types of shear reinforcement, because punchingshear failure can happen behind the bent-up bars. Hawkins (1974) reported tests performed with different punchingshear reinforcements and he found that the shear reinforcement increases the punchingshear capacity of the slabs. Broms (2000) combined the bent-up bars in the first two perimeters with closed stirrups and such arrangement was able to avoid any punchingshear failure. Closed stirrups were also used by many researchers, as another type of shear reinforcement; among others Islam and Park (1976), Hanna et al. (1975), Pillai et al. (1982) and Robertson et al. (2002). Slabs with shear heads were tested by Corley and Hawkins (1968) and by Dilger and Ghali (1981). The shear studs that consist of individual vertical bars were used in slabs tested by Seible et al. (1980), Dilger and Ghali (1981), Elgabry and Ghali (1987), Megally and Ghali (2000), Robertson et al. (2002), Kang and Wallace et al. (2005) and Tan and Teng (2005). Shear heads are an expensive type of shear reinforcement, however, it is essential to be used in cases where large openings close to the connection area are needed and thus this demands large adjustments to the flexural reinforcement. The shear studs have been widely used due to the advantages that they provide such as mechanical anchorage and highly quality. Shear studs are difficult in installation, however they are the most popular punchingshear reinforcement. Adetifa and Polak (2005) used a new type of shear reinforcement post-installed in flat slabs, called shear bolts.
reinforcedconcrete 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 punchingshear behaviour of five interior L-shaped slab-columnconnections, one without a slab opening and four with slab openings, subjected to static concentric loading are analyzed using a plasticity-based nonlinearfiniteelement model (FEM) in ABAQUS. The FEM is similar to models previously calibrated at the University of Waterloo and was calibrated considering nine slabs that were tested to study the impact of column rectangularity on the punchingshear behaviour of reinforcedconcrete slabs. The finiteelementanalysis 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.
problem that can occur in flat slabs, are high stresses in the slab-column connection area that can result in a punchingshear failure. In this paper, a 3-D analysis of the reinforcedconcreteslab with the finiteelement software ABAQUS using the damage-plasticity model is presented. The simulations of the reinforcedconcreteslab are compared to the behavior of a specimen that has been tested at the University of Waterloo. This study involves the investigation on the punchingshear behavior of reinforcedconcreteslab- columnconnections without shear reinforcement.
2000; Rankin and Long, 1997; Wood, 1961) for RC, SFRC and strengthened fibre-reinforced polymer (FRP) members (Zeng et al., 2016), sector models based on axisymmetric assumptions (Einpaul et al., 2015, 2016) and finite-element methods (Belletti et al., 2016; Soares and Vollum, 2015). Membrane action effects on continuous slabs have been recently analysed using nonlinearfinite-elementanalysis (NLFEA) and different modelling approaches, for example using three- dimensional (3D) hexahedral elements (Genikomsou and Polak, 2017) or multi-layered shell elements (Cantone et al., 2016). In this paper, the shrinkage effects on concrete cracking and on the punchingshear resistance are studied. This aspect could be significant for the structural assessment of existing structures carried out using refined numerical tools, such as NLFEA methods, which are able to take into account hidden resistance capacities, but are less conservative than analytical approaches (Belletti et al., 2015a, 2015b).
Seismic evaluation of an old nuclear facility indicated a potential vulnerability related to the behavior of unreinforced concretecolumn capitals which were designed and constructed prior to the adoption of adequate seismic design detailing provisions. Such column capitals are provided to improve the punchingshear capacity of the connection under gravity loads, but the lateral response due to seismic loading can lead to spalling of unreinforced capitals, resulting in a punchingshear failure of the slab. Due to the lack of adequate guidance in existing building codes to predict the capacity of such capitals under lateral load, nonlinearfiniteelementanalysis was used in this study to evaluate the seismic vulnerability of such connections. The cost of performing a full scale physical tests of the column capitals of interest subject to cyclic load was not feasible at the time this study was carried out.
