Punching shear behavior of recycled aggregate concrete slabs with and without steel fibres

Abstract

A study on the punching shear behavior of 8 slabs with recycled aggregate concrete (RAC) was carried out. The two main factors considered were the recycled coarse aggregate (RCA) replacement percentage and the steel fibre volumetric ratio. The failure pattern, load-displacement curves, energy consumption, and the punching shear capacity of the slabs were intensively investigated. It was concluded that the punching shear capacity, ductility and energy consumption decreased with the increase of RCA replacement percentage. Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab, but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern. On the basis of the test, the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed.

Keywords

recycled aggregate concrete / steel fibres / slab / punching shear / recycled coarse aggregates replacement percentage

Introduction

Punching shear failure is an undesirable failure mode of the reinforced concrete flat slabs subjected to a concentrated load [¹,²], which occurs suddenly with a small displacement. The punching shear resisting capacity of a normal concrete slab has been extensively researched in the past decades. Talbot [³], Elshafey et al. [⁴], Choi et al. [⁵], and Theodorakopoulos and Swamy [⁶] have conducted a large amount of experimental study for the punching shear resisting capacity of concrete slabs. Based on the extensive experimental database of normal concrete slab, several computational models to predict the punching shear resisting capacity of slabs were developed [⁷–¹²]. Youm et al. [¹³] have conducted a full-scale light weight aggregate concrete (LWAC) test, and proposed a modified design equation for LWAC. Chinese scholars have begun to conduct a series of experimental and theoretical analysis on the punching shear behavior of reinforced concrete slabs since the 1970s [¹⁴–¹⁶]. Most of the previous research provided the foundation for the punching design of normal concrete slabs.

There are a number of factors influencing the punching shear behavior of natural aggregate concrete (NAC) slabs: the area of the slab where a force is exerted on, the concrete compressive strength, the span length and slab thickness, the position where the force is exerted, flexural reinforcement and the condition of supports. It is concluded that adding steel fibres into NAC can improve not only the shear behavior but also the deformation capacity of concrete slabs [¹⁷], and that longer fibres and higher fibres content (volumetric percentage of fibres) generally provide higher energy absorption in NAC slabs [¹⁸,¹⁹]. Moraes Neto et al. [²⁰] have developed a model for punching resistance prediction of centrically loaded steel fibres reinforced concrete slabs. Belletti et al. [²¹–²³] have utilized the nonlinear finite element methods for the numerical assessment of the punching shear resistance.

To apply recycled aggregate concrete (RAC), Xiao et al. [²⁴] have conducted a series of experimental studies on the structural behaviors of RAC components. There is sufficient research data on the bending, shear, compression, and even seismic performance of RAC components, such as RAC beams, columns and frame structures [²⁵,²⁶].

In this paper, 8 RAC slabs with and without steel fibres are designed and cast as constructed in a real building project, one among which is a NAC slab as reference for the comparative study. Base on the experimental results, the effects of steel fibres volumetric ratio and recycled coarse aggregate (RCA) replacement percentage on the punching shear failure are analyzed. Finally, a formula of estimating punching shear capacity of RAC slabs with and without steel fibres is proposed and discussed.

Research significance

To the best knowledge of the authors, little research work on the punching shear behavior of RAC slabs has been published worldwide. This fact significantly limits the expansion and application of RAC, as well as the development of the research for the punching shear behavior of the fibre reinforced RAC slabs. This study is mainly focused on the influence of RAC strength (varying the RCAs replacement percentage) and steel fibres volumetric ratio. The outcome of this investigation will provide basis for the future research and design based on RAC slab’s punching shear performance.

Test design

Test materials

The cement selected was a PO42.5 ordinary Portland cement, whose technical indicators were in accordance with the Methods of testing cement-Part 2: Chemical analysis of cement (BS EN 196-2:2005) and Methods of testing cement-Part 3: Determination of fineness (BS EN 196-6:1992).

