Researches On Calculation Method For Internal Force Of RC Two-Way Slab Considering Effect Of Beam

Cast-in-situ two-way RC slabs have been applied in engineering practice more and more, but the calculation methods used at present don't consider the effect of beam. So it is a necessary problem to give some reasonable design suggestion about the calculation method for internal force of RC two-way slab considering the effect of beam.In the aspect of experiment, test of four simple-spanned cast-in-situ two-way RC slabs reinforced by cold-rolled deformed bars are carried out. The deformation and internal force distribution is studied. The experiment shows that the crack of cast-in-situ RC two-way slab reinforced by cold-rolled deformed bars is thin and densely covered. The research also shows that not only the stiffness ratio to beam to slab but also the width coefficient of beam has an effect on the internal force of beam-supported RC two-way slab.In the aspect of theoretical analysis, finite element analysis program ANSYS is used for researches on the internal force distribution of beam-supported RC two-way slab and the calculation method for internal force of slab is discussed according to the results of ANSYS. The conclusions are as follows:Firstly, when stiffness ratio of beam to slab is less than one, the traditional equivalent frame method should be used in the design of two-way slab. That is to say, the slab should be divided into the column strip and the middle strip under this condition.Secondly, when stiffness ratio of beam to slab is more than one and less than three and it works under uniform load, the positive middle span moment at midway strip and the negative support moment at exterior strip is biggest. When stiffness ratio of beam to slab is more than three and less than five and it works under uniform load, the positive middle span moment and the negative support moment at midway strip is biggest. In the design of slab, the above-mentioned moment should be used as criterion.Thirdly, when stiffness ratio of beam to slab is more than one and it works under skip load, the negative support moment is very small and it may be ignored. Under this condition, the positive middle span moment at midway strip is less than the moment obtained from the plastic theory, so the moment should be adjusted and the slab should be designed according to the adjusted moment.Lastly, if the width coefficient of beam is large, the applicable support moment of slab is occurring at the support face, but the position of the moment obtained from the plastic theory is at the axis of beam. The support moment of slab at support face and the middle span moment is studied in this paper. It shows that when stiffness ratio of beam to slab is more than one and the width coefficient of beam is bigger than 0.05, the moment of slab has some difference from the moment which is adjusted only take into account the influence of stiffness ratio of beam. So, under this condition, not only the stiffness ratio of beam to slab but also width coefficient of beam should be take into account in the process of calculating the moment of slab. And the moment should be seen as criterion when the slab supported by wide-flat beam is designed.