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A study on the punching shear behavior of 8 slabs with recycled aggregate concrete (RAC) was carried out. The two main factors considered were the recycled coarse aggregate (RCA) replacement percentage and the steel fibre volumetric ratio. The failure pattern, load-displacement curves, energy consumption, and the punching shear capacity of the slabs were intensively investigated. It was concluded that the punching shear capacity, ductility and energy consumption decreased with the increase of RCA replacement percentage. Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab, but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern. On the basis of the test, the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed. [ABSTRACT FROM AUTHOR]

The punching shear behavior of steel fiber-reinforced concrete (SFRC) slabs with or without traditional steel bar reinforcement was investigated. Test results of 26 SFRC slabs with traditional steel bar reinforcement reported in the literature and 12 slabs without steel bars tested in this study were analyzed. The test parameters covered different multi-hook end fibers, concrete compressive strength, fiber reinforcing index, and slab thickness. The statistical performance of eight existing models for predicting punching shear capacity of SFRC slabs was reviewed. A modified model that is applicable for both SFRC slabs with or without steel bars is proposed and it was found to predict the punching shear capacities of the SFRC slabs with good accuracy. The load-carrying capacity of SFRC slabs without steel bars was also assessed by the yield line theory. It is observed that the SFRC slabs with steel bar reinforcement experienced either a punching shear or a flexural punching mode of failure, whereas those without steel bars failed primarily in flexure. [ABSTRACT FROM AUTHOR]

Highlights • A punching shear strength model was proposed for UHPFRC-RC composite flat plates. • UHPFRC overlay increases the load-carrying capacity, but it is limited at a certain point. • The punching shear strength can be defined as a function of the thickness and strength of UHPFRC overlay. Abstract Reinforced concrete (RC) flat plates are vulnerable to punching shear failure due to small effective area for shear resistance. To strengthen the behavior of existing flat plates, use of ultra high performance fiber reinforced concrete (UHPFRC) as a laminate has been pursued. This study focuses on punching shear behavior of RC flat plates retrofitted with UHPFRC overlay (i.e., UHPFRC-RC composite flat plates). To model the axisymmetric UHPFRC-RC composite flat plate, use of the unified strength theory-based punching shear strength model was proposed. Predictions using the proposed model, when compared to existing test results of UHPFRC-RC composite flat plates under concentric load and nonlinear analysis results using ABAQUS, agreed well with the results. Additionally, from the parametric analysis results using the proposed model and nonlinear analysis, the effects of UHPFRC overlay thickness and tensile strength on the punching shear strength were identified. [ABSTRACT FROM AUTHOR]

Highlights • Simplified model to predict the punching shear failure of RC slabs under impact. • Proposed approach is validated with experimental and numerical results. • Review of the response of the concrete slabs under low velocity impact. • Significance of various governing parameters is highlighted. Abstract A simplified analytical approach to predict the punching shear failure of a concrete slab under low velocity (<10 m/s) impact loading has been proposed. The proposed analytical approach has further been validated against a backdrop of experimental results available in the public domain. The efficacy of the proposed approach has further been tested against the results obtained by conducting numerical simulations designed by the authors. The results obtained from this simplified approach have on the whole shown good agreement with the experimental results. Furthermore, on the basis of extensive literature review, a state-of-the-art investigation to examine the structural response of concrete slabs under low velocity impact loading has also been presented in this paper. The paper aims to explore and present a quantum of the undertaken research under the sections dealing with the experimental studies, numerical simulations and the analytical modeling. Thus, in addition to the proposition of a simplified approach for predicting the punching shear failure of a concrete slab under low velocity impact loading condition, the paper also sets forth to establish the current knowledge base in this field and identify the key areas with a need for further research with regard to this domain. [ABSTRACT FROM AUTHOR]

Highlights • The structural behaviour of a novel shear reinforcement system in the slab-column connection using experimental data is explored. • A detailed numerical modelling approach is developed to obtain a thorough understanding of the use of the proposed system. • The performance of the proposed strengthening system under fire conditions is explored for the first time. • The proposed shearhead provides significant shear strength enhancement at both ambient temperature and in fire conditions. Abstract Traditional means of reinforcing concrete flat slab-column connections against punching shear, such as increasing slab thickness, or provision of shear links, all have drawbacks. This paper proposes a novel type of punching shear reinforcement in the form of a shearhead to enhance connection strength and ductility. The structural behaviour of the connection is explored experimentally by testing nine specimens under various loading conditions including eccentric loads that produce combined axial and bending effects. Specimens with and without shearheads are compared. This is followed by a detailed numerical investigation using finite element analysis to obtain more in-depth insights into the connection behaviour when shearheads are present. The performance of the proposed system is also investigated under fire conditions for the first time. It is found that the proposed shearheads improve the performance of slab-column connections in all conditions and particularly under concentric loading and in fire conditions. [ABSTRACT FROM AUTHOR]

