Study On The Torsional Behavior Of Reinforced Concrete Special-shaped Columns Under The Actions Of Pressure And Torque

Reinforced concrete structures with special-shaped columns are widely used in building structures and have gained good social and economic benefits. Many studies have been done on normal sectional load bearing capacity, diagonal sectional bearing capacity, pure torsional performance, seismic performance and fire resistance performance of reinforced concrete special-shaped columns. But, the study on the torsional behavior of reinforced concrete special-shaped columns under the actions of pressure and torque has rarely been reported in the literatures.When a reinforced concrete column is under a torque, it is normally also under an action of axial force at the same time. With the popularization and application of special-shaped columns, it has great significance to study the torsional behavior of reinforced concrete special-shaped columns under the combined actions of pressure and torque. In this paper, the torsional behavior of reinforced concrete special-shaped columns under the actions of pressure and torque is investigated from experiment, numerical simulation and practical calculation. The main work and conclusions are as follows:1. Nine columns with special-shaped cross section, including three reinforced concrete L-shaped columns, two reinforced concrete T-shaped columns, one reinforced concrete +-shaped column, and three plain concrete columns with L-, T-, +-shaped cross section, were experimental investigated under the combined actions of pressure and torque. The effects of axial load ratio, cross sectional shape and reinforcement on the torsional behavior of reinforced concrete special-shaped columns under the actions of pressure and torque were analyzed. The experimental results show that: (1) the axial-load ratio has significant effects on the torsional behavior of special-shaped columns. Comparing with reinforced concrete L-shaped column with an axial load ratio of 0.063, the cracking torque and ultimate torque of reinforced concrete L-shaped columns with axial load ratios of 0.189 and 0.314 were increased by 23.7% and 73.3%, 14.2% and 38.7%, respectively. Comparing with reinforced concrete T-shaped columns with an axial load ratio of 0.189, the cracking torque and ultimate torque of T-shaped column with an axial load ratio of 0.314 were increased by 71.0% and 16.0%, respectively. (2) The reinforcement can significantly improve the cracking torque and ultimate torque of special-shaped columns. When the axial load ratio is 0.189, the crack torque and ultimate torque of L-shaped, T-shaped, +-shaped columns are increased 40.8%, 18.9%, 26.2%, and 102.0%, 106.1%, 54.4% by the reinforcement, respectively. (3) When the axial load ratio, cross sectional area and reinforcement ratio are just the same, the ultimate torque of columns with differently-shaped cross sections decreased in the following order: L-shaped column > T-shaped column > +-shaped column. 2. The nonlinear finite element analysis for the torsional behaviour of reinforced concrete +-shaped columns with various axial load ratios were conducted by the general software ANSYS. The numerical examples show that: (1) the crack torque and ultimate torque of reinforced concrete special-shaped columns under the combined actions of axial force and torque can be predicted with a reasonable accuracy. (2) Comparing with reinforced concrete +-shaped column with an axial load ratio of 0.063, the cracking torque and ultimate torque of reinforced concrete +-shaped columns with axial load ratios of 0.189 and 0.314 were increased by 28.3% and 71.9%, 79.4% and 96.0%, respectively.3. Based on the practical calculation methods for the crack torque and ultimate torque of reinforced concrete rectangular columns under the actions of pressure and torque, and the assumption that the special-shaped cross section can be deal as an combination of two rectangle cross section, practical calculation formula for the cracking torque and ultimate torque of reinforced concrete special-shaped columns are proposed preliminarily through data regression.