2021 Research Reports No R967-R969

Abstract
Steel crane runway girders are subjected to torsion by their eccentric loads. The twist rotation of the principal axes caused by torsion induces additional bending moments, and reduces the resistance to lateral buckling. There is little guidance on how to design for torsion, and design procedures are often intuitive, with varying degrees of rationality and precision.

This paper seeks to establish a logical procedure for designing crane runway girders which is based on an extension of the limit states methods of designing for biaxial bending. An additional term for the ratio of the design torque to the section torsion resistance is included in the interaction equations. Proposals are made for determining this section resistance. Research has shown that this addition can allow for the reduction in the lateral buckling resistance caused by the twist rotations. A linear elastic analysis of the twist rotations is used to determine the moment increases caused by torsion.

An example of the proposed method is developed and illustrated by a design example. The small twist rotations are not enough to have a major effect on the bending moments. The additional torsion term is also small, and the design capacity is primarily governed by the resistance to lateral buckling.

Keywords
Analysis, bending, capacity, crane, design, steel, torsion

Abstract
It is difficult to obtain closed form exact solutions for the non-uniform torsion of beams. Advanced finite element methods easily produce very accurate solutions, but simple programs are not widely available. One simple program is validated by comparing its solutions with closed form solutions.

A simple approximate method is proposed which combines the uniform and warping torsion stiffness approximations. The determination of the warping stiffness approximation is simplified by using the moment-area method. The approximate twist rotations are compared with the accurate solutions, are shown to be of generally acceptable accuracy, and in most cases to be conservative.

Approximate solutions for the central twist rotations of simply supported beams with off-centre torques can be combined using superposition to find solutions for a wide range of torque loadings. A worked example is given.

Keywords
Analysis, Bimoment, Rotation, Steel, Torque, Torsion, Warping

Abstract
This report presents a new analysis approach that incorporates macro-element joint models based on the Generalised Component Method in the FE analysis of steel frame buildings. The new analysis approach is termed Generalised Component Method-based finite-element (GCM-FE) analysis. The fundamental aspects and principles of the GCM-FE analysis approach are established in this report, including the framework of GCM-FE analysis, the constitutive models for the connection components and the implementation of GCM-FE analysis in commercial numerical software including an automatic modelling technique. The GCM-FE joint modelling method is first validated against the experimental results of three steel beam-to-column connection types, including the bolted moment end-plate connection, top-and-seat angle connection and web angle connection. GCM-FE analysis is subsequently performed on a two-storey four-bay irregular steel frame, showing apparent advantages over the traditional analysis methods which adopt simplified joint models. The GCM-FE analysis not only provides the ultimate resistance and failure mode of the frame, but also accurately predicts the load-redistribution process inside the connections and the resultant effect on the structural framework.

Keywords
Direct Design Method, advanced analysis, Component Method, steel frame analysis, steel connections