Civil Engineering Study 95-4
INTRODUCTION 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 width included in the AISI Automotive Steel Design Manual 1 are based on the test results for static loading condition, an investigation was conducted at University of Missouri-Rolla from January 1988 through December 1991 to study the validity of these effective design width formulas for the design of cold-formed steel automotive components subjected to dynamic loads. The results 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. The test results of material properties, stub columns, and beams with evaluations were summarized in the Eighteenth Progress Report 2. In the previous UMR research, stub column and beam specimens fabricated from two different sheet steels (35XF and 5OXF) were tested under different strain rates to study the behavior of stiffened and unstiffened compression elements. Because the previous studies were limited only to the structural members which were assembled with the same material in a given section, this portion of the research was concentrated on a study of the structural strength of hybrid automotive structural components using different sheet steels. In the first phase of the investigation, two selected sheet steels (25AK and 5OSK) have been tested in order to study the effect of strain rate on the tensile and compressive mechanical properties. The nominal yield strengths of these two types of sheet steels were 25 and 50 ksi and the range of strain rates used in the tests varied from 10- 4 to 1.0 in. /in./sec. The test results obtained from this study were presented in the Seventeenth Progress Report 3. The structural behavior and strength of cold-formed steel stub columns assembled with these two selected sheet steels were studied experimentally and analytically under dynamic loads. In the second phase of the investigation, ninety-six (96) box-shaped stub columns and forty-eight (48) hat-shaped stub columns were tested under the strain rates varied from 10-4 to 10-1 in./in./sec. at the University of Missouri-Rolla. In addition, fifty-two (52) drop tower tests of stub columns were conducted at General Motors Corporation. Details of stub column tests with evaluations were presented in the Nineteenth Progress Report 4. The test results showed that a good prediction for the ultimate strength of hybrid stub columns can be achieved by employing the dynamic material properties in the calculation of the effective cross-sectional area. The study of beam specimens fabricated from two types of sheet steels (25AK and 50SK) subjected to dynamic loads was initiated in October 1993. A total of 72 hat-shaped beams were tested to investigate the structural behavior and strength of hybrid sections using different sheet steels. The range of strain rates used in the beam tests were from 10-4 to 10-2 in./in./sec. The test results of beam specimens are reported herein. A review of the available literature on the effect of impact loads or dynamic loads on the structural strength of beams is presented in Chapter II of this report. The experimental investigation of the structural behavior of hat-shaped beam specimens subjected to dynamic loads is discussed in Chapter III. In Chapter IV, the test data for beam specimens are evaluated and presented. Finally, the research findings are summarized in Chapter V.
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 Jun 1995
© 1995 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 effect of strain rate on the structural strength of cold-formed steel hybrid beams" (1995). CCFSS Library (1939 - present). 97.