Voided Slab Research Articles

Nonlinear behavior of existing pre-tensioned concrete beams: Experimental study and finite element modeling with the constitutive Serial-Parallel rule of mixtures

The performance of existing prestressed concrete (PC) beams and their time-dependent behavior have been concerns for bridge maintenance services. In this paper, laboratory tests of three PC void slab beams taken away from an obsolete bridge were conducted and an alternative more efficient finite element (FE) method was developed. In preparing the three beam specimens, two retained their original reinforced concrete (RC) overlay and one chiseled off its RC overlay. Through the four-point loading tests, the load response plots of the beams from elastic to plastic failure were carefully documented, including the strains along the mid-span section, the strains of longitudinal rebars and strands, and the mid-span deflection. The test results showed that no interface slip was observed between the RC overlay and the top of void slab during the whole loading process, and the yield load of the test beams with the overlay was approximately 45 % higher than that without the overlay. Regarding the proposed nonlinear numerical formulation, the modelling process avoided the treatment of complex reinforcement and prestressing tendon layouts. The prestressed concrete was simulated as a composite material whose behavior is depicted by a constitutive serial-parallel rule of mixtures (SP-RoM). The generalized Maxwell model and generalized Kelvin model were applied to calculate the time-dependent losses of prestress. All the developments have been implemented within the open-source FE code Kratos-Multiphysics environment and are fully available. Compared with the test outcomes, it shows that the numerical results are in good agreement with the solutions in terms of stiffness, load-deflection curves, and damage evolution. The differences between the experimental and numerical values of ultimate load for the specimens with and without RC overlay were all within 10 %. Furthermore, the proposed nonlinear models can also predict the time-dependent prestress losses of existing PC beams.

Toughness Characteristics of Microfiber-Based Geopolymer Concrete Voided Slabs under Soft Impact

Toughness Characteristics of Microfiber-Based Geopolymer Concrete Voided Slabs under Soft Impact

One-way shear strength design of flat-plate voided slabs

Current design standards do not include design provisions to handle the reduced shear capacity of voided flat-plates, and the current design practice considers its shear capacity as a percentage of the solid slab. The study presents an investigation of the one-way shear capacity of flat-plate voided slabs. The investigation is carried out using a compiled evaluation experimental database and an experimental program. A capacity reduction factor for flat-plate voided slabs, λvoid, is proposed and is a function of void height to the slab height (hvoid/h) ratio. The proposed factor is calibrated to the ACI 318-19 shear model. The proposed factor allows for section optimization based on shear capacity, where the height of the void former can be selected based on the shear load subjected to and the required shear strength. This is not possible using the current practice of the manufacturers, where they use either a constant capacity reduction factor or a factor that is slightly affected by the hvoid/h ratio. The model is applicable for voided slabs with a void former clear spacing of 0.10–0.16 of its diameter, or higher. Incorporating the reduction factor, λvoid, resulted in an average experimental-to-predicted (Vexp/Vpred) of 1.67 and COV of 16 %. By comparing the average Vexp/Vpred and COV of voided slabs to solid slabs, the strength reduction factor (ϕ) of 0.75 for shear will still be applicable.

Experimental Investigation on the Residual Flexural Behavior of 28-Year-Old Decommissioned Prestressed Concrete Voided Slab Girders

Experimental Investigation on the Residual Flexural Behavior of 28-Year-Old Decommissioned Prestressed Concrete Voided Slab Girders

Shear Reinforcement Effectiveness of One-Way Void Slab with the Hollow Core Ratio and Shear Reinforcement

Void slabs offer a promising solution for sustainable construction due to their reduced weight and potential for recycled materials. However, their inherent hollowness can compromise shear capacity compared to solid slabs. This study investigates the effectiveness of shear reinforcement in mitigating this vulnerability. Experimental testing with a four-point support loading confirmed shear failure in all specimens and revealed a significant reserve of shear strength exceeding predictions from ACI 318-14 by at least 1.436. This suggests the potential for more efficient designs that utilize less shear reinforcement while maintaining structural integrity. An inverse relationship between porosity and shear strength was observed, highlighting the importance of considering void content during design. Among established design codes (ACI 318-14, UBC 2, and CEB-FIP 1990), CEB-FIP 1990 provided the most accurate prediction of shear capacity for these reinforced hollow slabs. These findings offer valuable insights for optimizing the shear design of voided slabs. The observed strength reserve suggests the potential for reduced shear reinforcement while maintaining safety. Additionally, the influence of porosity and the code comparison provide crucial considerations for future design practices. This research paves the way for developing efficient and safe voided slab applications, promoting sustainability in the construction industry.

