Slab Length Research Articles

Wave theory-based fourth harmonic generation of Bessel–Gauss beam by total internal reflection-quasi phase matching in a rectangular slab of beta barium borate

This work presents a theoretical approach to a highly multimode-guided wave-based fourth harmonic (FH) generation method by exploiting a zero-order Bessel–Gauss beam through the total internal reflection quasi phase-matching technique. An anisotropic crystal featuring a rectangular structure of beta barium borate has been used to carry out this analysis. In contrast to the conventional frequency conversion scheme using a Gaussian beam, the projected scheme yields a maximum six times superior efficiency of 6.9547% in a crystal length of nearly 6.3 mm, corresponding to a 266-nm FH wavelength. The analysis has also taken into account optical losses, such as absorption, Goos–Hänchen-shift, surface roughness, and the effect of the nonlinear law of reflection. Finally, a systematic study has been performed to describe the influence of parametric modification, such as variations in slab length and thickness, to provide a more comprehensive picture of the overall analysis.

Bayesian approach to the tomographic problem with constraints from geodynamic modeling: Application to a synthetic subduction zone

Geodynamic tomography, an imaging technique that incorporates constraints from geodynamics and mineral physics to restrict the potential number of candidate seismic models down to a subset consistent with geodynamic predictions, is applied to a thermal subduction model. The goal is to test the ability of geodynamic tomography to recover structures harbouring complex deformation patterns. The subduction zone is parameterised in terms of four unknown parameters namely the slab length L, thickness R, temperature Tc, and dip angle θ that define its thermal structure. A temperature-dependent viscosity is then prescribed with an activation coefficient E controlling the sensitivity. Using the full forward approach to geodynamic tomography, we generate anisotropic surface wave dispersion measurements as synthetic data. We then attempt to retrieve the five unknown parameters by inverting the synthetics corrupted with random uncorrelated noise. The final output is an ensemble of models of L, R, θ, Tc and E cast in terms of a posterior probability distribution and their uncertainty limits. Results show that the parameters are tightly constrained with the apparent existence of a single misfit minima in each of them, which implies the implicit retrieval of the complete patterns of upper mantle deformation, and correspondingly, the 21-independent coefficients defining elastic anisotropy. Each model realisation however fails to swarm around its true value. Such results are attributed to the inability of the surrogate model to accurately replicate the correct forward model for computing anisotropy due to the inherent complexity of the deformation patterns considered. Nevertheless, this proof of concept shows a self-consistent method that incorporates mantle flow modeling in a seismic inversion scheme.

Flexural performance of prefabricated composite beams with grouped bolt shear connectors under positive bending moments

Four prefabricated steel–concrete composite beams (PSCCBs) with grouped bolt shear connectors were designed and tested to investigate their flexural performance under positive bending moments. The effect of shear connection degrees and segmented precast concrete (PC) slabs on the flexural performance of PSCCBs was investigated. Experimental results show that all the specimens failed due to the yielding of steel girders and concrete crushing in the mid-span regions, presenting typical characteristics of flexural failure. Compared to the PSCCB with a monolithic PC slab, the PSCCBs with segmented PC slabs experienced a short fast increasing stage of mid-span deflection after the steel girders yielded, of which the initial flexural stiffness and ductility coefficient decreased by 47.8% and 44.1% at most, respectively. Then, finite element (FE) models of PSCCBs with different design parameters were developed to assess their flexural behaviors under positive bending moments. Numerical results demonstrate that the initial flexural stiffness was significantly affected by the girder web height and the length of the middle PC slab. Enlarging the gap width, the length of the middle PC slab, and the girder web height are beneficial for the ductility of PSCCBs. The research findings might provide references for the design of PSCCBs with segmented PC slabs and grouped bolt shear connectors.

Flexural behaviors of prefabricated composite beams with segmented precast concrete slabs

The flexural behaviors of prefabricated steel-concrete composite beams (PSCCBs) with segmented precast concrete (PC) slabs were investigated through four-point bending tests. Experimental results showed that all the tested PSCCBs failed in flexural failure. The PSCCBs with segmented PC slabs exhibited good deformability and ductility, and the displacement ductility coefficient was not less than 13.3; the ultimate load-carrying capacity of the beams decreased by 8.7% when the shear connection degree reduced from 1.0 to 0.65. Three-dimensional finite element (FE) models were developed to evaluate the influence of parameters, such as the gap width (GW) between adjacent PC slabs and the length of the middle PC slab (LM), on the flexural behaviors of PSCCBs. Numerical results showed that the LM and GW are tightly correlated with the flexural behaviors of PSCCBs with segmented PC slabs, but their effect on the ultimate load-carrying capacity is negligible. A prediction method for the mid-span deflection of PSCCBs with segmented PC slabs was proposed based on the numerical analyses. The comparisons show that the theoretical and numerical results agree well with each other. The proposed method could be used for the preliminary prediction of the mid-span deflection of PSCCBs with segmented PC slabs when the design load is no more than half of the load-carrying capacity.

