This paper presents the results of an extensive experimental campaign on 16 flat-slab specimens with and without punchingshear reinforce- ment. The tests aimed to investigate the influence of a set of mechan- ical and geometrical parameters on the punchingshearstrength and deformationcapacity of flat slabs supported by interior columns. All specimens had the same plan dimensions of 3.0 x 3.0 m (9.84 x 9.84 ft). The investigated parameters were the column size (ranging between 130 and 520 mm [approximately 5 and 20 in.]), the slab thickness (ranging between 250 and 400 mm [approximately 10 and 16 in.]), the shear reinforcement system (studs and stirrups), and the amount of punchingshear reinforcement. Systematic measurements (such as the load, the rotations of the slab, the vertical displace- ments, the change in slab thickness, concrete strains, and strains in the shear reinforcement) allow for an understanding of the behavior of the slab specimens, the activation of the shear reinforcement, and the strains developed in the shear-critical region at failure. Finally, the test results were investigated and compared with reference to design codes (ACI 318-08 and EC2) and the mechanical model of the critical shear crack theory (CSCT), obtaining a number of conclu- sions on their suitability.
The nine specimens tested by Hawkins et al.  are summarized in Tab. 1. All slabs were 2133.6 mm square in plan, 152.4 mm thick, and supported on rectangular columns located at the slab center. The investigated parameters included the column aspect ratio, β, concrete compressive strength, the loading pattern and the flexural reinforcement. The column length was 1041.4 mm for all nine specimens, and the column aspect ratio varied between 1 and 4.33. For slabs 1 through 6, eight equal concentrated loads were applied to the slab edges parallel to the short side of the column, except for slab 6, where the loads were applied on the slab edges parallel to the long side of the column. The eight equal concentrated loads are labelled as P in Fig. 3. For slabs 7-9, four additional concentrated loads were applied to the slab edges parallel to the long side of the column. The magnitude of each of these additional loads was 65% of the loads on the other slab edges, as shown in Fig. 3. The flexural reinforcement also varied between the slabs. One flexural reinforcement layout was used for slabs 1-4 and 6, and modified layouts were used for all remaining slabs. The parameters investigated included the flexural reinforcement ratio, effective depth, spac- ing and adding additional reinforcement in the vicinity of the column. For all slabs, the top reinforcement layer was placed in the direction of the P loads. A summary of the experimental setup is shown in Fig. 3a, and the modified slab dimensions used in the L-shaped column study are shown in Fig. 3b. The reasoning behind these modifications is discussed at the end of this section. The reinforcement layout for slab 1 was used in the L-shaped column study.
Specimen MB2  was reinforced with No. 13 high strength bars like specimen MU2  except that the reinforcing bars were banded together near the column. The reinforcement ratio in the band was 1.36% which is similar to MU1 (ρ=1.18%). It had been shown previously that slabs with a banded distribution of reinforcement have a higher punchingshearstrength than companion slabs with uniform reinforcing. The experimental results though show the opposite; the capacity of MU2 was higher than MB2. The authors contributed this irregularity to bond failure of the bars whereby the combined effect of closely spaced bars and the high strength over-stressed the concrete surrounding the bars and the bars subsequently de-bonded from the concrete. The authors proposed that this failure could be remedied with longer development lengths of the bars. The steel bar to concrete bond interaction is beyond the scope of this FEA model. Rather, this model assumes that the bars are properly detailed for development and assigns a ‘perfect’ bond between the two elements. Therefore, the results of this model show the load-deflection results that Yang et al. would have experienced if their slab did not fail
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 punchingshearcapacity using shear heads. The proposed equation is based on calculation the punchingshearcapacity 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 punchingshearstrength 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 flat slabs with square and rectangular columns respectively.
This paper deals with the modeling of punchingshear failure in reinforced concrete slabs using nonlinear finite element analysis. The 3D finite element analyses (FEA) were performed with the appropriate modeling of element size and mesh, and the constitutive modeling of concrete. The FE numerical models are validated by comparing with the experimental results obtained from tested specimens and previous research. One slab served as a control without any modification while three slabs were strengthened. The ultimate behavior of FRP strengthened RC flat slabs under a centrally applied load. Each method of repair or strengthening is reviewed with emphasis on its performance with respect to the application details. The punchingshearcapacity, stiffness, ductility were investigated. In addition, the analytical results were compared with the predictions using the provision of ACI 318-08. The results showed that for control slab and strengthened specimens an increase varied from 4% to 105% in punchingshearcapacity is determined.