The punchingshear strength results of 57 FRP reinforcedconcrete slabs were collected from published literature [1-5, 7, 12-17] to evaluate the current shear design guidelines, predicted models and calibrate the proposed equation in this study. All specimens were FRP-reinforcedconcreteslab–columnconnections without column capitals and drop panels. All the slabs were tested under concentric punching load and failed in punchingshear before reaching the design flexural capacity. Table 1 gives the distribution of the main shear design parameters in the database. They cover a relatively wide range of the material and geometric properties of FRP-reinforcedconcrete slabs. (The concrete cylinder compressive strength (fc), for the analyzed database ranges from 26 to 118 MPa, the young’s modulus of FRP bars (E fl ) ranges from 28 to 148 GPa, the ratio of flexure reinforcement (ρ fl ), ranges from 0.15%
36 deflection response from the experimental observation. In general, all five slab specimens that were modeled showed a very strong correlation between the finiteelement model and the experimental results (Figure 2-16). The ascending branch followed a very similar line as the experimental data and then, at the point of punchingshear, the FEA curve experienced a very sharp downward trend. The two experiments (N-GR-C slab and L-SH-C slab) shown in Figure 2-16 have concrete compressive strengths that varies from 34 MPa to 47 MPa and a flexural reinforcement ratio, ρ, which varies from 0.24% to 0.15%. In developing the tension-stiffening curve the author only describes selecting 0.4 for the weakening function (see Equation (2-18)), but neglected to disclose what effect of varying the weakening function would have on the load- deflection results. Even though the concrete strength and flexural reinforcement varied in the specimens, the weakening function remained constant. The constant value of the weakening function appears to suggest that it is independent of the value of 𝑓 𝑐 ′ and ρ. This assertion would be in contrast to the literature data which showed tension-stiffening increases with increases in 𝑓 𝑐 ′ and ρ.
The proposed design equation has been applied to predict the punchingshear capacity of 28 FRP-reinforcedconcrete slabs reported in the literature. The geometry of the tested slabs, the material properties, the analysis and the results are shown in Table 1. It can been seen that the slabs analyzed cover many variables that influence punchingshear behaviour, such as, size of loaded area, effective depth of slab, concrete strength, FRP reinforcement ratio and, very importantly, different types of FRP reinforcement with varied manufacturing processes, elastic modulus and ultimate tensile strength. For the proposed design model the predicted-to test punchingshear strength ratio is 0.934 with a standard deviation of 0.102. The latter is much less than 0.150, which is generally acceptable from a structural point of view. Thus, the design model appears to be equally reliable and consistent as the authors’ proposed theoretical analysis , and compares favourably to existing design models for FRP slabs [1, 5-6].
Organization of the present work is as following out- lined. Equilibrium, compatibility, and sectional con- stitutive relations of the Timoshenko frame model are first derived. Stiffness-based framework of the model formulation is presented next. The virtual displacement principle is at the core of the model formulation and the resulting model can be programmed with ease. To rem- edy the problematic shear locking phenomenon, linked displacement interpolation functions are employed, thus resulting in the locking-free Timoshenko frame element. Subsequently, the shear–flexure interaction procedure is discussed. The present study adopts and modifies the interaction procedure proposed by Mergos and Kap- pos (2008, 2012) within the framework of the so-called “UCSD Shear-Strength Model” proposed by Priestley et al. (1993). Finally, three correlation studies are con- ducted to examine the model accuracy and its ability to represent the rather complex responses of non-ductile RC columns. The first two correlation studies focus on flexure–shear critical columns while the third empha- sizes on a shear-dominated column. The finiteelement platform FEAP (Taylor 2000) is used to host the pro- posed frame element.
assess the behavior and phenomenon of typical failures like flexural, shear, torsion, buckling etc. of the Reinforcedconcrete structures. Typically, the behavior of reinforcedconcrete is studied by full-scale experimental investigations. With the invention of sophisticated numerical tools for analysis like the finiteelement method (FEM), it has become possible to model the complex behavior of reinforcedconcrete members using FiniteElement modeling. In the present paper models of reinforcedconcrete columns subjected to axial symmetric and eccentric loading are used. Nonlinearfiniteelementanalysis is used to analyze reinforcedconcrete columns up to failure with FEM software ANSYS. Reinforcedconcretecolumn subjected to the axial symmetric loading, are modeled considering the frequent use in the laboratory.
