Slab Corner Research Articles

Effect of cleaning parameters on the molten pool shape and molten slag dynamics in the corner scarfing process of the casting slab

In the steel industry, improving the hot charging and heat delivery ratio in the continuous casting of slabs and thick slabs can effectively reduce carbon emissions, lower energy consumption, and improve production efficiency. However, this puts very strict requirements on the surface quality of continuous-casting slab. Flame scarfing (or cleaning) technology is currently an important process in the metallurgy field, which can effectively remove impurities and crack defects on the surface and corners of continuous casting slab to ensure the quality and performance of the final product. Under the action of cleaning flame and iron oxide reaction heat, a cleaning molten pool is formed in the corner of the casting slab, and the shape and depth of the molten pool have an important influence on the cleaning effect. A three-dimensional mathematical model is developed to study the effect of slab cleaning speed and oxygen flow rate on the shape of the molten pool in the corners for the corner flame cleaning process. Simultaneously, a two-phase flow volume of fluid (VOF) model for gas-slag interactions is employed to examine the motion behavior of the molten slag. The results showed that when the operating conditions changed, the cleaning speed increased by 1 m/min, the length of the wide and narrow sides decreased by approximately 9.2 mm, and the depth of the corner pool decreased by approximately 5.3 mm. Moreover, a slag-blocking device was designed to mitigate the issue of slag splashing effectively based on the numerical simulation results compared with and without the slag-blocking device. These study works provide beneficial theoretical support and practical guidance for refining and optimizing flame-cleaning techniques.

Experimental study on the dynamic characteristics of bi-block ballastless track under the combined action of vehicle load and temperature gradient

The unit ballastless track structure, persistently exposed to environmental conditions, experiences significant vertical temperature gradients, leading to warping deformation of the track bed and impacting track smoothness. This study investigates the relationship between temperature gradients and warping deformation of the track bed through the analysis of on-site measurement data combined with a dynamic simulation model. It also examines how temperature gradients influence the dynamic response and the interlayer contact area of the ballastless track. Findings reveal that vertical displacement of the track bed follows a diurnal cycle and shows a positive correlation with temperature gradients, with pronounced differences between the slab's corners and center. Under a positive temperature gradient, the vertical displacement of the track bed is high in the middle and low at the ends, with the vehicle load causing longitudinal tensile strain in the slab’s side surface center. Conversely, under a negative temperature gradient, the vertical displacement is low in the middle and high at the ends, with the vehicle load inducing longitudinal compressive strain in the slab’s side surface center. Additionally, warping deformation of the track bed leads to incomplete contact with the base plate, creating a local support state and reducing interlayer contact area as the gradient increases. Positive temperature gradients result in an "oval" distribution of interlayer delamination areas, while negative gradients mainly affect the sides and ends. Dynamic loads from trains temporarily counteract warping deformation, briefly increasing the interlayer contact area, but their effectiveness diminishes as temperature gradients rise.

Interlayer damage evolution of CRTS III slab track under passenger and freight train loads

To study the interface damage in CRTS III slab tracks under the concurrent interactions of temperature and mixed passenger and freight train loads, a refined fatigue cohesive zone model (F-CZM) considering the stiffness, strength, and energy fracture degradation factors was presented. Utilizing this model, a finite element model (FEM) of the CRTS III slab track was developed. The interface fatigue damage between the track slab and self-compacting concrete (SCC) under various adhesive strengths and mixed operation modes was calculated. The interface characteristic degradation and stress change of door-type steel bars were revealed. Results show that good performance is ensured within the design service life with intact interface adhesion. The interface damage develops from the slab corner to the edge and then into the inner. The diminished interfacial tangential adhesive strength causes two patterns of interfacial damage procession. Enhanced freight train ratio escalates interface damage. During the development of interface damage, the door-type steel bars act as a safety margin.

