Mechanical Behavior of Composites for Construction

Abstract

Abstract This article deals with the mechanical behavior of so‐called FRP ( fiber‐reinforced polymers ), which are materials composed of long continuous fibers embedded in a polymeric matrix. The emphasis is mainly placed on the aspects that are of interest to civil engineering. In the first section, the constitutive behavior of such materials is examined. From a macroscopic point of view, FRPs can be considered linear elastic orthotropic materials up to failure and elastically homogeneous. Composites for construction are frequently made of thin sheets bonded together to form a laminate; thus, plane‐stress conditions often occur. The simplified expression of the relationship between stresses and strains for such case is specifically examined. In the same section, the main failure criteria are also analyzed. The second section deals with the mechanical behavior of composite plates. They are widely used in technical applications due to the possibility to assemble layers with various thicknesses and different fiber inclinations, which can be opportunely chosen by the designer in order to obtain the required strength and stiffness. The model examined is known as First‐order Shear Deformation Theory (FSDT). It is widely adopted by the majority of the calculation codes currently available. The third and final section deals with the mechanical behavior of FRP pultruded thin‐walled beams. From a constitutive point of view, they can be supposed to be linear elastic, homogeneous, and transversely isotropic with the isotropic plane perpendicular to the axis of the beam and parallel to the direction of the fibers. Pultruded beams are now being used in civil engineering both as principal and secondary members. The kinematic model here presented is a generalization of the classical Vlasov one. It is able to take into account the contribution of the shear deformability. The lateral buckling problem of such beams is also analyzed. In particular, some numerical results are presented for the case of an “I” beam constrained by torsional supports at the ends and subjected to a uniform distributed load applied to the upper flange of the beam. Various ratios between the values of the normal and the tangential elasticity moduli of the beam are considered. Comparisons with the less conservative results obtained through Vlasov theory are also presented.