Cold-formed steel structural members are used extensively in building construction, with a common application being wind load bearing steel studs. The studs frame into horizontal steel track members at the top and bottom of the wall assembly, with the stud-to-track connection typically being made with self-drilling screws or welds. The wall studs are designed to carry lateral loads only and must be checked for web crippling at the end reactions. While a design expression currently exists for the single stud-to-track connection, there is no similar design expression for multiple jamb stud members. An experimental investigation was carried out, consisting of 94 jamb stud assembly tests subjected to end-one-flange loading. The stud-to-track connections consisted of single C-section studs located at the end of a track simulating a door opening, and a built-up jamb made up of two studs simulating framing at either a window or door opening. The members were attached to the track with self-drilling screws. The research objective was to determine the failure modes and develop a design expression for these structural assemblies. The scope of the experimental investigation covered the following range of parameters: i) Stud and track depths of 92 mm and 152 mm; ii) Stud and track thickness (0.84 mm, 1.12 mm, 1.52 mm and 1.91 mm); iii) Configuration of jamb studs (back-to-back, toe-to-toe and single); iv) Location of jamb studs in the track (interior and end); v) Screw size (#8, #10 and #12); vi) Screw location (both flanges and single flange). Based on the findings of this investigation, design expressions are proposed to predict the capacity of this connection for two limit states: web crippling of the jamb stud; and, punch-through of the track. The web crippling design expression was taken from the North American Specification for the Design of Cold-Formed Steel Structural Members [AISI 2007a; CSA 2007] with new coefficients developed from the test data of the jamb stud-to-track assemblies. A new design expression is also proposed for the track punch-through failure mode, which differs from the approach currently used in the North American Standard for Cold-Formed Steel Framing – Wall Stud Design [AISI 2007b]. A proposal is also recommended to revise the wording in the North American Standard for Cold-Formed Steel Framing – Wall Stud Design [AISI 2007b] to include provisions for the design of jamb studs based on the results of this research.

In recent years, light gauge cold-formed steel members have been used extensively in low and mid- rise residential building construction. In cold-formed steel design there are several applications where built-up box girders are used to resist load induced in a structure when a single section is not sufficient to carry the design load. The cold-formed steel box girders may be subjected to eccentric loading when the web of one of the sections receives the load and transfers it through the connection to another section. There may be an unequal distribution of load in built-up girder assemblies loaded from one side. In the current North American Specification for the Design of Cold-Formed Steel Structural Members (CSA-S136-01, 2001), there is no guideline or design equation to calculate the flexural capacity of this type of section. AISI cold-formed steel framing design guide (2002) has recommended that the moment of resistance and inertia of the built-up section are the simple addition of the component parts, based on deflection compatibility of the two sections. However, this design approximation has not been justified by any experimental or numerical study. Very little information was found in literature about this topic. The objective of this study is the investigation of the flexural behaviour of built-up box girders assembled from cold-formed stud and track sections when subjected to eccentric loading. Finite element analysis is conducted for this purpose, being much more economical than expensive experimental testing. Detailed parametric studies are carried out to identify the factors affecting the flexural capacity of built-up cold-formed steel sections. The parametric results are used to develop a design equation for calculating the flexural capacity of built-up cold-formed steel sections.

Vibrations associated with lightweight floor systems, as a serviceability criterion, are not well addressed in current residential construction practice. Cold-formed steel floor systems are usually lighter and have less inherent damping. If designers are going to use the current span deflection criteria when designing residential floor systems, it is imperative to find the construction and design details that will limit these annoying vibrations in cold-formed steel floor systems. Presented in this seminar are the results from a recent laboratory study and field study on the vibration characteristics of cold-formed steel floors performed at the University of Waterloo. Several full-scale floor systems with varying construction and design details were constructed and tested, and several in situ floor systems were tested. The objectives of this research were: to evaluate the dynamic response of residential floor systems supported by cold-formed steel joists; to investigate the influence of span length, joist types, subfloor materials, toppings, ceilings, strongbacks, live loads and framing conditions on the vibration characteristics of cold-formed steel floor systems; to identify the critical construction details that will limit annoying floor vibrations; to compare the vibration characteristics of in situ floor systems and laboratory constructed floor systems; and to evaluate the vibration performance of laboratory and in situ floor systems based on current acceptability criteria.

