with flatslabs with no beams and no enlarged column heads .These slabs are subjected to punchingshear failure of slab-column connections. Load concentration around the column head generally leads to increased stresses which cannot be absorbed solely in thin slab thicknesses. The punchingshear strength is an extremely significant parameter for the design of flatslabs. Solution of architecture often imposes the necessity of openings near the columns .In this paper will examine the effect of openings in different positions and with different dimensions in the punchingshear strength. The calculations performed in the punchingshear application are based on the standard EN1992-1-1:2004.
Figure 12 shows both radial and tangential stresses ( σ rad and σ tang ) for the continuous flat slab with concrete shrinkage. The most interesting strain limits are marked as follows: cracking of concrete (corresponding to ε cr , see also Figure 12(a)); maximum crack opening with residual tensile strength (corres- ponding to w ctu , see Figure 12(a), calculated as w ctu = ε t,u a m , where a m is the distance between cracks; see Belletti et al. (2017)); and yielding strain of reinforcement ( ε sy ). It can be seen from Figures 12(b) –12(d), that the peak value of radial stresses σ rad corresponds to the achievement of the residual tensile strength of concrete (crack opening w ctu ) in the sagging area, which corresponds to the maximum ring effect for self- confined slabs. Depending on the intersection with the CSCT failure criterion, punchingshear failure occurs before yielding of hogging and sagging reinforcement for high reinforcement ratio ( ρ hogg = 1·5%), after yielding of hogging reinforcement for medium reinforcement ratio ( ρ hogg = 0·75%) and after yielding of hogging and sagging reinforcement for low reinforcement ratio ( ρ hogg = 0·375%). Even if not reported in the present study, it is important to observe that the sequence of events remains the same without considering shrinkage of concrete.
The above findings are specific for flat slab specimens in which connected by columns which have aspect ratio equal 1 and 2 and for shear head arrangement which have 4 legs. General findings could be established by conducting future experiments with different column aspect ratios and different arrangement of shear heads. The method of calculating the use of shear heads was reviewed according to the American code and found that the method gives conservative values. The research proposed a new equation for calculating the punchingshear capacity using shear heads. The proposed equation is based on calculation the punchingshear capacity at the two proposed critical perimeters and calculate the length of shear heads used. This equation differs from the equation of the American code in taking effect of changing column aspect ratio and the lack of punchingshear strength with increasing length of shear heads. The results of the proposed equation were compared with the results of the empirical study and the American code method. Results were close to the experimental results within the limits of 3% and 15% of the flatslabs with square and rectangular columns respectively.
Baskaran and Morley (2004) developed a new experimental method to test flatslabs with simple uniform loading with improved boundary conditions. A new form of punchingshear reinforcement which will increase the punchingshearresistance without affecting the flexural resistance is used. Available experimental methods to test flatslabs are revived to demonstrate the simplicity of the new approach. To show the effectiveness of the both the method and shear reinforcement, some experimental results are included. Ehab EI-Salakawy et.al., (2004) reported the test results of seven full scale reinforced concrete slab-column edge connections strengthened against punchingshear. In this study, three slabs contained openings in the vicinity of the column and the other four were without openings .The dimensions of the slabs were 1,540 x 1,020 x 120 mm with square columns (250 x 250 mm). The openings in the specimens were square (150x150 mm) with the sides parallel to the sides of column. The slabs were reinforced with an average reinforcement ratio of 0.75%, except for the two reference slabs. Two different strengthening techniques were considered. Based on the test results, it is concluded that the presence of FRP sheets and steel bolts substantially increase the punching capacity of the connection. Kumar et al. (2004) analyzed t h e reinforced concrete r e c t a ng u la r s l a b s for different boundary conditions with corner opening by yield line theory. The ratios of the corresponding lengths of the sides of the opening and the slab are kept the same and the size of opening up to half of the length of the slab is considered. The ratio of the span moments to support moments is kept equal to 0.75. The design
Nowadays, concrete with strength higher than 50 MPa is utilized due to the ever-increasing need for higher strength and prolonged healing properties. Reinforced concrete flatslabs are widely employed in structural systems. Flat slab formatting is very simple and no beam or column heading is used in it. However, a disturbing failure occurs at the junction of the slab- column in this system. The location of the slab-column connection is the most sensitive part of the flat slab due to the existence of high flexural anchor and shear force. Owing to the occurrence of the punchingshear failure, failure load may be considerably less than the flexural capacity of the slab. The use of high-strength concrete improves the punchingshear strength of the slab and causes the transfer of higher forces in the place of slab-
