Flat Plate Slab Research Articles

Effectiveness of Limestone Powder as a Partial Replacement of Cement on the Punching Shear Behavior of Normal- and High-Strength Concrete Flat Slabs

The objective of this study is to investigate the performance of normal- and high-strength concretes including limestone powder (LP) through their mechanical properties. Moreover, sustainable flat plates made of these concretes were investigated through their punching strength. For this purpose, two different types of concrete (normal- and high-strength) with various limestone replacement ratios of 0%, 5%, 15%, and 20% by weight were designed. The fresh and hardened characteristics of the mixtures were investigated at various ages. By this means, the experimental behavior of reinforced concrete (RC) flat plate slabs made with limestone powder subjected to punching shear failure was studied. Slump value increased up to a 5% replacement of LP; after that, there was a tendency for the slump value to decrease as the replacement of limestone in normal-strength LP concrete increased. However, slump values for high-strength LP concrete increased as the LP replacement amount increased. There was a steady decrease in the compressive strength and splitting tensile strength values with the increase in LP content in normal concrete. However, in the high-strength LP concrete, with more than 10% of replacement LP, a decrease in the compressive strength values and splitting tensile strength values occurred. Compared to the control slab specimen without LP, in normal strength, the slab specimens with LP exhibit a larger ultimate shear load for slab specimens containing 5% and 10% of LP. The maximum increment for RC slabs containing 10% limestone powder was 3.8%. However, in high-strength concrete, the slab specimens with LP remained at the same ultimate shear load as control slabs, up to 10% of LP. high-strength concrete slabs with 5–20% LP showed an overall increase of (17.2%) in punching strength over the corresponding LP normal-strength concrete slabs. The corresponding increase for control slabs was 18.8%. It can be concluded that introducing LP improves the slab punching strength in a similar way that is found in non-sustainable slabs when using either normal- or high-strength concrete.

Finite Element Analyses of Cast-in-situ RC Flat Slab with an Equivalent Frame for Horizontal Loads

In structural construction practice, the use of reinforced concrete slabs is extremely common due to their structural and economic advantages. An important issue is the study of structural behavior given to horizontal effects. The significance of this is centered not only on the scales caused by wind and construction loads, which are considered to be “normal” i.e., the quasi-static, which is essentially one-way monotonically increasing but also the most researched seismic, i.e., cyclically varying, direction and magnitude effects. The most widespread methods for sizing flat plate slabs to unidirectional, quasi-static horizontal loads are the so-called Equivalent Frame Method and the Effective Beam Width Method. In addition to analytical and basically linear numerical theoretical methods, several laboratory experiments have been performed and published. In this paper, we investigate the behavior of column-supported flat plate slabs against unidirectional, monotonically increasing horizontal loads using an advanced nonlinear numerical modeling method. Numerical models constructed with different geometric dimensions were created with ATENA 3D three-dimensional nonlinear finite element software. In the numerical studies, in addition to the vertical loads in the global sense, the horizontal loads were also taken into account. In our studies, we analyzed the global behavior of the structure, crack propagation, and internal stresses. The results were illustrated on force - displacement diagrams and compared with the results of the laboratory experiments used, thus showing the accuracy and limitations of the numerical modeling procedure. The numerical results were also compared with the results determined on the basis of the equivalent framework models.

Experimental research and numerical simulations of the actual response flat slab in case of column loss

AbstractThis study reports the influence of tie reinforcement on the load‐bearing capacity of a flat plate slab in a failure situation due to the removal of an edge column. The results are based on numerical model analysis, experimental investigations, and analytical estimation. A numerical model was developed using the ATENA FEM program and validated based on the test results of the materials used. Experimental studies on the edge column removal were carried out for three models of 16 field flat plate slabs with varying degrees of tie reinforcement. Furthermore, the columns removed in Models M1 and M2 were near the corner edge columns, whereas in Model M3, they were the middle edge columns. The behavior of a reinforced concrete flat plate subjected to large deflections was estimated analytically based on the current literature and compared with the results obtained from numerical analyses and experimental investigations. During the experimental investigations, many traditional and modern techniques were used to measure the strains and displacements of reinforcing steel and concrete.