Cold-formed steel structural members are used extensively in building construction, with a common application being wind load bearing steel studs. The studs frame into horizontal steel track members at the top and bottom of the wall assembly, with the stud-to-track connection typically being made with self-drilling screws or welds. The wall studs are designed to carry lateral loads only and must be checked for web crippling at the end reactions. While a design expression currently exists for the single stud-to-track connection, there is no similar design expression for multiple jamb stud members. An experimental investigation was carried out, consisting of 94 jamb stud assembly tests subjected to end-one-flange loading. The stud-to-track connections consisted of single C-section studs located at the end of a track simulating a door opening, and a built-up jamb made up of two studs simulating framing at either a window or door opening. The members were attached to the track with self-drilling screws. The research objective was to determine the failure modes and develop a design expression for these structural assemblies. The scope of the experimental investigation covered the following range of parameters: i) Stud and track depths of 92 mm and 152 mm; ii) Stud and track thickness (0.84 mm, 1.12 mm, 1.52 mm and 1.91 mm); iii) Configuration of jamb studs (back-to-back, toe-to-toe and single); iv) Location of jamb studs in the track (interior and end); v) Screw size (#8, #10 and #12); vi) Screw location (both flanges and single flange). Based on the findings of this investigation, design expressions are proposed to predict the capacity of this connection for two limit states: web crippling of the jamb stud; and, punch-through of the track. The web crippling design expression was taken from the North American Specification for the Design of Cold-Formed Steel Structural Members [AISI 2007a; CSA 2007] with new coefficients developed from the test data of the jamb stud-to-track assemblies. A new design expression is also proposed for the track punch-through failure mode, which differs from the approach currently used in the North American Standard for Cold-Formed Steel Framing – Wall Stud Design [AISI 2007b]. A proposal is also recommended to revise the wording in the North American Standard for Cold-Formed Steel Framing – Wall Stud Design [AISI 2007b] to include provisions for the design of jamb studs based on the results of this research.

No description available.

The use of cold-formed steel structures is increasing rapidly around the world due to the many advances in construction and manufacturing technologies and relevant standards. However, the structural behaviour of these thin-walled steel structures is characterised by a range of buckling modes such as local buckling, distortional buckling or flexural torsional buckling. These buckling problems generally lead to severe reduction and complicated calculations of their member strengths. Therefore it is important to eliminate or delay these buckling problems and simplify the strength calculations of cold-formed steel members. The Hollow Flange Beam with two triangular hollow flanges, developed by Palmer Tube Mills Pty Ltd in the mid-1990s, has an innovative section that can delay the above buckling problems efficiently. This structural member is considered to combine the advantages of hot-rolled I-sections and conventional cold-formed sections such as C- and Z-sections (Dempsey, 1990). However, this structural product was discontinued in 1997 due to the complicated manufacturing process and the expensive electric resistance welding method associated with severe residual stresses (Doan and Mahendran, 1996). In this thesis, new fastening methods using spot-weld, screw fastener and self-pierced rivet were considered for the triangular Hollow Flange Beams (HFBs) and the new rectangular hollow flange beams (RHFBs). The structural behaviour of these types of members in axial compression was focused in this research project. The objective of this research was to develop suitable design models for the members with triangular and rectangular hollow flanges using new fastening methods so that their behaviour and ultimate strength can be predicted accurately under axial compression. In the first stage of this research a large number of finite element analyses (FEA) was conducted to study the behaviour of the electric resistance welded, triangular HFBs (ERW-HFBs) under axial compression. Experimental results from previous researchers were used to verify the finite element model and its results. Appropriate design rules based on the current design codes were recommended. Further, a series of finite element models was developed to simulate the corresponding HFBs fastened using lap-welds (called LW-HFBs) and screw fasteners or spot-welds or self-piercing rivets (called S-HFBs). Since the test specimens of LW-HFBs and S-HFBs were unavailable, the finite element results were verified by comparison with the experimental results of ERW-HFB with reasonable agreement. In the second stage of this research, a total of 51 members with rectangular hollow flanges including the RHFBs made from a single plate and 3PRHFBs made from three plates fastened with spot-welds and screws was tested under axial compression. The finite element models based on the tests were then developed that included the new fasteners, contact simulations, geometric imperfections and residual stresses. The improved finite element models were able to simulate local buckling, yielding, global buckling and local/global buckling interaction failure associated with gap opening as agreed well with the corresponding full-scale experimental results. Extensive parametric studies for the RHFBs made from a single plate and the 3PRHFBs made from three plates were undertaken using finite element analyses. The analytical results were compared with the predictions using the current design rules based on AS 4100, AS/NZS 4600 and the new direct strength method. Appropriate design formulae based on the direct strength method for RHFBs and 3PRHFBs were developed. This thesis has thus enabled the accurate prediction of the behaviour and strength of the new compression members with hollow flanges and paved the way for economical and efficient use of these members in the industry.

