| Reinforced concrete deep beams are widely used in parts with complex loading conditions,such as the transition floors of high-rise buildings and cover beams in bridges,because of their advantages in stiffness and bearing capacity.However,the design of deep beams are difficult because they are complex force members whose force characteristics are different from those of ordinary beams,and the force becomes more complicated after the opening of the beam web.At present,the current code in China still recommends an empirical design method based on the correction of plane section assumption,which lacks sufficient mechanical support.;strut-and-tie model design method recommended by the mainstream European and American codes has clear mechanical concepts,but it is difficult to build the model.Therefore,it is of great engineering significance to explore the rationality and reliability of the relevant design formulas of current code in China and to improve the stress design method with topology optimization assisted strut-and-tie model design.The main contents are as follows:(1)The test data of 83 members designed according to the appendix of the current code of China for deep flexural members are collected.The predictive ability of calculation formula of shear bearing capacity of our code under different loading,opening rate,bearing width and shear-to-span ratio is explored based on the test data,and then its reliability in the design of deep flexural members are analyzed.The results show that the experimental values of shear bearing capacity under different loading differ from the calculated values and are poorly coordinated;opening of the beam web has a greater impact on the safety of the member;bearing width may have an effect on the shear load capacity of beam without web;the inappropriate restriction of the shear-to-span ratio in the code leads to the inaccurate calculation value of the shear bearing capacity in the code formula.The above problems with Chinese code are more difficult to solve in the short time.(2)Although the strut-and-tie model method can effectively solve the above difficulties,but its configuration is not unique.This problem can be overcome by topology optimization,which makes it feasible to design reinforced concrete deep beams using the strut-and-tie model.In order to understand the auxiliary capability of this new method and promote it to maturity,the optimal topological solutions of opening deep beams under different loading conditions are obtained in the paper using topology optimization.The differences between them and the corresponding mechanical mechanisms are explored.Based on the topological solution to guide the establishment of the strut-and-tie model,the optimal topology and the strut-and-tie model are proved to comply with the Michell truss criterion by comparing with the Michell structure,and the force mechanism of the opening deep beams under different loading conditions are elaborated.(3)In order to verify the reliability and rationality of the constructe of strut-and-tie model based on topology optimization and complete with reinforcement design.In this paper,based on nonlinear finite element analysis,simulation analysis of opening deep beams under different loading positions of empirical design and strut-and-tie model design.The analysis results show that the members of strut-and-tie model designed based on topology optimization have reasonable arrangement of reinforcement and conform to the force mechanism of opening deep beams,which can effectively solve the problem of surplus bending capacity but insufficient shear capacity of empirical method.In summary,the use of topology optimization to guide the reinforcement design of the strut-and-tie model can effectively solve the design difficulties of the current code in China for deep flexural members,which is very important for improving the design of concrete structures. |
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