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Highlights • The reliability of the models for the assessment of the punching capacity. • The modification of the failure criterion for the model based on the CSCT. • Relations between ratio V test / V Rc and parameters influencing the punching capacity. Abstract Reinforced concrete flat slabs are structural members frequently used in building construction. Despite their many advantages, such structural systems suffer from several drawbacks. From a safety point of view, the concentration of shear forces at the vicinity of local supports, e.g., columns, edges and corners of walls, can lead to possible structural failure from punching. Punching is a dangerous phenomenon due to its brittle mode of failure and its ability to spread over a whole structure, which can be followed by a progressive collapse. Several models for the assessment of punching capacity have been developed and calibrated using experimental results from laboratory tests. Some models are fully empirical, e.g., EC2 (2004), while other models reflect the physical nature of the phenomenon; however, their safety level was calibrated using experimental data, as the model presented in Model Code 2010 or the CSCT-based model, which is expressed in a closed form. This paper deals with a statistical evaluation of the safety level of the previously mentioned models for punching resistance without transverse reinforcement. A database which includes the results of more than 600 experimental tests of flat slab specimens has been used. The relations between the safety of the model and the quality of the concrete used, the amount of the bending reinforcement, and the effective depth were found using advanced statistical methods. [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 • Punching strengthening is required due to design/construction errors, load increase, etc. • Strengthening techniques are compared using the Critical Shear Crack Theory. • A case study is dealt with to give indications for strengthening pre-dimensioning. • Predicted punching strength of strengthened slabs agrees with experimental data. • A design tool is provided to choose which technique better fits the specific case. Abstract Over the years, the flat slab system has become a popular form of construction in many countries, particularly for multi-storey buildings such as offices or carparks. Nowadays, a considerable number of flat slab buildings requires strengthening against punching. Reasons are several, like design or construction errors, poor quality materials, not complying with new codes provisions, or increase of vertical load. This paper discusses different techniques for strengthening of R/C slabs against punching: insertion of post-installed shear reinforcement, application of external fibre reinforced polymers or a bonded reinforced concrete overlay (BRCO) on the slab top surface, enlargement of the support, application of a post-tensioning system. The authors propose a unified approach, based on the Critical Shear Crack Theory (CSCT), to evaluate the effectiveness of each strengthening technique. The attempt is to give a reading key capable of adapting to different strengthening techniques and providing a comprehensive view of the problem. The study shows that the CSCT could be easily adapted to all strengthening techniques and punching strength predictions are in good agreement with literature experimental results. This work also proposes to give designers the tool to choose which strengthening technique suits better to the specific case. [ABSTRACT FROM AUTHOR]

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

A punching shear strength mechanical model for RC flat slabs with and without shear reinforcement, based on a beam shear model previously developed by the authors, is presented. The differences in resisting actions between beam shear and punching shear have been identified and incorporated into the governing equations and failure modes, resulting in simple but accurate punching design equations. The model consistently explains and quantifies some experimentally observed phenomena, such as the higher contribution of the concrete to the punching shear strength of slabs than in the case of beams subjected to shear, mainly due to the multi-axial state of stresses that takes place near the support. Furthermore, the model provides physical meaning to some parameters used in the design, such as the position of the critical perimeter or the effective stress of the punching reinforcement, among others. Very good agreement has been obtained between the model predictions and the results of 560 punching tests of concentrically loaded slabs, with and without shear reinforcement, included in two available large databases. The mechanical character of the model allows its extension to post-tensioned flat slabs, border or corner columns, steel fiber and FRP reinforced concrete slabs or different strengthening systems in a consistent way. [ABSTRACT FROM AUTHOR]

Fracture resistance of concrete column-slab connections, with low reinforcement ratios and strengthened by carbon fibre reinforced polymer (CFRP) plates, is often governed by debonding failure modes. In this paper, a three-dimensional finite element model is conducted to predict the punching behaviour of concrete column-slab connections which incorporate bonded non-prestressed and prestressed CFRP plates to the tension surface of the slab. The adopted interfacial behaviour, between the FRP materials and concrete, takes into account the effect of mixed mode behaviour on the displacement fields at the critical diagonal cracks (CDC). Results are then presented in terms of the ultimate load capacities, load-strain relationships in the FRP and internal steel reinforcement, load-interfacial stress relationships, and stress distributions in the FRP reinforcement. It can be stated that by adopting the mixed mode behaviour at the interface between the fibres and concrete, the onset of debonding is effectively captured by the FE analysis, which is very difficult in a laboratory test. [ABSTRACT FROM AUTHOR]

In this study, various reinforcement and strengthening details for the improvement of the punching-shear behavior of concrete footings were developed. Eight test specimens of reinforced-concrete (RC) footings were constructed and tested to investigate the punching-shear behavior of the concrete footings with the developed details. The test parameters include the additional placement of a longitudinal reinforcement around the column-footing connections, the inclination of the shear reinforcement, an additional cast of high-strength concrete, and an additional concrete cast with amorphous metallic fibers (AMFs). The test specimens were supported on a bed of steel car springs that simulate the elastic behavior of soil. The test results show that the punching strength was significantly enhanced by the additional placement of the longitudinal reinforcement around the column-footing connections and by the addition of the retrofit materials (high-strength concrete and AMF-reinforced concrete). Contrarily, the shear reinforcement that was placed around the connections did not significantly affect the punching-shear strength of the footings. The test results were also compared with strength predictions for which the current design codes and the existing theoretical models were used. [ABSTRACT FROM AUTHOR]

“Small Punch” (SP) tests, at present frequently employed for mechanical characterizations of structural metals, particularly for diagnosis of plant components, are here considered in view of employment also for assessments of stresses. In the procedure proposed herein the standardised sample removal from an in-service component for SP tests is exploited as external action altering the residual stress state possibly present near to the surface in the location considered. Full-field measurements of consequent displacements in the surrounding surface are employed as input for inverse analysis based on the following features: computer simulations of the sample removal as for its consequences due to relaxation of the pre-existing stress state; “non-uniformity” of residual-stress dependence on depth described as layer-dependent with uniformity in each layer of a pre-defined set of layers; “discrepancy function” minimization with employment of the elasticity parameters provided by the subsequent SP test. The advantages of the novel method consist of no-more need of traditional usual “Hole Drilling” (HD) tests or other tests for residual-stress estimation. The SP experimental procedure proposed herein for estimations of both stress state and elastic-plastic material properties would imply reductions of damages, costs and times in structural diagnoses. [ABSTRACT FROM AUTHOR]

