This research examines the seismic energy dissipation potential of steel structures by focusing on new types of specially engineered cladding-to-frame connections. Traditional connection details consist of rigid restraints of cladding panels, resulting in seismic design that only considers the panel self-weight with connection design left up to the precast fabricators and typical details. It is postulated that by considering these elements to actively participate in building response a more efficient and resilient structure could be designed which accurately captures the effects of non-structural cladding elements on building behavior. In this preliminary research, two mechanisms to dissipate seismic energy using engineered cladding systems are presented. Analysis results on a reference steel building indicate that demands on structural elements may be significantly reduced.

Structural fuses are ductile elements of a structure that are designed to yield and protect the surrounding members from damage, and then be replaceable after a major seismic event. A promising type of seismic structural fuse consists of a steel plate with engineered cutouts leaving a configuration of shear-acting links remaining. There have been several studies on various cutout patterns for shear-acting structural fuses including butterfly-shaped links, hourglass-shaped links, elliptical holes, and link shapes obtained from topology optimization. In most cases, the links are designed to undergo flexural yielding as it is believed to exhibit more ductility than other limit states. However, computational and experimental studies on the shear yielding limit state are limited. Additionally, the transition between shear dominated and flexural dominated limit states has not been previously investigated. Hence, a systematic and thorough study on the different limit states of these structural fuse shapes is necessary to provide better understanding on the structural behavior of each shape and accurately predict the controlling limit state during a seismic event. In addition, a previous study recognized that delaying shear buckling while promoting yielding is a way to improve the seismic performance of shear-acting structural fuses. However, the resulting new topologies were not experimentally validated. Furthermore, the computational study revealed that large localized plastic strain is one major challenge for these optimized configurations which might lead to potential for fracture. With the goals of filling the gaps in previous research, a computational and experimental program was conducted to (1) understand seismic performance of five structural fuse shapes, (2) develop a new ductile structural fuse shape with both buckling and fracture resistance, and (3) create design guidelines for practical design. This study consisted of the following parts (a) Creation of a new structural fuse shape called the Tied Butterfly Shape, (b) An experimental program with 20 specimens categorized into five groups including the shape created using topology optimization to resist buckling, the new shape called Tied Butterfly Shape, the butterfly shape, the hourglass shape and the elliptical holes, (c) Use of finite element models to better understand and interpret test data, (d) Two computational parametric studies conducted to investigate the effect of geometrical parameters on structural behavior of the optimized shape and Tied Butterfly Shape, (e) Development of design recommendations for each structural fuse shape. The computational and experimental results reported in this dissertation demonstrate that these structural fuse shapes are capable of improving the seismic performance of buildings. The presented design recommendations allow designers and researchers to continue exploring these structural fuse shapes. / Doctor of Philosophy / Structural fuses are ductile elements of a structure that are designed to yield and protect the surrounding members from damage, and then be replaceable after a major seismic event. Several studies on various cutout patterns for shear-acting structural fuses including butterfly-shaped links, hourglass-shaped links, elliptical holes, and link shapes obtained from topology optimization, reported that they offer several advantages for use in structural systems. Nevertheless, systematic studies on key limit states of these structural fuse shapes are limited. In addition, some analytical results have not been validated by experiments. The research work provides a comprehensive study on these structural fuse shapes. First, generalized design equations are derived using plastic mechanism analysis and key limit states of these structural fuse shapes are investigated. Second, an experimental program was conducted to further understand the cyclic behavior of these shapes associated with each limit state (i.e flexural yielding, shear yielding, lateral torsional buckling, transition between the flexural and shear yielding limit states). Then, nonlinear finite element modeling was implemented to validate against experimental results and provide better understanding of the behavior of the specimens which is not obvious during the test. Lastly, design recommendations are developed for each structural fuse shape.

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.

