The Research On The Size Effect Of Concrete Behavior Under Triaxial Compression

The influence of size on the mechanical properties of concrete is closely related.The research on the size effect of concrete will help to accurately describe the difference in mechanical properties of different concrete.At present,the size effect of mechanical properties of concrete under uniaxial compression has achieved fruitful results both at home and abroad.However,many engineering structures are not subjected to single tension or compression loads,but are subjected to multiple axial loads.At present,there are few reports on the size effect of mechanical properties of concrete under three axial compression.The research in this area needs to be deepened.Based on this,the three axial compression test of concrete is carried out,and the size effect of concrete under three axial compression is systematically studied.The main research contents are as follows:(1)Three axial compression tests were carried out on 100 mm,150mm and 200 mm concrete cube specimens with stress ratios of 0.05:0.05:1,0.10:0.10:1,0.15:0.15:1 and 0.20:0.20:1.The test results show that the compressive strength,the peak strain and the limit strain of concrete under three axial compression all have size effect.The compressive strength of concrete under three axial compression increases with the increase of stress ratio,and the phenomenon of size effect is not obvious.The peak strain of concrete under three axial compression varies with stress ratio,and the size effect is the least obvious at 0.05:0.05:1~0.10:0.10:1.The size effect is more obvious at 0.15:0.15:1~0.20:0.20:1.The ultimate strain of concrete under three axial compression varies with the stress ratio.When 0.10:0.10:1,the size effect is most obvious,and the other stress ratios are less obvious.When the three axis compression secant modulus of concrete varies with size,the change is less than 0.5%.The size effect is very obvious.It can be neglected in analysis and calculation.At 0.05:0.05:1~0.15:0.15:1,the failure mode of concrete under three axial compression is columnar cleavage,and flow and deformation failure occur at 0.20:0.20:1.(2)The size effect of the increase coefficient of concrete's three axis compression performance is analyzed.Analysis results show that the compressive strength increasing coefficient of concrete under three axial compression,the increase coefficient of peak strain of three axis compression and the increase coefficient of ultimate strain of three axial compression all have size effect.The compressive strength increasing coefficient of concrete under three axial compression is more obvious with the increase of stress ratio.The peak strain increase coefficient of concrete under three axial compression increases with the increase of stress ratio,the smaller the size effect is,the less obvious.With the change of stress ratio,the size effect of the limit strain increase factor of concrete under three axial compression is small.Based on the results of the test and the test results at home and abroad,factors such as lateral stress ratio,concrete strength grade and specimen size were taken into account comprehensively.The formula for calculating the increase factor of compressive strength of concrete under three axial compression and the increase coefficient of peak strain of three axis compression are obtained.(3)On the basis of systematic analysis of statistical size effect theory,based on experimental data,the value of each parameter in the formula of statistical size effect law for compressive strength of concrete under three axial compression is determined.The critical size and critical strength of three axial compressive strength of concrete under different stress ratios are analyzed.