Slab Thickness Research Articles

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.

Application of Foamed Concrete and Cold-Formed Steel Decking as Lightweight Composite Slabs: Experimental Study On Structural Behaviour

This paper presents an investigation of ultimate load, maximum deflection and failure mode of foamed concrete composite slabs (FCCS). Of interest are the effects of dry density and slab thickness. Unlike conventional composite slabs, FCCS has the advantage of eliminating the selfweight penalty and thus reducing the underlying structural members.With the advanced research in concrete technology, foamed concrete with sufficient strength propertiesto meet the requirements of standard code of practise has been successfully introduced. Foamed concrete isknown for its lightweight and versatility.In the experimental study, the slab specimens with a span of 1800 mm, a width of 840 mm and different slab thicknessesof100 mm to 150 mm were prepared for the three-point bending test. The dry density of foamed concrete is 1400 kg/m3, 1600 kg/m3, and 1800 kg/m3, which has a compressive strength of about 20 MPa to 40 MPa. Dry density and slab thickness have been observed to have significant effects on ultimate load and maximum deflection. Higher dry density of foamed concrete provides better slip resistance and thus reduces shear bond failure. On the other hand, slab specimens with a higher slab thickness tend to have better bearing capacity due to greater bending stiffness. The main failure mode is dominated by localised bending on the profiled steel deck, slip-displacement and fracture ofthe foamed concrete.

Mapping the Spectral and Mineralogical Variability of Lunar Breccia Meteorite NWA 13859 by VNIR Reflectance Spectroscopy

We provide the first visible near-infrared (VNIR) reflectance spectroscopy characterization of a sample from the lunar feldspathic breccia NWA 13859. The sample is a 2 mm thick slab with an approximate area of 35 ± 2 cm2. We characterized the spectroscopic variability by choosing and analyzing representative spots throughout the sample. Our results show a distinct spectral contribution from orthopyroxene, which, according to a preliminary mineralogical characterization, should be a minor phase in the sample. In a second step, we measured several spectra along a transect between a clast and the matrix. In order to oversample the signal, the points analyzed along the sample were partly superimposed to each other (80% areal superposition). The same approach was extended to a grid of points covering an area of about 8.6 cm2, with the goal of obtaining a spatial resolution of the spectral parameters higher than the instrument’s spot size. Using this strategy, we obtained 2D maps of spectral parameters, which allowed us to infer the major mineralogical composition of the sample.

Numerical assessment of an enhanced stiffened extended end-plate joint for composite frame structures

This paper presents the numerical assessment of a novel enhanced Bolted Stiffened Extended End-Plate (BSEEP) connection for steel frames with composite beams and H-shaped columns in the strong direction. Strain demand is a critical local response that directly controls rupture initiation, and it is more crucial in composite beams since the neutral axis shifts upwards due to the composite action. The proposed connection, called URBS-BSEEP, employs a reduced section in the beam upper flange to mitigate the strain demand problem and provide a stable and symmetric plastic hinge in the desired location. Nonlinear FEM is employed to study joint cyclic behavior. Eleven specimens are designed to compare the proposed connection with existing configurations and to investigate the effects of the slab isolation from the column, shear stud removal, reduced section geometry, and slab thickness. Hysteresis curves, ductilities, failure modes, strain profiles, and energy dissipation capacities are compared. The results indicate the superior performance of the connection compared to the conventional counterparts.

The DISCS method for perforation simulation of thin metallic plates by a rigid projectile

