Bottom Face Research Articles

Experimental study and numerical modelling of post-tensioning systems on the transverse direction of composite steel deck-concrete structures

This study introduces the first investigation into the impact of post-tensioning layouts on the specific transverse direction of steel-deck concrete structures due to the significant limitations of current practice. The experimental work investigates the flexural capacity, structural failures, and crack characteristics of post-tensioned composite (PTC) systems using different tendon profiles and anchorage positions. Three specimens were tested under the four-point bending tests, in which one specimen employed a straight tendon and the remaining two used a profiled tendon (parabolic) with different anchorage positions. The specimens failed due to flexural failure with heavy crushing of concrete and without any damage to the steel sheeting. As compared to conventional concrete structures, the testing revealed a unique crack pattern in the composite system, with cracks initiating 90 degrees at the top edge of the ribs instead of the bottom face of the concrete. The load capacity of specimens using profiled tendon was higher by 15.2 % in the service stage and 17.3 % in the ultimate stage than that of straight tendon. The anchorage positioned at the mid-depth of the section brings the most effective placement to the PTC specimens, where the stress losses can be reduced by 2 % to 4 % and the bending stiffness increased by 4 %. The proposed finite element (FE) models of the PTC specimens were developed and validated against experimental results, ensuring the use of modelling techniques available in the software package ABAQUS.

Wake characteristics of near-wall submerged bluff bodies with varying streamwise length

This study aims to investigate the effect of streamwise length on the wake characteristics of submerged sharp-edged bluff bodies in the presence of an underbody gap using large eddy simulation. To this end, three bodies with identical width (W) and height (h), but varying only in their streamwise lengths (L) were employed resulting in streamwise elongation ratios of L/h = 1, 2, and 3, respectively. The underbody gap between the bottom face of the body and the wall was fixed at 0.14 h for all cases. A fully developed turbulent boundary layer with a thickness of 3.6 h was used as the approaching flow. It was noted that the mean flow and turbulent stresses were significantly affected by the streamwise length. Premultiplied frequency spectra of the velocity fluctuations were utilized to examine the fluctuating properties of the wake. A single dominant vortex shedding frequency was observed for L/h = 1 and 3, whereas dual mode vortex shedding was noted for L/h = 2. The latter case exhibited an intermittent reattachment on the top surface of the body. The fluid structures evaluated using the λ2 criterion, indicated that they were strongly influenced by L/h. Interestingly, even with the presence of a gap, a weak horseshoe vortex which occurred intermittently was captured close to the bed for the three cases.

Flow of water out of a funnel

The unsteady Bernoulli equation is used to numerically determine the surface height and velocity distribution of water flowing out of a conical tube as a function of time. The speed is found to interpolate between freefall for a cylindrical pipe of constant radius and Torricelli’s law for a funnel having a small exit hole. In addition, the applied force needed to hold the conical vessel in place is calculated using Newton’s second law including the rocket thrust due to the water flowing out of the funnel. A comparison is made with the analogous expressions for the flow through and holding force on a right cylindrical tank having a hole in its bottom face. The level of presentation is appropriate for an undergraduate calculus-based physics course in mechanics that includes a module on fluid dynamics.

Soundbox-based sound insulation measurement of composite panels with viscoelastic damping

Sound transmission loss (STL), an essential index for assessing the sound insulation performance of composite laminated structures, typically relies on experimental methods to measure. The soundbox method (SBM), a straightforward technique for measuring the STL, is sensitive to microphones’ positions. Within the framework of the Chebyshev-Ritz method, a semi-analytical vibro-acoustic model extended to composite laminated panels with viscoelastic damping (VED) is proposed for the first time. Based on the developed simplified layer-wise theory, the panel is modeled using three layers: the top face layer, the VED layer, and the bottom face layer. A closed cavity is added to the model as the soundbox enclosure used in actual measurements. By employing the Hamilton's principle, the governing equation for the coupling system is derived, and the vibration and internal acoustic responses of the coupling system are calculated. A discretization strategy is introduced to address the frequency-dependent properties of the VED layer, avoiding the need to reconstruct the stiffness matrix at each frequency. To obtain the STL of the panel, sound pressures at external measurement points are calculated based on the Rayleigh integral. The proposed model is validated against numerical results from finite element analyses. The influences of the microphone position inside and outside the cavity on the measured STL are studied. Furthermore, parametric studies over the microphones' positions are performed to enhance the SBM-based evaluation of the composite panel's sound insulation performance. The optimal locations for two internal microphones and one external microphone are recommended. Finally, experimental studies are carried out to guide the implementation of the SBM.