Conventional modeling techniques are based on empirical relationships developed from the experiment a l data. Within last few year, researchers have explored the capabilities of artificial intelligence techniques such as ANN [20–25], Support Vector Machines (SVM), Fuzzy Logic, M5 model tree, GRNN, ANFIS [25–33] for various problems in the field of civil engineering. A need to derive a simpler method to compete with the simplicit y of empirical formula can be use of data mining techniques. The use of data mining technique can very well reduce the formulations and calculations required with best model to estimate the punchingshearcapacity of the slab-column connections, with optimu m parameters. The modelling techniques are used where failure of classical and empirical equations occurs to predict the punchingshearcapacity. The modelling techniques, if properly optimised with various parameters, can estimate the strength very close to actual strengths and thus, can be used for the simulation of results, instead of time consuming experiment a l processes or may be finite element simulations. Most of the studies are focussing only on Artificial Neural Network (ANN), with few studies on use of Adaptive Neuro-fuzzy Inference System (ANFIS), and Generalize d Neural Network (GRNN) and their comparison here forth. The objective of the paper is to examine the capability of ANN, GRNN, and ANFIS for estimating punchingshearcapacity of slab-column connections, so as to reduce the experimental work in the laboratory and onsite; also the cost of casting of specimens.
ABSTRACT: Steel-Concrete-Steel (SCS) sandwich structures are composed of two steel face plates and one concrete core. SCS as slab has more advantages than reinforced concrete (RC) slab that their most important are impermeability and higher resistance against impact loads. SCS sandwich slabs are widely employed in civil engineering and onshore and offshore structures due to their better performance and advantages. Mechanical connectors are used for better performance of the slabs. In the present research, stud bolt connectors are used together with nuts. The core is composed of ordinary concrete. Nine test samples of SCS slabs are made with stud bolt connectors and are put under concentrated load at the center of the slab. The observed failure modes included concrete core crack, lower plate slip and upper plate buckling, and stud bolt separation. To study load vs. displacement at the center and load vs. interlayer slip behavior, stud bolts diameter and concrete thickness were varied. The results of the tests were compared with the results of sandwich slabs with J-hook connectors and a better behavior was observed. One theoretical model was used to predict the bending strength of the slabs. The results of the theoretical model were consistent with test results.
Several studies have investigated the effects of openings on the punchingshearstrength of RC ﬂat slabs. The pioneering work of Moe  was the ﬁrst to propose a semi-empirical formula in order to estimate the punchingshearstrength of RC slabs and footings, which is proportional to the square root of the concrete compressive strength and critical section perimeter around the slab-column connection. The reduction of the critical section perimeter due to the existence of openings near columns was ﬁrst considered in the work by American Concrete Institute-American Society of Civil Engineers (ACI-ASCE) Committee 326. This publication suggested that the critical section perimeter is reduced by projecting lines from the center of the column to openings and by deducting the perimeter between the lines from the original critical section perimeter. This approach was later conﬁrmed to be conservative in a publication by ACI-ASCE Committee 426. More recently, Teng et al.  experimentally examined the effects of openings with relatively large aspect ratios on the punchingshearcapacity of RC ﬂat slabs. Based on their results, they proposed a new method to estimate the effective critical perimeter. Borges et al.  compared various methods to determine the effective critical section perimeter of RC ﬂat-plate slabs with openings and concluded that straight projection of the widths of openings onto the critical section perimeter predicts strength more consistently than any of the forms of radial projection. However, the above mentioned studies are done in laboratory, and it appears that there are few numerical models in this field.
problem studied is one of the vital points to ensure the success of this method. On the other hand, the number of parameters must be large enough to represent the system properly since the number of input parameter should also be chosen according to the number of training data. However, it is not recommended to train ANN with a large number of input neurons since it may reduce the efficiency and accuracy of the training process (Perera et al. 2010). In this case, the choice of the input parameters is guided based on the shearcapacity equations of the different design proposals (3.3.3) as summarised previously. Moreover, a parametric study was applied by using ANN to study the most effective parameter affecting the punchingshear. Five parameters were chosen based on the literature review in the application of ANN to predict the punchingshearstrength of two-way flat slabs. These were column perimeter (𝑏), Young’s Modulus for the reinforcement (𝐸), compressive strength of the concrete (𝑓 𝑐 ), reinforcement ratio (𝜌 𝑓 ) and slab effective depth (𝑑).
