During propped construction the steel-concrete composite action resists dead as well as imposed loads. Conversely, the steel section alone resists the floor self-weight in unpropped beams. The major difference between propped and unpropped composite beams lies in the ductility requirements rather than in the strength requirements. Relatively few studies have been carried out to assess the rotation requirements for unpropped semi-continuous composite beams. The outstanding critical factor in the case of unpropped construction is the dead load stress that must be carried by the steel beam alone prior to hardening of the concrete. This research overcomes the difficulties involved in modelling the composite and noncomposite stages by using a numerical integration technique developed from the basic principles of structural mechanics. The method incorporates the fully non-linear material properties and requires very little assumption. The technique was initially validated using the experimental results from plain steel beam bending tests. The subsequent comparison between the model predictions and the results from the large-scale frame test carried out for this research purpose, showed that the method is capable of predicting non-elastic load vs. end rotation behaviour within a high degree of accuracy. Thus the model can be used with confidence in order to predict the connection rotation requirements for a wider range of loading configurations than is practically possible from experimental testing alone. A parametric study is carried out using the numerical integration technique developed for the semi-continuous composite beam on a total of 2160 different beam configurations, utilising different steel grades and loading conditions. In this study the influence of dead load stress on the connection rotation requirement has been thoroughly evaluated along with several other factors including span to depth ratio, location within the building frame, ratio between the support (connection) moment capacity and span (beam) moment capacity, loading type, steel grade and percentage of the beam strength utilised during design. The connection rotation capacity requirements resulting from this study are assessed to establish the scope for extending the use of composite connections to unpropped beams. The large-scale experiment that has been carried out provided an opportunity to investigate the behaviour of a modified form of composite connection detail for use at perimeter columns (single-sided composite connections) with improved rebar anchorage. Additionally, another extensive parametric study is carried out using the numerical integration technique developed for the steel beam to establish the influence of strainhardening on elastic-plastic frame instability design.

During propped construction the steel-concrete composite action resists dead as well as imposed loads. Conversely, the steel section alone resists the floor self-weight in unpropped beams. The major difference between propped and unpropped composite beams lies in the ductility requirements rather than in the strength requirements. Relatively few studies have been carried out to assess the rotation requirements for unpropped semi-continuous composite beams. The outstanding critical factor in the case of unpropped construction is the dead load stress that must be carried by the steel beam alone prior to hardening of the concrete. This research overcomes the difficulties involved in modelling the composite and noncomposite stages by using a numerical integration technique developed from the basic principles of structural mechanics. The method incorporates the fully non-linear material properties and requires very little assumption. The technique was initially validated using the experimental results from plain steel beam bending tests. The subsequent comparison between the model predictions and the results from the large-scale frame test carried out for this research purpose, showed that the method is capable of predicting non-elastic load vs. end rotation behaviour within a high degree of accuracy. Thus the model can be used with confidence in order to predict the connection rotation requirements for a wider range of loading configurations than is practically possible from experimental testing alone. A parametric study is carried out using the numerical integration technique developed for the semi-continuous composite beam on a total of 2160 different beam configurations, utilising different steel grades and loading conditions. In this study the influence of dead load stress on the connection rotation requirement has been thoroughly evaluated along with several other factors including span to depth ratio, location within the building frame, ratio between the support (connection) moment capacity and span (beam) moment capacity, loading type, steel grade and percentage of the beam strength utilised during design. The connection rotation capacity requirements resulting from this study are assessed to establish the scope for extending the use of composite connections to unpropped beams. The large-scale experiment that has been carried out provided an opportunity to investigate the behaviour of a modified form of composite connection detail for use at perimeter columns (single-sided composite connections) with improved rebar anchorage. Additionally, another extensive parametric study is carried out using the numerical integration technique developed for the steel beam to establish the influence of strainhardening on elastic-plastic frame instability design.