Two-way flexural behavior of biaxial voided slab using cuboidal shape of void formers

A biaxial voided slab is an innovative type of slab system developed recently, that has proven its excellence in terms of its structural, environmental, and economic benefits. In the present research, an experimental study was carried out to investigate the two-way flexural behavior of biaxial voided slab using the cuboidal shape of void formers. Two-way flexure test was performed over two voided slab specimens (VS-100 and VS-140) and one solid slab specimen using a new technique of sixteen-point loading. An innovative type of positioning reinforcement was used to fix the voids at their desired locations in voided slab. The ultimate load carrying capacity, deflection, flexural stiffness, and crack pattern were examined through experimental and theoretical investigations and compared the results with solid slab. Nonlinear finite element analysis was performed to validate the experimental results using ABAQUS software. Parametric study was undertaken to investigate the flexural performance of voided slab thoroughly; varying the factors like type of loading, positioning reinforcement, and grade of concrete. These investigations revealed that the voided slab with a cuboidal shape of void former exhibits classical flexural behavior which was same as that of a solid slab. Also, it was observed that yield line theory and the finite element model predicts the similar load-carrying capacity precisely enough with the experimental investigations. Parametric study reveled that prediction of ultimate load capacity of voided slab depends on type of loading, and with uniformly distributed loading predicting relatively higher load carrying capacity. Incorporating the proposed positioning reinforcement helps to improve the overall two-way flexural behavior of voided slab.

Reduced Volume Approach to Evaluate Biaxial Bubbled Slabs’ Resistance to Punching Shear

The bubbled slab, a type of reinforced concrete (RC) slab with plastic voids, is an innovative design that employs a biaxial distribution of voiding formers within the slab to reduce the slab’s self-weight while preserving a load-carrying capacity that is approximately comparable to that of solid slabs. This paper presents a new approach for figuring out the effective critical shear perimeter of voided slabs using the reduced-volume concept of concrete. This approach aims to reduce the coefficient of variation of the current design standards, namely the ACI 318-19 and Eurocode 2, for assessing the slabs’ resistance to punching shear. Our experimental program investigated the impact of voiding former patterns and the location of an opening near a column on the punching shear resistance of biaxial hollow slabs. The factors under consideration included the opening’s size, location, and distance from the loaded area, as well as the voiding formers’ placement concerning the critical shear boundaries. The results of experiments on 10 full-scale, 2000 × 2000 × 230 mm, reinforced concrete biaxial voided slabs with an opening are presented in this study. Two design expressions were used to estimate the biaxial hollow slabs’ shear strength. These expressions take into account the reduced volume of concrete and the distribution of voiding formers up to the section 4d from the periphery of the column. The proposed approach to determine the effective punching shear perimeter has the lowest coefficient of variation among the methods suggested by these standards. This indicates the validity of our proposed expressions. The coefficient of variation of the proposed expressions does not exceed 0.057.

Life-cycle thinking-based decision support framework for multispan simply supported bridges under typhoon-induced wave, current and surge conditions

Coastal bridges usually suffer from wave, current, and storm surge hazards simultaneously under typhoons. Comprehensive mitigation measures can reduce the structural failure probability under these hazards but usually lead to a conservative structural design and a significant increase in the project budget. With the recent development of sustainable structural design, the multicriteria decision-making method can assist engineers in incorporating the life-cycle investment and probability of hazards in the design selection. In this paper, a life-cycle thinking-based decision support framework that considers multicriteria trade-offs and sustainable design was proposed for the design of coastal bridges under typhoon-induced wave, current and surge conditions. The simulation of the typhoon-induced wave, current and surge conditions was developed using SWAN + ADCIRC model, joint probability and environmental contours. The multispan simply supported (MSSS) bridge was then used to illustrate the framework. The main findings include that the void slab girder is better than the other girder types in the equal-weighted, risk-averse and pro-economic scenarios for the example bridge, but the change in girder types has a small impact on the economic cost index score. The increase in the girder height can increase the failure probability when deck shifting dominates the superstructure's failure.

