A Comparison of the ACI and EC2 Codes Provisions for Flexural Deflection

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Title: A Comparison of the ACI and EC2 Codes Provisions for Flexural Deflection

Author(s): F. A. Malhas and A. Rahman

Publication: Special Publication

Volume: 210

Issue:

Appears on pages(s): 93-114

Keywords: concrete beams; creep; curvature; deflections; serviceablility; shrinkage

Date: 2/1/2003

Abstract:
ACI 318-99(1999) and EC2-92(1992) building design codes are the two major design code documents of reinforced concrete structures worldwide. Therefore, a detailed comparative analysis of these codes is justified and can be useful in understanding rational behind both codes. This type of comparative work can help identify iiscrepancies in either code and would substantiate their validity. In this regard, deflection computations and estimation of the flexural stiffness would be particularly attractive for detailed comparison. The analytical procedure adopted by ACI is particularly characterized by inconsistent correlation with test results, due to the fact that a number of factors affecting deflection have been ignored. In this study, detailed comparison with parametric analysis is conducted using the deflection provisions of ACI318-99 and EC2-92. First, the permissible deflections are compared and significant differences between the limits of the two codes are noted. The differences in the rationale of the deflection limits are identified. The span-to-depth ratio limits adopted by the two codes were found to have significant differences, with EC2 exhibiting more conservative limits. In comparing the two procedures for computing flexural deflection, all the pertinent quantities are investigated. These include: the cracking moment, the modulus of elasticity, the gross and cracked moment of inertia, the effective moment of inertia. A special form of the effecive moment of inertia equation is used to facilitate a parametric comparison between the two equations. Long-term flexural deflection is aslo compared and exhibits the differences between the two codes in relation to the impact of shrinkage, creep and compression reinforcement. This study is concluded by a numerical example that shows the differences between the codes in estimating short and long term deflection.