The main objective of this study is strengthening of flat slabs in punching shear with a new model. For this purpose 15 numerical samples include a control and 14 strengthened defined and nonlinearly analyzed up to failure. The strengthening method is new method of grooving in two orthogonal direction (x and y axes of slab plan) and then mounting the external bars (sticking) in one direction and FRP in EBROG (externally bonded reinforcement on groove) method in another direction. The results showed the great efficiency of the method so that the punching shear capacity of strengthened samples increased between 28 and 62% compare to control one. Also the mode of failure changed in strengthened specimens from shear to flexure-shear and the punching critical area was broader and developed from the loading point. In the grooving method the sticking bars yielded in all specimens and the FRP tensile strain was closer to rupture strain compared to EBR. [ABSTRACT FROM AUTHOR]

Effects of slab flexural reinforcement on the punching shear strength and deformation capacity of corner slab-column connections without shear reinforcement were evaluated in this study. Four isolated corner slab-column subassemblages were tested under combined gravity-type loading and lateral displacement reversals. Results from present and previous studies indicate that provisions per ACI 318-14 are not conservative for corner slabcolumn connections. For connections subjected to gravity-type loads only, a shear strength model considering effects of the equivalent slab top flexural reinforcement ratio and the critical section aspect ratio (bo/d) is proposed. For connections subjected to combined gravity-type loads and lateral displacement reversals, this proposed shear strength model provides a more conservative estimate of gravity shear ratio when applied to shear decay model per ACI 318-14. [ABSTRACT FROM AUTHOR]

An adaptive neuro-fuzzy inference system (ANFIS)-based model was developed to predict the punching shear strength of flat concrete slabs without shear reinforcement. The model was developed using a database collected from 207 experiments available in the existing literature. Five key input parameters were used to build the model, which were slab effective depth, concrete strength, reinforcement ratio, yield tensile strength of reinforcement, and width of square loaded area. The output parameter of the model was punching shear strength. The results from the adaptive neural fuzzy inference model were compared to those from the simplified punching shear equations of ACI, BS-8110, Model Code 2010, Euro-Code 2, and also experimental results. The root mean square error (RMSE) and the correlation coefficient (R) were used as evaluation criteria. Parametric studies were presented using ANFIS to assess the effect of each input parameter on the punching shear strength and to compare ANFIS results to those from the equations proposed in commonly used codes. The results showed that the ANFIS model is simple and provided the most accurate predictions of the punching shear strength of two-way flat concrete slabs without shear reinforcement. [ABSTRACT FROM AUTHOR]

Highlights • The load resisting mechanisms and failure modes noticeably varied between different corner reinforcement configurations. • The applied load was mainly transferred to edge columns adjacent to the removed corner column. • The risk of progressive collapse can be reduced with the existence of overhangs surrounding a removed corner column. • Yield line theory can be used to estimate the slab flexural capacities under corner column removal scenarios in this study. Abstract Reinforced concrete (RC) flat plate structures are broadly used in car parks, residential and office buildings due to their economic and architectural advantages. However, this structural system is inherently prone to punching shear failure, which may propagate horizontally and vertically, ultimately leading to the progressive collapse of the entire structure or of a large portion of it. This paper presents the experimental results from two quasi-static large-displacement tests performed on a 1/3 scale, 2 × 2-bay, RC flat plate substructure subjected to corner column removal scenarios. The specimen was tested twice with different corner reinforcement configurations: (i) firstly, one corner column, with torsional strips, was removed and the Uniformly Distributed Load (UDL) on the bay adjacent to the removed column was increased to failure (Test T1), and (ii) secondly, as the damage was concentrated in the vicinity of removed corner column in (i), the corner column diagonally opposite to the first removed one, without torsional strips, was removed. The UDL on the bay adjacent to the second removed column was also increased to failure (Test T2). Different failure and post-failure behaviours, failure modes, and collapse resisting mechanisms between the two tests were witnessed, presented and analysed. Results show that 80% to 110% of the applied load is transferred to the two edge columns adjacent to the removed corner column throughout the entire two tests. The ultimate load carrying capacity for T1 is found to be 1.7 times smaller than the one for T2. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the findings of an experimental investigation undertaken to evaluate the influence of externally bonded CFRP laminates on the punching shear capacity of a two-way spanning slab-column connection. Two control and five strengthened RC slabs were prepared and tested under concentrated load. The variables of the experiment were the anchorage type and width of the CFRP plates used. The structural response of the samples in terms of load, deflection, strain and cracking was monitored and analysed throughout the experimental procedure. It was found that strengthening increases the ultimate load by up to 25% and reduces the maximum deflection by up to 50%. The strengthening increases the cracking load and significantly reduces the cumulative length of radial cracks. The samples strengthened with transverse anchorages exhibited significantly high level of residual strength. The experimental findings for unstrengthen cases are compared with several design codes. [ABSTRACT FROM AUTHOR]

