Design of Perforated Thin-Walled Steel Columns (No. R949)

Abstract

The strength database from the parametric study presented in (Yao and Rasmussen 2014) was used to evaluate an overall number of 19 design methods based on the DSM for non-perforated and perforated thin-walled steel columns with the Ramberg-Osgood material model defined by n=20. These methods included the current codified DSM, the design options proposed by Moen and Schafer (2011), the methods based on simple modifications to these aforementioned methods, the methods considering buckling interactions (in addition to LG interaction), and the methods based on regression analyses. A concerted effort was made to compare the 19 DSM methods by presenting the detailed statistics of the predictions for each section type and failure mode, as well as figures illustrating the corresponding simulation to predicted ratios. This led to the best-performing method proposed for the design of perforated cold-formed carbon steel columns. This method was based on modifying the Option 4 method proposed by Moen and Schafer (2011) such that (i) DG interaction was included, (ii) Pcr-l-nh and Pcr-d-nh based on gross section were used, and (iii) a factor based on a regression analysis was added to improve the final design strength. The proposed method was based on a reliability analysis with a target reliability index of 2.5, carried out on 60132 data points. A linear regression equation was taken to calculate the additional factor in the method. Two sets of best-fit constants were proposed for the regression equation, one for general section types including C, Z, Hat, Rack, and Stiffened C sections, the other for Stiffened C section only. When calculating the design strength of a perforated column as per the proposed method, the major effort will be calculating the elastic local and distortional buckling loads Pcr-l-nh and Pcr-d-nh based on the gross section (which can be readily calculated by a SAFSM software such as THIN-WALL or CUFSM), and the elastic global buckling load Pcr-e-h including the influence of hole(s).