To verify the beneficial use of UHPC in the highly stressed region of column-slab connections, a total of ten punching tests on reinforced concrete slabs were performed. All interior column-slab connections included double-headed studs as shear reinforcement. Nine test specimens were in addition strengthened by fibre-reinforced Ultra High Performance Concrete (UHPC) units. These elements were built in around the columns in the slab compression zone, replacing there the normal strength concrete (NSC). UHPC units with three different diameters were applied. To allow for a flexible combination of UHPC unit and double-headed studs, most of the UHPC units were separated into four parts with joints in between and were provided with channels for the double-headed studs. The slabs including a UHPC element reached significantly higher failure loads than the test specimens without such an element. In the slabs including the UHPC units with smaller diameter, a clear punching shear failure outside the elements was observed. In the case of the larger UHPC units, significant cracks occurred inside the elements, indicating the initiation of a failure of the UHPC. [ABSTRACT FROM AUTHOR]

In this study, punching-shear tests were performed to investigate the behavior of slabs supported by rectangular columns with capital. The slabs were subjected to an uneven shear transfer in two orthogonal directions by using the rectangular columns and different span lengths. Column capitals were used at the slab-column joints and preassembled bar trusses were placed at the periphery of the column capital to enhance the punching-shear capacity. Furthermore, the corners of the rectangular column and column capital were rounded to alleviate the shear stress concentration at the corners of the critical perimeter for shear. The test results show that the punching-shear strength of the slabs were significantly enhanced by the bar trusses. The shear resistance of the bar trusses was mostly contributed by the diagonal bars undergoing significant strains. On the basis of the results, the effects of the uneven shear transfer and bar truss arrangement on the slab shear behavior were investigated. In addition, the punching-shear strengths predicted by ACI 318-14, Eurocode 2, and KCI 2012 were compared with the test strengths. [ABSTRACT FROM AUTHOR]

Flat slab concrete buildings are widely found in infrastructure such as office and residential buildings or industrial facilities. The susceptibility of progressive collapse of such structures due to accidental loads is highly dependent on the structural performance of the slab-column connections. This paper presents a framework for a simplified reliability analysis and derivation of safety factors for computing the probability of punching of flat slab concrete buildings subjected to accidental loads such as column removal, slab falling from above or blast load. The main advantage of the proposed approach is that it considers in a simple manner, the uncertainty in the gravity load applied in the slab before the accidental event, which affects the inertial effects and demand/capacity ratio in the slab-column connections. Eurocode 2 and the Critical Shear Crack Theory for punching are used and extended to dynamic cases for the assessment of the demand/capacity ratio using computer-based time history finite element simulations. The proposed reliability method is applied to a case study of an existing building showing that the column removal situation is not always critical whereas the slab falling from above is much more detrimental. [ABSTRACT FROM AUTHOR]

Failure of reinforced concrete (RC) slabs without shear reinforcement in punching has been a challenging problem for nonlinear finite element (FE) analysis. To improve the analysis approach, this study was conducted by developing a nonlinear FE analysis method for slabs subjected to punching failure without shear reinforcement, using three-dimensional continuum elements. The influence of several modelling choices were investigated by comparing such results as loadcarrying capacity, load-deflection response and crack pattern from the FE analyses with available experimental data. The proposed method shows the possibility of accurately predicting the load-carrying capacity and realistically describing the behaviour of slabs. [ABSTRACT FROM AUTHOR]

The behaviour of tie rod anchor plates is at present not well established, and the criteria suggested do not seem to have consistent theoretical basis. This paper suggests a theoretical approach to determine the load-carrying capacity of stiff anchor plates acting on a masonry wall. According to this approach the punching strength is the lower of two values. The first value follows from the hypothesis that collapse occurs because of the slippage of the units on the mortar bed, whereas the second comes from the alternative hypothesis that punching creates a solid consisting of a truncated cone in which the outer face is the surface of the anchor plate (units break whereas the mortar does not crumble). When doing so it is supposed that the anchor plate is so stiff that pressure it applies on the masonry wall is almost constant. The issue of setting an adequate stiffness is solved for the most common types of anchor plate. Some numerical examples show the capabilities of the suggested approach. [ABSTRACT FROM AUTHOR]

Adding a thin layer of Ultra-High Performance Fiber Reinforced cement-based Composite (UHPFRC), with or without steel rebars, over a Reinforced Concrete (RC) slab is an efficient reinforcement method for existing structures. The thin layer of UHPFRC serves as a tensile reinforcement for the RC slab, creating a composite element. A recent experimental campaign showed that the layer of UHPFRC significantly increases the rigidity and the punching shear resistance of a RC slab submitted to a point force. An analytical composite model is developed herein to predict the global bending behavior of the composite slab and the punching shear resistance. A multilinear moment–curvature relation for composite sections is proposed to calculate the global force-rotation behavior of a slab which can then be used in combination with a composite failure criterion to predict the punching shear resistance. The contribution of the concrete section to the punching shear resistance is obtained with existing models from the literature. The UHPFRC layer resists to punching shear by out-of-plane bending over a limited length equal to its height. This mechanism induces tensile stresses perpendicularly to the interface with the concrete. The contribution of the UHPFRC layer to the punching shear resistance thus depends on the tensile strength of concrete. The results of this analytical composite model are in good agreement with the experimental result. A method is also proposed to consider pre-existing deformation of the RC section for a post-installed UHPFRC layer. [ABSTRACT FROM AUTHOR]