Analytical equations found in the literature to give the ultimate load of folding, punching shear and local slab collapse mechanisms have been generally derived assuming a uniform load on all flat slab panels. Regarding that these formulas are not able to consider the impact of unbalanced bending moment due to partial loading, they cannot be applied to evaluate scenarios like overcrowding during operation and change of occupancy. This paper categorizes various collapse modes due to overloading in a cluster of exterior panels as well as presenting analytical equations for the ultimate loads using virtual work method and yield line theory. The study also introduces two novel local slab collapse patterns around interior columns located at the corner of overloaded area. Predicted ultimate loads indicate that flat slabs on a square column grid are expected to be more prone to punching shear and asymmetric local modes around the internal columns supporting two adjacent overburdened panels compared to other column locations. [ABSTRACT FROM AUTHOR]

A general criterion is proposed as a supplement to the most recent ACI 318 Code. The proposed criterion applies to slabs with or without prestressing having vertical or inclined legs of stirrups or headed shear stud reinforcement in a crucifix layout. Yielding of the top flexural reinforcement in a zone above a column can induce punching. This flexure-induced punching can occur when a pattern of yield lines develop a local mechanism. To avoid punching, a minimum amount of top flexural reinforcement is generally required. The structure may be subjected to gravity loads and lateral forces due to wind or earthquake. For the universal design, shear and flexural reinforcements should first satisfy the requirements of an applicable code, then verify that the zone and amount of top flexural reinforcement in two orthogonal directions are adequate. [ABSTRACT FROM AUTHOR]

This paper investigates the punching behavior of reinforced concrete flat slabs supported on rectangular columns under concentric loading. Based on the critical shear crack theory, a new model is proposed to determine the punching shear strength of slabs. In this model, a rectangular slab is replaced with an elliptical surface with the same area. The efficiency of the model is validated through comparisons made with experimental studies in the literature. Furthermore, results are compared with three different codes, namely, ACI, Eurocode 2, and FIB Model Code 2010. Finally, an alternative approach is introduced to facilitate the calculation of the punching shear capacity of slabs with column rectangularity considerations. For the experimental tests available in the literature, good shear strength predictions were obtained by the two proposed models. [ABSTRACT FROM AUTHOR]

Installation of building utilities often requires the creation of openings near existing slab–column connections. These openings reduce the concrete area that sustains the shear stresses, thus, the developed shear stresses are increased and contribute to the risk of punching shear failure. In this paper, nonlinear finite element analysis (FEA) using a previously calibrated coupled plasticity‐damage model for concrete is performed for interior slabs with square openings. An interior reinforced concrete flat slab without shear reinforcement, which was tested under gravity loading, is considered as the reference slab. The effect of the location and the size of the opening on the punching shear resistance are examined. Punching shear predictions according to ACI 318‐14, Eurocode 2‐2004, and fib Model Code 2010 are compared to the FEA results. Finally, probabilistic analyses using the Monte Carlo simulation are considered, and fragility analysis is performed to estimate the probability of the punching shear resistance related to the size and distance of the opening. [ABSTRACT FROM AUTHOR]