Evaluation of void beneath the airport pavement slab corner based on the strain monitoring

ABSTRACT Void beneath the slab corner as a significant problem of airport pavement maintenance is always paid more attention by airport operators. The objective of this paper is to establish neural network models to predict the void sizes and load position based on the monitored strain values. A finite element model was established and validated by the data collected from a full-scale test pavement. Pavement strain values of 3168 scenarios considering different pavement structure parameters, load positions and void sizes were calculated. The simulated bottom strains at concrete pavement slabs were analysed for different void sizes and loading conditions. A coefficient and its warning thresholds were proposed to predict the occurrence of voids. Then, two Genetic Algorithm Backpropagation (GA-BP) neural network models were developed to predict void sizes and load position using the numerical simulation results as the training dataset.

3D Local Earthquake Tomography of the Andaman–Nicobar Subduction Zone Using Ocean-Bottom Seismometer Data

ABSTRACT The Andaman–Nicobar (A–N) subduction zone is one of the most seismically active subduction zones of the world where the Indian plate subducts beneath the Burmese–Sunda plate. Imaging the subducting Indian plate (SIP) geometry in this region is important to understand the subduction process, earthquake genesis, and associated seismic hazards. Therefore, we imaged the SIP for the first time using local earthquake data recorded from a network of nine ocean-bottom seismometers and six surface seismic stations. We inverted 2819 P and 2171 S phases picked from 410 local earthquakes recorded between December 2013 and May 2014 to obtain the tomographic images in the A–N region. The images show high-VP and VP/VS anomalies linked to colder and thicker SIP in the A–N region. We also observed seismic signatures of strong structural heterogeneity all along the SIP. The low-velocity anomaly at 60–100 km depth beneath the Andaman back-arc spreading center indicates mantle upwelling. Likewise, low-VP anomalies beneath the active volcano Barren Island indicate production of arc magmas by slab dehydration and corner flow in the mantle wedge.

Collapse-resistant mechanisms induced by various perimeter column damage scenarios in RC flat plate structures

This paper aims at assessing the impact of removing various numbers of perimeter columns on the integrity of RC flat plate substructures. Compared to interior columns, those at the corner and edge positions on the building perimeter are more likely to damage by accidental and abnormal loads, which in turn may cause progressive collapse of the entire structure. Given the uncertainty of the loading events, the likelihood of multiple perimeter columns being simultaneously destroyed is also high. However, existing research has primarily focused on the single column removal cases. To address this research limitation, a 3D high-fidelity finite element model of a flat plate substructure with a missing corner column (named Model C) was developed. The accuracy of the model was validated based on our previous experiment of the same substructure. The validated model was subsequently modified to cover two and multiple perimeter column removal scenarios. The two new models are namely, Model C_1e in which a corner column and an adjacent edge column were damaged and Model C_2e, with a corner column and two adjacent edge columns being removed. The simulation results reveal that flexural action was the primary load resisting mechanism in all three models. The load carrying capacity with three column removals was reduced by 75.6% compared to the removal of a single corner column. Full-depth cracks were found at the cut-off position of the top slab rebars for the columns adjacent to the removed one(s). In Model C and Model C_2e, cracks exhibited a diagonal axisymmetric failure pattern of the corner of the slab, with equal load transfer to two adjacent columns. In contrast, Model C_1e exhibited a diagonal non-axisymmetric failure pattern of the slab corner, with more loads being transferred to the adjacent column along the shorter bay. The energy-based dynamic response analyses were also performed to obtain the Dynamic Increase Factor (DIF) for the substructure models under different column removal scenarios. Based on the nonlinear regression analysis, the DIFs for the substructures with one and two column removals were found to be ranged between 1.22 and 1.51, and 1.28–1.68, respectively.

