Biaxial Slab Research Articles

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.

SPECIFIC BENDING STIFFNESS COMPARISON OF SPHERICALLY VOIDED BIAXIAL CONCRETE SLABS AND SOLID SLABS

Spherically hollow or voided biaxial concrete slab (SVBS) configurations that implement empty composite balls as a filling material are gaining momentum due to the reduction in mass-to-capacity and mass-to-stiffness fractions. The SVBS configuration depends on taking out the ineffective concrete mass near the mid-section of a floor in which bending stress is less. This will in turn dramatically reduce the overall structural dead weight. This paper presents comparison of normalized bending stiffnesses for a representative spherically voided biaxial concrete slab with its counterpart solid slab. A representative SVBS element is chosen for capturing the volume action (RVE). The RVE is the primary sub-unit that is periodic and it is modeled in finite element software to determine the stiffness values noting that the SVBS is macroscopically similar, elastic in the linear range, and exhibits isotropic behavior transversely with no thermal stresses. An example SVBS system is shown to be more efficient with 16% higher normalized (specific) stiffness values when compared to solid slabs of equal thicknesses.

Epsilon-near-zero characteristics of near-field radiative heat transfer between α-MoO3 slabs.

Epsilon-near-zero (ENZ) materials, which manifest a wealth of exotic optical characteristics, have attracted significant research interest in recent years. However, these characteristics have rarely been considered in the study of near-field radiative heat transfer (NFRHT). In this work, we investigated the ENZ characteristics of the NFRHT between two symmetric biaxial α-MoO3 slabs. The numerical results show that the NFRHT is greatly enhanced around the ENZ frequency of 1.604 × 1014 rad s-1. Notably, near the other two ENZ frequencies (1.832 × 1014 rad s-1 and 1.891 × 1014 rad s-1), only the NFRHT between α-MoO3 slabs of certain thicknesses is enhanced. The reasons can be explained by the fact that the VHPs can be excited in almost all azimuthal angles at angular frequencies of 1.604 × 1014 rad s-1 and 1.891 × 1014 rad s-1. For the ENZ frequency of 1.832 × 1014 rad s-1, the VHPs can be excited at the top and bottom, while the SHPs excited at the left and right sides. It is worth noting that both the hyperbolic and ENZ characteristics affect the NFRHT between α-MoO3 slabs. Moreover, the excitation is strongly dependent on the thickness of the slab. Our findings contribute to understanding the physical mechanisms underlying the characteristics of the NFRHT at ENZ frequencies.

Comparative analysis of two models for phonon polaritons in van der Waals materials: 2D and 3D.

Phonon polaritons with ultralow losses and high confinement in extremely anisotropic media have opened up new avenues for manipulating the flow of light at the nanoscale. Recent advances in var der Waals (vdW) materials reveal unprecedented dispersion characteristics of polaritons using a two-dimensional (2D) model, treating the slab as a surface without thickness. However, the difference between the 2D and three-dimensional (3D) models of hyperbolic polaritons remains largely unexplored. Herein, we compare the polaritonic difference between these two models for biaxial vdW slabs. In addition, we demonstrate that the fundamental mode in slab configuration corresponds to the polaritonic mode in surface sheet and higher-order modes vanish in the latter configuration. In particular, we reveal that the difference in in-plane polaritons along the [100] and [001] crystal directions between the two models is associated with the inverse of the dielectric function along these two directions. For example, we compare the near-field radiative heat transfer (NFRHT) between two vdW slabs based on these two models. It is found that when the attenuation length of the higher-order hyperbolic mode is less than the gap distance, the enhancement achieved using the 3D model comes from only the fundamental mode, resulting in a negligible difference between these two models. Therefore, our findings may help to understand in-plane anisotropic polaritons and provide guidance for the application of the 2D model in the analysis of vdW materials.

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.

Twisted Polaritonic Crystals in Thin van der Waals Slabs

AbstractPolaritons – hybrid light–mater excitations – are very appealing for the confinement of light at the nanoscale. Recently, a particular interest has been focused on thin anisotropic slabs of van der Waals (vdW) materials supporting polaritons with hyperbolic dispersion, which can exhibit ultrahigh momenta and strongly directional in‐plane propagation and thus promise novel nano‐optical applications in a planar geometry. However, the excitation and manipulation of in‐plane hyperbolic polaritons have not yet been well studied and understood. Here, twisted polaritonic crystals (PCs) are introduced – lattices with periods comparable to the polaritons wavelength rotated with respect to the natural vdW crystal axes – to efficiently excite and control in‐plane hyperbolic polaritons. A general analytical theory valid for an arbitrary PC made in a thin biaxial slab is developed and the excitation of Bragg resonances tunable by the twisting angle is demonstrated. The findings open novel avenues for both fundamental studies of PCs in vdW crystals and the development of midinfrared sensing and photodetection applications.

