Experimental Study On Seismic Performance Of Reinforced Concrete Columns Under Combined Compression, Flexure, Shear And Torsion

In reinforced concrete structure, the components are in a single stress state rarely, in most cases, the components are in complex stress state. Especially in the earthquake, many structur are in combined flexure, shear, tensile (compression) and torsion stress state, the damage is difficult to analyze, so the performance and its engineering application problems of reinforced concrete members under composite stress are need to be studied and resolved. Therefore, this article through to carry out low reversed cyclic tests of six reinforced concrete columns under combined compression, flexure, shear and torsion to study the crack law of development, failure pattern and torsion and bending hysteretic curves, skeleton curves, ductility, energy dissipation, stiffness and bearing capacity degradation of reinforced concrete columns that of different torsion bending than, shear span ratio, reinforcement ratio and stirrup ratio.The results show that:(1) The first cracks appear in the right surface of the specimens, the cracks are mainly concentrated in the middle and lower section of the specimens, the tilt angle is generally between 10°～60°. All specimens show bending and torsion type failure pattern.(2) Torsional characteristics:with the increase of torsion bending than and reinforcement ratio, the torsional moment-rotation angle hysteretic curves of the specimens are full, but the number of cycles are fewer; when shear span ratio increases, the number of cycles are more, but the pinch effect of torsional moment-rotation angle hysteretic curve is more obvious. The larger of torsion bending than, its torsional ductility performance will become worse, but torsional energy dissipation performance will be better; when shear span ratio increases, the torsional ductility performance of the specimens will be better, but the energy dissipation performance will be worse; reinforcement ratio has little influence on torsional ductility performance, but energy dissipation performance with the increase of reinforcement ratio will be better; increasing stirrup ratio of the specimens can enhance the torsional ductility performance. When the torsion bending than and shear span ratio increase, the speed of torsional stiffness degradation will be slow down, but the torsion bearing capacity degradation is more obvious; increaseing reinforcement ratio and stirrup ratio can slow down the speed of torsional stiffness and torsional bearing capacity degradation.(3)Bending characteristics:with the increase of torsion bending than and reinforcement ratio, the bending moment-displacement hysteretic curves are more full, the number of cycles are fewer; when the hear span ratio increases, the number of cycles are more, but the pinch effect of bending moment-displacement hysteretic curve is more obvious; The pinch effect of RC7 hysteretic curve is the most obvious, because its stirrup ratio is the smallest. Increasing the torsion bending than, reinforcement ratio and stirrup ratio of the specimens can improve the bending ductility and energy dissipation performance; increasing shear span ratio, the bending ductility performance of the specimens will be better, but the energy dissipation performance will be worse. When torsion bending than and shear span increase, the speed of the bending stiffness degradation will be slower, but its bending bearing capacity degradation is more obvious; increasing reinforcement ratio and stirrup ratio, the speed of bending stiffness and bending bearing capacity degradation can slow down.(4) Intermediate longitudinal reinforcement torsional moment-strain curves and bending moment -strain curves are forming the butterfly-shaped hysteresis loop, indicating that the position of the longitudinal reinforcement not only play the role of structural reinforcement, but also play a role of bearing resistance to torsional moment. In addition, torsional moment-strain curves and bending moment -strain curves of two longitudinal bars in the corners are the opposite direction.