Resrarch On Some Key Problems In Prestressed Concrete Floors

For its prominent merits, Bondless-Prestressed Concrete Structures (BPCS) have been paid much attention, and applied more and more widely. Designing a BPCS, however, we would encounter some problems worthy of analyzing and investigating further. In this paper, based on analysis of existing experiments and examples related to prestressed concrete slab system and finite element method, some problems in prestressed concrete beamless slab and reinforced concrete two-way slab supported by beam as the following items are studied.1. On the design method of tendon arrangement in beamless slabs. As for beamless slabs with the same amount of prestressed reinforcement and non-prestressed reinforcement but different reinforcing ways, the bearing capacities are considered to be the same according to former experiment results. Based on this point, the arrangement of tendons is considered to be arbitrary by equivalent frame method as long an the amount of tendon is unchangeable. However, in designing the beamless slabs with equivalent frame method, the stress is an average values along the depth of section, which varies with the normal service state. Compared with the results by finite element method (FEM), the results gained by equivalent frame method cannot satisfy the requirement under the normal service state. Therefore, the tendons of beamless slabs should be designed and arranged based on the results of FEM taking account into vertical load and prestressed load.2. On mechanical behaviour of beamless slabs with bondless tendons disposed along width of columns. According to existing design methods, tendons in slab arranged in the range of column width are considered blind beams supporting the two-way slab, and the slabs encased by the tendons are designed in terms of the two-way slab. Herein, mechanical behaviour of beamless slabs that bondless tendons are disposed along width of columns is studied. The conclusion is that the mechanical behaviour of slabs in which prestressed reinforcement is designed in two-way designed by existing methods is different with the slabs supported by real beams. Therefore, the general steel reinforcement in the slabs should not be disposed according to the stress distribution of slabs supported by beams. Based on the FEM, for the slabs with tendons arranged along column width, the method that the amount of two-way tendons is determined by end reaction of slabs supported by beams is proposed.3. On reaction of support in two-way slabs supported by beams. In the practice, for the slabs supported by beams, the rigidity of beams cannot be infinitely great, the load distribution on two-way beams is influenced by the rigidity of beams and relative rigidity of two-way beams. Besides, the deflection of beams under vertical...