Flatplates are favor structure systems usually used in parking garages and high-rise buildings due to its simplicity for construction. However, flatplates have some inherent structural problems, due to high shear stress surrounding the supporting columns which cause a catastrophic brittle type of failure called "PunchingShear Failure". Several solutions are used to avoid punchingshear failure, including the use of drop panels or punchingshearreinforcement. The latter is being a more sophisticated solution from the structural ductility, the architectural and the economical point of view. This study aims at investigating the effect of stirrups as shearreinforcement in enhancing the punchingstrength of interior slab-column connections. A total of four full-scale interior slab- column connections were tested up to failure. All slabs had a side length of 1700 mm and 160 mm thickness with 200 mm x 200 mm square column. The test parameters were the presence of shearreinforcement and stirrups concentration around the supporting column. The test results showed that the distribution of stirrups over the critical punchingshear zone was an efficient solution to enhance not only the punchingshear capacity but also the ductility of the connection. Furthermore, the concentrating of stirrupsshearreinforcement in the vicinity of the column for the tested slabs increases the punchingshear capacity by 13 % compared to the uniform distribution at same amount of shearreinforcement.
Columns had 8 bars 14 at each corner and middle point of the four faces and were transversally reinforced with Ø8 stirrups posed at 100mm. All connections were uniformly supported on rubber bearings along the four sides at an average distance of 30 mm from the edges. This study presents a failure analysis upon four shearreinforcedflat slab column connections with thin plates. tension reinforcement ratio was 0.5%. Five perimeters of shearreinforcement, 10@100mm, under star direction were fitted in the critical perimeter. Average effective depth of the slab was 155 mm and designed concrete strength was C20/25. The results showed that the concrete uniaxial compressive strength does not influence the final failure values. Load- deflection behavior was mainly influenced by the type of shearreinforcement than the concrete strength. Bond conditions and anchorage length highly influence the effectiveness of double headed stud-rails reinforcement. Specimens reinforced with stirrup beams showed rotations 50% smaller that the compared ones, stud-rails showing better ductility behavior.
become ܨ ൌ 1.17 MN and ܨ ௦ ൌ 1.01 MN, respectively, and the shear capacity of the plate is 1.58 MN. The averaged force ܨ in case X4 is 1.63 MN. In previous tests X1 and X2 the cubic compression strength values of concrete were 41.6 MPa and 46 MPa, respectively. The reinforcement in slab X1 was similar to the reinforcement used in slabs X3 and X4. The shearreinforcement was reduced for test X2 and the shear capacity due to stirrups is 0.24 MN. Punching capacities predicted by formula (1) for tests X1, X2, X3 and X4 are compiled in Table 1. These results are in agreement with the experimental observations. Except case X4 the shearpunchingstrength of the slab has not yet been exceeded. According to these calculations, scabbing capacity was exceeded in tests X3 and X4. The observed scabbing area was about 0.7 m 2 after the test X3. No scabbing was observed in test slabs X1 and X2 and this is also in agreement with the calculation results shown in Table 1. Only in the case X4 the average value of time dependent force resultant exceeds the total punching capacity of the wall.
Abstract Punchingshearreinforcement systems such as studs and stirrups are used to improve the punchingshearstrength of ﬂat slabs. A three dimensional ﬁnite element model (FEM) is developed through Ansys 10 computer software, to carry out the nonlinear analysis of 16 ﬂat-slab models with and without punchingshearreinforcement. Several important parameters are incorporated in the analysis, namely the column size, the slab thickness and the punchingshearreinforcement system in order to study their effects on the ﬂat slab behavior. A parametric study was carried out to look at the variables that can mainly affect the mechanical behaviors of the model such as the change of loading types and positions and slab with openings. Good correlation is observed between the results of the proposed model and other experimental one, resulting in its capability of capturing the fracture of ﬂat slab under punchingshear behavior to an acceptable accuracy.
strength of concrete slabs: 1- increasing the slab thickness in the vicinity of the column by providing a drop panel or a column head; 2- Providing shearreinforcement. Sometimes, after the construction of some building, the increase of punchingshear resistance for reinforced concrete slab-column connection may be needed. The strengthening of slab-column connection against punchingshear resistance by using traditional methods (steel plates, steel stirrups, steel studs, or increasing concrete dimensions) was studied [3-5]. Few studies concerned with using the FRP strengthening systems for flat slabs . The present study aims to evaluate the using of FRP materials to increase the punchingshear resistance of concrete slab-column. The values of punchingshearstrength were predicted taking into account the contribution of the applied strengthening systems. The calculated values were compared with the corresponding experimental results in order to evaluate the used equations.