Shear-acting structural fuses are steel plates with cutouts subjected to in-plane lateral displacements during extreme loading events such as earthquakes, that dissipate energy through localized shear or flexural yielding mechanisms. Although previous studies have reported that fuses with specific geometry can develop a stable hysteretic behavior, their small thickness makes them prone to buckling, reducing strength and energy dissipation capacity. In this work, topology optimization using genetic algorithms is performed to find optimized shapes for structural fuses with a square domain and constant thickness. The objective function uses the fuse's shear buckling load VB obtained from a 3D linear buckling analysis, and shear yield load VY obtained from a material nonlinear, but geometrically linear 2D plane-stress analysis. The two analyses are shown to be computationally efficient and viable for use in the optimization routine. The variations VY/VB=0.1,0.2,0.3 are investigated considering a target volume equal to 30%, 40% and 50% the fuse's original volume. A new set of optimized topologies are obtained, interpreted into smooth shapes, and evaluated using finite elements analyses with models subjected to monotonic and cyclic displacements histories. It was found that the drift angle when out-of-plane buckling occurs can be controlled using the VY/VB ratio, with optimized topologies buckling at drift angles (when subjected to a cyclic displacement protocol) as large as 9% as compared to 6% for previously studied fuses. / Master of Science / Shear-acting structural fuses are steel plates with cutouts that dissipate energy during extreme loading events such as earthquakes. These structural fuses have a fixed edge and an opposing edge subjected to in-plane lateral displacements. Although previous studies have reported that fuses with specific geometry have a good cyclic performance, their small thickness makes them prone to bend or buckle, reducing strength and energy dissipation capacity. Considering a structural fuse with a square domain and constant thickness, a mathematical method called topology optimization is implemented to optimize the distribution of material with the goal of controlling the amount of yielding in the structural fuse before it buckles. The optimization routine uses the fuse’s shear buckling capacity (VB) and shear yield strength (VY ) obtained from relative simple and computationally inexpensive procedures that are also valid to characterize the potential for buckling in a structural fuse. The variations VY /VB = 0.1, 0.2, 0.3 are investigated considering a target volume equal to 30%, 40% and 50% the fuse’s original volume. A set of optimized topologies are interpreted into smooth shapes and evaluated using finite elements analyses. It was found that the drift angle when out-of-plane buckling occurs can be controlled by using the VY /VB ratio, with optimized topologies buckling at drift angles (when subjected to a cyclic displacement protocol) as large as 9% as compared to 6% for previously studied fuses.

The objective of this research is to create a computationally efficient seismic analysis framework for cold-formed steel (CFS) framed-buildings supported by hysteretic nonlinear models for CFS members and screw-fastened connections. Design of CFS structures subjected to lateral seismic forces traditionally relies on the strength of subassemblies subjected to lateral loading of systems, such as strapped/sheathed shear walls and diaphragms, to provide adequate protection against collapse. Enabling performance-based seismic design of CFS buildings requires computationally efficient and accurate modeling tools that predict the nonlinear cyclic behavior of CFS buildings, the individual CFS components and connections. Such models should capture the energy dissipation and damage due to buckling and cross-sectional deformations in thin-walled CFS components subjected to cyclic loads such as those induced by earthquakes. Likewise, models for screw-fastened CFS connections should capture the energy dissipation and damage due to tilting, bearing, or screw shear when subjected to cyclic loading. In this dissertation, an analysis framework for CFS structures that captures the nonlinear cyclic behavior of critical components including axial members, flexural members, and screw fastened connections is presented. A modeling approach to simulate thin-walled behavior in CFS members is introduced where parameters were developed using results from an experimental program that investigated the cyclic behavior and energy dissipation in CFS axial members and flexural members. Energy dissipation and cyclic behavior of CFS members were characterized for members experiencing global, distortional and local buckling. Cyclic behavior and energy dissipation in thin steel plates and members was further investigated through finite element analysis in ABAQUS to provide a strategy for modeling steel columns cyclic behavior including local buckling. Model parameters were developed as generalized functions of the hysteretic energy dissipated and slenderness. The capabilities of the analysis framework are demonstrated through simulations of CFS wood sheathed shear wall cyclic responses validated with experimental results from full scale shear wall tests. / Ph. D.