Flexural Behavior of Reinforced Concrete Voided Slabs Strengthened with Different Types of FRP: State-of-the-Art Review

Some reinforced concrete slabs may require rehabilitation or strengthening due to load increment caused by a change in the function for which they were built or unintentional errors during design or execution. There are numerous techniques for such problems. The rehabilitation or strengthening of structural members using fiber-reinforced polymer (FRP) is one of the most recent techniques. This technique is widely spread due to its high tensile strength and lightweight; also, the thickness of the strengthened structural member decreases when these materials are used. This paper provides a comprehensive review of several strengthening techniques in terms of their results, advantages, and the extent of their effect on the flexural behavior of voided concrete slabs. Research has shown that this type of strengthening contributes to improving the slabs’ performance, as it contributes to increasing the first crack load and the ultimate load, and it contributes to decreasing the value of the deflection corresponding to the ultimate load and improves the ductility and toughness of these slabs. Also, the flexural strength of these slabs increases with the number of strengthening layers used. CFRP is one of the best types of FRP. It was found that the presence of voids caused a decrease in the flexural strength and an increase in the deflection value; however, the process of strengthening with polymer fibers for this type of slab recovers and compensates for losses from the presence of voids.

Behavior of two-way reinforced concrete voided slabs enhanced by steel fibers and GFRP sheets under repeated loading

Moderately thick voided slab systems are used in the construction of long-span slab buildings to incorporate lower weight on foundations and enhance the thermal and sound insulation of the slab. In some cases, these slabs required an enhancement if there is an increase in the applied loads or a defect in their construction properties. This research is focused on giving better enhancement techniques for such cases with keeping the flexural ductile failure of the tested slabs. Eight slab specimens of (1000 × 1000 mm2) were cast and tested as two-way simply supported slabs. The tested specimens consist of one solid slab and seven voided slabs. The study variables comprised the nature of the slab (solid and voided), the thickness of the slab (100 and 125 mm), the presence of steel fibers (0% and 1%), and the number of GFRP layers. The voids in slabs were made using high-density polystyrene of dimensions (200 × 200 × 50 mm) with a central hole of dimensions (50 × 50 × 50 mm) to give the shape of donat. These voids are made at the ineffective concrete zones to give a reduction in weight by (34%–38%). The slabs were tested as simply supported slabs under partial uniform repeated loading. The results of tested specimens showed that the enhancement with a combination of steel fibers and GFRP sheets gave the least deflection (4.2 mm), higher ultimate loading capacity (150 kN), larger stiffness at cracking, and at ultimate load (52.5, and 35.7 kN/mm) respectively, more ductility index (1.35), and larger energy absorption (1098.7 kN mm)..At the same stage of loading, the effect of adding steel fibers by (1%) for voided slab leads to a decrease in the deflection by (30%) and increase the ultimate loads by (31%). Therefore the strengthening technique adopted in this research enhances the behavior of moderately thick voided slabs effectively and preserves a ductile flexural behavior.

Punching Shear Capacity of RC Biaxial Voided Slab – Prediction by Critical Shear Crack Theory

In this study the applicability of critical shear crack theory (CSCT) to biaxial voided slab is investigated, which predicts the punching shear capacity of solid slab. Based on the experimental results of biaxial voided slab available in the literature (40 specimens) the research is carried out. The experimental results showed that the load-rotation behaviour of biaxial voided slab is remain same as that of solid slab except for specimens with void located within 0.5d from face of the column. Further, the punching shear capacity of slab specimens with voids located beyond 2d distance from column face is almost the same as that of the solid slab. Depends on the available load-rotation data modified CSCT was developed depends on the location of the void from face of the column. The predictions were observed to be very scattered with a mean and standard deviation of 0.752 and 0.412, respectively. This is reasonable as the modified CSCT estimates the capacity with respect to the location of voids and ignores the area of void at the section considered. The CSCT approach needs to be further modified by including location and area of void to predict the punching shear capacity of biaxial voided slab with reasonable accuracy.

