Preliminary R-values for Seismic Design of Steel Stud Shear Walls

Design codes recognize the ability of some structures to undergo significant inelastic deformation during a seismic event without reaching the point of collapse. In consideration of this behaviour, building codes provide force modification factors (R-values) to determine the reduced lateral loads that engineers may use in design. This paper presents an overview of the seismic requirements for various design standards and an explanation of how R-values may be determined from test results. The findings of an evaluation of existing steel stud shear wall test data, in addition to preliminary force modification factors for use in seismic design, are presented

Influence of Gypsum Panels on the Response of Cold-Formed Steel Framed Strap-Braced Walls

In cold-formed steel construction the steel frame is supplemented with either diagonal strap braces or structural sheathing panels (typically steel or wood) to provide overall stability to the structural system and to directly transfer lateral wind and seismic loads through to the foundation as per the design provisions found in AISI S240 (2015) and AISI S400 (2015). Gypsum panels are often specified to provide a fire-resistance rating for the CFS frame, as well as to ensure that adequate sound-proofing exists between adjacent rooms or building units. The engineer may choose to rely on this gypsum to provide additional lateral resistance, as permitted in the AISI Standards. However, in the majority of cases the gypsum panels are considered to be non-structural elements of the building specified by the architect, and as such, are not taken into account in the design of the lateral load carrying system. Whether considered in the design process or not, these gypsum panels do augment the shear resistance of the lateral load carrying system. This study was carried out to evaluate the performance of combined strap-braced / gypsum-sheathed wall systems, with the intent of defining a corresponding design approach. Described herein are the findings of the laboratory phase of the project, comprising 35 wall specimens

Behaviour of Thin G550 Sheet Steel Screwed Connections

This paper provides a summary of results detailing the behaviour of screwed connections tested in shear, which were composed of thin G550 and G300 sheet steels (to the 1993 Australian Standard AS 1397). Recommendations concerning the adequacy of current design standards with respect to the design of thin sheet steel screwed connections are made

Ductility Measurements of Thin G550 Sheet Steels

Cold formed structural members are fabricated from sheet steels which must meet various material requirements prescribed in applicable national design standards. These requirements ensure that; I) stress concentrations can be redistributed and 2) members and connections can undergo a minimum amount of displacement without a loss in structural performance. The Australian / New Zealand, AS/NZS 4600, and both North American, CSA-S136 and AlSI, Cold Formed Steel Design Standards allow for the use of thin (t \u3c O.9mm), high strength (fy = 550MPa) sheet steels if the yield stress and ultimate strength are reduced to 75% of their minimum specified values. This paper provides a summary of results detailing the ductility and net cross-section tensile resistance of G550 sheet steels (to Australian Standard AS 1397) tested as solid and perforated coupons. Material properties of the test specimens are compared wIth the Dhalla and Winter requirements for ductility and ultimate strength to yield stress ratio. limit states tensile design equations are calibrated according to procedures defmed by the American Iron and Steel Institute (AlSI) Commentary

Behaviour of Thin G550 Sheet Steel Bolted Connections

This paper provides a summary of results detailing the behaviour of bolted connections tested in shear, which were composed of 0.42 mm G550, 0.60 mm G550 and 0.60 mm G300 sheet steels (to the 1993 Australian Standard AS 1397). Recommendations concerning the adequacy of current design standards with respect to the design of thin sheet steel bolted connections are made, along with the calibration of applicable limit states resistance equations for the three observed modes of failure; end pull-out, bearing, and net section fracture

Comparison of the Distortional Buckling Method for Flexural Members with Tests

For thin-walled flexural members composed of certain geometric proportions and/or made of high-strength steel, a mode of buckling at half-wavelengths intermediate between local buckling and flexural-torsional or flexural buckling can occur. The mode is most common for edge (lip) stiffened members such as C and Z-sections, and involves rotation of the lip-flange component about the flange-web junction. This mode is commonly called distortional buckling. Presented in this paper is a design method for distortional buckling of flexural members recently submitted for ballot with the AISI Specification Committee for Cold-Formed Steel Structures. Currently, the North American Cold-Formed Steel Design Standards do not contain such a distortional buckling provision. The distortional buckling procedure is compared with the current North American Design Standards using the results of beam tests carried out at the University of Waterloo and data available in the literature. Statistical results of the investigation indicate that the distortional buckling method is slightly conservative yet provides a better fit to the test data in comparison with current Design Standards. More importantly, the distortional buckling procedure accounts for recently observed significantly unconservative test results. It is recommended that the design method for the distortional buckling of flexural members, using Strength Curve 1 as presented herein, be adopted by the North American Design Standards

Cold Formed Steel Flat Width Ratio Limits, d/t and d\u3csub\u3ei\u3c/sub\u3e/w

This paper reports the findings of an investigation of the flat width ratio limit for simple edge-stiffeners of channels in bending. Willis & Wallace concluded that the lip flat width ratio limit, d/t, should have a value of 14 based on a comparison of the 1980 and 1986 editions of the American Iron and Steel Institute (AISI) Cold Formed Steel Specification. This conclusion was made using the results of only three channel beam tests with various lip sizes, Case III flanges and locally unstable webs. The CAN/CSA-S136 Technical Committee adopted the recommendations of Willis & Wallace and included the lip flat width ratio limit in the 1989 and 1994 S136 Standards. A test program was initiated at the University of Waterloo to investigate the findings of Willis & Wallace. The investigation consisted of the testing and analysis of 44 C-section beams with Case I, II and III flanges, locally stable and unstable webs, and systematically varied lip depths. The d/t and dáµ¢/w ratios of these C-sections were compared with the applied test moments and flange Cases . The objectives of this study were to determine when the use of the existing d/t limit is required, if its current value is accurate, and whether it should remain in the next edition of the S136 Standard. Analysis of the Waterloo, as well as, the Willis & Wallace test data revealed that a d/t or dáµ¢/w limit is not required in the S136 Standard

Interaction of Flange/edge - Stiffened Cold Formed Steel C - Sections

A revision to the Canadian Standard (S136-94)[1] and the American Specification (AISI- 89)[2], in which the procedure to calculate the effective width of an edge-stiffened compressive flange is modified, has been proposed by Dinovitzer et al.[3]. The proposal involves a change of the equations for the flange plate buckling coefficients of Case II compressive elements, which eliminates a discontinuity in the effective width formulation. The modified local buckling procedure was compared with the current Canadian Cold Formed Steel Standard using a program of beam tests at the University of Waterloo[4] and data available in the literature[8,9, 10, 11,12]. Statistical results of the comparison indicate that the revised method is more accurate than current design standards and use of this procedure simplifies the current plate buckling equations. It is recommended that the Dinovitzer approach be adopted by the North American Design Standards