Shear Behavior Of UHPC Members Under Combined Action Of Compression And Bending Moment At Different Types Of Loading

In order to clarify the shear failure mechanism of UHPC members under combined action of compression and flexural,explore the effects of axial compression ratio,steel fiber volume content and stirrup ratio on the shear capacity of UHPC members under combined action of compression and flexural,quantify the degradation degree of steel fiber under different loading modes and establish the calculation formula of shear capacity under monotonic load and low cyclic load,combined with the National Natural Science Foundation Project "seismic performance and design method of reactive powder performance concrete compression specimens",this paper carries out the experimental research and theoretical analysis on the shear performance of inclined section of UHPC members under combined action of compression and flexural under monotonic,repeated and low cycle repeated loading,in order to provide reference and basis for the engineering application of this kind of structure.The main contents and achievements of this paper are as follows:1.The shear performance test of six UHPC compression bending members under monotonic load is completed.The results show that the shear capacity of reinforced UHPC members under combined action of compression and flexural increases with the increase of axial compression ratio and the content of steel fiber.When the axial compression ratio is 0,the volume content of steel fiber increases from 0% to 2%,and the shear capacity of the specimen increases by 54.3%;When the axial compression ratio is 0.2,the volume content of steel fiber increases from 0% to 2%,and its shear capacity increases by 42.7%.For the specimens with 2% steel fiber,when the axial compression ratio increases from 0 to 0.1 and 0.2,the shear capacity of the specimens is increased by 30.3% and 33.3% respectively.2.The shear performance test of UHPC members under combined action of compression and flexural under 1 repeated load and 5 low cycle repeated load were completed.The test parameters include steel fiber volume content(0%、2%),axial compression ratio(0、0.1、0.2)and stirrup ratio(0%、0.38%).(1)The failure mode,load displacement curve,crack distribution and width of the specimen are obtained,and the effects of different test parameters on the shear performance of reinforced UHPC members under combined action of compression and flexural are clarified.The results show that the shear capacity and ductility coefficient of reinforced UHPC members under combined action of compression and flexural increase with the increase of steel fiber content;For the specimens with axial compression ratio of 0,when the content of steel fiber is increased from 0% to 2%,the shear capacity of the specimens is increased by 33.1% and the ductility coefficient is increased by 20.4%;The shear capacity of reinforced UHPC members under combined action of compression and flexural increases obviously with the increase of axial compression ratio,but its ductility coefficient decreases slightly;For the specimens with 2% steel fiber content,when the axial compression ratio increases from 0 to 0.1,the shear capacity of UHPC compression bending members increases by 22.6%,and the ductility coefficient decreases by 3.7%.(2)The effects of axial compression ratio and steel fiber on the shear capacity of UHPC members under combined action of compression and flexural under monotonic,repeated and low cyclic loading are clarified.The results show that under repeated and low cycle reciprocating loads,the normal section cracks in the middle span and the inclined section cracks in the shear span area of the specimen undergo repeated opening and closing processes,resulting in steel fiber sliding,pulling out and buckling,which weakens the gain effect of steel fiber on the section bearing capacity.When the volume content of steel fiber is 2% and the axial compression ratio is 0,the shear capacity of UHPC compression bending members under repeated and low cycle reciprocating loads is reduced by 11.7% and 11.3% respectively.Under low cycle reciprocating load,increasing the axial compression ratio also weakens the shear capacity of UHPC members under combined action of compression and flexural.When the volume content of steel fiber is 0% and the axial compression ratio is increased from0 to 0.2,the shear capacity of UHPC compression bending members is reduced by23.7%;When the volume content of steel fiber is 2% and the axial compression ratio is increased from 0 to 0.1,the shear capacity of UHPC compression bending members is reduced by 16.6%..3.The applicability of relevant codes at home and abroad to the calculation of shear capacity of reinforced UHPC members under combined action of compression and flexural is evaluated.Combined with the shear test results in this paper,the calculation formula of shear capacity of UHPC members under combined action of compression and flexural considering the influence of axial compression ratio and steel fiber is established,and the relevant literature and test data are introduced to verify its applicability.Based on the calculation formula of shear capacity of reinforced UHPC compression bending members under monotonic load and considering the influence of steel fiber volume content and axial compression ratio,the calculation formula of shear capacity of UHPC members under combined action of compression and flexural under repeated and low cycle reciprocating load is established.