This paper presents the results of an extensive **experimental** campaign on 16 flat-slab specimens with and without **punching** **shear** reinforce- ment. The tests aimed to investigate the influence of a set of mechan- ical and geometrical parameters on the **punching** **shear** **strength** and **deformation** **capacity** 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 **punching** **shear** 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.

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The nine specimens tested by Hawkins et al. [8] 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.

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Specimen MB2 [18] was **reinforced** with No. 13 high **strength** bars like specimen MU2 [18] 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 **punching** **shear** **strength** 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

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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 **punching** **shear** **capacity** using **shear** heads. The proposed equation is based on calculation the **punching** **shear** **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 **punching** **shear** **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 flat **slabs** with square and rectangular columns respectively.

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This paper deals with the modeling of **punching** **shear** 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 **punching** **shear** **capacity**, 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 **punching** **shear** **capacity** is determined.

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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 **punching** **shear** **capacity** 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 **punching** **shear** **capacity**. 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 **punching** **shear** **capacity** of slab-column connections, so as to reduce the **experimental** work in the laboratory and onsite; also the cost of casting of specimens.

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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.

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Several studies have investigated the effects of openings on the **punching** **shear** **strength** of RC ﬂat **slabs**. The pioneering work of Moe [9] was the ﬁrst to propose a semi-empirical formula in order to estimate the **punching** **shear** **strength** 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. [10] experimentally examined the effects of openings with relatively large aspect ratios on the **punching** **shear** **capacity** of RC ﬂat **slabs**. Based on their results, they proposed a new method to estimate the effective critical perimeter. Borges et al. [11] 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.

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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 **shear** **capacity** 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 **punching** **shear**. Five parameters were chosen based on the literature review in the application of ANN to predict the **punching** **shear** **strength** 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).

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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 **punching** **shear** provisions in the latest edition of the Model Code (2010).

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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 **experimental** **investigation** 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.

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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 **punching** **shear** **capacity** under relatively high construction loads is one of the common reasons of failure of flat slab structures during construction. They also reported that **punching** **shear** 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.

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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 **punching** **shear** resistance of FRP-**reinforced** **slabs**. This paper provides the designer with a reliable and accu- rate design tool for estimating the **punching** **shear** **strength** of two way **slabs** **reinforced** 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 **punching** **capacity** as explained previously.

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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.

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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 **punching** **shear** reinforcement. Therefore, the principal aim was the nonlinear ﬁnite element analysis of ﬂat **slabs** with large amounts of **punching** **shear** 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 **punching** **shear** **strength** and the rotation at failure. Its results are compared with the previously investigated **experimental**

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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.

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Ospina et al. (2003) [3] 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**-**shear** **capacity** as the FRP bars owing to the difference in bond behaviour and concentration of stresses in the grids. Nguyen- Minh and Rovnak [5] 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. [7] reported that the reinforcement type significantly influenced the **punching** **strength** of **slabs** and the concrete **strength** significantly affeced the load carrying **capacity** and the post-**punching** **capacity** of **slabs**. However, it was found to be a little influence on the stiffness of the cracked **slabs**.

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