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.

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。

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.

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.

Influence of key factors on deflection of bonded prestressed concrete simply supported slabs subjected to fire

In order to validate the accuracy of nonlinear fire simulation programs,comparison analysis is carried out between simulation and experiment induced from small-scale specimens,and then fire resistance of large-scale prestressed concrete slabs is further investigated through parameter expansion.The influences on fire resistance ratings controlled by deflection are explored and discussed,including effective span,concrete cover thickness,load level,prestress degree,effective prestress,composite reinforcement index and other factors.The calculated results indicate that fire resistance ratings of large-scale bonded prestressed concrete simply supported slabs are bigger than those of small-scale ones.Finally,the calculation formulas of fire resistance ratings controlled by deflection are established,which rationally consider the influence of effective span,concrete cover thickness,load level,composite reinforcement index and so on key factors.

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.

Sensor location in concrete slabs with various layout of opening using modified ‘FEMS-COMAC’ approach

Two-way concrete slabs are widely used around the world for the construction of many types of infrastructures and common buildings. The optimal sensor placement(OSP) in slabs with various opening positions is the most important issue in structural health monitoring(SHM) to increase reliability. In this study, a novel approach of OSP was evaluated to obtain the number and placement of sensors using examination of the closed loop performance. The nonlinear finite element(NFE) was used to discretize the mechanism behavior of slab. Multi-Objective Optimization based on the coordinate modal assurance criterion(COMAC) and cost considerations was considered in the optimization processes. All of the analysis, discretization and optimization process was designed and developed as a novel approach in Matlab by the author under the name ‘FEMS-COMAC’(FEM analysis of slab with COMAC). The points in the finite element method(FEM) mesh were classified as line by line information along the slab. The OSP in each line was optimized according to the objective function. The slabs with various width, thickness, aspect ratio and opening position were selected as case studies. The results of the OSP using the COMAC algorithm around the slab openings were compared with the novel ‘FEMS-COMAC’ method. The statistical analysis according Mann-Whitney criteria shows that there were significant differences between them in some of the case studies(mean P-value=0.54).

Longitudinal surface cracks on continuous casting slabs of P and Cu containing container steel

The fact that the amount of the mold flux components differs at differentlocations on the cracking surface indicates that the longitudinal surface cracks are initiallyformed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductilitymeasurement of two typical container used steels, it is known that the steels are in severeembrittlement state in the temperature range of 825-775 deg C. By means of increasing Cr/Ni platingthickness on the upper part of the mold, reducing mold heat flux, adopting new secondary coolingpattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuouscasting) slabs has been significantly reduced.

Analytical Solutions to Strain Rates of Reinforced Concrete Simply Supported Slabs under Blast Loads

Based on the Duhamel integral, a couple of analytical solutions are derived to predict the strain rates of concrete and steel reinforcement in reinforced concrete slabs under blast loads and to estimate their variation over depth of a cross-section along the entire length of the member. The analytical approach utilizes the single-degree-of-freedom mode for the analysis of reinforced concrete simply supported one-way panels subjected to blast loads. These analytical solutions can give the strain rate profile for any cross-section at any time and permit variations of strain rate in each time step of numerical iteration method, thus making it possible to directly incorporate strain rate effects into non-linear dynamic response analysis of structural members subjected to blast loads.

Acoustic Polaron in Free-Standing Slabs

The ground-state energy and its derivate of the acoustic polaron in free-standing slab are calculated by using the Huybrechts-like variational approach. The criteria for presence of the selftrapping transition of the acoustic polaron in free-standing slabs are determined qualitatively. The critical coupling constant for the discontinuous transition from a quasi-free state to a trapped state of the acoustic polaron in free-standing slabs tends to shift toward the weaker electronphonon coupling with the increasing cutoff wave-vector. Detailed numerical results confirm that the self-trapping transition of holes is expected to occur in the free-standing slabs of wide-bandgap semi-conductors.

Vibration Reduction Performance of Damping-Enhanced Water-Lubricated Bearing Using Fluid-Saturated Perforated Slabs

As the first link element for the transmission of shaft vibration to the pedestal and even to the hull,water-lubricated bearing plays a key role in suppressing vibration.Although the porous structure is considered as one of the main methods for improving the wideband vibration and noise reduction performance of materials in many industrial fields,the studies in the field of water-lubricated bearing remain insufficient.To enhance vibration reduction performance,a fluid-saturated perforated slab is designed in this study,and via the establishment of a fluid-solid coupled vibration model,the influence law and impact levels were analyzed and verified by simulation and experiments.The results obtained verified that the total vibration amplitude of damping-enhanced stern bearing in the vertical direction was smaller than that of the normal stern bearing,and the reduction amplitude of the characteristic frequency agreed with the optimal value at approximately 0.1 of the volume fraction of the liquid phase when the solid-fluid phase was rubber–water.Additionally,the increase in fluid fraction did not enhance the damping effect,instead,it unexpectedly reduced the natural frequency of the raw material significantly.This research indicates that the design of the fluid-saturated perforated slab is effective in reducing the transmission of the vibration amplitude from the shaft,and presents the best volume fraction of the liquid phase.

Spallation Mechanism of RC Slabs Under Contact Detonation

The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely.Correctly predicting the damage caused by any potential contact detonation can lead to better for-tification design to withstand the blast loadings.It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls.Existing studies on this topic of-ten employ simplified material models and 1D wave analysis,which cannot reproduce the realistic response in the spallation process.Numerical simulations are therefore carried out under different contact blast loadings in the free air using LS-DYNA.Sophisticated concrete and reinforcing bar material models are adopted,taking into account the strain rate effect on both tension and com-pression.The erosion technique is used to model the fracture and failure of materials under tensile stress.Full processes of the deformation and dynamic damage of reinforced concrete (RC) slabs and plain concrete slabs are thus observed realistically.It is noted that with the increase of quantity of explosive,the dimensions of damage crater increase and the slabs experience four different damage patterns,namely explosive crater,spalling,perforation,and punching.Comparison be-tween the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent,and mean-while attenuate the ejection velocity and decrease the size of the concrete fragments.Therefore,optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.

NONLINEAR ANALYSIS OF REINFORCED CONCRETE RECTANGULAR SLABS USING FINITE ELEMENT METHOD

The nonlinear analysis of reinforced concrete rectangular slabs undermonotonic transverse loads is performed by finite element method.The layered rectangu-lar element with 4 nodes and 20 degrees of freedom is developed,in whichbending-stretching coupling effect is taken into account.An orthotropic equivalentuniaxial stress-strain constitutive model of concrete is used.A program is worked out andused to calculate two reinforced concrete slabs.The results of calculation are in goodconformity with the corresponding test results.In addition,the influence of tension stif-fening effect of cracked concrete on the results of calculation is discussed.

FREQUENCY-DOMAIN METHOD FOR RECONSTRUCTION OF THE PARAMETERS OF DIELECTRIC SLABS

The complex parameters of dielectric slabs can be reconstructed according to thescattered field data if the slabs are illuminated by a harmonic electromagnetic wave and thescattered field is measured.This paper describes a method for reconstruction of the parametersof single or double inhomogeneous lossy dielectric slabs.The numerical results are demonstrated.