Report on Deflection of Nonprestressed Concrete Structures
|Publication Date:||1 November 2020|
The principal causes of deflections taken into account in this report are those due to elastic deformation, flexural cracking, creep, shrinkage, and temperature effects. This document is composed of two introductory chapters and four main chapters that provide information on calculating and controlling deflections of members constructed using reinforced concrete. The organization of the report is:
a) Chapter 1-Introduction and Scope provides background information on the document.
b) Chapter 2-Notation and Definitions provides a listing of the notation used throughout the document.
c) Chapter 3-Material Properties discusses material properties that affect deflections.
d) Chapter 4-Deflection of Reinforced Concrete One-Way Flexural Members discusses behavior of uncracked and cracked members, and time-dependent effects. It also includes the relevant code procedures and expressions for deflection computation in reinforced concrete beams. Numerical examples are included to illustrate the standard calculation methods for simply supported and continuous concrete beams.
e) Chapter 5-Deflection of Two-Way Slab Systems covers the deflection behavior of reinforced two-wayaction slabs and plates. This chapter gives an overview of classical and other methods of deflection estimation, such as the crossing beam analogy and the finite element method for immediate deflection computation. It also discusses approaches for determining the minimum thickness requirements for two-way slabs and plates and gives a detailed computational example for evaluating the longterm deflection of a two-way reinforced concrete slab. The chapter emphasizes the uncertainties inherent in estimating deflections of two-way slab systems.
f) Chapter 6-Reducing Deflection of Concrete Members gives practical and remedial guidelines for improving and controlling the deflection of reinforced concrete members, hence enhancing their overall longterm serviceability.
It should be emphasized that the magnitude of actual deflection in concrete structural members, particularly in buildings, which are the emphasis and the intent of this report, can only be estimated with limited accuracy. This is because of the large variability in the properties of the constituent materials of these members, the quality control exercised in their construction, and the construction methods used. Therefore, for practical considerations, the computed deflection values in the illustrative examples at the end of each chapter should be interpreted with this in mind.
In summary, this single document gives design engineers the key tools for estimating, and thereby controlling through design, the expected deflection in nonprestressed reinforced concrete building structures. The material presented and the design examples will help to enhance serviceability when used judiciously by the engineer. Designers, constructors, and codifying bodies can draw on the material presented in this document to achieve serviceable deflection of constructed facilities.