Steel fabricators and connection designers in the building construction industry often rely on traditional connection design methods, which involve using connection design software or spreadsheets to simulate and design connections with the goal of minimizing costs associated with fabrication and erection. However, accurately assessing the efficiency and cost implications of these designs can be a significant challenge. This is due to the complexity of the process, which involves considering a wide range of parameters such as material tonnage, machinery availability, connection type, labour cost, fabrication and erection constraints, and available optimization tools.

Steel Multi-Tiered Buckling-Restrained Braced Frames (MT-BRBFs) are commonly used in moderate-to-high seismic regions of Canada and United States as the lateral-load resisting systems of tall single-storey buildings, such as sports facilities, airplane hangars, and warehouses, as well as in tall stories of multi-storey buildings. MT-BRBFs consist of two or more bracing panels stacked vertically between column out-of-plane support locations. A multi-tiered configuration is utilized when the use of a single bracing panel within a storey height is not practical nor economical. Although MT-BRBFs enjoy robust cyclic performance and large ductility capacity of their Buckling-Restrained Braces (BRBs), their seismic response differs from standard multi-storey BRBFs. Namely, lateral deformation under seismic loads may not evenly distribute along the frame height in MT-BRBFs as the tiers with tension-acting BRBs tend to deform more than those with compression-acting BRBs. This response may induce in-plane flexural demands on the braced frame columns, which may lead to plastic hinge formation or even column instability in the presence of a large axial force induced due to gravity loading and BRB capacity design forces. Furthermore, uneven distribution of frame lateral deformation can impose excessive strain demands on the BRBs yielding in tension, which can potentially cause fracture in the BRB core. In Canada, there are no design guidelines for MT-BRBFs in the 2019 Canadian steel design standard, CSA S16-19. Special design requirements were introduced for MT-BRBFs in the 2016 edition of AISC Seismic Provisions in the U.S. to improve column stability response and control tier drift demands. However, very limited supporting research data is available to verify these requirements. Given the extensive application of MT-BRBFs, often times in critical structures, there is an urgent need to develop a better understanding of their seismic response, estimate seismic force and deformation demands on their members, evaluate the current U.S. seismic design provisions and propose potential improvements, and develop an enhanced design method in the framework of CSA S16.

Multi-tiered braced frames are commonly used as the lateral load-resisting system of tall single-storey buildings or tall storeys of multi-storey buildings. This framing system divides the frame or storey height into multiple bracing panels, resulting in more economical member sizes and practical connections. Although multi-tiered concentrically braced frames are preferred in practice, multi-tiered eccentrically braced frames (MT-EBFs) offer an alternative solution in high seismic regions due to their high ductility, stable and reliable yielding mechanism, and architectural versatility. Despite extensive research studies conducted to examine the seismic response of and develop design requirements for multi-tiered concentrically braced frames, there is limited research on the seismic performance of steel MT-EBFs. Furthermore, there exist no special design requirements for MT-EBFs given that there are several concerns associated with the stability response of their unbraced intermediate links and columns. Due to the lack of background research, the current edition of the Canadian steel design standard, CSA S16-19, does not recognize MT-EBFs as ductile EBF. This Ph.D. research project aims to improve understanding of the behaviour of MT-EBFs under seismic loads and develop new analysis and design requirements to improve their seismic stability of MT-EBFs with emphasis on their link beams and columns.

Embedded plates (embeds) are a common method of joining steel and concrete members in

structures. Research at the University of Alberta emphasized the lack of consideration in the

Canadian concrete design standard CSA A23.3:19 Annex D for the eect of reinforcement

on anchorage capacity, as well as the treatment of combined loading for common shear-type

connections. Conservatism in design and confusion for designers are manifestations of the

current limitations of the design standard. There is currently no practical approach, codied

or otherwise, that can accurately describe the behavior of embeds in reinforced concrete.