The wide spread use of limit states design procedures in both the Canadian and American steel design codes has created a need for a better understanding of how structures behave. Current design practice, however, allows and often encourages engineers to use an approximate linear analysis to determine the member forces in a structure. This is then followed by an even more approximate amplification of forces through the use of several design equations. It is believed that this practice is no longer acceptible as more accurate second-order computer programs have become a very practical alternative. With this as motivation, this thesis will provide a comparison between a second-order computer program available at the University of British Columbia called ULA (Ultimate Load Analysis) and the Canadian and American building code designs, CAN3-S16.1-M84 and LRFD 1986 respectively. It was felt that ULA should be verified, even though the theory it is based on is well established. Thus, ULA was used to generate a load versus L/r curve for a pin ended column (with the parameters modified slightly to allow direct comparison with the curves available in the codes). ULA was then used to predict load-deflection curves for two existing test frames. The resulting curves compared well with the test data. To ensure simplicity, the building codes make several approximations in the derivation of their design equations. This results in the equations being applicable to a very narrow range of structures. Specifically, the equations apply to rigidly connected frames in which all of the columns reach their critical buckling load simmultaniously. Consequently, the results from ULA were compared to the codes for structures of this type. It was found that the codes were conservative for these structures in relation to the results from ULA, yet the amount of conservatism varied greatly between structures. That is, the codes are not consistant in how conservative they are. Results from ULA were then compared to the codes for structures that do not satisfy all of the code limitations. Alhough using the codes to design structures beyond the limit of applicability is not a recommended practice, engineers do use the codes to design all types of structures, with little appreciation for the applicability limits. Consequently, it was deemed appropriate to extend this study to such structures. Though only a few were investigated, it was found that the codes were unreliable, being highly conservative, very accurate, or in one case highly unconservative when compared to the results from ULA. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2016 / This dissertation presents a parametric study conducted on the dimensions of an inverted box rib (IBR) sheet. The objectives of the study were (i) to obtain the optimum dimensions that would be used to simulate new IBR profiles made from standard sheet input coils whilst meeting the stiffness criterion; and (ii) to perform a cost analysis to determine the most economic simulated profile. The dimensions which were varied in the parametric study were rib-height, rib-width, sheet thickness and the number of pans per 686 mm cover width of a single IBR 686 sheet. Numerical experiments were conducted using the Finite Elements Method and Abaqus/CAE software. The results were compared to the predictions obtained from Euler-Bernoulli beam theory. The outputs from the experiments were the sheet deflection from which stiffness was determined, and eigenvalues from which the profiles’ stability and buckling modes were calculated. This study found that sheet stiffness increased as the rib-height, sheet thickness and number of pans per 686 mm cover width increased. In contrast, the rib-width had little effect on the sheet stiffness. Hence, it was concluded that, for any IBR sheet profile, the rib-width should be kept at approximately 23 mm to avoid using more material in the sheet. The optimum dimensions found were rib-height of 34 mm, rib-width of 23 mm and four pans per 686 mm cover width. The commercially available IBR 686 sheet is made up of four pans and has a rib-height and a rib-width of 37 and 33 mm, respectively. It is manufactured from an input sheet coil of 925 mm. Reducing the rib-height from 37 mm to 34 mm and the rib-width from 33 mm to 23 mm resulted in increasing the cover width by 8 %. The optimum dimensions were further used to simulate profiles made from the 925, 940, 1000, 1175, 1219, 1225, 1250 and 1320 mm standard sheet coils in order to find the most economic IBR profiles that met the stiffness criterion. The 1250 mm coil yielded the most economical IBR profile, which has six 97 mm wide pans, and a 996 mm cover width. This profile resulted in a 10 % cost saving compared with the next closest profile. / MT2017

The wider use of cold-formed steel framing is hindered by the lack of generic sections. This study puts forth an effort to develop a performance section designation code without specifying the geometry of the sections. A PC-based program to analyze C-section was developed and used to produce typical Performance Section Tables for both wall studs and joists. For curtain walls the <i>Uniform Lateral Load Capacity Tables</i> and for bearing walls the <i>Axial Load with Specified Lateral Load Tables</i>, the <i>Strong Axis Axial Load Capacity Charts</i>, and the <i>Weak Axis and Torsional Axial Load Capacity Charts</i> were developed. The typical design aids for roof/floor joists include the <i>Uniform Load Capacity Tables</i> for single and two continuous spans, the <i>Moment-Shear Interaction Capacity Charts</i>, and the <i>Web Crippling Capacity Tables</i>. Design examples are provided to illustrate the usage of the above tables and charts. / Master of Science

The purpose of this thesis is to approach a partial theoretical understanding of the design of lamella structures and to determine the economic merit of the lamella structure as a structural steel hangar. A survey revealed no literature that discusses the design of lamella past the concept that the lamella could be designed as independent arches. In this thesis the analysis and design of the main structural steel members are attempted. In the analysis of the hangar it is assumed that the intersecting arches will not interact under load. The effect of the error of this assumption is minimized by furnishing partial support to the free edge of the lamella system by the use of an arch that spans the structure at the transverse edge. The effect of this edge arch is to cause the maximum stresses to occur in the interior of the lamella system where the interaction is minimized by the symmetry of the system. The method of analysis is a combination of graphic statics and virtual work. Graphic statics was used to determine the pressure line of the arches and virtual work summations were used to determine the redundant loads and reactions. At the conclusion the structure is compared on a tonnage of steel basis, with a structure of the same approximate size composed of steel rigid frames. / Master of Science

In recent years there has been a constant search for better and more economical structures in the field of structural engineering. Within the past ten to twenty years this search has resulted in the introduction of two new structural systems: prestressed concrete and composite design. Each of these new construction methods has advantages and limitations. A new idea of combining these two structural systems into one could result in more economical structures particularly suited for long span bridges. The slab-and-stringer bridge is one of the most common types in highway construction. Such a bridge is composed of two principal load-carrying elements: the steel beams which transfer the loads in the direction along the bridge axis, and the concrete slab which distributes the loads in the transverse direction to the steel beams. If some appropriate mechanical device is used to connect the steel beams end concrete slab together, the concrete slab can act as a cover plate for the beams and assist the beams in carrying the load in the longitudinal direction. Such a structure is known as a Conventional Composite Structure. If such a structure is prestressed with high-strength steel cables, it acquires additional qualities. The principle of prestressing in steel structures is not used to overcome tensile deficiencies of the material, as ls the case for concrete, but to build opposing stresses into members in order to counteract the stresses caused by external forces. When favorable residual stresses have been induced in such structures they will be capable of carrying greater loads than their conventional counterpart. It is the objective of this thesis: (1) to investigate the physical properties of the materials used in prestressed composite structures, (2) to discuss the methods for construction, (3) to develop a usable design technique for simply supported and continuous beams, (4) to discuss the layout of prestressing cables in continuous prestressed composite beams, (5) to show the use of equations for selecting the steel beam cf the prestressed composite structure, and (6) to illustrate the design of prestressed composite structures with typical problems. / Master of Science

A light gage steel folded plate model structure was fabricated and tested under a uniform pressure to determine the relative stiffness of this type of structure. Deflections at mid and quarter spans were measured and compared with values determined by a rational method of analysis. A different approach to the analysis was introduced in which values of equivalent moment of inertia were determined for each plate cross-section so that compatibility along adjoining longitudinal edges would be assured. The experimental and theoretical results were in good agreement. / Master of Science

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.

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.