Культура – знак – значение: о природе и структуре культуры и знака

The article examines the concept of culture as a paradigmatic structure that defines the variety of possible forms of social life, activity, and behavior in a certain community. It examines the structure and nature of the sign and its place in culture. The author sets this concept of culture and ideas about the structure of the sign, starting from some of F. Saussure’s ideas. He accepts Saussure’s distinction between language and speech within “linguistic activity”, but in the language itself he also distinguishes two areas of existence: language as a paradigmatic structure of a single subject and language as a paradigmatic system existing at the community level. As a result, the author sees not two, but three areas of manifestation in “language activity”. He identifies similar three areas in any semiotic activity and in activity in general. At the same time, in the course of generalization in the series “linguistic activity – sign activity – activity”, the social paradigmatic aspect of these activities is also generalized from language to the sign system and culture as a whole. Since language in public form, and language in individual form, and speech have the word as a basic structural unit, then we can talk about three ontological forms (modi) of the word: in public language, in individual language, in speech. The author identifies similar three ontological modi for an arbitrary sign. Taking as a basis the binary structure of an abstract sign (the plan of expression and the plan of content associated with each other) and the idea of the three ontological modi of the sign, we obtain a triangular prism as an ontological scheme of the sign, where the nodes of the prism correspond to various aspects of the sign, three vertical edges – three ontological modi of the sign, the upper face – the plan of expression (syntax), the bottom face – the plan of content (semantics). Based on the obtained ontological scheme of the sign, the author interprets the semiotic representations of some alternative research programs

Broadband circularly polarized MIMO antenna in single layer substrate for Wi‐Fi 7 applications

AbstractIn this paper, a MIMO antenna with broadband circular polarization is designed in a single‐layer substrate for the next‐generation Wi‐Fi 7 applications. The top of the substrate is designed with a periodic array of 5 × 5 circle patches and orthogonally placed four L‐shaped aperture CPW feeds on the bottom face of the substrate are used to feed the patches. The stubs are arranged across the apertures to achieve a broad bandwidth. The array of patches is used to achieve high gain over resonant frequency range and L‐shaped apertures are used to achieve circular polarization. The designed antenna with the above specifications has gained an impedance bandwidth of 20.4% (5.37–6.59 GHz), a 3 dB axial ratio bandwidth over the entire resonant frequency range of 25.61% (5.14–6.65 GHz) and a peak gain of 8.5dBi.

Elastic Foundation Solution for the End Notched Flexure (ENF) Mode II Sandwich Configuration

Abstract This paper presents a closed form solution for the energy release rate of face/core debonds in the Mode II end notched flexure (ENF) sandwich configuration. The finite-length sandwich specimen is considered to have a “debonded” region and a “joined” region. In the later, the interface between the top face and the substrate (core and bottom face) is modeled by an elastic foundation, which is a uniform distribution of shear and normal springs. Based on the Timoshenko beam theory, the solution for a general asymmetric sandwich construction is derived. The energy release rate expression is derived via the J-integral. Another closed form expression for the energy release rate is derived from the energy released by a differential spring as the debond propagates. In this closed form solution there is no fitting and everything, including the foundation constants, are given in closed form. Results are produced for a range of face/core stiffness ratios and debond length/core thickness ratios, and are compared with the corresponding ones from a finite element solution. A very good agreement is observed except for small debond lengths vs specimen thickness.

