Structural strength and crushing behavior of hybrid cold-formed steel stub columns under dynamic loading conditions

It has been recognized that the mechanical properties of sheet steels and the structural strength of cold-formed steel members can be influenced by strain rate. Since most studies were limited only to the structural members which were assembled from the same material in a given section, this investigation was concentrated on a study of structural strength and crushing behavior of hybrid cold-formed steel stub columns affected by strain rate. In addition, some stub-column specimens fabricated from the same material were also tested for the comparison purpose. The results showed that the ultimate loads and mean crushing loads of cold-formed steel stub columns increase with increasing strain rates. The amount of increase was found to be dependent on the material strength, the type of steel, the width-to-thickness ratio, and the strain rate used in the test. In the determination of ultimate loads for hybrid sections, the effective cross-sectional area calculated on the basis of the dynamic yield stresses can be employed. An empirical equation was also developed to predict the mean crushing loads for single and bi-material, box-shaped and hat-shaped stub columns under dynamic loading conditions.