The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA). Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures. The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.

The research was focused on the three major structural elements of a typical cold-formed steel building - shear wall, floor joist, and column. Part 1 of the thesis explored wider options in the steel sheet sheathing for shear walls. An experimental research was conducted on 0.030 in and 0.033 in. (2:1 and 4:1 aspect ratios) and 0.027 in. (2:1 aspect ratio) steel sheet shear walls and the results provided nominal shear strengths for the American Iron and Steel Institute Lateral Design Standard. Part 2 of this thesis optimized the web hole profile for a new generation C-joist, and the web crippling strength was analyzed by finite element analysis. The results indicated an average 43% increase of web crippling strength for the new C-joist compared to the normal C-joist without web hole. To improve the structural efficiency of a cold-formed steel column, a new generation sigma (NGS) shaped column section was developed in Part 3 of this thesis. The geometry of NGS was optimized by the elastic and inelastic analysis using finite strip and finite element analysis. The results showed an average increment in axial compression strength for a single NGS section over a C-section was 117% for a 2 ft. long section and 135% for an 8 ft. long section; and for a double NGS section over a C-section was 75% for a 2 ft. long section and 103% for an 8 ft. long section.

<p>Twelve large-scale reinforced concrete (RC) specimens were tested at Purdue University’s Bowen Laboratory to evaluate the deformability of structural walls with longitudinal lap splices at their bases. Eight specimens were tested under four-point bending and four specimens were tested as cantilevers under constant axial force and cyclic reversals of lateral displacement. All specimens failed abruptly by disintegration of the lap splice, irrespective of what loading method was used or what splice details were chosen. Previous work on lap splices has focused mainly on splice strength. But, in consideration of demands requiring structural toughness (e.g. blast, earthquake, differential settlement), deformability is arguably more important than strength. </p> <p>Approximations of wall drift-strain relationships are presented in combination with estimates of splice strength and deformability to provide lower-bound drift capacity estimates for RC walls with lap splices at their bases. Deformations in slender structural walls (with aspect ratios larger than 3) are controlled by flexure. Shear deformations must be considered for walls with smaller aspect ratios. For slender walls with lap splices comparable to those tested, the observations collected suggest that drift capacities can be as low as 0.5%. That is: splices with minimum concrete cover, minimum transverse reinforcement (0.25% transverse reinforcement ratio) terminating in hooks, and lap splice lengths selected to reach yielding in the spliced bars (approximately 60 bar diameters for splices of Grade-60 reinforcement) can fail as yield is reached or soon after. For splices of the same length, doubling the amount of hooked transverse reinforcement increases deformation capacity by nearly 50%. By maintaining the same transverse reinforcement ratio but confining splices with closed hoops (instead of hooks), deformation capacity nearly doubles. Increasing splice length increases the expected splice strength but also increases the strain required to reach the same drift ratio. </p> <p>Evidence from this and similar experimental programs suggests that lap splices with minimum cover and confined only by minimum transverse reinforcement terminating in hooks should not be used in critical sections of structural walls when toughness is required. To prevent abrupt failure during events that demand structural toughness, it is recommended that lap splices be shifted away from locations where yielding in structural walls is expected.</p>

<p>Coupled Composite Plate Shear Walls / Concrete Filled (CC-PSW/CFs) are being employed as a seismic lateral force resisting system for the design and construction of mid- to high-rise buildings around the world. The coupled system consists of two or more Composite Plate Shear Walls – Concrete Filled (C-PSW/CFs) connected to each other using composite coupling beams located at the story heights. The CC-PSW/CF system can provide higher overturning moment capacity, lateral stiffness, and ductility than uncoupled walls. Concrete-filled steel box sections are typically used for the composite coupling beams, which are designed to be flexure critical members. When the CC-PSW/CF system is subjected to lateral seismic forces, plastic hinge formation and inelastic deformations (energy dissipation) occur near the ends of most of coupling beams along the structure's height, followed by flexural hinging of the C-PSW/CFs, typically at the base. </p> <p>This work presents the details and design of four composite coupling beam-to-C-PSW/CF connection configurations. Six connection specimens, representing the four connection configurations, with beam clear span-to-section depth, <em>Lb</em>/<em>d</em>, ratios of 3.5 and 5.1, were designed, fabricated, and tested. The experimental program focused on the force-displacement and moment-rotation responses, behavioral observations, limit states, and flexural capacities of the tested specimens. Major limit states and events included yielding of the steel plates comprising the coupling beam, followed by local inelastic buckling, fracture initiation in the base metal (near the weld toes) in the connection region, and fracture propagation through the beam flange and web plates leading to loss of flexural strength and failure. All specimens developed and exceeded the capacity and chord rotation requirements, in accordance with ANSI/AISC 341-22 guidelines.</p> <p>Detailed nonlinear 3D finite element models of the tested specimens were developed and verified using experimental results. The 3D finite element models accurately simulate the stiffness, flexural capacities, and monotonic responses of tested specimens. Nonlinear fiber-based models of the tested coupling beam-to-C-PSW/CF specimens were developed and verified using experimental results. The nonlinear fiber-based models can accurately simulate the stiffness, flexural capacities, and cyclic responses of tested specimens. The benchmarked fiber models were used to estimate the moment-rotation response of full-scale archetype connections. </p>

