Cracks In Slabs Research Articles

Study on early shrinkage and cracking of slab in UHPC light-weight composite deck based on ambient temperature and humidity effects

This study investigates the early performance and potential issues of ultra-high-performance concrete (UHPC) light-weight composite decks (LCBDs) used in municipal highway bridge design. The major objective of this research was to understand the complex evolution of temperature and humidity within immature UHPC thin layers, which can lead to deformation and secondary stress, potentially causing cracks and threatening the long-term applicability and safety of steel-concrete composite bridges. Understanding of the mechanism of this process will be the basis for subsequent work. The early performance of UHPC with ordinary concrete is compared. Besides, discussions are conducted on the basic thermal conductivity theory of three-dimensional porous media and the hydration mechanism of cement-based materials that are appropriate for early-stage UHPC. Subsequently, a refined thermo-mechanical coupling analysis method for steel-UHPC LCBD was proposed, implemented using ABAQUS, and validated through a UHPC composite beam test. This method was applied to calculate the early shrinkage of the UHPC layer in a steel-UHPC LCBD and evaluate the risk of cracking in an actual bridge expansion project, providing a rationality evaluation of a bridge design and its construction procedure.

Research on slurry diffusion and seepage law in mining overburden fractures based on CFD numerical method

It is of great theoretical significance and engineering application value to research the diffusion law of slurry in mining fractures of rock strata to enrich grouting theory and improve grouting sealing effect. In this paper, the law of grout diffusion in fractures under different working conditions is systematically explored and analyzed, and a numerical simulation scheme of grout diffusion in a single slab crack is established. Then, the diffusion law of grouting slurry in crack under different rheological index and different consistency index is further investigated. The results show that the diffusion time of grouting slurry has no relation with the rheological index. The grout pressure at the same point increases with the increase of rheological index. When the rheological index increases by 0.1, the grout pressure increases by about 12.5%. The closer the grouting mouth is, the more the grouting pressure is affected by the rheological index. There is little relationship between the diffusion time of grouting slurry and consistency index. The grout pressure at each measurement point increases with the increase of the consistency index. When the consistency index increases by 1, the grout pressure increases by about 15% on the basis of the origin. The closer the grouting mouth is, the more the grouting pressure is affected by the consistency index. In engineering practice, when grouting slurry with large rheological index or consistency index exists, it is necessary to moderately increase the grouting pressure value.

Analysis on crack propagation of CRTS III slab ballastless track under temperature loads and freeze–thaw deterioration

In seasonal frozen region, the Chinese Rail Track System (CRTS) III slab track is subject to temperature loads and freeze–thaw deterioration, which may lead to further expansion of microcracks in track slabs. Mechanical parameters of track structure materials after freeze–thaw cycles are obtained through the experimental tests in this study. A finite element model of CRTS III slab track on subgrade section is then established by ABAQUS. Based on fracture mechanics theory, the types of cracks generated in track slabs under temperature loads and freeze–thaw deterioration, and crack expansion law are analyzed by using extended finite element method. The results show that under temperature loads, the expanded cracks in track slab are mainly Mode Ⅰ - Opening mode. There is the possibility of expansion for transverse cracks with larger size on the upper surface of track slab under negative temperature gradient load. Vertical capillary cracks at the location where track slab is bonded to self-compacting concrete are more likely to expand. Freeze-thaw deterioration will reduce the difference between the SIFs of cracks and fracture toughness of track slab material, which has a certain promotion effect on crack expansion.

Mindlin cracked plates modelling and implementation in train-track coupled dynamics

Nowadays, the widely constructed ballastless track in high-speed railways will inevitably suffer from localized damage cracks induced by complicate environmental effects, which would change its designed dynamic performance under train dynamic loads and further affect its service life and durability. To this end, a semi-analytical approach of the in-plane and the out of plane forced vibration for Mindlin plates with a side crack are derived, and is further implemented into the train-track coupled dynamic (TTCD) system which comprehensively considering nonlinear wheel-rail contact and 3D spatial flexibility of the cracked track slab. The dynamic partial differential equation of the cracked slab is derived by Hamilton principle and discretized by Galerkin method. Then the eigenvalues and forced vibrations of the cracked slabs for both in-plane and flexural vibrations are tackled utilizing a set of powerful trigonometric modified by special corner function, which can effectively explain the singularity of stress at the crack tip and the discontinuity of deformation on both sides of the crack. The eigenvalue analysis and mode shapes of the cracked plate mode in free boundary condition are compared with the finite element method to verify its accuracy. Meanwhile, the reliability of the proposed dynamics model is verified by comparing with the responses predicted by the co-simulation technology. Finally, the discrepancies of dynamic responses of the track slab with or without a side crack are analyzed, and the effects of various operation speeds and support stiffness on the dynamic behaviour of both slabs are revealed. Results indicates that the track slab with a side crack has significant distinctions on the slab dynamic signals in both time and frequency domains, and the amplitude amplification phenomenon occurs in some specific areas compared with the intact slab; The type-Ⅱ stress intensity factor (SIF) is more sensitive to train speeds, while the support stiffness is highly correlated to all types of SIFs. This work may contribute to the scientific maintenance and health monitoring of high-speed railway tracks.

