Experimental Researches On Mechanical Behaviors And Calculation Method For Load-Bearing Capacity Of RC Two-Way Slabs

Cold-rolled deformed bar with double-wing, which is made of HPB235 bar through special production technology, is a kind of new-type cold-rolled deformed bar. This kind of bar has advantages of high tensile strength, good capacity to bond with concrete, convenience for building etc, and it is suitable for various kinds of cast-in-situ concrete slabs.To understand the mechanical behaviors of cast-in-situ concrete slabs reinforced by cold-rolled deformed bars with double-wing, an experiment of two-way slabs subjected to vertical loads is carried out and the behaviors, which include crack resistance capacity, crack distribution, inner-force distribution, deformation, and load-bearing capacity etc, are studied. The following conclusions can be obtained from the results of experiment. Firstly, the cast-in-situ concrete two-way slabs reinforced by cold-rolled deformed bars with double-wing have higher load-bearing capacity and yield lines can be developed when slabs approach to destruction. Secondly, the deflections of two-way slabs'mid-point are small at working load, so the requirements of some codes can be satisfied. Thirdly, there is good capacity of bars to bond with concrete, so great quantities of cracks are found on the bottom of each slab and the spaces between cracks are small, as well as the widths of cracks.Finite element analysis (FEA) program ANSYS are used to analyze the mechanical behaviors of cast-in-situ concrete two-way slabs reinforced by cold-rolled deformed bars with double-wing. The results show that the calculated curves of load-displacement, curves of load-stress of bars, figures of bars'stress distribution etc, are conformed to the results of experiment. These prove that program ANSYS can simulate the mechanical behaviors of cast-in-situ concrete two-way slabs reinforced by cold-rolled deformed bars with double-wing in all stages of elastic state, elastic-plastic state and limited state accurately. The results calculated by program ANSYS are reliable, so finite element method is an effective method.Both finite element method (in which dome effect of slabs can be calculated) and classical yield-line theory (in which dome effect of slabs can not be calculated) are used to calculate the ultimate load-bearing capacity of cast-in-situ concrete two-way slabs reinforced by cold-rolled deformed bars with double-wing. The results show that the ultimate load-bearing capacity of two-way slabs tested in experiment are equal to that calculated by finite element method approximately, but more than that calculated by classical yield-line theory. These prove that the ultimate load-bearing capacity of two-slabs can be enhanced by dome effect. In order to understand how dome effect impact the ultimate load-bearing capacity of two-way slabs, the ultimate load-bearing capacity of inside and side square slabs of various cast-in-situ RC two-way-slab structures are calculated by finite element method. The results show that the less the steel content or height-span ratio is, the greater the impact of dome effect is. Based on the researches above, some formulas are provoked to calculate the ultimate load-bearing capacity, which have enhanced by dome effect, of inside and side square slabs of cast-in-situ RC two-way-slab structures.