The fine aggregates used were the medium sand (see Table 1). All the technical indicators were in accordance with the Admixtures for concrete, mortar and grout-Test methods-Part 1: Reference concrete and reference mortar for testing (BS EN 480-1:2006).

The coarse aggregates used included natural coarse aggregates (NCAs) and RCAs. The NCAs used were gravel stones, while the RCAs used were manufactured from demolished waste concrete by a Shanghai local company. The original waste concrete strength grade is 30 MPa. The waste concrete underwent crushing, sieving and screening into smaller size aggregates, mainly divided into two groups, namely 5 mm–15 mm and 15 mm–25 mm, and they were then mixed together in the mass ratio of 2:1 when preparing RAC. For the grading requirements of the RCAs, 5 mm–25 mm, was displayed in Fig. 1. The basic properties of NACs and RCAs are listed in Table 2.

The steel fibres used were wire-type shaped with angles on both ends, with an average of 50 mm length and a 0.9 mm diameter, and with a length-diameter ratio of 55. In this investigation, two volumetric ratios of fibres were considered, namely 0.5% and 1.0%, respectively. The water used was ordinary tap water.

RAC and reinforcement mechanical properties

The test was carried out in a laboratory of Tongji University. The RCAs replacement percentages used in the test were set as 30%, 50%, and 100%, respectively. See Table 3 for the mix proportion. The consistency class of fresh concrete is class S3: 100 mm–150 mm according to the European standard. The mean values of 28d-cube compressive strength and the modulus of elasticity are listed in Table 4.

The reinforcements used were HRB335 (Hot-rolled Ribbed Bar, f_yk = 335 MPa), with a diameter of 12 mm. The steel reinforcement mechanical test was carried on 3 specimens, the average yield strength was 334.69 MPa, while the average elastic modulus was 2.0\times10⁵ MPa, and its average yielding strain was about 1674 me.

Test specimen design

The specimen was a flat concrete slab model. 8 concrete slabs were all designed with dimensions of 1500 mm\times1500 mm\times120 mm, and their effective depths were h_{\mathrm{0}}=h-a_s=h-\left(c+{\displaystyle \frac{d}{\mathrm{2}}}\right)=\mathrm{120}-\left(\mathrm{15}+{\displaystyle \frac{\mathrm{12}}{\mathrm{2}}}\right) = 99 mm. Besides, the reinforcement ratios were \rho ={\displaystyle \frac{A_s}{b{h}_{\mathrm{0}}}}={\displaystyle \frac{\mathrm{15}\times {\displaystyle \frac{\mathrm{\pi }}{\mathrm{4}}}\times {\mathrm{12}}^{\mathrm{2}}}{\mathrm{1500}\times \mathrm{99}}}=1.142%. The slab diagram and its reinforcements are displayed in Fig. 2.

The fabrication and curing of the specimen were conducted under the same condition with a real engineering, each stage of fabrication, binding of reinforcements, erecting of molds, casting concrete, and curing of the concrete specimens were done accordingly.

The loading setup and measuring apparatus

The loading setup is shown in Fig. 3. The slabs were set up on the same reinforced concrete frame. The slab properly fitted on the area covered by an angle steel frame, in order to simulate the boundary conditions of four simply-supported edges. It is well accepted that the boundary condition may strongly affect the resisting capacity of punching shear [²⁷]. This boundary condition is to simulate the real condition of slabs which are simply-supported on the edge beams. The concentrated load was applied on a concrete-filled square steel tubular short column by a hydraulic jack.

The measured indicators mainly included strain of longitudinal reinforcement and concrete, the slab displacement at the center in the vertical direction, as well as observing the crack propagation and failure process during loading. During the test, the data from the load transducers, displacement transducers and strain gauges were retrieved automatically through the computer static strain testing system. At the beginning of the test, a pre-test was conducted to make sure all the equipment can function properly.

