Structural analysis of CFRP-plated pultruded GRP beams

Abstract

Within the context of small deflection beam theory, an exact analysis is presented for a pultruded glass reinforced plastic (GRP) beam stiffened by carbon fibre reinforced plastic (CFRP) plating, which is adhesively bonded to the inner and outer faces of the top and bottom flanges and extends over the central part of the span. The analysis assumes full composite action between the GRP and CFRP and takes account of shear deformation as well as the effects of the rotational stiffness of the connections at the ends of the beam. Exact expressions for the mid-span deflection, the end rotations and the required end rotation capacity for a prescribed mid-span deflection–span limit are presented for the two practical load cases of a point load at mid-span and a uniform load extending over the whole span. The deflection–load–span relationships for these two load cases are recast into three structural performance indices, λδ, λQ and λL, which quantify the benefits of the partial CFRP plating and the stiffness of the end connections in reducing the mid-span deflection, increasing the load capacity and the span relative to an otherwise identical unplated simply supported beam. The analysis requires the increase in cross-sectional area and second moment of area, due to the bonded CFRP plating to be specified. Closed-form expressions are presented for the determination of both of these quantities. Two examples of the use of the equations are presented, which show the structural performance benefits of CFRP plating for pultruded GRP wide flange beams with idealised and practical (bolted cleat) end connections. An important result arising from one of the examples is that there is little point in plating more than 60% of the beam's span.