Axial compression capacity of steel circular tube with large initial curvature: Column curve and application in structural assessment

摘要

From the inspection of existing steel bar structures (composed of members subjected to pure axial force), some axially compressed steel circular tubes (SCT) exhibit large bending under axial compression. This is induced by the large initial curvatures of the SCTs. To assess the structural safety in these cases, a process is proposed in this paper. The process involves three steps: (1) determine the initial member curvature (without load) from the inspected member curvature (under load), (2) estimate the axial compression capacity of the SCTs with large initial curvatures, and (3) conduct structural assessment considering the effect of large member curvatures. To address step (1), an iterative procedure is proposed. The assumed initial member curvature is modified in the iteration to approximate its actual value. The effectiveness of the procedure was validated via a space truss example. To address step (2), a column curve that incorporates the large initial curvature of axially compressed SCTs is derived. The column curve was developed based on the extreme-fibre-yielding criterion and calibrated using 4800 data points obtained from the FEA. Generally, the buckling factor decreases by approximately 25% as the amplitude of the initial curvature varies from l/1000 to l/100 (l is the member length). As an illustration, the iterative procedure proposed in step (1) and the column curve derived in step (2) are adopted for assessing the safety of an existing steel latticed roof. According to the result, there could be a 20% underestimation of the design stress ratio of SCT members if the large member curvatures are ignored. (C) 2020 Elsevier Ltd. All rights reserved.