the finite element method had been carried out in order to investigate the effect of this additional reinforcement for both normal strength and high strength concrete. The computer program ANSYS-V12.0 has been utilized in the finite element analysis. The obtained results indicate that, the proposed shearreinforcement system has a positive effect in the enhancement of both the punchingshear capacity and the strain energy of interior slab-column connection of both normal and high strength concrete. The general finite element software ANSYS can be used successfully to simulate the punchingshear behaviour of reinforced concrete flatplates. Joaquim A.O. Barros et.al, (2015) presented a new type of carbon-fibre-reinforced-polymer (CFRP) laminate of U-shape is used by adopting a novel hybrid technique for the simultaneous flexural and punching strengthening of existing RC slabs. Besides, this hybrid technique aims to provide a better bond performance for the embedded-through- section (ETS) and near-surface mounted (NSM) CFRPs by improving the anchorage conditions.Moreover,a higher resistance to the susceptibility of occurrence of other premature failure modes, like concrete cover delamination, is offered by using this hybrid technique. A 3D nonlinear finite-element (FR) model is developed to simulate the experimentaltests by considering the nonlinear behaviour of the constituent materials. The experimental program and numerical model are described, and the relevant results are analysed. Francisco Natario et.al, (2015) investigated the behaviour of cantilever bridge deck slabs under fatigue loads. A specific experimental programme consisting on eleven tests under concentrated fatigue loads and four static tests (reference specimens) is presented. The results show that cantilever bridge deck slabs are significantly less sensitive to shear –fatigue failures than beams without shearreinforcement. Some slabs failed due to rebar fractures. They presented significant remaining life after first rebar failure occurred and eventually failed due to shear. The test results are finally compared to the shear-fatigue provisions for the fib-Model Code 2010 and the critical shear crack theory to discuss their suitability.
Punchingshearreinforcement is an efficient way to increase the strength and deformation capacity of flat slabs and thus increase their safety. Although different shear reinforce- ment systems and detailing rules may lead to rather different behaviors and strengths, scarce systematic research on this subject can be found in the literature for full-scale speci- mens. In this paper, the results of an experimental campaign on specimens with thicknesses ranging from 250 to 400 mm (approximately 10 to 16 in.) and reinforced with stirrups or studs is presented. The detailed measurements performed allow for direct comparisons of the performance of the shearreinforcement and provide an understanding of the influence of various physical parameters on the shearstrength and deformation capacity of the members.
The punchingshear resistance of reinforced concrete ground supported slab represents a wide category of concrete structure and subsoil interaction problems. The spatial fracture mechanism itself is inﬂuenced by various input parameters. The most important ones include geometrical dimensions of the structure, properties of the selected con- crete materials, load or properties and characters of soil underneath. The importance of this research area is testiﬁed by the extensive research underway—see Kueres et al. (2017), Hoang and Pop (2016), Alani and Beckett (2013), Halvonik and Fillo (2013), Siburg et al. (2012), Siburg and Hegger (2014), Song et al. (2012), and Husain et al. (2017). General evaluation of tests of typical slabs is provided in Alani and Beckett (2013) and Ricker and Siburg (2016). An interesting comparison and critical review of the punchingshearstrength of ﬂat slabs can be found in Bogda´ndy and Hegedus (2016) or Zabulionis et al. (2006). Important overall results from the ﬁeld of behaviour of reinforced concrete footings are presented also in Siburg and Hegger (2014), Hegger et al. (2006, 2007), Aboutalebi et al. (2014) and Siburg et al. (2014). The approaches to calculation, modelling and computer programs are focused on in
An experimental program was carried out by Rizk et al. (2011) to investigate the influence of the slab size on the punchingshear resistance. Five thick square slabs were tested. The slabs were 300 mm and 400 mm thick with side dimension of 2650 mm. The slabs were loaded through a small column stub 400 × 400 mm. Four slabs were cast using high strength concrete and one using normal concrete. Shearreinforcement was used in one of the high strength concrete slab. The results of the punchingshearstrength showed good agreement with the values predicted using the CEB-FIP Model Code (1990). The ACI 318-11 code was found to underestimate the punchingshearstrength for all slabs by an average of 17% except for one high strength concrete slab. This high strength slab had the lowest reinforcement ratio and the predicted value was overestimated by 19%. It was highlighted by the authors that the experimentalshearstrength was different in two slabs. The slabs had different concrete strength, similar slab thickness and reinforcement ratio. Both slabs were designed to fail under punchingshear stresses. This finding showed that having a constant number for the size effect factor depending on the slab depth only, as used in major design codes, may not account for the size effect and it should also include the concrete compressive strength.
