The 2000s

Sloof and Schuster (2000) investigated the yield strength increase of cold-formed sections due to cold work of forming. Extensive testing was performed to substantiate the simplified design approach developed by Lind and Schroff in the early 70s at the University of Waterloo, which is Eq. 1. This additional test data provided the needed information to conclude that Eq. 1 is indeed the best predictor expression when compared to the more complex approach used by AISI.

Beshara and Schuster (2000) performed additional web crippling tests to obtain data of C – and Z – sections subjected to interior two-flange loading and end two-flange loading. In addition, new web crippling coefficients were generated using the data from this study and all of the available published data. Calibrations for resistance factors and factors of safety were also carried out (Beshara and Schuster, 2002). The results of this work have been adopted by the North American Specification for the Design of Cold-Formed Steel Structural Members.

Craig and Schuster (2000) carried out calibrations of the cold-formed steel shear equations in an effort to correct a discontinuity in the nominal shear equation that was being considered by the North American Specification for the Design of Cold-Formed Steel Structural Members. Again, the results were adopted by the Specification.

Fox and Schuster (2000) investigated the lateral strength of wind load bearing wall stud-to-track connections. Typically in this case, stud sections are framed into a channel track section, resulting in the possibility of web crippling at the end of the stud connection due to the action of the wind load. The governing cold-formed steel Design Standards/Specifications in North America do not cover this case specifically. The web crippling provisions are based on the member being supported by a rigid bearing plate. Based on this, testing was carried out to develop a design approach for this specific end condition load case. The recommended procedure recognizes two different observed failure modes, i. e., 1) web crippling of the stud and 2) punch-through of the track. The basic web crippling expression was used (Eq. 7) with different web crippling coefficients and a new expression was developed for the punch-through case. Again, the results were adopted by the North American Specification for the Design of Cold-Formed Steel Structural Members.

Fox and Schuster (2000, 2003) continued their work of 1998 to establish a simplified design approach for bearing stiffeners in cold-formed C-Sections. It was found that in all of the tests with stud or track stiffeners the failure mode was local buckling of the stiffener in compression. There are a number of variables affecting the strength of the assembly, but in general, the study found that a simple expression for the nominal bearing resistance of the stiffener types tested can be used.

Xu et al. (2000) carried out a study on the optimum design of cold-formed steel residential roof trusses. A computer-based optimal design approach for residential roof trusses was developed, using cold-formed steel C-sections. The truss design was based on the CSA S136-94 and the truss design guide published by the American Iron and Steel Institute and the Canadian Sheet Steel Building Institute. A generic algorithm was adopted to obtain the minimum cost design with due consideration to truss topology and member size simultaneously.

Xu et al. (2000, 2005) investigated the dynamic/vibration behaviour of floors with cold-formed steel joists. Both static and dynamic tests were conducted on cold-formed C-section floor joists with different span lengths based on different design criteria. The static tests were done to obtain the stiffness and the degree of load sharing between the joists, and the purpose of the dynamic tests was to establish the frequencies of the floor systems. To identify the critical parameters that contribute to the control of floor vibration, tests were also carried out on floors without attached ceiling materials, with different bridging and blocking patterns, and with different support conditions. Test results are presented in comparison with the analytical results obtained from different design methods.

Xu et al. (2001) carried out compressive tests of cold-formed corrugated steel curved panels. In the absence of a standard test protocol, presented in this paper are two types of compressive tests, i. e., 1) corner and flange-section tests, and 2) full-panel tests. The purpose of these tests was to investigate the influences of panel curvatures and transverse corrugations on the buckling behaviour of the cold – formed corrugated steel curved panels. The full section tests yielded consistent results, with the deviation of the individual test ultimate load less than 6% and 8% of the average ultimate load with regard to CSA S136-94 and AISI-96, respectively. For corner and flange section tests, the deviation of the ultimate load was generally less than 7%, except one group. Based on this, both test approaches and associated experimental set-ups could be regarded as reliable.

Xu and Cui (2002) undertook a study relating to the connection flexibility of cold-formed steel C – shape connections” Current design practice on cold-formed steel trusses assumes that web-to-chord connections of trusses are ideally pin-connected. The most recent revision of the AISI Standard for Cold-Formed Steel Framing – Truss Design permits the connection flexibility to be taken into account in the analysis and design of such trusses. However, no specific guidelines on how to incorporate this connection flexibility into the design process are provided, which is primarily due to the lack of information on the moment-rotation behaviour of such connections. This paper presents results from a series of tests on web-to-chord connections of cold-formed steel trusses. A mathematical model was developed to represent the behaviour of the connections. The objective of the investigation was to assess connection flexibility via the moment-rotation behaviour for the purpose of design of cold – formed steel trusses.

Tangorra et al. (2002) performed calibrations for resistance factors and factors of safety on cold – formed steel welded connections, using all of the published data. The North American Specification again adopted these results for the Design of Cold-Formed Steel Structural Members.

Wallace and Schuster (2002) carried out tests on bolted cold-formed steel tension member connections in bearing (with and without washers). Additional data was needed to complete the pool of data required to properly establish the best design method for bolted tension members failing in bearing. Comparisons were made with the two design methods used in North America and the resulting recommended the North American Specification adopted design approach for the Design of Cold-Formed Steel Structural Members. Calibrations for resistance factor and factor of safety were also carried out as part this study (Wallace et al., 2002).

Wallace et al. (2002) investigated the bending and web crippling interaction of cold-formed steel members. With the recent adoption of the new web crippling design approach (Eq. 7), the web crippling and bending interaction expressions contained in the North American Specification for the Design of Cold-Formed Steel Structural Members need to be re-evaluated. In addition, changes in the bending strength calculation (effective web method) have been introduced, hence, possibly affecting the interaction evaluation. The Specification contains interaction expressions for single web geometry, I-section geometry, and two nested Z-shapes. Based on the recommendations of this study, the North American Specification for the Design of Cold-Formed Steel Structural Members adopted the design approach.

Wallace and Schuster (2004) carried out tests on web crippling of cold-formed steel multi-web deck sections subjected to end one-flange loading. The resulting data was virtually the only data in this category. New web crippling coefficients have been developed along with the respective calibrated resistance factors and factors of safety. And once again, the North American Specification has adopted the results of this work for the Design of Cold-Formed Steel Structural Members.

Conclusions

It has been clearly demonstrated in this paper that in the past 35 years a great deal of research in the field of cold-formed steel has been produced at the University of Waterloo. What is even more remarkable is, that so many of the resulting information has been adopted by North American and International cold-formed steel design Standards/Specifications. I have truly enjoyed having played a small part at this remarkable University over the past 35 years and I look forward to being around and involved in future research in cold-formed steel.