Abstract One of the major problems of flat slab is the punching shear failure of slab-column connection. This form of failure must be avoided. Fourteen slab-column connections are tested to failure and categorized in two phases. The first "Phase I" consisted of testing ten interior square slabs axially loaded. The second "Phase II" consisted of testing four specimens under eccentric loading to study the influence of moment transfer at the slab-column connection on the punching shear failure of the slabs. The main parameters evaluated were, fiber volume ratio which was 0.5%, 1.0% and 1.5% and, punching area as dimensions of the square portion of the slab having steel fibers at the column vicinity of lengths d + 200 mm, 2d + 200 mm and 3d + 200 mm. All slabs have same dimensions of 1700 mm × 1700 mm with thickness 150 mm and reinforcement ratio of 1.2%. All tested specimens were loaded incrementally up to failure. However using steel fiber increased both the failure load and energy absorbing capacity. Summarily, it was found that slabs with a 1.5% steel fiber ratio led to high failure load capacity. Results showed that using steel fiber only in a portion of slab that is equal to slab thickness from column face was sufficient to give the optimum enhancement in both failure load and ductility behavior. Three-dimensional finite element model was created to using ANSYS R14.5 ANSYS (2012) program to simulate the behavior of the tested specimens. Crack pattern, mode of failure and energy absorption were analyzed here in this study. [ABSTRACT FROM AUTHOR]

Abstract Flat-slab system is widely used nowadays. Major and critical problem of this system is its sudden brittle failure is called punching shear failure. To overcome the punching failure problem, there are many ways to increase the punching shear strength of concrete slabs, increasing slab thickness in the area adjacent to the column, increasing column thickness which is against the architectural desire, and finally providing slab with shear reinforcement. Shear reinforcement is more advanced from both the structural and economical point of view. An experimental program includes seven full scale square flat slab interior column specimens tested under gravity loads. All slabs have same dimensions of 1700 mm × 1700 mm with thickness 160 mm and reinforcement ratio of 1.2%. Column was square of 200 mm length and 250 mm height. Elongated steel strips of 25 mm width and 1.5 mm thickness undulated into the slab in different ways to investigate punching shear resistance. The program is divided into five groups. First group investigates the effect of installing the shear-band reinforcement (hanged up on top mesh, knit the top and bottom mesh together). The second group investigates the effect of inclination of shear reinforcement (shear band with vertical leg, with bended leg 45°). The third group investigates the effect of concentrating the shear reinforcement by increasing the quantity around the column. The fourth group investigates effect of radial distribution of shear-band system around the column. Finally, the fifth group investigates the effect of box distribution of shear-band system around the column. [ABSTRACT FROM AUTHOR]

• Uncertainty quantification of strain-based resistance models for structural concrete. • Model uncertainty of the global resistance model can be lower than those of sub-models. • Model uncertainties of Critical Shear Crack Theory for punching shear for different Levels-of-Approximation. • Derivation and discussion on the relationship between partial safety factors for strain-based approaches. The development of mechanical models relating the state of strains and the resistance of reinforced concrete structures has become a trend in the last decades. These types of models are referred to as strain-based approaches. Since strain-based approaches usually involve multiple sub-models and take implicit forms, their model uncertainties tend to be more complex than those of the explicit design equations commonly used in design codes. The characteristics of the model uncertainties of strain-based approaches is investigated using the Critical Shear Crack Theory (CSCT) for the punching shear resistance of structural concrete members as example. Both by performing theoretical parametric analyses and by evaluating relevant experimental data, it is shown that the model uncertainty of global resistance solution of strain-based approach can be viewed as resultant of the model uncertainties of the sub-models. In addition, it is also shown that the model uncertainty of the global resistance solution can be lower than those of the sub-models, depending on their sensitivity relationship. The model uncertainties of different Levels-of-Approximation (LoA) of the CSCT for punching are also compared. The LoA approach intends to provide consistent and progressively refined model for different design tasks in practice. The model uncertainty quantification result confirms that the model uncertainty of higher LoA of CSCT has lower variability and also less conservative bias than lower LoA. Finally, based on the obtained model uncertainties, different types of partial safety formats for strain-based approaches are compared and discussed. Using the CSCT punching shear model as an example, it is shown that the partial factors applied to the sub-models are more suitable for higher LoAs since they can effectively account for the change of model uncertainty associated to the change of failure mode. Based on the assumptions described in this work, the relationship between the partial factors of the punching shear provisions in the 2nd generation of Eurocode 2 for the design of new structures and the assessment of existing critical ones is established. [ABSTRACT FROM AUTHOR]