The DISCS method had been developed for penetration analysis of an axisymmetric projectile with a slender nose into a semi-infinite medium. Recently, the authors developed an approximate approach to assess perforation of concrete slabs of finite thickness, using the DISCS method. The present paper extends the approximate model to the perforation analysis of ductile metallic thin plates and determines the key parameters of the projectile residual velocity, the target perforation limit, and the ballistic limit. The present investigation focuses on thin metallic plates, the thickness of which is considerably smaller than that of the concrete slabs and smaller in comparison to the projectile nose length. The method is rather simple, easy to implement and provides a fast solution. An idealized target is characterized by a set of discs of small thickness responding in the plate plane, disregarding the local damage around the penetration ductile hole. The in-plane response of the discs during penetration and perforation of an idealized target are calculated. The Residual Velocity upon perforation of the Idealized Target (RVIT) is lower than the residual velocity of the real plate since it disregards the local damage, hence, the RVIT is the lower bound of the true residual velocity of the real perforated thin plate. Therefore, a positive RVIT for the thin plate with a given thickness indicates right away that the real target will be perforated. Using the RVIT parameter, the proposed DISCS method turns into a series of RVIT-perforation problems of plates with thicknesses that are smaller than the real thickness, to determine the decreasing RVIT with increasing thickness, until the full thickness is considered. The analysis is carried out using the modified (hybrid) DISCS method, that aims at analyzing penetration depth into a thick target. The analysis is based on the theoretical field equations and the constitutive equations of the plate material. The proposed method is based on a theoretical model and on engineering insight. Neither empirical constants nor any calibrations are required. Validation of the proposed method is carried out thorough comparisons with numerous test data on ductile aluminum and steel plates of different thicknesses that are struck by rigid projectiles at different impact velocities. All the comparisons demonstrate very good correspondence between the proposed method predictions and the test data.

Spatial variations of effective elastic thickness of Eastern Arabia: Implications for lithospheric weakening in the Oman-UAE mountain belt

The continental lithosphere of the Arabian Plate has evolved through a long and complex tectonic history and comprises major geological features such as an ophiolite complex, Cenozoic basalt extrusion, and Proterozoic basement outcrops. In eastern Arabia, an NW-SE to N-S oriented orogenic belt is present in Oman and the United Arab Emirates (UAE). The mountain belt formed due to the Late Cretaceous obduction of the Semail ophiolite, where a thick slab of oceanic crust and upper mantle was emplaced on the rifted Arabian continental margin. However, the mechanical strength of the lithosphere over the entire region is poorly known. In this study, we employ Bouguer gravity anomaly and topographic data, along with data on crustal properties obtained from teleseismic analyses, to assess the spatial variations in the effective elastic thickness (Te) of the eastern Arabian Plate. The joint inversion of coherence and admittance yielded Te values ranging from 10 to 50 km and an initial subsurface-to-surface load ratio (F) of 0.1 to 0.8. Te values in the southern part of eastern Arabia are low (< 20 km), while the northeastern regions of Saudi Arabia, the UAE, and Qatar exhibit intermediate to high Te values ranging from 30 to 45 km. The Oman-UAE mountain belt is associated with an intermediate Te of 30 km in the northern segment and a low Te of 20 km in the southern segment. The reduction in Te observed along the strike of the mountain belt suggests weakening of the lithosphere during the obduction of the Semail ophiolite. Te correlates well with both the seismic thickness of the lithosphere (Ts) and the decrease in shear-wave velocity at a depth of 150 km. The seismogenic thickness in eastern Arabia, however, is about 15 km, which is significantly less than Te and shows that both the crust and upper mantle contribute to the strength of the continental lithosphere. The Ts/Te ratio ranges from 1 to 9, with a maximum peak at 3–5, which is similar to the results observed for the oceanic lithosphere.

Enhanced radiative heat transfer via the coupling of multi-particle interactions with combined surface models

Radiative heat transfer (RHT) has been playing a pivotal role in the study of all length scales from macroscopic to microscopic. This work aims to theoretically enhance the RHT between nanoparticles in multi-particle and slab systems. The results show that the strong coupling between the multi-particle interactions and the combined slab surface modes including transmission and reflection can significantly enhance the inter-particle RHT at a proper slab thickness, and the maximum amplification ratio can reach up to two orders of magnitude. For larger thicknesses of the slab, the RHT decreases due to the weakening of coupled evanescent models. In addition, we show that adding graphene sheets to both sides of the middle slab produces a surface hybrid model, which can regulate the coupling properties of the multi-particle and slab by changing the chemical potential of graphene. When the resonance frequency of nanoparticles is higher than that of the slab model, the RHT between the particles at both ends increases. Instead, the conclusion is the opposite. This work may exhibit potential applications for enhancing, guiding, and regulating contactless energy management in complex many-body systems at mesoscopic scales.