This thesis is focused on quantifying the dynamic performance of lightweight metal sandwich systems under confined explosions, where this effort represents the first of a multi-phase comprehensive research program that is focused on developing blast damage mitigation techniques in submerged structures. A confined explosion occurrence inside such facilities may lead to paralyzing all operations depending on the functions of the affected sections. Subsequently, using sacrificial cladding placed as a physical barrier over critical components that might be vulnerable to a potential explosion is considered to be an effective blast damage mitigation technique. Furthermore, sandwich panels can be an ideal system to be used as sacrificial cladding, as it can be manufactured to possess high stiffness-to-weight ratio and superior energy absorption capabilities. Consequently, an experimental program was performed to investigate the performance of lightweight cold-formed steel sandwich panels under both quasi-static loads and confined explosions, where a total of fifty-seven sandwich panels were tested, considering various core configurations, different core sheet thickness, and different blast load intensity levels. The American ASCE/SEI 59-11 and The Canadian CSA/ S850-12 blast design standards predict the dynamic response of a structure component based on the static resistance function by applying dynamic increase factors. Subsequently, the static resistance functions for the proposed panel configurations were investigated experimentally and compared with the introduced analytical model, in order to quantify accurately the inelastic panel response. The quasi-static test program was performed in two stages, where the first included eighteen single layer core sandwich panels, which represented longitudinal and transverse corrugated core configurations. The results of the first stage configurations demonstrated an efficient strength and stiffness, but showed a lack in energy absorption capabilities and ductility capacity. Therefore, in the second stage, different core configurations were developed, including twenty-one panels representing Bi-directional and X-core double layered core configurations and its counterpart Uni-directional single layer core configuration. The results of the second stage demonstrated an enhancement in the ductility and energy absorption capabilities compared to the configurations tested in the first stage. The residual deformations and failure modes demonstrated were assessed and discussed in details, where web crippling, local buckling and global buckling induced by shear or flexurewere determined. In general the static resistance functions for each tested panel were used to quantify the panels’ yield loads, ultimate capacities, and corresponding displacement levels. Moreover, the influences of both the core configuration and the core sheet thickness on the panels’ stiffness, ductility levels and energy absorption were quantified. Based on the conclusions of the static testing and considering the ductility, capability of energy absorption, and the behavior beyond the elastic zone, two different core configurations were chosen to be tested under confined explosions. Eighteen panels were tested in a cylindrical shape blast chamber representing a typical submerged structure under different scaled distances ranged from 2.82 to 1.09 m/kg1/3, in order to demonstrate different damage state levels in accordance with the blast design standards (ASCE/SEI 59-11, CSA/ S850-12). In the blast testing results, the incident and reflected pressure time histories of the blast wave were measured, while the modified Friedlander equation was used to fit the first positive phase of the reflected pressure histories. In addition, the displacement response histories of the back face of the tested panels were recorded. The measured values of peak incident pressure, peak reflected pressure, incident impulse and the reflected impulse were compared to the predicted values using ConWep (Hyde 1990) considering the spherical explosion, and have shown a good agreement. Furthermore, the failure modes and the post blast damage were determined and compared to the static observations. In order to complement the experimental program, a nonlinear inelastic single degree of freedom model was developed in order to predict the dynamic response of the sandwich panels. The model used the recorded blast load and the static resistance while applying the dynamic increase factors recommended by the standards (ASCE/SEI 59-11, CSA/ S850-12). The model results were in a good agreement with the experimental data. Furthermore, the different ductility and support rotation values obtained experimentally and predicted analytically were related to the different damage levels specified by blast standards. Finally, the influence of sandwich panel core configuration on the dynamic blast response of the tested sandwich panels was discussed. / Thesis / Doctor of Philosophy (PhD)