Assessing Premature Cracks in Urban Concrete Pavements

There are many urban jointed plain concrete pavements (JPCPs) constructed annually in the U.S. by counties, cities, and municipalities, which typically use state department of transportation standards but are not part of a systematic check to determine if design, construction, and performance are meeting expectations. A field evaluation survey with nondestructive testing was initiated on urban JPCPs throughout Illinois to assess performance and identify any deficiencies in design and construction. A total of 67 JPCPs were selected based on their design features and age. A significant number of sections (57%) were selected because they exhibited some level of premature cracking. Based on the field investigation, multiple mechanisms were proposed to explain the premature cracks. Many transverse and longitudinal cracks observed had excessive slab lengths or widths that were inconsistent with best slab geometry practices. There was no link established between observed cracking and the slab-base frictional restraint or the concrete mixture. For some sections, ultrasonic tests over the contraction joints determined certain joints had not activated and likely contributed to transverse cracks in adjacent slabs. Lack of dowel bar lubrication at the transverse contraction joints was also a plausible mechanism that restrained joint movements and produced excessive tensile stresses in the slab, which led to premature transverse cracks. The mechanisms leading to almost all observed premature cracks for these urban JPCPs were attributed to not adhering to existing state standards (slab geometry limits) and specifications (saw-cut timing/depth and dowel lubrication) during the pavement design and construction phases.

Prediction of Residential Slab Foundation Movement Through a Finite Element-Based Deep Learning Algorithm

Deep learning networks were employed to predict the maximum differential deflection of stiffened and waffle rafts due to reactive soil movements, Δmax. Four deep learning networks were used to predict Δmax, these are (1) stiffened rafts on shrinking soil, (2) stiffened rafts on swelling soil, (3) waffle rafts on shrinking soil, and (4) waffle rafts on swelling soil. The deep learning models were used to create design lines, which showed that both soil and structural features strongly influence the stiffened rafts. In contrast, waffle rafts showed a strong dependence on soil features in shrinking soils and beam depth in swelling soils. This demonstrates that the finite element-based deep learning networks captured the effect of the embedment of the beams. The results of the deep learning models led to non-linear design curves, which are disparate from the suggested standard Australian design. These results suggest that increasing the value of beam depth can have a positive or negative impact on the global residential slab depending on the type of substructure and whether the founding reactive soil is shrinking or swelling. Global sensitivity analyses of the deep learning models showed that for stiffened rafts on shrinking soil, the slab length, slab width and active depth zone of reactive soil had the most significant influence on Δmax, whilst for stiffened rafts on swelling soil, the primary drivers are ground movement, beam depth, and slab width. The prediction of Δmax for waffle rafts on shrinking soil was driven by the surface characteristic and mound movements, and the active depth zone, whilst waffle rafts on swelling soil was driven by the beam depth. Overall, the finite element-based deep learning showed the capacity to estimate Δmax in both shrinking and swelling design scenarios for different types of residential footing systems to further understand the characteristic behaviour of shallow residential slab foundations on reactive soils leading to improved designs.

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.

Failure mode of interlayer connection of longitudinally-connected ballastless track-bridge system under uneven pier settlement