Rajiv M S, Guru Prasad T N, (2015)in their paper analyzed about work to compare the behavior of multi- storey buildings having flatslabs with drops to that of having two way slabs (conventional slab). The consequence of part shear walls on the performance of different types of buildings [(G+7) and (G+14)] under seismic forces are considered. Equivalent static force method, Response spectrum method and Time history analysis were considered for diverse types of models and relative results were drawn. The natural mode (time) period increases as the height of building increases, irrespective of type of building conventional slab (bare), flat slab (bare) and flat slab with shear wall. On the other hand, the time period is more for conventional slab and flat slab with bare frame compared with that of flat slab with shear wall for dissimilar models due to stiffness participation factor being less in bare frame for both storeys. This presents a summary of the project work, for conventional R.C.C building, flat slab building and flat slab building with shear wall at diverse locations for different types of building [(G+7) and (G+14)] in the seismic region. Rajini .A .T, Dr. Manjunath N Hegde (2016) in their paper analyzed about comparative study of the behaviour of flat slab and conventional slab structures of 20 stories in diverse cases. Conventional RC slab and flat slab structure, flat slab structure with column drop, conventional structure and flat slab structure with shear wall at diverse locations were analyzed by taking into consideration two typical zones of zone III and zone V, through dynamic response spectrum analysis by using ETABS software. Comparing the results of all models in condition of time period and frequency, lateral displacements, story shear and story drifts by plotting graphs.. Flat slab structure with arrangement of column drop and shear wall is performed extremely fine under seismic loads to decrease the displacements and drifts with enhancement in stiffness of building. This paper summerized a review of the study, for conventional R.C. Mitan Kathrotiya, Dr. Kaushal Parikh (2017) in paper summarizes, the revised study of the performance of multi-storey building having conventional RC frame structure, flatSlabs and to study the consequence of the models under the seismic forces. The model was subjected to various loading condition in special Seismic Zone and for diverse Soil condition. The seismic performance of the flat Slab and the conventional RC building was analyzed using different software aid. Due
ANNs can be used to determine a functional relationship between measured input and output data. Usually, the func- tional relationship is better than that obtained using regression methods. The number of the neurons in the input layer is equal to the number of the independent variables in the experiment. The number of the hidden layers and the number of the neu- rons in each layer are chosen to provide a minimum value for the error between the measured output and the network’s output while maintaining the ability of the network to general- ize. In this work, Neural Network Fitting Tool with one input layer was used (it contains six independent variables that may affect the punching load), one hidden layer had 11 neurons, and one output layer was designed to predict the punching load. The TRAINLM training function available in MATLAB Neural Toolbox  was used to train the network using the LERNGDM adaption learning function. The input data were divided into three sets. The ﬁrst set consisting of 70% of the data was used to train the network. The second and third sets, each consisting of 15% of the data, was used to validate and test the generalization ability of the network, respectively. The sets are taken randomly out of the data set. Each hidden layer has a bias neuron as shown in Fig. 2. Several architec- tures were tried and the one that gave the least error was cho- sen. Adding more neurons increases the training time, limits the ability of the network to generalize and does not improve the results. All the parameters that may affect the punching load were considered in the input layer. These parameters are: column size (C x and C y ), slab depth (d), concrete’s
Punchingshear capacity is an important factor for governing the collapsed form of slabs. In the link of slab - column, high shear stresses are the main reason for punchingshear failure. The failure mode of punching is fragile in nature and diagonal cracks chase the surface of a truncated cone around the column. The failure that occurs at the connection between the slab and the column, called punchingshear failure has been of concern for the designers and engineers [1, 2]. The most common practice in evaluating the punching strength of the concrete slabs is to use the empirical expressions available in different building design codes for calculating punching loads. The empirical expressio ns given in design codes are based on experimental results on specimens of a column and a portion of the slab .
Normal weight ready-mix concrete of nominal strength C35 (35 MPa) was used. The specification for the concrete was: nominal maximum aggregate size 20 mm; slump 50 mm. Cubes, cylinders and prisms of concrete were taken for control purposes. The four slabs were cast at the same time in specially prepared wooden forms, from the same batch of concrete to eliminate variations in concrete quality. Concrete was compacted by poker-vibrators. After casting, the slabs were cured for one week. For control purposes, sets of four cubes, split cylinders and prismatic specimens were cast along side each of the slabs. The results from control specimens tested on the same day as the slabs are summarized in table 3.
