This thesis presents experiments and numerical analysis of the cold-formed steel clip angle in three different limit states which are shear, compression, and combination of the screw connection. A previous cold-formed steel clip angle test program (which is Phase 1) developed design methods for clip angle. Therefore, the object of this thesis is to further investigate the behavior and design methods of loading-bearing cold-formed steel clip angles under different screw pattern. For each limit state, a test program was conducted to investigate the behavior, strength, and deflection of the clip angle. The test result were compared with previous CFS clip angle design method. Amending existing CFS clip angle method were developed by each of the four limit states studied in this project.

The mechanical and material properties of structural steel at elevated temperatures play an important role in structural fire design. The South African 350W and S355 structural steels are common in building structures with S355 slowly replacing the older 350W. The cost and feasibility of full scale fire tests are some of the causes for the lack of experimental data on the behaviour of steel structures when exposed to fire. Therefore excessively conservative design codes based on isolated laboratory experiments are used in practice which leads to increased material costs. Another area of concern with respect to building safety is the reusability of structural steels post fire exposure, which is not effectively addressed within these codes. This study aims to establish greater insight into structural fire design and simulation on which further research can be built. Experimental programs on the temperature dependent behaviour of these steel members loaded axially are conducted and compared with theory and the Eurocode 3 standard [1]. The reusability of steel exposed to fire and after being cooled down is investigated and compared to the findings by Outinen [2]. Further testing on material to determine the relationship between remaining life and hardness degradation after cooling down was conducted. Experimental data from various external studies are used to develop novel computer models using the finite element analysis software, SimXpert [3]. These are verified against the original data and compared to existing design codes. A parametric approach is used with these models to demonstrate the advantages of computer simulations in structural fire design. Different cross sections and slenderness ratios are evaluated for their susceptibility to buckling at elevated temperatures. The results of this study show that as temperature and exposure time increase the integrity of steel members decrease. The current design codes accurately predict the behaviour of isolated specimens but lack data on real situations where the specimen is part of a complex structure. It was found that steel members can be reused if their exposure temperature does not exceed 700°C, after which their strength can reduce to 90%. This temperature dependant behaviour was successfully modelled using basic computer simulations and then demonstrated the ease in which they can be used in place of experimental regimes. The parametric advantages of these simulations were demonstrated by predicting the effects of slenderness ratios and geometry cross sections on the buckling behaviour. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.

In this research, monotonic and cyclic tests on cold-formed steel shear walls sheathed with steel sheets on one side were conducted to (1) verify the published nominal shear strength for 18-mil and 27-mil steel sheets; and (2) investigate the behavior of 6-ft. wide shear walls with multiple steel sheets. In objective 1: this research confirms the discrepancy existed in the published nominal strength of 27-mil sheets discovered by the previous project and verified the published nominal strength of 18 mil sheet for the wind design in AISI S213. The project also finds disagreement on the nominal strength of 18-mil sheets for seismic design, which is 29.0% higher than the published values. The research investigated 6-ft. wide shear wall with four framing and sheathing configurations. Configuration C, which used detailing, could provide the highest shear strength, compared to Configurations A and B. Meanwhile, the shear strength and stiffness of 2-ft. wide and 4-ft. wide wall can be improved by using the seismic detailing.

