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.

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.

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.

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