Practical flexural design approach for one-way hybrid fiber-reinforced concrete slabs based on a parametric study on slenderness limits

Fiber-reinforced concrete (FRC) is increasingly used for structural applications. Slabs are a particularly attractive use for FRC due to a potentially increased redistribution capacity, as well as the efficient cracking control that fibers provide. However, methods for reliably establishing slenderness limits of such elements are missing. Therefore, in this study, a previously developed closed-form solution for slenderness limits of hybrid FRC (HFRC) slabs (steel reinforcement bars and steel fibers) is presented and updated. Subsequently, a comprehensive parametric study on one-way solid slabs is performed, drawing clear conclusions on which parameters are the most influencing and offering a practical flexural design approach in the form of graphs and tables for determining minimum thicknesses of HFRC slabs that may be used as design aids for practitioners.

Effect of Transverse Base Width Restraint on the Cracking Behavior of Massive Concrete

The effect of considering the third dimension in mass concrete members on its cracking behavior is investigated in this study. The investigation includes thermal and structural analyses of mass concrete structures. From thermal analysis, the actual temperature distribution throughout the mass concrete body was obtained due to the generation of heat as a result of cement hydration in addition to the ambient circumstances. This was performed via solving the differential equations of heat conduction and convection using the finite element method. The finite element method was also implemented in the structural analysis adopting the concept of initial strain problem. Drying shrinkage volume changes were calculated using the procedure suggested by ACI Committee 209 and inverted to equivalent temperature differences to be added algebraically to the temperature differences obtained from thermal analysis. Willam-Warnke model with five strength parameters is used in modeling of concrete material in which cracking and crushing behavior of concrete can be included. The ANSYS program was employed in a modified manner to perform the above analyses. A thick concrete slab of 1.5m in thickness and 10m in length was analyzed for different widths 2, 4, 8, and 10m to produce different aspect ratios (B/L) of 0.2, 0.4, 0.8, and 1.0 respectively. The results of the analyses show an increase in cracking tendency of mass concrete member as the aspect ratio of the same member is increased due to the effect of transverse base restraint. Accordingly, such effect cannot be ignored in the analysis of base restrained mass concrete structures subjected to temperature and drying shrinkage volume changes.

The Machine-Learning-Based Prediction of the Punching Shear Capacity of Reinforced Concrete Flat Slabs: An Advanced M5P Model Tree Approach

Reinforced concrete (RC) flat slabs are widely employed in modern construction, and accurately predicting their load-carrying capacity is crucial for ensuring safety and reliability. Existing design methods and empirical equations still exhibit discrepancies in determining the ultimate load capacity of flat slabs. This study aims to develop a robust machine learning model, specifically the M5P model tree, for predicting the punching shear capacity of a RC flat slab without shear reinforcement. A comprehensive dataset of 482 experimentally tested flat slabs without shear reinforcement was gathered through an extensive literature review and utilized for the development of the M5P model. The model takes into account influential parameters, such as slab thickness, longitudinal reinforcement ratios, and concrete strength. The performance of the proposed M5P model was compared with existing design codes and other empirical models. The comparison highlights that the developed M5P model tree provides a more accurate and reliable prediction of the punching shear capacity of RC flat slabs. This study contributes to the advancement of structural engineering knowledge and has the potential to improve the design and safety assessment of concrete flat slab structures.

