Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.

Mode coupling with Fabry-Perot modes in photonic crystal slabs

Fabry–Perot(FP)modes are a class of fundamental resonances in photonic crystal(PhC)slabs.Owing to their low quality factors,FP modes are frequently considered as background fields with their resonance nature being neglected.Nevertheless,FP modes can play important roles in some phenomena,as exemplified by their coupling with guided resonance(GR)modes to achieve bound states in the continuum(BIC).Here,we further demonstrate the genuine resonance mode capability of FP modes PhC slabs.Firstly,we utilize temporal coupled-mode theory to obtain the transmittance of a PhC slab based on the FP modes.Secondly,we construct exceptional points(EPs)in both momentum and parameter spaces through the coupling of FP and GR modes.Furthermore,we identify a Fermi arc connecting two EPs and discuss the far-field polarization topology.This work elucidates that the widespread FPs in PhC slabs can serve as genuine resonant modes,facilitating the realization of desired functionalities through mode coupling.

Moment Redistribution Effect of the Continuous Glass Fiber Reinforced Polymer-Concrete Composite Slabs Based on Static Loading Experiment

This study aimed to investigate the moment redistribution in continuous glass fiber reinforced polymer(GFRP)-concrete composite slabs caused by concrete cracking and steel bar yielding in the negative bending moment zone.An experimental bending moment redistribution test was conducted on continuous GFRP-concrete composite slabs,and a calculation method based on the conjugate beam method was proposed.The composite slabs were formed by combining GFRP profiles with a concrete layer and supported on steel beams to create two-span continuous composite slab specimens.Two methods,epoxy resin bonding,and stud connection,were used to connect the composite slabs with the steel beams.The experimental findings showed that the specimen connected with epoxy resin exhibited two moments redistribution phenomena during the loading process:concrete cracking and steel bar yielding at the internal support.In contrast,the composite slab connected with steel beams by studs exhibited only one-moment redistribution phenomenon throughout the loading process.As the concrete at the internal support cracked,the bending moment decreased in the internal support section and increased in the midspan section.When the steel bars yielded,the bending moment further decreased in the internal support section and increased in the mid-span section.Since GFRP profiles do not experience cracking,there was no significant decrease in the bending moment of the mid-span section.All test specimens experienced compressive failure of concrete at the mid-span section.Calculation results showed good agreement between the calculated and experimental values of bending moments in the mid-span section and internal support section.The proposed model can effectively predict the moment redistribution behavior of continuous GFRP-concrete composite slabs.

Field observation of the thermal disturbance and freezeback processes of cast-in-place pile foundations in warm permafrost regions

The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the thermal stability of permafrost.In this paper,temperature data from inside multiple CIP piles,borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations.The following conclusions are drawn from the field observation data.(1)The early temperature change process of different CIP piles is different,and the differences gradually diminish over time.(2)The initial concrete temperature is linearly related with the air temperature,net radiation and wind speed within 1 h before the completion of concrete pouring;the contributions of the air temperature,net radiation,and wind speed to the initial concrete temperature are 51.9%,20.3%and 27.9%,respectively.(3)The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center.It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.

Experimental investigation of ultra-early-strength cement-based selfcompacting high strength concrete slabs(URCS)under contact explosions

In this paper,UR50 ultra-early-strength cement-based self-compacting high-strength concrete slabs(URCS)have been subjected to contact explosion tests with different TNT charge quality,aiming to evaluate the anti-explosive performance of URCS.In the experiment,three kinds of ultra-early-strength cement-based reinforced concrete slabs with different reinforcement ratios and a normal concrete slab(NRCS)were used as the control specimen,the curing time of URCS is 28 days and 24 h respectively.The research results show that URCS has a stronger anti-explosion ability than NRCS.The failure mode of URCS under contact explosion is that the front of the reinforced concrete slab explodes into a crater,and the back is spall.With the increase of the charge,the failure mode of the reinforced concrete slab gradually changed to explosive penetration and explosive punching.The experiment results also show that the reinforcement ratio of URCS has little effect on the anti-blast performance,and URCS can reach its anti-blast performance at 28 days after curing for 24 h.On this basis,the damage parameters of URCS for different curing durations were quantified,and an empirical formula for predicting the diameter of the crater and spalling was established.