In this paper, punching shear behavior of Ultra-High Performance Concrete (UHPC) was investigated experimentally and numerically. In this study, six 1350 * 1350 * 80 mm flat slabs with extended 200 mm column stubs above the slabs were constructed to study the effect of the increased strength of UHPC and its ductility with different concrete mix ratios and different column aspect ratios. All specimens contained steel fibers which increased slabs ductile behavior and shared directly in increasing punching shear capacity of the examined specimens. Numerical investigation was performed as nonlinear finite element analysis adopting ABAQUS software using concrete damaged plasticity model (CDPM), ABAQUS/Explicit. Compression and tensile behaviors of concrete were modeled by Hognestad Parabola and Bilinear tensile stress versus crack width respectively. The average strength of test specimens ranged between 164 MPa and 193 MPa in compression and 9.6 MPa to 13.1 MPa in tension. In this study, analysis parameters were concrete strength, column aspect ratio, column shape, and flexural reinforcement ratio. The results showed an increase in punching shear capacity in the six specimens ranged between 32% and a 20.8% relative to ACI 318-19 punching strength formula and Euro code EN1990.2012 formula, respectively. [ABSTRACT FROM AUTHOR]

• 12 tests on one-way slabs under concentrated loads are discussed. • Large shear redistribution around the load occurred after local punching. • One-way shear, punching shear and flexural failure mechanism are discussed. • The predicted governing failure mechanism from such slabs is addressed. • The Extended Strip Model provided the best predictions of the failure load for the slabs. One-way slabs under concentrated loads may fail by one-way shear such as wide beams, punching shear, flexure, or by combining two or more of these mechanisms. Nevertheless, most publications have only addressed shear and punching failures without flexural reinforcement yielding. This study investigates the ultimate shear capacity of one-way slabs under concentrated loads with local reinforcement yielding. In total, 12 tests were conducted on six reinforced concrete slabs. Simply supported slabs of 1.60 m × 3.40 m × 0.15 m were tested. Three parameters were varied: the load position, the span length and the reinforcement ratio. All slabs failed initially by punching with limited or extensive reinforcement yielding. Due to the relatively large amount of transverse reinforcement (0.44 %), most slabs underwent a large shear redistribution around the load, resulting in a wide beam shear failure after the local punching failure. The test results were compared to the theoretical predictions of shear, punching and flexure capacity using code expressions and the Extended Strip Model (ESM). The ESM resulted in the closest predictions of the experiments. These experiments confirm that a brittle shear and punching failure mechanism can occur even after extensive reinforcement yielding. Moreover, the results indicate that the ESM can be used to assess one-way slabs under concentrated loads with local reinforcement yielding. [ABSTRACT FROM AUTHOR]

• Review of punching shear models for RC flat slabs and footings without shear reinforcement. • Development of the punching shear response theory (PSRT). • Validation of new theory with experimental data of pre- and post-peak punching shear responses (forces, rotational and translational deformations, punching strength, deformation capacity). • Quantification of punching shear contributions by direct strutting, aggregate interlock, fracture process zone and rebar dowel action. • Physical explanation for punching shear failures. Punching failures of reinforced concrete flat slabs and footings without shear reinforcement have been responsible for a number of catastrophic collapses. Despite intense scientific efforts in recent decades that have led to failure criteria-based phenomenological models, our current mechanistic understanding is still not sufficiently advanced to fathom the physical background of punching phenomena in RC structures. That is why, this paper proposes a novel two degree of freedom mechanical theory - called Punching Shear Response Theory (PSRT) - that interconnects all relevant effects of punching shear behavior, namely strutting action within a conical concrete shell at the slab-column interface, shear transfer actions elicited along the circumferential punching shear crack, including cohesive fracture process zone behavior, aggregate interlock and dowel action of reinforcement, as well as transfer of normal forces within tangential and radial cracks between slab segments in one all-encompassing algorithm. The PSRT can thoroughly mimic and efficiently reproduce the entire punching failure process of flat slabs and squat members (footings, pile caps, column bases) including prediction of pre- and post-peak punching shear vs. deformation response, quantification of different punching shear contributions and analysis of their evolution and mutual interaction within the failure process. The paper illustrates the analytical development of the PSRT, exemplifies its ability to reproduce the punching shear response of selected benchmark problems, proves its validity by database evaluations (incl. punching strength and deformation capacity) and eventually discloses the physical causalities of punching failures in RC structures. [ABSTRACT FROM AUTHOR]