Influences of cement asphalt emulsified mortar construction on track slab geometry status

PurposeThe construction of cement asphalt (CA) emulsified mortar can obviously disturb the slab status after the fine adjustment. To decrease or eliminate the influence of CA mortar grouting on track slab geometry status, the effects of grouting funnel, slab pressing method, mortar expansion ratio, seepage ratio and grouting area on China Railway Track System Type (CRTS I) track slab geometry status were discussed in this paper.Design/methodology/approachCombined with engineering practice, this paper studied the expansion law of filling layer mortar, the liquid level height of the filling funnel, the pressure plate device and the amount of exudation water and systematically analyzed the influence of filling layer mortar construction on the state of track slab. Relevant precautions and countermeasures were put forward.FindingsThe results showed that the track slab floating values of four corners were different with the CA mortar grouting and the track slab corner near CA mortar grouting hole had the maximum floating values. The anti-floating effect of “7” shaped slab pressing device was more efficient than fixed-joint angle iron, and the slab floating value could be further decreased by increasing the amount of “7” shaped slab pressing devices. After CA mortar grouting, the track slab floating pattern had a close correlation with the expansion rate and water seepage rate of CA mortar over time and the expansion and water seepage rate of the mortar were faster when the temperature was high. Furthermore, the use of strip CA mortar filling under the rail bearing platform on both sides could effectively reduce the float under the track slab, and it could also save mortar consumption and reduce costs.Originality/valueThis study plays an important role in controlling the floating values, CA mortar dosage and the building cost of projects by grouting CA mortar at two flanks of filling space. The research results have guiding significance for the design and construction of China's CRTS I, CRTS II and CRTS III track slab.

Formation Mechanism and Control Technology of Transverse Corner Cracks During Slab Continuous Casting of Microalloyed Steels

Microalloyed steel with Nb, V, Ti, and other alloying elements is one of the important steel grades in the steel industry. During continuous casting process, high occurrence rate of transverse corner cracks in slabs restricts the quality and efficiency of the production of microalloyed steel grades, and it has not been effectively solved for a long time. Herein, the research progress on the formation mechanism, influential factors, and typical control technologies of transverse corner cracks during slab continuous casting are reviewed. Considering high‐temperature solidification process of microalloyed steel, the control of growth of microstructures and the precipitation behavior of carbonitrides in slab corners are supposed to be the key to avoid transverse corner cracks during slab continuous casting.

Influence of Reflective Coating on Temperature Field and Temperature Effect of CRTS III Slab Ballastless Tracks on Bridges.

To minimize the adverse effects of high temperatures on the service performance of track structures, research on the application of reflective coatings on track structures is urgently needed. Based on meteorological data and the characteristics of the multi-layer structure of the ballastless track, refined finite element models (FEMs) for the temperature field and temperature effect analysis of the CRTS III slab ballastless track structure on bridges were established. The temperature deformation characteristics and temperature stress distribution of the CRTS III slab ballastless track under natural environmental conditions were investigated. Similarly, the influence of a reflective coating on the structural temperature field and temperature effect was studied. The results showed that the temperature and vertical temperature gradient of the track slab were significantly reduced after the application of the reflective coating. Meanwhile, the thermal deformation and thermal stresses of the track slab and the self-compacting concrete (SCC) layer were minimized. Under high-temperature conditions in summer, the maximum temperature of the track slab decreased from 47.0 °C to 39.6 °C after the application of the reflective coating, and the maximum vertical temperature gradient of the track slab decreased from 61.5 °C/m to 39.1 °C/m after the application of the reflective coating. Under the maximum positive temperature gradient, the peak displacement of the upper arch in the middle of the slab and the peak displacement of the sinking in the slab corner decreased from 0.814 mm and 1.240 mm to 0.441 mm and 0.511 mm, respectively, and the maximum transverse tensile stresses of the track slab reduced from 2.7 MPa to 1.5 MPa as well. In addition, the reflective coating could also inhibit the failure of the interlayer interface effectively. The results of this study can provide a theoretical basis and reference for the application of reflective coatings on ballastless tracks on bridges.

Identification of Cement Pavement with Temperature Effect and Evaluation of Polymer Grouting Effect.