The dynamic response and damage models of rebar reinforced polymer slabs subjected to contact and near-field explosions

Non aqueous reactive polymer materials produced by the reaction of isocyanate and polyol have been widely used in infrastructure construction,which may be subjected to explosion loads during complex service conditions.The blast response of composite materials is a crucial aspect for applications in engineering structures potentially subjected to extreme loadings.In this work,damage caused to rebar reinforced polymer slabs by surface explosive charges was studied experimentally and numerically.A total of 6 field tests were carried out to investigate the performances of the failure modes of rebar reinforced polymer slabs under contact and near-field explosions.The influence of explosive quantity(10-40 g)and stand-off distances(0-20 cm)at the damage modes were studied.The results show that the failure modes of rebar reinforced polymer slabs under near-field explosion mainly were bending and surface spalling,while under the impact of contact explosion,the failure modes were craters of the top surface,spalling of the bottom surface,and middle perforation.Furthermore,a detailed fully coupled model was developed and validated with the test data.The influences of explosive quantity and slab thickness on rebar reinforced polymer slabs under contact explosion were studied.Based on this,the calculation formula between breach diameter,explosive quantity,and slab thickness is fitted.

Lead spall velocity of fragments of ultra-high-performance concrete slabs under partially embedded cylindrical charge-induced explosion

When an explosion occurs close to or partially within the face of a concrete structure, fragments are rapidly launched from the opposite face of the structure owing to concrete spalling, posing a significant risk to nearby personnel and equipment. To study the lead fragment velocity of ultra-high-performance concrete(UHPC), partially embedded explosion experiments were performed on UHPC slabs of limited thickness using a cylindrical trinitrotoluene charge. The launch angles and velocities of the resulting fragments were the determined using images collected by high-speed camera to document the concrete spalling and fragment launching process. The results showed that UHPC slabs without fiber reinforcement had a fragment velocity distribution of 0-118.3 m/s, which are largely identical to that for a normal-strength concrete(NSC) slab. In addition, the fragment velocity was negatively correlated to the angle between the velocity vector and vertical direction. An empirical Eq. for the lead spall velocity of UHPC and NSC slabs was then proposed based on a large volume of existing experimental data.

Numerical analysis of high‑speed railway slab tracks using calibrated and validated 3D time‑domain modelling

Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks,provide safe and smooth rides,and reduce the maintenance frequency.In this paper,the elastic performance of a novel slab trackform for high-speed railways is investigated using three-dimensional finite element modelling in Abaqus.It is then compared to the performance of a ballasted track.First,slab and ballasted track models are developed to replicate the full-scale testing of track sections.Once the models are calibrated with the experimental results,the novel slab model is developed and compared against the calibrated slab track results.The slab and ballasted track models are then extended to create linear dynamic models,considering the track geodynamics,and simulating train passages at various speeds,for which the Ledsgard documented case was used to validate the models.Trains travelling at low and high speeds are analysed to investigate the track deflections and the wave propagation in the soil,considering the issues associated with critical speeds.Various train loading methods are discussed,and the most practical approach is retained and described.Moreover,correlations are made between the geotechnical parameters of modern high-speed rail and conventional standards.It is found that considering the same ground condition,the slab track deflections are considerably smaller than those of the ballasted track at high speeds,while they show similar behaviour at low speeds.

Effect of temperature gradientinduced periodic deformation of CRTS Ⅲ slab track on dynamic responses of the train-track system

Purpose-Temperature is an important load for a ballastless track.However,little research has been conducted on the dynamic responses when a train travels on a ballastless track under the temperature gradient.The dynamic responses under different temperature gradients of the slab are theoretically investigated in this work.Design/methodology/approach-Considering the moving train,the temperature gradient of the slab,and the gravity of the slab track,a dynamic model for a high-speed train that runs along the CRTS Ⅲ slab track on subgrade is developed by a nonlinear coupled way in Abaqus.Findings-The results are as follows:(1)The upward transmission of the periodic deformation of the slab causes periodic track irregularity.(2)Because of the geometric constraint of limiting structures,the maximum bending stresses of the slab occur near the end of the slab under positive temperature gradients,but in the middle of the slab under negative temperature gradients.(3)The periodic deformation of the slab can induce periodic changes in the interlayer stiffness and contact status,leading to a large vibration of the slab.Because of the vibration-reduction capacity of the fastener and the larger mass of the concrete base,the accelerations of both the slab and concrete base are far less than the acceleration of the rail.Originality/value-This study reveals the influence mechanism of temperature gradient-induced periodic deformation in the dynamic responses of the train-track system,and it also provides a guide for the safe service of CRTS Ⅲ slab track.