Superstructure loads are transmitted to the underlying soil strata through a suitably designed foundation. Therefore, the foundation of a structure is considered the most crucial structural element in a building. The foundation may be classified into two main categories, shallow and deep foundations. Shallow foundation comprises isolated column footings, combined footings and reinforced concrete mat. The design of isolated column footing is accomplished through the application of geotechnical and structural analysis concepts. So that, the input research into isolated column footings comes from two different disciplines, geotechnical and structural. This may be one of the main causes that attributed to the limited research input to the subject. Therefore, the structural design of isolated column footings is based on empirical rules and the calculations of bending moments (BM) and shearing forces (SF) induced in a footing are based on the rules of beam theory, which is questionable. On the other hand, punching theory was developed on relatively thin floor slab, even though the theory is implemented for the calculation of punching shear in relatively thick footings. Also experimental research on isolated column footings is scarce, due to the difficulties involved in the setup of the laboratory models and the cost of experiments. The work presented in this article deals with the correlation between failure loads predicted by different code provisions, ECP203-11, ACI318-08, BS 8110.1-1997 and EC2-2004, of isolated column footings, and the corresponding measured values. The study showed that shear span to depth ratio of a footing and distributions of contact stress at footing–soil interface are key factors in the structural design of the footing. ECP203-11, ACI318-08, and EC2-2004 code provisions, underestimate the structural failure loads of isolated column footings, while BS 8110.1-1997 overpredicts the failure loads of isolated column footings, if punching provisions at perimeter of column are pulled out from the code.

This paper deals with the modeling of punching shear failure in reinforced concrete slabs using nonlinear finite element analysis. The 3D finite element analyses (FEA) were performed with the appropriate modeling of element size and mesh, and the constitutive modeling of concrete. The FE numerical models are validated by comparing with the experimental results obtained from tested specimens and previous research. One slab served as a control without any modification while three slabs were strengthened. The ultimate behavior of FRP strengthened RC flat slabs under a centrally applied load. Each method of repair or strengthening is reviewed with emphasis on its performance with respect to the application details. The punching shear capacity, stiffness, ductility were investigated. In addition, the analytical results were compared with the predictions using the provision of ACI 318-08. The results showed that for control slab and strengthened specimens an increase varied from 4% to 105% in punching shear capacity is determined.

An experimental and analytical study on the punching strengthening of reinforced concrete two-way slabs using external steel plates is presented. Five reinforced concrete square slabs of 100 mm thickness were tested over simply supported four sides of 1000 mm span under central square patch load of 100 mm size up to failure. One control slab was tested without strengthening; however, four tested slabs were strengthened using four configurations of square steel plates provided with steel anchor shear studs. Such configurations considered two different plate thickness, two plate side dimensions and different arrangement and diameter of shear studs. The strengthened four slabs showed improved stiffness and punching shear capacity. The magnitude of improvement depended on the plate dimensions and the studs diameter and arrangement. An analytical approach was proposed for predicting the punching shear strength increase due to using the strengthening steel plate. The proposed approach was applied to the tested specimens with the use of the punching shear strength equations adopted by several codes of practice and proved to be in good agreement with the test results. Generally, this research presented a practical strengthening concept that can be used to increase the punching shear capacity of two-way slabs.

The scope of the paper is to propose a method for determining the size of shear caps in a slab–column-connections-reinforced concrete structure. Usually, shear heads are used to enhance slab–column connection, especially when the transverse reinforcement does not give the required punching shear load capacity. The dimensions of the shear head should provide the punching shear resistance of the connection inside and outside the enhanced region. The process of selecting the size of the shear head is iterative. The parametric analysis of the ACI 318 code and EC2 standard has the objective of indicating which control perimeter (inside or outside the shear head) has a decisive impact on the punching shear capacity of the connection. Based on the analysis, the authors propose methods for selecting the dimensions of the shear head with practical application examples. The paper is intended to provide scientists, civil engineers, and designers with guidelines to design the process of the slab–column connections with the shear caps.

The design of a post-tensioned transfer plate is typically controlled by shear force—in particular, punching shear at the slab-column connection. To verify the accuracy of the separated model only for one floor currently used in the design of a post-tensioned transfer plate, results were compared to a complete model with multi-story building system for which two representative residential building plans were used to emulate physical structural systems. Punching shear stress for the separated model was calculated using the eccentric shear stress model presented in ACI 318. Punching shear stress was found to be overestimated in the separated model, given that interaction between transfer plates and upper shear walls cannot be reflected therein. Differences at column locations were also noted as the number of stories below the transfer floor increased. Consequently, the separated model is not recommended for design of post-tensioned transfer plates. A complete model is more suitable for more realistic and potential cost-effective design, through the inclusion of the interaction between transfer plates and upper shear walls.

