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This article investigates the punching shear behavior of recycled aggregate concrete (RAC) two-way slabs. Ten 1500 mm × 1500 mm × 100 mm slabs were tested monotonically. Eight slabs were cast with RAC, whereas two control slabs were cast with natural aggregate concrete (NAC). The RAC incorporated coarse recycled concrete aggregate (RCA) at replacement levels of 25%, 50%, 75% and 100%. Two flexural reinforcement ratios (0.8% and 1.5%) were examined. The results show that the normalized punching shear strength of 100% RAC slabs decreased by 6.5% and 9% compared to NAC slabs for ρ = 1.5% and ρ = 0.8%, respectively. Doubling the amount of flexural reinforcement can increase the punching shear capacity of 100% RAC slabs by up to 45%. A punching shear database of 44 RAC slabs from literature and the 8 RAC slabs presented in this study revealed that the punching shear strength of RAC slabs predicted by ACI 318 was conservative, except for slabs with low reinforcement ratios (

Shear reinforcement is one of the common measures used to strengthen slab–column connections. It can make the joint’s load capacity increase. However, when the connection is subjected to an unbalanced bending moment, the reduction effect of the shear reinforcement on the bending moment is worth investigating. Nonlinear finite element analysis was performed on reinforced concrete slabs with shear reinforcement for various moment-to-shear (M/V) ratios. The effects of the number and diameter of shear reinforcement and different loading methods on the slab were investigated, as along with a correction to the ACI-318 and China Concrete Structure Design code GB50010 formula for the moment transfer coefficient. The 3D finite element modeling was performed using appropriate element types and a constitutive model for concrete. The concrete damage plasticity model parameters were calibrated using the experimental results of a specimen. The amount of shear reinforcement had a certain contribution to the strength of the slab, but the diameter of the shear reinforcement had little effect. The plate’s bearing capacity decreased as the M/V increased. The corrected moment transfer coefficient formula demonstrates that M/V is positively correlated with the coefficient and that the calculated values specified in ACI-318 and GB50010 are overly conservative.

This article provides experimental data on the punching shear behavior of synthetic fiber-reinforced slabs reinforced with glass fiber reinforced polymer (GFRP) bars and cast from self-consolidating concrete (SCC). The data was collected from tests performed on six full-scale specimens centrically loaded until failure as indicated by penetration of the column stub into the slab and achieving a sharp drop in the load carrying capacity. Three different reinforcement bar spacings were used to consider the effect of reinforcement ratio on punching shear resistance. Three of the specimens tested were reinforced by 1.25% of volume of synthetic fiber, and three were control specimens cast from regular SCC. Applied load, central deflections, and bar strain were monitored during the experiment and are provided in the supplementary data. Any future models for analyzing the punching shear behavior and capacity of flat slabs reinforced with GFRP rebars will find this data valuable for model validation, and for establishing suitable safety factors for design. Numerical studies on the simulation of fiber-reinforced concrete would also find value in this data to validate the numerical model and enable it to be used for further studies.

abstract: Reinforced concrete flat slabs are structural systems in which slabs are directly supported by columns, without the use of beams. A structural phenomenon that deserves attention in these systems is the punching shear, characterized by the occurrence of shear stresses close to the slab-column interface, which can produce fragile rupture in those regions. This study presents some results of reliability index β obtained for slab-column connections based on FORM, according to the Brazilian standard’s model, considering the model error. The critical contours C and C’ without shear reinforcement are analyzed. The results showed that failure in the C contour is very unlikely, while the probabilities of rupture in the C' contour when considering the influence of the model error are greater than the target values recommended in the literature for the ULS.

Abstract Research on behavior of flat slabs under punching shear, performed by Kinnunen, Regan and Muttoni influenced the main design recommendations. Meanwhile, studies about strut and tie model developed by Schlaich for beams, deep beams and corbels also influenced these design codes. This work aimed to adapt the strut and tie model for the punching shear resistance analysis in flat slabs. The punching shear resistance of 30 flat slabs verified through strut and tie model was compared to the one designed following Brazilian, American and European codes recommendation. Subsequently, this same model was validated by comparing the test results of 32 flat slabs. The strut and tie model results, when compared with the test results, showed a better average than those from codes, and the modified strut and tie model can become an alternative for punching shear strength prediction.

This study presents an investigation about the effect of fire flame on the punching shear strength of hybrid fiber reinforced concrete flat plates. The main considered parameters are the fiber type (steel or glass) and the burning steady-state temperatures (500 and 600°C). A total of 9 half-scale flat plate specimens of dimensions 1500mm×1500mm×100mm and 1.5% fiber volume fraction were cast and divided into 3 groups. Each group consisted of 3 specimens that were identical to those in the other groups. The specimens of the second and the third groups were subjected to fire flame influence for 1 hour and steady-state temperature of 500 and 600°C respectively. Regarding the cooling process, water sprinkling was applied directly after the burning stage to represent the sudden cooling process. Generally, the obtained results exhibited a significant increase in the punching shear capacity of the fiber-reinforced slabs as compared to the corresponding no fiber-reinforced slabs even at elevated burning temperatures 600°C. The ultimate load was increased by about 16.6, 19, and 21.5% at temperatures of 25, 500, and 600°C respectively, for steel fiber reinforced slabs and by about 13.9, 27.2, and 34.6% for slabs containing two mixed types of fibers (steel and glass), as compared with the reference specimen at the same temperatures respectively. In addition, the results indicated that fibers' presence in concrete resulted in gradually punching failure with more ductile mode, whereas the failure was sudden with a brittle mode in the slabs that did not contain fibers. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed to analyze the punching shear resistance in flat slabs of reinforced concrete in the presence of openings and stud-type shear reinforcement. Openings in flat slabs reduce resistance to punching. The magnitude of the loss of strength is influenced by the quantity, size, and position of the opening in the slab. The theoretical method presented in this work describes that once a load is applied onto the slab, a rotation occurs, giving rise to seven forces. These forces are related to the concrete and the flexural and shear reinforcement. The failure load is calculated by finding the solution of nonlinear equations developed from horizontal, vertical, and rotational balance of these forces. The failure criterion of these slabs with shear reinforcement was classified as internal or external to the shear reinforcement. The results showed theoretical breaking loads similar to those obtained experimentally, with a maximum variation of 7%. [ABSTRACT FROM AUTHOR]

