Web crippling of galvanized steel tube strengthened by CFRP sheets

Web crippling is the major failure mode of galvanized steel tube members when they are subjected to concentrated loads or reactions. Carbon fibre-reinforced polymer (CFRP) sheets were found to be promising for strengthening metallic structural members. This paper presents a test program on strengthening of high strength galvanized steel tubular structural members using externally bonded CFRP sheets. The results of 16 web crippling tests were presented, with 8 tests conducted on galvanized steel square hollow sections without CFRP sheets strengthening and 8 tests conducted on galvanized steel square hollow sections with CFRP sheets strengthening. The experimental scheme, failure modes and load-displacement curves were also presented. The investigation was mainly focused on the effects of boundary condition, loading condition and CFRP sheets layers for the strengthening of galvanized steel square hollow sections against web crippling. Significant increase in web crippling ultimate capacity was obtained due to CFRP sheets strengthening. Enhancement of web crippling ultimate capacity was not obvious when CFRP sheets layers exceeds 3 layers. Finite element models were developed to numerically simulate the experimental results. Based on the results of the parametric study, a number of design formulas proposed in this paper can be successfully employed as a design rule for predicting web crippling ultimate capacity of galvanized steel tubular sections strengthened by CFRP sheets under four loading and boundary conditions.