Hybrid-Input FCN-CNN-SE for Industrial Applications: Classification of Longitudinal Cracks during Continuous Casting

In the presented research, machine learning methods were applied to the prediction of longitudinal cracks in steel slabs during continuous casting. We employ a deep learning approach to process 68 thermocouple signals as a multivariate time series (MTS) along with 32 static features, which encompass both chemical composition and process information. Our deep learning approach integrates two distinct parallel modules, followed by an aggregation block; a Convolutional Neural Network (CNN) processes the thermocouple MTS, while in parallel, the static data undergo processing via a Fully Connected Network (FCN). To enhance the performance of the CNN, we incorporate two Squeeze and Excitation (SE) blocks, which act as an attention mechanism across different channels. By integrating chemical information with MTS in the detection system, we improve the performance of defect detection by 15% relatively.

Method of computational models of resistance for reinforced concrete

Based on a comprehensive analysis of the experimental studies from the standpoint of their convergence with the theoretical solutions, the computational models of resistance (CMR) of reinforced concrete are proposed. These models include CMR1 - modeling of normal cracks, CMR2 - modeling of inclined cracks, CMR3 - modeling of diagonal cracks, CMR4 - modeling of intersecting cracks in the wall, CMR4* - modeling of cracks in a flat slab, and CMR5 - modeling of spatial cracks in torsion with bending, CMR5* - modeling of spatial cracks in bending with transverse force. Also, a hierarchy of computational models of the second and third levels is proposed. The distribution of intensity of working reinforcement along the cross-section of the calculated element was obtained in an analytical form by creating closed equations of blocks, corresponding to the blocks of the reinforced concrete element under the condition of equality to zero of partial derivatives of the Lagrange function to determine the maximum crack opening width. It is considered the effect proposed by the author on the additional deformation impact of the reaction “concrete - reinforcement” from the discontinuity of concrete during the formation of the crack by means of a special model of the two-cantilever element of fracture mechanics. Hypotheses about the distribution of linear and angular deformations during cross-section with account of gradients of deformations caused by formation of cracks were formulated for a complex-stressed element subjected to torsion with bending. Crack opening is defined as mutual displacements of reinforcement and concrete, taking into account deformation. The consolidation of substructures in the building system is performed by the method of initial parameters.

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.

Multifractal characteristics of fatigue cracks in the full-scale reinforced concrete hollow-slab beams

Highway Reinforced concrete (RC) bridges bear the repeated vehicle loads for a long time, promoting cracks' sprouting and development. Establishing a quantitative evolution model of cracks will improve the management and maintenance of similar bridges. Therefore, this paper introduces the multifractal theory into crack characterization and carries out the study on the multifractal characteristics of fatigue cracks in full-scale RC hollow slabs. Firstly, the basic procedure of the multifractal analysis method for concrete cracks is introduced, and the sensitivity of the multifractal spectrum under different influencing factors is analyzed. Secondly, the basic information and scheme of the experimental beam are introduced. The experimental results and the development law of fatigue cracks are analyzed. Finally, the variation law of the multifractal spectrum with cycle number is analyzed based on the multifractal theory, and a simplified evolution model of fractal dimension (FD) under fatigue load is established based on the experimental results. The experimental results prove that the multifractal theory is effective in describing the cracking state of RC members under fatigue load. The fatigue cracks' development of the experimental beam presents an obvious three-stage pattern: rapid stage, stable stage, and destabilized stage. The FDs of fatigue cracks also develop in a three-stage pattern along with cycle number, which can be expressed by a linear equation of cycle percentage. The evolution model can provide technical support for the maintenance decisions of RC bridges in service.

Application of Fractal Theory to the Analysis of Failure Characteristics of Low-Velocity-Impact Concrete Slabs

The fractal characteristics of low-velocity-impact concrete slabs were studied using fractal theory, and the fractal dimension value of cracks of each concrete specimen plate was calculated using box dimension as the basic principle and digital image analysis technology in conjunction with MATLAB software (R2021b) calculation functions. The energy dissipation of concrete slabs during low-velocity impact is calculated using the elastic sheet theory. The calculation results are realistic, and the energy conversion of concrete slabs during low-velocity impact is analyzed based on these results. The research findings indicate that concrete slab cracks exhibit good fractal characteristics during low-velocity impact, and their values can be utilized as a parameter to determine the extent of concrete slab failure. Moreover, the study found that the fractal dimension value of concrete slab cracks and the associated plastic deformation energy display good exponential function characteristics in the energy dissipation mechanism of low-velocity concrete slabs.