With the emergence of fiber-reinforced polymer (FRP) reinforcement as a substitute for conventional steel reinforcement, different design codes have been developed to account for the different mechanical properties of the FRP, specifically the elastic modulus. The ACI 440.11-22, CSA/S806-12, and JSCE-97 are well-known standards for FRP-reinforced concrete structures. In particular, these design standards show significant variations in estimating the punching shear resistance and accounting for the elastic modulus. This study provides a statistical and machine learning-based evaluation of the punching shear models in design standards. An Artificial neural network (ANN) framework is used to develop a generalized punching resistance model of flat slabs reinforced with steel and FRP bars utilizing a large experimental dataset with 539 tests. The study presents a parametric study to examine the effect of different factors on the punching shear strength. The parametric study provided a graphical presentation and comparison between the design models and the developed ANN model. [ABSTRACT FROM AUTHOR]

This paper presents the application of a thick-shell nonlinear finite element analysis procedure to estimate the punching shear resisting performance of reinforced concrete slab-column connections under variable connection shear stress conditions. In the analyses performed, varied connection shear stress conditions stem from slabs being supported by columns with different cross-section aspect ratios, being subjected to different distributions of gravity loading, being constructed with different planar reinforcement ratios in orthogonal directions, as well as the application of unbalanced bending moments. Forty-eight isolated slab-column connection specimens presented in the literature were modelled and analyzed using a thick-shell finite analysis procedure. All numerical results were developed using a predefined set of material models and analysis parameters, a consistent meshing procedure, and are shown to provide meaningful agreement with experimental data without the need for case-specific model calibration or the adoption of specialised failure criteria. The results show that thick-shell modelling methods can be suitable for estimating the punching shear response of slabs subjected to non-uniform shear stress development in connection regions, and can provide similar levels of precision to that obtained for the analysis of idealised slab-column connections typically used for design procedure and model development. • Low-cost shell FEA for punching shear assessment of reinforced concrete flat plates. • Analysis of 45 non-idealised connection specimens representative of real-world construction. • Good agreement between FEA simulations and reported results without model calibration. • Result accuracy comparable to that obtained for more typical idealised connection specimens. [ABSTRACT FROM AUTHOR]

The use of steel fibre reinforced concrete (SFRC) is a well-known method for enhancing the punching and flexural resistances of flat slabs. The structural performance of SFRC elements depends significantly on the fibre distribution and orientation, which are typically unknown. One of the largest uncertainties regarding the performance and reliability of SFRC concerns the determination of its post-cracking mechanical properties in the real structural element, normally performed via standardised tests. However, due to differences in element sizes and casting procedures, and to the presence of rebars, the fibre spatial distribution and orientation in the standard specimens differ in general from those of the structural member. Several researchers have studied the correlation between the orientation of fibres and the mechanical performance of SFRC, yet tests were rarely carried out under representative conditions of the actual behaviour of the target structural member. The present paper analyses the spatial distribution and orientation of steel fibres in six SFRC flat slabs that were previously tested in concentric punching at the University of Brescia. The aim of this work is to analyse the fibre orientation and spatial distribution in structural elements. Cores were extracted from the specimens after the punching tests and scanned using micro-computed tomography (μ -CT) to reconstruct the fibre skeleton. The fibre arrangement was analysed focusing on the variation of the fibre spatial distribution and orientation through the slab thickness. A formulation to express the actual fibre dispersion in concrete is proposed, and effectiveness factors are defined to reflect the efficacy of fibres in punching shear and flexure, based on their location in the slab thickness. Pseudo-horizontal fibre orientations are found to be governing, with closer distributions to a 2D scenario for thicker slabs and higher fibre contents. Furthermore, the influence of flexural reinforcement on the fibre orientation has been observed to be significant. The observed fibre orientations are detrimental for the direct transfer of shear forces across cracks, but are favourable for enhancing the flexural capacity of the slab. • 18 cores extracted from six SFRC flat slabs previously tested in punching. • 3D core reconstruction and fibre skeletonization with micro-Computed Tomography. • Fibre distribution and orientation analysed for various slab sizes, fibre dosages. • Fibre orientation parameters defined for comparison with an isotropic distribution. • Effectiveness factors evaluate enhancement of punching and flexural slab resistance. [ABSTRACT FROM AUTHOR]

Reinforced concrete flat slabs are widely employed in structural systems. The location of the slab-column connection is the most sensitive part of the flat slab due to the existence of a high flexural anchor and shear force. On the other hand, the utilization of flat slabs directly resting on columns, in the case of punching shear failure, reveals their vulnerability that the presence of openings will increase the probability of punching shear failure. This study is the numerical study of the effect of strengthening the reinforced concrete flat slabs with opening and external steel plates on the punching shear capacity. Initially, verification of the numerical model by the experimental sample conducted. Then some reinforced concrete flat slabs with reinforced opening and external steel plates with various dimensions and thickness as well as diameter, length, number and order of the different shear studs under the load, by using the finite element method analysis and the results of the various samples were compared with each other. The strengthening of the reviewing slabs improved the condition of stiffness and increased the punching shear capacity. The reviews also indicated that this situation improve dependent on the dimensions and the thickness of the plate and the diameter, length, number, and order of the shear studs. The results of this research suggested that if you use the right behavioral model in the simulation process, the finite element method can be a useful tool for analysis and secure and optimum design of reinforced concrete slab.

