Study On Dynamic Characteristics And Strength Criteria Of Three-Dimensional Compressed Concrete

As the most widely used building material in hydraulic engineering construction,it is of great significance to study the dynamic characteristics of concrete under complex stress state for evaluating the safety and stability of concrete buildings and structures.In this dissertation,the dynamic and static true triaxial compression tests of concrete under different lateral compression ratios and initial stresses are carried out.The mechanical properties of concrete under dynamic and static loading and the failure mechanism under complex stress state are studied.The spatial failure criteria of dynamic and static octahedron stresses considering strain rate and Lord angle are also established.The main conclusions are as follows.1)True triaxial static compression tests of concrete under different initial stresses(4.5 MPa,6 MPa,9 MPa,12 MPa)and different constant lateral compression ratios(1:1,2:1,3:1,4:1)are carried out.The stress-strain curves,peak stress and elastic modulus of concrete affected by different lateral compression ratios are analyzed.The results show that the three axle lateral static loading,lateral pressure is,the longer the compacting concrete,the stress-strain curve is decreased slightly;the peak stress increases with the increase of lateral pressure increases;the elastic modulus increases with the increase of lateral pressure increased first and then decreased.2)The dynamic true triaxial compression tests of concrete with different constant lateral compression ratios(1:1,2:1,3:1,4:1)at different strain rates(-510 /s,-410 /s,-310 /s,-210 /s)were carried out to study the variation of stress-strain curves,peak stress,peak strain,elastic modulus and energy absorption capacity of concrete under dynamic compression.The results show that with the increase of strain rate,the complete stress-strain curve of concrete decreases more rapidly after reaching the peak value,and the effect of rate increases the length of concrete compaction stage.The peak stress of true triaxial compression of concrete increases quadratically with the increase of strain rate,and the peak strain and energy absorption capacity increase with the strain rate.The elastic modulus increases first and then decreases with the increase of strain rate.3)The failure mechanism of concrete under triaxial compression is revealed by analyzing the results of true triaxial dynamic and static mechanical properties of concrete.The results show that when the true triaxial strength value of concrete is 0.6~1.2,the failure surface is mainly diagonal shear failure,and in the process of failure,the two lateral compressive surfaces gradually change from compressive failure to tensile failure,and the tensile failure of the principal stress surface with the smallest stress value of concrete is more obvious under the influence of the increase of strain rate;the expression of "Guowang strength criterion" under dynamic condition is established to further prove the failure process of concrete under true triaxial compression test.4)Based on the test results,a unified expression of octahedral stress spatial failure criterion considering the effects of Lord angle and strain rate is established,and the failure criterion is verified.