In this paper a finite element (FE) analysis is used to investigate the flat slab response and to show how the slab’s behavior will change while are strengthened using different methods. The comparison between the results of the analytical model and the experimentally obtained results enables the validation of the performance of the proposed FE model. The FE model are verified and evaluated by experimental results of the study conducted by Meisami et al. . The control slab is a 1200*1200 mm 2 square slab with 105 mm thick and simply supported on the edges and loaded by a hydraulic jack through a 150*150*30 mm steel plate in the center of slab. Fig. 1 describes the dimensions and reinforcement arrangement of original and 3D model of control slab. The proposed model delivered valuable outputs concerning the behavior of the flat slab such as load and the deflection of the slab. Good agreement is noticed between the results of FE model and experimentally results obtained by Meisami et al. .
Abstract. An innovative solution to the corrosion problem is the use of fiber-reinforced polymer (FRP) as an alternative reinforcing material in concrete structures. In addition to the non corrodible nature of FRP materials, they also have a high strength-to-weight ratio that makes them attractive as reinforcement for concrete structures. Extensive research programs have been carried out to investigate the flexural behavior of concrete members reinforced with FRP reinforcement. On the other hand, the shear behavior of concrete members, especially punchingshear of two-way slabs, reinforced with FRP bars has not yet been fully explored. The existing provisions for punching of slabs in most international design standards for reinforced concrete are based on tests of steel reinforced slabs. The elastic stiffness and bonding characteristics of FRP reinforcement are sufficiently different from those of steel to affect punching strength. In the present study, the equations of existing design standards for shear capacity of FRP reinforced concrete beams have been evaluated using the large database collected. The experimental punchingshear strengths were compared with the available theoretical predictions, including the CSA S806 (CSA 2012), ACI-440.1R-15 (ACI 2015), BS 8110 (BSI 1997), JSCE (1997) a number of models proposed by some researchers in the literature. The existing design methods for FRP reinforced concrete slabs give conservative predictions for the specimens in the database. This paper also presents a simple yet improved model to calculate the punchingshear capacity of FRP- reinforced concrete slabs. The proposed model provides the accurate results in calculating the punchingshear strengths of FRP-reinforced concrete slender slabs.
Abdullah et al.  tested four slabs measuring 1800 1800 150 mm together with a reference specimen used for comparisons. One of the specimens was strengthened with non- prestressed CFRP laminates, whereas the other three had prestressed laminates. It was shown that the load capacity of the non-prestressed specimen increased considerably up to 43%. The three specimens with prestressed laminates failed due to debond- ing and will not be considered in this investigation. Suter and More- illon  tested four FRP strengthened slab specimens, along with a control specimen, measuring 2400 2400 200 mm. The aim of this series was to investigate on the serviceability behaviour and increase of strength resulting from different strengthening materi- als, such as FRP’s (carbon, glass and aramid) laminates or tissues. According to the authors , the results showed that the increase on strength is dependent on the strengthening type and layout, reaching a maximum of approximately 20%. Wang and Tan  tested four slab specimens, from which one was a reference slab. The specimens measured 1750 1750 120 mm. The adopted strengthening consisted of glued CFRP tissues. It was found that the strengthening slabs presented almost no improvement in the load capacity, but a stiffer behaviour was recorded. It can be noted that, in some cases, the failure of the slabs was accompanied by deb- onding of the FRP’s. These debonding phenomena are probably related to the relative vertical displacement associated to the coni- cal failure surface during the punching failure process (Fig. 3).
A nonlinear pushover analysis is conducted in this study by using FEM for RC1 and SR3 in order to compare and examine the tensile strain rates and stress distribution according to the plas- tic redistribution of the main reinforcement (See Figure 17). For the analysis program, we used ATENA 2 and assumed that the structural equation of concrete was stiffened orthotropic. As for Material modeling, compressive stress-strain relationship of con- crete complies with the CEB-FIP model before reaching maxi- mum compressive stress and linear decrease equation was applied characteristics of softening after maximum compressive stress. Elasticity theory complied with tensile stress-strain relationship before cracking. The smeared crack model also was applied for crack. Model proposed by Hordijk complied with biaxial stress failure mode and model proposed by Rankine et al. complied with failure criteria of concrete. In addition, it is assumed that the rein- forcement is fully attached to the concrete and that it only has axial stiffness in uniaxial strain as a two-joint point truss element included within the concrete. The comparison between load and displacement on slabs (Figures 11 (a) and (d)) proves that the anal- Fig. 10 Loading protocol with displacement control.
reinforced concrete slabs supported on columns with L, T, and cruciform shapes. Reference studies verifying the accuracy of these code provisions are typically not provided. Empirical data of punching failures of slabs supported on columns with L, T, and cruciform shapes are limited due to the cost and time required to test specimens with slab thicknesses and column sizes commonly used in practice. In this paper, the punchingshear behaviour of five interior L-shaped slab-column connections, one without a slab opening and four with slab openings, subjected to static concentric loading are analyzed using a plasticity-based nonlinear finite element model (FEM) in ABAQUS. The FEM is similar to models previously calibrated at the University of Waterloo and was calibrated considering nine slabs that were tested to study the impact of column rectangularity on the punchingshear behaviour of reinforced concrete slabs. The finite element analysis results indicate that shear stresses primarily concentrate around the ends of the L, and that current code predictions from ACI 318-19 and Eurocode 2 may be unconservative due to the assumed critical perimeters around L-shaped columns.