In the paper the effectiveness of external steel and composite reinforcement was compared and discussed. The differences between the physical features of both materials, which are relevant for their use as additional, external reinforcement of the support zones, were presented. The results of authors’ and others experimental studies on strengthening reinforced concrete slabs by using external longitudinal reinforcement in the form of CFRP strips and steel flat bars, as well as by increasing the stiffness od support zone with steel sheets and CFRP tapes, were discussed. It was stated that moderate effectiveness of composite materials as external punching shear reinforcement resulted from higher deformability of CFRP as well as premature deboning (prior to rupture of fibers).

Abstract The effects of flexural reinforcement and shear reinforcement on the punching shear strength of slab–column connections are analyzed in this study. For the study, six slab–column connection specimens were constructed with varying flexural reinforcement and shear reinforcement, and were subjected to gravity load tests. Experimental results showed that all specimens were destroyed by punching failure, and that the slab–column connection behaved differently depending on the amount of shear reinforcement and flexural reinforcement. Particularly, the flexural reinforcement in the slab–column connection improved the punching strength of the specimens with or without shear reinforcement. In addition, in this study, a design formula that considers the flexural reinforcement ratio in the calculation of the punching shear strength of the shear reinforced slab–column connection was proposed and was verified using experimental results and existing test data.

In this article, one of the robust systems of soft computing namely adaptive neuro-fuzzy inference system (ANFIS) is used to estimate the punching shear capacity of the concrete column-slab connections reinforced with FRP. For this purpose, a collection of experimental tests was used to train and test the ANFIS model. Five parameters including the area section of the column, Young’s modulus of the FRP bars, the effective flexural depth of the slab, FRP reinforcement ratio and also the compressive strength of concrete are used as inputs of the neuro-fuzzy system to estimate the considered output. The whole structure of the ANFIS also presented in mathematical steps. The obtained results of the created model of this paper indicated that the proposed ANFIS structure with a suitable accuracy could be used as a predictive model to determine the punching shear capacity of the considered elements. Also, the formulated model of the ANFIS in this paper can easily apply for codes and other researches.

In the paper the results of experimental investigations concerning flat slabs made from reinforced lightweight concrete with sintered fly ash aggregate CERTYD were presented. In the research program 6 models made in a natural scale were included. The main variable parameter was slab longitudinal reinforcement ratio. The aim of investigation was the experimental verification of efficiency of double-headed studs as punching shear reinforcement. In the existing technical approvals such kind of reinforcement was allowed only in normal concrete slabs. It was demonstrated that double-headed studs can be an effective transverse reinforcement of lightweight aggregate concrete slabs. The use of double-headed studs resulted in increase in the ultimate load from 19% to 44%, depending on the slab reinforcement ratio which ranged from 0.5% to 1.2%. The comparative analysis showed that the Eurocode 2 provisions were conservative in relation to the experimental results, which were on average 42% higher than the theoretical ones however with a very low 7% coefficient of variation.

Punching shear behaviour of steel fibre reinforced flat slabs with punching shear reinforcement The guideline "Steel Fibre Reinforced Concrete" published by the German Committee for Reinforced Concrete (DAfStb) contains the current normative regulations for the punching shear design of steel fibre reinforced flat slabs. Due to a lack of sufficient experience and knowledge, a consideration of the combined action of steel fibres and shear reinforcement was explicitly excluded. While numerous punching shear tests on steel fibre reinforced flat slabs without shear reinforcement are available in literature, only eight tests in combination with shear reinforcement are known to the authors. These few tests used types of shear reinforcement which are not common for engineering practice in Germany, or showed bending failure, which limits the reliability of statements about the behaviour of such a combination. In this context and the expected favourable behaviour, seven tests were carried out to systematically investigate the punching shear behaviour of steel fibre reinforced flat slabs with stirrups and shear studs as shear reinforcement. The test program included one fibre reinforced test without punching shear reinforcement, two fibre‐free and four fibre reinforced tests with punching shear reinforcement. This paper describes the experimental investigations carried out and discusses the results obtained. [ABSTRACT FROM AUTHOR]

This paper presents test results from an experimental program conducted to study the punching-shear response of reinforced concrete (RC) edge column-slab connections (ECS connections) reinforced with glass fiber-reinforced polymer bars (GFRP). Five full-scale ECS connections were tested under vertical shear force and unbalanced moment until failure. Four of the five connections were reinforced with GFRP bars as flexural reinforcement; one connection was reinforced with steel bars for comparison. All slabs measured 2500 x 1350 x 200 mm (98.4 x 53 x 7.9 in.) with a 300 mm (11.8 in.) square column stub protruding 700 mm above and below the slab surfaces. The test parameters were flexural-reinforcement type, concrete strength, and moment-to-shear force ratio (M/V). The test results revealed that all the connections failed by punching shear with no signs of concrete crushing. The high-strength concrete (HSC) directly enhanced the punching-shear capacity, load-deflection response, and initial stiffness of the connections. These connections also evidenced fewer and narrower cracks compared to their counterparts cast with normal-strength concrete (NSC). Increasing the M/V produced significant shear stresses, thereby reducing the vertical load capacity by 31% and 30% for the NSC and HSC connections, respectively. A simple design approach to predicate the punching-shear capacity of FRP-RC ECS connections is proposed. The proposed approach yielded good, yet conservative, predictions with respect to the available test data. [ABSTRACT FROM AUTHOR]