A novel concept of steel–concrete–steel (SCS) sandwich conical structure has been developed for the Arctic offshore platforms. In this structure, punching shear resistance to localized patch loading is the main concern that considers the high pressure zones due to nonuniform distribution of the ice contact pressure. In this paper, quasi-static tests on nine large scale SCS sandwich shell structure were firstly carried out to investigate the ultimate strength behavior of the SCS sandwich shell structure under patch loading. Based on these test results, the influences of different parameters on the ultimate resistance were discussed and analyzed. These studied parameters are composite action, steel shell thickness, spacing of connector, strength of concrete core, and curvature of the sandwich shell. Theoretical models were developed to predict the shear resistance of the SCS sandwich shell structure. The innovations of the developed models include developing formulae to predict the resistances of the connector used in the sandwich shell structure, redefining the critical perimeter to analyze the punching shear resistance of SCS sandwich shell, and modifying the formulae in Eurocode 2 to calculate the punching shear resistance. The accuracy of the developed prediction models were checked and confirmed by nine reported tests and 11 tests in the literature. Finally, design recommendations on the punching shear resistance of the SCS sandwich shell were offered based on the discussions and validations. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the behaviour of reinforced concrete flat slab structures under combined vertical and horizontal cyclic loading. A total of five specimens were cast and tested: a control specimen was punched without eccentricity, one specimen was tested under constant vertical loading and monotonically increased eccentricity until failure and the remaining three were tested under constant vertical load, at different shear ratios, and cyclic horizontal loading with increasing horizontal drift ratios. All slabs were similar, measuring 4.25 × 1.85 × 0.15 m 3 . The reinforced concrete slab specimens were connected to two steel half columns by 0.25 × 0.25 m 2 rigid steel plates, prestressed against the slab using steel bolts, to ensure monolithic behaviour. The cyclic tests were performed using an innovative test setup that allows bending moment redistribution, line of inflection mobility, assures equal vertical displacements at the North-South borders and symmetrical shear forces. Results show that cyclic horizontal actions are very harmful to the slab–column connection, resulting in low horizontal drifts and energy dissipation. [ABSTRACT FROM AUTHOR]

Shear strength of reinforced concrete slab–column connections can be increased through the use of headed shear studs. To reduce interference with slab flexural reinforcement, stud rails are often placed in an orthogonal layout. In this layout, no stud rail is placed in regions extending from the corners of a column, as opposed to stud placement in a radial layout. Some experiments have found the absence of radial stud rails could lead to premature shear failure at slab–column connections. This problem may not have been noticeable in experiments that tested slabs with either short-spans or with a high flexural reinforcement ratio. This paper presents an experimental study to evaluate the effectiveness of these stud layouts in slab–column connections whose slabs have relatively low flexural reinforcement ratios. Three full-scale slab–column connections that represent a flat plate structure with 25 ft (7620 mm) spans were tested. All three specimens had an identical flexural design, in which the reinforcement ratio was 0.8%. One specimen was built without shear reinforcement, and the remaining two specimens were reinforced with shear studs in either a radial or orthogonal layout. For the specimens with shear studs, calculated shear strengths were higher than their estimated flexural strengths. [ABSTRACT FROM AUTHOR]

This research study is aimed at evaluating the effects of carbon fiber reinforced polymer (CFRP) strengthening on the punching shear behavior of two-way reinforced concrete (RC) slabs strengthened with CFRP strips having openings varying in size and location. In the scope of the research study, series of experiments are conducted on eight test specimens of CFRP strengthened two-way square RC slabs having openings with variable locations and sizes. In the experimental study, the specimens (with dimensions of 2000 × 2000 × 120 mm) are tested by applying an axial load from the top of a square column (200 mm × 200 mm) located at the center of the test specimen. Each test specimen has one opening with the dimensions of 300 × 300 mm or 500 × 500 mm located adjacent or 300 mm far from the central column in a parallel or diagonal position. The test specimens are strengthened with four CFRP strips (150 mm wide) located under the slab next to the opening of the specimen. Additionally eight U shaped CFRP strips (150 mm wide) located at the corners of the opening are used to further retrofit the test specimens. The effects CFRP strengthening and varying size and location of openings on the punching shear behavior of the test specimens are considered by examining the slabs’ bearing capacities and stiffnesses obtained from the results of the experiments in comparison to the results of a former experimental study. Furthermore, the experimental results obtained from the study are used to evaluate the accuracy of the available code equations to predict the punching shear capacity of flat slabs. From the comparison, it is observed that the punching shear capacities of the retrofitted test specimens significantly increased with respect to the punching shear capacities of the bare specimens with opening tested in a former study. Moreover, it is also observed that the several equations proposed by structural codes underestimate the punching shear capacities of the test specimens. [ABSTRACT FROM AUTHOR]

This paper presents experimental, numerical and analytical investigations about the effects of incorporating coarse recycled concrete aggregates (CRCA) on the punching behaviour of reinforced concrete (RC) slabs. For this purpose, four concrete mixes were designed with various substitution ratios of natural coarse aggregates (NCA) by CRCA: 0% (reference mix), 20%, 50% and 100%. Subsequently, eight 1100 × 1100 × 90 mm reinforced concrete slabs (two per concrete type) were cast and subjected to punching tests. The experimental results indicate that the incorporation of CRCA affects the mechanical behaviour of RC slabs according to the following trends: (i) the punching resistance of slabs made of concrete with CRCA (CRCAC) is similar to that of the reference mix; (ii) the stiffness decreases, particularly in the uncracked state; and (iii) the cracking load slightly decreases. The numerical study comprised the development of three-dimensional non-linear finite element models of the slabs. The numerical models were able to trace the experimental responses of the slabs tested, highlighting the influence of the concrete fracture energy on the numerical results. The best predictions of punching strength were obtained when similar fracture energy was adopted for all concrete mixes. Finally, the accuracy of some of the most relevant design codes in predicting the punching strength of CRCAC slabs is assessed. The most accurate estimates were obtained using Model Code 2010 (MC 2010) with levels of approximation II to IV. Eurocode 2, ACI 318 and MC 2010 with level of approximation I provided less accurate and relatively conservative punching strength predictions. [ABSTRACT FROM AUTHOR]

