Expermental Researches On Deflection Of Cast-in-Situ RC Two-Way Slab

Cast-in-situ RC two-way slab by cold-rolled deformed bars with double-wing is a kind of two-way slab. In this paper, there are four experimental models of Cast-in-situ RC two-way slab by cold-rolled deformed bars with double-wing(two slabs are supported on ordinary beam, the other two slabs are supported on wide-flat beam).This paper analyze the mechanical characteristics of the four experimental models subjected to vertical uniform loads. This researches is emphasized on the mechanical performances of cast-in-situ RC two-way slab by cold-rolled deformed bars with double-wing and on the deflection of two-way slab at elastic stage and at inelastic stage with cracks. .This paper have several material researching tasks as following . In the aspect of experiment, the appearance and the development of the cracks is observed and the stiffness and deflection are studied. It is discovered that the cracks of Cast-in-situ RC two-way slab by cold-rolled deformed bars with double-wing is thin and densely covered;- torsion restraint of the beam is notable, which reflected from the bigger measured crack load and the less measured mid deflection, so the beam-torsion restraint need considering.In the aspect of theoretical analysis, this paper accounts for the calculative methods of short-term deflection deflections and gains formula at elastic stage under the service load.(1) In the analysis on stiffness, deflection and internal force of the ordinary beam-supported slab, classical elastic plate theory is used. Based on this theory, we get the deflection-formula considering the influence of beam-torsion restraint, in which the ratio coefficientλof beam's torque stiffness to plate's flexural stiffness reflecting degree of beam-torsion restraint. For continuous multi-span ordinary beam-supported slab, the influence of adjacent slab and disadvantage load is considering, and this paper work out the calculative methods in this conditions. In the analysis on wide-flat beam-supported slab, there are more factors when calculates deflection, so finite element analysis for plate is used. Through analysis on the thirty five finite element models, we get the fitted deflection-formula. For continuous multi-span wide-flat beam-supported slab, the fitted deflection-formula under the influencing of adjacent slab and disadvantage load is present.(2)The analysis on short-term stiffness and short-term deflection at inelastic stage with cracks. It is difficult to calculate the short-term stiffness and short-term deflection at the service load. According this paper research, the section-stiffness of mid plate-strip in the two-way slab have an analogy with one-way flexural member, so stiffness can be obtained through calculating the section-stiffness of one-way flexural member."The least stiffness principle"is not suitable for deflection-calculation of two-way slab because it is two-way resisting outside force and the larger moment-area is small. Therefore this paper present the short-term deflection-calculation of the two-way slab through calculating the deflection of mid plate-strip in the two-way slab. The mid plate-strip can be divided several segments, then calculate the moment, stiffness and curvature (even curvature) of each segment. Through curvature-area moment method ,we can calculate the mid deflection of the mid plate-strip and the result is satisfactory.The all above calculations are testified reliable and reasonable by experiments, which can be applied by civil engineers.