Owing to their high strength-to-weight ratio, superior corrosion resistance, and convenience in manufacture, fiber-reinforced polymer (FRP) bars can be used as a good alternative to steel bars to solve the durability issue in reinforced concrete (RC) structures, especially for seawater sea-sand concrete. In this paper, a theoretical model for predicting the punching shear strength of FRP-RC slabs is developed. In this model, the punching shear strength is determined by the intersection of capacity and demanding curve of FRP-RC slabs. The capacity curve is employed based on critical shear crack theory, while the demand curve is derived with the help of a simplified tri-linear moment-curvature relationship. After the validity of the proposed model is verified with experimental data collected from the literature, the effects of concrete strength, loading area, FRP reinforcement ratio, and effective depth of concrete slabs are evaluated quantitatively. [ABSTRACT FROM AUTHOR]

This paper describes a numerical study of the punching shear resistance of unbonded post‐tensioned slabs without shear reinforcement. This research aimed to develop a methodology for modeling unbonded tendons and numerically evaluate the prestressing effects on the punching shear capacity. To validate the modeling approach, a series of well documented experimental tests were simulated using the finite element software DIANA. The nonlinear analyses were performed using three‐dimensional solid elements, incorporating the cracking behavior of concrete by the smeared crack approach. In addition, interface elements were included, providing bond‐slip properties to simulate the friction between tendons and concrete. A good agreement was found between the numerical results and experimental data. Load capacity, cracks patterns, and the prestressing effects were accurately simulated. After the validation, a parametric study was conducted to analyze the influence of distribution, force and profile of prestressing tendons. Finally, the numerical results were compared with current design code provisions and the approach provided by the Critical Shear Crack Theory. [ABSTRACT FROM AUTHOR]

This study experimentally assessed the behavior of interior slab–column connection in a system of reinforced concrete slabs subjected to symmetrical loading, with anchorage variation of shear reinforcement. Eight slab models (with equal flexural reinforcement and same dimensions) were assessed, being seven with shear reinforcement (different anchorages of shear reinforcement in the flexural reinforcement) and one slab for reference only reinforced for flexion. Experimental data were compared with the theoretical methods established by the following code designs: ACI 318 (2019), Eurocode 2 (2004), ABNT NBR 6118 (2014), and fib Model Code (2010). Although anchoring is an important parameter, it was found that the anchorage of the shear reinforcement in the flexural reinforcement did not significantly interfere with punching shear. The adopted shear reinforcement anchoring obtained better results concerning ultimate load only in the compressed longitudinal reinforcements. [ABSTRACT FROM AUTHOR]

This paper is concerned with the finite element modeling of strengthened interior slab‐column connections in the existing continuous flat slab structural system by employing steel angle plates at the slab‐column junctions and fastened by shear bolts. This technique utilizes the advantage of combined action between the angle plates and bolts in resisting shear particularly at the slab‐column edges. Three‐dimensional analysis was carried out on such slabs employing concrete damaged plasticity model in ABAQUS to investigate their performance in terms of punching shear resistance, load–displacement response, and crack pattern at failure. The numerical models were first validated against the experimental results reported by other researchers. The proposed strengthening technique results in a substantial increase of load‐carrying capacity ranging from about 59 to 79% compared to the unstrengthened slab, and has also provided better stiffness, ductility and energy absorption in the slab system that change the mode of failure from a pure punching shear to flexural failure. The finite element results are compared with the calculated values according to provisions in the current design codes for evaluation purposes. A simple but reliable approach which is based on yield line theory to estimate the flexural capacity of the strengthened slabs is also outlined in this paper. [ABSTRACT FROM AUTHOR]

Use of steel fibre reinforced concrete in floor slab for automated high‐bay warehouses In automated high‐bay warehouses, very strict requirements are placed on the deformation of the floor slab, which lead to largely jointless constructions. Steel fibres can be used here on the basis of the DAfStb guideline "Steel fibre concrete" for the verification of the necessary crack width limitation. Furthermore, there are usually very high loads on the floor slab from the racking supports, and in the case of clad rack construction loads from the roof structure must also be taken into account. The inclusion of steel fibres in the punching shear check can help to reduce the slab thickness, as far as the deformation requirements allow, or to do without costly punching shear reinforcement. By means of a practical example, it is shown that a combination of steel fibres and conventional reinforcing steel can be economical. Furthermore, it is explained by way of example which details must be taken into account in terms of execution. [ABSTRACT FROM AUTHOR]