Nonlinear finite element analyses of reinforced concrete slab-column connections under static and pseudo-dynamic loadings were conducted to investigate their failures modes in terms of ultimate load and cracking patterns. The 3D finite element analyses (FEA) were performed with the appropriate modeling of element size and mesh, and the constitutive modeling of concrete. The material parameters of the damaged plasticity model in ABAQUS were calibrated based on the test results of an interior slab-column connection. The predictive capability of the calibrated model was demonstrated by simulating different slab-column connections without shear reinforcement. Interior slab-column specimens under static loading, interior specimens under static and reversed cyclic loadings, and edge specimens under static and horizontal loadings were examined. The comparison between experimental and numerical results indicates that the calibrated model properly predicts the punching shear response of the slabs. [ABSTRACT FROM AUTHOR]

It is widely recognized that Compressive Membrane Action (CMA), also called Arching Action, increases both the bending and punching capacities of reinforced concrete (RC) structures. In this paper a non-linear finite element (NLFE) approach which adopts multi-layered shell modeling of RC slabs is presented. NLFE analyses (NLFEA) were carried out with ABAQUS Code and UMAT.for user subroutine in which the crack model denoted as Physical Approach for Reinforced Concrete for Cyclic Loading (PARC_CL) was implemented. Post-processing of NLFEA results is presented which exploits the Critical Shear Crack Theory (CSCT) to evaluate the punching shear resistance of shell elements. The capability of the proposed numerical procedure, to properly determine the punching shear resistance of RC slabs, is checked by comparing numerical predictions with experimental punching shear capacities obtained on circular slabs tested at the Stevin Laboratory of TU Delft. Subsequently the same numerical procedure was adopted to evaluate CMA effects on the punching shear resistance of the Corick bridge deck in Northern Ireland, UK, subjected to concentrated loads. Finally the design punching shear resistances achieved with the presented procedure are compared with the analytical values obtained using the British Code BD81/02. [ABSTRACT FROM AUTHOR]

The punching shear strength of interior column connections of flat slabs has traditionally been investigated with isolated test specimens subjected exclusively to hogging bending moments. However, the behavior of such specimens is different from that of actual flat slabs, as the potentially beneficial phenomena of moment redistribution between hogging and sagging moments and compressive membrane action cannot take place in the conventional experiments. In the present paper, an axisymmetric numerical model is introduced that allows analyzing the role and significance of these effects on the flexural deformations of continuous flat slabs. Combined with the failure criterion of the Critical Shear Crack Theory, this model can be used to predict the punching capacities of such slabs. Comparisons are made to the results of some unconventional punching tests from the literature showing sound agreement between the modeling results and the experimental observations. The results suggest that the punching capacity of continuous slabs with low amounts of flexural reinforcement in the interior column regions may be underestimated in the current codes of practice. [ABSTRACT FROM AUTHOR]

• Push-out tests were conducted to investigate the bond behavior between the steel tube and the foundation concrete. • Punching tests were conducted to reveal the working mechanism of the embedded column base with shear studs. • A method was proposed to determine the punching shear resistance of the embedded column base for CFSTs. In this paper, the punching shear behavior of the embedded column base for the concrete-filled steel tube is experimentally studied. Push-out tests were firstly conducted to obtain the bond strength between the steel tube and the foundation concrete. Punching tests were then performed on ten specimens to reveal the working mechanism of the embedded column base with shear studs. The test results indicated that shear studs changed the load path, enlarging the punching section of the foundation and improving the punching shear resistance of the column base. It was also found that the diameter of the shear studs and the distance between the shear studs could affect the punching shear resistance significantly. Finally, a method was proposed to determine the punching shear resistance of the embedded column base for the concrete-filled steel tube, by adding up the contributions from the different components of the system, including the bond force and shear resistance of studs above the punching section, and the resistance of foundation. The predicted results showed good agreement with the experimental results, with errors not greater than ± 15%. [ABSTRACT FROM AUTHOR]

Punching shear resistance usually constitutes the decisive design criterion for reinforced concrete flat slabs supported by columns. Modeling approaches based on Kinnunen and Nylander’s rotation-symmetric sector model, such as the Quadrilinear Sector Model (QSM), allow the prediction of the slab’s load–rotation behavior. To take into account an orthogonal reinforcement layout, the steel Young’s Modulus is usually reduced. A mechanically better justified flexural stiffness reduction factor is derived here which depends on the longitudinal reinforcement and modular ratio. The QSM also neglects shear deformations, which may reduce the flexural capacity. A Modified Sector Model (MSM) is derived which considers the influence of shear on the flexural behavior. A strength reduction factor for the shear crack-crossing longitudinal reinforcement is introduced which depends on the mechanical longitudinal reinforcement ratio. The factor takes into account that the longitudinal reinforcement also has to transmit forces resulting from shear. The MSM can also be applied to predict the load–rotation responses and punching shear resistances of flat slabs strengthened with prestressed carbon fiber-reinforced polymer (CFRP) straps. [ABSTRACT FROM AUTHOR]

The use of prestress in flat slabs is a common solution, mainly because it allows larger spans and thinner slabs. Nevertheless, smaller thicknesses near the slab-column connections, along with the superposition of high shear and flexural stresses, arise the question of the slab capacity to resist punching. The punching failure results from the superposition of shear and flexural stresses near the column, and is associated to the formation of a pyramidal plug of concrete which punches through the slab. It is a local and brittle failure. The use of prestress can increase the punching capacity of flat slabs-column connections. This work presents the experimental analysis of flat slab specimens with tendons under punching. Nine slabs were tested using unbonded prestress with high strength steel tendons. The influences on the punching capacity of the vertical component of the prestress forces resulting from inclined tendons near the column and their distance to the column are analysed. The in-plane compression force due to prestress was not applied to the slabs, in order to evaluate only the deviation force influence. This work aims to improve the understanding of the behaviour of prestressed flat slabs under punching load in order to properly evaluate the punching resistance of this kind of structures. The experimental punching loads are compared with the provisions of EC2, ACI 318-11 and MC2010. [ABSTRACT FROM AUTHOR]