The falling weight deflectometer (FWD) detection system benefits from its outstanding characteristics of no damage, fast speed, and high precision. The warping deformation of cement concrete pavement occurs due to the temperature difference along the depth of the slab, which makes FWD detect different results under different temperature fields. In this study, we systematically carried out the cement pavement's temperature field and deflection test. The experimental data were analyzed to obtain the temperature variation law of the top and bottom of the pavement slab every day. By establishing a three-dimensional finite element model of cement pavement with a multi-layer elastic foundation type, the influence of the temperature difference at the bottom of the slab on the deflection of the center point of the slab corner load under different working conditions, different seasons, different loads and whether there is polymer filling in the void area was studied. We summarize the correlation between the temperature difference and the influence coefficient and propose the cement pavement void identification and polymer grouting effect evaluation method considering the temperature effect.

Finite Element Analysis of High-Strength Concrete Pavement Made With The Addition Of Fibres

This paper provides an analytical Solutions and software-based analysis on the determination of Stress-Strain behaviour of High strength concrete pavement slab by applying number of axle load parameters given in the guideline of IRC-58 in the construction of Rigid pavement. The effect of the use of hybrid fibres, such as steel fibres and polypropylene fibres, on the behaviour of stress distribution is also studied. Shrinkage in HSC due to the incorporation of Hybrid fibres in different proportions at four Curing Temperatures is also analysed. FEA has been used to analyse the Shrinkage behaviour of High Strength Concrete Pavements with different geometry and thermal curing temperatures as (5°C, 20°C, 35°C, and 50°C). In the present research, the shrinkage analysis, Stress distribution behaviour in High Strength concrete pavement will be studied using Hybrid fibre of steel and polypropylene with a dosage of 1%, 1.5% and 0.1%, 0.2% respectively and by applying axle loadings of single, dual, tri and tandem axle as per IRC 58. Axle load is applied at the centre, edge and corner of the pavement slab and the stress distribution results are obtained. The Analytical solutions are obtained from Westergaard’s equations and software-based results are compared with the analytical solutions and there are very less dissimilarities between both the results.

TESTING OF HOLLOW-CORE END NOTCHED FLOOR SLAB

This paper examines the test results of a hollow-core reinforced concrete prestressed end-notched floor slab of formwork formation subjected to uniformly distributed load.
 The research of the end-notched slab was carrying out in the testing hall of the State Enterprise "State Research Institute of Building Structures" according to the procedure of standard DSTU B B.2.6-7.
 Vertical uniformly distributed load was applied to the end-notched slab with cross-rails and support fixtures for loading, with hydraulic jacks and pumping station equipped with force meter.
 The end-notched slab was subjected to step-by-step loading with load steps of 100 kgf/m2.
 Inspection of the surface of the end-notched slab in the test area, with recording in the register of measurement results of displacements and potential damages was carried out after every loading step.
 Vertical displacements of the end-notched slab corners were measured with four clock type indicators ICH-10. Vertical displacements of the middle slab span were measured with two deflectometers 6PAO. The middle span deflection of the end-notched slab was calculated considering corner displacements.
 Based on the results of research, it was established that before applying the load of 800 kg/m2 there were not detected cracks the opening width of which exceeded the limit values.
 The loss of loadbearing capacity of the end-notched slab was detected after the load of 1280 kgf/m2, which which exceeded the design load by 1.6 times. The end-notched slab collapsed due to loss of shear resistance.
 According to the test results, it was established that hollow-core reinforced concrete prestressed end-notched floor slab meets the requirements of strength, stiffness and crack resistance.

Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces

The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax, followed by secondary cooling. The negative effect of a low Tmin on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the Ar3, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a Tmin of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when Tmin was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels.

Hybrid rubber‐concrete isolation slab system with various shape factors for structures subjected to horizontal and vertical vibrations

