DESIGN GUIDE AND AID FOR MOMENT OF BUILT-UP CRANE RUNWAY GIRDERS

摘要

It is a common practice in crane runway girders to place a channel, open-side down, over the top flange of a W- or S-section. The built-up WC (W-section with Channel) or SC (S-section with Channel) section has been proven to be efficient and economical. However, the theoretical moment calculation for WC/SC section is not an easy task and the difficulty comes from the evaluation of the torsional properties including warping constant (C_w), monosymmetric parameter (β_x), and torsional constant (J). The current LRFD provides no theoretical formulas for moments of WC/SC sections, but does give the approximate formulas (without the use of C_w and β_x ) which were derived from singly symmetric I-shaped sections. Results from this study show that the LRFD formulas underestimate the elastic moment strength of WC/SC girders. This paper first summarizes the formulas of the torsional properties (C_w, β_x, J) for WC/SC sections using the complex mathematical integrations. Those sophisticated mathematical functions were solved numerically by a developed computer program. The moment parameters and torsional properties of WC/SC sections calculated based on the theory and LRFD are furnished in tabular form to assist engineers to design the built-up girders. Finally, a rational yetrnsimplified design approach is proposed and applied to the WC/SC girder sections included in the current ASD and LRFD design manuals.