Simplified Model to Predict Load-Bearing Capacity of Concrete-Filled Steel Tubular Laced Column

A simplified method using an equivalent slenderness ratio was suggested to calculate load-bearing capacity of concrete-filled steel tubular laced column in this paper. The significant differences between compressive and tensile strengths of concrete-filled steel tube were considered. The comparisons between the predicted Nuc and the tested Nue showed that the predicted method gives generally good predictions of the test results.

Equivalent Slenderness Ratio Method for Design of T-Struts Subject to Compressive Force

T-struts subject to centroid compression buckle flexural-torsionally about their axis of symmetry. When the force is applied at the shear center of the section, T-struts buckle either flexurally or torsionally without coupling of flexure with twisting. Although the buckling load about the symmetry-axis of shear center loading is greater than that of centroid loading, the design capacity of T-struts with defect such as fabrication error, load eccentricity and residual stress decrease by shifting the working line of a T-section compression chord to the shear center. This feature is not well known to designer of constructional steel. This article presents the equivalent slenderness ratio method, a new method for the design of T-struts subject to compressive force, introduces another three methods including the one presented by Shaofan Chen, the one in code and the one in ANSYS, contrasts the calculation results of those four methods and recommends the implementation of equivalent slenderness ratio method in the design of T-struts subject to compressive force.

Slenderness ratio of main members between interconnectors of built-up compression members

Many steel design standards, including CAN/CSA-S16.1-M89 "Limit states design of steel structures," specify maximum slenderness ratios for the individual main members between the interconnectors of built-up compression members. Previous research on which these requirements are based is reviewed. It is shown that the imperfection sensitivity due to coupled instabilities is measured from bifurcation critical loads. However, steel standards are based on a compressive resistance determined for a member with an initial out-of-straightness and a suitable residual stress pattern. It is shown that the use of an equivalent slenderness ratio equation is sufficient to predict the compressive resistance of these built-up members. Further restrictions on the slenderness ratio of built-up members between interconnectors are not warranted. Thus, the elimination of these requirements from S16.1-94 is justified. Key words: built-up members, codes, compressive resistance, coupled instabilities, equivalent slenderness ratio, interconnectors.

Local effective length factor in the equivalent slenderness ratio

The Canadian Standard S16.1 specifies an equivalent slenderness ratio to be used when determining the compressive resistance of a built-up member when buckling occurs about an axis perpendicular to the interconnectors. This equivalent slenderness ratio is the square root of the sum of the squares of the slenderness ratio of the built-up member acting as a unit and the maximum slenderness ratio of a component part between fasteners. The Standard specifies for this second component that an effective length factor be used, the magnitude of which depends on the type of connection. An effective length factor of 0.65 is specified when welds are used. This is of concern to the authors. It is pointed out that the derivation of this equation by Bleich, and by Timoshenko and Gere, does not contain an effective length factor in the second term. The effective length factor of 0.65 comes from a paper by Duan and Chen. Results of tests on five built-up members, channels arranged in the toe-to-toe configuration, indicate that the use of an effective length factor of 0.65 gives unconservative results, especially when the member is slender. It is recommended that a factor of 1.0 be used in the second term of the equivalent slenderness ratio equation. Key words: battens, built-up members, equivalent slenderness ratio, interconnectors, standards.

Buckling of built-up compression members in the plane of the connectors

An examination of the requirements for the design of built-up compression members in the North American and European standards and specifications reveals a great variation in the allowable maximum slenderness ratio for an individual main member, and also in the determination of an equivalent slenderness ratio. The requirements of the Canadian standard with regard to the determination of the maximum allowable slenderness ratio of a main member between points of connection can be a bit confusing.This research involved a study of model built-up members that buckled about an axis perpendicular to the plane of the connectors. Twenty-four tests were conducted on model built-up members. The theoretical analysis consisted of a finite element analysis of the model built-up struts. In addition, an equivalent slenderness ratio was calculated by several methods. These equivalent slenderness ratios were then used in conjunction with the requirements of the Canadian standard to calculate a compressive resistance, which was compared with the experimental failure load.From this research on built-up members that buckle about an axis perpendicular to the plane of the connectors it was found that at least two connectors should be used, that the slenderness ratio of the main member between points of connection has a significant effect on the compressive resistance, and that Timoshenko's equivalent slenderness ratio when used in conjunction with the Canadian standard gives results that are in the best agreement with the experimental results. Key words: battens, built-up members, compressive loads, connectors, equivalent slenderness ratio.

Equivalent slenderness ratio for built-up members

Built-up struts that buckle about an axis perpendicular to the plane of the connectors should be treated as a "built-up" member as opposed to a "simple" member. This mode of buckling causes shear and moments in the connectors which deform the connectors. These deformations increase the lateral deformation of the member and hence affect the load-carrying capacity. To account for this effect the easiest method is to use an equivalent slenderness ratio such as the one included in the Canadian Standard. This note outlines the derivation of the equivalent slenderness ratio equation, discusses when it should and should not be used, and includes a numerical example. A rewording of the applicable clause in the Canadian Standard is suggested. Key words: battens, built-up members, connectors, slenderness ratio.