Analysis Of Internal Force And Research Of Design Methods For Cast-in-situ Concrete Hollow Floor System

Cast-in-situ concrete hollow floor structure has been widely used all over the country. But its present design methods, without enough consideration of practical rigidity offering, make the results be conservative. Combined with one of the important supporting projects of Constructive Hall of Hunan Province, the main contents of this paper are introduced below:Based on summing-up the developing situation of cast-in-situ concrete hollow floor technology all over the country, current design methods are introduced. Calculating results indicate that these methods cannot faithfully reflect the influence of hollows to local stresses of slabs, so that it is necessary to establish three-dimensional solid elements to make mini-model simulating analysis by FEM.ANSYS, an analytic software for FEM, is used to make three-dimensional nonlinear analysis overall for cast-in-situ concrete hollow floor. The difference of internal force distribution between this floor and waffle slabs is compared and analyzed. The laws of internal force distributing of this floor is summarized, such are: (1) structure as"orthotropic slabs"; (2) abnormity of internal force distribution; (3) greatly changing grads of negative bending values. From above analysis, it is proved that, because the internal force distribution of cast-in-situ concrete hollow floor is notably different to that of waffle slabs, designed as grillage beams and reinforced by these results, the technical advantage of this structure may not be exerted sufficiently so that leading to the increase of reinforcement.Furthermore, anti-punching characteristic at the end of column and geometric parameters of cast-in-situ concrete hollow floor are analyzed. Realized from the punching cracking characteristic, its punching shear capacity is related closely to the number of hollows crossing the punching cracks. Geometric parameters of this floor with both box filler and tube filler are analyzed respectively. Indicated from the results: influenced by geometric parameters analyzed above, the effect on tube filler hollow floor is similar with box filler hollow floor; though differing from section properties between these two structures, the bear bending rigidities in the two perpendicular directions are almost the same.In the end, according to the conclusion of the analysis of mechanic properties acquired above, a new design method and reinforcement manner is put forward for this structure.