Tests on Bolted Steel Angles in Compression with Varying End Support Conditions

Structural steel angles are often used as bracing members in buildings or in lattice transmission towers. Bolted end-connections of single steel angles allow for easy fabrication and quick erection, but induce additional bending moments due to the eccentric load introduction. This leads to a complex load carrying behavior, especially for members in compression. This causes a decrease in capacity compared to the case of a simply supported column with centric loading for smaller slenderness ratios. For larger slenderness ratios the beneficial effect of end restraints is assumed to compensate this drawback. Current design standards account for these effects via modified effective slenderness ratios resulting in significantly different predictions for the member capacities according to the individual regulations. The paper presents execution and results of a test series on single steel angles in compression with varying end support conditions and slenderness ratios. In total 27 specimens with one-bolt and two-bolt connections are tested. Three different boundary conditions on both ends are investigated: Boundary condition 1 (BC1) is a clamped support with all rotational degrees of freedom restraint at the member's ends. BC2 is a knife edge support that allows only for rotations about the axis parallel to the connected leg. BC3 is a fully hinged support with only the rotation about the longitudinal axis restraint. Accompanying to the results of the member tests, imperfection measurements and results of material tests are presented in order to allow for comparison with American and European design standards. The comparison of test results shows a significant difference in the compression member capacity between clamped and hinged support conditions. This difference is even more pronounced than the difference between one-bolt and two-bolt connections - a state of affairs that is either not, or only insufficiently, reflected in current design code regulations.

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