Second-order analysis and design of angle trusses and frames

Abstract

Single angle members have a broad range of applications. Very often angle members are connected eccentrically. As a result, not only is an angle member subject to axial force, but it is also subject to a pair of end moments. In addition, the connection at each end provides some fixity so neither pinned nor the fixed end represents the reality. Many national design codes allow for the effects due to load eccentricity and end restraint by modifying the slenderness ratio and reducing the compressive strength of the member. The concept behind this method is inconsistent with strength design of members of other cross-sectional types such as I or box sections of which the buckling strength is controlled by the Perry constant or the initial imperfection parameters. Moreover, in practice, it is difficult to determine accurately the effective length. Sometimes, it is assumed the two ends of the member are immovable. The thesis proposes a few methods for design of angle frames and trusses by the second-order analysis. Laboratory tests of angles as web members of a truss were carried out. The test results are compared with the proposed theoretical and code design loads. In the computational method proposed in this thesis, there is no need to consider any effective length because the second-order P - A and P - 8 effects are considered automatically by geometry update. The proposed method is readily applicable to design of practical steel trusses made of angle sections and demonstrated by a few worked examples. It is further expected the developed design method will improve the safety and economy of structures made of angle sections while he concept can be extended to second-order analysis and design of structures made of other asymmetric sections like channels and T-sections commonly connected eccentrically.