• Proposing the characterization model of uneven pier settlement and interlayer connection failure in LBTBS. • Analysing the generation mechanism and development law of interlayer connection failure caused by uneven pier settlement. • Describing the evolution law of interlayer contact behavior of each layer of track caused by uneven pier settlement considering the existing interlayer connection failure. The generation and mechanical balance mechanisms and the deformation compatibility relationship of interlayer connection failure (ICF) of a longitudinally-connected ballastless track-bridge system (LBTBS) caused by uneven pier settlement is analyzed in this paper. The characterization model of the uneven pier settlement and the ICF of the LBTBS was derived based on Castigliano's Second Theorem, Linear Superposition principle, Heaviside function, and Tension-free Winkler beam. The characterization model was further verified by the field measured data and finite element model results. Finally, the development law of the ICF of the LBTBS caused by uneven pier settlement based on the characterization model was analyzed. The results show that the calculated results of the characterization model agree well with the field measured data and finite element model results, which verifies the correctness of the characterization model. Under uneven pier settlement, a void beneath the slab first appeared between the base slab and bridge, and then mortar debonding occurred between the CA mortar and track/base slab when settlement value is 193.48 mm. The maximum height of void beneath the slab developed away from the beam gap, and when the settlement value was less than 8.434 mm, the void beneath the slab length in the left area of the settlement pier was greater than that of the adjacent pier. With the increase in mileage, the height of the void beneath the slab and mortar debonding increased first and then decreased. In practical engineering, mortar debonding is not easy to notice, and the void beneath the slab between the base slab and the bridge should be inspected regularly. The existing fastener failure had little influence on developing a void beneath the slab caused by the uneven pier settlement. The existing mortar void aggravated the occurrence of mortar debonding. When the existing mortar void length exceeded 5 m, the mortar debonding length at both ends of the adjacent pier was about 1/2 of the existing mortar void length. When the length of the existing mortar void was less than 1 m, there was little effect on the length of the void beneath the slab.

Broadband High-Gain SIW Horn Antenna Loaded With Tapered Multistrip Transition and Dielectric Slab for mm-Wave Application

A substrate integrated waveguide (SIW) H-plane horn antenna loaded with tapered multistrip transition and dielectric slab is proposed for broadband high-gain operation. The broadband characteristic of the proposed antenna is obtained by loading a tapered multistrip transition. The theory of coupled resonator is introduced to reveal the mechanism of bandwidth enhancement. On the other hand, a dielectric slab is used to enhance the gain of the proposed antenna. The optimal length of this dielectric slab is determined based on the design principles of a dielectric rod with maximum gain. Besides, the tapered multistrip transition also contributes to the gain improvement by suppressing the feed radiation and prompting the transverse expansion of the surface wave. To verify the design theory and concept, a prototype operating at the K- and Ka-bands is fabricated and measured. The measurement results show that the impedance bandwidth of the proposed antenna is from 20.6 to 38.4 GHz (60%). Within the operating band, a peak realized gain of 19.1 dBi and excellent endfire radiation patterns with low cross polarization (<−30 dB) and high front-to-back ratio (FBR >20 dB) are achieved simultaneously. With its broad bandwidth, high gain, low cross polarization, and high FBR, the proposed antenna is promising for various millimeter-wave applications.

Incorporating the effect of approach slab to the dynamic response of simply supported bridges under moving vehicle

Reinforced concrete approach slabs serve as a transitional component between the roadway pavement and the bridge deck. Due to the settlement of the embankment soil, the slab is bent, and its slope grade will be suddenly changed resulting in bumps at both ends of the deck; this may increase the dynamic response of bridges induced by the interaction with moving vehicles. In addition, the presence of such bumps not only causes an uncomfortable ride but also exhibits a potentially hazardous condition to the traffic. Since most of the studies have considered either the interaction model between the slab and soil or between the bridge and moving load; in this study, a novel finite element model is established for the bridge under traffic loads, considering the presence of the approach slab that is simulated as a beam rested on a dynamic soil model. The separated models of the approach slab and bridge deck are validated by previous studies and demonstrate their accuracy in predicting the dynamic response of the bridge-vehicle system. A comprehensive parametric study is then performed considering the effect of the soil stiffness, the stiffness of the shear layer of the foundation, and the approach slab length. The results of the study are useful criteria for the practice design of the approach slab in different embankment conditions.

Controlled synthesis of efficient NiWS active phases derived from lacunary polyoxometalate and the application in hydrodesulfurization

Efficient catalysts with abundant NiWS active phases for hydrodesulfurization (HDS) were prepared based on structural diversity as well as unique electrostatics property of lacunary Keggin polyoxometalates (POMs). Owing to super nucleophilicity and coordinative ability, the trivacant Keggin [PW9O34]9- (PW9) can accurately capture and anchor Ni2+ promoters into its skeleton to form nanosized Nix@PW9 molecule in impregnating solution, thereby achieving ultra-dispersion of Ni promoters, high Ni/W ratio, and atomic-scale Ni–W proximity. The superior structure of Nix@PW9 promoted the simultaneous reduction and sulfuration of Ni and W species, thus obtaining shorter slab length, less stacking number, highly efficient synergism, and high concentration of NiWS active phases. Therefore, the resulted S-NiPW9/Al2O3 catalyst exhibits efficient HDS activity for dibenzothiophene (DBT) removal compared to that of reference catalysts prepared from monovacant [PW11O39]7- (PW11), saturated [PW12O40]3- (PW12), and conventional oxide precursors. The structure-directing effects of oxidic POM precursors on the texture and performance of HDS active phases were revealed by employing a variety of characterization methods, including transmission Fourier transform infrared (TS-FTIR), attenuated total reflectance Fourier transform infrared (ATR-FTIR), ultraviolet–visible spectroscopy (UV–Vis), single crystal X-ray diffraction, H2 temperature programmed reduction (H2-TPR), CO adsorbed Fourier transform infrared spectroscopy (IR/CO), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). This POMs-based molecular methodology opens a new avenue to better understand the evolution behavior of precursors and the formation mechanism of active species during the preparation of catalysts.

