Steel Centre Engineering Reports (SCERs) can be found here from 2014 to present. For earlier publications, please see the archive.

Michael Manarin, Robert G. Driver, and Yong Li

SCER 016 Numerical Investigation of Lateral–Torsional Buckling of T-Shaped Steel Beams

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.  

Dimple Ji, Robert G. Driver, and Ali Imanpour

SCER 015 Large-scale Lateral–Torsional Buckling Tests of Welded Girders

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. 

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.

Daniel Unsworth, Robert G. Driver, and Leijun Li

SCER 014 Characterization of Residual Stresses in Modern Welded Girders

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.

Pablo Antonio Cano and Ali Imanpour

SCER 013 Evaluation of the Seismic Design Methods for Steel Multi-Tiered Concentrically Braced Frames

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. 

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.

Victoria Buffam, Robert G. Driver, and Logan Callele

SCER 012 Stability of Extended Shear Tab Connections Under Combined Loading

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. 

Riley Quintin, Robert G. Driver, and Logan Callele

SCER 011 Design of Axially-loaded Wide-flange Columns Subjected to Torsion Through One Flange

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. 

Christopher T. DiGiovanni, Leijun Li, Robert G. Driver, and Logan Callele

SCER 010 Cracking in Hot-dip Galvanized Welded Joints of Steel Platform Structures

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. 

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. 

Amirhoushang Jamshidi and Robert G. Driver

SCER 009 Steel Shear Connections in Composite Frames Subject to Progressive Collapse

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. 

Pouya Salem, Robert G. Driver, and Logan Callele

SCER 008 Unified Design Criteria for Steel Cantilever Plate Connection Elements

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. 

Muhammad Ahmad, Robert G. Driver, Logan Callele, and Bo Dowswell

SCER 007 Behaviour and Design of Unstiffened Wide-flange Members Subjected to Torsional Moment Through One Flange

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. 

Graeme Johnston, Robert G. Driver, and Logan Callele

SCER 006 Strength and Behaviour of Double-coped Steel Beams Under Combined Loads

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. 

Kristin Thomas, Robert G. Driver, Logan Callele, and Steven Oosterhof

SCER 005 Design and Behaviour of Extended Shear Tabs Under Combined Loads

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. 

Hassan Moghimi and Robert G. Driver

SCER 004 Steel Plate Shear Walls for Low and Moderate Seismic Regions and Industrial Plants

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. 

Steven A. Oosterhof and Robert G. Driver

SCER 003 Behaviour of Steel Shear Connections for Assessing Structural Vulnerability to Disproportionate Collapse

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. 

Hossein Daneshvar and Robert G. Driver

SCER 002 One-sided Steel Shear Connections in Column Removal Scenario

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. 

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