Aspect Ratio and Relative Beam-Slab Stiffness Effects on the Long-term Deflection of Flat Plates and Beam Supported One-Way Slabs

This study investigates the ACI 318-19 two-way slab provisions for the long-term deflection control in flat plate slabs with an aspect ratio ranging between 1 to 3 at different panel locations (interior, edge, and corner) with a large span of 5.0 m, 7.5 m, and 10.0 m. Further, the study examines the effects of the relative beam-slab stiffness of the beams provided at the two long sides of flat plat slabs of aspect ratio greater than two using ACI318-19 recommended one-way slab thickness. The paper uses the Finite Element SAFE software to calculate the long-term deflection (LTD) by using nonlinear analysis (long-term cracked analysis) that considers concrete creep and shrinkage of two-way slabs and one-way slabs for different beam-slab stiffnesses and aspect ratios. The aspect ratio of a flat plate slab had a considerable effect on the LTD, where for slab panels of the same long span length and variable aspect ratio, as the aspect ratio gets smaller (square slab), the LTD increases, a behavior that ACI318-19 two-way slab deflection control procedures overlook. So, the deflection under the beams is within the ACI318-19 long-term deflection limits for different panel locations (interior, interior, exterior, and exterior edge). In addition, this part has been conducted to recommend a minimum relative beam-slab stiffness for the supporting beams.

Flexural Strength and Stiffness of Donut-Type Voided Slab

The voided slab system has been known as an effective technique to replace a heavy reinforced concrete slab system without the decrease in flexural strength. However, according to the previous studies, the flexural capacities such as flexural strength, stiffness and ductility of the voided slabs were practically lower than that of the solid slabs depending on the void shapes and details. Therefore, in this study, an analytical and experimental study were conducted to derive the optimal void shape and details focused on the flexural capacities of voided slabs. Based on a finite element (FE) analysis, a donut-type void shaper, which was a hexahedron with rounded edges and a hole penetrating the center, was suggested as the optimal shape in voided slabs, and an experimental study was conducted to verify flexural capacities of the donut-type voided slab. The flexural strength, stiffness and deflection of the donut-type voided slab were investigated by void shape and fixing method of void shaper as variables. The ductility of voided slab was also evaluated, because ductility is as important as strength for the safe design of slab member. The test results showed that the flexural strength of the donut-type voided slabs was equivalent to 98% and 105% that of the solid RC specimen, and the donut-type voided slab specimens had enough ductility for the flexural member. The stiffness of the donut-type voided slab was decreased about 8~9% compared with the solid slab, but it was improved up to 7% compared to the non-donut-type voided slab. Based on test results, the flexural design method of the donut-type voided slab associated with the void shape and fixing device of void shaper was suggested, and it was confirmed that the donut-type voided slab is one of the efficient alternatives to replace heavy flat plate slabs.

Experimental Study on Punching Shear Behavior of Crushed Clay Brick Lightweight Concrete Flat Plate Slabs

Experimental Study on Punching Shear Behavior of Crushed Clay Brick Lightweight Concrete Flat Plate Slabs

Comparison of methods of monitoring structure deformations based on tests of a column-plate slab

This work includes a comparison of the methods of monitoring the deformations of a structure on the example of a flat plate slab test. Classic ESG (electrofusion strain gauges) and modern DFOS (distributed fiber optic sensors) were compared. During the research, both types of sensors were used on some of the reinforcing bars. The study aims to indicate the differences between the compared monitoring methods, both in terms of the obtained results and their utility values.

Experimental study of punching shear in post-tensioned slabs with unbonded tendons

Post-tensioning in flat plate slabs provides the advantage of deflection and crack control under service loads, and can reduce slab thickness. However, due to the reduced slab thickness, post-tensioned flat plate slabs may be susceptible to punching shear failure under ultimate load. This study performed experimental research of the punching shear resistance of posttensioned flat plate slabs with unbonded tendons. A total of four 3,100 mm square specimens of 150 mm thick slab were fabricated with the variables of average compressive stress in concrete, tendon layout, and aspect ratio of the column stub. Based on the test results, the load-deflection relationship, patterns of cracks, strains of flexural reinforcement, and force increments in tendons were compared. In addition, the equations for punching shear strength of unbonded post-tensioned flat plate slabs specified in the design codes (ACI 318, Eurocode 2, Model Code) were evaluated in detail.

Punching Shear Strength Model for Reinforced Concrete Flat Plate Slab–Column Connection without Shear Reinforcement

AbstractMany existing studies on punching shear in a RC flat plate slab without shear reinforcement consider uncracked concrete in the compression zone or the aggregate interlock mechanism in the c...