Laminated Solid Timber Slab with Transverse Prestressing Using the Strategy of Interleaved Vertical Displacement of Lamellae

This article presents a study on the structural behavior of transversely prestressed laminated timber slabs,focusing on an innovative approach:vertically misaligned lamellae.This misalignment,achieved by sliding vertically the wooden lamellae rather than aligning them,enhances the slab’s cross-section moment of inertia,thereby improving load-bearing capacity and stiffness.Testing involved two groups of structural size specimens:one with vertically aligned lamellae(control group)and the other with misaligned lamellae(study group).Results showed the study group exhibited 42%superior stiffness and 10%less load capacity compared to the control.Failures typically occurred individually in the lamellae,particularly in those with defects or lower modulus of elasticity,concentrated in the middle third of the slabs’free span where tensile stresses peak.Despite a higher number of failed lamellae,the study group demonstrated promising performance.Analysis of prestressing bar indicated no damage at all in the thread,suggesting potential for reducing bar diameter.These findings offer crucial insights into applying these slabs in timber construction as well as to any kind of construction.

基于SLAB和AFTOX模型的LNG加气站大气环境风险评估

通过设定LNG加气站环境风险事故情景,分别采用SLAB和AFTOX模型模拟预测LNG加气站泄漏和火灾伴生/次生污染物CO的大气环境风险影响程度。结果表明:在风险事故情景下,下风向5 km范围内不同距离的甲烷和CO最大浓度未超过大气毒性终点浓度,甲烷最大浓度出现在下风向10m处,浓度值为32637.575 mg/m^(3);CO最大浓度出现在下风向5 km处,浓度值为1.746E-4 mg/m^(3)。考虑低温液态LNG的危险性和事故触发具有不确定性,LNG加气站在运营过程中仍需重点做好风险防范措施,编制企业突发环境事件应急预案,建立企业/区域环境风险防控体系,有效防控环境风险。

Exploring the Synergy: Experimental and Theoretical Investigation of Steel and Glass Fiber Reinforced Polymer (GFRP) Reinforced Slab Incorporating Alccofine and M-Sand

Introduction: This study investigates the Experimental and Theoretical Investigation of Steel and Glass Fiber Reinforced Polymer (GFRP) Reinforced Slab Incorporating Alccofine and M-sand. Objective: Specific objectives include evaluating the mechanical properties and structural behaviour of steel and GFRP-reinforced one-way slabs and comparing experimental and theoretical predictions. Methods: Four different mix proportions were arrived at, comprising both conventional concrete and Alccofine-based concrete. In each formulation, a combination of normal river sand and M-sand was utilized. Results: Concrete with Alccofine exhibits superior mechanical properties, while M-sand incorporation minimally affects strength but reduces reliance on natural sand. GFRP-reinforced slabs display distinct brittle behaviour with significant deflections post-cracking, contrasting steel-reinforced slabs’ gradual, ductile failure. Discrepancies between experimental data and design recommendations underscore the need for guideline refinement. Conclusion: Alccofine and M-sand enhance concrete properties, but reinforcement type significantly influences slab behaviour. GFRP-reinforced slabs, though exhibiting lower values than steel, offer advantages in harsh environments, warranting further optimization.

Mechanics analysis of vehicle bumping at approach slabs with superelevation

In order to analyze the pavement stress caused by vehicle bumping at an approach slab, a simplified four-wheeled bi- axle vehicle-moving model is proposed. The effect of damping and vibration reduction in the process of vehicle-moving is not considered. Based on the position change of vehicle wheels at the approach slab, the vehicle dynamic vibration equations are summarized. Meanwhile, the undetermined coefficients of the vibration equations are obtained using the boundary and initial conditions of the vehicle. The analytical motion solutions of rear and front wheels at different stages are concluded. Consequently, a four-wheeled vehicle model is developed and vibration equations are provided, which can be used to analyze the impact of complicated stress on pavement. The results show that the excessive stress and stress concentration will occur at the approach slab, and it needs to be strengthened.

Surface Phonon-Polaritons in Slabs of Ternary Mixed Crystals

Surface phonon-polaritons in slabs of polar ternary mixed crystals are investigated with the modified random-element-isodisplacement model and the Born-Huang approximation, based on Maxwell＇s equations with the usual boundary conditions. The numerical results of the surface phonon-polariton frequencies as functions of the wave-vector and thickness for slabs of ternary mixed crystals AlxGa1-xAs, Znx Cd1-x S,and Gax In1-x N are obtained and discussed. It is shown that there are four branches of surface phonon-polaritons in slab systems. The “two-mode” and “one-mode” behaviors of surface phonon-polaritons are also shown in their dispersion curves.