Vulnerability of buildings to disproportionate (or progressive) collapse has become an increasingly important performance issue following the collapses of the Alfred P. Murrah Federal Building in Oklahoma City in 1995 and the World Trade Center in 2001. Although considerable research has been conducted on this topic, there are still numerous unresolved research issues. This dissertation is aimed at developing structural models and analysis procedures for robustness assessment of steel building structures typical of construction practices in the United States, and assessing the performance of these typical structures. Beam-column connections are usually the most vulnerable elements in steel buildings structures suffering local damage. Models of three typical frame connections for use in robustness assessment have been developed with different techniques, depending on the experimental data available to support such models. A probabilistic model of a pre-Northridge moment-resisting connection was developed through finite element simulations, in which the uncertainties in the initial flaw size, beam yield strength and fracture toughness of the weld were considered. A macro-model for a bolted T-stub connections was developed by considering the behavior of each connection element individually (i.e. T-stub, shear tab and panel zone) and assembling the elements to form a complete connection model, which was subsequently calibrated to experimental data. For modeling riveted connections in older steel buildings that might be candidates for rehabilitation, a new method was proposed to take advantage of available experimental data from tests of earthquake-resistant connections and to take into account the effects of the unequal compressive and tensile stiffnesses of top and bottom parts in a connection and catenary action. These connection models were integrated into nonlinear finite element models of structural systems to allow the effect of catenary and other large-deformation action on the behavior of the frames and their connections following initial local structural damage to be assessed. The performance of pre-Northridge moment-resisting frames was assessed with both mean-centered deterministic and probabilistic assessment procedures; the significance of uncertainties in collapse assessment was examined by comparing the results from both procedures. A deterministic assessment of frames with full and partial-strength bolted T-stub connections was conducted considering three typical beam spans in both directions. The vulnerability of an older steel building with riveted connections was also analyzed deterministically. The contributions from unreinforced masonry infill panels and reinforced concrete slabs on the behavior of the building were investigated. To meet the need for a relatively simple procedure for preliminary vulnerability assessment, an energy-based nonlinear static pushdown analysis procedure was developed. This procedure provides an alternative method of static analysis of disproportionate collapse vulnerability that can be used as an assessment tool for regular building frames subjected to local damage. Through modal analysis, dominant vibration modes of a damaged frame were first identified. The structure was divided into two parts, each of which had different vibration characteristics and was modeled by a single degree-of-freedom (SDOF) system separately. The predictions were found to be sufficiently close to the results of a nonlinear dynamic time history analysis (NTHA) that the method would be useful for collapse-resistant design of buildings with regular steel framing systems.

Current research on thermal effects on guideways has addressed many aspects of the behavior of guideways using two-dimensional models. The two-dimensional models are acceptable for existing guideway designs, in which cross sectional shapes are uniform along the length of the guideway. However, three-dimensional models are necessary for a modular design, in which the track structures that interact with Maglev vehicles are made separately and are assembled into the support structure, and in which the cross sectional shapes are not uniform. A three-dimensional numerical model of the thermal environment, in which the effect of partial shading is taken into account, is implemented for the study of guideway behavior under various thermal environments. The numerical model of the thermal environment is calibrated to the experimental results under the thermal environment at Austin, Texas, and is extrapolated to predict the behaviors of guideways under the thermal environment in Las Vegas, Nevada, which is one of the candidate sites for the implementation and deployment of the high speed Maglev transportation system. This study addresses the suitability of a modular steel guideway design under such a thermal environment. Characteristics of the behavior of guideways under various thermal environments are identified, and the behavior of guideways under the effect of partial shading is summarized. / text

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.

This thesis presents experiments and numerical analysis of a novel cold-formed steel framed shear wall sheathed with corrugated steel sheets. The objective of this newly designed shear wall is to meet the growing demand of mid-rise buildings and the combustibility requirement in the International Building Code. The strength of the novel shear wall is higher than currently code certified shear wall in AISI S400-15 so that it could be more favorable for mid-rise building in areas that are prone to earthquakes and hurricanes. Full-scale monotonic and cyclic tests were conducted on bearing walls and shear walls under combined lateral and gravity loads. Though the gravity loads had negative effects on the strength and stiffness of the shear wall due to the buckling of the chord framing members, it still shows promise to be used in mid-rise buildings. The objective of numerical analysis is to quantify the seismic performance factors of the newly design shear wall lateral-force resisting system by using the recommended methodology in FEMA P695. Two groups of building archetypes, story varied from two to five, were simulated in OpenSees program. Nonlinear static and dynamic analysis were performed in both horizontal directions of each building archetype. Finally, the results of the performance evaluation verified the seismic performance factors(R=Cd=6.5 and Ω =3.0) were appropriate for the novel shear wall system.

An analytical model for lateral deflection in cold-formed steel shear walls sheathed with steel is developed in this research. The model is based on the four factors: fastener displacement, steel sheet deformation, and hold-down deformation, which are from the effective strip concept and a complexity factor, which accounts for the additional influential factors not considered in the previous three terms. The model uses design equations based on the actual material and mechanical properties of the shear wall. Furthermore, the model accounts for aggressive and conservative designers by predicting deflection at different shear strength degrees.

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.