FRP-strengthening of webs of steel plate-girders

Abstract

Fibre-reinforced polymer, FRP, composites have been used successfully for the strengthening and repair of steel beams in order to increase the flexural strength of the beams by up to 40%. However, little attention has been given to the use of FRP composites to increase the ultimate strength of steel plate-girders where failure is initiated by shear buckling of the slender webs. This thesis presents the details and results of an experimental and numerical investigation in which the web panels of the steel plate-girders were strengthened either by bonding GFRP pultruded section stiffeners or layers of carbon or glass FRP composite fabrics. The objective of the strengthening was to obtain an increase of a minimum of 20% in the ultimate load of the steel plate-girders by increasing the out-of-plane stiffness of the web in the web panels. The tests of one un-strengthened control specimen and seven FRP-strengthened specimens were carried out. The test results showed an increase up to 54% in the ultimate load of the FRP-strengthened specimens, compared to that of the unstrengthened control specimen. In the tests there was no breakdown of the steel-GFRP bond, at the ultimate load, in the specimens strengthened using the GFRP pultruded sections, whilst a breakdown of the steel-fabric bond occurred in the specimens strengthened using FRP fabrics. Before testing, nonlinear finite-element analyses, FEA, of the specimens were carried out using shell elements and the LUSAS FE program. Both material and geometrical nonlinearities were modelled. The test results and the FEA predictions for the un-strengthened and GFRP pultruded section strengthened specimens were in good agreement. For the FRP fabric-strengthened specimens, there was agreement between the test results and FEA predictions up to the breakdown of the steel-fabric bond. Design procedures for FRP-strengthened plate-girders have been developed based on those in Eurocode 3. The design procedures can be used to estimate the ultimate loads of the FRP-strengthened plate-girders and to determine suitable cross-sections of GFRP pultruded sections as intermediate, load-bearing and diagonal web stiffeners. The procedures have been validated using the results of the tests and FE analyses of nine FRP-strengthened plate-girder specimens and those of the FE analyses of thirty-five models of the plate-girders. The design procedures for the FRP-strengthened plategirders can therefore be used in practice.