“Tension Property of Concrete and its Role in the Immediate Deflection of Reinforced Concrete Beam under Serviceability Limit State”
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Date
2015-12
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Addis Ababa University
Abstract
Modeling the behavior of cracked tensile concrete is a complicated issue. Due to
bond with reinforcement, the concrete between cracks carries a certain amount of
tensile force normal to the cracked plane. The concrete adheres to reinforcement
bars and contributes to overall stiffness of the structure. The phenomenon, called
tension-stiffening, has significant influence on the results of short-term
deformational analysis. The main objective of this thesis is to investigate the current
norms of calculating deflection and propose a free-of-shrinkage deflection
calculation alternative that incorporates tension-stiffening law for flexural reinforced
concrete (RC) members subjected to short-term loading.
It consists of an introduction, four Chapters and general conclusions. Reasons for
investigation and main objective are discussed in the first Chapter. The second
Chapter presents literature review on deformational models of RC members.
Furthermore design code and numerical methods for determining deflections of
reinforced concrete members are reviewed.
The third Chapter presents the current practice of calculating deflection along the
span of a beam. This is accomplished by taking a representative simply supported
beam with expected set of loads acting on it. The influence of shrinkage is not
included to emphasize on the role of the concrete in tension of RC members
subjected to short-term loading. A numerical procedure has been carried out for
computing free-of-shrinkage deflection of the beam using the current two most
prevalent codes; ACI 318 and EC2, as well as prominent deflection calculation
approach (Bischoff’s Method).
The fourth Chapter presents the findings of an experimental investigation as a
stepping stone to point out the role of concrete in the tension zone of a reinforced
concrete section under flexure. Also two approaches are discussed to include the
tension stiffening effect. First, the effective stiffness approach where the modulus of
elasticity of steel is modified to incorporate the tension stiffening role, and later the
modeling of the post–crack tensile property of concrete and quantify its effect in
relation to the area of concrete in the tension zone. This is followed by a proposed
method of using the two approaches to come up with a procedure to compute the
deflection of RC beam which is more practical and refined. The result of the
approach is compared with that of the results computed in Chapter three. The fifth
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Chapter presents the comparison and discussion of the predictions made in Chapter
three and four and the proposed model. Recommendations are expressed at the end
of the Chapter.
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Structures