(1) The setup of the strain gauges:

As Fig. 4 shows, in order to clearly observe and properly analyze the strain changes in the reinforcement and concrete during the loading process, this test set up 5 reinforcement strain gauges and 6 concrete strain gauges on each slab specimen. The distance between the reinforcement strain gauges was 200 mm. The concrete strain gauges fixed on the top surface of each specimen were mainly arranged in a perpendicular way and at an angle 45° to the loading column, and the distances between them being 200 mm and 283 mm respectively.

(2) The setup of the displacement transducer:

During the loading test, each slab was fixed with 8 linear variable displacement transducers (LVDTs). Among them, 6 were on the slab surface, and the other 2 were under the slab (LVDTs No. D-5 and No. D-8 in Fig. 5).

Loading program

The testing was controlled by the loading force. The load increased consistently until the specimen failed. To retrieve data properly, the loading and unloading speeds during the test process were maintained at a constant for enlarging the deformation.

Main test results

Test phenomenon and failure characteristics

When the initial load was small, no crack appeared on the surface of slabs, and the specimen was under elastic state. As the load increased, the tensile area of the slab diagonal to the column first showed micro cracks. When the load continued to increase, the cracks propagated toward the columns, and some cracks then developed perpendicular to the slab edge, and later curved while increasing in number toward the slab edge. During the process when the column load gradually increased, it can be detected visually that the curved cracks on the slab developing from the area around the loading column went toward the edges of the slab. At about 0.8P_u, the slab surface cracks developing from the middle section and toward the corner columns had fully developed, but because a plastic hinge line had not yet formed or had not yet fully developed, the slab specimen had not formed geometric variables to cause bending failure. Between the load of 0.8P_u– P_u, the slab-column joint load-mid span displacement curve clearly showed bending deflection on the displacement axis, when the slab punching shear reached the ultimate load, a loud sound was heard, and the cut cone shaped section under the slab was pushed downward, which was also found in Ref [²⁷].

As Figs. 6(a)–6(h) shows, during punching failure, with the increasing of RCA replacement percentage, the slab surface integrity is reduced, and the cut cone partial shedding phenomenon is significant. However, with the increasing of steel fibre volumetric ratio, the slab surface and the cut cone integrity are both improved.

Punching ultimate load and its deflection

The punching ultimate load and the deflection of each slab are summarized in Table 5. With the increase of RCA replacement percentage, the punching ultimate load is reduced. And the deflection of each slab is gradually reduced except the RAC100, which may be caused by the randomness of RAC, when compared to NAC and RAC with lower replacement percentages.

When RCA replacement percentage was set as a constant, with the increasing of steel fibres volumetric ratio, the punching ultimate load is improved, and the deflection follows a growing trend. Taking into account the non-uniform distribution of steel fibres, with the increase of steel fibres volumetric ratio, sometimes the failure deflection is reduced instead.

Test analysis

Analysis of the steel reinforcement strain

Typical strain developments of the slab reinforcement are shown in Figs. 7(a)–7(k). During the initial load, the longitudinal reinforcement stress is relatively small, primarily the tension zone in concrete bears the load. After reaching the cracking load, the tension zone of concrete gradually lost its bearing resistance; the longitudinal reinforcement strain begins to increase significantly. As load continues to increase, the reinforcement strain is increased following a nonlinear relationship. The longitudinal reinforcement stress increases slowly to the formation of a punching cone.

From observing Figs. 7(b), 7(c) and 7(f), due to the increase of the RCAs replacement percentage, the longitudinal reinforcement strain decreases when reaching the punching failure. When reaching the ultimate load, most of the longitudinal reinforcements have not reached their yielding strain. However, from observing Figs. 7(c)–7(e), or Figs. 7(f)–7(h), due to the increase of the steel fibres volumetric ratio, it is found that the longitudinal reinforcement strain increases when reaching the punching failure, and a part of reinforcements have reached their yield strength.

