Analysis And Application On Two-way Effects For Concrete Invertible T Composite Slab Floor Of Underground Structure

The concrete composite structure is one kind of prefabricated concrete structures which is poured concrete on precast element. The structure uses the prefabricated component in the base (pre-stressed or non-pre-stressed) and pours the cast-in-place concrete on the top, then forms the structures of global stress together. The precast slab of the traditional thin composite plate is too thin and rather difficult for prefabrication, transportation and hoisting. A main problem that need establish the temporary support in the process of construction and installation enormous limits the composite structure to use widely. In order to overcome this flaw, we use the pre-stressed concrete invertible T composite slab to replace the traditional thin composite plate.The pre-stressed concrete invertible T composite slab's costal part designs the final design thickness and the composition plane sets both sides of flange. The whole process does not install any support in the construction. It is bulit the composite floor of high effective pre-stressed concrete by using the high strength reinforced bar and high strength concrete. The pre-stressed concrete invertible T composite elements are manufactured by the factory and transported to the construction site for installation, compositing the new prefabricated concrete floor structures with the cast-in-place concrete superposition.This paper first discusses composite structure to secondary the load and mechanical behavior of invertible T composite structure. The composite construction shows the stress excess of tensile steel (precast element) strain hysteresis (late poured concrete) in the design calculation. Due to two-stage loading for composite structure, namely the precast element bears the construction load in the first stage, the precast part and the cast-in-place one form a complete to work together in the second stage. Invertible T precast slab composites the prefabricated concrete floor structures by late poured concrete, superadd entirety action of late poured concrete. So the two-way effects exist in the invertible T concrete composite structures. Using the large finite element software ANSYS to build model, through nonlinear analyzing researches the change of two-way effects for the invertible T composite floor. The results show that there exists the two-way effects to the invertible T composite slab, and reflects obviously of the two-way effects along with higher plate thickness. When the ratio of the long side and short side increases for identical thickness of slab, the two-way effects show decrease tendency. It may utilize the characteristics in the design construction of the invertible T slab, make it play a better role in construction of project and improve advantage of composite structure. The paper also uses the aeolotropic theory to analyze the invertible T composite floor structure. The example shows that the most important difference is deflection to isotropic plate and anisotropic plate, internal force and stress are not affected. But the anisotropy of inverted T hollow is limited. In practice, the anisotropic hollow is simplified to isotropic hollow. Inverted T hollow can solve the difficulty of span and weight, as well as retains its advantages. It performs a great advantage in mechanical behavior. Therefore, the design can be based upon the isotropic hollow. So the invertible T composite slab still carries on designing according to the isotropic plate.A comparative analysis of the pre-stressed concrete invertible T composite slab and PK pre-stressed composite slab, PK slab easily causes fracture failure in the construction process. Because the floor part of precast slab is only 30 mm. And the perforation steel of slab rib means construction difficulty. A comparative analysis of the pre-stressed concrete invertible T composite slab and the cast-in-place concrete slab, invertible T composite slab floor can save steel to a great extent by calculation.