Firstly, the fresh and mechanical properties of the four developed SCC mixtures were determined. The fresh properties were tested during the casting process by performing slump flow, V-Funnel, and L-Box test. Then, after 28 days, and in the day of testing the slab, the mechanical properties were determined by performing the compressive strength, and the flexure strength tests. Secondly, the slabs were tested in the structural lab by applying concentric load and recording the test data using data acquisition system. Then, the recorded data was processed and analysed in terms of deflection, strain in the reinforcement and concrete, crack development, and ultimate capacity. Finally, the experimental data was compared with current design codes and the Critical Shear Crack Theory (CSCT) which was proposed by Muttoni (2008) and subsequently formed the basis for punchingshear provisions in the latest edition of the Model Code (2010).
Punchingshear failure of flat concrete slabs is a complex phenomenon with brittle failure mode, meaning sudden structural failure and rapid decrease of load carrying capacity. Due to these reasons, the application of appropriate punchingshear reinforcement in the slabs could be essential. To obtain the required structural strength and performance in slab-column junctions, the effect of the shear reinforcement type on the punching resistance must be known. For this purpose, numerous nonlinear finite element simulations were carried out to determine the behavior and punchingshearstrength of flat concrete slabs with different punchingshear reinforcement types. The effi- ciency of different reinforcement types was also determined and compared. Accuracy of the numerical simulations was verified by experimental results. Based on the comparison of numerical results, the partial factor for the design formula used in Eurocode 2 was calculated and was found to be higher than the actual one.
engineering that the actual load carrying capacity of restrained RC slabs is much higher than that calculated using yield line analysis. This load enhancement is attributed to a phenomenon called ‘compressive membrane action’ (CMA). There have been many researches in the past which include both experimental and analytical studies on how percentage of reinforcement, support conditions, shape of slab, aspect ratio of slab, coefficient of orthotrophy of reinforcement, grade of concrete, type of load affect the load enhancement due to CMA. This paper investigates experimentally the effect of ‘steel fiber reinforced high strength sel-compacting concrete’ (SFHSSCC) in the deformation behavior of two way rectangular slabs with three edges fixed and one long edge free under simulated uniform loading. SFHSSCC is considered to be a very important material in the field of structural engineering in recent decades. High toughness, high ductility, high residual strengths after first crack and improved workability are the main advantages of using SFHSSCC. In the present study a total of eight slabs (1mx1.5m) 75mm thick were cast and tested under simulated uniform loading using sixteen-point load disperser. Four slabs were of high strength traditionally vibrated concrete (SFHSTVC) and other four were of high strength self-compacting concrete. All four slabs in each group had fixed conventional reinforcement along with steel fiber reinforcement of 0.25%, 0.5%, 0.75% and 1% respectively for first to fourth slabs. The experimentalinvestigation included determining central deflections and crack width at different stages of loading, ultimate load carrying capacity, partial safety factors and comparing them with theoretical results and Indian codal provisions. It is concluded that SFHSSCC slabs behaved almost similar to SFHSTVC slabs and load enhancement due to CMA increased with increase in fiber percentage.
Premature loading of reinforced concrete flat slabs during construction generally occurs because of the efforts to meet project time targets (Ding et al., 2009). Hongyan, 2015, reported that the loads applied on the partially completed structure due to the construction process could be larger than the design service load. This construction load may exceed the design loads, which in turn, led to early failure of slabs . Wood (2003) reported that the available strength of the immature partially completed structure is dependent upon the concrete strength in those members, which may be less than the specified strength, and the failure would occur if the available strength were less than that required to support the construction loads. Premature failure of such slabs is generally associated with a concentration of high shear forces and bending moments at the column peripheries (Rizk et al., 2011). This type of failure is catastrophic because there are no external visible signs prior to the occurrence of the failure (ACI SP-232, 2005). When a slab is loaded prematurely, its serviceability is compromised (RILEM Committee 42-CEA, 1981). Therefore, it is necessary to investigate the effect of premature loading on reinforced concrete slabs to avoid cracking and possible failure (Hongyan, 2015). Hawkins et al., 1974; Gardner, 1990; Abdel Hafez, 2005; Wood, 2003; Sagaseta et al., 2014; Rankin and Long, 2019, reported that insufficient early-age punchingshearcapacity under relatively high construction loads is one of the common reasons of failure of flat slab structures during construction. They also reported that punchingshear failure is caused by the failure of concrete in tension. Figure 1 shows real case studies for the collapse of a factory building (Vetogate, 2014) and a residential building (Elshorouk City Website, 2019) in Egypt as a result of premature loading of reinforced concrete flat slab. Sudden punching failure took place during the concrete casting process of second floor. The consultant reported that the low strength of concrete at the time of early removal of the first-floor formwork was the main reason for the building collapse.