The typical data of No.S-3 reinforcement strain gauge, and the result of comparison among Figs. 7(i)–7(k) were observed. From observing Fig. 7 (i), due to the increase of the RCA replacement percentage, it is found that the increasing rate of reinforcement strain tends to increase. Due to the increase of the RCA replacement percentage, the concrete elastic module decreases, the longitudinal reinforcement bears more force, and the development rate of reinforcement strain increases gradually. From observing Figs. 7 (j) and 7(k), the reinforcement strain increased to yield. It can be explained by the fact that thanks to the incorporation of steel fibres, which increased residual stresses perpendicular to inclined shear cracks, the ductility of the slab was highly increased, which obviously delayed the failure occurring of punching shear.

Analysis of the slab top surface concrete strain

To facilitate the contrast, each concrete compressive strain value on the top of the slab was multiplied by -1 when analyzing, and the typical strain development of the slab surface concrete is displayed in Figs. 8(a)–8(j). During the initial load, the concrete strain slowly increases under a linear relationship. As the load continues to increase, concrete strain curve begins to tend to strain axis, while the rate of stress continues to increase, and concrete strain increasing rate of the slab angular direction is significantly larger than that of the parallel direction to slab edge.

As is shown in Fig. 8(a), the No.C-1 concrete strain of normal concrete slab (1503me) has approximately reached its peak strain (1500 me–2000 me) when the punching cone formed. Because of the variability and brittleness of RAC material are higher than that of normal concrete material [²⁸], the RAC slab without steel fibres punching failure occurs before the slab surface concrete fully exert its compressive strength, just as shown in Figs. 8(b), 8(c) and 8(f).

Choose the typical concrete strain to analyze, as shown in Fig. 8(j). When the RCAs replacement percentage is 100%, due to the increase of steel fibres volumetric ratio, slab surface concrete strain increases visibly. When the steel fibre volumetric ratio is 1%, the concrete strain of slab surface (1720 me) has approximately reached its peak strain (1500 me–2000 me) when the punching cone formed.

It could be concluded that the reason of punching failure is not simply the surface of slab concrete reaching its compressive strength. When it comes to the punching failure of concrete slab, there existing a controversy of two modes that is cable-stayed damage and the baroclinic damage. For example, Moe [¹²] considered that the punching failure is virtually shear-compression failure. Zhou [²⁹], after analyzing the concrete stress distribution on the oblique cone by FEM, concluded that the punching failure of slab-column node specimens is mainly the combine effects of compressive stress, shear stress and the ring compressive stress on the oblique cone. Through the analysis of concrete strain of 8 concrete slabs, this paper supports that the main reason of NAC slab and RAC slab with a certain amount of steel fibres punching failure are the compression damage of shear-compression zone concrete. However, combine with analysis of the development of longitudinal reinforcement strain, the RAC slab punching failure tends to cable-stayed damage of the bottom concrete of the slab.

P-\Delta Curves

The load-displacement (P-\Deltacurves) of the concrete slab punching shear, as shown in Figs. 9(a)–9(f), reflects the slab punching capacity, deformation, ductility and other characteristics [²⁸]. According to the slab’s mid-point displacement (No. D-5) and the rectified deflection of the slab’s 4 simply-supported edges, it is easy to obtain each slab specimen’s

P-\Delta

curve.

As the RCA replacement percentage increased from 0% to 30% to 50% to 100%, the slab punching shear failure tended to occur. During the initial load, the slab was basically in elastic stage. After reaching the cracking load, the slab deflection curves begin to deviate from the load axis, but P-\Delta curves were still linear. When up to about 0.85P_u, the deflection curves began to tend to the deflection axis. When reaching the ultimate load, punching cone formed, and slab’s bearing capacity declined significantly. Thereafter, the load gradually stabilized at the 25%–35% of the ultimate load, the deflection of slab continued to develop under the relative steady load up to finally losing its bearing capacity.