Study on flexural behavior of BFRCM-autoclaved aerated concrete composite slabs: Effects of slab and strengthening thickness

Using basalt fabric-reinforced cementitious matrix (BFRCM) to strengthen existing masonry or concrete structures has become increasingly popular in recent years. To address the structural problems (e.g., easy cracking) caused by low tensile and flexural strength in autoclaved aerated concrete (AAC) slabs, this study demonstrates the results of an experimental and analytical investigation on the flexural behavior of BFRCM-AAC composite slabs. A group of unreinforced and five groups of composite specimens were prepared and subjected to four-point bending loads. The variables considered in the study were the thickness of BFRCM layer and slab thickness (cross-sectional height). Failure pattern, load–midspan deflection curves, and flexural performance indices of AAC slabs were compared and discussed. In general, the external BFRCM layer can significantly improve the first cracking load and peak load of AAC slabs. With the increase of BFRCM overlay thickness (reinforcement ratio), the ultimate deflections of composite slabs decreased. Finally, the results obtained from the present investigation, such as the approximately linearly distributed strain on the cross section, allowed the use of plane cross section hypothesis to predict the flexural strength of BFRCM-AAC composite slabs.

Performance of bridge approach system under a moving tandem load-numerical analysis

With one end supported by the sleeper slab and the other end supported by the bridge abutment, the approach slab provides a smooth transition between the bridge abutment and its adjacent pavement. Therefore, the sleeper slab, embankment soil, and bridge abutment support the truckload on the approach slab together. However, load distributions among these three supporting components have not been investigated thoroughly yet, especially, as the truckload approaches the bridge. In this study, a simulation model was constructed and validated based on a field case study. Then, the performance of the pavement, sleeper slab, and approach slab (i.e., the approach system) was explored as a tandem load approached the bridge abutment. Finally, the effects of some parameters on the approach system performance were investigated and these parameters included the embankment and foundation soil elastic modulus, connection type between the approach slab and bridge abutment, pavement and approach slab thickness, sleeper slab layout, and sleeper slab width. According to this study, increasing the pavement and approach slab thickness and integrally connecting the approach slab with the bridge abutment increased the load transferred to the bridge abutment; while increasing the foundation soil elastic modulus decreased the load transferred to the bridge abutment. In addition, when placing one-half of the sleeper slab under the pavement, contact stresses under the sleeper slab were more uniform and smaller than those when placing one-third or two-thirds of the sleeper slab under the pavement. Furthermore, a wider sleeper slab resulted in more load transferred to the sleeper slab but smaller contact stresses under the sleeper slab.

Surface direct conversion of 511 keV gamma rays in large-area laminated multichannel-plate electron multipliers

We have used the TOPAS simulation framework to model the direct conversion of 511 keV gamma rays to electrons in a micro-channel plate (MCP) constructed from thin laminae of a heavy-metal-loaded dielectric such as lead-glass, patterned with micro-channels (LMCP). The laminae serve as the converter of the gamma ray to a primary electron within a depth from a channel-forming surface such that the electron penetrates the channel surface (‘surface direct conversion’). The channels are coated with a secondary-emitting material to produce electron multiplication in the channels. The laminae are stacked on edge with the channels running from the top of the resulting ‘slab’ to the bottom; after assembly the slab is metalized top and bottom to form the finished LMCP.The shape of the perimeter of a lamina determines the dimensions of the slab at the lamina location in the slab, allowing non-uniform cross-sections in slab thickness, width, and length. The slab also can be non-planar, allowing curved surfaces in both lateral dimensions. The laminar construction allows incorporating structural elements in the LMCP for modular assembly in large-area arrays.The channels can be patterned on the laminae surfaces with internal shapes and structure, texture, and coatings optimized for specific applications and performance. The channels can be non-uniform across the LMCP and need not be parallel in either transverse direction.Surface direct conversion of the gamma ray to an electron eliminates the common two-step conversion of the gamma ray into an optical photon in a scintillator followed by the conversion of the photon into an electron in a photodetector. The simulations predict an efficiency for conversion of 511 keV gamma rays of ⪆ 30% for a 2.54 cm-thick lead-glass LMCP. The elimination of the photocathode allows assembly at atmospheric pressure.

