| The multi-ribbed slab with good mechanical properties has been widely used in large space structure, but because of the complexity of the structure itself, the unclarity of mechanism behavior and not uniform of design methods, so there are many problems need to be studied. Moreover, with the increaseing of span, the issues has become increasingly prominent between the height increase of ribbed beams and edge beam with the control of storey height, against conflict of beams with pipeline, improvement of the mechanical properties of structure. To solve these problems, it is a good method of adding steel fibers in the multi-ribbed slab. Taking into account the influence of steel fiber, the multi-ribbed slab, edge beam and whole beam-slab system are be researched by the methods of experiment research, the theory analysis and numerical simulation. And the study are mainly on the calculation model and methods on mechanism parameters, equivalent stiffness, deflection and internal forces of multi-ribbed slab, bearing capacity subject torsion of edge beam and the behavior of the whole structure system. The main research contents and the results are as follows:(1) Based on the composite material theory, taken into account the influence of steel fiber, the calculation model and formulas on mechanism parameters of steel fiber reinforced concrete(SFRC) structure are given. According to the tiny deflection theory of the elastic thin slab, the formulas on equivalent stiffness are derived. The analytical solution of deflection and internal forces for SFRC multi-ribbed slab simply supported by four edge are given. The numerical solution of deflection and internal force for multi-ribbed slab fixed supported by four edge are also given. (2) For absence of calculation of the SFRC beam under torsion or composite torsion, basing on the mechanics capacity of SFRC beams in torsion and considering the influence of the steel fiber, formulas on ultimate torque of the nonprestressed and prestressed SFRC beams are given using the variable angle space truss analogy. The calculation formulas have two types named parameter modification method and equivalent steel bar method. The calculation results are compared with test results, which indicate the formulas have high precision, and can joint with the calculation formulas on ultimate torque of common reinforced concrete beams well. Considered the influence of steel fibers on ultimate capacity, the formulas of ultimate torque in three failure types of nonprestressed and prestressed SFRC beams under composite torsion are given. Moreover the determination method of failure type and ultimate torque in practice are also given.(3) Because the steel fibers are chaos in the distribution, it is impossible to accurately determine the location of each fiber and the direction in the analysis. According to the theory analysis the whole equivalent bars method is given to simulate the function of steel fibers. The comparison results of numerical solutions with test results indicate the analysis method can simulate the behavior of SFRC structure.(4) The study on behavior of whole slab system are made by the numerical analysis using the whole equivalent bars method. The researches indicate the failure mode, development of cracks and the location of plastic hinge lines of SFRC multi-ribbed composite slab system are in close agreement with the theoretical analysis. The value and distributions of stresses are influenced by the internal force distributions of the structure. Basing the result of parameters analysis, the steel fiber volume fraction should is limited 1% to 2%, the cubic compressive strength of concrete should is more than 40Mpa,and the compressive zone can not add to steel fibers if the edge beam with enough stiffness and bearing capacity. Moreover, taking into account the influence of constraint between edge beam and multi-ribbed slab, the calculation method of elastic compatibility torsion of edge beam and deflection and internal forces of multi-ribbed slab are given.The originalities of this dissertation lie in:(1)The calculation model and methods on mechanism parameters, equivalent stiffness and deflection and internal force of SFRC multi-ribbed slab are put forward.Based on the composite material theory, taken into account the influence of steel fiber, the calculation model and formulas of steel fiber reinforced concrete(SFRC) structure are given. Taking into account the influence of steel fiber, the formulas on equivalent stiffness are derived. The calculation formulas of deflection and internal force for SFRC multi-ribbed slab are given using pseudo-plate method. The theory calculation results are compared with numerical results which indicate the calculation formulas have high precision and can satisfy the request of engineering..(2) The practical calculation formulas on ultimate torque of nonprestressed andprestressed SFRC beams are given For absence of calculation of the SFRC beam under torsion or composite torsion, basing on the mechanics capacity of SFRC beams in torsion and considering the influence of the steel fiber, the practical formulas on ultimate torque of the nonprestressed and prestressed SFRC beams are given. The calculation results are compared with test results which indicate the formulas have high precision, and can joint with the calculation formulas on ultimate torque of common reinforced concrete beams well. Considered the influence of steel fibers on ultimate capacity, the formulas of ultimate torque in three failure types of nonprestressed and prestressed SFRC beams under composite torsion are given. Moreover the determination method of failure type and ultimate torque in practice are also given.(3)The study on behavior of whole slab system are made by the numerical analysis,and the calculation method of elastic compatibility torsion of edge beam and deflection and internal forces of multi-ribbed slab are given.According to the theory analysis the whole equivalent bars method is given to simulate the function of steel fibers. the study on behavior of whole slab system and parameters analysis are made by the numerical analysis. Basing the result of parameters analysis, the Steel Fiber Volume Fraction should is limited 1% to 2%, the cubic compressive strength of concrete should is more than 40Mpa,and the compressive zone can not contain steel fibers if the edge beam with enough stiffness and bearing capacity. Moreover, taking into account the influence of constraint between edge beam and multi-ribbed slab, the calculation method of elastic compatibility torsion of edge beam and deflection and internal forces of multi-ribbed slab are given. |
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