| Because of the variety of the materials,shapes and sizes of concrete,the specimens will reveal different mechanical characteristics under different stress state,of which failure strength will also vary.However,there are still rare triaxial tests around the world with regard to prismatic concrete specimen.This paper is mainly about the study of a new test method of prismatic concrete specimens under triaxial compression in the hydraulic chamber by using the conventional triaxial testing machine,by the means of the specimens under triaxial compression with different constant confining pressure are tested,as well as some uniaxial compression tests of prismatic specimens with 4 length width ratios.According to the uniaxial and triaxial compression test results,the strength characteristics,deformation and failure characteristics of prismatic concrete specimens are analyzed,then the stress-strain curves under triaxial tests are fitted.Finally the uniaxial tests carried out by the same test machine are summarized and and develop them into a systematic research about the concrete mechanical properties,the content of concrete research are as follows:(1)The key test method of conventional triaxial compression tests of prismatic concrete specimens is studied,which has been proved to be practical.1)The horizontal displacement sensor matched with the shape of the specimens has been made,which is easy to use in the limited space and meets the precision requirement.2)The special upper and lower intenter which is matched with the prismatic specimens are designed and made,as well as the base intenters.3)Reforming the current measurement system by adding an advanced data acquisition system.It is more convenient and accurate to collect data from the testing machine by combining these two systems,and the problems such as inadequate signal channel,low sampling frequency and instable potentiometer values are also solved.(2)From the triaxial tests,the strength and deformation properties of prismatic concrete under triaxial stress are analyzed.1)The failure mode of the specimens subjected to uniaxial compression and triaxial compression tests are analyzed,the results show that there is a significant influence on which by the confining pressure and friction reduction.2)The relationship between the triaxial compression strength of the concrete and its corresponding deformation and confining pressure is studied by analyzing the tests data.3)By coMParing the stress-strain curve and the characteristic value of the specimens with and without antifriction,it is found that with the increasing of confining pressure,the end constraint has a decreasing effect on the strength,when the confining pressure is 30MPa,the two kinds of stress-strain curve is extremely similar.4)Fitting the axial stress-strain curve,then three popular failure criterions are used to fit the strength of concrete respectively including D-P criterion and Rechart failure criterion and Ansari failure criterion.The results show that Ansari failure criterion and modified D-P criterion are verified.(3)Four prismatic specimens(70.7mm×70.7mm×175mm,70.7mm×70.7mm×105 mm,70.7mm×70.7mm×70.7mm and 70.7mm×70.7mm×40mm)in various dimensions are used in the uniaxial test.1)The dimensional effect of prismatic concrete specimens are analyzed through the uniaxial tests.The results reveal that with the increase in the cube's height,the peak stress and its corresponding strain of concrete decreased under uniaxial compression while the the peak stress of the specimen decreases and the corresponding strain increases as dimension decreases,which reflects the dimensional effect. |
PDF Full Text Request