Comparison of Environmental Impact of Three Different Slab Systems for Life Cycle Assessment of a Commercial Building in South Korea

The environmental impacts of the construction stage should be considered since a large amount of building materials are used to construct a building at this stage. Studies on the improvement of construction techniques or the application of newly developed construction methods for reducing the environmental impacts are relatively scant compared to other topics of studies. This study aimed to assess and compare the environmental impacts of the ordinary solid slab, the flat plate slab and the voided slab system during the construction phase. A process-based quantitative model was adopted to evaluate the environmental impacts and the comparative results were analysed to demonstrate the significant characteristics of the environmental impacts of the construction of slab in a building. The assessment results show that the environmental impacts from the ordinary solid slab are the highest and the voided slab system is the lowest among three slab systems. As the slab system of the studied building was replaced, it was shown that the environmental impact indicators showed the decreased tendency. Based on the results of environmental impact reduction from the ordinary solid slab, the flat plate slab and the voided slab system, the voided slab system would have the least environmental impact in all indicators.

Nonlinear finite element analysis of reinforced concrete flat plate punching using a thick-shell modelling approach

The punching shear resistance of reinforced concrete flat plates is an area where design is typically done in a highly-idealized manner, using provisions developed from experimental results of isolated slab-column connections; yet, involves structures where performance may be greatly impacted by system-level response. This paper presents the development and application of a practical thick-shell finite element-based nonlinear modelling procedure for reinforced concrete flat plate slab systems. Cracked concrete material modelling based on the formulations of the Disturbed Stress Field Model is employed in conjunction with computationally-efficient layered thick-shell finite elements that accommodate through-thickness shearing effects and are shown to be capable of capturing brittle punching-governed failure modes. A simple low-cost sectional analysis modification procedure is proposed to incorporate strength enhancements attributed to confining effects stemming from disturbances in slab-column connection regions. Load-displacement responses and failure modes developed using the proposed modelling procedure are shown to capture observed experimental responses and provide response estimates similar to those obtained using more costly three-dimensional solid continuum finite element modelling techniques. Finally, the analysis results presented were developed using simple-to-define concrete property input without the need for supplemental material model or analysis parameter calibration.

Analytical modeling and thermal performance analysis of a flat plate latent heat storage unit

The thermal performance of a flat plate latent heat storage unit (LHSU) consisting of parallel flat plate slabs of phase change material (PCM) was investigated with analytical techniques. The approximate analytical expressions of the heat transfer fluid (HTF) transient temperature distribution and the time wise solid-liquid PCM interface location were developed by solving the energy conservation equations and were validated by comparing the present results with fully converged numerical predictions and analytical solutions in published literature. An index of effective latent heat storage ratio, Er, which was defined as the ratio of the actual amount of available latent thermal energy before HTF outlet temperature reaches a specified value to the total latent heat storage capacity, was proposed to evaluate the thermal performance of a LHSU. The effects of geometric parameters and the thermal conductivity of PCM (kp) on Er were investigated. The results show that the analytical model is valid as the Stefan number is less than 0.15. Moreover, Er increases with the rise of the given dimensionless HTF outlet temperature and the enhancement of kp, and decreases linearly with the increase of HTF channel height and PCM slab thickness, with an abrupt change in the derivative of Er at an inflection point. A dimensionless criterion was proposed to help design thermally efficient flat plate LHSU. Additionally, we found that increasing PCM mass by lengthening the PCM slab could significantly improve Er, while thickening the PCM slab would lead to the opposite trend. This investigation provides guidelines for the optimal design of a flat plate LHSU.

Behavior of Sustainable Reinforced Concrete Building Containing Waste Plastic and Fibers

Plenty of waste plastic is one of the major problems for environmental sustainability as plastic contaminates the mainland, rivers, and seas. Moreover, many-sided behavior of waste plastic (lightweight, flexible, cheap, strong, and moisture-resistant) can make it a replacement for or alternative to coarse aggregate in concrete. This paper investigates the properties and strength of reinforced concrete flat plate slabs using recycled waste plastic as a coarse aggregate instead of the conventional aggregate to produce lightweight concrete. Also studying the effectiveness of adding polypropylene fibers for enhancing both concrete properties and shear strength of the reinforced concrete respectively in a flat slab. All specimens had the same dimensions and main flexural reinforcement ratio and they were subjected to concentrated vertical loads. Four mixes had been tested in this work, the results showed that using waste plastic mixed with polypropylene fibers to produce lightweight concrete was very promising. It was observed that by adding polypropylene fibers the failure pattern was shifted from punching to flexural. Ultimate load, crack pattern, and deflection had been included and discussed for all specimens.

