Investigation on Buckling Behaviour of GFRP Angle Sections with Bolted Connections in Lattice Towers

Glass fibre-reinforced polymer (GFRP) angle is an emerging alternative material to conventional steel angle sections in transmission line (TL)/communication towers, because of their superior characteristics such as high strength to weight ratio, high tensile strength, better corrosion resistance, light in weight for handling and transportation, etc. The GFRP angle sections are used as leg, bracing, tie and redundant members in towers, in which these members are subjected to reversal of tensile and compressive forces due to wind. The compression strength is mainly governed by the buckling characteristics of angle sections. There is lack of design criteria concerning the use of GFRP angle sections with bolted connections in lattice towers. In the present study, experimental investigation is conducted on concentrically loaded GFRP angle sections with bolted connections in TL/communication towers. The material properties were determined based on compression and in-plane shear coupon test. The existing mathematical model to determine the buckling characteristics such as torsional–flexural, flexure and pure torsion is considered. The theoretical approach to determine its limiting effective length governing the transition from torsional–flexural to flexural buckling mode for GFRP angle sections with bolted connections is proposed in this paper. The proposed formulation is validated with experimental investigation conducted at component level on GFRP angle sections with bolted connections at both ends for different slenderness ratios ranging from 40 to 100 along with numerical investigation using FEA software, ANSYS. Experimental investigation was also carried out for validation at sub-structural level on ‘X’-braced panel made entirely of GFRP angle sections. The panel failed prematurely during testing, and the reason for this failure was observed due to excessive bending stress exerted on the free length of stub member. Based on the results of the investigations, suitable recommendations for use of GFRP angle sections in lattice tower are proposed.