| A simple “engineering” method was formulated for computing the axial load vs. axial shortening relationship of pin-ended tubular members damaged by a dent and/or out-of-straightness. The method predicts the pre- and post-ultimate load-shortening response, and can be used in analyzing the strength and behavior of offshore platform frames containing damaged members. The method was developed from a parametric study and regression analysis of a database containing load-shortening data from published tests results on damaged columns and data generated from a finite element analysis.; The effects of geometric nonlinearity and elasto-plastic material properties were included in the finite element analysis of the pre- and post-ultimate response of damaged tubular columns. Prior to generating data for the parametric study and regression analysis, the finite element model was verified by comparing calculated (finite element) load-shortening responses with experimental data.; The regression model used as a basis for the simplified engineering method, was developed by considering the geometry of the load vs. axial shortening curves for a wide range of column geometries and yield strengths. A parametric study was conducted to determine the influence of each independent variable on the axial behavior of damaged members. The object of the study was to select the shortest suitable approximating function for each independent variable. The variables considered were: column slenderness, D/t ratio, dent-depth to diameter ratio, out-of-straightness, yield stress, and axial shortening. The regression analysis of the load-shortening relationships in the database resulted in a set of 80 constants which is reduced to a five-term approximating function for the load-shortening response, once specific values are given for the member geometry, material and damage. The procedure is illustrated with an example and comparisons with test results. Implementation of the method only requires computational resources for matrix multiplication and basic function evaluation typically within the capability of a handheld calculator. The method is valid for member geometries and material properties typically found in fixed offshore platforms. |
