Determination of Bond Capacity in Reinforced Concrete Beam and Its Influence

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Mechanics, Materials Science & Engineering, September 2016

ISSN 2412-5954

Determination of Bond Capacity in Reinforced Concrete Beam and Its Influence on the Flexural Strength Mohammad Rashidi1, Hana Takhtfiroozeh2 1

Department of Civil Engineering, Sharif University of Technology, Tehran, Iran

2

Department of Civil Engineering, Building and Housing Research Centre, Tehran, Iran DOI 10.13140/RG.2.2.18300.95361

Keywords: flexural strength, bond capacity, tensile bars, reinforced concrete beam, compressive strength

ABSTRACT. This paper presents results of an experimental investigation of actual performance of the reinforced concrete beam in bond under flexure, when reinforced with tension steel is going to consider. In this experiment four specimens of beam and a bar in the middle of the width of the beam has been used and 2.5 cm of concrete cover has been considered from the center of the bar. In addition, transverse bars have been used to reassure lack of shear yield at the two ends of the beam. Flexural bar has been put in the middle of the beam symmetrically and the length of the flexural bar in each of the samples shall be: 15, 20, 30 and 40 cm. Three cylindrical samples were made in order to determine f'c and were examined at 28 days and the compressive strength of concrete used in this study was about 35 MPa. The beam samples were examined after 28 days via two-point loading system. Based on the results, increasing the length of bar causes increase of flexural strength. The presence of longitudinal rebar resulted in the ultimate momentum to be more than the crack momentum of the cross-section in parts which have broken at the point of longitudinal bar cut.

Introduction. Concrete is of a lot of use in constructions due to availability, appropriate compressive strength and ease of implementation; although, its weakness in traction has resulted in not being able to use this material solely in construction. In order to eliminate the weak traction of concrete, usually bar is used in the tensile area of the concrete. The goal of this experiment is to determine the bond strength between steel reinforcing bars and concrete. The main parameters that influence this bond strength are well documented in the technical literature. Important among these parameters include development/splice length, diameter of the reinforcing bar, and concrete compressive strength [1, 2, 3, 4]. The type of cracking leading to failure has been investigated using deformed bars in tension by injecting ink around the bars [5, 6]. The bond strength of rebars in concrete decreases as the embedment length increases, and decreases with increasing the bar diameter [7]. The previous investigations proved that the bond strength of rebars in concrete is influenced by the development length rather than the bar diameter [8]. The ultimate bond strength seems to be a function of c f 'c when other parameters are constant, since the bond strength is related to the tensile strength of concrete. Studies on understanding the nature of bond, modes of failure and factors influencing the failure, bar spacing and beam width, end anchorage, flexural bond and anchorage bond with high strength ribbed bars have been reported [9]. The slip of deformed bars is due to (i) splitting of concrete by wedge action, and (ii) crushing of concrete in front of the ribs [9]. Nilson [10] used slope of steel strain curve to evaluate the bond stress at a given load in reinforcing bar, and a new test method was adopted to study the local slip, secondary cracking and strain distribution in concrete [11]. A bond stress-slip model has been proposed to predict the load end slip and anchorage length of bars extended from adjoining beams in to exterior columns under large nonlinear actions [12]. Effect of bar diameter, confinement and strength of concrete on the bond behaviour of bar hooks in exterior beam-column joints has been reported [13]. The bond strength decreases as the bar diameter increases. The post-peak bond-slip response was not influenced by the bar diameter [14], while confinement has direct influence on the local bond stress [15]. A new bond MMSE Journal. Open Access www.mmse.xyz

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