Experimental Study Of The Mechanical Properties Of Concrete Under Different Strain Rates

With the increases of strain rate, the mechanical properties and failure modes ofconcretes differ from which in static condition because of its strain rate sensitivity.Without considering the influence of strain rate, it should be cause a greater error inanalysis of the concrete structure under dynamic loading such as earthquake, impactand explosion. The results were discrete getting from the lots dynamic test due to thedifference of equipment, experimental methods, specimen types and loading rate.There is still no system dynamic test covering the most common concrete fromlow-strength to high-strength and dynamic test data of concrete above C30is lacked.It is difficult to establish reasonable and effective compression constitutive relationinvolving strain rate.In order to overcome the short of traditional test device, which can not obtain thewhole stress-strain curve because of its limited load capacity, a new device isdesigned by the using disc spring and additional steel frame with MTSelectro-hydraulic servo actuator. And depending on it, a series of dynamic testsincluding184prismatic concrete compression specimens produced by the mold and120specimens cutting from some large concrete blocks are implemented in differentstrain rates(from10-5/s to10-1/s) involving the most commonly concrete strength(from C25to C60). The compressive strength, elastic modulus, Poisson's ratio, thepeak strain, ultimate strain and stress-strain curve are studied in different productionmethods and different loading rates. It can be drawn from the results, the peak stressincreased about22%~28%from the lowest rate of10-5/s to the highest rate of10-1/sand corresponding strain is improved roughly around23%~39%. While the initialmodulus of concrete in each strength grade changes little under different strain rate.The cutting specimens can reduce the discrete nature of the test data.For applying to dynamic analysis, the constitutive relationships of the concretecode and finite element ADINA are verified rely on the dynamic parameter collectedfrom experiment. Based on this, the finite element analysis of short columns is carriedout in uniaxial compression. M φCurve of reinforced concrete componentconsidering the effect of strain rate is constructed to analysis the characteristics of thebearing capacity in reinforced concrete beams under different loading rates. Theresults show that the data obtained from displacement loading (corresponding to thehydraulic equipment) is more realistic and reliable than that of the stress load(corresponding to the drop hammer system). The growth of concrete strengthincreases after the strain speed surpasses10, which is probably due to the inertiacaused by the accretion acceleration of high rate. With the increase of the strain rate,the beam of moment–curvature shows a rising trend. The yield moment does not change significantly, but the ultimate moment, yield curvature and ultimate curvaturehave significant change. The higher the loading rate of the reinforced concrete beamincreases, the clearer the arch effect represents.The study of the concrete is confined within cylinder-shaped CFRP and its staticmechanical properties so far. Dynamic test characteristics under different strain ratesfor square columns have never been detected. The uniaxial compression test andtheoretical analysis are made on84carbon fiber sheet concrete under different strainrates. The results show that under static loading, the strength of the various forms offiber wrapped concrete square columns improves with the number of the layers ofcarbon fiber sheet increases.After the stress-strain curve pass a peak stress, differentconcrete of CFRP may occur three development trends: sluggish rise of the stress,hold the line basically and slow decline. The shapes of the stress-strain curves are thesame roughly at different strain rates. Loading rate increased every10times, thecompressive strength increased by8~15%, peak strain and elastic modulus increaseslightly. The sensitivity of the confined concrete is stronger than the nonrestraintconcrete.Experimental study is carried out on six reinforced concrete frame beam modelsunder different loading rates (loading time differ among3s,5s,10s,100s,1000s or3600s). The variety of reinforced concrete frame beam is contrasted under differentload rate about stride middle carrying capacity, axis force, seat's restriction bend andductility. The mechanical properties of reinforced concrete frame beam is studiedon P/PJ~δ/h, ε~δ/h, M o~δ/hand Pu/PJ with load rate curve. Archingeffect and cable effects in the framework of beams is confirmed, whose carryingcapacity is significantly improved. The greater the loading rate, the greater thecapacity improvement factor.This study experimentally studied the gravity load capacity of axially restrainedreinforced concrete beams and the critical parameters affecting the compressive archaction. Three modes are used in this test, which are "common anti-seismic design""strong shear and weak moment" and "strong moment and weak shear", includingnine beam specimens which are loaded by sudden force during the experiment. Theexperiment focuses on researching the failure forms and dynamic responses of beamswith sudden load, and the influence on moment and shear in frame beams by archingaction. By considering the arching action and analyzing the experiment results, themethod for calculating beams' limit load is shown in this paper.