Numerical simulation of seismic damage and cracking of concrete slabs of high concrete face rockfill dams

Based on the damage constitutive model for concrete, the Weibull distribution function was used to characterize the random distribution of the mechanical properties of materials by finely subdividing concrete slab elements, and a concrete random mesoscopic damage model was established. The seismic response of a 100-m high concrete face rockfill dam(CFRD), subjected to ground motion with different intensities, was simulated with the three-dimensional finite element method(FEM), with emphasis on exploration of damage and the cracking process of concrete slabs during earthquakes as well as analysis of dynamic damage and cracking characteristics during strong earthquakes. The calculated results show that the number of damaged and cracking elements on concrete slabs grows with the duration of earthquakes. With increasing earthquake intensity, the damaged zone and cracking zone on concrete slabs grow wider. During a 7.0-magnitude earthquake, the stress level of concrete slabs is low for the CFRD, and there is almost no damage or slight damage to the slabs. While during a 9.0-magnitude strong earthquake, the percentages of damaged elements and macrocracking elements continuously ascend with the duration of the earthquake, peaking at approximately 26% and 5% at the end of the earthquake, respectively. The concrete random mesoscopic damage model can depict the entire process of sprouting, growing, connecting, and expanding of cracks on a concrete slab during earthquakes.

Longitudinal surface cracks of thin slabs

Based on the production practice of medium carbon thin slabs in the CSP plant,the reasons and influencing factors for the formation of longitudinal cracks were investigated,and some industrial measures were taken to eliminate the cracks.The results show that the efficient solutions to reduce longitudinal cracks are improving the performance of the mold powder,stabilizing the mold heat flux,and maintaining a proper taper of the mold during casting.Proper pouring temperature and secondary cooling also play important roles in preventing longitudinal surface cracks.

Refreezing of cast-in-place piles under various engineering conditions

In the construction of the Qinghai-Tibet Power Transmission Line （QTPTL）, cast-in-place piles （CIPPs） are widely applied in areas with unfavorable geological conditions. The thermal regime around piles in permafrost regions greatly affects the stability of the towers as well as the operation of the QTPTL. The casting of piles will markedly affect the thermal regime of the surrounding permafrost because of the casting temperature and the hydration heat of cement. Based on the typical geological and engineering conditions along the QTPTL, thermal disturbance ofa CIPP to surrounding permafrost under different casting seasons, pile depths, and casting temperatures were simulated. The results show that the casting season （summer versus winter） can influence the refreezing process of CIPPs, within the first 6 m of pile depth. Sixty days after being cast, CIPPs greater than 6 m in depth can be frozen regardless of which season they were cast, and the foundation could be reffozen after a cold season. Comparing the refreezing characteristics of CIPPs cast in different seasons also showed that, without considering the ground surface conditions, warm seasons are more suitable for casting piles. With the increase of pile depth, the thermal effect of a CIPP on the surrounding soil mainly expands vertically, while the lateral heat disturbance changes little. Deeper, longer CIPPs have better stability. The casting temperature clearly affects the thermal disturbance, and the radius of the melting circle increases with rising casting temperature. The optimal casting temperature is between 2 ℃ and 9 ℃.

Strain in solidifying shell of continuous casting slabs

Two-dimension unsteady heat transfer model was applied to obtain the surfacetemperature and the shell thickness of continuous casting slabs during the process ofsolidification. On the basis of which, the mathematical model of strain at the interface of solidand liquid steel was set up. Through which, the strain in the solidifying shell under normal andabnormal operation conditions was gained. The results indicate that the strain is small under thenormal operation conditions and the internal crack never happens. However, when the variation of theroll gap is above 2 mm, the strain caused by which is greater than that caused by bulging.Furthermore, the total strain exceeds the critical one and the internal crack is the result. So itis of great importance to maintain the fine state of continuous casting machine to avoid theappearance of internal crack.

Analytical solutions of transient heat conduction in multilayered slabs and application to thermal analysis of landfills

The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.

Behavior of steel-concrete composite slabs subjected to standard fire

Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in good agreement with those of tests. Fire resistance of the two kinds of composite slabs is calculated by using a numeric method. The results show that: due to heat absorbing of concrete, the performance of composite slabs under fire is better than that of unprotected steel structure, and fire resistance of composite slabs mentioned in this paper is at least 30 min subjected to standard fire. Parameters related to the fire resistance are discussed. It was found that with increasing of concrete strength and thickness of slab, fire resistance increases, and with increasing of steel strength and steel ratio, fire resistance decreases. Also thickness of fire proof is calculated by a numeric method. The results obtained in this paper may be referenced for practical engineering.