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This study investigates the relationship between transferred shear force and relative displacement of the shear connector in steel-concrete sandwich beam. The models, which can consider the effects of the height, thickness and shape of the shear connector, concrete strength, and thickness of the base steel plate where the shear connectors were attached, were proposed. The predicted relationship between transferred shear force and relative displacement as well as the curvature distribution along the vertical part of the shear connector are found to agree with the experimental results. Finite element analysis with the proposed model indicates its applicability as a constitutive model for shear connector.

Abstract:The research is focused on evaluating the average crack spacing of overlay-strengthened reinforced concrete (RC) beams. The current equations in different structural codes for predicting the average crack spacing of RC beam with multilayered-reinforcing bars is proved to be inapplicable for overlay-strengthened RC beam, although these two kinds of beams are both with reinforcement in multi-layers. Therefore, a simple, practical and new analytical model that is capable of predicting the average crack spacing of overlay-strengthened beams is developed. An overlay-strengthened beam element is analyzed based on equilibrium and compatibility equations to formulate the average stresses of concrete, overlay and tension reinforcement. A series of verification comparisons with the experimental investigations, which involved various types of beam elements, are performed to verify the validity and reliability of the model. The proposed model performs satisfactorily with respect to measured response from the experimental database.Keyword: crack spacing; overlay; strengthening; interface; bond; multilayered-reinforcement BackgroundOverlaying is considered as a major retrofitting method for flexural and fatigue strengthening or retrofitting of concrete flexural members. As illustrated in Fig Cracks in overlay-strengthened RC structures may be expected because of the relatively low tensile strength of concrete and overlay materials and the use of high strength reinforcement in substrate and overlay. Cracking in overlay-strengthened RC structures has a major influence on structural performance, including tensile, bending and shear stiffness, energy absorption capacity, ductility and corrosion resistance of reinforcement. Moreover, the average crack spacing of overlaystrengthened beams plays an important role in transferred shear stress along overlay-substrate interface and normal stress generated in the substrate concrete in case when the premature debonding failure is investigated (Zhang et al. 2010;Wang and Ling 1998;Raoof and Hassanen 2000). It is, therefore, necessary to predict the cracking behavior of overlay-strengthened RC beam.Despite the fact that many design models have been provided by different structural codes or individual researchers with respect to average crack spacing of RC members with single or multilayered-reinforcement (JSCE 2007; EC2 2004; CSA 2004; NS 1992; CEB-FIP 1990;Broms 1965;Albandar and Mills 1974;Bặzant and Oh 1983;Rizk and Marzouk 2010;Dawood and Marzouk 2010;Marzouk et al. 2010;Rizkalla et al. 1983;Rizkalla and Hwang 1984), which are similar to overlay-strengthened RC member with reinforcement layers in the substrate and overlay, their applicability for overlay-strengthened beams has not yet been investigated.The main objective of this study is to develop a rational methodology for predicting the average crack spacing of overlay-strengthened RC beam. Firstly, the predicted average crack spacing based on existing models from several design specifications is compared with that from expe...