Keywords: steel angles, tension members, rupture of net section, block shear failure, finite element analysis, nonlinear.

Steel angles are extensively used as tension members in bracings, roof trusses and lattice towers. These are usually connected at ends through one leg only. The Limit State of collapse of such members is governed by yielding of the gross area, rupture of net section at end connections or block shear around the bolt group at the end connections.

The strength of these members at the end net section is influenced by several factors such as the length of connection, the size and spacing of fasteners, the net area of cross section, the type of fabrication, the connection eccentricity, shear lag at the end connection etc. Considerable amount of experimental and analytical research is already available dealing with the behaviour of steel angle tension members and some of the results have been incorporated in various international codes of practice. However, there are large differences in the strengths evaluated based on these design provisions and test results. Current design codes [1,2,3,4,5,6,7] do not adequately consider all factors that affect the net section strength of single angle and double angle tension members. There are limited experimental or analytical studies which systematically explore the affects of various parameters on the behaviour and strength of single angle and double angle tension members, connected at their ends by bolting or welding one leg to end gussets [8]. Hence there is a definite need to study the behaviour of steel angle tension members systematically.

The finite element analysis (FEA) has become a practical tool for engineering analysis and design in recent years. The FEA model once calibrated with test results facilitates a more extensive parametric study of the underlying behaviour than is possible in an experimental investigation. Further, additional information about stress distribution at the initial elastic, pre-ultimate and ultimate stages can be obtained easily and reasonably accurately by FEA, even when the stress or strain gradients are large, as around bolt holes.

Therefore, a nonlinear FEA study of the behaviour of steel angle tension members up to failure was carried out considering the material and geometrical nonlinearities as well as interaction between angle, gussets and bolts. Through the FEA model, it was possible to study all modes of failure of the angle tension members. The FEA model was calibrated with test results corresponding to different modes of failures encountered. The strengths obtained from the FEA are in very good agreement with the experimental values.

1

IS: 800, "Code of Practice for General Construction in Steel", Bureau of Indian Standards, New Delhi, 1984.

2

AISC-LRFD, "Load and Resistance Factor Design Specification for Structural Steel Buildings", American Institute of Steel Construction, Chicago, III, 1999.

3

AS4100, "Australian Standards- Steel Structures", Standards Association of Australia, 1 The Crescent, Homebush, NSW 2140, 1998.

4

ASCE Manual No.52, "Guide for Design of Steel Transmission Towers", American Society of Civil Engineers, 1988.

5

BS-5950 - Part 1, "Code of Practice for Design in Simple and Continuous Construction: Hot rolled sections", British Standards Institute, London, 1990.

6

CAN/CSA-S16.1-M94, "Limit States Design of Steel Structures", Canadian Standards Assoc., Rexdale (Toronto), Ontario, Canada, M9W 1R3, 1994.

7

Eurocode3, "Design of Steel Structures", General Rules and Rules for Buildings, 1992.

8

Usha, P., "Analytical Study of Nonlinear Behaviour of Steel Angle Tension Members", M.S. Thesis, Department of Civil Engineering, IIT Madras, India, 2003.

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