Civil Engineering Study 98-1
INTRODUCTION It has been recognized that material properties and stress-strain relationships of sheet steel can be influenced by the strain rate. Because the member strength is also influenced by dynamic loading, a large number of research projects were conducted for a variety of structural members under specified loading conditions during past three decades. In cold-formed steel design, local buckling is one of the major design features because of the use of large width-to-thickness ratios for compression elements. For the purpose of determining the load-carrying capacity of automotive components, the effective width approach has been used. In view of the fact that the design criteria for effective design widths included in the current AISI Automotive Steel Design Manual  are primarily based on the results of static tests of cold-formed steel members corresponding to a strain rate approximately 1.7x10-6 in./in./sec., an investigation was conducted at University of Missouri-Rolla (UMR) since 1989 under the sponsorship of the American Iron and Steel (AISI) to study the validity of these effective design width formulas for the design of cold-formed steel automotive components subjected to dynamic loads (Pan and Yu , Kassar and Yu ). The results presented in Reference  showed that the effective cross-sectional area calculated on the basis of the dynamic yield stresses can be employed in the determination of ultimate loads. Because previous research projects were limited only to the structural members which were fabricated from one material or assembled with the same material in a given section, and it is known that the application of higher strength steels to structures often results in significant material-cost savings, the study of beam specimens fabricated from two types of sheet steels subjected to dynamic loads was initiated in October 1993. In this study, a total of 72 beam specimens fabricated from two different sheet steels (25AK and 50 SK) were tested under different strain rates to study the structural strength and behavior of hybrid sections. The strain rates used in the beam tests were from 10-4 to 10-2 in./in./sec.. The test results of hybrid beam specimens were presented in the Twentieth Progress Report . In 1964, Ronald Frost and Charles Schilling  studied the behavior of hybrid plate girders consisting of higher-strength steel flanges connected with lower-strength steel webs, under pure bending and combined shear and bending. They suggested that the maximum bending strength of a hybrid beam may be considered to be (1) the moment causing the cross section to become fully plastic or (2) the moment causing initial yielding in the flange, because it has been demonstrated that the yielding which occurs in the webs of hybrid beams has little effect on the behavior of such beams. Pan and Yu  concluded that the available effective design width formulas using dynamic material properties can be adequately used for the design of hybrid structural members fabricated from two different materials subjected to dynamic loads. In addition, the procedures discussed in the 20th Progress Report  can provide a reasonable approach for calculating the critical local buckling moment, the yield moment, and the ultimate moment. However, due to the complexity for the calculation of ultimate moment using inelastic reserve capacity and the possible excessive deflection, it is suggested that for practical design, the yield moment can be used for the load-carrying capacity of hybrid beams. In this report, an alternative computing procedure was developed and utilized in the calculation of load-carrying capacity of cold-formed steel hybrid beams. The tests of hybrid beam specimens subjected to dynamic loading conditions are discussed in Chapter 2 of this report. In Chapter 3, the alternative procedures for calculating the flexural strength of hybrid beams are presented. Finally, the research findings are summarized in Chapter 4.
Civil, Architectural and Environmental Engineering
American Iron and Steel Institute
Wei-Wen Yu Center for Cold-Formed Steel Structures
Cold-Formed Steel Series
Missouri University of Science and Technology
01 Feb 1998
© 1998 Missouri University of Science and Technology, All rights reserved.
Pan, Chi-Ling and Yu, Wei-wen, "Design of automotive structural components using high strength sheet steels transformed section method for the calculation of yield moment of cold-formed steel hybrid beams" (1998). CCFSS Library (1939 - present). 98.