Experimental Study On Constitutive Relation Of Steel Fiber Reinforced Concrete Under Uniaxial Compression

Steel fibers were mixed into concrete can effectively improve the strength and toughness of concrete.Although steel fibers have been used in water conservanvy,hydropower engineering,oceam and coast engineering,civil engineering as well as road and bridge engineering,the constitutive relation of compressive steel fiber reinforced concrete(SFRC)have seldomly been studied.Therefore,the application of steel fiber for SFRC structure design and numerical simulation are limited.In this study,the uniaxial compressive tests of SFRC were conducted to inveatigate the compressive strength and constitutive relation.The main contens of thesis are as follows:(1)The compressive test of 90 SFRC cube specimens was carried out.On the condition of varying concrete strength,the effects of volume fraction of steel fiber and steel fiber strength on the failure mode and compressive strength of SFRC cube specimens were investigated.Results show that the failure mode was changed from brittleness to plasticity by introducing steel fibers.Whthin the concrete strength of C30/CF30~C60/CF60 and with the increase of volume fraction of steel fiber ranged from 0% to 2%,the compressive strength of cube specimens was improved by 2.5%~41.66%.High strength steel fiber has better performance on increasing compressive strength of cube specimens than low strength steel fiber.(2)Based on the self-stiffness of testing machine,the uniaxial compressive test of 90 SFRC prisms was carried out to investigate the effects of volume fraction of steel fiber,concrete strength and steel fiber strength on the failure mode and constitutive relation of SFRC prisms.Results show that the strength and toughness of SFRC were significantly improved by steel fibres in the case of crack propagation and failure.The descent stage of stress-strain curves was difficult to be measured due to the low selfstiffness of test machine.Whthin the concrete strength of C30/CF30~C60/CF60 and with the increase of volume fraction of steel fiber ranged from 0% to 2%,the stressstrain curve got plumper and showed the increasing peak stress and peak strain at peak stress.For C80/CF80 prisms,peak stress increased with the increasing of volume fraction of steel fiber,but the peak strain at peak stress was reduced.High strength steel fibers performed a better action of increasing toughness of high strength prisms.Based on the SFRC characteristics,the constitutive relation of SFRC under uniaxial compression was proposed.(3)Based on the additional rigid components of test machine,the uniaxial compressive test of 90 SFRC prisms was carried out to investigate the effects of volume fraction of steel fiber,concrete strength and steel fiber strength on the constitutive relation of SFRC prisms.Results show that whthin the concreten strength of C30/CF30~C60/CF60 and with the increase of volume fraction of steel fiber ranged from 0% to 2%,the stress-strain curve got plumper and the peak stress,peak strain at peak stress and area under stress-strain curve were improved.With the increase of concrete strength ranged from C30/CF30 to C80/CF80,the peak stress and solpe of ascent stage of stress-strain curve were increased,but the curvature and deformation of ascent stage of stress-strain curve were reduced.High strength steel fibers have significant performace on increasing toughness of high strength strength.Compared with the test using test machine without additional rigid components,the test machine with additional rigid components could obtained the descent stage and increased the parameter of ascent stage of stress-strain curve.Also,the descent stage of stress-strain curve showed an obvious regularity.The proposed constitutive relation of SFRC under compression is also suitable for the test by using the test machine without additional rigid components.