When comparing Fig. 9, it can be observed that:

(1) Figs. 9(a) and 9(b) demonstrate that, as the RCAs replacement percentage increases from 0~100%, the slab punching shear failure all occurs. In comparison to NAC, the increase in the RCA replacement percentage reduces the slab deformation and the ductility at failure, however, the probability of the brittle punching shear failure increases, while for the bending failure occurs before the punching shear failure it decreases. This may be caused by the inferior interlock within the RAC. It is well known that the shear capacity of reinforced concrete components is consisted with the interlock of aggregates, dowel action of longitudinal reinforcements, and the stress in stirrups. Excluding other identical parameters, it can be induced that the decrease of shearing capacity of RAC slabs is caused by the degradation of interlock within RAC.

(2) As Figs. 9(b) and 9(c) demonstrate that, for the RAC slab, the increase in the volumetric ratio of steel fibres results in higher deformation at failure, and the number of cracks in the punching shear cone obviously increases. At failure the slab somehow still maintains its full shape without appearing a localized punching drop phenomenon, demonstrating a punching shear failure at the same time showing a bending failure trend. The P-\Delta curves gradually become gentle, the slab deformation ability improves, and the brittle property reduces.

(3) As Figs. 9(d) and 9(e) demonstrate that, for the steel fibre reinforced RAC slab, the slab failure being punching shear failure becomes obvious with the increase of the RCAs replacement percentage. Therefore, when the RCAs replacement percentage decreases, it is helpful to improve the slab punching shear performance, at the same time increases the slab ductility and deformation ability at failure.

(4) As Fig. 9(f) illustrates that, when the steel fibres content is relatively high (i.e., 1%), the negative effect of RCAs replacement percentage will be reduced.

Deformation capacity and energy consumption

Deformation ability

It is widely accepted that the ductility is a measure of component, structure or cross-section’s ability to undergo significant plastic deformation before failure. The displacement ductility coefficient expression is {\mu }_{\Delta }={\Delta }_0/{\Delta }_y. For slabs that fail due to punching shear, the yielding of the longitudinal reinforcement in tension in the slab has no direct link to the shape of the member at failure, but at punching shear failure the bearing capacity suddenly decreased, therefore the definition of the ‘ductility’ should be adjusted to ‘equivalent ductility’. To describe the punching slab’s equivalent ductility, the ratio of the deflection {\Delta }_0 corresponding to the ultimate load P_u and using the energy law to determine the yield deflection{\Delta }_y. The equivalent ductility of various slabs was calculated and compared. The principle of determining the {\Delta }_y is: to replace the ideal linear elastic stage of the ascent stage of the actual measured P-\Delta curve, which should make the area covered by the deformation axis be equal, and the corresponding displacement point where the two lines meet is the calculated {\Delta }_y [³⁰], as demonstrated in Fig. 10, respectively.

Comparing the obtained displacement equivalent ductility coefficient (see Table 6), when the RCA replacement percentage is the same, the slabs with steel fibres shows a higher displacement ductility coefficient with the increase of the volumetric fibres. Whereas, the increase of the RCA replacement percentage, follows a gradual decrease in the displacement ductility coefficient.

Energy consumption

The energy consumption S_{\Delta } is the area formed by the equivalent ductility line and the horizontal axis on the P-\Delta curve (see Fig. 10). The calculation results (see Table 6) show that the steel fibre reinforced RAC slab’s energy consumption ability is higher than that of slabs without steel fibres, and the increase in the steel fibres meets a gradual increase in the slab’s energy consumption. The increase in the recycled aggregates replacement percentage meets a gradual decrease in the slab energy consumption. It should be mentioned that for RAC50 and RAC 100, the effect of the volumetric ratio of steel fibres on the energy consumption shows a different trend. For RAC50, even an addition of 0.5% steel fibres can increase the slab’s energy consumption obviously. However, for RAC100, a 0.5% steel fibre addition is not enough to compensate the decrease of energy consumption induced by RCA. And when the volumetric ratio of steel fibre increased to 1%, the ductility was significantly improved, which make a gap between the energy consumption of SFRAC100-0.5% and SFRAC100-1%.