Analysis of Goos–Hänchen shift from an orthorhombic anisotropic slab with/without topologically insulating surface states

A Goos–Hänchen shift (GHS) due to an orthorhombic biaxial slab with/without topological conducting states placed in isotropic media was investigated. The effect of varying host media, changing topological conducting states, and left/right asymmetries on the co/cross-polarized reflection coefficients and the corresponding GHS was investigated. Numerical calculations revealed that large negative/positive GHS occurs near the reflectance dips (local reflectance minimum) due to sudden changes in the amplitude of the reflection coefficient. Position and amplitude of the GHS near these reflectance dips are affected by anisotropy and surface admittance. Furthermore, numerical calculations also revealed that the GHS is left/right symmetric for an orthorhombic biaxial slab with/without topological conducting states. However, if the optic axes of a slab with/without a topological conducting state are rotated along any direction, the resulting GHS becomes left/right asymmetric.

Active Tuning of Highly Anisotropic Phonon Polaritons in Van der Waals Crystal Slabs by Gated Graphene

Phonon polaritons (PhPs) -- lattice vibrations coupled to electromagnetic fields -- in highly anisotropic media display a plethora of intriguing optical phenomena (including ray-like propagation, anomalous refraction, and topological transitions, among others), which have potential for unprecedented manipulation of the flow of light at the nanoscale. However, the propagation properties of these PhPs are intrinsically linked to the anisotropic crystal structure of the host material. Although in-plane anisotropic PhPs can be steered (and even canalized) by twisting individual crystal slabs in a van der Waals (vdW) stack, active control of their propagation via external stimuli presents a significant challenge. Here, we report on a technology in which anisotropic PhPs supported by biaxial vdW slabs are actively tunable by simply gating an integrated graphene layer. Excitingly, we predict active tuning of optical topological transitions, which enable controlling the canalization of PhPs along different in-plane directions in twisted heterostructures. Apart from their fundamental interest, our findings hold promises for the development of optoelectronic devices (sensors, photodetectors, etc.) based on PhPs with dynamically controllable properties.

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.

Analytical approximations for the dispersion of electromagnetic modes in slabs of biaxial crystals

Anisotropic crystals have recently attracted considerable attention because of their ability to support polaritons with a variety of unique properties, such as hyperbolic dispersion, negative phase velocity, or extreme confinement. Particularly, the biaxial crystal $\alpha$-MoO$_3$ has been demonstrated to support phonon polaritons, light coupled to lattice vibrations, with in-plane anisotropic propagation and unusually long lifetime. However, the lack of theoretical studies on electromagnetic modes in biaxial crystal slabs impedes a complete interpretation of the experimental data, as well as an efficient design of nanostructures supporting such highly anisotropic polaritons. Here, we derive the dispersion relation of electromagnetic modes in biaxial slabs surrounded by semi-infinite isotropic dielectric half-spaces with arbitrary dielectric permittivities. Apart from a general dispersion relation, we provide very simple analytical expressions in typical experiments in nano-optics: the limits of short polaritonic wavelength and/or very thin slabs. The results of our study will allow for an in-depth analysis of anisotropic polaritons in novel biaxial van der Waals materials.

Voided Biaxial Slabs - State of Art

A bubble deck slab is a technique of realistically disposing the concrete in the center of the slab, which does not perform any structural role, thus significantly reducing the dead weight of the structure. High-density hollow voids of polyethylene replace the actual concrete in the middle of the slab, as a result reducing the dead load and productivity of the slab will be increased. This paper reviewed the numerous studies have been prepared on voided biaxial slab system. conventional Slab are a standout amongst the most widely recognized parts in present day building development devouring a large portion of the concrete. The Advantages are lower power as comparison consumption than conventional slab - in both production, transport, emissions gases especially CO2 and reducing materials, load, cost reduction and it is ecological structure element. A range of recycled plastic bubbles allows columns spacing of 50% without any symptoms. This offers a wide range of benefits and construction cost. The bubble system usually combines the benefits of the industrial elements in the controlled conditions with the completion of the final concrete site, leading to a finalized floor slab.

Investigation of flexural and shear behaviors of biaxial voided slabs containing steel cages

AbstractIn some of biaxial voided slabs, spherical or ellipsoidal plastic balls enclosed in steel cages are used to eliminate ineffective concrete. To investigate the bending and shear behavior of this system, five full‐scale specimens were cast including two bending specimens for investigating bending capacity and cracking distribution as well as three shear specimens used to study the shear capacity, cracking distribution, and concrete casting effect on the shear behavior. Moreover, the effects of the steel cage rods were studied on the bending and shear capacity. It was found that while both solid and biaxial voided specimens exhibited almost similar failure mode, both the bending and shear capacity of biaxial voided specimens were affected by the steel cages. In contrast, the voided specimens exhibited a significantly lower shear capacity than the solid ones while the different concrete casting methods had no effects on the capacity and behavior of biaxial voided specimens. Finally, a comparison was made with experimental results and ACI 318‐14, MC 2010, and Eurocode 2 recommendations.