This research project aims to improve the design of embeds by identifying limitations in

current design practices, and then testing previously standardized embedded plates to assess

the eects of supplementary reinforcement and common shear connections, parameters that

are inadequately addressed by CSA A23.3:19 Annex D.

Numerical simulation and hybrid simulation are extensively used in earthquake engineering

to evaluate the seismic response of structures under seismic loading. Despite the advances

in computing power and the development of efficient integration algorithms in the past,

numerical simulation techniques suffer from a high computational cost and the uncertainty

associated with the definition of constitutive material models, boundary conditions, and mesh

density, in particular in highly nonlinear, large or complex structures. On the other hand, the

results of hybrid simulation can become biased when only one or limited number of potential

critical components, seismic fuses, are physically tested due to laboratory or cost constraints.

Deep wide-flange columns are commonly used in the construction of steel moment-resisting frames (MRFs) to resist lateral seismic loads in high seismic regions in North America. Past studies on deep columns with base plastic hinges located at the first storey of MRFs have indicated that such sections can be prone to significant axial shortening and out-of-plane instability under design-level seismic excitation. Despite significant advancement in the seismic performance of steel wide-flange columns, the effect of limit states observed in the past studies on the member seismic stability response has not been quantified in the framework of the Canadian design practice. Moreover, the influence of three-dimensional response of steel MRFs on the stability of the first-storey columns with base plastic hinging using more representative loading protocols expected under seismic loads, e.g., earthquake accelerations, has not been well comprehended yet. Finally, new supporting data is needed 1) to evaluate the current stability design requirements; and 2) to propose enhanced seismic stability recommendations to improve the design of steel MRFs in Canada. Therefore, this study aims to evaluate the stability response of wide-flange columns of Ductile steel MRFs under seismic loading and propose enhanced stability design recommendations in the framework of the Canadian steel design standard (CSA S16).

Due to a lack of readily available industry-wide standard embedded plate designs, embedded plates are often custom designed for each project. This leads to many inefficiencies in the design, fabrication, and installation stages of the construction process. Additionally, the current Canadian design standard for concrete structures, CSA A23.3:19, requires many assumptions when evaluating embedded plate capacity, leading to inconsistency among designers. This research project aims to improve the efficiency of the embedded plate construction process by proposing standard embedded plates, and then testing selected embedded plates to verify the predicted capacities and key design assumptions.

Three standard embedded plates having four, six or eight end-welded stud anchors, with design tables developed using CSA A23.3:19, are proposed through collaboration with industry partners involved in the construction process. From the eight full-scale test results, A23.3 was deemed adequate in predicting the failure loads if the connection eccentricity, caused by the gap between the bolt line on the shear tab and the exposed surface of the plate, is considered in the capacity predictions. A test-to-predicted ratio of 0.92 was found when not considering connection eccentricity, compared to 1.11 when considering it. Additionally, embedded plate rotation during testing (0.01 to 0.02 rad at peak load, and further rotation post-peak), suggests connection eccentricity significantly affects the behaviour of the embedded plate and should be considered in design.

Lateral–torsional buckling (LTB) is a stability failure mode that occurs in unbraced segments of flexural members and is associated with simultaneous out-of-plane lateral defection and cross-section rotation. The LTB behaviour of doubly symmetric I-shaped members is generally well understood. However, there is concern that current understandings of inelastic LTB in welded steel girders may be inaccurate and not representative of the current fabrication methods employed in Canada. Moreover, recent studies (MacPhedran and Grondin 2011; Kabir and Bhowmick 2018) have indicated the current Canadian design provisions for LTB may be inaccurately estimating the inelastic LTB resistance of welded steel girders. The purpose of this study is to address these concerns and assess the LTB behaviour of modern welded steel girders through experimental and numerical means. Additionally, to assess the LTB behaviour and load-carrying performance of heat-straightened welded steel girders.

