The shear provision for members without shear reinforcement in the second generation of Eurocode has been changed to a new set of formulas based on the critical shear crack theory (CSCT). The formula is based on a shear failure criterion originally developed for reinforced concrete members without shear reinforcement. To allow its application as a design code type for formula, the original CSCT failure criterion undergoes several modifications, such that it can be used to verify the shear resistance of prestressed members as well. Since the new Eurocode shear provision will be applied to design and assess prestressed concrete members in Europe and many other countries in the world, it is important to extensively validate this model. This paper presents a validation study of three different variations of the CSCT strain-based failure criteria, including the one eventually employed in the second generation Eurocode shear provision, using the ACI-DAfStb shear database. The results are also compared with the current Eurocode shear provisions. The second generation Eurocode shear formula appears to be able to determine the shear resistance more accurately than the current one, even for prestressed concrete members without shear reinforcement while it was not actually developed for this. However, Annex I.8 shear formula may lead to an overestimation of the shear resistance for higher values of the effective span to depth ratio (acs/d).

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Prestressed hollow-core slabs (PHCS) are generally fabricated through an automated extrusion method by using an extremely dry concrete mixture to maximize productivity in precast factories. In consequence, it is very challenging not only to provide shear connectors along the interface between the PHCS unit and cast-in-place (CIP) topping concrete but also to secure code-compliant intentional roughness due to its extremely hard and flat surface condition. Thus, it is difficult to have sufficient horizontal shear strength required to achieve flexural performances of the prestressed composite members. To this end, extensive pushoff tests were conducted in this study considering various interface roughness conditions, from which some viable options were chosen. Then, flexural tests on full-scale composite PHCS specimens were performed with selected surface conditions from the pushoff tests. On this basis, the applicability of various surface roughness conditions that are inevitably faced in practices is examined based on ACI 318 design criteria and nonlinear analysis. It was confirmed that sufficient horizontal shear strength can be achieved not only by properly roughened surface conditions but also by placing wire meshes between PHCS units even with no intentional roughness.

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Many existing studies on punching shear in a RC flat plate slab without shear reinforcement consider uncracked concrete in the compression zone or the aggregate interlock mechanism in the cracked tension zone as shear resistance to external shear forces. However, recent studies have provided clear experimental evidence indicating interdependency between the resistance mechanisms in uncracked and cracked concretes. This study aims to extend the dual potential capacity model (DPCM) for estimating the punching shear strengths of RC slabs. The proposed model can consider both the shear resistance mechanisms of the compression and tension zones by introducing dual demand curves and corresponding potential capacity curves based on a robust theoretical background. In addition, a simplified method was also developed for a better applicability, and test results collected from existing studies were compared against those estimated from the proposed methods and design code models. Based on a total of 224 punching shear test results, the proposed methods were verified, and their analytical accuracy was also compared with those estimated by design codes. The punching shear strengths estimated by the proposed method agreed well with the test results regardless of key variables. The estimation presented the average and coefficient of variation (COV) of the ratio of calculated to tested strength equal to 1.023 and 17%, and the simplified model showed 0.993 and 15.9%, respectively.

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For the assessment of existing slab-between-girder bridges, the shear capacity and failure mode are under discussion. Previous research showed that the static and fatigue punching capacity of the slabs is sufficient as a result of compressive membrane action. The girders then become the critical elements. This research studies the shear capacity of prestressed concrete bridge girders. For this purpose, four (half) girders were taken from an existing bridge that was scheduled for demolition and replacement and tested to failure in the laboratory. Two loading positions were studied. The results show that there should be a distinction between the mode of inclined cracking and the actual failure mode. In addition, the results show that for prestressed concrete girders, the influence of the shear span-depth ratio should be considered for shear span-depth ratios larger than 2.5. These insights can be used for the assessment of existing slab-between-girder bridges in the Netherlands.@en