Tension Property Of Concrete And Its Role In The Immediate Deflection Of Reinforced Concrete Beam Under Serviceability Limit State

Modeling the behavior of cracked tensile concrete is a complicated issue. Due tornbond with reinforcement, the concrete between cracks carries a certain amount ofrntensile force normal to the cracked plane. The concrete adheres to reinforcementrnbars and contributes to overall stiffness of the structure. The phenomenon, calledrntension-stiffening, has significant influence on the results of short-termrndeformational analysis. The main objective of this thesis is to investigate the currentrnnorms of calculating deflection and propose a free-of-shrinkage deflectionrncalculation alternative that incorporates tension-stiffening law for flexural reinforcedrnconcrete (RC) members subjected to short-term loading.rnIt consists of an introduction, four Chapters and general conclusions. Reasons forrninvestigation and main objective are discussed in the first Chapter. The secondrnChapter presents literature review on deformational models of RC members.rnFurthermore design code and numerical methods for determining deflections ofrnreinforced concrete members are reviewed.rnThe third Chapter presents the current practice of calculating deflection along thernspan of a beam. This is accomplished by taking a representative simply supportedrnbeam with expected set of loads acting on it. The influence of shrinkage is notrnincluded to emphasize on the role of the concrete in tension of RC membersrnsubjected to short-term loading. A numerical procedure has been carried out forrncomputing free-of-shrinkage deflection of the beam using the current two mostrnprevalent codes; ACI 318 and EC2, as well as prominent deflection calculationrnapproach (Bischoff’s Method).rnThe fourth Chapter presents the findings of an experimental investigation as arnstepping stone to point out the role of concrete in the tension zone of a reinforcedrnconcrete section under flexure. Also two approaches are discussed to include therntension stiffening effect. First, the effective stiffness approach where the modulus ofrnelasticity of steel is modified to incorporate the tension stiffening role, and later thernmodeling of the post–crack tensile property of concrete and quantify its effect inrnrelation to the area of concrete in the tension zone. This is followed by a proposedrnmethod of using the two approaches to come up with a procedure to compute therndeflection of RC beam which is more practical and refined. The result of thernapproach is compared with that of the results computed in Chapter three. The fifthrnAddis Ababa University Addis Ababa institute of technology-AAiTrnSchool of Civil and Environmental Engineering Page 2 of 72rnChapter presents the comparison and discussion of the predictions made in Chapterrnthree and four and the proposed model. Recommendations are expressed at the endrnof the Chapter.

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