Study On Mechanical Properties Of GFRP-confined Expansive Concrete Columns

Fiber reinforced polymer(FRP)has been applied more and more in engineering structuresbecause of its light weight,high strength and corrosion resistance.One important application of FRP is as the confinement material for concrete.It is used for the strengthening and rehabilitation of existing structures and the construction of new structures.However,it has been found that there was a confinement lag of FRP on concrete.To solve this problem,expansive concrete is proposed to be used as the core concrete.The expansion of core concrete and confinement of external GFRP could produce prestress.It also presents advantages including low cost and easy construction.Therefore,the axial compression mechanical properties of GFRP-confined expansive concrete columns are studied in this paper,including:(1)Experimental and theoretical study on mechanical properties of GFRP-confined normal strength expansive concrete columns under monotonic axial compressionMonotonic axial compression tests were carried out on eighteen GFRP-confined normal strength concrete columns,and the unexpansive concrete columns were compared with the expansive concrete columns.Results show that compared with GFRP-confined unexpansive concrete columns,the expansion effect of GFRP-confined normal strength expansive concrete columns with 10% expansive agent content can make up for the insufficient number of FRP confinement layers to make the stress-strain relation curve transition from softening section to non-softening section.The expansion of core concrete and confinement of CFRP makes use of the confinement of GFRP more effectively and improves the normalized inflect stress and compressive strength.In addition,the widely used axial stress-strain model of FRP-confined concrete column has been modified.The modified model can accurately predict the mechanical properties of both the GFPR-confined normal strength unexpansive concrete and GFRPconfined expansive concrete columns under monotonic axial compression.(2)Experimental and theoretical study on mechanical properties of GFRP-confined normal strength expansive concrete columns under cyclic axial compressionThe mechanical properties of twenty-four GFRP-confined normal strength concrete columns under cyclic axial compression were studied.The studied parameters consist of the number of layers of GFRP confinement,the type of core concrete and the loading mode.Results show that the confinement effect of GFRP-confined normal strength unexpansive concrete and expansive concrete(10% expansion agent content)under cyclic axial compression is higher than those under monotonic axial compression.It also indicates that theloading mode has no significant effect on the normalized compressive strength of GFRP-confined unexpansive concrete and GFRP-confined expansive concrete.It exhibits that there is a significant linear relationship between the plastic strain and the envelope unloading strain under cyclic axial compression,and the linear relationship is independent of the GFRP confinement layer as well as core concrte type.Meanwhile,the expansion of core concrete shows no effect on the stress degradation rate of FRP-confined columns.Last but not least,the existing models of FRPconfined unexpansive concrete columns is also applicable to FRP-confined expansive concrete columns.(3)Experimental and theoretical study on mechanical properties of GFRP-confined high strength expansive concrete columns under monotonic and cyclic axial compressionThe axial compression behavior of twenty-four GFRP-confined high strength concrete columns was studied.Parameters studied include the number of layer of GFRP confinement,core concrete type and loading mode.The results show that,compared with normal strength concrete columns,high strength concrete columns need more external confinement due to the high strength and brittleness.The confinement effect of GFRP on high strength expansive concrete with an expansive agent content of 5% is less than that of GFRP on high strength unexpansive concrete.The peak strain of the GFRP-confined high strength concrete column increases with the number of confinement layers,and the peak strain of the confined expansive concrete column is less than that of the confined unexpansive concrete column.Both the normalized peak stress and ultimate stress of GFRP-confined expansive concrete column are slightly smaller than that of the confined unexpansive concrete column.It indicates that the loading mode has no significant effect on the axial compression behavior of confined high strength concrete columns.In addition,a strength calculation model suitable for FRP-confined high strength concrete columns was obtained after the regression analysis.It shows that the proposed model can accrurately predict the experimental results.