Long-term monitoring of slab deflections of a multi-level office building

Excessive deflections in concrete members during the service life of a building that are not accounted for in design lead to structurally inefficient buildings. Indirect results are the visible appearance of cracks in partition walls and other elements supported by these members, leading to serviceability problems. Hence, deflection analysis is important to ensure that the reinforced or prestressed concrete flexural member will deflect within the allowable limits during its lifetime. Many factors contribute to the deflection of concrete members such as concrete properties, reinforcement and tendon properties, creep and shrinkage, loading sequence, cracking, bond-slip behaviour between concrete and steel. Hence, the primary objectives of this research are to develop an analytical model to evaluate the time-dependent deflections in post-tensioned concrete suspended slabs considering above factors and validate this model by using real-life measurements of long-term slab deformations. For this purpose actual deflections of one-way spanning slabs and band beams of a multi-level office building under construction are being measured and experimental testing of concrete compressive strength, concrete creep, shrinkage, modulus of rupture and modulus of elasticity were carried out. This paper presents a comparison between measured on site deflections of slabs and beams during construction with calculated deflections using the simplified method given in AS 3600.