Database for punching shear resistance of steel fibre reinforced concrete flat slabs without shear reinforcement – Verification of design approaches according to DAfStb guideline and Model Code 2010 The punching shear design of steel fibre‐reinforced flat slabs is currently carried out in Germany based on the DAfStb Guideline "Steel fibre reinforced concrete". The addition of steel fibres to the concrete allows an effective transfer of tensile forces across the crack and limits the progressive crack opening, which proves to be particularly favourable for the punching shear strength. Numerous investigations since the mid‐1970s have confirmed this and have enabled the derivation of empirical and partly mechanically based approaches for the calculation of the steel fibre contribution in the punching shear capacity of steel fibre reinforced flat slabs without punching shear reinforcement. For the evaluation and further development of these approaches, a critically reviewed database of punching shear tests on steel fibre reinforced flat slabs without punching shear reinforcement was created. Considering the practical construction requirements regarding the slab thickness, the degree of longitudinal reinforcement as well as the concrete compressive strength and the post‐cracking tensile strength, about 116 tests could be included in the punching shear database "Steel fibre reinforced concrete". This paper presents the database and discusses its evaluation about the prediction accuracy and the safety level of the design approaches according to the DAfStb guideline "Steel fibre reinforced concrete" as well as according to the Model Code 2010. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A laboratory research program was undertaken to compare the failure mechanisms and strengths of concrete foundation slabs subjected to punching shear and concrete breakout loadings. Four nominally identical reinforced concrete slabs were constructed and tested in a laboratory. One of the slabs was loaded in compression through a bearing surface to produce punching shear failure. The other three slabs were loaded in tension through eight anchor bolts arranged around a square perimeter to produce a similarly sized breakout failure. Variations in bearing area and local reinforcement detailing were introduced in the breakout tests to explore their effect on strength. One additional specimen was cast with a single anchor bolt to gather data on basic breakout strength. The test results indicate that punching shear and anchor breakout developed similar failure modes. Punching shear resulted in the largest strength with the largest failure surface. Ultimate load capacities normalized by the square root of the concrete compressive strength and by an effective failure area showed that the nominal failure stresses were nearly equal for the different test cases. The addition of slab deformed reinforcement in the vicinity of the anchor bearing head and oriented perpendicular to the direction of the anchor bolts resulted in a modest increase of the breakout ultimate capacity and of the residual strength. [ABSTRACT FROM AUTHOR]

Abstract This research aimed to compare the ultimate load of 10 waffle flat slabs with different sizes of solid area and spacing between ribs. For this, a non-linear computational simulation of the slabs was carried out until their failure using the engineering software ANSYS. The failure modes and loads were analyzed, and the results showed that the models with less solid area presented less bearing capacity in comparison to the models with greater solid area when the failure mode was shearing of the ribs. The slabs with the largest solid regions experienced punching shear and behaved in a similar way as solid flat slabs, indicating compliance with the codes in relation to their punching shear strength provisions, especially with the NBR 6118. The results show that a square solid area whose length is 15% of the span is reasonable and that the ACI, Eurocode 2 and NBR 6118 provisions underestimate the shear strength of the ribs.

Although lightweight concrete is implemented in many mega projects to reduce the cost and improve the project’s economic aspect, research studies focus on investigating conventional normal-weight concrete. In addition, the punching shear failure of concrete slabs is dangerous and calls for precise and consistent prediction models. Thus, this current study investigates the prediction of the punching shear strength of lightweight concrete slabs. First, an extensive experimental database for lightweight concrete slabs tested under punching shear loading is gathered. Then, effective parameters are determined by applying the principles of statistical methods, namely, concrete density, columns dimensions, slab effective depth, concrete strength, flexure reinforcement ratio, and steel yield stress. Next, the manuscript presented three artificial intelligence models, which are genetic programming (GP), artificial neural network (ANN) and evolutionary polynomial regression (EPR). In addition, it provided guidance for future design code development, where the importance of each variable on the strength was identified. Moreover, it provided an expression showing the complicated inter-relation between affective variables. The novelty lies in developing three proposed models for the punching capacity of lightweight concrete slabs using three different (AI) techniques capable of accurately predicting the strength compared to the experimental database

The recent failure of buildings because of punching shear has alerted researchers to assess the reliability of the punching shear design models. However, most of the current research studies focus on model uncertainty compared to experimentally measured strength, while very limited studies consider the variability of the basic variables included in the model and the experimental measurements. This paper discusses the reliability of FRP-reinforced concrete slabs’ existing punching shear models. First, more than 180 specimens were gathered. Second, available design codes and simplified models were selected and used in the calculation. Third, several reliability methods were conducted; therefore, three methods were implemented, including the mean-value first-order second moment (MVFOSM) method, the first-order second moment (FOSM) method, and the second-order reliability method (SORM). A comparison between the three methods showed that the reliability index calculated using the FOSM is quite similar to that using SORM. However, FOSM is simpler than SORM. Finally, the reliability and sensitivity of the existing strength models were assessed. At the same design point, the reliability index varied significantly. For example, the most reliable was the JSCE, with a reliability index value of 4.78, while the Elgendy-a was the least reliable, with a reliability index of 1.03. The model accuracy is the most significant parameter compared to other parameters, where the sensitivity factor varied between 67% and 80%. On the other hand, the column dimension and flexure reinforcement are the least significant parameters compared to other parameters where the sensitivity factor was 0.4% and 0.3%, respectively.