An experimental study of full-scale reinforced concrete flat slabs crosswise strengthened with prestressed carbon fiber-reinforced polymer (CFRP) straps against punching shear was performed. The effects of two strap anchoring systems and of slab thickness on punching behavior were compared. In one system the anchors were adhesively bonded to the concrete surface, while an external steel frame balanced the horizontal strap force components in the second system. Strap activation and thus strap force increments were higher in cases with either lower prestressing or higher strap stiffness. The deformability of the steel frame allowed a balancing of the strap forces. In the cases with steel frame, the friction bond between the steel anchors and the concrete surface reduced the concrete compressive zone. The system stiffness was thus increased and the rotation capacity reduced compared to the case with bonded anchors. The thickest slab exhibited a reduced rotation capacity and thus strap activation. The slab therefore failed at the lowest load increase, which however was still 67% above the theoretical resistance of the non-strengthened slab. [ABSTRACT FROM AUTHOR]

Highlights: [•] 15 Test results are presented investigating the effects of prestressing on the punching shear strength. [•] Contrary to available tests, the different effects of prestressing are investigated separately. [•] The results are investigated on the basis of the physical model of the Critical Shear Crack Theory. [•] The suitability of this theory for punching design of prestressed slabs is demonstrated. [•] The evaluation of the physical parameters of this theory is adapted to the case of prestressed slabs. [Copyright &y& Elsevier]

Highlights: [•] Settlement/punching behavior of full-scale RC and SFRC precast tunnel lining segments were investigated. [•] Peak load capacity of RC segments was higher than that of SFRC segments for both settlement and punching behavior. [•] SFRC segments had higher initial cracking load and more stable post-peak cracking pattern compared to that of RC segments. [•] SFRC segments achieved significant reduction in crack width, providing serviceability advantages. [•] SFRC is attractive for fabrication of segmental tunnel linings where the initial cracking load is a governing criterion. [Copyright &y& Elsevier]

Highlights: [•] A modeling technique is proposed for post punching resistance of flat plates. [•] The model accounts for discontinuity developed due to punching shear. [•] The results of modeling technique are validated against experimental data. [•] Progressive collapse resistance of a flat plate after column removal is evaluated. [•] Post-punching resistance mainly from integrity rebars help resist progressive collapse. [Copyright &y& Elsevier]

• The failure mechanism of high-strength welded hollow spherical joints is clarified. • The basic mechanical properties of Q460 steel are obtained through tests. • SWDM fracture model is developed to investigate the bearing capacity of the WHSJ. • Four WHSJ full-scale specimens made of Q460 high-strength steel are tested. • New design formulae for the bearing capacity of high-strength WHSJ are proposed. High-strength large-span reticular shells have proliferated in recent years in engineering projects. Thus, appropriate rules should be developed to ensure the safe and efficient design of high-strength welded hollow spherical joints (WHSJ). However, to date, even the compressive failure mechanism of normal-strength WHSJ has not been fully recognized yet. In this paper, the failure mechanism and load bearing capacity of high-strength WHSJ are experimentally studied with four Q460 steel full-scale specimens under uniaxial loads. Also, three-dimensional refined finite element (FE) models are built, and their numerical results are shown to be in good agreement with experimental data. In addition, a micromechanical ductile fracture model, which can account for the effects of both stress triaxiality and Lode angle, is incorporated in FE models to improve the accuracy of joint failure prediction. Furthermore, focusing on the rib stiffener, the effects of two parameters, including the diameter-to-thickness ratio of the spherical joint and the ratio of spherical joint and chord diameters, on the performance of high-strength WHSJ are comprehensively studied. It was found that the failure of WHSJs subjected to uniaxial tension load is the punching shear rupture due to fully developed plastic strain, while the collapse of the WHSJs subjected to uniaxial compression load is caused by elasto-plastic buckling. Finally, new design formulae for the bearing capacity of high-strength WHSJ are proposed and validated using parametric analysis. It will be shown that these formulae help eliminate the potential risk in current specification provisions. [ABSTRACT FROM AUTHOR]

Abstract: The conversion of existing buildings, development of standards, material deterioration and detailing deficiencies have led to a need for strengthening an increasing number of concrete flat slabs against brittle punching shear failure. However, existing analytical and design models do not yet take into account the specific aspects of strengthening slabs against punching shear. More than 40 models exist for predicting the punching shear strength of new slabs. A three-level classification is proposed to provide a consistent overview of the wide range of approaches adopted for resistance calculation. Based on this classification, models are evaluated with regard to their applicability for problems specific to the strengthening of existing slabs, such as pre-damage of existing slabs, insufficient anchorage lengths of tensile reinforcement outside the punching zone, new openings in slabs within the punching zone, and the prestressing of post-installed shear reinforcement. The efficiency of current strengthening solutions is evaluated, suggesting local prestressing as a promising method. [Copyright &y& Elsevier]

Abstract: This work refers to experimental and 3D nonlinear FEA on punching. Numerical results were compared with experimental ones in order to benchmark the FE model and afterwards a parametric study was conducted, changing the reinforcement ratio, slab thickness, concrete strength and column dimensions, running a total of 360 models, where their effect on punching capacity is shown. EC2 and MC2010 provisions agreed approximately with experimental and FEA results. Based in the FEA results it is proposed an equation to predict the punching capacity with the introduction of fracture mechanics parameter, which was compared with several experimental results, giving good approximation. [Copyright &y& Elsevier]

Abstract: This work presents an experimental study concerning the post-punching behaviour of flat slabs strengthened with a new technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. This strengthening technique proved efficient with respect to ultimate and serviceability states. Five slab specimens were tested in the post-punching range and it was found that the post-punching resistance was on average 78% of the punching resistance. This paper reports the development of strand forces and slab displacements from the beginning of the tests, including the bond stresses developed at several stages of the loading process. It was observed that top reinforcement bars were capable of transmitting post-punching loads to the prestressing strands. Taking this into account and based on the load bath envisaged from the column to the slab, expressions for the vertical load capacities corresponding to the parts of the load path are presented and compared with the experimental results, showing their ability to predict both ultimate loads and modes of failure. Compared with other strengthening techniques, the one proposed here not only upgrades ultimate and serviceability behaviour but also adds post-punching resistance, which is a great advantage in the event of progressive collapse, since it may avoid the collapse of an entire structure, thus reducing the risk of material and human losses. [Copyright &y& Elsevier]