Analytical models of wood-frame shear walls and diaphragms for use in monotonic, quasi-static (cyclic), and dynamic analyses are developed in this thesis. A new analytical model is developed to accurately represent connections between sheathing panels and wood framing members (sheathing-to-framing connections) in structural analysis computer programs. This new model represents sheathing–to–framing connections using an oriented pair of nonlinear springs. Unlike previous models, the new analytical model for sheathing-to-framing connections is suitable for both monotonic, cyclic, or dynamic analyses. Moreover, the new model does not need to be scaled or adjusted. The new analytical model may be implemented in a general purpose finite element program, such as ABAQUS, or in a specialized structural analysis program, such as CASHEW. The analytical responses of several shear walls and diaphragms employing this new model are validated against measured data from experimental testing. A less complex analytical model of shear walls and diaphragms, QUICK, is developed for routine use and for dynamic analysis. QUICK utilizes an equivalent single degree of freedom system that has been determined using either calibrated parameters from experimental or analytical data, or estimated sheathing-to-framing connection data. Application of the new analytical models is illustrated in two applications. In the first application, the advantages of diaphragms using glass fiber reinforced polymer (GFRP) panels in conjunction with plywood panels as sheathing (hybrid diaphragms) are presented. In the second application, the response of shear walls with improperly driven (overdriven)nails is determined along with a method to estimate strength reduction due to both the depth and the percentage of total nails overdriven.

A key consideration in seismic design of buildings is to ensure that the lateral load resisting system has an appropriate combination of strength, stiffness and energy dissipation capacity. Hybrid coupled wall systems, in which steel beams are used to couple two or more reinforced concrete shear walls in series, can be designed to have these attributes and therefore have the potential to deliver good performance under severe seismic loading. This research presents an investigation of the seismic behavior of this type of structural system. System response of 12- and 18-story high prototypes is studied using transient finite element analyses that accounts for the most important aspects of material nonlinear behavior including concrete cracking, tension stiffening, and compressive behavior for both confined and unconfined concrete as well as steel yielding. The developed finite element models are calibrated using more detailed models developed in previous research and are validated through numerous comparisons with test results of reinforced concrete walls and wall-beam subassemblages. Suites of transient inelastic analyses are conducted to investigate pertinent parameters including hazard level, earthquake record scaling, dynamic base shear magnification, interstory drift, shear distortion, coupling beam plastic rotation, and wall rotation. Different performance measures are proposed to judge and compare the behavior of the various systems. The analyses show that, in general, hybrid coupled walls are particularly well suited for use in regions of high seismic risk. The results of the dynamic analyses are used to judge the validity of and to refine a previously proposed design method based on the capacity design concept and the assumption of behavior dominated by the first vibration mode. The adequacy of design based on the pushover analysis procedure as promoted in FEMA-356 (2000) is also investigated using the dynamic analysis results. Substantial discrepancies between both methods are observed, especially in the case of the 18-story system. A critical assessment of dynamic base shear magnification is also conducted, and a new method for estimating its effects is suggested. The method is based on a modal combination procedure that accounts for presence of a plastic hinge at the wall base. Finally, the validity of limitations in FEMA-368 (2000) on building height, particularly for hybrid coupled wall systems, is discussed.

The objective of this thesis is to determine if the single sided resistance spot weld (RSW) can be used as a feasible connection method for cold formed steel (CFS) shear walls subject to lateral force of either seismic or wind loads on mobile shelters. The research consisted of three phases which include: a design as a 3D BIM model, connection tests of the resistance spot weld, and full-scale testing of the designed solid wall panels. The shear wall testing was conducted on specimens with both resistance spot weld and self-drilling screws and the results from tests gave a direct comparison of these connections when the solid wall panel was subjected to in-plane shear forces. The full-scale tests also included 4-point bending tests which was designed to investigate the wall panel's resistance to the lateral loads applied perpendicularly to the surface. The research discovered that the singled sided resistance spot weld achieved similar performance as the self-drilling screws in the applications of CFS wall panels for mobile shelters. The proposed single sided resistance spot weld has advantages of low cost, no added weight, fast fabrication, and it is a feasible connection method for CFS wall panels.