Calculation of the punching shear capacity

Taking into account the versatility of formula, this paper utilizes the design equation of BS EN 1992-1-1 2004 for verification, and the design punching shear resistance may be calculated as follows:

(1)V_{R\mathrm{d,}c}=\left[C_{Rd,c}\cdot \left(\mathrm{1}+\sqrt{{\displaystyle \frac{\mathrm{200}}{d}}}\right)\cdot {(\mathrm{100}{\rho }_{\mathrm{1}}\cdot f_{ck})}^{\frac{\mathrm{1}}{\mathrm{3}}}+k_{\mathrm{1}}\cdot {\sigma }_{cp}\right]\cdot {\mu }_1\cdot d\ge [{\nu }_{\min }+k_{\mathrm{1}}\cdot {\sigma }_{cp}]\cdot {\mu }_1\cdot \mathrm{d,}

where V_{R\mathrm{d,}c} is the design value of the punching shear resistance of a slab without punching shear reinforcements along the control section considered. The recommended value for C_{Rd,c}is {\displaystyle \frac{0\mathrm{.18}}{{\gamma }_c}}({\gamma }_cis the partial factor for concrete, its value could be 1.4), and that for k_{\mathrm{1}} is 0.1, d is effective depth of a cross section and its value is about 99 mm, {\rho }_{\mathrm{1}}=\sqrt{{\rho }_{\mathrm{ly}}\cdot {\rho }_{lz}}\le \mathrm{0.02} is the reinforcement ratio for longitudinal reinforcement, {\rho }_{\mathrm{ly}} and {\rho }_{lz} are related to the bonded tension steel in y- and z- directions respectively, and the values should be calculated as mean values taking into account a slab width equal to the column width plus 3d in each side, in this paper, its value is about 0.01142. f_{ck} is the characteristic compressive cylinder strength of concrete for 28 days and it could be calculated as Table 7 shows. {\sigma }_{cp}={\displaystyle \frac{{\sigma }_{\mathrm{cy}}+{\sigma }_{cz}}{\mathrm{2}}}is the compressive stress in concrete from the axial load or pre-stressing, {\sigma }_{\mathrm{cy}}and {\sigma }_{cz} are the normal concrete stresses in the critical section in y- and z- directions (MPa, positive if compression) . {\mu }_{\mathrm{1}} is the basic control perimeter and its value here is about 2384 mm.

In consideration of steel fibres’ effective to the punching shear capacity, the formula could be written as follows:

(2)V_{R\mathrm{d,}c}=\left[C_{Rd,c}\cdot \left(\mathrm{1}+\sqrt{{\displaystyle \frac{\mathrm{200}}{d}}}\right)\cdot {(\mathrm{100}{\rho }_{\mathrm{1}}\cdot f_{ck})}^{\frac{\mathrm{1}}{\mathrm{3}}}+k_{\mathrm{1}}\cdot {\sigma }_{cp}\right]\cdot {\mu }_1\cdot d\cdot \left(1+{\beta }_p\cdot V_f\cdot {\displaystyle \frac{l_f}{d_f}}\right),

where V_{\mathrm{f}}and {\displaystyle \frac{l_{\mathrm{f}}}{d_{\mathrm{f}}}}are the volumetric of fibres and the length-diameter ratio, respectively. When{\lambda }_{\mathrm{f}}>\mathrm{1.2}, take{\lambda }_{\mathrm{f}}=1\mathrm{.2}. {\beta }_P is the influencing factor of the steel fibres on the steel fibre reinforced RAC, it can be easily decided through the test, when the steel fibre reinforced concrete strength is CF20–CF40, take {\beta }_P=0\mathrm{.5}.

Equation (2) is adopted to be the RAC slab punching shear capacity calculation formula. All the variables are substituted in the formula, and the ultimate bearing capacity can be calculated, see Table 8 for details.