Abstract: The ultimate strength of reinforced concrete slabs is frequently governed by the punching shear capacity, which may be increased with addition of traditional fitments such as reinforcing steel, headed studs or shear heads. In addition to these traditional methods of strengthening against punching, steel fibre reinforcement has proved to be an effective and viable alternative. The addition of fibres into the concrete improves not only the shear behaviour but also the deformation capacity of reinforced concrete slabs. This paper presents a mechanical model for predicting the punching strength and behaviour of concrete slabs reinforced with steel fibres as well as conventional reinforcement. The proposed model is validated against a wide number of available experimental data and its accuracy is verified. On this basis, a simple design equation for the punching shear capacity of steel fibre reinforced concrete (SFRC) slabs is proposed. [Copyright &y& Elsevier]

Abstract: This work aims to study a new flat slab strengthening technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. The main advantages of this technique over the traditional prestress strengthening systems that use mechanical anchorages are that it does not need external permanent anchorages, meaning that the forces are introduced into the concrete gradually instead of being localized, thereby preserving aesthetics and useable space. The seven tested slab models show that this technique meets its objective as it is able to reduce reinforcement strains at service loads by up to 80% if the strengthening technique is applied in two directions and slab deformations by up to 70%, consequently making crack widths smaller. It can also increase punching load capacity by as much as 51% when compared to non-strengthened slabs. The results are compared with the EC2 (2004) , ACI 318-08 (2008)  and MC2010 (2010)  provisions. The main conclusions are that this strengthening technique is effective regarding ultimate and serviceability states and that it represents an advance in RC slab strengthening techniques. [Copyright &y& Elsevier]

Abstract: The punching shear strength of two way slabs without shear reinforcement and without unbalanced moment transfer is estimated using both neural networks and new simplified punching shear equations. An artificial neural network (ANN) was used to predict the punching shear strength of internal slab–column connections. Neural network analysis is conducted using 244 test data available in the literature and experiments conducted by the authors to evaluate the influence of concrete strength, reinforcement ratio and slab effective depth on punching shear strength. A wide range of slab thicknesses (up to 500 mm) and reinforcement ratios were used. In general, the results obtained from the neural network are very close to the experimental data available. The test results were used to develop two new simplified practical punching shear equations. The equations also showed a very good match with available experimental data. Four equations for the punching shear strength prescribed in well-known specifications were evaluated based on the available experimental results. This paper includes a discussion of the parameters of punching shear strength in the American, Canadian, British and European specifications. [Copyright &y& Elsevier]

Abstract: In this paper, punching shear strengthening of flat slabs using Carbon Fiber Reinforced Polymer (CFRP) sheets is studied. Fifteen specimens of reinforced concrete slabs were tested. Thirteen of them were strengthened by CFRP sheets and two specimens were kept as control specimens. Four of these strengthened specimens were tested under cyclic vertical loading. The width of CFRP sheets varied in different specimens. The CFRP sheets were located at the tension side of the slabs in two perpendicular directions. Vertical load was applied downward through a column stub using a hydraulic Jack. In all specimens, no rupture of CFRP sheets was observed. The test results showed that the use of CFRP sheet, in addition to steel reinforcing bars, as flexural reinforcement improves the punching shear strength of slabs. This improvement can be significant for the slabs made of high strength concrete and low steel reinforcement ratio. However, the improvement of punching shear strength due to FRP strengthening reduced under cyclic vertical loading. The test results were compared with the equations proposed by ACI 318 and BS 8110 Codes. The ACI Code underestimates the punching shear strength of slabs and this underestimation becomes more pronounced with the increase in the flexural reinforcement. The BS 8110 Code appropriately accounts for the effect of flexural reinforcement on punching shear strength of slabs. However, for the strengthened slabs, an equivalent reinforcement ratio should be used to include the effect of both steel and CFRP flexural reinforcement. [Copyright &y& Elsevier]

• Proposed a model to predict punching shear failure. • Predicted the punching shear failure by monitoring the column drift ratio. • The ASCE 41 stiffness can be used in conjunction with the proposed modeling method. • The lateral strength is estimated by flexural strength over slab column strip. • The proposed model provided good estimation for tests in the literature. A nonlinear modeling approach was developed to capture the response of slab-column (SC) frame members under combined gravity and lateral load demands. The occurrence of punching shear or flexure-punching shear failures at slab-column connections is detected by monitoring the column drift and providing a limiting drift value based on the gravity shear demand at the connection. Following detection of failure, plastic springs at the member ends are adjusted to provide a reduced stiffness and moment carrying capacity. Nonlinear modeling parameters developed for use in ACI 369.1 and ASCE 41 for SC connections without shear reinforcement were then reviewed by applying the developed nonlinear model to several SC connection tests reported in the literature. The model was implemented in the OpenSees computational platform. The backbone responses predicted by the proposed SC connection model are consistent with the experimental measurements. In addition, the proposed nonlinear modeling parameters are shown to provide a good estimate of the nonlinear response of SC connections under gravity and lateral loads that induce punching shear or flexure-punching shear failures. [ABSTRACT FROM AUTHOR]

• Nonlinear finite analysis (NLFEA) of punching failure at biaxially loaded edge columns of flat slabs. • Development of Joint Shell Punching Model for edge columns. • Development of edge column shear enhancement factor for closed form version of Critical Shear Crack Theory. • Validation of proposed shear field methodology for calculating shear resisting perimeter for use with Critical Shear Crack Theory. The paper investigates the influence of biaxial loading on punching resistance at square and elongated edge columns of flat slabs which is virtually neglected in the literature. In the absence of experimental data, the influence of biaxial loading is determined using nonlinear finite element analysis (NLFEA) with 3D solid elements. The resulting baseline punching resistances are compared with the predictions of various implementations of the Critical Shear Crack Theory (CSCT) including a Joint Shell Punching Model (JSPME) in which punching failure is simulated using nonlinear joint elements inserted between the nodes of nonlinear shell elements located around the punching control perimeter. The failure criterion of the JSPME, which is most suited for structural assessment, implicitly accounts for the effect of biaxial loading unlike the original (classic) and closed form versions of the CSCT. The classic CSCT indirectly accounts for loading eccentricity by reducing the punching control perimeter by a multiple k e which is determined in this paper using shear field analysis. Conversely, the closed form CSCT, which is adopted in the draft for the next generation of Eurocode 2 (EC2), enhances the design shear force by a multiple β. The paper uses experimental data to determine an expression for β for edge column connections subject to inwards eccentricity normal to the slab edge. Subsequently, shear field analysis on representative flat slab to edge column connections is used to extend this expression for β to edge column connections subject to biaxial eccentricity. NLFEA simulations with 3D solid elements are used to validate the predictions of the JSPME, the shear field methodology used to determine k e in the classic CSCT and the proposed expression for β in the closed form CSCT. Reasonable agreement is achieved between all these analysis methods. The main advantage of the JSPME over NLFEA with 3D solid elements is its increased computational efficiency which makes it more suitable for the assessment of large structures. [ABSTRACT FROM AUTHOR]