Les travaux de thèse visent à améliorer les connaissances sur le comportement parasismique des bâtiments à ossature en bois. Le comportement de ces bâtiments sous sollicitations sismiques est lié à celui de ses assemblages par connecteurs métalliques (pointes, vis, équerres, etc.). La modélisation numérique d'une telle structure s'appuie sur une démarche multi-échelles, afin de représenter les comportements locaux à l'échelle de l'ouvrage. Trois échelles sont définies. Échelle 1 : assemblages, échelle 2 : éléments de structure (mur, plancher, toiture), échelle 3 : bâtiment. A chaque échelle, une loi de comportement dédiée (hystérétique avec endommagement) permet la modélisation. Les calages ou validations s'appuient sur des campagnes d'essais expérimentaux. Diverses configurations de spécimen et divers chargements sont testés afin de construire une vaste base de données de résultats. Les essais sur les assemblages par connecteurs métalliques ont permis le calage du modèle numérique à l'échelle 1. Un modèle éléments finis (EF) détaillé de mur est validé expérimentalement en quasi-statique et en dynamique. Un modèle EF simplifié de mur (macro) permet de passer à l'échelle du bâti. Cet élément macro, calibré sur le modèle détaillé, permet de reproduire avec une précision satisfaisante le comportement dynamique d'un mur. L'assemblage d'éléments de murs (pleins ou avec ouverture) permet de tendre vers la modélisation tridimensionnelle d'une structure. Ce modèle numérique de structure permettra d'étudier, localement et globalement, le comportement parasismique des constructions à ossature bois afin de proposer des dispositifs constructifs et un dimensionnement adaptés à ces ouvrages en zone sismique. / This research aims at a better understanding of the vulnerability of timber-frame buildings against earthquakes. The behavior of these structures under seismic loading relies on their joints with metal fasteners (nails, screws, 3 dimensionnal connections, etc.). The numerical modeling of such a structure is based on a multi-scale approach, which allows to take into account the local behaviors at the structural scale. Three scales are defined: Scale 1: joints, scale 2: structural elements (shear walls, floors, roofs), scale 3: buildings. At each scale, a behavior law (hysteretic with damage) is used. The calibrations or validations are based on experimental tests. Tests on joints with metal fasteners are used to calibrate the numerical model at scale 1. A detailed finite elements (FE) model of shear wall is developped and its predictions are confronted to quasi-static and dynamic experimental results for validation. A simplified FE model of shear wall (macro element) is used to generate a numerical model at the building scale. This macro element, calibrated on the detailed FE model, accurately reproduces the dynamic behavior of a shear wall despite its simplicity. The numerical model of timber-frame buildings will be used to study, locally and globally, their behavior against earthquake in order to propose construction details and design adapted to these structures in seismic areas.

Masonry structures constitute a significant portion of building stock worldwide. Seismic performance of unreinforced masonry has been far from satisfactory. Masonry is purported to be a major source of hazard during earthquakes by reconnaissance surveys conducted aftermath of an earthquake. Reasons for the poor performance of masonry structures are more than one namely lack of deformational capacity, poor tensile strength & lack of earthquake resistance features coupled with poor quality control and large variation in strength of materials employed. Fibre Reinforced Plastic (FRP) composites have emerged as an efficient strengthening technique for reinforced concrete structures over the past two decades. Present thesis is focused towards analysing the behaviour of Fibre Reinforced Plastic (FRP) strengthened masonry under axial compression and in-plane shear loading. Determination of in-planes hear resistance of large masonry panels requires tremendous effort in terms of cost, labour and time. Masonry assemblages like prisms and triplets that represent the state of stress present in masonry walls and masonry in-fills when under the action of in-planes hear forces present an alternative option for research and analysis purposes. Hence, present research is focused towards analysing the performance of FRP strengthened masonry assemblages and unreinforced masonry assemblages. Chapter1 provides a brief review on the behaviour of masonry shear walls and masonry in-fills under the action of in-plane shear forces in addition to the performance of masonry structures during past earthquakes. Review of available literature on FRP confinement of masonry prisms with bed joints inclined from 00 to 900 to the loading axis under axial compression, analytical models available for FRP confined concrete, shear strength of masonry triplets attached with FRP is presented. Chapter 2 primarily focuses on determining the various properties of the materials involved in this research investigation. Test procedure and results of the tests conducted to determine the mechanical and related properties of the materials involved are presented. Elastic properties and stress-strain response of burnt clay brick, mortar and FRP laminates are presented. Studies conducted on behaviour of GFRP confined masonry prisms under monotonic axial compression are included in Chapter 3. The study comprised of testing masonry prisms, both unconfined and FRP confined masonry prisms under axial compression. Stretcher bond and English bond prisms, with bed joints normal and parallel to loading axis are included in this study. Two grades of GFRP,360g/m2 and 600 g/m2 are employed to confine masonry prisms. The experimental program involved masonry prism types that accounted for variations in masonry bonding pattern, bed joint inclination to the loading axis and grade of GFRP. Review of the available analytical models predicting compressive strength of FRP confined masonry prism is presented. Available models for FRP confinement of masonry are re-calibrated using the present experimental data generating new coefficients for the already existing model to develop new expression for predicting the compressive strength of FRP confined prisms. In addition to the prism types mentioned earlier, behaviour of unconfined and GFRP confined stretcher bond prisms with bed joints inclined at 300, 450 & 600 to the loading axis are further investigated. Chapter 4 primarily deals with the shear strength and deformational capacity of masonry triplets that represent joint shear failure in masonry. An experimental program involving masonry triplets attached with different types of FRP(GFRP and CFRP), grade of FRP, percentage area covered by FRP and reinforcement pattern is executed. This exercise determined the influence of these parameters over the enhancement achieved in terms of shear strength and ultimate displacement. Results of tests conducted on stretcher bond prisms presented in chapter 3 and results of tests on shear triplets presented in this chapter are combined to study the interaction between shear and normal stresses acting along the masonry bed joint at different angles of inclination. The thesis culminated with chapter 5 as concluding remarks highlighting the salient Information pertaining to the behaviour of FRP strengthened masonry under axial compression and in-plane shear loading obtained as an outcome of the research conducted as a part of this thesis.