The NLFEA model is a 16 stories reinforcedconcrete tube in tube tall building with typical storey height of 3.50m except ground floor is 6.0m heights. The full tube model is symmetrical in both axes in plan. The internal tube 7.50m x 7.50m is surrounded by perimeter frame tube 22.50m x 22.50m. All perimeter columns were arrange closely spaced at 4.5m center to center with the size of 0.90m x 0.90m from ground floor up to level 10 and 0.75m x 0.75m column after level 10. The spandrel beams are dimensioned 250mm thick and 750mm depth and tied to the perimeter column to form a perimeter tube. The thickness for slab is 175mm and presumed to act as a horizontal diaphragm to transfer the lateral load as well as vertical loads. The internal tube is formed by square perforated shear wall with the thickness of 350mm and the coupling beam is kept similar as thickness of the shear wall with the depth of 1000mm. COSMOS/M 2.0 (64K Version) finiteelement software is used to generate the model and perform subsequent non linear static analysis. For modelling idealization and domain discretization viability, only a modified quarter of tube in tube tall building is modelled in view of symmetrical and to cater limitation of COSMOS/M. After several attempts of NLFEA Run were performed out, the final model as indicated in Figure 2(b) was adopted as a final result in this study.
punching of adjoining connections due to gravity load redistribution, dynamic effects and excessive slab deformation (Wood, 2001; Park, 2012; and King and Delatte, 2004). In many cases, failure also progressed vertically due to impact of falling slabs on lower lying ones. However, in some cases such as the partial collapse of the Pipers Row Car Park at Wolverhampton in 1997 (Figure 1.2.a), punchingshear failure at one column led to the punchingshear failure of eight adjacent columns (Wood, 2001) with no vertical propagation of failure. Punchingshear failure of a connection at the roof slab of a 16- story apartment building (Figure 1.2b) in Boston in 1971, led to the progressive collapse of all floor slabs below it (King & Delatte, 2004). Other cases of progressive collapse of flat slab structures include collapse of the 26 story Skyline Plaza apartment building in Virginia (1973), flat slab building in Bluche Switzerland (1981), 5 story Harbor Cay Condominium in Florida (1981), Gretzenbach under-ground parking garage in Switzerland (2004) and the 5 story Sampoong Departmental Store in Seoul (1995). Of the various cases of progressive collapse involving flat slab structures, Seoul’s Sampoong Departmental Store disaster is the most fatal. It resulted in 502 recorded deaths, 6 missing persons, 937 persons injured and damage to property worth KRW 100billion (Park, 2012). This shows that, though progressive collapse is a relatively rare event, its consequences could range from the multi-million loss worth of property, to very high casualty figures.
The aim of this research was to address a better analytical understanding of punching of ﬂat slabs with shear reinforce- ment. Thereby, the focus should be set on the analysis of the maximum increase in strength and rotation capacity due to punchingshear reinforcement. Therefore, the principal aim was the nonlinear ﬁnite elementanalysis of ﬂat slabs with large amounts of punchingshear reinforcement. Within this frame- work, several aspects should be investigated such as the load– deformation response of the slab, the failure mechanism, and the load contribution of the shear reinforcement. Based on this investigation, a simpliﬁed analytical model through Ansys 10 software is developed in order to enable the prediction of the punchingshear strength and the rotation at failure. Its results are compared with the previously investigated experimental
Nguyen-Minh(2011), They studied behavior and capacity of steel fiber reinforcedconcrete (SFRC) flat slabs of different dimensions. In addition, Amen Agbossou studied the experimental and theoretical behavior of slabs strengthened by FRP. The experimental results show that FRP significantly increases punching failure stress, resulting in a reduction of slab rotation around the loading column. The theoretical investigation presents a finiteelement model for the bending of strengthened slabs.
More high-rise buildings are being built during resent years. The ability to resist lateral force plays an important role in earthquake. Shear walls are widely used for their good performance in resisting lateral forces. As a new kind of shear wall structure, double skin steel-concrete composite shear walls have high capacity and good ductility compared to traditional shear walls and they can be used in high-rise buildings with good efficiency for energy dissipation and seismic performance.
In this study, we propose a model that estimates the shear strength of beam–columnconnections in RCS composite systems. After ﬁrst analyzing previously proposed shear strength equations including existing researches regarding connections of framing system (Kim and Choi 2006, 2015; LaFave and Kim 2011; Yang et al. 2007; Lim et al. 2016), we developed a shear strength equation for general con- nections in RCS composite systems, encompassing the effect of extended face bearing plates (E-FBP), transverse beams, and cover plates. Statistical analysis was conducted to verify the proposed equation. This analysis showed that our pro- posed equation accurately represented the shear strength in RCS composite system connections.
