•Description of the concrete damaged plasticity model used in ABAQUS.•Calibration of the material parameters in the adopted model.•Simulation of five different concrete slabs with the calibrated ...material model.•Good agreement between test and FEA responses for all slab specimens.
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.
•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.
•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.
Punching is an important process of the production for ultra-high-strength steel automobile components. By selecting the appropriate punching parameters, the punching quality can be effectively ...improved and the punching force can be reduced. In this study, several typical fracture damage models applicable to the punching process of high strength steel were compared, where the critical damage values were calculated through an iterative predictor–corrector approach. Meanwhile, the effects of punching parameters on maximum punching force (MPF) and punched face quality for hot stamped ultra-high strength steel Usibor1500P were investigated experimentally. The results show that the Oyane damage model is the most suitable one in simulating the punching process of Usibor1500P, which can better predict the punched profile features and the variation of punching force within one stroke. The increase in die clearance decreases the MPF, while the plate thickness, punch diameter and punch corner radius increase the MPF. The change of the punch corner radius has the most significant effect on the improvement of the punched face quality.
•Rubber-wooden composite blocks to simulate and measure the reaction of soil foundation.•The effect of flexural bars on the punching shear strength of the column footing under eccentric ...load.•Punching shear failure in the column footing with low flexural reinforcement ratio.•A new prediction model for the punching shear strength of the column footing under eccentric load.
In reinforced concrete (RC) column footings, the soil stiffness can significantly affects the punching shear strength of the foundation slab. The present study conducted eccentric compression tests on three RC column footings considering the complex interaction between the soil and structure, and investigated the load-carrying capacity, displacement distribution, reaction distribution, failure mode, crack development, and strain distribution. The test parameter was flexural reinforcement ratio in the foundation slab. The test results showed that the footing specimen with lower reinforcement ratio was susceptible to brittle punching shear failure, and the flexural reinforcement ratio affected the crack distribution and the spalling of concrete cover. Since only one specimen was used in each flexural reinforcement ratio, however, the test results should be carefully considered. On the basis of the test results including existing studies, the effect of design parameters on the punching shear strength was evaluated. As a result, a new method was developed to predict the punching shear strength by addressing the eccentric compression force.
•Evaluation of two FEA concrete models (Concrete damage plasticity and Cementitious2).•Non-linear finite element simulation of slabs with different reinforcement ratios.•Capturing the punching and ...the flexural-punching failures of the tested specimens.•Comparison of FEA results with the predictions of ACI 318-19 and EC2-2004.•Parametric studies of slab-column connections with various reinforcement ratios.•New formulations to correlate the punching shear strength to the deflection.
Two types of failures can be observed in reinforced concrete slabs supported on columns: flexural and punching. Flexural failure occurs due to the formation of a yield-line mechanism, while punching failure occurs when a punching shear crack with a truncated cone shape develops around the connection. However, flexure-driven punching shear failures due to the yielding of the slab’s flexural reinforcement can occur in the immediate vicinity of the column. These failures appear in a similar manner to “pure” punching shear failures with an additional ductility resulting from the flexural reinforcement yielding. Since these flexure-driven punching failures occur in reinforced concrete slabs with low reinforcement ratio, the paper investigates the punching shear response of reinforced concrete slab-column connections with various flexural reinforcement ratios to distinguish the different failure modes that can be observed: punching and flexural-punching. First, the study presents the calibration procedure needed in three-dimensional non-linear finite element analyses (FEA) to simulate the punching shear failure of reinforced concrete two-way flat slabs without transverse reinforcement under static concentric loading. The calibration approaches are developed with reference to two advanced constitutive concrete models available in two different FEA software. Two series of experimental tests are selected from literature: plain concrete specimens under uniaxial and biaxial loadings and slab-column connections under concentric punching. It is shown that the numerical solutions using both concrete models can capture the cracking and failure mode accurately. It is emphasized that the numerical models provide a valuable tool to characterise failure processes and behavioural mechanisms for the simulation of slabs with varied reinforcement ratios. Numerical simulations showed that the failure mode transition within low and high reinforced concrete slabs can be highlighted by flexural-punching and punching shear mechanisms. In addition, the new code predictions of ACI 318-19 for punching shear of slabs with low reinforcement ratios are presented and discussed in comparison to EC2-2004 predictions and the experimental results. Finally, a numerical assessment of slab-column connections with reinforcement ratios varying between 0.2 and 2.2% is conducted to thoroughly investigate the effect of the flexural reinforcement ratio on the punching behaviour.
•A detailing approach to enhance post-punching strength of slab-column connections.•Residual strength of slab-column connections after cooling from high temperatures.•High temperatures up to 800 °C ...were applied to slab compression face.•Applied high temperature did not cause serious shear strength reduction.•Finite element simulations for post-heating strength of slab-column connections.