This research introduces a proposed model for predicting tilting angle and limit states of single-fastened cold-formed steel-to-steel shear connections. Predictions are validated through an experimental study considering ply configuration and a single Hex #10 -washer head fastener, centered in a 102 mm by 102 mm three boundary window. The fastener tilting angle is captured using an automated, optical non-contact measurement procedure. The results are used to identify cold-formed steel shear connection deformation as load progresses, including tilting, bearing, and combined tilting bearing at the plies and thread tension, shear and bearing fastener failure. Results shows that fastener tilting plays a kinematic affect for the connection. Fastener tilting is predicted in function of ply thickness and fastener pitch. Local ply bending deformation is reported to be the main deformation of the connection during fastener tilting. While fastener bending and shear failure occurred if the fastener does not tilt. / Master of Science

The current specification provisions for the prediction of lateral restraint forces in Z-purlin supported roof systems under gravity loads are in Section D3.1 of the 1996 AISI Cold-Formed Specification. The design equations contained in these provisions are empirical and based on statistical analysis. They were developed using elastic stiffness models of flat roofs and were verified by experimental testing. The provisions need refinement, because the treatment of roof slope and system effects is incorrect. Also, the current design provisions are based upon an assumed panel stiffness value, ignoring the significant difference in required restraint force that occurs when panel stiffness is varied. Therefore, a new restraint force design procedure, having a stronger reliance on engineering principles, is proposed. This new treatment of the static forces in Z-purlin roofs led to a more accurate method of addressing roof slope. Elastic stiffness models, with varying roof slope, panel stiffness, and cross-sectional properties, were used to develop the proposed procedure. The basis of the procedure is to determine the lateral restraint force required for a single purlin system and then extend this result to systems with multiple restrained purlin lines. Roof slope is incorporated into the calculation of the single purlin restraint force, which includes eccentric gravity loads and forces induced by Z-purlin asymmetry. The procedure includes a system effect factor to account for the observed nonlinear increase in restraint force with the number of restrained purlins. An adjustment factor varies the predicted restraint force depending on the shear stiffness of the roof panel. The proposed procedure applies to five bracing configurations: support, third-point, midspan, quarter point, and third-point plus support restraints. / Master of Science

This thesis introduces an approach for modeling the monotonic and cyclic response of cold-formed steel framing screw-fastened connections in commercial finite element programs. The model proposed and verified herein lays the groundwork for seismic modeling of cold-formed steel (CFS) framing including shear walls, gravity walls, floor and roof diaphragms, and eventually whole building seismic analysis considering individual fastener behavior and CFS structural components modeled with thin-shell elements. An ABAQUS user element (UEL) is written and verified for a nonlinear hysteretic model that can simulate pinching and strength and stiffness degradation consistent with CFS screw-fastened connections. The user element is verified at the connection level, including complex cyclic deformation paths, by comparing to OpenSees connection simulation results. The connection model is employed in ABAQUS shear wall simulations of recent monotonic and cyclic experiments where each screw-fastened connection is represented as a UEL. The experimental and simulation results are consistent for shear wall load-deformation response and cyclic strength and stiffness degradation, confirming the validity of the UEL element and demonstrating that light steel framing performance can be directly studied with simulations as an alternative to experiments. / Master of Science