Comparative Analysis for Building with Flat Plate Slabs and Void Slab using U-Boot Technology

The flat slab is gaining popularity among architects. The flat plate slab provides a way for architect to achieve completely flat ceiling with no beam protrusion. There is also improvement in the construction speed and cost savings from using this system which requires only simple formwork. But when load acting on the slab is large or clear span between columns is more so it is required to increase the slab thickness; hence the self –weight of slab is increased due to increased volume of slab and also more amount of steel is required to resist this increased weight of slab. Voided slabs eliminate concrete where it isn’t needed and the subsequent weight reduction due to this eliminated concrete makes longer span possible. In this study the design process for flat plate slab is compared with voided slab lightened with U-Boot Beton through a design comparison of total slab area 40m by 40m having panels of 10m by 10m and also the deformation of both type of slabs is analysed by using ETABS software.

Evaluation of Carbon Dioxide Emissions amongst Alternative Slab Systems during the Construction Phase in a Building Project

Global warming is now considered to be one of the greatest challenges worldwide. International environmental agreements have been developed in response to climate change since the 1970s. The construction industry is considered one of the main contributors to global warming. In order to mitigate global warming effects, the construction industry has been exploring various approaches to mitigate the impacts of carbon dioxide emissions over the entire life cycle of buildings. The application of different structural systems is considered a means of reducing the carbon dioxide emissions from building construction. The purpose of this research is to assess the environmental performance of three different slab systems during the construction phase. In this study, a process-based life cycle assessment (LCA) method was applied in order to evaluate the level of performance of the three slab systems. The results showed total CO2 emissions of 3,275,712, 3,157,260, and 2,943,695 kg CO2 eq. for the ordinary reinforced concrete slab, flat plate slab, and voided slab systems, respectively. The manufacturing of building materials is by far the main contributor to CO2 emissions, which indicate 3,230,945, 3,117,203, and 2,905,564 kg CO2 eq., respectively. Comparing the building materials in the three slab systems, reinforcing bars and forms were significant building materials to reduce the CO2 emissions in the flat plate slab and voided slab systems. In this study, reinforcing bars were the main contributor to lowering the carbon dioxide emissions in the flat plate slab and voided slab systems. The results of this study show that amongst all the three different slab systems, the voided slab system shows the greatest reduction potential. Moreover, replacing the ordinary reinforced concrete slab system by alternative methods would make it possible to reduce the carbon dioxide emissions in building projects.

Punching Shear Behavior of Interior Slab-Column Connections Reinforced with Vertical Bolts

Punching shear failure in flat plate slabs is considered as a vital topic to investigate. The fact that this failure is brittle makes it an essential field to study. Many researches have been carried out to investigate the punching shear of flat plate slabs. Nevertheless, using prestressing in enhancing punching behavior wasn't of such a big contribution. An experimental study for enhancing punching shear volume of interior slab-column links in flat plate slabs by prestressing is presented through a parametric study in this research. The parameters taken into consideration in this study are prestressed vertical studs of different number of rows. Through the experimental program, deformation features, the load carrying capacity, and the cracking patterns have been examined. A comparative study between the behavior of the improved slabs and their controls has been made. This study showed that the suggested system might be of a good benefit in practice to be used. A comparison between the experimental punching load and the calculated using various design codes has also been made. It offered acceptable agreement.

Increasing ultimate strength of reinforced concrete slab by using Reactive Powder Concrete and study the effect of high temperature on them

The main purpose of this search is to study the punching shear behavior of fourteen specimens of Reactive Powder Concrete (RPC) two-way flat plate slabs, half of these slabs have been exposed to a high temperature up to 400 C° by using an electric oven. All slabs have dimensions of (400x400x60) mm, with steel reinforcement mesh of (Ø6mm) diameter. Laboratory tests show that there is an increase in the value of First Crack Loading (FCL) and Ultimate Load (UL) by (208, and 216.67) % and a decrease in deflection by (56.85) % due using slab with complete reactive powder relative to a slap made of normal concrete. The use of the (RPC)mixture in layers in slabs gave results close to the slab which consists of full (RPC) this gives the benefit of more than the use of a slab that contains full reactive powder concrete in terms of cost, the increase was in FCL and UL by (130.8, 169.23, 102.7 and 135.135) % and a decrease in the value of deflection by (37.17, 47.64) %. The use of a partial reactive powder mixture also showed good results, and by increasing the dimensions of the RPC area, the results were better. the increase in FCL and UL by (54, 116, and 185) % and (53, 116.67, and 166.67) % and a decrease in value of deflection by (36.12, 42.4, and 50.26) % from reference slab. When slabs are subjected to high temperatures, there may be a decrease in the value of the FCL and UL and an increase in the value of deflection when compared to models not exposed to high temperature. But when compared to the reference slab with the same circumstance showed an increase in the value of the FCL and the rate ranged between (50- 200) % and the UL was the ratio ranged between (51.35-208.1) % and a decrease in the value of the deflection where the ratio ranged (21-46) %