Large-scale experiments were conducted on six isolated slab-column connection specimens. Each specimen contained a 300 mm square center column and a 150 mm thick slab. The objectives of the experiments were to study the effects of fire-induced high temperatures on the residual punching shear strength of reinforced concrete flat-plate structures after cooling and to examine the effectiveness of a detailing approach for enhancing the post-punching load-carrying capacity. Ceramic fiber heating panels were used to apply high temperatures to slab shear-critical regions at the compressive face. The test results indicate that the high temperatures up to 800 °C did not seriously impact connection punching shear strength. Moreover, the use of crossties can effectively engage slab tensile reinforcement in resisting post-punching loads with a loading capacity close to or even greater than the punching failure load. Complementary to experiments, finite element simulations were conducted. The numerical simulations predicted the punching failure load of slab-column connections at room temperature with a good accuracy; however, the simulations underestimated the post-heating punching strength of the cooled slab-column connections by up to 11%.
•A new method for improving punching strength of voided slabs was presented.•The punching behavior of slabs was investigated experimentally and numerically.•Introducing voids inside the slabs ...remarkably influenced their responses.•The proposed method was excellent in improving an overall behavior of voided slabs.•The efficiency of sheets increased with augmenting their thickness.•The sheets were more active when they placed below or near the column stub.
In recent modern buildings, voided slabs have been extensively employed because of the high reduction in their self-weight up to 35%. Limited studies have been conducted on such slabs, and no significant drop in the flexural strength was reported due to introducing voids. In contrast, a considerable drop in the punching strength of the voided slabs was addressed. Therefore, this study presented a new and simple method for improving the punching shear strength and behavior of such slabs by employing steel sheets. Five half-scale specimens were fabricated. One slab was solid and kept as a reference specimen, while the others were voided slabs. They contained 96 spherical voids distributed uniformly throughout the slab area, three of them were strengthened by six embedded steel sheets, three sheets in each direction. The sheets were orthogonally configured and intersected below the column stub. The variable of the study was the sheet thickness (0.8 mm, 1.0 mm, and 1.2 mm). The specimens were subjected to a gradually concentrated load through the column up to collapse. The test results revealed that significant losses were recorded in the strength, stiffness, ductility, and energy absorption of the voided slab without sheets compared with the reference one. However, the strengthening of voided slabs by sheets was superior not only in retrieving these losses but also in exceeding them. Besides, FE analysis was conducted, utilizing the ABAQUS program, for profoundly illustrating the experimental findings and performing a parametric study. Based on the FE observations, the activation of sheets was found to be increased by enlarging their thickness, and the best activation was observed when gathering the sheets below or nearer the column stubs.
•Three full-sized flat slabs were tested at ambient and elevated temperatures.•The punching shear bearing capacity of the specimens was greatly weakened by fire.•Cracks mainly presented a radiating ...pattern, and oblique cracks rapidly developed on the plate surface under fire.•Infrared (IR) detection was used to realize real-time monitoring of crack development at high temperatures.•Detonation of concrete occurred at the plate bottom under the fire. A 3D scanner was used to record the explosive crushing characteristics and scan overall structural deformations.•The rigid-plastic model based on unified strength theory could be used to solve the punching shear bearing capacities of plate-column structures under and after fire.
In this paper, three full-sized flat slabs measuring 4800 × 4000 × 200 mm3 supported by a circular column stub were tested at ambient and elevated temperatures to investigate their punching shear performance. During the fire tests, three slabs were submitted to the ISO-834 curve for 180 min. Infrared detection and 3D scanning were utilized to record crack information and overall deformations. Furnace temperatures, temperature distributions, horizontal and vertical displacements, torque angles, residual ultimate punching loads, and punching shear taper angles were recorded and described in detail. A rigid-plastic model based on unified strength theory was used to calculate the effect of fire on the punching capacity of the flat slab. The calculated results fitted the test results well; thus, the rigid-plastic model can be used to predict the punching capacity of flat slabs.
•Investigate the mechanical behavior of Steel-UHPC-Steel composite slabs under concentrated loads.•Define two failure modes of Steel-UHPC-Steel composite slabs considering composite action.•Analyze ...the failure mechanisms of Steel-UHPC-Steel composite slabs.•Establish a design method to predict the bearing capacity of Steel-UHPC-Steel composite slabs.
Steel-concrete-steel (SCS) composite structure is widely used as the protective structure in the containment of nuclear power plants, offshore platforms, subsea tunnels, and so on. This study investigates the mechanical properties of SCS composite slabs with ultra-high performance concrete (UHPC) as the core material under concentrated loads. Five S-UHPC-S composite slabs were tested with different parameters of the spacing of headed studs and the thickness of the concrete core. Besides, one S-C-S composite slab with the normal concrete as the core material was tested for comparison. Two failure modes, i.e. punching shear failure and interfacial debonding failure, were defined considering different composite action between the concrete core and bottom steel plate. A punching shear cone was formed in punching shear failure, while interfacial debonding failure had an obvious interfacial slippage between the concrete core and bottom steel plate. The failure mechanism of these two failure modes was analyzed. Moreover, a design method to predict bearing capacities was developed, which could take the effect of the concrete core, steel fibers in UHPC, steel plates, and tie bars into consideration. In particular, a reduction coefficient was introduced to reflect the effect of composite action between the concrete core and bottom steel plate. The design method was suitable with six specimens in this study and other specimens in literature, which could provide theoretical guidance for the application of SCS composite structure in practical engineering.