Experimental investigation of punching shear behaviour of ultra-high performance self-compacting concrete slabs

The use of heavy reinforced and thick transfer-slab in multipurpose tall buildings is crucial to dealing with many issues such as high bending and punching shear stresses created from relocation of columns in floors above transfer-slab. Ultra-High Performance Self-Compacting Concrete (UHPSCC) is a proper option for coping with the problem of dense reinforcement. In predicting the punching shear capacity of concrete slabs, most existing code provisions limited the concrete compressive strength up to 70 MPa. Furthermore, no code provisions deal with estimating the punching shear capability of UHPSCC slabs. For these reasons, the present paper aims to investigate experimentally the punching shear behaviour of the interior slab-column joint made of a developed UHPSCC blend had a compressive strength of more than 120 MPa. The study takes into account the effect of design parameters such as type of concrete, slab thickness, and reinforcement ratio on the punching shear capacity. The study explores if the existing code shear provisions could be utilized to estimate the punching shear strength of UHPSCC and UHPC slab-column connections. In terms of estimating the punching shear capacity of such slab-column joints using available code provisions, regardless of their concrete compressive strength limits (using the available code formulae to estimate punching shear strength twice, once with the code restrictions of concrete compressive strength and once without), the available code shear models were significantly conservative, indicating the need to develop a new punching shear model for such slab-column connections. The European Code (EC2, 2004) has the best appropriate formula for predicting the nominal punching load capacity of UHSC slabs among the present well-known code punching provisions. The critical punching section of the UHPSCC slab was detected at 1.5 times the slab's effective depth measured from the column face. For a slab thickness of 200 mm, increasing the tensile steel ratio from 1.3% to 2.0% increased the punching strength of UHPSCC by 77.6%. At a reinforcement ratio of 1.7%, raising the slab thickness from 160 to 240 mm boosted the punching strength by 118.6%. In view of the study's outcomes, in addition to its ability to address the issue of dense reinforcement, the use of UHPSCC provides great potential for improving the punching shear capacity of heavy-loaded slab-column connections.

Conditions for Minimizing the Computational Complexity of the RCWA Calculation of the Diffraction Efficiency of Sawtooth Two-Layer Double-Relief Microstructures

In this study, novel recommendations are presented and substantiated for selecting the number of modes and optical thicknesses of flat lattice slabs that make up microreliefs, which minimize the computational complexity of the rigorous coupled-wave analysis calculation of the diffraction efficiency (DE) of a sawtooth two-layer two-relief microstructure, while maintaining the specified reliability of the calculation results. The computational complexity can be controlled by allowing one or another level of oscillation of the DE curves, depending on the angle of incidence of the radiation incident on the microstructure. In particular, the complexity of the thousands of DE calculations in the optimization process can be reduced by using the proposed methodology as well as increased computational complexity to verify the accuracy of the solution obtained as a result of the implemented optimization.

Understanding the role of oxygen-vacancy defects in Cu2O(111) from first-principle calculations

The presence of defects, such as copper and oxygen vacancies, in cuprous oxide films determines their characteristic carrier conductivity and consequently their application as semiconducting systems. There are still open questions on the induced electronic re-distribution, including the formation of polarons. Indeed, to accurately reproduce the structural and electronic properties at the cuprous oxide surface, very large slab models and theoretical approaches that go beyond the standard generalized gradient corrected density functional theory are needed. In this work we investigate oxygen vacancies formed in proximity of a reconstructed Cu2O(111) surface, where the outermost unsaturated copper atoms are removed, thus forming non-stoichiometric surface layers with copper vacancies. We address simultaneously surface and bulk properties by modelling a thick and symmetric slab, to find that hybrid exchange-correlation functionals are needed to describe the oxygen vacancy in this system. Our simulations show that the formation of oxygen vacancies is favoured in the sub-surface layer. Moreover, the oxygen vacancy leads to a splitting and left-shift of the shallow hole states in the gap, which are associated with the deficiency of copper at the surface. These findings suggest that surface electronic structure and reactivity are sensitive to the presence of oxygen vacancies, also when the latter are formed deeper within the film.