Sustainability Performance of Voided Concrete Slab Using Waste Plastic Bottles

The present study is aimed at investigating the cost assessment of incorporating waste plastic bottles in the manufacture of voided concrete slabs; assessing the depth ratio vis-à-vis the cost reduction of incorporating waste plastic bottles in the manufacture of voided concrete slabs; assessing the energy consumption and CO2 emission obtained by incorporating waste plastic bottles in the manufacture of voided concrete slabs; and evaluating the impact of the depth ratio on embodied energy consumption and CO2 emission. The study was conducted on five types of slab specimens made: (1) conventional solid slab specimens; (2) slab specimens incorporated with 5% air-filled plastic bottles; and (3) slab specimens incorporated with 10% air-filled plastic bottles. Slab specimens of size 1000×1000×150 mm thick incorporated with 0, 5, and 10% waste plastic bottles were considered for the analysis of sustainability with respect to cost, energy, and CO2 savings. As part of the findings, it was revealed that the incorporation of waste plastic bottles into concrete slabs results in a reduction in the cost and volume of concrete. Again, using recycled plastic bottles in the slabs saved money, but for each percentage of bottles used, additional materials (plastic bottles, chicken wire, etc.) and labour were needed, which added to the cost. It was also revealed that embodied energy and CO2 emissions decrease as the percentage of plastic bottles in the slab increases. The study has confirmed that the void slab made with plastic bottles is more sustainable than the traditional solid slab system when it comes to cost, energy use, and CO2emissions. Doi: 10.28991/CEJ-2022-08-11-09 Full Text: PDF

Transfer Matrix Method for Calculating the Transverse Load Distribution of Articulated Slab Bridges

Articulated slab bridges have been widely used by transportation administration for short-to-medium span bridges because of their good economy, convenient construction, and environmental advantages, while the presence of shear keys increases the complexity of structural behavior. Developing more reasonable analysis approaches of quick assessment, pre-design, and hand calculations for the articulated slab bridges is a challenge because of the peculiar shear key mechanism. This paper is devoted to presenting a recursive algorithm, based on the force equilibrium conditions of each individual slab, thus resulting in simultaneous equations of the transfer matrix method (TMM). In this procedure, the state vector is an array composed of vertical displacement, shear force, unit constant; and the transfer matrix contains the bending and torsional stiffness parameters of simply supported slabs. Then, the influence line of transverse load distribution (TLD) is calculated for each slab by introducing boundary conditions. To validate and verify the efficiency of the TMM algorithm, a transversely prefabricated void slab bridge with a span of 20 m is considered as a case study. The traditional force (FM) and finite element (FEM) methods are used for comparison and validation. It is demonstrated that the TMM can provide good results with higher algorithm efficiency by exempting the modeling tasks in FM and FEM and capture variations in TLD along the bridge’s span. In addition, the influence of the span length and relative stiffness coefficient of slabs on the TLD of articulated slab bridges are analyzed from the parametric analysis.

Analysis and Comparative Study of Conventional Slab With Voided Slab

Abstract— As the infrastructure is developing there is need for some changes in the construction field, as one cannot rely on the same method for a long time as it can have different consequences. The main consequence is the shortage of material and manpower. Also, money matters a lot in construction department along with it the machines, equipment and technology in some region is not at a level, which we want. Hence in order to satisfy these results Bubble deck slab is one of the most effective slab techniques to replace conventional slab in terms of money and materials. In this study a hollow shell is made by recycled plastic and is kept in the slab and comparison is to be done between voided slab and conventional slab regarding further points such as stresses at the centre and end of the slab, steel and concrete quantity is to be calculated and cost analysis is also done of both slabs by software such as Ansys or ETABS and cost analysis is done is done by hand. After that comparison of both void slab and conventional slab is shown. Keywords— Reuse of plastic, Use of plastic in construction sector, Environmental friendly, Void slab

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.

Flexural behavior of Two-Way voided slab

Slab is an essential part of a structure that consumes large quantity of concrete among all structural elements. Large self-weight of slab contrebutes to the larger dimensions of beams, columns & foundations which causes the increase in overall dead load and cost of structure. Voided slabs can be used as an economical and ecofriendly alternative to existing RCC slab systems. In voided slab concrete from the tension zone of the slab is removed partially; where concrete doesn’t have any structural benefit by creating voids using recycled plastic void formers. Therefore, self-weight of slab is decreased without changing the depth of slab, which in turns reduces the number of columns and offers more floor space for utilization. As it transfers lesser load on beams, columns & foundations, it reduces the overall sizes of all structural components and overall cost can be saved. In this study, finite element analysis is carried out using ANSYS Workbench 18.1. Five specimens are analyzed in this study out of which one of the slabs is a solid slab and the other four are voided slabs. Dice (cube) shaped voids are used as a void former in the biaxial voided slabs with variation in sizes and spacing between each other. The two-way flexural strength has been evaluated by applying sixteen point loading over full area of a slab. Load vs. deflection curves are plotted for each voided slab and compared it with solid slab. The flexural strength is evaluated using Rankine-Grashoff Theory and results are compared with the software results. The primary objective of the work is to study elastic behavior of voided slab and to compare it with solid slab. The present study proved that flexural behavior of voided slab with dice shaped void former shows good correlation with the solid slab system.

