Use of FRP composites for strengthening of slender steel web panels subjected to shear

Fibre-reinforced polymer, FRP. composites have been used successfully to strengthen and repair steel members because they have low density, suitable mechanical properties and durability. Little attention has been given to increasing the shear strength of slender steel web panels where failure is initiated due to shear buckling of the panel. This paper presents results of an experimental and numerical investigation in which slender web panels of the steel plate-girders were strengthened either by bonding GFRP pultruded section stiffeners or by layers of carbon or glass FRP composite fabrics to the web panels. The objective of the application of the FRP was to obtain an increase of minimum 20% in the ultimate strength of the steel plate-girders by increasing the out-of-plane stiffness of the web panels. The test results showed an increase up to 54% in the ultimate strength of the FRP-strengthened specimens, compared to that of the un-strengthened control specimen. In the tests, there was no breakdown of the steel-GFRP bond, at the ultimate load, in the specimens strengthened using the pultruded sections, whilst a breakdown of the steel-fabric bond occurred in the fabric-strengthened specimens. Before testing, finite-element analyses. FEA. of the specimens were performed. 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 good agreement between the test results and FEA predictions up to the breakdown of the steel-fabric bond. Design procedures for strengthening using FRP composites have been developed.