Punching Shear Strength of Post-Tensioned Concrete Flat Plates

摘要

Flat slabs are an economical structural system for medium height residential and office buildings. Prestressed concrete flat slabs have the additional advantages that longer spans can be used and deflection problems are less significant. Punching shear of reinforced or prestressed concrete flat slabs is an undesirable mode of failure in that it occurs without warning and can lead to progressive collapse of large areas of slab or even complete structures. Modellingthepunchingshearstrengthof prestressed concrete slabs is conceptually difficult as the tendons can be bonded or unbonded, the tendons can pass through the columns or not, the stress in the tendons at punching failure is indeterminate, the tendons can be banded and the tendons can be draped resulting in beneficial vertical components of the prestressing force. The paper describes the code provisions, ACI318-05, BS 8110-97, CEB-FIP1990 Model Code (Comite Euro-International du Beton and Federation International de la Precontrainte), CSA A23.3-04, DIN 1045-1:2001-07 and Eurocode 2-2003. In general, the code provisions for punching shear of prestressed concrete flat slabs are extensions of the punching shear provisions for reinforced concrete flat slabs. Most codes require supplementary bonded reinforcement in negative moment regions which complicates analysis. The literature has been reviewed to locate experimental results of punching sheartests for isolated prestressed concrete flat plates, continuous prestressed flat plate systems and tests of flat plate column connections under shearand moment transfer. Recent research has indicated that the limitations on concrete strength in code equations and ignoring the precompression close to the slab edge are too conservative. The simplifications of an effective slab depth not less than 80% of the slab depth permitted by ACI 318 and CSAA23.3 in calculations of the punching shear capacity of prestressed concrete flat slabs should be eliminated.