Fibre-reinforced polymer (FRP) rebars are being increasingly used to reinforce concrete structures that require long-term resistance to a corrosive environment. This study presents structural performance of large scale two-way concrete slabs reinforced with FRP rebars, and their performances were compared against conventional steel reinforced concrete. Both carbon FRP (CFRP) and basalt FRP (BFRP) were considered as steel replacement. Experimental results showed that the CFRP- and BFRP-RC slabs had approximately 7% and 4% higher cracking moment capacities than the steel-RC slab, respectively. The BFRP-RC slabs experienced a gradual decrease in the load capacity beyond the peak load, whereas the CFRP-RC slabs underwent a sharp decrease in load capacity, similar to the steel-RC slab. The BFRP-RC slabs demonstrated 1.72 times higher ductility than CFRP-RC slabs. The steel-RC slab was found to be safe against punching shear but failed due to flexural bending moment. The FRP-RC slabs were adequately safe against bending moment but failed due to punching shear. At failure load, the steel rebars were found to be yielded; however, the FRP rebars were not ruptured. FRP-RC slabs experienced a higher number of cracks and higher deflection compared to the steel-RC slab. However, FRP-RC slabs exhibited elastic recovery while unloading. Elastic recovery was not observed in the steel-RC slab. Additionally, the analytical load carrying capacity was validated against experimental values to investigate the efficacy of the current available standards (ACI 318-14 and ACI 440.1R-15) to predict the capacity of a two-way slab reinforced with CFRP or BFRP. The experimental load capacity of the CFRP-RC slabs was found to be approximately 1.20 times higher than the theoretical ultimate load capacity. However, the experimental load capacity of the BFRP-RC slabs was 6% lower than their theoretical ultimate load capacity.

In this paper, the punching shear behavior of interior slab-rectangular column connections without shear reinforcement under static concentric loading is studied using a three-dimensional, nonlinear, finite element model (FEM) in ABAQUS version 6.12 based on the concrete damaged plasticity model. The FEM was calibrated based on seven experimental tests selected from literature. The predicted shear capacities were compared to punching and one-way shear predictions according to published standards and the critical shear crack theory (CSCT). The finite element analysis results show that the impact of column rectangularity on punching shear capacity is not only dependent on the column aspect ratio but becomes more severe as the ratio of the minimum column dimension to the effective depth of the slab increases. This behavior was found to be implicitly accounted for in some published European standards and the CSCT. [ABSTRACT FROM AUTHOR]

Many times, existing RC flat slabs must be retrofitted to enhance their structural performance and service life. Among other retrofit techniques, concrete flat slabs can be strengthened with a top thin layer of ultrahigh-performance fiber-reinforced concrete (UHPFRC). Since UHPFRC is a relatively expensive material compared to conventional concrete, an optimized investigation regarding the location and thickness of the UHPFRC layer may be necessary. This study examines the punching shear performance of isolated RC flat slabs retrofitted with various layouts of UHPFRC. Two optimal retrofitting configurations are proposed and evaluated using three-dimensional (3D) nonlinear finite-element analysis, where both regular concrete and UHPFRC are simulated using a combined damaged plasticity–based model. The model is verified by analyzing previously tested slab–column connections from the literature. Then the predictive capability of the model is further verified by conducting parametric studies to investigate the effect of varying the thickness and area of the UHPFRC layer on the punching shear performance of the slabs. The maximum shear resistance, deformation, and crack propagation patterns of the composite slabs with different thicknesses, areas, and orientations of the UHPFRC layer are examined. The increase in thickness of the UHPFRC layer increases the punching shear capacity. However, the displacement at the maximum resistance decreases when the thickness of the UHPFRC layer increases. The use of a UHPFRC layer only on the critical areas of a slab can be more effective and economical since the amount of UHPFRC is reduced and the ductility of the slab is increased. [ABSTRACT FROM AUTHOR]

Punching shear is the most important problem in flat slabs, which usually requires strengthening for safety reasons. One of the most popular strengthening methods is the employment of shear reinforcement. Also, in order to reduce the self-weight of slabs, lightweight aggregate concrete as well as the bubble deck technology were used in this research. To study the influence of shear reinforcement type on lightweight aggregate voided slab behavior under punching shear, three slabs having the same geometrical and mechanical properties, with different shear reinforcement type (hook, inclined bar and stud) were cast and prepared for testing. As well as a control specimen with no shear reinforcement was used for comparison reason. The results showed that the inclined shear reinforcement has the most positive influence on slab behavior, between the three types of reinforcement that were adopted in the experimental work. [ABSTRACT FROM AUTHOR]

The paper presents comparison between the punching shear calculations from six different codes and two equations from the literature. It utilizes 257 punching tests data collected from the literature. The concrete strengths, f'c, range between 12.3 MPa and 68 MPa, the reinforcement ratios range between 0.2% and 5.01%, and the slab depths range between 80 mm and 500 mm. It is found that the smallest error is for CEB-FIP-90 and EC2-2004 while the largest error is for JSCE-2002 and ACI318-19. Also, modifications to one of the equations of the Egyptian reinforced concrete code and two of the equations of ACI318-19 code for calculating the punching strength of flat plates without shear reinforcements are presented. The modified Egyptian and ACI318-19 codes equations for punching strength are compared to the experimental data and good correlations are noticed. The obtained errors are lesser than those of the original codes equations and the average errors are on the conservative side. [ABSTRACT FROM AUTHOR]

Frequently, construction requirements demand to provide service pipelines passing laterally within slab thickness near the slab-column connections of flat slabs. The flat slabs including such conducted pipelines are expected to undergo a significant reduction in the punching shear capacity. For this purpose, experimental program was conducted in this study incorporating 10 specimens of reinforced concrete flat slab. One slab specimen was solid slab with no pipeline as a reference specimen and the other nine slab specimens were fabricated with either single or double pipelines passing through the slab thickness at different locations. Test results indicated that including pipelines within the slab thickness at a horizontal distance equal to or less than one-half of the slab thickness from the face of the column led to a substantial reduction in the ultimate load and the stiffness of the flat slabs. It was also found that the structural performance of a flat slab with double small pipelines horizontally aligned near tension face was more desirable than that of a flat slab with a single large pipeline. Furthermore, a modification is suggested to be introduced to the punching shear equation of Eurocode 2 to include the effect of the embedded pipelines in flat slabs. [ABSTRACT FROM AUTHOR]