Effect of void former shapes on one-way flexural behaviour of biaxial hollow slabs

The Two-way hollow slab system (biaxial voided slab) is an innovative slab system, being adopted all over the world as an alternate for the conventional solid slab. It reduces the self-weight up to 50% in comparison with solid slabs without significant change in its structural performance. The voided slab consists of void formers in shapes like spherical, donut, and cuboid. Experimental and analytical investigations were carried out to study the behaviour of biaxial voided slab under one-way flexure. Voided slab specimens were prepared and tested with two different shapes of voids namely sphere and cuboid, which were manufactured using recycled polypropylene. Comparison of experimental and analytical studies showed that the ultimate load-carrying capacity of voided slabs was higher or similar to that of solid slab. An analytical study was carried out using the yield line analysis in conjunction with Indian Standards. It was found that the capacity of voided slab can be estimated by yield line analysis. The flexural stiffness of voided specimen is approximately 50% lesser in comparison with solid slab of identical dimensions and reinforcement at yield stage. The reduction in flexural stiffness is mainly due to the presence of void former and the maximum void ratio at a section defines the flexural stiffness of the voided slab. Nevertheless, the deflection is under serviceable limit for both the specimens for 75% of ultimate load. Ultimately, it is found that the behaviour of voided slabs under one-way flexure can be predicted by provisions of Indian Standards with necessary correction for loss of cross-section caused by voids.

MACROMECHANICAL ANALYSIS OF SPHERICALLY VOIDED BIAXIAL CONCRETE SLABS

The use of spherically voided biaxial concrete slab (SVBS) system, which uses hollow plastic balls as infill material, has increased widely because of its reduced weight-to-strength and weight-to-stiffness ratios when compared to solid concrete slabs. However, SVBS is a heterogeneous composite structure in which building a representative continuum model poses a significant challenge. To mitigate this challenge, the feasibility of determining the macromechanical structural behavior of spherically voided biaxial concrete slabs is studied using plate theories, aided by mechanical properties that were determined from a homogenization process of the representative volume element (RVE). This paper presents numerical analysis results of SVBS using both Mindlin-Reissner (thick) and Kirchhoff-Love (thin) plate theories. The results from both theories predicted the slab behavior reasonably well and they were within 10% of each other with the exception of the prediction of the twisting moment. Possible explanation of this deviation is provided in the paper.

Experimental and analytical investigation of punching shear capacity of biaxial voided slabs

Biaxial voided slab is an emerging slab system which reduces its self-weight up to 50% in comparison with the conventional reinforced concrete solid slab. The reduction in the concrete volume does not affect its flexural capacity significantly, however, it reduces both one-way and two-way (punching) shear capacity about 40%. Therefore, an effective way of predicting the punching shear capacity is investigated as the presence of voids alters the critical failure section. The applicability of conventional methods for solid slabs in the design standards, such as ACI 318 (2014), EN 1992-1-1 (2004) and IS 456 (2000) to predict the punching shear capacity of the voided slab is examined. In addition, eight full-scale specimens were tested with the sphere and cuboid shape of voids. Finally, experimental results of present study and test data collected from literature (33 specimens) were compared with predictions by the relevant code provisions. The estimation of punching shear capacity of biaxial voided slab by existing provisions for solid slabs in standards does not lead to satisfactory results. Hence, the presence of voids is considered by modifying the critical section depending on the void location. Further, only the effective concrete area is considered to predict the punching shear capacity. After the modifications, the predictions by all three building standards lead to satisfactory results.

Vibration Control Performance Analysis and Shake‐Table Test of a Pounding Tuned Rotary Mass Damper under the Earthquake

The voided biaxial concrete slab has been widely used in the engineering field. The slab has become a popular choice for designers and architects looking to reduce slab thickness and overall structure weight recently. Utilizing the empty space in the voided slab and introducing the structural control technology of mass damper into it, a new pounding tuned rotary mass damper (PTRMD) is proposed in this paper. This damper is designed to locate in the prefabricated hollow module to mitigate response of structure subject to disastrous excitations. The damper combines the characteristics of pounding mechanisms (PMDs) and tuned rotary mass dampers (TRMDs). This is achieved by a ball rolling on a curved orbit and a fixed stroke‐limiting plate. The structural control performance of the PTRMD is studied numerically and verified experimentally. Specifically, first, the motion equations for a single‐degree‐of‐freedom (SDOF) and multiple‐degree‐of‐freedom (MDOF) system with PTRMDs are derived. Furthermore, numerical results show that the PTRMD provides significant energy dissipation, and thus, is quite effective in reducing the structure response. Besides, the PTRMD generally exhibits better control performance and robustness in terms of vibration suppression compared with the TRMD proposed by the authors before. Finally, a shake‐table test is conducted to verify the damping effect of a PTRMD‐controlled SDOF system. Pertinent results confirm the effectiveness and robustness of PTRMDs for structural control.

Experimental Study on Voided Biaxial Slab and its Application

Experimental Study on Voided Biaxial Slab and its Application