• The activation of punching reinforcement in flat slabs and column bases is analyzed. • The mechanical background of activation for next Eurocode 2 (prEC2) is explained. • An extended activation formula considering bond and anchorage is derived for prEC2. • Different types of shear reinforcement are considered on a uniform basis. • Focus is on transformation from a mechanical model to a simplified design formula. • The proposed activation formula is validated by systematic punching test results. Various types of punching shear reinforcement have been developed during the past decades to increase the punching capacity and ductility of slab-column connections. Due to diverse geometries and thus varying anchorage conditions, the effectiveness of these elements contributing to total punching resistance can differ significantly. Generally, the degree of activation of shear reinforcement can be described by contributions of anchorage and of bond. Yet, most of current punching design provisions follow a simplified, empirical approach. Despite its mechanical background, the punching design according to the next generation of Eurocode 2 still does not consider the effect of better anchorage of, for example, double headed studs compared to simple stirrups. In this paper, an extended activation formula for flat slabs as well as column bases is proposed as refinement for the next generation of Eurocode 2. This unifying approach considers different anchorage categories and thus enables more progressive design results. After discussing the background of possible activation scenarios, the effects of bond and anchorage in cracked concrete and the kinematic deformation behavior of slabs subjected to punching are identified as governing constraints. The major focus is on the transformation process from mechanical considerations to a simplified design formula to ensure practical applicability. [ABSTRACT FROM AUTHOR]

• Load resisting mechanisms of eccentrically loaded slab-column joints with in-plane restraints were discussed. • Effects of eccentricity, slab thickness and steel ratio on the pre- and post-punching performances were studied. • Effects of in-plane restraint and unbalanced moment were quantified based on the FE analysis. • Interactions between the unbalanced moment and shear force were explored and compared with code predictions. In flat plate structures, interior slab-column joints are subjected to in-plane restraints and bending-shear actions, which can significantly impact their mechanical performance to resist progressive collapse. However, research in this area is still lacking. This paper presents experimental and numerical studies of pre- and post-punching performances of eccentrically loaded slab-column joints with in-plane restraints. Quasi-static tests were conducted on seven joint specimens, including one concentrically loaded (CL) joint and six eccentrically loaded (EL) ones. The effects of critical structural parameters (i.e., eccentricity, slab thickness and reinforcement ratio) on the pre- and post-punching performances were investigated by analysing the load–displacement relationships, failure modes and material strains. The experimental results indicated that larger eccentricity could lead to more reduction of the peak punching shear capacity by as much as 62%, whereas it has little effect on the post-punching capacity. In addition, the strain results of the through-column rebars showed that, with the well-restrained boundary conditions, the slab flexural reinforcement (FR) was found to resist the applied load to a large extent at small deformations and still able to contribute greatly during the post-punching stage. Numerical analysis was conducted to gain an in-depth understanding toward the effects of varied levels of in-plane restraints on both slab-column joints and actual flat plate structures. It was found that the lateral stiffnesses in the CL joint model with boundary beams and the substructure model were similar, which was around 400 N/mm. Finally, the interactions between the unbalanced moment and shear force were explored and compared with code predictions (ACI318-19 and EC2-04). Without considering the enhancement effects from in-plane restraints, the codes produced over-conservative predictions. Based on the FE analyses, the correlation between the dimensionless ratio e / d (eccentricity/effective thickness of slab) and punching shear strength was simplified by a combined straight line and a power curve. [ABSTRACT FROM AUTHOR]

• The behaviour of UHPC/NC hybrid slab is investigated. • A validated FE model is used to study a wide range of parameters. • A design model is developed to predict the punching capacity of hybrid slabs. Flat slabs are commonly used in the construction of multi-storey buildings due to their ease of placement and installation, relatively short construction time, minimal structural floor depth and economic credentials. However, flat slabs are vulnerable to punching shear, a failure mode that typically occurs without any warning at slab-column connections. While various methods exist to improve punching shear capacity, the use of ultra-high performance concrete (UHPC) offers a highly buildable alternative to use of shear reinforcement in normal strength concrete (NC). However, UHPC is an expensive material and recent research has focussed on its partial use in column zones only, with NC elsewhere i.e. hybrid NC/UHPC. In this paper, a non-linear finite element (FE) model using ABAQUS was developed to simulate the punching shear performance of hybrid NC/UHPC flat slabs without shear reinforcement. The FE model was validated against experimental results from the literature. The validated model was then used to investigate the influence of slab thickness, column size, UHPC area and UHPC compressive strength. The results show that punching shear capacity of the slabs increases with the area of the UHPC zone. Additionally, the ratio of concrete compressive strength of UHPC to that of NC has a significant effect on the behaviour of the hybrid slabs which should be accounted for in future design guides. In order to understand the performance of existing design guides and codes in this context, a comparison between FE results and code predictions is also presented. The results suggest that the code models including ACI 318-14, Eurocode2 and Model Code 2010 cannot accurately estimate the punching shear capacity of reinforced UHPC slabs and hybrid NC/UHPC slabs. A modification to the existing ACI equation is proposed which yields accurate predictions for reinforced UHPC and hybrid slabs. [ABSTRACT FROM AUTHOR]

