The Development And Application Of A New Measure Equipment Of Shear Force

Compression-shear test is one of most common tests in the study of Civil Engineering structure.In the process of compression-shear testing,the experimental components go through cyclic loading horizontally under constant vertical pressure.The actuator that produces the vertical load could generate friction force between its upper bottom and counter force bearing in the horizontal reciprocating motion along with the test components.The horizontal load of the horizontal actuating device includes friction and the restoring force produced by the deformation of the test components.In order to obtain an accurate restoring force and displacement curve of the test component,the friction of the horizontal load must be deducted.However,an obvious pattern of friction cannot be perceived from the horizontal load and displacement curve,leading to the impossibility of an accurate deduction of the friction.Currently,there are no relevant measuring instruments to measure the friction;therefore,this paper aims to develop a new type of shear test device to measure the friction synchronously in the experiment mentioned above.The main contents are as follows:First of all,according to the form of force of the measured shear device for measuring friction,the working principle could be determined.Under the horizontal shear forces the elastic bodies produce bending moment.The bending moment is obtained by the strain measurement on the special fixed point of the elastic body,thus establishing a connection between strain and shear force.From the linear relationship between the resistance of the resistance strain gauge and the resistance change rate,the relationship between the shear resistance and the strain rate of the strain gauge can be obtained.The whole bridge circuit is formed by series and parallel connection of the strain piece with special fixed point according to the law of tension and compression.The linear relationship is thus derived between the shear force and the output signal of the circuit.The output signal of the test device under different conditions is given as well.Second,the sensitivity coefficient of shear test device,which is the ratio of total strain to the output of the whole bridge circuit,was tested for calibration.For this purpose,two identical test shear devices were fabricated,and the test was carried out on the 20000 k N multi-function space loading device in the Civil Engineering Department of Tsinghua University.In the tests,two devices were subjected to horizontal loading under different vertical constant load.The total strain and horizontal resultant force of the two devices were obtained.The sensitivity coefficient of the two test shear device s was dealt with by using MATLAB processing data.The calibration tests also show that the shear stress of the two devices is linea r with the total strain,and the shear strain curves obtained under different vertical loads coincide well with the experimental data.Finally,the shear device was applied to the structural tests,and the application cases of shear wall,composite column and grid tube were collected.The load displacement curves of the specimens before and after deduction of friction were compared,and the load displacement curve turned out to be sooth and accurate after deduction of friction.At the same time,the comparison was made between the friction force displacement curve and the load displacement curve without deduction of friction.The sudden changes of the friction in the dynamic-to-static and static-to-dynamic conversion were also measured and prove to be consistent.When the specimen was loaded to one side smoothly,the sliding friction force,measured in the process,remained unchanged,in line with the actual situation.The application effect of the test shear device in structural tests is satisfactory.