Low-aspect-ratio reinforced concrete (RC) shear walls, characterized by height-to-length ratios of less than two, have been widely used as a seismic force-resisting system (SFRS) in a wide array of structures, ranging from conventional buildings to critical infrastructure systems such as nuclear facilities. Despite their extensive applications, recent research has brought to light the inadequate understanding of their seismic performance, primarily attributed to the intricate nonlinear flexure-shear interaction behaviour unique to these walls. In this respect, the current research dissertation aims to bridge this knowledge gap by conducting a comprehensive evaluation to quantify the seismic performance of low-aspect-ratio RC shear walls when used in different applications. Chapter 2 focuses on low-aspect-ratio RC shear walls that are employed in residential and industrial structures. Considering their significance, the seismic response modification factors of such walls, as defined in various standards, are thoroughly examined and evaluated utilizing the FEMA P695 methodology. The analysis revealed potential deficiencies in the current code-based recommendations for response modification factors. Consequently, a novel set of response modification factors, capable of mitigating the seismic risk of collapse under the maximum considered earthquake, is proposed. Such proposed values can be integrated into the forthcoming revisions of relevant building codes and design standards. While the FEMA P695 methodology offers a comprehensive approach to assessing building seismic performance factors, its practical implementation is associated with many challenges for practicing engineers. Specifically, the methodology heavily relies on resource-intensive and time-consuming incremental dynamic analyses, making it less feasible for routine engineering practices. To enhance its practicality, a data-driven framework is developed in Chapter 3, circumventing the need for such demanding analyses. This framework provides genetic programming-based expressions capable of producing accurate predictions of the median collapse intensities—a key metric in the acceptance criteria of the FEMA P695 methodology, for different structural systems. To demonstrate its use, the developed framework is operationalized to low-aspect-ratio RC shear walls and the predictive expression is evaluated considering several statistical and structural parameters, which showed its adequacy in predicting the median collapse intensities of such walls. Furthermore, the adaptability of this framework is showcased, highlighting its applicability across various SFRSs. Chapters 4 and 5 tackle the scarcity of experimental assessments pertaining to the seismic performance of low-aspect-ratio RC walls in nuclear facilities. The seismic hybrid simulation testing technique is employed herein to merge the simplicity of numerical simulations with the efficiency of experimental tests. Hybrid simulation can overcome obstacles related to physical specimen sizes, limited actuator capacities, and space constraints in most laboratories. In these two chapters, the experimental program delves into evaluating the seismic performance of three two-storey low-aspect-ratio nuclear RC walls under different earthquake levels, including operational, design, and beyond-design-level scenarios. Diverse design configurations, including the use of increased thickness boundary elements and different materials (i.e., normal- and high-strength reinforcement), are considered in such walls to provide a comprehensive understanding of several structural parameters and economic metrics. Key structural parameters, such as the force-displacement responses, multi-storey effects, lateral and rotational stiffnesses, ductility capacities, displacement components, rebar strains, crack patterns and damage sequences, are all investigated to provide direct comparisons between the walls in terms of their seismic performances. Additionally, economic metrics, including the total rebar weights, overall construction costs and the expected seismic repair costs, are considered in order to evaluate the seismic performance of the walls considering an economic perspective. The findings of this experimental investigation are expected to inform future nuclear design standards by enhancing the resilience and safety of their structures incorporating low-aspect-ratio RC shear walls. / Thesis / Doctor of Philosophy (PhD)