Shear strength of prestressed composite encased beams with unbonded or bonded tendons

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Shear strength of prestressed composite encased beams with unbonded or bonded tendons

 

Author: Choy, Siu-chung Adam
Title: Shear strength of prestressed composite encased beams with unbonded or bonded tendons
Degree: M.Sc.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Tendons (Prestressed concrete) -- Testing
Prestressed concrete beams -- Testing
Shear (Mechanics) -- Testing
Department: Multi-disciplinary Studies
Dept. of Civil and Structural Engineering
Pages: v, 210, [44] p. : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1643166
URI: http://theses.lib.polyu.edu.hk/handle/200/3223
Abstract: This paper focuses on the shear transfer mechanism of Prestressed concrete encased steel (PCES) beams- a hybrid structural member that has not been thoroughly studied. It is well known that the shear-carrying mechanism of conventional prestressed concrete beam after the occurrence of shear cracks can be satisfactorily modeled by truss models, such as a classical 450 truss model or a refined truss model (Diagonal Compression field Theory). In the case of steel beams or concrete encased steel beams subjected to shear, the steel web area is considered to resist the shear force, with the maximum average shear stress reaching 60% of the tensile yield stress. This occurs as a result of "Diagonal Tension Field Action" in which the diagonal web tensile stresses act with the transverse stiffeners and the flanges to the shear load. concrete beams and structural steel beams, it is doubtful that either one of the above-mentioned mechanisms or both can be used to model the shear resistance of the hybrid beam because the mechanisms of the diagonal compressive field and the diagonal tension field are different or even contradictory. In view of the above, it is important to conduct research in shear strength on PCES in order to gain a better understanding towards this type of structure for future application. In this paper, the results of shear tests on 14 prestressed composite encased beams with unbonded tendons (tested by others) and 6 with bonded tendons are examined. The purpose of the test was to elucidate the shear performance of PCES with unbonded and bonded tendons under monotonic loading. Evaluation and comparison of test results of PCES with the effect of various arrangements were made such as number of stirrups, shear span depth ratio and eccentricity of I beam. The load was plotted against deflection, and strains in steel beams. The test results indicate that the shear resistance of PCES beams can be predicted by adding the contributions due to (i) concrete Vc, (ii) web of I section Vweb, (iii) stirrups Vs, and (iv) vertical component of prestressed force Vp,. Among which, Vweb plays a major role to the shear resistance. The failure mode of most of the tested PCES beams is shear compression failure of the concrete. Based on the experimental results, an approach for predicting the shear strength of PCES has been proposed. The limitations of the proposed formula and suggestions for further study are also discussed.

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