Study on the vibration evaluation method and allowable differential settlement of road-bridge transition section with full-car model

ABSTRACT The differential settlement between bridge approach slab and abutment causes bump problems when vehicles passing this area. This study aims at evaluating the roughness of area between road-bridge transition properly and putting forward the allowable differential settlement value based on the comfortable feeling of passengers. In this research, the maximum transient vibration value (MTVV) was chosen to be the evaluation index of roughness vibration comfort, and full-car model and bridge approach pavement models were established using Carsim software. Then, the interactions of human-vehicle-road were simulated when the car passed the bridge at different speeds, and the influences of step height, approach slab length, approach relative slope and vehicle speed on MTVV were studied. According to the simulation results and the comfortable feeling questionnaire when a testing car passed different bridge areas, the specific grading standard of MTVV was given, and for the bridge with and without approach slab, the allowable differential slope and the step height of the bridge under difference were put forward. The results have a significant value for the roughness evaluation of the road-bridge transition area and can be used to judge whether this area is needed or not to maintain.

Plastic Hinge Length Mechanism of Steel-Fiber-Reinforced Concrete Slab under Repeated Loading

The plastic hinge is the most critical damaging part of a structural element, where the highest inelastic rotation would occur. In particular, flexural members develop maximum bending abilities at that point. The current paper experimentally investigates the influence of steel fiber reinforcement at the plastic hinge length of the concrete slab under repeated loading, something which has not been reported by any researcher. Mechanical properties such as compressive strength and tensile strength of M20-grade concrete that are used for casting specimens are tested through the compressive strength test and the split tensile strength test. Six different parameters are considered in the slab while carrying out this study. First, the conventional concrete slab and then the steel-fiber-reinforced slab were cast. The plastic hinge length of the slab was calculated through different empirical expressions taken from methods by Baker, Sawyer, Corley, Mattock, Paulay, Priestley and Park. Finally, the steel fiber was added as per methods detailed by Paulay, Priestley and Park in the plastic hinge length mechanism in the concrete slab at 70 mm and 150 mm separately. The results arrived through experimental investigation by applying repeated loads to the slab, indicating that steel fibers used at critical sections of plastic hinge length provide similar strength, displacement, and performance as that of the conventional RCC slab and fully steel-fiber-reinforced concrete slabs. Steel fiber at a plastic hinge length of slab has a better advantage over a conventional slab.

Moment modification factor for link slab with single beam model in jointless bridges

Link slab is the portion of bridge deck that connects two adjacent simply-supported girders. In the practical design of link slabs, the determination of their internal forces is based on the single-beam model in which the clear span is the length of deboned link slab on top of beams. It can lead to detune moments of link slabs due to the eccentricity of link slab and girders, and the interaction between link slab and girders through the deboned layer. In this paper, a numerical analysis model is established based on finite element method to investigate moment performance of link slabs. Then, moment modification factors for link slab with single beam models are suggested to allow engineers to make better decisions on the detailing of link slabs.

Moment modification factor for link slab with single beam model in jointless bridges

Link slab is the portion of bridge deck that connects two adjacent simply-supported girders. In the practical design of link slabs, the determination of their internal forces is based on the single-beam model in which the clear span is the length of deboned link slab on top of beams. It can lead to detune moments of link slabs due to the eccentricity of link slab and girders, and the interaction between link slab and girders through the deboned layer. In this paper, a numerical analysis model is established based on finite element method to investigate moment performance of link slabs. Then, moment modification factors for link slab with single beam models are suggested to allow engineers to make better decisions on the detailing of link slabs.