Instrumented Mouthguard Decoupling Affects Measured Head Kinematic Accuracy

Many recent studies have used boil-and-bite style instrumented mouthguards to measure head kinematics during impact in sports. Instrumented mouthguards promise greater accuracy than their predecessors because of their superior ability to couple directly to the skull. These mouthguards have been validated in the lab and on the field, but little is known about the effects of decoupling during impact. Decoupling can occur for various reasons, such as poor initial fit, wear-and-tear, or excessive impact forces. To understand how decoupling influences measured kinematic error, we fit a boil-and-bite instrumented mouthguard to a 3D-printed dentition mounted to a National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform. We also instrumented the headform with linear accelerometers and angular rate sensors at its center of gravity (CG). We performed a series of pendulum impact tests, varying impactor face and impact direction. We measured linear acceleration and angular velocity, and we calculated angular acceleration from the mouthguard and the headform CG. We created decoupling conditions by varying the gap between the lower jaw and the bottom face of the mouthguard. We tested three gap conditions: 0 mm (control), 1.6 mm, and 4.8 mm. Mouthguard measurements were transformed to the CG and compared to the reference measurements. We found that gap condition, impact duration, and impact direction significantly influenced mouthguard measurement error. Error was higher for larger gaps and in frontal (front and front boss) conditions. Higher errors were also found in padded conditions, but the mouthguards did not collect all rigid impacts due to inherent limitations. We present characteristic decoupling time history curves for each kinematic measurement. Exemplary frequency spectra indicating characteristic decoupling frequencies are also described. Researchers using boil-and-bite instrumented mouthguards should be aware of their limitations when interpreting results and should seek to address decoupling through advanced post-processing techniques when possible.

Effects of CFRP sheets on the flexural behavior of high-strength concrete beam

Abstract The aim of this study is to evaluate numerically the effects of carbon fiber-reinforced polymer (CFRP) sheets strengthening on the flexural performance of high-strength concrete (HSC) beam using ABAQUS 3D finite element (FE) modeling software. The developed FE models were verified against the experimental results found in literature. The FE models can accurately estimate the performance of CFRP-strengthened high-strength reinforced concrete (RC) beams. Subsequent parametric analysis was performed to assess the performance of CFRP-strengthened concrete beams considering various parameters including compressive strength of concrete, CFRP width, thickness, length, number of CFRP layers, and CFRP strengthening schemes. Based on the results of FE analysis. It was demonstrated that using HSC significantly enhances the performance of CFRP-strengthened RC beams. It was also confirmed that width, thickness, and layer number of CFRP sheets improve the flexural behavior of CFRP-strengthened HSC beams by increasing the ultimate loads and strain-hardening behavior of the specimens. The strengthening schemes contribute to delaying or inhabiting the debonding especially when the CFRP sheets are added along the bottom of the beams. It was demonstrated that using CFRP sheets U-wrapping contributes to the prevention or delay of debonding and increases the capability of resisting the stress imposed on the concrete. Therefore, installing the CFRP sheets at the bottom face of beam below the tensile reinforcement enhances the performance of CFRP-strengthened HSC beams.

Leakage detection applied to the Da Hedong Reservoir dam (China) based on the flow-field fitting method

Detecting leakage in concrete gravity dams presents a formidable challenge. The flow-field fitting (FFF) method is used to identify leaks in China’s Da Hedong Reservoir dam. We develop vertical- and horizontal-gradient approaches based on the transmitted signal electrical field. A plastic frame is developed to allow the probe to measure horizontal gradients. We determine the exact location of leaks at the reservoir’s bottom and upstream face, respectively, assuming that current leakages are located in hydraulic leakage zones. Numerical experiments and water pressure tests reveal that the conductive silt layer beneath the reservoir can lower the response of the potential values at the leakage inlet, and the effect of the silt layer should be considered and not ignored when interpreting measured data. In addition, with regard to the principle of superposition, the contribution associated with metal pipes in the dam body can be roughly determined by subtracting it from the original potential field data, thereby aiding in locating leaks around the metal pipes. In addition, the FFF measurements from the reservoir’s bottom also confirm the position of existing faults in the substratum at the reservoir site. Last, the results of the FFF method are tested against supporting evidence, such as ground penetrating radar and water pressure tests. In conclusion, these independent data confirm the effectiveness of the FFF method for leakage localization in the concrete gravity dam.

