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The punching shear design procedures according to current codes (e.g., Eurocode 2 or Model Code 2010) are similar. However, the predicted punching shear capacities may differ significantly depending on the background (e.g., semi‐empirical or physical) of the design provisions and the considered influences. For the evaluation and improvement of the existing provisions for flat slabs without and with high amounts of shear reinforcement, a large number of punching test series on reinforced concrete flat slabs is available in the literature. Nevertheless, the evaluation of the code equations for the design of the shear reinforcement (failure inside the shear‐reinforced zone) is still not possible since only few punching tests on flat slabs with low and medium amounts of shear reinforcement have been conducted. To investigate the punching shear behavior of flat slabs with a varying amount of shear reinforcement, three systematic test series without and with stirrups as shear reinforcement were conducted. The experimental program included three reference tests without and eight tests with low and medium amounts of shear reinforcement. In the tests, the amount of shear reinforcement was varied by changing the stirrup diameter only. Further investigated influences were the shear span‐depth ratio and the effective depth. The results of the test series are discussed and compared to the predictions according to Eurocode 2, Model Code 2010 and the draft of the second generation of Eurocode 2. [ABSTRACT FROM AUTHOR]

The existing punching shear design provisions according to current codes have either a semi‐empirical (e.g., Eurocode 2) or a more physical (e.g., Model Code 2010) background. Although the design procedures are very similar, the predicted punching shear capacities may differ significantly, depending on the background of the design provisions and the considered influences. Recent test series on reinforced concrete footings without shear reinforcement and with high amounts of shear reinforcement are available and can be used for the evaluation and improvement of the current provisions. Nevertheless, the evaluation of the code equations for the design of the shear reinforcement (failure inside the shear‐reinforced zone) is still not possible since systematic test series on footings with a varying amount of shear reinforcement have not yet been conducted. To investigate the punching shear behavior of reinforced concrete footings with low and medium amounts of shear reinforcement, three systematic test series (11 specimens) with stirrups as shear reinforcement were conducted. In the tests, the amount of shear reinforcement was varied by changing the stirrup diameter only. Further investigated influences were the shear span‐depth ratio and the effective depth. In this paper, the results of the test series are discussed and compared to the predictions according to Eurocode 2, Model Code 2010, and the draft of the second generation of Eurocode 2. [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]

Besides significantly higher punching strength, footings and ground plates generally exhibit much steeper shear crack inclinations than flat plates. Thus, punching shear reinforcement elements with inclined bars seem to be more efficient than elements with vertical bars. To account for this observation, a punching shear reinforcement element with inclined bars was developed, especially intended for the application in footings and ground plates. In a first test series, seven punching tests on reinforced concrete footings with the newly developed punching shear reinforcement, failing inside the shear-reinforced zone, were performed. Based on the test results, seven further tests were conducted to investigate the maximum punching shear capacity of the new punching shear reinforcement. The test parameters included the shear span-depth ratio av/d, the column perimeter-depth ratio u0/d, the concrete compressive strength fc,cyl, and the layout of punching shear reinforcement. Compared to stirrups and studs, the improved punching shear reinforcement reached significantly larger failure loads. The high efficiency was also confirmed by a comparison of the experimental results with the ACI 318-14 provisions. [ABSTRACT FROM AUTHOR]

Due to a smaller shear span-depth ratio and soil-structure interaction, footings and ground slabs achieve significantly higher punching shear capacities than flat plates. Because the inclination of shear cracks is steeper in footings, punching shear reinforcement elements with inclined bars seem to be more efficient than vertical bars. On the basis of previous experimental investigations on footings with punching shear reinforcement, a new punching shear reinforcement element with inclined bars was developed. To evaluate the efficiency of the punching shear reinforcement element, seven tests on reinforced concrete footings with uniform soil pressure and a failure within the shear-reinforced zone were conducted. The tests were planned considering the results of a previous systematic test series on reinforced concrete footings without and with stirrups as punching shear reinforcement. The main parameters investigated in the present test series were the shear span-depth ratio, the ratio of column perimeter and effective depth, the number and layout of punching shear reinforcement elements, and the effect of longitudinal reinforcement at the compression side. The comparison of the results of the new test series with the previous test series proves a significant increase in punching shear capacity with the newly developed punching shear reinforcement. [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]