L-header Testing, Evaluation and Design Methodology

Cold-formed steel L-shaped headers have gained popularity over the past few years due to their simplicity and cost effectiveness. While cold-formed steel conventional headers are widely used and can be designed for most applications, often it is necessary to reduce cost by using less material and labor hours. The L-shaped header provides both, a fast and economical solution to safely transfer applied loads to other structural elements in a building. As the name suggests, the main components of an L-shaped header is a piece of cold-formed steel formed into a shape resembling the letter L. An L-header assembly consists of a cold-formed steel angle with one short leg lapping over the top track and one long leg extending down the side of the wall above openings. The current design equations in the AlSI Specification do not provide a reasonable design values for L-header assemblies. Testing of the assemblies was necessary to develop an easy to use design equations that can be used by designers. A total of 71 gravity tests and 38 uplift tests of L-header assemblies having variable sizes and thicknesses and spans were conducted at the NAHB Research Center. Results of the tests as well as a proposed design procedure is presented here

Bending and Web Crippling Interaction of Cold-formed Steel Members

The North American Specification has recently adopted a new web crippling approach for the Design of Cold-Formed Steel Structural Members (NAS, 2001). This approach is similar to what is currently in the Canadian S136 Standard (CSA, 1994). The current web crippling and bending interaction equations for single-web sections in the North American Specification (NAS 2001) are based on the previous web crippling methods that are contained in the American Iron and Steel Institute (AISI) Specification (AISI, 1996). As well, the moment component of the interaction equations was based on the previous reduced web strength method instead of the stress gradient approach that is now contained in the North American Specification (NAS, 2001). Using the available data found in the literature, regression analyses were carried out using the new web crippling equations and the stress gradient method to substantiate the current web crippling and bending interaction equations in the North American Specification (NAS, 2001). Based on the results of this investigation, new web crippling and bending interaction equations have been developed

Calibrations of Bolted Cold-formed Steel Connections in Bearing (With and Without Washers)

The bearing strength of bolted connections is treated differently in the two current North American Cold-Formed Steel Design documents, the AISI Specification in the USA (AISI 1996a) and the S136 Standard in Canada (CSA 1994). In the case of the S136 Standard (CSA 1994), only one expression is presented that applies to all bolted connections such as single and double shear, as well as, with and without washers. In the AISI Specification (AISI 1996a), however, a distinction is made between single shear and double shear connections and the use of washers. Contained in this paper are the calibration results of single and double shear cold-formed steel bolted connections with and without washers that failed in bearing. Calibrations were carried out in accordance with the AISI Commentary (AISI 1996b) to establish the resistance factors and respective factor of safety, which have already been adopted by the North American Specification (NAS 2001)

Behavior of web elements with openings subjected to linearly varying shear

PREFACE An experimental investigation of the shear buckling limit state was conducted on single web, cold-formed steel flexural members with web openings. The purpose of the investigation was to develop a better understanding of the behavior of web elements having a web opening, and to propose appropriate design recommendations based on the observed behavior. The present AlSI ASD and LRFD specifications do not contain design provisions for webs with openings, thus the findings of this study will aid in enhancing the shear design provisions. The test specimens, constructed from C-sections, were subjected to linearly varying shear resulting from the application of a uniform load. Test data from this investigation was combined with previous test data which was based on test specimens subjected to a constant shear. Three hole geometries, rectangular with comer fillets, circular, and diamond, were represented by the available test data. All openings were centered at mid-depth of the web. Based on the findings of this study, it was concluded that the slenderness ratio of the web element above or below the opening was dominant parameter influencing the shear behavior. It was also discovered that the distribution of the shear across the opening affected the shear capacity of the web. Based on the findings and conclusions obtained from the experimental investigations, a design expression was developed. The design expression recognizes the reduction in shear capacity of a web when an opening is present in the web. This report is based on a thesis presented to the faculty of the University of Missouri-Rolla in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering. The report was prepared for the AlSI Committee on Specifications for the Design of Cold-Formed Steel Structural Members. The investigation was sponsored by the American Iron and Steel Institute (AlSI). The technical guidance provided by the AlSI Stud Design; Perforated Elements Subcommittee is acknowledged. The Subcommittee members are: E. R. Estes, Jr. (Chairman), F. M. Bolio, R. E. Brown, C. R. Clauer, E. R. diGirolamo, L. Hernandez, W. Guiher, J. Klaiman, R. A. LaBoube, R. Madsen, J. P. Matsen, W. R. Midgley, T. H. Miller, K. T. Niu, T. B. Pekoz, C. W. Pinkham, G. S. Ralph, V. Sagan, R. J. Schrader, R. M. Schuster, T. W. Trestain, S. Walker, R. Zadeh. Thanks are also extended to D. F. Boring, R. B. Haws, H. Chen, K. C. Slaughter, and S. P.Bridgewater, AlSI staff. The cold-formed steel C-sections that were used in the test program were kindly donated by Dale/Incor Industries and Dietrich Industries. Their generosity is acknowledged. Thanks are also extended to J. J. Bradshaw, J. M. McCracken, and S. Gabel, staff of the Department of Civil Engineering, for their technical support

Calibrattions of Cold-Formed Steel Welded Connections

The purpose of this project was to recalibrate the welded connection equations currently contained in the American Iron and Steel Institute (AISI) Specification for the Design of Cold Formed Steel Structural Members (AISI 1996a). Only one factor of safety of 2.50 is presented for the each of the various types of welded connections when using allowable stress design (ASD), but different respective resistance factors are given for load and resistance factor design (LRFD). The data used was solely taken from the research conducted by Pekoz and McGuire (Pekoz and McGuire 1979). Calibrations were carried out and based on both the AISI Specification (AISI 1996a) and the Canadian Sl36 Standard (CSA 1994). The results of this study have already been adopted by both of these cold formed steel design agencies, as well as by the North American Specification for the Design of Cold-Formed Steel Structural Members (NAS 2001)

Top Arc Seam Weld Shear Strength and Stiffness for Sheet-to-sheet Connections

The North American Specification for the Design of Cold-Formed Steel Structural Members does not provide specific design guidance for sheet-to-sheet top arc seam welds in shear. A collaborative industry study has developed design guidance for both strength and stiffness of the connection to facilitate analytical evaluation of floor and roof diaphragm assemblies and wall assemblies. The test program was performed per AISI S905 and addressed material ductility, weld length, sheet thickness and the distribution of the force being transferred by the weld connection

Rubble Pile Characterization Model

Rubble piles created following the collapse of a building in a combat situation can significantly impact mission accomplishment, particularly in the area of movement and maneuver. Rubble characteristics must be known, for example, in order to predict the ability of a vehicle to override the collateral damage from weapon effects in urban areas. Two types of models are developed: a first-order model and a first-principles-based model. In both models, we assume complete rubblization of the building and develop a rubble profile model using the size and composition of the collapsed structure to predict the rubble volume. In both cases, this profile model includes the size of the footprint area surrounding the original building assuming that the rubble is free to expand horizontally as well as the resulting height of such a rubble pile. Empirical data is now needed to verify the predictive capabilities of these models