Shear mechanisms generally govern the behaviour of reinforced concrete structures subjected to localised impact loads. Existing experimental results investigating punchingshear in ﬂat slabs subjected to impact loading shows that when increasing the loading rate, the punchingshearstrength also in- creases whereas the deformationcapacity reduces. This behaviour is due to a combination of inertial effects and material strain-rate effects which leads to a stiffer behaviour of the slab for higher loading rates. This can also lead to a change of mode of failure from ﬂexural to pure punchingshear with increasing loading rates. Current empirical formulae for punchingshear are unable to predict this behaviour since the slab deformations are not considered for calculating the punchingshearstrength.
4. The collected test results show that most of the existing for- mulas gave inaccurate results with a large scatter in com- parison with the testing results, and thus, a new formula or technique should be proposed for more accurate estima- tion of punchingshear resistance of FRP-reinforcedslabs. This paper provides the designer with a reliable and accu- rate design tool for estimating the punchingshearstrength of two way slabsreinforced with FRP bars or grids. Two approaches are presented; the ﬁrst is the proposed equation and the second is the Neural Networks Technique. Each of them contains two new parameters, never used before; the effects of the elastic stiffness of the FRP reinforcement and the continuity effect of slabs on punchingcapacity as explained previously.
The results of this study indicate that additional deformations other than those induced by pure flexure could be significant particularly in FRP RC beams and slabs with moderate to high reinforced ratio. However, it seems that most of the existing simplified methods to predict deflections of FRP RC elements do not adequately take into account these additional deformations. This usually leads to un-conservative predictions especially at higher load levels. It should be mentioned that additional deformations may not always be significant at the serviceability load. Nevertheless, it is still important to predict deformation of FRP RC elements over the entire loading range with good accuracy. This requires developing more fundamental methods to evaluate shear and bond-slip induced deflections [24, 25]. Further analytical investigations will be published by the authors in a separate, forthcoming paper.
Punchingshearcapacity of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) slabs has been the subject of a number of studies. There is, however, only limited information available on this parameter of UHPFRC without conventional reinforcement. This is due to the complexity of punchingshear behaviour within concrete and is also limited by the lack of suitable test methods currently available. Therefore, in this study, attempts to design a novel testing method to measure the punchingshearcapacity of the concrete was carried out. The designed test arrangement was employed to carry out an extensive experimental study on UHPFRC slabs subjected to punchingshear failure. From the results obtained, the relationship between the punchingshear load and the angle of the shear plane, the critical value of the basic control perimeter and failure mode were studied. The experimental study undertaken here provides significant insight into the punchingshearcapacity of UHPFRC slabs. The results illustrate and highlight many of the advantages of using UHPFRC compared to normal concrete in structural designs. The novel punchingshear test presented here has established itself as a suitable procedure for testing UHPFRC and potentially, other fibre reinforced composites.
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 element analysis 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 punchingshearstrength and the rotation at failure. Its results are compared with the previously investigated experimental
They used different CFRP systems to increase the flexural capacity of two way simply supported slabs , (strips of laminate plates with Cold cured adhesive bonding, prestressing strips of laminate plates, wet lay-up ply of Fiber laminate sheets, near surface mounted strips of laminate bars (NSM) ). They found that CFRP increased the flexural strength between 63% to 145% and remarkably reduced the deflections and crack widths, especially the prestressing CFRP system. Two modes of failure were observed. Delamination occurred in the cases CFRP with cold cured adhesive and prestressing CFRP while rupture of the CFRP reinforcement was observed in the other cases of the CFRP system.
Ospina et al. (2003)  reported that the behavior of an FRP-RC slab-column connection is affected by the elastic stiffness of the reinforcing material as well as the quality of its bond characteristics with the concrete. However, the FRP grids may not provide the same punching-shearcapacity as the FRP bars owing to the difference in bond behaviour and concentration of stresses in the grids. Nguyen- Minh and Rovnak  concluded that both the size factor and the effect of the span-to-effective-depth ratio (L=d) should be taken into account in computing the punching-shear resistance of the FRP-RC slab-column connections. Zhang et al.  reported that the reinforcement type significantly influenced the punchingstrength of slabs and the concrete strength significantly affeced the load carrying capacity and the post-punchingcapacity of slabs. However, it was found to be a little influence on the stiffness of the cracked slabs.