The application of fiber-reinforced polymer (FRP) bars and ultra-high performance concrete (UHPC) in the field of civil engineering is promising. An innovative FRP bar-reinforced UHPC short-ribbed bridge deck slab, with low self-weight and high structural performance, was proposed in this study. The behavior of one-way basalt FRP (BFRP) bar-reinforced UHPC slabs under concentrated load was experimentally investigated, and compared with that of a steel bar-reinforced UHPC slab. The ultimate capacity of the one-way BFRP bar-reinforced UHPC slab was 0.59 times that of the steel bar-reinforced UHPC slab, while its ductility was better. Increasing the reinforcement ratio and loading area was beneficial to the ductility of one-way BFRP bar-reinforced UHPC slabs. Moreover, the model proposed by EI-Gamal et al. was found to be suitable for evaluating the punching shear capacities of one-way BFRP bar-reinforced UHPC slabs. However, the model failed to consider the unique strain-hardening characteristics of UHPC, which led to conservative prediction.

This study presents the structural behavior and punching shear strength of the concrete slab-column connections strengthened with carbon fiber reinforced polymer (CFRP) laminates. The variables considered for the twelve specimens included the compressive strength of the concrete, the ratio of the tensile steel reinforcement, and the amount of the CFRP laminates. Square concrete slabs were simply supported along four edges. During the test, monotonically concentrated load was applied to the stub column located at the center of the slab. The punching shear strength, stiffness, and mode of failure were investigated. Test results demonstrated that increasing the compressive strength of concrete, ratio of the steel reinforcement, and amount of the CFRP laminates led to an increase in the punching shear strength of the slabs. Moreover, the CFRP laminates were effective in appreciably increasing the punching shear strength of the slab-column connections. An analytical approach was conducted to calculate the punching shear strength of the slab-column connections strengthened with CFRP laminates. Based on the theory of reinforced concrete members, the application of the CFRP laminates increased the flexural strength of the slab and resulted in an increase of the effective depth of the slab section. Consequently, the punching shear strength was increased. The results of the analytical calculation revealed that the analytical work accurately predicted the experimental punching shear strength.

This study is conducted to test experimentally the punching shear of reinforced concrete flat plate slabs made with hybrid concrete (two types of concrete in two layers in specimens. Twelve test slab with ( 450×450×50 ) mm dimension The tested slabs have been. divided into four groups, each of which consisted of three slab specimens identical in size and shape but different in concrete type and steel bar reinforcement. All slabs are simply supported along the all edges and subjected to single point load applied at the center of gravity of each slab.Experimental results show that the use of hybrid concrete and high strength concrete improves the punching shear resistance and allows higher forces to be transferred through the slab-column connection. For slab specimen which fully cast using high strength concrete, the ultimate shear capacity increased by (40%) in comparison with the normal concrete slabs. While, for slab specimens cast using with hybrid concrete the ultimate shear capacity increased by (5%-45%) in comparison with the normal concrete slabs.This experimental results revealed that the ultimate load capacity increase with the addition of super plasticizers to the mix of concrete.

A finite element model (FEM) was constructed using specialized three-dimensional (3D) software to investigate the punching shear behavior of interior slab-column connections subjected to a moment-to-shear ratio of 0.15 m. The FEM was then verified against the experimental results of full-scale interior slab-column connections reinforced with glass fiber reinforcement polymer (GFRP) bars previously tested by the authors. The FEM results showed that the constructed model was able to predict the behavior of the slabs with reasonable accuracy. Afterward, the verified model was used to conduct a parametric study to investigate the effects of reinforcement ratio, perimeter-to-depth ratio, and column aspect ratio on the punching shear behavior of such connections. The test results showed that increasing the tested parameters enhanced the overall behavior of the connections in terms of decreasing deflections and reinforcement strain and increasing the ultimate capacity. In addition, the obtained punching shear stresses of the connections were compared to the predictions of the Canadian standard and the American guideline for FRP-reinforced concrete structures.

