Lateral Torsional Buckling of Castellated Beams Analyzed Using Collapse Analysis

Abstract

In designing a steel beam, one of the limit states is lateral torsional buckling. When a beam is subjected to bending moment about its strong axis at a certain value, the beam would be displaced laterally and accompanied by torsion. The value of the bending moment limit is called critical moment. AISC specification only provides formulas for calculating the critical moment in prismatic beams, but not for non-prismatic beams like castellated beams. The objective of this paper is to study about lateral torsional buckling of castellated beams. The methodology of this study is collapse analysis using finite element method, and analyzed by ADINA 8.9. In collapse analysis, a geometrically imperfect beam is loaded with increasing load. At a certain value of load, the lateral displacement increase progressively. The value of maximum load is considered as critical load. In this study, the imperfection is taken 1/1500 of the unbraced length of the beam. The critical moment of castellated beam obtained from finite element analysis is up to 42,31% lower than critical moment of full beams with the same dimension calculated by using AISC formula. Therefore, a correction factor for AISC formula to calculate the critical moment of castellated beam is established.