SummaryThe present framework proposed the development of a Hybrid Rubber‐Concrete Isolation Slab System (HRCISS) to support building structures subjected to horizontal and vertical vibration due to ground motion and machine or equipment operation in the structure. Given that the effect of the shape factor on both horizontal and vertical stiffness has yet to be reported, the proposed composite system was comprised of two layers under the nodal points of the upper layer near the slab corners with four High Damping Rubber (HDR) components positioned between the slab layers to dissipate multidirectional (horizontal and vertical directions) vibrations. The ABAQUS software was utilized to model the finite element model (FEM) and simulate the HRCISS subjected to cyclic horizontal and vertical displacements. For the optimal HDR design, the model was applied in five 3‐story buildings, and the effect of distinct shape factors (0 S 2) of the HDR bearings—the ratio of bearing's loaded area to unloaded area (free to bulge)—within the hybrid system was evaluated. For each building with a specific HDR shape factor, the HRCISS was installed in the first, second, and third stories, separately, to investigate the influence of the installation level of the isolation system on the overall structural performance. The multistory buildings were subjected to two types of vibration loads: the interior machine‐induced vibrations, and the exterior seismic‐induced vibrations in the horizontal and vertical directions. Based on the results, the FEM results proved the significant influence of the shape factors on the dynamic response of the HRCISS under both interior and exterior 3D vibrations when applied in multistory buildings. The lateral drift of the three‐story one‐bay buildings decreased with the decrement of shape factor with buildings of HRCISS installed in 1st story recording more reduction. Moreover, the deflection in the structural slab under the HRCISS decreased for lower shape factor bearings. Nevertheless, the reduced deflection was less affected by the level of the machine‐equipped story. The rubber layer also stiffened in shear and compression directions with a higher shape factor.

Application of Optimizing Slab Corner Shapes to Reduce Edge Seam Defect on Heavy Plates

The edge seam defect is a common defect in hot rolling heavy plates. It can be improved by optimizing the corner shapes of slabs. Based on a numerical analysis of the effects of the slab corner shape on the temperature distribution after the slab’s exit from the heating furnace, three rolling methods are proposed for controlling the two-chamfered slab corner shape. The stress and deformation of the corner of the slab during the two-chamfered rolling process are investigated using a numerical simulation. The results show that a two-chamfered shape slab has the smallest temperature drop during the cooling process, and the slab corner can maintain higher temperature and uniformity, which is beneficial for controlling the deformation during the rolling process. Among the three kinds of two-chamfered rolling methods, frontal rolling using a two-roller has the smallest rolling force and rolling resistance to the casting machine, followed by horizontal rolling and then vertical rolling, which has the largest. The favorable slab corner in a two-chamfered shape can be obtained by frontal rolling using a two-roller. Industrial trials confirm that an edge seam defect rate of less than 5% in heavy plates can be achieved under the condition of a large broadside ratio.

Torsional behavior of a non‐eccentric structure considering the effect of shear deformations in vertical members

AbstractTorsional moments can occur in a column owing to the geometric nonlinearity when the top of the column undergoes a large displacement in two horizontal directions. Periodically generated torsional moments can excite the torsional mode of a building owing to the internal resonance. For high‐rise buildings, there is a risk that long‐period seismic motions can cause a non‐negligible torsional response due to this phenomenon. To investigate this risk, this study focuses on non‐eccentric single‐story and two‐story shear‐type structural models with an aggregate column, which is assumed to be an elastic Timoshenko beam. We derived the equations of motion for the models under horizontal ground motions and confirmed that the equations were identical to those of the models with an aggregate column of an elastic Euler beam. We then performed time‐history response analyses of the models satisfying the internal resonance conditions under the input ground motions of harmonic waves, Gaussian white noise acceleration, acceleration records of previous earthquakes, and a long‐period design wave. The results showed that the maximum horizontal acceleration at the corner of the top floor slab could be increased by more than 60% of the acceleration at the center of the slab in the worst case.

Effect of Temperature and Solidification Structure Evolution of S355 Slabs with Different Corner Shapes on Transverse Corner Cracks

The evolution process of corner temperatures for a typical micro-alloyed steel S355 is numerically simulated under various working conditions. The microstructure near the corner cracks of the S355 slab is experimentally examined, and the austenite/ferrite transformation temperatures of S355 steel during heating and cooling are measured. The results indicate that the right-angle slab corner temperature at the exit of the mould rapidly decreased to below Ar3 under intensive cooling in the foot roller zone. The film-like ferrite began to precipitate along the austenite grain boundary at the slab corner. The transformation from ferrite to austenite cannot be fully realized because the corner temperature cannot be quickly returned to Ac3 or higher. The slab transverse corner cracks occur along the film-like ferrite during the bending process. The chamfered slab, which modifies the original right angle of the slab into the 30° chamfered angle with a chamfered length of 60 mm, can significantly weaken the heat transfer and cooling effect of the slab corner. The chamfered slab corner temperature always remained above Ar3 during the bending and straightening processes. Precipitation of the pro-eutectoid film-like ferrite along the grain boundary cannot occur during cooling for the chamfered slab. The chamfered slab can keep the corner temperature above Ar3 and effectively avoid the occurrence of transverse corner cracks caused by grain boundary embrittlement.