Response of the orthogonal corrugated sandwich panel under low-velocity impact with different shaped impactors

This study aims at investigating the low-velocity impact resistance of the composite orthogonal corrugated sandwich panel through experimental and simulation methods, considering different shaped impactors. To that scope, the progressive damage model with the sandwich panel is developed and numerical investigations are carried out in ABAQUS / Explicit. The results show that as the impactor changes from flat to hemispherical and then to conical shape, the first peak load gradually decreases, and the maximum displacement of the impactor and total energy absorption gradually increase. The high impact energy makes the sandwich panel more compliant. Furthermore, the expansion area of fiber damage, matrix damage and delamination in the top face sheet, core and bottom face sheet depends on the impactor shape and impact energy. Under high impact energy, the damage under the conical impactor mainly expands along the thickness direction of the sandwich panel rather than in the in-plane direction, while the flat impactor causes large damage area in the in-plane direction as well.

Extraction of uniaxial stress–strain curve from bending test using DIC measurements

This paper presents a novel methodology for the analytical determination of the uniaxial tensile/compressive stress–strain curve derived from the four-point bending test without a pre-assumed constitutive model. While the concept of extracting the stress–strain curve from a bending test is not new, the proposed methodology differs from existing methods by recognising the force equilibrium in a deformed configuration, resulting in a temporal variation of both a bending moment and an axial force. In addition, the deformation of the beam cross-section is taken into account according to the principles of finite strain theory either via Poisson’s ratio or by assuming volume conservation. The crucial data for this methodology are obtained from an experimentally conducted bending test in which the loading force, displacement and strain fields at the top, bottom and front faces of the specimen are measured using a stereo DIC. While the method is completely analytical, it reconstructs the stress–strain curve in discrete form by solving a system of linear equations. While the existing methods for the four-point bending test allow extraction of the stress–strain curve from a single experiment only for strains up to a few per cent, our methodology allows the extraction of the stress–strain curve in tension and compression up to five times the strains obtained with methods that neglect the above features.

Transient Heat Transfer Analysis in Metal Plates with Variable Thickness

Nonlinear transient heat transfer via conduction–radiation is a dynamic topic of long-standing interest with applications ranging from aeronautical and mechanical engineering to industrial and civil security. To gain a better understanding of the performances of materials having thermal proprieties that change during nonlinear heat transfer, several studies using the finite element method (FEM) have been conducted. Such studies apply nonlinear thermal material characteristics to describe the complete system under different loading conditions in each region by adjusting the temperature values for the other three edges and the thickness parameter with Dirichlet boundary conditions. As a result, while modeling and simulating temperature distributions for such situations, nonlinearities generated by temperature-dependent thermal conductivity must be considered. In this work, we focus on the analysis of coupled transient heat transfer through two metal plates with temperature-dependent thermal characteristics in which the temperature is fixed along the bottom edge and heat is transferred from both the top and bottom faces of the two plates. FEM is employed to solve the nonlinear heat equation and compute the temperature as a function of time for variable thickness. The study examines the effect of modifying the thickness parameter values on the temperature distribution over time for various edge values over 5,000 s.

Prismatic-element SBPML coupled with SBFEM for 3D infinite transient wave problems

