Research On Bearing Behavior Of Strut And Tie Model Of Slab-column Joints

The slab-column structure is widely used in various kinds of buildings because of its high space utilization and flexible layout.However,due to the lack of beam reinforcement at the slab-column joint,as well as the multiple situations under the combinations of axial load and unbalanced bending moment,the slab-column joint is prone to punching failure.At present,the research on punching failure of the slab-column joint is deficient in both bearing mechanism and calculation of bearing capacity.Therefore,the bearing behavior of punching failure at the slab-column joint is selected as the research content in this paper.Based on the numerical simulation and theoretical analysis,the paper studies the bearing behavior of slab-column joint in three cases,which are: under axial load;only compression in the column bottom under the combination of axial load and unbalanced bending moment;tension and compression in the column bottom under unbalanced bending moment.For each case,the research method is qualitative study(bearing mechanism:transfer mechanism and failure mechanism)first and quantitative study(calculation of bearing capacity)later.The specific work is as follows:1.Qualitative study(1)For the slab-column joint under axial load,the numerical simulation of entire process was conducted by using ADINA software,the principal stress distribution and crack distribution status were achieved,the transfer mechanism of spatial strut and tie model was presented,It was pointed out that the strut is simplified as an equal width fan-shaped strut,It was made clear that the failure of the strut is an indication of the loss of the punching capacity under this case.(2)Based on the above-mentioned research,the numerical simulation of entire process was conducted for the case of only compression in the column bottom under the combination of axial load and unbalanced bending moment,the principal stress distribution and crack distribution status were achieved,it was revealed that the transfer mechanism is asymmetric spatial strut and tie model,it was made clear that the failure experiences three stages: precrack in the slab bottom,post-crack in the slab bottom and punching failure,it was obtained that the indication of the punching failure is fan-shaped strut’ failure near the load side of the column.(3)Based on the qualitative study of the above-mentioned two parts,the numerical simulation of entire process was conducted for tension and compression in the column bottom under unbalanced bending moment,the principal stress distribution and crack distribution were achieved,it was revealed that the transfer mechanism is strut and tie model with two diagonal connected,the studies exhibited that the indication of punching failure is bottle shaped strut’ failure.2.Quantitative studyBy using ADINA numerical simulation,combined the gradual least-square method for multiple variables,the calculating formulae on the punching capacity of slab-column joints under axial load were obtained.Based on these,combined with relevant literature,the calculating formulae of punching capacity were obtained for the compression in the column bottom.Based on theoretical analysis and relevant literature finally,the calculating formulae of punching capacity were obtained for the tension and compression in the column bottom.The formulae are rational by comparison with large test data.