Concrete is an isotropic heterogeneous composite material made by cement, water and aggregates, however, macroscopically, it is considered as homogeneous. The compressive strength of concrete is much higher than its tensile strength and its complex behaviour requires the development of appropriate constitutive models for its simulation and analysis. All of the proposed constitutive models, e.g. (Willam and Warnke 1975, Simo and Ju 1987, Mazars and Pijaudier-Cabot 1989, Yazdani and Schreyer 1990, Feenstra and de Borst 1995, Lee and Fenves 1998, Imran and Pantazopoulou 2001, Grassl et al. 2002, Addessi et al. 2002, Jirasek et al. 2004, Salari et al. 2004); may show limitations and they are not suitable for all types of analysis. In continuum mechanics, the macroscopic response of concrete can be characterized through its evolution law of the failure envelope in multi-axial loading. A brief description on the mechanical behaviour of concrete and then an overview on its non-linear modelling with respect on cracking models, plasticity theory, continuum damage mechanics and damage coupled with plasticity, are presented in this chapter.
The force time function due to a deformable missile impact was calculated with the Riera method and by using a FE model. Also a more accurate folding model in which the actual formation of folds is taken into consideration was used. Two finite element codes, Abaqus and a special purpose finite element program, are used in calculating the responses of the present test plates. Additionally a TDOF model is used for structural response studies. Displacements calculated with three different methods applying two different loading functions were compared with the experimental recordings. The shape of the loading function did not significantly affect the results in the considered cases. Maximum deflections obtained by Abaqus and TDOF model were somewhat underestimated. Bending vibration behavior of the slab could not be properly calculated with the solid model. A 3D solid FE model is needed in studying local shearpunching behavior of test plate in detail.
36 deflection response from the experimental observation. In general, all five slab specimens that were modeled showed a very strong correlation between the finite element 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.
Much research has been dedicated to the study of the punchingshear behaviour of rein- forced concrete flat slabs due to the brittleness of the failure. The majority of this past research has been experimental, and has involved the testing of isolated slab-column connections, where the portion of the slab included in the test approximates the negative moment area around the column. Even though the existing experimentalpunchingshear database is extensive , , not all parameters have been sufficiently studied. For example, the punchingshear behaviour of reinforced concrete slabs supported on L, T, and cruciform-shaped columns has received limited attention ,  even though most current worldwide design codes include provisions for these column shapes , . The derivation and reasoning behind these code provisions are unclear.
The first set of inclined shear cracks appears to have started from near the top reinforcement and ended near the column. Even though at the end of testing, it was noticed that the column penetrated into the slab, the first two legs of shearreinforcement were actually avoided by the first inclined shear cracks, which propagated inside the cover. These cracks were more inclined away from the column and appeared to span at least two legs of shearreinforcement. It can be concluded that substantial yielding and rigid body rotations must be responsible for the apparent penetration of the column into the slab, which explains why the load was maintained during this process. Because there was shear failure surface through the concrete in compression, the shear resistance of concrete along that surface can be considered to have been adversely affected by shear cracking. This assumption appears to be supported by the ACI code of practice, which adopts a reduced concrete shear contribution when the slab requires shearreinforcement (V c in
For specimen JD9B-E, the cracking pattern occurring between 365 and 600 kN shown in Fig. 10(b) reveals the occurrence of inclined cracks propagating from the slab section to the top and numerous punchingshear cracks developing concentrically around the loading point. Compressive cracks appeared at 648 kN and propagated gradually over the whole width of one deck. However, these compressive cracks did not occur in the deck that was not directly subject to the load. At 676 kN and 733 kN, sudden loss of the load occurred due to punchingshear and, beyond 733 kN, the load experienced small increase . Compared to specimen JD9B-C, the punchingshear cracks show U-shapes rather than closed polygons around the loading plate, and punching failure occurred earlier in the case of eccentric loading.
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 punchingstrength. 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 experimentalpunchingshear 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.
The deflection profiles at the time of reaching the maximum central displacement are shown in Figure 11. Both solutions are computed by the Reissner-Mindlin theory FE method. In case labelled by FE-MR the transverse shearstrength is infinitely large. In both cases elastic transverse shear deformations are taken into account. Figure 11 indicates the formation (at an early stage of loading) of punching cone. Similarly, the TDOF solutions predict shearpunching under the adopted heavier impact load.
Gross, S. P., Yost, J . R., Dinehart, D. W., Svensen, E. & Liu. N. (2003). ShearStrength of Normal and High Strength Concrete Beams Reinforced with GFRP Bars. High performance materials in bridges, Proceedings of the International Conference, ASCE, Kona, Hawaii, pp. 426-437.
the model for PG1 is presented in Fig. 3 ). Eight node multi-layered shell elements ( 34mm 34mm in average) accounting shear deformation with reduced integration were adopted for the rein- forced concrete  . The slab thickness was subdivided into seven layers according to rebar setup. Three Simpson integration points were used for each layer, yielding a total of twenty-one integration points in total over the slab thickness. The vertical support pro- vided by the columns in the centre of the slabs were modelled using nonlinear non-tension spring elements providing stiffness in compression only as described in the following section. On the symmetry faces, all displacements perpendicular to the cross- sections and rotations were fixed. The column was fixed in the ver- tical direction.
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 flat slabs 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 flat slabs 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.