Percorrer por autor "Santos, Pedro M. D."
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- Recommended improvements to current shear-friction provisions of model codePublication . Santos, Pedro M. D.; Júlio, Eduardo N. B. S.The shear-friction theory, first proposed by Birkeland and Birkeland (1966), was adopted by CEB-FIP Model Code 1990 to predict the longitudinal shear strength between parts of concrete members cast at different times. This is a relevant subject for different situations, such as the connection between precast members with cast-in-place parts and strengthening of existing RC members with a new concrete layer. Other situations, such as corbels; metallic supports subjected mainly to shear forces; regions near supports; and the connection between columns and foundations can also be designed using the shear-friction theory. It is known that surface roughness plays a significant role on the bond strength of concrete-to-concrete interfaces. Recent studies, using a laserbased device specifically developed to quantify the texture of concrete surfaces, proved that roughness can be measured and, moreover, correlated with the cohesion and friction coefficients present in the Model Code's design expression. Therefore, the current qualitative assessment of the surface roughness, merely based on a visual inspection, can be replaced by an accurate and quantitative approach. The curing conditions of the substrate concrete (old concrete) and of the added concrete layer (new concrete) are not considered either. This can have a significant influence because additional stresses can appear at the interface between both concrete layers due to differential shrinkage. Differential stiffness due to the difference between Young modulus is not addressed either. In this paper, improvements to Model Code 90's design expression for longitudinal shear strength between concretes cast at different times are recommended. Furthermore, a comparison between the design expressions proposed by the CEB-FIP Model Code 1990, the Eurocode 2 and the ACI 318 is presented.
- A state-of-the-art review on roughness quantification methods for concrete surfacesPublication . Santos, Pedro M. D.; Júlio, Eduardo N.B.S.Surface roughness plays an important role in the behavior of concrete-to-concrete interfaces. Methods like sand-blasting and hydrodemolition are usually adopted to improve the surface roughness of the concrete substrate. Before placing the new concrete layer it is common to verify the roughness level by visual inspection. However, this procedure can lead to inaccurate conclusions since it is influenced by the technician’s opinion and, therefore, it is subjective. Current design codes of concrete structures implicitly propose this type of assessment since there is not a specified method or device to verify the conditions of the substrate surface. To overcome the drawbacks of this qualitative methodology, a quantitative approach should be adopted instead. Thus, it is necessary to measure the surface roughness and, from this, to compute roughness parameters. This paper presents a review on roughness quantification methods that can be adopted for concrete surfaces.