Punching Shear Strength Characteristics of Flat Plate Panels Reinforced with Shearhead Collars: Experimental Investigation

This paper presents an experimental investigation on the punching shear strength of reinforced concrete flat plate slabs with shearhead collars. Eight reinforced concrete slab specimens were casted and tested under static load test, the load was applied at the center of slab by 100x100 mm steel column. The effect of the shapes, diameter and number of stiffeners has been discovered for shearheads through studying its effect on the load-deflection behavior, ultimate capacity, cracking load, failure mode, stiffness, ductility and energy absorption of tested specimens. The experimental results indicates that using square shearhead had achieved a slight increase in punching shear strength about 3% over that circular shearhead using the same surface area. Also, utilize 550 mm shearhead diameter will contribute to increase the punching shear strength about 14.5%. The increase in the number of stiffeners in specimen (CS4) had reduced the ultimate punching shear capacity by 20.3% over reference specimen. The first crack was decreased from 12.5kN to 7.5kN, when increases the number of stiffeners from one to two. The cracking load was increased with the increase of the diameter of circular shearhead from 10kN to 15Kn in specimens of 336mm and 550mm respectively. The specimen with 336mm diameter and 30mm height circular shearhead achieved 427 kN.m energy absorption, it is higher than the energy absorption of reference specimen by 2.6%. Also, using two stiffeners improved the energy absorption by 110.2% higher than the specimen with one stiffener.

Minimum thickness of flat plates considering construction load effect

In the construction of flat plate slabs, which are widely used for tall buildings but have relatively low flexural stiffness, serviceability problems such as excessive deflections and cracks are of great concern. To prevent excessive deflections at service load levels, current design codes require the minimum slab thickness, but the requirement could be unconservative because it is independent on loading and elastic modulus of concrete, both of which have significant effects on slab deflections. In the present study, to investigate the effects of the construction load of shored slabs, reduced flexural stiffness and moment distribution of early-age slabs, and creep and shrinkage of concrete on immediate and time-dependent deflections, numerical analysis was performed using the previously developed numerical models. A parametric study was performed for various design and construction conditions of practical ranges, and a new minimum permissible thickness of flat plate slabs was proposed satisfying the serviceability requirement for deflection. The proposed minimum slab thickness was compared with current design code provisions and numerical analysis results, and it agreed well with the numerical analysis results.

Non-linear finite element analysis of reinforced concrete flat plates with opening adjacent to column under eccentric punching loads

Nonlinear finite element analyses were performed on interior slab-column connections to investigate the effects on the punching strength of flat slabs. A total of twenty-seven three-dimensional finite element models were constructed to represent large-scale flat plate slabs (2000 × 2000 × 155 mm) subjected to concentric and eccentric punching loads. The main parameters in this study were the eccentricity of the load, the opening size, the location of the opening relative to the direction of the transfer moment, and the configuration of the reinforcement adjacent to the opening that is used to compensate the cutting bars. The dimensions and reinforcement of the slab and column were kept constant. Predictions of the numerical models were in good agreement with experimental results published in the literature for slab column connections subjected to concentric loading. The numerical investigation showed that the presence of an opening adjacent to a column in a specimen subject to concentric loads could cause a significant reduction in the ultimate shear capacity which increases with the increase in the size of the opening. Specimens with 250 × 250-mm size openings indicated a reduction of 35% in their ultimate shear strength capacity while specimens with 250 × 450-mm size openings indicated a reduction of 45%. Specimens without openings subjected to load eccentricities of 112.5 and 225 mm resulted in a reduction in the load capacity of 18 and 28%, respectively. It was found that providing continuous bars adjacent to the opening to compensate the cutting areas of reinforcement could result in a considerable improvement in the serviceability of the slab represented by an increase the stiffness of the slab-column connection and no significant effect on the punching capacity for the case of concentric loads. Finite element analyses performed are in good agreement with provisions in the building code (e.g., ACI-318) for the case when the opening is located parallel to the direction of the principal moment and provide conservative values when the opening is in the upward side of the bending moment.