Title:
Concrete Flat Plates of Optimum Thickness: Serviceability and Strength—Part I: Serviceability
Author(s):
Amin Ghali and Ramez B. Gayed
Publication:
Symposium Paper
Volume:
353
Issue:
Appears on pages(s):
142-163
Keywords:
bridge deck; concrete floor; creep; deflection; grid analysis; prestressed reinforcement; relaxation; serviceability; shrinkage.
DOI:
10.14359/51737116
Date:
7/1/2022
Abstract:
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.
Related References:
ACI 209.2R-08, 2008, Guide for Modeling and Calculation of Shrinkage and Creep in Hardened Concrete, American Concrete Institute, Farmington Hills, MI, 48 pp.
ACI 435R-95, 2000, Control of Deflection in Concrete Structures, American Concrete Institute, Farmington Hills, MI, 77 pp.
Fédération Internationale du Béton, fib. CEB-FIP, Model Code for Concrete Structures, 2010, Vol. 1, 317 pp.
Gayed, R.B. and Ghali, A., 2019, “Control of Long-Term Deflection by Prestressing”, Structural Concrete Journal of fib, doi: 10.1002/suco.201800340, August, pp. 1-12.
Gayed, R.B. and Ghali, A., 2020, “Avoiding Shear Failures and Excessive Deflection of Concrete Flat Plates,” ASCE, Journal of Structural Engineering, DOI: 10.1061/(ASCE)ST.1943-541X.0002796.
Ghali, A., Elbadry, M. and Megally, S.H., 2000, “Two-Year Deflections of the Confederation Bridge,” Canadian Journal of Civil Engineering, Vol. 27, No. 6, pp. 1139-1149.
Ghali, A., Favre, R. and Elbadry, M., 2012, Concrete Structures: Stresses and Deformations, CRC Press, Spon Press, 4th Edition, 637 pp.
Ghali, A. and Neville, A.M., 2017, Structural Analysis: Analytical and Matrix Approach, CRC Press, Spon Press, 7th Edition, 933 pp.
Magura, D., Sozen, M.A. and Siess, C.P., 1964, “A Study of Stress Relaxation in Prestressing Reinforcement,” PCI Journal, Vol. 9, No. 2, pp. 13-57.
Neville, A.M., Dilger, W.H. and Brooks, J.J., 1983, Creep of Plain and Structural Concrete, Construction Press, 361 pp.