In this paper, an enhanced prismatic-element scaled boundary perfectly matched layer (SBPML) is developed, which is a novel time-domain artificial boundary method for 3D infinite wave problems. The SBPML permits the utilization of an artificial boundary with general geometry and can consider planar physical surfaces and interfaces extending to infinity. Moreover, this enhancement enables the seamless integration with surface meshes of arbitrary polygonal faces (such as triangles, quadrangles, pentagons, heptagons, octagons, etc.) at the truncation boundaries. The interior domain can be modelled by polyhedrons formulated by the scaled boundary finite element method (SBFEM). The geometric shape of the SBPML elements in the proposed method, within the local coordinate system, takes the form of a regular prism with regular polygonal top and bottom faces. Consequently, it is referred to as the Prismatic-element SBPML. Local scaled boundary coordinates based on the polygonal shape function are firstly introduced into the truncated infinite domain to describe its general geometry properties and provide the coupled capabilities with arbitrary polygonal face meshes at the truncation boundaries of numerical models. Then, a complex stretching function from PML is applied to radial direction of the local scaled boundary coordinates to map the physical space onto the complex space, resulting in a SBPML domain. Upon spatial discretization, the proposed method is formulated using a 2nd-order mixed displacement-stress unsplit-field formulation, allowing seamless coupling with FEM and SBFEM originally designed for the interior computational domain. Finally, three benchmark examples of wave propagation problems in unbounded domains and two soil-structure interaction problems of engineering problems are presented to demonstrate the accuracy and robustness of the Prismatic-element SBPML.

Experimental study on the fire resistance of all-composite and hybrid web-core sandwich panels for building floors

Fibre-reinforced polymer (FRP) composites and polymeric foams used in construction are susceptible to elevated temperatures, but little is known about the behaviour of composite sandwich panels under fire exposure. This paper presents an experimental study on the fire resistance of web-core composite sandwich panels with polyurethane foam infill for building floors. Two panel variants were considered: (i) an all-composite panel, with glass-FRP (GFRP) face sheets and webs; and (ii) a hybrid panel, with an additional fibre reinforced concrete (FRC) top layer. Five full-scale specimens were loaded in a four-point bending configuration, subjected to a constant service load, and subsequently exposed to a standard fire (ISO 834) on their bottom face. The effectiveness of passive fire protection systems, consisting of calcium silicate boards installed either adherent to the panels or forming an air cavity, was assessed. The following features were investigated: (i)temperature progression across the thickness of the panels, (ii)their mechanical response, (iii)failure modes, and (iv)fire resistance. The results obtained indicate that despite the vulnerability of composite sandwich panels to fire, relatively high fire resistances of 44 min and 49 min were obtained for the unprotected web-core all-composite and hybrid variants, respectively. The failure mechanism of the sandwich panels generally involved local compression and in-plane shear failure of the webs. The use of suitable passive fire protections provided significant fire resistance increases of at least 45 min (adherent) and 60 min (with air cavity), allowing to exceed the 90 min threshold.

Vibration Analysis of Damaged Viscoelastic Composite Sandwich Plate

This paper presents a study of free and forced vibration of composite sandwich plate with and without damage using the finite element analysis developed under ANSYS APDL software. This modeling uses the 8-node shell 281 element to modelized the composite laminates of the top and bottom face sheets of the sandwich plate and the 20-node higher order solid 186 element to modelized the viscoelastic core. Two sets of boundaries are considered; Simply supported and clamped boundary conditions at all edges. The effect of damaged face sheets layers on natural frequencies, mode shapes, the frequency and transient responses of the sandwich plate is investigated. Numerical results show remarkable shifts of the natural frequencies, frequency and transient responses due to the presence of damage. It is concluded that the natural frequencies decreasing is due to the loss of structural stiffness. Natural frequencies of the sandwich plates are close to those issued from numerical results available in the literature.

Study on stress distribution law of surrounding rock of roadway under the goaf and mechanism of pressure relief and impact reduction

To safely extract residual coal from a mine affected by rock bursts, the concept of “roadways under goafs” has been proposed as an effective layout. The pressure relief and shock reduction mechanism of roadways under goafs is elucidated through theoretical analysis, numerical simulation, and engineering verification. The stress model for goafs is established based on elastoplastic mechanics, followed by the construction of a force model for coal beneath the goafs. The stress composition of roof, floor and two sides of roadway under a goaf are analyzed. Using the FLAC-PFC coupling simulation method, the excavation process from top coal mining to bottom coal mining roadways of a No. 17 coal mine in Heilongjiang Province was simulated. The simulation results validate the spatiotemporal evolution of the stress and displacement in the surrounding rock mass of the roadway situated beneath goafs and determine the precise location of the roadway and length of its bottom coal face. A large diameter borehole of the roadway and presplitting blasting of the coal face roof are used to solve the local high stress danger area. Moreover, the roadway support mode of the “steel shed + spray arch support + monomer + π steel beam” is proposed. Finally, through the data of the field micro-seismic and stress monitoring system, the effectiveness of the pressure relief and shock reduction of roadways under goafs, the high efficiency of local danger relief of the roadways and working faces, and the practicability of the “steel shed + spray arch support + monomer + π steel beam” support of the roadways broken by surrounding rock are verified. A good basis for choosing a reasonable location for roadways and surrounding rock control methods for residual bottom coal mining and rock burst mining can be found in the research results.