A numerical study on flexural behavior of biaxial voided slabs containing steel cages

Several roofing systems have been proposed given their significance in concrete structures, in terms of time and resources. A biaxial voided slab system is introduced to improve the solid slab system's performance by creating voids in the concrete and removing ineffective material. In this study, the bending behavior of voided slabs is investigated numerically. For this purpose, a numerical ABAQUS model is presented and then verified using available experimental results. Then, a parametric study was carried out focusing on the plastic balls and their spacing, steel cages, and the position of plastic balls relative to the slab height. As shown in this paper, the presence of plastic balls improves the flexural capacity, because of steel cages. However, the spacing between plastic balls and their position have not a significant effect on flexural behavior. Finally, the numerical results were compared with the ultimate moment capacities from ACI 318-19, AS 3600-18, EC2 2004, and CSA A23.3-19, and were shown that considering steel cages have better consistencies with numerical results.

Quasi-static analysis of biaxial voided slabs with openings

In this paper, 3D nonlinear finite element analyses (FEA) were conducted using the ABAQUS program to investigate the openings’ influences on voided slabs’ structural behaviors. In these FEAs, the quasi-static solution was adopted, and the concrete behavior was represented by the concrete damaged plasticity model (CDPM). CDPM parameters were calibrated versus voided slab's test results taken from the literature. The calibrated FEA model's efficiency to describe the opening effect was then verified by matching with external experimental observations of conventional slabs with openings. Finally, a parametric study was implemented, in which eleven slabs’ models with or without openings were contrasted. The considered variables were the size, shape, arrangement, and location of openings. The FEA results showed that the openings adversely affected the mechanical properties of voided slabs, and they became more influential as the interrupted reinforcement bars due to openings increased. However, constructing the opening near the support far away from the zone of high flexural stresses resulted in slight deteriorations in the strength, stiffness, and toughness of voided slabs.

Construction Waste Reduction through Application of Different Structural Systems for the Slab in a Commercial Building: A South Korean Case

Construction waste generation along with the extensive consumption of natural resources has propelled researchers to investigate effective measures for minimising the waste. While several studies have shown that the structural design would be an influencing factor on the carbon dioxide emissions of a building, there is a lack of studies to corroborate the effect of different structural systems to generate waste during the construction stage. This article seeks to bridge some of the knowledge gaps regarding the waste generation from different structural systems during the construction phase in a building project in South Korea and demonstrate its potential for waste reduction. In this study, the amount of waste generation during the construction phase was calculated based on the quantities and the material loss rate of each building material to estimate the quantity of construction waste by the changes in the application of different structural systems for the slab of the studied model. The total waste generation during the construction phase of the different slab systems shows that the solid slab system produces the largest amount of construction waste, which is 101,361.385 kg. On the other hand, the void slab system generates 87,603.958 kg of the construction waste, which is the lowest amount among the four variables of this study. The additional purchasing costs due to the loss of construction materials indicate that the solid slab system would require 80,709.76 USD, which is the highest value of the four variables in this study. The void slab system would cost USD 50,054.12 for additional materials purchasing costs, which is approximately 38% lower than the solid slab system.

Investigation of the behavior factor of Reinforced Concrete Moment Frame with concrete Voided slab constructed by Spherical and Cubic Balls

In order to prevent damage caused by earthquakes in different types of structures including concrete structures, various methods are used by structural engineers considering terms of design and working conditions. Simple slabs, bubble hollow slabs (Spherical) and Cubic hollow slabs may be used to meet the structural requirements and also to increase performance level of the structures against earthquakes. This research aimed to evaluate the performance of these structures in different conditions and evaluate their impact on the structural behaviour coefficient. For this purpose, ABAQUS finite element software has been utilized to model a concrete moment frame with one span in one floor equipped with simple concrete slab, Spherical and Cubic hollow slabs in different conditions. Then the required analysis has been performed to evaluate the behaviour of these different type slabs. Verification of the model is implemented According to the study of Leimam et al. Then, in different models, the coefficient of structural behaviour is calculated and studied. The results show that using Cubic and Spherical slab could increase the behaviour coefficient of concrete moment frame in comparison with simple slabs. In the case of concrete moment frame with Cubic and Spherical slab, behaviour coefficient increases 32.79% and 46.3% respectively.