Vol. 1, No. 1, pp. 157-172 (2005)
SECOND-ORDER P-Δ-δ ANALYSIS AND DESIGN OF ANGLE TRUSSES
ALLOWING FOR IMPERFECTIONS AND SEMI-RIGID CONNECTIONS
S.L. Chan* and S.H. Cho
*Department of Civil and Structural Engineering,
The Hong Kong Polytechnic University, Hong Kong
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ABSTRACT
Single angle members have a broad range of applications, such as web members in roof trusses and bracingmembers in latticed towers. The structural behaviour of a single angle compression member in a truss is complicated.It is not uncommon to connect one angle member to another through their legs. Therefore, in practice, the member isunder an eccentric force which introduces a pair of end moments. However, in most design codes such as BS5950(2000) and Eurocode 3 (2003), these end moments are often ignored. To compensate for this load eccentricity, theRobertson constant in the Perry-Robertson formula is amplified so that the compressive strength is reduced for thenegligence of end eccentricities. In this method of analysis, all connections are assumed to be pin-jointed; while in thedesign, the effective length is assumed on the basis of connection types (e.g. single-bolted, double-bolted or welding)which violates the assumption in the analysis. This paper proposes a design method for angle trusses using nonlinearanalysis which eliminates the inconsistency between the analysis and the design. Laboratory tests of angles as webmembers of a truss were carried out. The test results are compared with the proposed theoretical and code designloads. In the proposed design method, there is no need to consider any effective length. The second-order P-Δand P-δeffects are considered automatically by geometry update. The proposed method is readily applicable to design ofpractical steel trusses made of angle sections.
KEYWORDS
Eccentricity, effective length, initial curvature, nonlinear analysis, second-order effects
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