Modularization of buildings comes in several types, from prefabricated members to full volumetric models. Recently, the introduction of modular construction methods brought numerous benefits to the construction industry. Reducing construction time and costs together with improving quality and safety helped in growing the interest of designers and contractors toward modularization. Although there is wide agreement on modularization benefits to the construction industry, the transition to these new building techniques requires research and understanding of the structural behaviour of modular structures. Furthermore, despite a relatively vast body of research proposing innovative modular steel systems and connections, their application is still limited and they lack a sufficient design requirements in particular in seismic regions. Finally, it is felt that there is a need to develop a new and innovative modular steel lateral load resisting system (LLRS) that can be integrated with the modular system to help in improving construction efficiency, while offering a safe and satisfactory structural performance. 

A large proportion of MT-CBFs in Canada is located in low-to-moderate seismicity regions where low-ductile frames, such as Limited Ductility (Type LD) or Conventional Construction (Type CC) category, are often preferred to avoid relatively complicated seismic design and detailing requirements. Limited research studies have focused on the seismic stability and design of such low-ductile MT-CBFs. The current special seismic design provisions for Type LD MT-CBFs in the current Canadian steel design standard (CSA S16), which often requires performing multiple tedious analyses, particularly for tall frames, lack sufficient background research. For Type CC MT-CBFs, the Canadian steel design standard does not provide specific seismic design requirements. This research aims to investigate the seismic behaviour of Type LD and Type CC steel MT-CBFs with the focus on the stability of their columns, assess the current seismic design provisions, and propose enhanced and yet simplified design guidelines for the design of such frames in low-to-moderate seismicity regions. 

Lateral–torsional buckling (LTB) is a failure mode that is associated with simultaneous vertical displacement and twisting of a beam when subjected to flexural loading. LTB behaviour is generally well understood for I-shaped steel beams; however, the LTB behaviour of T-shaped steel beams is not as well understood. The aim of this study is to better understand the behaviour of T-shaped steel beams in single-curvature with the flange in compression through numerical finite element analysis, with a special focus on the moment gradient factor to consider the effect of varying moments along the beam axis.  

In recent years, several concerns have been raised regarding the adequacy of the Canadian steel design standard, CSA S16-14, in characterising the lateral–torsional buckling resistance of members made up of three plates welded together into an I-shaped section, as is commonly done for deep girders. 

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To improve the understanding of lateral–torsional buckling behaviour, an experimental programme was developed, consisting of 11 welded girders with unbraced spans of 9.75 m (32 ft). Preliminary finite element simulations were conducted to anticipate displacements and rotations of the test specimens, which were used to inform the design of an experimental test set-up capable of accommodating the full range of expected movement. Test results were compared against predictions from CSA S16-14.

Residual stresses can have a significant impact on the stability of structural members.

In the case of I-section beam elements, such stresses can impact lateral–torsional

buckling (LTB) capacity, particularly in the inelastic range. It is

possible for a built-up welded girder to have a lower LTB capacity than

that of a rolled one of identical cross-section. Concerns have been raised that such a

difference may render Canadian steel design standards unconservative for welded

girders. A paucity of residual stress data for current welded girders, however, prevents assessment of these assumed distributions.

In this study, residual stress measurements are carried out on a series of four reduced-scale

welded steel test girders. Testing consists of destructive sectioning tests and nondestructive ultrasonic measurements. A predictive residual stress model for modern welded girders is proposed, and the feasibility of the ultrasonic method for residual stress measurements addressed.

Multi-tiered concentrically braced frames (MT-CBFs) are widely used in North America as the lateral load-resisting system of tall single-storey buildings such as airplane hangars, recreational facilities, shopping centres, and industrial buildings. MT-CBFs consist of multiple concentrically braced panels along the height of the frame separated by horizontal struts. 

Past studies have shown that inelastic frame deformations tend to concentrate in one of the tiers over the frame height, which induces large in-plane bending moments in braced frame columns and high deformation demands in braces. This behaviour may lead to column buckling and/or brace fracture. 

