Influence of Filler Properties on the Axial Behaviour of Pultruded FRP Tubes

The low axial stiffness and high slenderness ratios of pultruded fibre reinforced polymer (PFRP) tubes make their axial behaviour is governed by the buckling issues. Increase the axial stiffness and support the PFRP walls against buckling can be obtained through filling with concrete. The improvement in the axial behaviour of PFRP tube-concrete columns depends on the properties of filler material and PFRP tubes. In this study square and circular PFRP tubes were selected to investigate effects of cross-sectional shape on the improvement degree of the load capacity. The influences of fibre orientation and wall thickness were studied by considering two types for each PFRP tube sections. Two types of both normal concrete and lightweight perlite concrete were considered to fill PFRP tubes and to cover a range of variation in the filler modulus from 5 to 30 GPa. The length of PFRP columns was set to provide length -to lateral dimension ratio of 5. The results show that the stiffness of filled columns is increased as the modulus of concrete filler increases as well as, the load carrying capacity unless the transverse resistance of PFRP tube to the lateral dilation of the infilled concrete is low. Moreover, the post peak behaviour depends on the properties of filler and PFRP tubes. It is changed to be gradual reduction instead of sharp dropping of hollow PFRP columns. The findings would contribute to enhance the usage of PFRP tubes in application of civil engineering as it provides an approach to overcome the shortages that were controlled the axial behaviour of PFRP tube columns.