Critical moment of I steel beam considering continuity effect

Abstract

Design of steel beam should consider lateral torsional buckling. In practice, to increase the critical bending moment usually lateral bracings is installed at some location. In AISC Specification for Structural Steel Buildings, the calculation of critical bending moment is based on part of the beam between two consecutive lateral bracing and it is assumed that the ends of the part of the beam is simply supported, torsional rotation is prevented but warping is free. Every part of the beam must be checked and the part that gives lowest critical moment is the critical part. Actually there is some restraint from the adjacent part of the critical part. Guide to Stability Design Criteria gives effective length method to consider stiffness of this adjacent part. In this paper effective length method is discussed and compared to the result of the finite element method. The result is that the effective length method is conservative and the difference between the result of finite element method and effective length method can be considerably high.