• Tests to investigate the performance of a new type of punching shear reinforcement. • Punching shear reinforcement whose anchoring is independent of the flexural rebars. • Experimental tests on slab-column connections with high shear reinforcement ratios. • Use of complimentary reinforcement to avoid premature failure due to delamination. • ACI, EC2 and MC10 presented conservative strength predictions for the tested slabs. This paper presents the results of tests on slabs with punching shear reinforcement formed by prefabricated truss assemblies disconnected from the flexural reinforcement, developed to optimize the construction process. General guidelines for design, detailing, and assembly of this reinforcement are presented, based on the recommendations presented by ACI 318, Eurocode 2, and fib Model Code 2010. One slab without shear reinforcement and one slab with stud rails were tested as a reference for tests on two slabs with the prefabricated truss modules as punching shear reinforcement. The load-rotation response and the failure loads are presented and discussed in comparison with theoretical estimates obtained following the design codes. The profile of stress and strain distribution on the flexural and shear reinforcement are also presented and discussed. The slab with inclined prefabricated truss bars registered similar response and resistance compared to the one with stud rails. These tests confirm the effectiveness of this kind of punching shear reinforcement, as one of the slabs had almost twice the strength and more than three times the deformation capacity of the reference slab without shear reinforcement. [ABSTRACT FROM AUTHOR]

• An extensive review for six decades of experimental punching shear testing of slabs under axial tension. • The effect of various parameter on punching shear behavior of slabs under axial tension. • A physically sound, simple, and accurate model for punching shear and axial tension is proposed. Punching shear failure of reinforced concrete (RC) slabs is a sudden one, which has catastrophic outcomes. Flat slabs with large restrained dimensions, may be subjected to in-plane tensile forces due to thermal or earthquake loading. With the growing demand for optimum design and reduced safety factors, neglecting the effect of these forces on the punching shear design is not an option. Over the last 6 decades, research efforts have explained many issues regarding punching shear behavior of RC slabs subjected to in-plane compression loading. However, hand full of research investigations were directed towards studying those subjected to in-plane tensile forces. Even those limited studies were mostly experimental testing and comparison with design codes. The purpose of this study is to develop a physically sound mechanical model for concrete slabs under combined punching shear and in-plane tensile forces. Literature review for the experimental investigations, design codes and mechanical models for slabs under punching shear and in-plane tensile forces was conducted. A punching shear mechanical model, which explains the experimentally observed behavior of RC slabs under combined in-plane tensile forces and punching shear was developed and proposed. It captured the effect of various parameters in a physically sound manner as well as being consistent with the well-established critical shear crack theory. [ABSTRACT FROM AUTHOR]

• Reliability assessment of punching shear capacity for? flat slabs without shear reinf. • Stochastic modelling of the random variables in the punching shear resistance function. • Safety level assessment of the resistance model and comparison to EN 1990 (β = 3.8). Punching shear is one of the main failure mechanisms in flat slabs. To prevent such failures, modern structural codes, as EN 1992-1-1, offer design provisions against punching shear. However, these provisions were calibrated based on experience, which can affect the precision of the resulting safety level. The use of modern reliability analysis techniques is required for a more precise evaluation of the safety level of these structural systems. This paper presents a comprehensive review of the state-of-the-art of reliability techniques where the safety level of design provisions for punching shear resistance without shear reinforcement is investigated. This study addresses three reliability analysis techniques: Mean-Value First Order Second Moment Method (MVFOSM), First-Order Second Moment Method (FOSM) and a Monte-Carlo simulation with Importance Sampling (MC-IS). Reliability indices β are used as a practical measurement of the safety level representing probabilities of failure. The parameters influencing the punching shear capacity without shear reinforcement were varied that the area of practical interest is covered. The estimated reliability indices β are evaluated and compared to a target safety level given by EN 1990 for a 50-year reference period where β is equal to 3.8. The results seem to confirm that the punching shear provisions for slabs without shear reinforcement according to EN 1992-1-1 achieve a required safety level, which is in accordance to the target level given by EN 1990. In addition, the study shows that the use of the techniques FOSM and MC-IS seems appropriate for determining the probability of failure of the design equation for the punching shear capacity without shear reinforcement. Furthermore, the study suggests that the method MVFOSM may not be suitable to assess the absolute safety level of such design equations. Finally, the study highlights the potential of using the aforementioned reliability analysis techniques and stresses the importance of modelling the uncertainties for a precise structural safety assessment of flat slabs without shear reinforcement. [ABSTRACT FROM AUTHOR]

• ABAQUS can be used to study the impact of column rectangularity on punching shear. • Slab shear stresses concentrate near the corner and along short side of the column. • Impact of column rectangularity on punching not a function of column geometry only. • Impact also dependent on ratio of minimum column dimension to effective slab depth. • ABAQUS results indicate that current American design methods may be unconservative. Design provisions for punching shear of reinforced concrete flat slabs supported on rectangular columns vary greatly and are typically based on empirical results. Due to the large cost and time required to conduct experimental tests the empirical database for slabs supported on rectangular columns is small. Properly calibrated, nonlinear finite element models (FEM) provide an efficient way to expand experimental databases, conduct parametric studies and verify design provisions. In this paper, the results from a parametric study of the impact of column rectangularity (aspect ratio) on the punching shear behaviour of interior slab-column connections without shear reinforcement under static concentric vertical loading are provided. The study was conducted using a three-dimensional nonlinear FEM based on the concrete damaged plasticity model available in ABAQUS. The FEM, summarized herein, was calibrated using seven experimental specimens of slabs supported on square and rectangular columns from literature. The parameters studied were the column aspect ratio, and the ratio of the minimum column dimension to the effective slab depth. These parameters were selected based on a review of literature and design provisions. The impact of column rectangularity on the predicted load-deflection response, slab crack patterns and shear stress distribution in the slab along the column perimeter are analyzed. The results for the 77 slab-column connections simulated in the parametric study demonstrate that the impact of column rectangularity is not dependent on the column aspect ratio alone, and becomes more severe as the ratio of the minimum column dimension to the effective slab depth increases. [ABSTRACT FROM AUTHOR]