In this paper, a system for repairing damaged flat plates as a result of punching shear is presented. The system depends mainly on repairing the damaged concrete and the addition of vertical studs with different arrangements through holes drilled in the plates. The experimental program consists of eight specimens with the same dimensions and flexural reinforcements, but with different concrete strength and shear reinforcement ratios. The main aim of the tests is to assess the efficiency of the suggested repairing system and to investigate the slabs load carrying capacity, deformation characteristics and cracking behavior. Test results showed that using the proposed system on repairing damaged flat plates due to punching shear is very efficient. Theoretical results obtained based on the formulas adopted by different codes and from the critical shear crack theory (CSCT), showed a satisfactory agreement with test results.

Punching shear reinforcement systems such as studs and stirrups are used to improve the punching shear strength of flat slabs. A three dimensional finite element model (FEM) is developed through Ansys 10 computer software, to carry out the nonlinear analysis of 16 flat-slab models with and without punching shear reinforcement. Several important parameters are incorporated in the analysis, namely the column size, the slab thickness and the punching shear reinforcement system in order to study their effects on the flat slab behavior. A parametric study was carried out to look at the variables that can mainly affect the mechanical behaviors of the model such as the change of loading types and positions and slab with openings. Good correlation is observed between the results of the proposed model and other experimental one, resulting in its capability of capturing the fracture of flat slab under punching shear behavior to an acceptable accuracy.

This paper presents applying gene expression programming (GEP) approach for predicting the punching shear strength of normal and high strength reinforced concrete flat slabs. The GEP model was developed and verified using 58 case histories that involve measured punching shear strength. The modeling was carried out by dividing the data into two sets: a training set for model calibration, and a validation set for verifying the generalization capability of the model. It is shown that the model is able to learn with high accuracy the complex relationship between the punching shear and the factors affecting it and produces this knowledge in the form of a function. The results have demonstrated that the GEP model performs very well with coefficient of determination, mean, standard deviation and probability density at 50% equivalent to 0.98, 0.99, 0.10 and 0.99, respectively. Moreover, the GEP predicts punching shear strength more accurately than the traditional methods.

This study presents an experimental investigation on the influence of embedded shearhead reinforcement (steel plate) on the punching shear strength of reinforced concrete slabs. This work includes the investigation and testing of one control slab and five scale models of slab-column connection simply supported along the four edges. A shearhead was made by using a steel plate with T-section stiffeners, the stiffeners were fabricated to be with two lines welded on the tension face of the plates. The main variables studied were the dimensions and thickness of the steel plate (used as punching resistance) .The results show that ultimate load capacity at failure increases by (16.48%) over the reference slab. Also, punching shear stress decreases about (29.24%) below the reference slab.

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]

Highlights • Two large-scale RC slabs representing an interior slab-column connection were tested. • Steel bolts increased the load capacity of the slab by 15.4%. • Strengthening technique change the punching shear failure to flexural failure. • Numerical results showed good correlations with the experimental results. Abstract This paper presents a strengthening technique of reinforced concrete (RC) flat slabs using post-installed steel bolts. Two large-scale RC slabs representing an interior slab-column connection were tested. One slab was without shear reinforcement and was used as a control slab and the second slab was strengthened against punching shear using steel bolts with end anchorage steel plates. The punching tests were compared with the numerical results using finite element method (FEM). Numerical results showed good correlations with the experimental results in terms of the load-displacement response, concrete strain and failure mode. The results showed that the strengthening technique increased the load up to flexural failure of the slabs and improved ductility of slab relative to the control. The strengthening technique was also successful and contributed to changing the failure mode from brittle punching shear mode to ductile flexural failure mode. Photogrammetry was used in this research. Photogrammetry technique holds several advantages over traditional contact instrumentations including that it is inexpensive, simple for analyzing the results and a remote visualization technique. The displacement profile along the span of the slab and rotation has been compared with the results obtained from the traditional sensors. [ABSTRACT FROM AUTHOR]

In order to increase the strength and deformation capacity of flat slabs, punching shear reinforcement is used as an effective solution. Several types of punching shear reinforcing systems have been developed in the past. This work aims to analyze the behavior of unbonded post-tensioned slab subjected to punching load provided with “Inverted-U Shaped Reinforcement”. By using a finite element software, the results were compared with that obtained from an experimental investigation previously done. The experimental results were also compared according to ACI provisions for punching shear strength. Good correlation was done between what was tested and the numerical results. [ABSTRACT FROM AUTHOR]