| The current design criteria for effective design width being used in the AISI Automotive Steel Design Manual{dollar}sp1{dollar} for the design of cold-formed steel members are based on tests under static loading condition. The primary objective of this investigation was to study the validity of these effective design width formulas for members subjected to dynamic loads. This dissertation presents a detailed description of an experimental study. Selected steels with nominal yield strengths ranging from 25 ksi to 100 ksi were uniaxially tested under different strain rates. In order to study the structural behavior and strength of cold-formed steel members having stiffened and unstiffened compression elements, a total of 97 stub column specimens and 60 beam specimens were fabricated from 35XF and 50XF sheet steels and tested under dynamic loads. It was found from test results that the mechanical properties of sheet steels and strengths of cold-formed steel members increased with increasing strain rate. The amount of increase is dependent on the material yield strengths, the stress-strain relationships, and the strain rates used in the tests. In the evaluation of the test data, it was found that the value of buckling coefficient, 0.43, used to calculate the effective width of unstiffened compression elements is conservative. For calculating the ultimate capacity of stub columns and beams, the values computed from Kalyanaraman's equations for unstiffened compression elements provide good agreements with test results. In addition, a better prediction for ultimate capacity of stub columns and beams can be obtained by using the dynamic yield strengths. |