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This report focuses on the evaluation of the seismic behaviour and design methods for MT-CBFs. Results obtained for the prototype frame designed excluding the special seismic design provisions confirmed column buckling and nonuniform distribution of the frame inelastic lateral deformations in the tier where brace tensile yielding takes place first. New brace force adjustment factors are proposed to achieve more realistic brace nonlinear forces when computing column force demands and tier drifts.

Extended shear tab connections are efficient for both fabrication and erection where a beam would otherwise need to be coped to clear the flanges of the supporting member, and are therefore used extensively in industry. Stability issues can arise as the plate becomes longer and more slender, as may be required in skewed connections or other complex geometries. Therefore, this research aims to determine when stability of the extended shear tab governs the behaviour and capacity of the connection as opposed to strength, considering the interaction of shear, axial and bending stresses.

A parametric study using finite element simulations was conducted in which the length of the extended shear tab was increased until instability of the plate became the governing failure mode. A full-scale experimental testing program was also completed to further validate the results of the numerical analysis. The study investigated the effect of plate depth, plate thickness and level of applied axial compression. The shear capacity of the connection is discussed and a design procedure for the critical length is proposed. The recommendation includes the effect of varying levels of axial load and initial imperfections. 

It has become common for steel fabricators to find torsional loads included in the design documents of many industrial steel structures. These loads arise in wide-flange beam-to-column moment connections when the beam is subject to weak axis bending, which in turn, is transferred to the column as torsion applied to the adjoining flange. If the wide-flange column is unstiffened at the connection, localized distortion of the web can lead to additional rotation of the connected flange that are not accounted for in classical elastic torsion theory. Due to a lack of codified guidelines or relevant literature on how to design for this behaviour, designers routinely add full- depth web stiffeners at the connection to prevent localized distortion of the member, which is costly and time consuming. Previous research has revealed some information about how the torsional moment is shared between the column web in bending and flange in torsion, but no full- scale tests considered the presence of axial load. The current study performs parametric numerical analysis studies to consider the effects of cross-sectional geometry and the deleterious effects of axial load on the strength and stiffness of the wide-flange column. Fifteen full-scale tests have been conducted to verify the findings from numerical simulations and develop a design procedure for predicting the strength and stiffness of the member. Formulations have been provided to calculate the behavior of unstiffened axially-loaded wide-flange members subjected to torsion through one flange. 

In a recent construction project, a platform structure made up of 350W and 300W steel un- derwent a double dip galvanizing process. Prior to the galvanizing process, the platform was fabricated to completion, which included numerous welds throughout the design. After galva- nizing, cracks were found originating in the welds and propagating into the base material. To the steel designer, this posed a new and curious problem. Previously, similar structures had undergone the same processing with no cracking. 

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Tension test samples were sectioned from the base material. The samples were heated to the galvanizing temperature and then fractured. The samples broke suddenly and showed little signs of ductile fracture and, more significantly, had a fracture surface matching the original cracks. To support the notion of temper embrittlement, material chemistry testing found high levels of phosphorus. Phosphorus is a key culprit in temper embrittlement, and given the elevated temperature and stress of the double dip process, it would have been able to diffuse to the grain boundaries causing brittle grain boundary separation. Finally, to quantify the thermal stresses induced from galvanizing, a three dimensional finite element analysis model was created to simulate the double dip process. The model found relatively high stresses but not enough to reach the yield point without an embrittlement factor present. 

The susceptibility of structures to extensive collapse when subjected to a localised failure due to an extreme loading event has in recent years gained considerable research attention. The scenario most often used to assess such performance, either experimentally or through finite element simulation, is the loss of a column, requiring the floor system to bridge across two building bays with the aid of arching and catenary actions. When a column is abruptly disengaged by an abnormal load, the resulting double-span beam must bridge over the removed column by developing a new equilibrium path to redistribute the load to the adjacent elements. This severe damage in a steel gravity frame, which is designed to carry primarily gravity loads, creates significant demands on shear connections. 

