprehensive database of the experimental response of freestanding structural systems. In these tests, a tower structure, which was adaptable to a variety of geometries and mass configurations, was subject to seismic excitation in unanchored single-body and dual-body arrangements. Test results emphasize the multi-modal and three-dimensional nature of the seismic response of these systems.

The final objective is to develop and validate a numerical model for predicting the seismic response of freestanding structures. This model was developed utilizing the contact-impact capabilities within the multi-physics solver, LS-DYNA. An analytical extension was developed in conjunction with the numerical model accounting for warped interfaces, an aspect that was revealed to have a pronounced effect on the response. The numerical model was validated against the experimental results, with particular attention given to capturing the multi-modal and multi-body behavior. Numerical simulations indicate that this model can be used to predict the dynamic response of freestanding structures with high fidelity.

During an earthquake, reinforced concrete members in a building will suffer cracking that oscillates as the building dynamically deforms. Equipment that services the building, such as mechanical and electrical items, are anchored to these components, and therefore will be subjected to this dynamic environment. Despite understanding this practical loading situation, as well as recognizing that anchor load capacity is significantly reduced when an anchor is embedded in cracked concrete, there remains a gap in knowledge regarding the effect of anchorage behavior on nonstructural component response. In particular, the effect of dynamic cyclic cracking coupled with inertia-generated tension load cycling on the anchor and component response has not been studied to date.

A new methodology involving experimental equipment and simulation tools is developed for investigating the seismic behavior of anchored nonstructural components and systems that accounts for the effects of simultaneous anchor tension load cycling and crack cycling on anchor behavior and anchored component response. To support the experimental ingredient of this work, a Cyclic Cracked Inertial Loading Rig (CCILR), Weighted Anchor Loading Laboratory Equipment (WALLE) system, and cracked concrete slabs, are designed and fabricated. Mounting the CCILR and WALLE onto a shake table results in a system that is able to simulate a concrete beam or slab from a building supporting an anchored nonstructural component. System-level shake table tests are conducted on floor mounted model nonstructural components anchored in cyclic cracks using epoxy, expansion, drop-in and undercut anchors to study the effect of a range of anchor types.

A nonlinear, lumped hysteresis anchor model is implemented and used to simulate anchor load-displacement response for tension load cycling dominant applications. The anchor model is calibrated against single anchor tests and subsequently extended for use in a system model of the anchored nonstructural components for predicting maximum system response.

It was determined that the load-displacement behavior of the anchorage, in particular, the ultimate displacement capacity of the anchor, plays an important role in the seismic response of tension load cycling dominated floor mounted nonstructural components. The experimental results also support the current code design philosophy for anchors, which specifies that either the anchor or the attachment should be ductile, or the anchor should be designed for a multiple of the expected load demand.

Baseplate connections, typically consisting of a steel baseplate welded to the terminus of a structural member, concrete anchors, and grout, are common features in buildings and nonbuilding structures. Incorporation of yielding anchors in these critical connections has received increased attention due to good performance observed during recent earthquakes. Such a strategy is attractive as a design approach, as the connections can provide a fuse at the location of seismic input, add to overall system ductility, and may elongate the system period. However, neither a systematic study of connection details that permit robust performance with yielding anchors, nor an investigation of the potential benefits of using such connections to reduce system-level seismic demands has been performed to date.

To these ends, a suite of baseplate component and system-level tests, as well as complimentary high-fidelity numerical simulations, was undertaken to systematically investigate detailing options to help advance the innovative concept of yielding-anchor base connections. First, a program of pseudo-static testing of a typical exposed steel column baseplate connection was executed to understand the details that may influence connection performance, including the anchor type, constituent materials, anchor stretch length, and connection setting arrangement. The impacts of these details on connection strength and rotation capacity are quantified. A novel categorization scheme of connection limit states was developed to track the evolution of damage in the connection. A 3-D, fiber-section numerical model was developed and verified against the results of this test program and several others available in the literature, providing a robust, generalized predictive method for the response of connections with parameters outside the current test program.

Subsequently, dynamic shake table testing of a miniature steel building was undertaken to probe the beneficial system-level effects that ductile, uplifting baseplate connections may have versus traditional "strong anchor" connections and superstructure fuses. These benefits were readily observed in testing and found in numerical analyses including reductions in total base shear of up to 50% and the virtual elimination of residual drift when compared to traditional systems. These results, combined with the ease of post-earthquake repair, demonstrate the usefulness of the ductile-anchor approach in improving overall seismic performance.

During earthquakes, nonstructural components and other objects of sizeable mass attached to building structures may be subjected to significant levels of seismic excitation. These systems require engineered anchorage systems to resist imposed demands, with the earliest attempts to produce qualitative and quantitative metrics for this process taking place in the early 1990s. Over the next two and a half decades, the provisions the design engineer must follow for determining a suitable anchorage system have rapidly expanded, and while some topics have been thoroughly researched and documented, others have not. One such term, the overstrength factor Ω0 used to modify code demands for ductile versus non-ductile anchorage

into concrete for tension-dominated systems, has suffered from particularly sparse academic and scientific background. The first portion of this dissertation establishes a scientific framework for evaluating existing code values of Ω0 by means of two full-scale testing programs on anchorage systems using a shaking table. Both real earthquake and broadband earthquake motions are used in the testing sequences, and four different major anchorage force-displacement responses are considered: brittle linear-elastic behavior with large initial stiffness, highly plastic ductile behavior with comparable initial stiffness to the brittle anchor, soft elastic behavior with large displacement capacity, and a pull-through anchor with non-material-based plastic response characteristics.

Results from these different anchor types are compared and benchmarked against expected code performance standards.

The second portion of this dissertation presents a highly efficient, customized numerical analysis tool that was developed for simulating the seismic response of seismically-driven oscillators with translational and rotational mass degrees of freedom. This program is validated against the structural testing results and existing finite element programs, and offers run times three orders of magnitude faster than standard analysis methods. Detailed parameter studies are then performed looking at both upright and hanging components, targeting specifically the appropriate values of Ω0 which result in intended system performance.

The structural testing and analytical results are then compiled into recommendations for existing code guidelines related to Ω0. Discussion is provided regarding existing ductility provisions for anchorage into concrete, specifically with respect to the expected benefits versus the real and measured benefits of ductile anchor response.