Experiment Study On The Compressive Behavior Of Circular Concrete Columns Confined With FRP Considering The Secondary Load

Fiber reinforced polymer (FRP) composites have been increasingly used in rehabilitation and strengthening of concrete structures. The secondary load effect is inevitable in the structure rehabilitation process. However, most of the existing researches referring to the confinement of concrete columns with FRP materials don't consider the effect of sustained loading on the column during repair/strengthening. Concerning the practical condition, an experimental study is run to test the compressive behavior of the confinement of circular concrete columns with FRP considering the secondary load effect.According to the experiment scheme, one special test unit is designed to simulate the secondary load effect, which can hold the sustained load effectively. In the whole test, 19 circular concrete columns confined with CFRP and GFRP that are different in modulus of elasticity are tested under different sustained axial load. The results of the test indicate that no obvious differences in compressive behavior of columns are discovered compared with those columns not considering initial axial load, when sustained load is lower than some level. Also the experiment verifies that CFRP with high modulus of elasticity is more suitable for the strength enhancement of the confined concrete, and GFRP with high modulus of elongation, more suitable for the ductility enhancement of the confined concrete.Some comparative analysis is done to discuss the existing stress -strain model of the confined concrete with FRP. On the base of such analysis and test results, some special assumption is forwarded. That is FRP confine the concrete with remained compressive strength under sustained loading that can be seemed as the concrete with same compressive strength without sustained loading. Then the stress -strain model on the confined circular concrete column with FRP considering the secondary load effect is proposed, which shows good agreement with the test results. Also some discussions on the designing method for strengthening circular concrete column confined with FRP and the feasibility of increasing its ultimate axial compression ratio are presented for reference.