Using FRP bars in the concrete structures under harsh environment produces extension of those service life and dropping of the cost of their lifecycle. This study investigated the influence of slab thickness, material of rebar, arrangement of reinforcement and mass’s dropped on the dynamic behavior of RC slabs by using laboratory experiments. Seven specimens 1550×1550 mm dimension with two thickness 120 and 150mm, single control specimen reinforced with steel bars and six specimens reinforced by CFRP bars were experimentally investigated under sequential dropping-weight ranged from 50 to 150kg, it was a rigid steel projectile, used to apply impacting load. 2.5m was the height of dropping. For estimated penetration depth, three empirical formulas have been used, ACE formulae was preferable predictor than other formulas. Different codes were used to calculation punching shear capacity and critical velocity of perforation and compared the experimental results with these codes. The experimental results showed that the shear properties of slabs have a significant effect in their general behavior. And preferable performance in FRP slabs than slabs reinforced with steel can be achieved which considering high strength and corrosion resistance of this material, which makes it a suitable choice for reinforcing materials. [ABSTRACT FROM AUTHOR]

The use of headed stud shear reinforcement has been widely accepted as an effective strategy to improve the punching shear resisting performance of reinforced concrete (RC) flat plates. However, the specific placement and layout of the shear studs provided in flat plates tends to vary throughout the world, and questions have been raised regarding the performance of the different shear stud layouts employed. This paper presents the results obtained from six large-scale flat-plate slab-column connection specimens that were tested under concentric shear loading conditions. The slabs were constructed with different flexural reinforcement ratios and employed headed stud rails placed in either a radial or cruciform configuration. The results showed that the use of shear studs provided in the cruciform or the radial shear stud layout greatly improved the shear-resisting behaviors of the slabs, and that the structural responses of the slabs employing the two different stud layouts were found to be comparable in nearly all respects. [ABSTRACT FROM AUTHOR]

Nonlinear time-history analyses are conducted on a flat-plate building to explore the damaging effects of vertical ground acceleration on punching shear failure of slab–column connections, which have been exposed by field observations. The structure is modeled three-dimensionally using grid beam elements for the floor slabs. Twenty unscaled near-source ground motions recorded during the 1979 Imperial Valley, 1994 Northridge, 2010 Darfield, and 2011 Christchurch earthquakes are considered. Both the punching failure criterion recommended by a standard design code and one developed based on a critical crack width theory are employed to identify punching shear failures. The numerical simulations indicate that, although the vertical ground-motion component has negligible effects on interstory drift demand, it can lead to punching failure that would otherwise not occur under horizontal ground motion only. On average, the vertical ground motion can reduce the lateral drift capacity at punching failure by 23%. Moreover, an extraordinarily strong vertical ground motion alone can cause a punching shear failure. The two considered punching failure criteria result in similar predicted failure drifts. The extra gravity load approach suggested by a standard design code to indirectly account for vertical ground-motion effects is found appropriate if the vertical spectral acceleration at the fundamental period of floor slab is less than 1.4g. The simulations also indicate slab-column frames can contribute around 15% of lateral stiffness and strength. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigations and numerical analyses performed on reinforced concrete flat slabs. Two tests were carried out on two flat slab specimens designed without specific shear reinforcement. The present paper deals only with the experimental behaviour and numerical modelling of such slabs, this representing the initial part of a larger study which aims to evaluate the shear capacity of such deficient slabs resulted from faulty design or execution and to identify viable and efficient strengthening solutions. ATENA finite element software package was used to numerically model the behaviour of the specimens. A very good agreement was achieved between the results of experimental investigations and numerical modelling with deviations of 0.2% in terms of maximum load carrying capacity and of 7% in terms of corresponding displacement. The specimens were able to carry loads of more than 950kN, larger than those evaluated using designated Eurocodes, displaying a safety factor of 2.72. [ABSTRACT FROM AUTHOR]

Most current concrete design codes include provisions for punching shear of reinforced concrete slabs supported on columns with L, T, and cruciform shapes. Reference studies verifying the accuracy of these code provisions are typically not provided. Empirical data of punching failures of slabs supported on columns with L, T, and cruciform shapes are limited due to the cost and time required to test specimens with slab thicknesses and column sizes commonly used in practice. In this paper, the punching shear behaviour of five interior L-shaped slab-column connections, one without a slab opening and four with slab openings, subjected to static concentric loading are analyzed using a plasticity-based nonlinear finite element model (FEM) in ABAQUS. The FEM is similar to models previously calibrated at the University of Waterloo and are calibrated considering nine slabs that are tested to study the impact of column rectangularity on the punching shear behaviour of reinforced concrete slabs. The finite element analysis results indicate that shear stresses primarily concentrate around the ends of the L, and that current code predictions from ACI 318-19 and Eurocode 2 may be unconservative due to the assumed critical perimeters around L-shaped columns.

abstract: This paper assesses the influence of slab continuity on the punching resistance of a realistically proportioned flat slab floor plate without shear reinforcement. The edge column punching resistance of a symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNO DIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 are seen to give similar predictions for punching resistance, while MC2010, which is based on the Critical Shear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, varies significantly with its levels of approximation with Level IV agreeing reasonably well with predictions from NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by the reinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear design are independent of span, unlike the results obtained with MC2010 LoA IV.