The role of CFRP strengthening in improving the punching shear behavior of heat-damaged flat slabs with openings of different sizes and locations

The punching shear behavior of twenty simply supported RC flat slabs of mm3) dimensions was examined in this study where concentrated loading was applied using a 150 mm central square column. However, the effect of the following parameters was evaluated: (1) CFRP strengthening, (2) ambient and elevated temperatures (23 C, 200 C, 400 C, and 600 C), (3) opening existence (with or without), (4) opening location (directly at the column face or 60 mm a way), and (5) square opening side length (70 mm or 200 mm). Strengthening was done by four 75 mm wide CFRP strips applied at the bottom face of the slab to surround the column and opening region. It was found that the cracking intensity is directly affected by the exposure temperature with the cracking visibility at the opening internal sides. In addition, strengthening increases the slab’s stiffness by larger percentages for slabs with small openings compared to those with larger ones at ambient and normal temperatures with the differences being reduced at higher temperatures. Moreover, strengthening plays a major role in improving the slab’s deflection capacities by 10–90 % compared to the control specimen. Finally, the punching shear failure brittleness was significantly reduced by the CFRP-strengthening as the ductility of the strengthened specimens was increased as a result of the cracking intensity reduction.

Stability constraints in a 3D knapsack problem with non parallelepipedic items

This paper concerns stability issues that we encountered while solving an industrial pallet loading problem. The practical problem can be modeled as a three-dimensional knapsack with original constraints related to the stability of the pallet: when the placement of the boxes on the pallet is computed, the weight of the boxes and the placement sequence are not known.Despite this lack of information, the placement must remain stable throughout the construction of the pallet. Even more important, the major difference with classical placement problems is that the boxes are parallelepipedic rectangle with edge reduction (the upper surface may be smaller than the bottom face).In this paper, we review stability constraints used in the literature and the assumptions under which these constraints can be used and we detail their adequacy to the problem we consider. We then propose a new stability constraint which takes into account the practical features, which can be integrated into a placement algorithm and which is not too restrictive.Numerical experiments on benchmarks from the literature show that this constraint, added to a classical placement algorithm, obtains results which are similar to algorithms from the literature dedicated to a specific stability constraint for parallelepipedic boxes. By adjusting the benchmark to take into account the practical problem specificities, we show that this new stability constraint is perfectly suited to the industrial problem and obtains very good results compared to classical constraints. Therefore, it has been integrated in the placement software developed by the company.

Mechanical performance of stitched foam-filled honeycomb sandwich panels

Foam-filled Honeycomb Sandwich panels (FHS) are widely used in various industrial applications due to their superior multifunctional properties. However, these sandwich panels fail in some extreme conditions due to interfacial failure between the face sheet and core. To overcome this issue, novel stitched foam-filled honeycomb sandwich panels (SFHS) were fabricated by integrating the top face sheet and bottom face sheet by the stitching technique. Stitching through the face sheet and core is to improve the interfacial strength and increases the mechanical properties of the sandwich panel. FHS and SFHS were prepared by the Vacuum Assisted Resin Transfer molding (VARTM). Flexural, flatwise, and edgewise compression analysis values for SFHS panels are 2.02, 1.28, and 1.25 times higher than for FHS panels. SFHS panel weight increased slightly but had superior mechanical properties than FHS. These innovative SFHS panels can be broadly used for applications including structural, flooring, and body panels.