Concrete Flat Plates of Optimum Thickness: Serviceability and Strength—Part I: Serviceability
Amin Ghali and Ramez B. Gayed
Appears on pages(s):
bridge deck; concrete floor; creep; deflection; grid analysis; prestressed reinforcement; relaxation; serviceability; shrinkage.
Optimum thickness of a concrete flat plate is the best or the most favourable for an objective. The most common objective is often miuimum cost; however, it can also be noise insulation, least vibration or plane soffit, with or without beams or drop panels. The minimum cost is often achieved by the smallest thickness that avoid excessive deflection in service. With small thickness, reinforcement is commonly needed for safety against shear failure. Part I: Serviceability, presents a procedure to predict long-term deflection of floors and bridge decks considering the effects of cracking, creep and shrinkage of concrete and relaxation of prestressing reinforcement. The system consists of a solid slab with or without drop panels and/or beams. For analysis, the system is idealized as grid of rigidly connected short beam elements. Strain distributions at end sections are determined, assuming linear elasticity and that plane cross sections remain plane. The analysis is based on compatibility and equilibrium principles, combined with time-dependent parameters for concrete and prestressed reinforcement. The displacements – translations and rotations – are determined from strain parameters by virtual work. Part II is concerned with design of slabs for shear strength.