The Lark: reducing carbon emissions through collaboration and good relationships – a model for everyday concrete frames

Multistorey concrete-framed residential buildings are a common choice for developers because of their strength, durability, inherent fire resistance, design flexibility, and cost-effectiveness. However, with concrete accounting for a significant portion of global carbon emissions, engineers have a responsibility to both minimise concrete volumes and reduce the carbon intensity of concrete mixes to deliver a sustainable solution. In this article, Peyrouz Modarres of Walsh describes the consultant's approach to the engineering design of The Lark, a multistorey residential project at Nine Elms, London. The article examines the optioneering process through which the grid and slab thicknesses were optimised to reduce the embodied carbon of the sub- and superstructure, collaboration with the contractor over the concrete specification, and the benefits that a trusted relationship with the client brought to the project.

Propagation Characteristics of Terahertz Waves in Magnetized Dusty Plasma

The propagation characteristics, including reflectivity, transmissivity, and absorptivity, of terahertz (THz) waves in magnetized dusty plasmas sheath are investigated theoretically by the analytic method. Both the right-and left-hand circularly polarized (RCP and LCP) waves are considered. The calculation results illustrate that external magnetic field, plasma slab thickness, electron collision frequency, dust particles, and electron relaxation rate can affect the propagation characteristics of THz waves in plasmas. When dust particles are absent, a strong external magnetic field will cause the transmissivity of RCP waves to produce a transmissivity valley at the lower frequency band. Due to the action of external magnetic field and dust particles, a transmissivity peak appears at the lower frequency band for RCP waves. Increasing the density or radius of dust particles can cause an increase in transmissivity peak. For LCP waves, the transmissivity increases monotonously as the frequency of THz wave increases, whether the dust particles exist or not. These simulation results may provide a significant theoretical basis for solving the problem of “blackout.”

Effect of Temperature Variation on Rigid Pavement by using Sensor

Abstract: Variations in temperature have an impact on both stiff and flexible pavements. Although the main component of pavements is crushed stone aggregate, which is not temperature-sensitive, the binder that holds the aggregates together is more temperature-sensitive. Pavements made of Portland cement concrete (PCC) that are cast in the field experience volume fluctuations as a result of changes in temperature and moisture. Utilize sensors to examine the impact of temperature and moisture change on stiff pavement. Analyze the technical and physical characteristics of sensors. locating sensors in solid pavement in order to get accurate data. This research aims to analyze temperature differences for stiff pavement (mainly for the PQC layer). Table 1 in IRC:58-2015 lists the temperature differences for several Indian areas. In order to design pavement slabs of varied thicknesses, it offers temperature differential values. However, the table's footer also states that the data was collected in 1974 by the Government Road Experiment Station in New Delhi. This analysis is done to compare the temperature difference between that table, which is over 50 years old, and the present temperature. It has been noted that temperature measurements obtained from a temperature sensor closely match the information provided by the metrological department. (Data on temperatures from July to November) Data from the prior 10 years are collected for further examination when data from the IMD is confirmed to be the same (2012 to 2021). The temperature disparity over the next 10 years is forecasted using those data (2022 to 2031). When compared to IRC, data have revealed a rise in the minimum and maximum temperature disparity.

The Effect of Steel Trusses on the Mechanical Performance of Laminated Precast Slabs

Laminated concrete slabs can deliver desirable structural properties and effectively improve the speed of construction. According to their basic specifications, laminated concrete slabs comprise a 60 mm precast concrete slab and a 70 mm concrete layer cast in situ, with a steel truss bar at a height of 80 mm. This paper studies the effects of the steel truss bar on the mechanical properties of precast slabs. A simple but accurate method is proposed for calculating the stiffness of precast slabs. The test results show that the steel truss bar has a limited effect on the stiffness of the precast slab but will weaken the compression strength of the concrete, resulting in a significant reduction in the ultimate bearing capacity of the precast slab. Further discussions show that eliminating the steel truss bar and appropriately increasing the thickness of the precast slab can effectively increase the stiffness and load-bearing capacity of the precast slab, as well as reduce the consumption of the floor reinforcement by about 26%.