Behaviour and capacity of steel angles in compression

Rolled single steel angle sections are frequently used in a variety of structures including, for example, steel joists and trusses, and latticed transmission towers and similar communication structures. In many practical applications, angles may be either bolted or welded to other structural members by one leg only. This results in axial load eccentricity with respect to the centroid of the cross section resulting in bi-axial bending and possible torsion in the case of compression loads. Such connection configurations combined with the asymmetric characteristics of angle sections result in the design of single angle members more complex than that of doubly symmetric sections such as W shapes. For the design of steel angles, the current LRFD Specification for Single-Angle Members (AISC 2000) suggests the use of interaction equations similar to those developed for doubly symmetric sections. A comparison of predicted values using these equations with available test results has indicated that, while the equation, in most cases, is unnecessarily conservative, it results in unconservative design values in other instances. In the current Canadian steel design code (CSA S16-01), although the use of interaction equation is suggested for the design of steel angles, there are no provisions explicitly addressing the determination of specific terms used in the interaction equation. The inconsistencies in conservatism of the interaction equation in the LRFD specification and the lack of codified provisions in the Canadian steel design code motivated this proposal. The objective of this proposal is to study the effects of length slenderness ratios and end eccentricities on the strength and behaviour of both equal and unequal leg angles. Realistically sized specimens will be tested under different loading combinations and an analytical model will be developed and validated using the experimental results. It is anticipated that this in-depth study will further the understanding of the behaviour of steel angles and will result in important beneficial refinements to present design procedures.