In the 1990ies, a new system was invented by Jorgen Breuing, eliminating the above problems, the so called BubbleDeck technology. The Bubble Deck technology uses spheres made of recycled industrial plastic to create air voids while providing strength through arch action. As a result, this allows the hollow slab to act as a normal monolithic two-way spanning concrete slab. These bubbles can decrease the dead weight up to 35% and can increase the capacity by almost 100% with the same thickness. As a result, bubble deck slabs can be lighter, stronger, and thinner than regular reinforced concrete slabs (3).
Punching in slabs is usually associated to the application of concentrated loads or to the presence of columns. One of the main concerns related to flatslabs is its punchingshear capacity at slab column connection. Provided that bending capacity is installed, punchingshear failure is hence characterized by the development of a truncated cone shaped surface at the slab-column connection. Frequently, there is the need to strengthen existing flatslabs against punchingshear failure. One of the strengthening practices, which have been tested within current experimental programmer, consists on gluing carbon fibre reinforced polymers on concrete surface. Moreover, we want to know the behaviour of RC flat slab under FRP material against punchingshear. The effect of FRP bars against punchingshear is checked.The objective of the current study was to explain the feasibility of RC flat slab to examine the application of steel rods, FRP rebar on the improving of punchingshear. Extensive applications of the fiber-reinforced polymer (FRP) as new construction materials have been recently accomplished. FRP materials are lightweight, high strength, and no-corrosive materials. By virtue of these advantages, there is a wide range of recent, current, and potential applications of these materials that covers both new and existing structures. Among different types of FRP materials, a fiber-reinforced polymer (FRP) is used extensively in the structural engineering field. This study was carried out to examine the viability of using FRP bars for the punchingshear strengthening of slab.
Structural failures of highway bridge structures are not common under static loading. However, in highway bridges, beam and slab failure usually occur in two common forms, direct flexural and/or punchingshear. The direct flexural failure typically occurs in beam or slab members and is associated with overall bending. This type of failure arises from the formation of diagonal tension cracks in the region of maximum bending moment and extends across the entire width of the member. However, punchingshear failure is a more localised effect associated with thin slabs or two-way slab-column members when subjected to a highly concentrated load. Punchingshear failure occurs when the principal stress across the critical surface of the section exceeds the tensile strength of the concrete due to applied loading and failure occurs with limited warning. An example of this type of complete failure is seen in Figure 1. Failure occurs with the potential diagonal crack following the surface of a truncated cone around the load. The failure surface extends from the bottom of the member diagonally upward to the top surface. For a normal concrete slab, the angle of inclination of the failure surface ranges approximately from 20 to 45 degrees depending on the amount of shear reinforcement . However, very little information on this parameter is available for UHPFRC.
labelled simple is obtained by calculating the cracking point and the point where steel begins to yield and assuming that this happens before concrete compressive strength is reached at the top of cross section. In finite element analyses an average simplified relationship (FE) is used. It is used also in deriving the force displacement relation for spring 1 of TDOF model.
Genikomsou and Polak  presented a finite element model for the slab specimen SB1 with the damaged plasticity model parameters of: dilation angle of 38 o , shape factor of 0.67, stress ratio of 1.16, and eccentricity of 0.1. A stress vs crack opening displacement approach was used to simulate the tensile response of the concrete. The fracture energy was calculated as 0.9 N/mm according to the CEB-FIB Model Code 1990 . This model only specified tensile damage parameters. A static analysis approach was used in ABAQUS/Standard with a viscosity, μ taken as 0.000085 and then compared to a quasi-static analysis with the dynamic procedure of ABAQUS/Explicit at a very slow rate of velocity. As shown in Figure 2-18, both analysis procedures compare well with the experimental results. The quasi-static analysis shows a noticeable downward trend which was interpreted by the authors as the point of punchingshear failure. The static analysis does not show this same downward trend and thus it is not clear how the authors determined that punchingshear had occurred and why the curve was cut-off at a deflection of 15 mm. The authors conducted a parametric study on the sensitivity of the viscosity parameter. Figure 2-19 shows the influence of the viscosity parameter on the load-deflection response. The graph shows that the higher the viscosity parameter the stiffer the load-deflection response. The authors also used the FEA model to show the influence that the flexural