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Highlights • Development of a kinematic punching theory considering flexural and translational deformations. • Development of a novel activation model for the contribution of the shear reinforcement. • Validation of the kinematic theory by means of tests with a varying amount of shear reinforcement. • Discussion of differences between punching shear behavior of slender and compact slabs. Abstract Previous investigations prove that the fracture kinematics of reinforced concrete slabs failing in punching are significantly influenced by the slab slenderness. While the deformation behavior of slender slabs is governed by flexural deformations, the behavior of very compact slabs is dominated by translational deformations. In the transition region between slender and very compact slabs, the fracture kinematics at punching failure can be described by both deformation components. Based on the aforementioned results, a two-parameter kinematic theory for punching shear without shear reinforcement was developed. In the theory, a total of four shear contributions (compression ring, aggregate interlock, residual tensile stresses, and dowel action) are considered and the magnitude of the contributions is estimated based on the slab deformations. The evaluation of the theory by means of systematic test series and databanks on both flat slabs and column bases without shear reinforcement revealed good agreement between predictions and experimental results. In this paper, the existing two-parameter kinematic punching theory is extended considering the beneficial effects of shear reinforcement on punching strength. The contribution of the shear reinforcement to the punching strength is determined based on a theoretical model describing the activation of the shear reinforcement depending on the slab deformations and the anchorage quality of the respective shear reinforcement system. The extended theory is validated by means of systematic punching test series on flat slabs and footings with varying amount of shear reinforcement. Further parametric studies are conducted to analyze the punching shear behavior of shear-reinforced concrete slabs in more detail. [ABSTRACT FROM AUTHOR]

Highlights • Development of a kinematic theory considering both flexural and translational deformations (two degrees of freedom). • Calculation of shear contributions along the failure crack based on slab deformations. • Validation of the kinematic theory by means of systematic punching test series and databanks. • Discussion of differences between punching shear behavior of slender and compact slabs. Abstract Measurements taken from recent test series with varying slenderness reveal strong differences between fracture kinematics of slender and compact slabs failing in punching. In accordance with the assumptions of the existing kinematic punching shear resistance models, the deformation behavior of slender slabs is governed by flexural deformations. However, in very compact slabs only small flexural deformations occur and the deformation behavior is dominated by translational deformations. In the transition region between slender and very compact slabs, the deformation behavior is influenced by both deformation components. As a consequence, the general application of the existing kinematic models to both slender and compact slabs might yield unexpected results. In this paper, a two-parameter kinematic theory for punching shear in reinforced concrete slabs without shear reinforcement is developed taking into account the aforementioned observations. In the theory, it is assumed that shear forces are transmitted along the failure crack by four shear contributions, namely the contributions of compression ring, aggregate interlock, residual tensile stresses, and dowel action. The magnitude of shear contributions is estimated based on the deformed slab accounting for two degrees of freedom (DOFs). While the first DOF accounts for flexural deformations, the second DOF considers translational deformations. Subsequently, the punching strength is calculated by summation of the contributions. The evaluation of the proposed theory by means of systematic test series and databanks yields good agreement between predictions and experimental results. Especially, the differences between flat slabs and column bases can be explained in a consistent manner by the theory. [ABSTRACT FROM AUTHOR]

Over the past decades, a large number of punching shear resistance models with different backgrounds have been developed. Among them, punching shear resistance models based on kinematic failure mechanisms have been found to be in good agreement with punching tests on slender slabs. The existing kinematic models generally determine the punching strength based on suitable failure criteria relating punching failure to a certain slab rotation. Hence, slab deformations are assumed to occur as a result of flexural deformations only. Yet, measurements taken from recent punching tests with varying slenderness reveal differences between fracture kinematics of slender slabs (e.g. flat slabs) and compact slabs (e.g. column bases). In this context, the deformation behavior of compact slabs is rather governed by translational deformations. Consequently, a general application of the existing models to both slender and compact slabs might yield inconsistent results. In this paper, the punching shear behavior of reinforced concrete flat slabs and column bases is investigated in detail. Based on measurements from tests and theoretical investigations, the fracture kinematics of slabs failing in punching are analyzed. The investigations verify that the total deformation of compact slabs at punching failure is significantly underestimated by considering the slab rotation as single degree of freedom (DOF). A more general description of the deformation behavior of both slender and compact slabs is possible by introducing a second DOF considering translational deformations. Based on the aforementioned observations, a general kinematic model is introduced to describe the fracture kinematics of reinforced concrete slabs by means of two DOFs. The proposed model is verified by means of measurements taken from punching tests. [ABSTRACT FROM AUTHOR]