Thermo-mechanical behaviour analysis of slab corner during special steel continuous casting

ABSTRACT The corner crack is an important issue during special steel continuous casting. To comprehensively investigate the heat transfer, stress, and shrinkage behaviours of slab corner, a full-scale thermo-mechanical model of a slab and its mould was developed, the inverse algorithm was applied to the model. The model was validated by comparing the calculated data with the measured data in the plant trials. The results showed that the thermo-mechanical behaviours of the slab corner showed a similar tendency but were not the same, which reflected the necessity of building a full-scale model. There exists ‘hot spots’ at the slab off-corner region, and its position moved away from the corner along the casting direction, which affects the temperature and stress distributions. The maximum stress value reached approximately 16 MPa at the mould exit. The model provides an in-depth understanding of slab corner during special steel continuous casting.

Study of the Dynamic Response of a Rigid Runway with Different Void States during Aircraft Taxiing

In this study, a set of numerical simulation analysis methods for studying the dynamic response of runway under the action of aircraft taxiing load are presented. An aircraft-runway coupled vibration model was established, and the runway pavement roughness was taken as the vibration excitation source; then, the aircraft taxiing dynamic load was obtained. A three-dimensional finite element model of the runway was established, and the vertical dynamic displacement (VDD) response and its variation law of the runway under different void conditions were studied under the action of the dynamic load of a taxiing aircraft. In addition, using wavelet packet transform, the acceleration signals at different positions of the pavement slab under the sliding load were decomposed into three layers. The relationship among the wavelet packet energy ratio (WPER), the wavelet packet energy entropy (WPEE) of each frequency band, and the void under the pavement slab was obtained. The results show that the established model could quickly and accurately solve the aircraft taxiing dynamic load. In the case of a slight void, the VDDs in the runway center and under the main landing gears had negative exponential and logarithmic relationships with the reduction coefficient of the dynamic elastic modulus of the base layer, respectively. When there was a severe void, the pavement slab was separated from the base layer. The VDDs in the runway center and under the main landing gears were exponentially and linearly related to the slab’s void area, respectively. The vibration signals were extracted at three measuring points, and the wavelet packet energy characteristics of the signals were compared and analyzed. It was found that the WPER and WPEE of the vibration signals in the void area of the slab corner could better reflect the void state of the slab bottom.

Impact resistance of concrete pavement surface reinforced with fibre mesh

ABSTRACT The surface layer of military airfield pavements is prone to damage, including cracking, abrasion, and spalling. It is proposed to strengthen the pavement mortar layer by laying fiber mesh to solve these issues. In this study, three meshes of carbon fiber, aramid fiber, and basalt fiber were selected for surface reinforcement across six pavement slabs of 1.5m (length) × 1.5m (width) × 0.25m (height). The drop hammer impact test was carried out on the six pavement slabs. The test data were analyzed using impact times, crack development characteristics, and development models on the surface deflection as evaluation indices. The results show that the fiber mesh can effectively improve the impact resistance of concrete pavement slabs. Aramid fiber mesh best strengthened the pavement surface, whereas the basalt fiber mesh had the least strengthening effect. However, the mesh size has a negligible influence on the impact resistance of concrete pavement slabs. The effect of fiber mesh on improving the impact resistance of the concrete pavement slab corner was greater than that of the concrete pavement slab edge midpoint. Considering the performance and cost indicators, within the scope of the study, aramid fiber mesh is the most suitable for surface strengthening of airfield concrete pavement.