Design Of Reinforced Concrete Deep Beam Based On Strut-and-tie Model

The strut-and-tie model is one of methods to determine the bearing capacity of reinforced concrete structures which the assumption of plane section is not satisfied and that in disturbed area. Up to now, the method has been introduced in foreign design codes of concrete structures. It is shown that the strut-and-tie model has been used in practice. Though a great progress has been made in recent years, the strut-and-tie model is difficult to use in design for its complicated modeling. The analysis and calculation of concrete structures under fixed loads using strut-and-tie model has been conducted in previous studies. However, few studies under moving loads and uniformly distributed loads has been stated until now. The main contents of this paper are as follows:(1) The topology optimization design is conducted using software ANSYS. The principles of transforming topology optimization into strut-and-tie model are given based on analysis of several examples.(2) Design of deep beam under moving loads based on strut-and-tie model is studied. The strut-and-tie model is changing constantly, resulting that the internal force in member, the angles between members and support reactions are characterized as a function of the distance from the moving load to the end of deep beam. The results show that there is a most unfavorable location during the course of moving. The area of reinforcements and concrete strength is controlled by the maximum of the stress in ties and struts.(3) Design of deep beam under uniformly distributed loads based on strut-and-tie model is studied and the integral expressions for calculating tension in tie are given. The results show that the concrete strength or section dimension is controlled by the compressive stress in struts corresponding to the minimum angle between the strut and tie while the minimum reinforcement ratio is controlled by the distributing reinforcement corresponding to the maximum angle between the strut and tie.(4) The design methods of deep beam in GB 50010-2002 are compared with that in ACI 318-05. Comparing with the semi-experience method in Chinese code, the strut-and-tie model can simultaneously consider the analysis of bending, shear and local bearing capacity in the same mechanical model, which let it be the development trend of reinforced concrete structure design.