Table 8 and Fig. 11 show the comparison of the slab punching shear capacity calculated valueP_u^{\mathrm{c}\mathrm{a}\mathrm{l}} and tested valueP_u^{}. In consideration of the safety of actual project application, P_u^{\mathrm{c}\mathrm{a}\mathrm{l}}should be lower than theP_u^{}, as list in Table 8, the average P_u^{\mathrm{c}\mathrm{a}\mathrm{l}}{\mathrm{/P}}_u of RAC is about 0.824, and the variance is about 0.001616. From observing the Fig. 11, it could find that the trend between P_u^{\mathrm{c}\mathrm{a}\mathrm{l}}and P_u^{}is well in coordinate with each other. Based on this experiment data, Eq. (2) could be adopted to the design for an actual project.

Conclusions

A test was carried out on the punching shear performance with 8 concrete slabs, of which 7 were RAC slabs and 1 was a NAC slab which was also used as a control reference. Among the 7 RAC slabs, 4 of them were reinforced with steel fibres, while the remaining 3 were RAC slabs without steel fibres. The steel fibre volumetric ratio was 0.5% and 1.0%, whereas the RCA replacement percentages were set as 0%, 50% and 100% respectively. The effects of the volumetric ratio of steel fibres and RCA replacement percentage on the shear punching resistance and ductility were analyzed. The following conclusions can be put forward:

1). Combining the development of longitudinal reinforcement strain and slab top surface concrete strain, the mechanism of RAC slab and RAC slab with a certain amount of steel fibres punching shear failure, are mainly, the compression-shear area concrete reaches its ultimate compression strain, then forms the punching cone, and finally leads to the punching failure. However, the mechanism of RAC slab without steel fibres mainly tends to cable-stayed damage.

2). The addition of steel fibres improves the punching shear capacity by about 7%–15%, and it is also found that the RAC slab’s punching shear capacity is lower than that of NAC slab’s.

3). When the steel fibres are added, not only the punching shear capacity increases, but the slab’s ductility, deformation and energy consumption are also improved.

4). For the RAC slab under punching shear, the addition of steel fibres helps to transform the failure pattern from shear failure to bending-shearing failure; the increase in the RCA replacement percentage, meets a gradual decline in the punching shear capacity, shear resistance performance and ductility.

5). Based on the test results, a formula was proposed on the basis of the punching failure calculation formula from BS EN 1992-1-1 2004 to estimate the punching shear bearing capacity of RAC slabs.

References

[1] Marzouk H, Hussein A. Experimental investigation on the behavior of high-strength concrete slabs. ACI Materials Journal, 1991, 88(6): 701–713

[2] Guandalini S, Burdet O L, Muttoni A. Punching tests of slabs with low reinforcement ratios. ACI Materials Journal, 2009, 106(1): 87–95

[3] Talbot A N. Reinforced Concrete Wall Footings and Column Footings. Engineering Experiment Station. 1913

[4] Elshafey A A, Rizk E, Marzouk H, Haddara M R. Prediction of punching shear strength of two-way slabs. Engineering Structures, 2011, 33(5): 1742–1753

[5] Choi K, Taha M, Sherif A. Simplified punching shear design method for slab-column connections using fuzzy learning. ACI Materials Journal, 2007, 104(4): 438–447

[6] Theodorakopoulos D D, Swamy R N. Ultimate punching shear strength analysis of slab-column connections. Cement and Concrete Composites, 2002, 24(6): 509–521

[7] American Concrete Institute (ACI). Building Code requirements for structural concrete. ACI 318-11. 2011

[8] Canadian Standards Association (CSA). Design of concrete structures for buildings. CSA-A23.3-04. 2004

[9] Eurocode 2: Design of Concrete Structures-Part 1–1. General rules and rules for buildings. BS EN 1992-1-1, 2004: 97–105

[10] CEB-FIP. Model Code. Bulletin D’ Information No. 203–205. 2004

[11] Richard C E, Hognestad E. Shearing strength of reinforced concrete slabs. ACI Materials Journal, 1956, 53(7): 29–58