Hydrothermal synthesis of bulk Ni impregnated WO3 2D layered structures as catalysts for the desulfurization of 3-methyl thiophene

Unsupported Ni/W catalysts were synthesized using a hydrothermal method to form WO3. The WH-x and WN-x (x is the hydrothermal time) samples were impregnated with Ni and calcined at 450 ºC. The X-Ray diffraction, Raman spectroscopy, and UV–vis results showed that the monoclinic tungsten oxide phase forms the WOx phase in tetrahedral and octahedral coordination. Only in the Ni/WN-x series was detected the octahedral Ni species responsible for promoting the active phase. The XPS analysis revealed that 70% of the Ni promotes the WS2 active phase, forming the NiWS phase and 90% of W formed the WS2 phase. The catalysts tested in the 3-methylthiophene hidrodesulfurization reaction showed good activity under low pressure conditions. The largest activity of the Ni/WN-24 catalyst correlates well with the shorter WS2 slab lengths and the Ni-promoting the active phase. Interestingly, isoprene was obtained as the main product, indicating that the reaction mechanism followed the direct desulfurization (DDS) pathway.

Nd:YAG end-pumped zigzag multi-pass slab amplifier optimization: numerical and experimental study regarding the saturation effects.

A numerical modeling of Nd:YAG end-pumped zigzag multi-pass slab amplifier is developed. Spatial dependent rate equations have been solved taking into consideration the pump and laser beam saturation effects with regard to overlap correction of the signal path through gain medium. Based on our results, efficient amplifier structure with optimized output power could be designed with respect to the change in the number of signal beam-pass, doping concentration and slab length. In order to verify our modeling an experimental setup is designed.

Slowdown of interpenetration of two counterpropagating plasma slabs due to collective effects.

The nonlinear evolution of electromagnetic instabilities driven by the interpenetration of two e^{-},e^{+} plasma clouds is explored using ab initio kinetic plasma simulations. We show that the plasma clouds slow down due to both oblique and Weibel generated electromagnetic fields, which deflect the particle trajectories, transferring bulk forward momentum into transverse momentum and thermal velocity spread. This process causes the flow velocity v_{inst} to decrease approximately by a factor of sqrt[1/3] in a time interval Δt_{αB}ω_{p}∼c/(v_{fl}sqrt[α_{B}]), where α_{B} is the magnetic equipartition parameter determined by the nonlinear saturation of the instabilities, v_{fl} is the initial flow speed, and ω_{p} is the plasma frequency. For the α_{B} measured in our simulations, Δt_{αB} is close to 10 times the instability growth time. We show that as long as the plasma slab length L>v_{fl}Δt_{αB}, the plasma flow is expected to slow down by a factor close to sqrt[1/3].

Experimental study of wave impact on a vertical wall with overhanging horizontal cantilever slab and structural response analysis

Two-dimensional model test of a vertical wall with overhanging horizontal cantilever slab has been carried out with the scale factor of 1:30. Different influences of wave condition and structural geometry on wave load are investigated. Wave pressure of cantilever slab highly depends on structural clearance and reaches the peak when clearance close to 0.2 times wave height. Larger wave steepness is responsible for larger wave pressure for vertical wall. With the increasing length of slab, wave forces are reduced on slab while enlarged on vertical wall. Besides, a negative correlation between rise frequency and rise time is observed and corresponding empirical formula has been proposed. Through finite element analysis, the structural response of a simple plate under wave load has been studied. In general, the cut-off frequency has a dramatic effect on the dynamic magnification factor, where the actual dynamic response keeps stable when cut-off frequency larger than 4 times structural natural frequency. Finally, it is adoptable to determine the adequacy of the structure under wave load by considering the quasi-static wave load and corresponding impact factor from 2.0 to 6.0.

Mesoporous Gamma‐Alumina‐Supported Mo Catalysts: Effect of Calcination Temperature

AbstractMesoporous γ‐Al2O3‐supported Mo oxides precursors were prepared by one‐step hydrolysis method without organic template at different calcination temperatures (MoOx/γ‐MA‐T) from 400 to 700 °C. Then MoS2 catalysts (MoS2/γ‐MA‐T) were obtained from the precursors through in‐situ sulfurization and applied for hydrodesulfurization (HDS) of dibenzothiophene (DBT). Effects of precursors calcination temperature on physicochemical properties and catalytic performances of catalysts were systematically investigated. With the increase of calcination temperature, the strength of metal‐support interactions and slab lengths of MoS2 increased. The slab stacks were inhibited by the strengthened strong interaction, leading to the reduction of edge/rim sites ratio that are favour for the HDS reaction. Appropriate calcination temperature (500 °C) could make the MoS2/γ‐MA‐500 possess favourable pore structure, particle dispersion, and edge/rim sites ratio, which were conducive to the mass transfer process of reactants and products, and lowered the carbon deposition rate, thus improving its catalytic activity, stability and direct hydrogenolysis desulfurization selectivity.