The Experimental Study On Torsional Behavior Of R.C. Members With Box Sections Subjected Biaxially To Eccentric Compression And Shear

In practice, many R.C. members are always subjected to one type or several types of force under the effect of compression, moment, shear and torsion. Up to now, it has still developed very slowly to study the torsional behavior of R.C. members subjected biaxially to eccentric compression and shear, and it might be the first to study the torsional behavior of R.C. members with box sections subjected biaxially to eccentric compression and shear both home and overseas. So the paper is very significant both in theory and practice.After studying the current situation on torsional behavior both home and overseas, the paper takes some reasonable measures on the test design and studies the development rules of the cracks, the failure modes, the mechanic principle, the elastoplasticity performance, the torsion load-carrying capacity, the characteristics of the relationship curve between torsion and torsional angle, and the energy dissipation capacity of specimens in terms of the torsional behavior test of nine box-section reinforced concrete specimens subjected to biaxially eccentric compression, biaxial shear and monotonic or reversed torsion. The paper also discusses the influence caused by the change of the axial stress level and the relative eccentricity, and comes to some conclusions from the test: the first crack appears in the middle of the side in which there is the longitudinal tension and the highest shearing stress, and some cracks in all sides can be lined together in the similarly spiral form when the specimen reaches to the ultimate state; the value of the crack torsion decreases with the increase of the value of the relative eccentricity.On the basis of the Variable-angle Space Truss Model theory, the paper arrives at the load-carrying capacity interaction equation of box-section members subjected to biaxially eccentric compression, torsion and biaxial shear. The paper also proposes a more simple and practical calculation equation of the torsion load-carrying capacity, which agrees well with the test results and has reference value to some extent. Through the comparisons betweenthis practical calculation equation and the calculation equation of rectangle-section members, the paper points out that it isn't completely reasonable for rectangle section members to neglect the action of the center concrete when the member is subjected to a high value of the axial stress level and the relative eccentricity. Besides, the paper builds up a finite element model of the members by employing the ANSYS program and then imitates the boundary conditions and the technology parameters of the test. The paper analyzes the elastoplasticity performance of the members by means of the ANSYS program and further studies the torsional behavior of the ones subjected to monotonic torsion through the comparisons between the results gotten by the ANSYS program and the test. Both of them agree well and show that the conclusions gotten by the test is reasonable, reliable and dependable.