[12] Moe J. Shearing Strength of Reinforced Concrete Slabs and Footings under Concentrated Loads. Development Department Bulletin D47. 1961

[13] Youm K S, Kim J J, Moon J. Punching shear failure of slab with lightweight aggregate concrete (LWAC) and low reinforcement ratio. Construction & Building Materials, 2014, 65: 92–102

[14] Zheng Z Q, Ouyang C S. Punching strength of reinforced concrete circular slabs. Journal of Building Structures, 1985, 6(6): 12–22 (in Chinese)

[15] Zheng Z Q. The punching strength of reinforced concrete slabs with consideration of bending impaction. Proceedings of the Second Symposium on the Basic Theory and Application of Concrete Structures, 1990: 501–508

[16] Zheng Y W. Experimental study on punching shear of reinforced concrete slabs. Thesis for the Master’s Degree. Changsha: Hunan University, 2009 (in Chinese)

[17] Swamy R N, Ali S. Punching shear behavior of reinforced slab-column connections made with steel fibres concrete. Journal of the American Concrete Institute, 1982, 79(5): 392–406

[18] An Y J, Zhao G F, Huang C K. The experimental research of the steel fibres reinforced concrete slab punching shear resistance (I). Journal of Building Structures, 1994, 15(2): 11–16 (in Chinese)

[19] An Y J, Zhao G F, Huang C K. The experimental research of the steel fibres reinforced concrete slab punching shear resistance (II). Journal of Building Structures, 1994, 15(3): 63–65 (in Chinese)

[20] Moraes Neto B N, Barros J A O, Melo G S S A. A model for the prediction of the punching resistance of steel fibre reinforced concrete slabs centrically loaded. Construction & Building Materials, 2013, 46: 211–223

[21] Belletti B, Walraven J C, Trapani F. Evaluation of compressive membrane action effects on punching shear resistance of reinforced concrete slabs. Engineering Structures, 2015, 95: 25–39

[22] Shu J, Belletti B, Muttoni A, Scolari M, Plos M. Internal force distribution in RC slabs subjected to punching shear. Engineering Structures, 2017, 153: 766–781

[23] Belletti B, Pimentel M, Scolari M, Walraven J C. Safety assessment of punching shear failure according to the level of approximation approach. Structural Concrete, 2015, 16(3): 366–380

[24] Xiao J Z, Li J B, Zhang C H. On relationships between the mechanical properties of recycled aggregate concrete: an overview. Materials and Structures, 2007, 39(6): 655–664

[25] Choi W C, Yun H D, Kim S W. Flexural performance of reinforced recycled aggregate concrete beams. Magazine of Concrete Research, 2012, 64(9): 837–848

[26] Xiao J Z, Huang X, Shen L M. Seismic behavior of semi-precast column with recycled aggregate concrete. Construction & Building Materials, 2012, 35: 988–1001

[27] Cantone R, Belletti B, Manelli L, Muttoni A. Compressive membrane action effects on punching strength of flat RC slabs. Key Engineering Materials, 2016, 711: 698–705

[28] Lin X J, Zheng Z Q, Qian Z Z. Experimental study on steel fibres reinforced concrete punching plate. Journal of Building Structures, 2012, 24(5): 73, 76–77 (in Chinese)

[29] Zhou K R. The process, working mechanics and carry capacity research of punching behaviour of concrete slabs. Dissertation for the Doctoral Degree. Shanghai: Tongji University, 1990 (in Chinese)

[30] Xiao J Z, Li W G, Fan Y H, Huang X. An overview of study on recycled aggregate concrete in China (1996–2011). Construction & Building Materials, 2012, 31: 364–383

[31] Yang K. The reliability analysis of reinforced concrete slabs in punching shear. Dissertation for the Doctoral Degree. Changsha: Hunan University, 2012, 14 (in Chinese)

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