The punching shear design of flat slabs and column bases was revised with the introduction of Eurocode 2. While in many former codes the punching shear resistance was determined regardless of the type of member, in Eurocode 2 two different design equations for flat slabs and column bases were introduced. Additionally, different control sections for flat slabs and column bases were defined. The differentiation between flat slabs and column bases and especially the iterative design procedure for the determination of the punching shear resistance of column bases require great effort in daily practice. Based on the punching shear provisions according to Eurocode 2, a new Uniform Design Method (UDM) for flat slabs and column bases is developed. The derivation of the design method is described in detail. To verify the changes in the current design provisions, the new design method is evaluated using large databanks for flat slabs and column bases without and with shear reinforcement as well as systematic test series. [ABSTRACT FROM AUTHOR]

• Kinematic punching theory for SFRC slabs considering flexural and translational deformations. • Application of Variable Engagement Model to estimate the fiber contribution to punching strength. • Validation of the kinematic theory by means of systematic test series and a databank evaluations. • Investigation of the influence of fiber properties on punching strength. There are several possibilities to enhance the punching shear behavior of reinforced concrete slabs. Among them, various shear reinforcement systems have been found to efficiently increase both the punching strength and the deformation capacity compared to similar slabs without shear reinforcement. Nevertheless, the biggest disadvantage of shear-reinforced concrete slabs is the large effort associated with the installation of the reinforcement elements. Another efficient solution to improve the punching shear behavior of slab-column connections is the application of steel fibers in the region of the column. Depending on the fiber volume and fiber properties, steel fibers may significantly enhance the tension-softening behavior of concrete leading to higher punching strengths combined with a more ductile failure mode. In this paper, the existing two-parameter kinematic theory for punching shear in reinforced concrete slabs is extended considering the beneficial effects of steel fibers on punching shear capacity. The contribution to the punching strength provided by fibers is determined based on a theoretical model described in literature. The model allows for the description of the tension-softening behavior of reinforced composites containing randomly orientated discontinuous fibers as a function of the normal opening of the failure crack. The proposed theory is validated by means of systematic punching test series with varying fiber volume and databank evaluations. Further parametric studies were conducted to analyze the influence of fiber properties on punching strength more in detail. [ABSTRACT FROM AUTHOR]

• Evaluation of systematic punching tests on shear-reinforced flat slabs with closed stirrups. • Constant concrete contribution independent of the shear reinforcement ratio according to EC2. • Presentation of two methods to determine the shear reinforcement contribution in flat slabs. • Evaluation of experimental results reveals a high degree of activation of the shear reinforcement. • Continuous decrease of concrete contribution with increasing shear reinforcement ratios. • Suggestion of a design approach based on a suspension strut-and-tie model. The punching strength of flat slabs and footings without and with high amounts of shear reinforcement on the level of maximum punching shear capacity has been investigated extensively by various researchers over the last decades. The existing investigations suggest that the punching strength of RC slabs with shear reinforcement can be described by means of a contribution of concrete and a contribution of the shear reinforcement (steel contribution). However, a systematic evaluation of concrete and steel contribution depending on the amount of shear reinforcement has not yet been adequately possible since only few test series with low and medium amounts of shear reinforcement and a failure within the shear-reinforced zone have been available. This lack of experimental data has been partly filled with eleven systematic punching tests on flat slabs and eleven further tests on footings conducted at RWTH Aachen University, Germany. In this paper, the development of the concrete and steel contributions in shear-reinforced flat slabs is investigated in detail and a method for calculating and analyzing both contributions is presented. The development of concrete and steel contribution depending on the amount of shear reinforcement is discussed and compared to the design provisions according to Eurocode 2, Model Code 2010 and the draft (of April 2018) of the next generation of Eurocode 2. [ABSTRACT FROM AUTHOR]

Open rib shear connectors are increasingly used as shear connectors and anchors between concrete and steel members of composite structures. In many cases, the rib connectors are subjected to combined shear and tension forces. However, until now, the structural response and interaction behavior of rib shear connectors exposed to tension and shear has not been analyzed. The current design guidelines do not provide a recommendation for computing the strength of rib shear connectors (traditionally used as shear connectors) under combined tension and shear. Therefore, the present paper presents systematic studies on the interaction behaviour of puzzle-shaped rib shear connectors, also called composite dowels. Based on tests results gained in a novel test setup and FE-simulations, the interaction properties of composite dowel rib connectors are analyzed and a model approach for the tension and shear interaction is proposed. [ABSTRACT FROM AUTHOR]