The shear capacity of deep beams is a major issue in their design. The behavior of reinforcedconcrete deep beams is dif- ferent from that of slender beams because of their relatively larger magnitude of shearing and normal stresses. Unlike slen- der beams, deep beams transfer shear forces to supports through compressive stresses rather than shear stresses. There are two kinds of cracks that typically develop in deep beams: ﬂexural cracks and diagonal cracks. Diagonal cracks eliminate the inclined principal tensile stresses required for beam action and lead to a redistribution of internal stresses so that the beam acts as a tied arch. The arch action is a func- tion of a/d (shear span/depth) and the concrete compressive strength, in addition to the properties of the longitudinal reinforcement. It is expected that the arch action in FRP rein- forced concrete would be as signiﬁcant as that in steel rein- forced concrete and that the shear strength of FRP- reinforcedconcrete beams having a/d less than 2.5 would be higher than that of beams having a/d of more than 2.5 . The application of the reinforcedconcrete deep beams within structural engineering practice has risen substantially over the last few decades. More specially, there has been an increased practice of including deep beams in the design of tall buildings, offshore structures, wall tanks and foundations. They differ from shallow beams in that they have a relatively larger depth compared to the span length. As a result the strain distribution across the depth is non-linear and cannot be described in terms of uni-axial stress strain characteristics . Prediction of behavior of deep beams by design codes which contain empirical equations derived from experimental tests has some limitations. They are only suitable for the tests con- ditions they were derived from, and most importantly, they fail to provide information on serviceability requirements such as structural deformations and cracking. Likewise, the strut and tie model, although based on equilibrium solutions thus pro- viding a safe design, does not take into account the non-linear material behavior and hence also fails to provide information on serviceability requirements. Cracking of concrete and yielding of steel are essential features of the behavior of
A series of the elements tested by Swamy and Ali  were selected to gain a better understanding of the predicted effect of the steel ﬁbre volume on the punchingshear strength of slab– columnconnections. The selected test elements had identical geometrical dimensions and ﬁbre type and the concrete compres- sive strength was similar for all batches. The failure criteria and the estimated load rotation relationships for the elements selected are presented in Fig. 9 a. As is shown in Fig. 9 b, the proposed model predicts well the increase of the punchingshear strength with the increase of the ﬁbre volume. Furthermore, an increase in the quantity of similar ﬁbres provides for an increase in the deforma- tional capacity. As the concrete contribution to the punching strength decreases with the increase of the slab rotation, the weight of the ﬁbre contribution becomes more relevant to the resistance mechanism. The predicted concrete and ﬁbres contribu- tions to the punchingshear strength for elements tested by Swamy and Ali (  are shown in Fig. 9 b, with an excellent correlation ob- served between the model predictions and the test results. 5. Code-like formulation
One quarter of the test slab and missile is modelled in more detail with FE code Abaqus, Abaqus, (2014) using eight-noded 3D solid elements for the slab and four-noded shell elements for the stainless steel missile. Reinforcement is modelled with beam elements. This model, shown in Figure 5a, contains over half a million degrees of freedom. Bending reinforcement and steel plates on slab edge are shown in green. Shear reinforcement is shown in red. Some solid elements (grey) representing concrete are removed from the plot.
punchingshear capacity increased by 27% when the concrete compressive strength rose from 38.6 to 75.8 MPa, when compared with that of the counterpart normal strength concrete flat slab. The specimen with the thickness of 350 mm increased the punchingshear capacity by about 7% compared with that of the counterpart normal strength concrete flat slab. The Hassan et al (2013b) concrete strength investigation showed a reduction effect of the concrete compressive strength on the punchingshear strength when slab depth increased. In the current research, the concrete compressive strength effect remained constant on the punchingshear strength when the slab depth increased from 150 mm to 250 mm. On the other hand, usually the application of concrete compressive strength in the equations of punchingshear strength is limited to a certain range in the most design of FRP codes and guides line, for example, CSA S806 (2012) which 60 MPa is the maximum concrete strength that must be used in calculating punchingshear strength. Concrete strength was one of the parameters included in Sayed (2015) research. The study revealed that increasing concrete compressive strength slightly enhanced the punchingshear capacity. It was also recorded that when the actual high concrete compressive strength value for one of the specimens used in the equation of the CSA S806 (2012) code yielded better results despite the limitation of 60 MPa by the code. Thus, further investigation for a wider range of HSC should be examined, with concentrated loading acting in the middle of the flat slab geometry to quantify effect HSC on punchingshear strength and verifying the accuracy with the current punchingshear prevision.