The problem related to the effect of the corner column load on the punching shear resistance of the slab was presented. Existing experimental studies on internal columns demonstrated that the column pressure could lead to an increase in the punching shear resistance. Because of different confinement conditions of corner column-slab connection joints, it is unclear if such an effect exists for corner columns. New experimental investigations were initiated to clarify this issue. They covered a total of three corner column-slab connection specimens – slabs with a thickness of 140 mm and a longitudinal reinforcement ratio ρl = 1.09% connected with columns of a cross-section of 200×200 mm. The only variable parameter was the column load equal to 500, 1000 and 1500 kN. A reduction of the slab load-carrying capacity of about 9% due to a three-fold increase in the column load was noted. Therefore, the effect of the column load turned out to be opposite to that observed for most previous tests on internal column-slab connections, which could have a result of a limited capacity of the slab reinforcement due to additional tensile forces from the lateral expansion of joint concrete. Comparison in the light of test results demonstrated, that EN 1992-1-1 procedure allowed for safe, yet conservative estimation of the punching shear resistance. An average ratio of experimental to theoretical load of 1.82 was obtained.

Premature loading of reinforced concrete flat slabs in multi storey buildings during construction may occur after shuttering removal and loading slabs earlier than usual to meet project time targets. Some case studies showed failure of flat slabs, which were prematurely loaded during the construction process before it reaches its full characteristic strength (at 28 days), which was used in structural design. This research aims to address this problem through experimental testing and design application according to current building codes. Eight specimens with dimensions of 1100 * 1100 mm and a total thickness of 120 mm were experimentally tested to study the effect of concrete age and actual compressive strength at loading on the punching shear capacity of reinforced concrete slabs. All specimens were supported by a square column with dimensions of 150 × 150 mm and loaded at the four corners with a span of 1050 mm. Accelerating admixture was used in three studied specimens to achieve higher concrete compressive strength at early ages compared to their companions of normal concrete without these admixtures. It was found that increasing concrete compressive strength of slab from 25 N/mm2 to 35 Nlmm2 (40 % increase) for normal concrete, without early admixture, improved punching shear capacity by 26 %, while increasing it to 45 N/mm2 (80 % increase) improved punching shear capacity by 49 % when the specimens were loaded 7 days after casting. In addition, using an accelerating admixture increased early concrete compressive strength, which improved punching shear capacity of reinforced concrete slab over that without accelerating admixture by 31 % and 29 % after 7 days and 14 days, respectively. According to inclusion of reinforcement ratio, BS8110 - 97 and Eurocode-2004 (EC2) design codes showed the most accurate prediction of punching shear capacity at 28 days, while ACI-2014 and ECP 203-2018 seemed conservative as their equations do not take steel ratio into consideration. At early ages, BS8110 - 97 and Eurocode-2004 (EC2) design equations did not provide accurate prediction of punching shear capacity while ACI and ECP provided reliable equations. It is recommended to use the actual compressive strength of concrete at early age (7 days for example) for calculating punching shear resistance of flat slabs prior to shuttering removal to prevent any premature loading.

The main aim of this paper is studied the punching shear and behavior of reinforced concrete slabs exposed to fires, the possibility of punching shear failure occurred as a result of the fires and their inability to withstand the loads. Simulation by finite element analysis is made to predict the type of failure, distribution temperature through the thickness of the slabs, deformation and punching strength. Nonlinear finite element transient thermal-structural analysis at fire conditions are analyzed by ANSYS package. The validity of the modeling is performed for the mechanical and thermal properties of materials from earlier works from literature to decrease the uncertainties in data used in the analysis. A parametric study was adopted in this study, it has many factors such as the ratios of length to thickness, fire temperature, time exposed to fire, concrete compressive strength, area exposed to fires and type of support. It can be concluded from this research the significant factors that affect the punching shear strength. However, the increasing ratio of length to thickness may be lead to increasing the deflection more than 123% at fire condition. Also, the increasing temperature leads to increasing the deflection about 40% at fire condition.

Over the last two decades, considerable attention has been devoted to the strengthening of sub-standard flat-slab constructions. With the evolution of composite materials and an increasing emphasis on the economical and sustainable use of natural fibers, many researchers have utilized them in the strengthening of flat flabs mitigating punching failures. This study aims at investigating and comparing the behavior of flat slabs strengthened with post-installed composite and natural reinforcements. An experimental program was devised consisting of eight flat-slab specimens. One specimen was tested in as-built condition to provide a reference. The remaining specimens were strengthened with Carbon Fiber-Reinforced Polymer (CFRP), Aramid Fiber-Reinforced Polymer (AFRP), and sisal rods. The pattern of post-installed rods was varied as single line, double line, and star shapes around the column. The results indicated that the single-line pattern could only enhance the maximum sustained load by up to 6% compared to that of the reference specimen. On the contrary, double line and star shape configurations resulted in a substantial increase in the maximum sustained load. An analytical assessment of ACI 318-19 provisions resulted in an over-estimation of the shear strengths of CFRP- and AFRP-strengthened slabs. Furthermore, the same provisions led to lower yields than experimental shear strengths for sisal-strengthened slabs.

In this study, finite element software ANSYS is used to model a three-dimensional finite element (FE) model to study the punching shear behavior of normal (NSC) and high strength concrete (HSC) flat plate slabs. The FE model is verified through application to experimental models, and high accuracy was obtained. The FE model was used to determine cracking load, ultimate load capacity, load-deflection curves, stress-strain relationship, and failure modes for all tested slabs. Results of nine NSC and HSC flat plate slabs were tested under punching loading. The main variables considered were the concrete compressive strength varied from 40 to 110 MPa, and column eccentricities 0%, 50% and 100% of column size. The behaviors of the finite element models showed good agreement with those got from experimental results in all linear, nonlinear and final failure stages.