Steel cantilever plate connection elements are rectangular steel plates that are distinguished from other connection plates by their two opposite unrestrained edges. The increased length of cantilever plate connection elements in some connection configurations raises concern regarding the potential of instability of the plate. Fearing that the plate may buckle due to its increased length has led engineers to utilize stiffeners at the plate free edges, which results in a significantly increased fabrication cost. 

Behaviour of the unstiffened wide flanged member is not characterized by the available literature or current design standards. Torsional moment applied on the one flange unstiffened member causes the member to undergo local distortions. Conventionally, to avoid these local distortions stiffeners are provided in the joint. However, these stiffeners may add unnecessary costs to the joint and elimination of these stiffeners will lead to more economical solution. Behaviour of the unstiffened member subjected to the torsional loading has been explored in this report. Parametric numerical analysis studies have been performed to distinguish the effect of cross sectional dimension on the response of the member. Nine full-scale laboratory tests were conducted to further the existing knowledge. The response of the member has been assessed under the combined axial load and torsional moment. Studies have been conducted to provide the basis to calculate the behaviour of the unstiffened member for design. 

Current design procedures for double-coped beams tend to be overly conservative and do not include considerations for axial load. The reduced strength and stability of the coped region increase the susceptibility of the connection to a local failure, and the complexity of the connection behaviour is compounded if axial load is present in addition to shear. However, this behaviour is not well understood due to a lack of research. No published research exists on the full-scale physical testing of double-coped beams. 

Current design procedures for extended shear tab connections tend to be conservative and often do not include considerations for axial load. To address these problems, an investigation into the behaviour of extended shear tabs was completed by testing 23 full-scale specimens. Both unstiffened and stiffened extended shear tab specimens were tested that varied in plate thickness, plate depth, and the number of horizontal bolt lines. The specimens were tested by rotating the beam to 0.03 radians, applying a horizontal load, and then applying vertical load until failure. The horizontal loads varied from 500kN in compression to 200kN in tension. Based on the test results, design recommendations were made for both unstiffened and stiffened extended shear tabs. The recommendations include strength equations for bolt group design and plate design, while connection ductility is addressed by ensuring the plate will fail prior to bolt or weld rupture. 

Steel plate shear walls have traditionally been perceived to be suitable mainly for high seismic regions due to their great ductility and cyclic energy dissipation capacity. Therefore, design and detailing requirements have become increasingly onerous in an attempt to maximize their performance, effectively making the system uneconomical in other regions. Developing applications specifically for low and moderate seismic regions has largely been neglected by researchers. Moreover, despite unique advantages of the system in terms of inherent high ductility and redundancy, its performance under accidental blast has not been investigated systematically. The objective of this research is to examine these neglected areas. 

The performance of structures under the effects of extreme loads can be a critical consideration in their design. The potential for disproportionate collapse following localized damage to a column can be mitigated by the provision of sufficient strength and ductility throughout a structural system to allow for the establishment of a stable alternative load path. An understanding of the behaviour of shear connections in steel gravity frames under the unique combinations of moment, shear, and axial force relevant to column removal scenarios is necessary to assess the vulnerability of a structure to disproportionate collapse. However, such an understanding is currently limited by a deficiency of physical test data. 

There are many design methodologies and philosophies intended to provide structural integrity or increase structural robustness, thereby making structures resistant to progressive collapse. However, there is little information that reveals sources and levels of inherent robustness in structural steel members and systems. The present study seeks to begin the process of behaviour evaluation of components and assemblages initially designed for other purposes than progressive collapse, such as gravity loads, and make recommendations regarding their performance and possible methods for improvements for the new scenario. These recommendations can lead to more economical design and safer structural steel systems in the event of localised damage that has the potential to spread to a disproportionately large part of the structure.