Impact behavior of concrete columns confined by both GFRP tube and steel spiral reinforcement
Previous studies showed that concrete column confined by both glass fiber reinforced polymer (GFRP) tube and inner steel spiral reinforcement (termed as GFRP-SR-confined concrete) is a hybrid structure exhibiting much better static structural performance (e.g. load carrying capacity and ductility) compared with concrete column filled GFRP tube (CFFT) or conventional concrete column with inner steel spiral reinforcement (SR). To date, very few studies have considered the dynamic behavior of this hybrid structure. This research reports an experimental study on the dynamic behavior of GFRP-SR-confined concrete columns under impact loadings using a drop-hammer with large capacities (i.e. impact height up to 6.42 m and weight of hammer up to 588 kg). The test variables considered include the different levels of impact energy and strain rate, GFRP tube thickness and volumetric ratio of SR. The impact behavior of this hybrid structure is also compared with the CFFT and conventional SR column counterparts. The test results indicate that the failure pattern of this hybrid structure is highly dependent on the level of impact energy. Increasing the tube thickness and SR volumetric ratio enhances the impact-resistant capabilities of the structure remarkably. In addition, the impact results are compared with the quasi-static compressive results of the GFRP-SR-confined concrete.