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

  • R. BalagopalEmail author
  • N. Prasad Rao
  • R. P. Rokade
Original Contribution


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.


GFRP angle Torsional–flexural buckling Flexural buckling Limiting effective length Transmission/communication towers GFRP X-braced panel 

List of Symbols


Ultimate compressive stress


Shear stress

Ex, Ey and Ez

Young’s modulus along x, y and z directions

Gxy, Gyz and Ezx

Shear modulus along xy, yz and zx planes

μxy, μzx

Poisson’s ratio


Effective length

(KL)lim, tf

Limiting effective length for torsional–flexural buckling

Puu, Pvv

Flexural buckling load about uu and vv axes


Torsional buckling load


Torsional–flexural buckling load


Torsional rigidity


Warping constant

Iuu, Ivv

Moment of inertia along uu and vv axes


Polar moment of inertia



The authors thank all the staff of Tower Testing and Research Station for their help and support in conducting the experiments. This paper is being published with the kind permission of The Director, CSIR-Structural Engineering Research Centre, Taramani, Chennai, INDIA.


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Copyright information

© The Institution of Engineers (India) 2020

Authors and Affiliations

  1. 1.TTRS, CSIR-Structural Engineering Research CentreChennaiIndia

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