Study On Mechanical Properties Of UHTCC Subjected To Uniaxial Cyclic Loading

Ultra High Toughness Cementitious Composites(UHTCC)is a new type cement-based composite material with excellent tensile toughness,crack control ability and energy absorption capacity.At present,UHTCC has been gradually applied to seismic structures such as beam,beam-column joint,shear wall,and has been verified to have good seismic performance.The uniaxial hysteretic constitutive model reflects the mechanical properties of UHTCC under cyclic load,which is of great significance to the nonlinear analysis,reliability design,seismic design and engineering application of UHTCC structures or components.In this paper,cylindrical specimens were used to conduct UHTCC tests under uniaxial tension,uniaxial compression,cyclic tension,cyclic compression and cyclic tension-compression,to study the mechanical properties of UHTCC under various loading modes.Based on this,some constitutive models of cyclic tension and compression behavior were established.Firstly,UHTCC uniaxial tensile and uniaxial compression tests were carried out.UHTCC uniaxial tension had obvious strain hardening phenomenon,and the ultimate tensile strain was about 0.2%.The failure mode under uniaxial compression was characterized by ductile failure and the peak strain under compression was about 0.6%.Secondly,The cyclic tension and compression tests of UHTCC were carried out,and the stress-strain curves of cyclic tension and cyclic compression were obtained.The results showed that the envelope of stress-strain curve under unidirectional cyclic loading was basically the same as that under monotonic loading.The variation law of mechanical property damage parameters such as tensile and compression residual strain,tensile and compression stiffness degradation,tensile and compression stress degradation,compression and tensile restoring force with unloading point strain was analyzed,and the function expressions of the above parameters were obtained.Different cyclic loading and unloading regimes had influence on the shape of stress-strain curve and residual strain.On the basis of experiments,the hysteretic constitutive models of UHTCC under cyclic tension and compression were presented.Finally,the UHTCC cycle tension-compression test was carried out,and the stress-strain curves of UHTCC cyclic tension-compression were obtained.It is found that the shape of the envelope of compression zone of the UHTCC cyclic tension-compression stress-strain curve was close to that of the uniaxial compression stress-strain curves.The skeleton curve of tensile zone was basically consistent with the stress-strain curve of uniaxial tension before the peak of compression,and there were some differences after the peak of compression.The differences of mechanical properties between cyclic tension-compression and single cyclic tension and compression were compared.The compression residual strain,compression stiffness degradation and compression stress degradation obtained by cyclic tension-compression loading were similar to the values and variation rules of cyclic compression tests.there was a great difference of tensile residual strain,tensile stiffness degradation,tensile stress degradation,compression and tensile restoring force between cycle tension-compression test and cyclic tensile(compression)test,which indicates that compression damage has a great influence on tensile properties.Based on the experimental results,the hysteretic constitutive model of UHTCC was given,which could be established only with the mechanical parameters of uniaxial tensile and uniaxial compression,and was in good agreement with the experimental results.