Dynamic evaluation method for Time-variant reliability of structural safety of Concrete-faced rockfill dam

The evaluation of the structural safety risk for concrete-faced rockfill dams (CFRDs) is susceptible to the time-varying parameters and the environments of topography, geology, and operations. Traditional evaluation methods, due to their involvement in numerical simulation, cannot meet the current requirements for intelligent monitoring in terms of timeliness and practicality. Therefore, a dynamic evaluation method of reliability in CFRDs is proposed in this paper. Due to the nonlinear mapping relationship between the time-variant reliability and the monitoring characterizations of CFRDs, the long and short-term memory neural network (LSTM) and support vector machine (SVM) models are introduced to construct the potential functional relationships between the reliability sequences and the monitoring characterizations, and the matching between the accuracy of the two models and the frequency of monitoring characterizations has been fully studied, forming an adaptive evaluation model of safety risk for the CFRDs according to the different monitoring frequencies of different monitoring items. The application of Sanbanxi CFRD shows an average relative error of less than 1% and 5% for dam slope stability and slab cracking simulations, respectively. These results demonstrate that the LSTM and SVM models with adaptive monitoring frequency exhibit high fitting and prediction accuracy and applicability, and possess theoretical and engineering application value.

Early-Age Cracking Behavior of Concrete Slabs with GFRP Reinforcement.

This paper reports on a combined experimental and numerical modeling investigation of cracking of concrete slabs with GFRP reinforcement. At this stage of the project, attention is given to early-age cracking driven by plastic shrinkage, preceding longer term considerations of cracking resistance over the service life of field applications. Of interest is the effectiveness of GFRP reinforcement in restricting plastic shrinkage cracking. Nine small-scale slab specimens were subjected to controlled evaporation rates. Images of crack development were acquired periodically, from which crack width estimations were made. Comparisons were made between slabs reinforced with conventional steel and those reinforced with GFRP, along with control specimens lacking reinforcement. During the period of plastic shrinkage, the time of crack initiation and subsequent crack openings do not appear to be influenced by the presence of the reinforcing bars. To understand this behavior, six early-age bond tests were conducted for both types of the bars after 1, 2, and 3 h exposure to the controlled evaporation rate. In addition, concrete strength development and time of settings were measured using penetration resistance tests on a representative mortar. The numerical modeling component of this research is based on a Voronoi cell lattice model; in this approach, the relative humidity, temperature, and displacement fields are discretized in three-dimensions, allowing for a comprehensive investigation of material behavior within the controlled environment. Based on the measured bond properties, our simulations confirm that the reinforcing bars restrict crack development, though they do not prevent it entirely.

Punching shear of reinforced concrete slabs bonded with reactive powder after exposure to fire

Abstract Reactive powder concrete (RPC) is one of the most recent and significant advancements in the world of building. Due to its higher concrete characteristics, it has a common excessive benevolence happening in the globe at the moment, excessive ductility, shrinkage resistance, and corrosion and abrasion resistance. Investigated is the method for amending the RPC experimentally in punching shear slab action and the properties of construction material to investigate properties of volumetric ratios of steel fiber, and silicas fume, tensile steel ratio, the most important component for construction is reinforced concrete, which works well with other materials to create structures in any shape that is needed. In the present research, investigational work of RC slab with (1,000 × 1,000 × 60) mm dimensions was tested. This study aims to see how the relative volume of steel fibers (Vf) and silica fume content (Sf) affect the actions of RC slabs after being exposed to fire. It originated that a concrete mix containing 2% steel fibers improved the RPC slab's cracking and final punching shear. The existence of reactive powder increases fire resistance. This study's experiment aimed to see how reactive powder and Slab's ultimate punching shear strength were affected by replacement ratio. Whenever a fire is present. After fire exposure, the initial and subsequent stiffness of reinforced concrete slabs reduced considerably the temperature grew from 25 to 750°C.

Hot Ductility Evolution Mechanism of Titanium‐Bearing Microalloyed Steels

Titanium‐bearing (Ti‐bearing) microalloyed steels have high strength and toughness by grain refinement effect of carbonitride precipitates. However, they can induce surface cracks of continuous casting slab when the Ti alloyed content is high. A microalloyed steel with Ti content (0.10–0.15 wt%) is carried out by thermalmechanical simulator over 600–1350 °C to analyze hot ductility evolution mechanism. Fracture surface morphology, phase transition, and behavior of precipitates of the tensile samples are investigated by experimental detection and thermodynamic calculation. The ductility–temperature curves show that the third brittle temperature range is 600–890 °C, which is mainly attributed to the thin proeutectoid ferrite film and precipitated titanium carbonitride particles, widening the embrittlement temperature ranges through of steel. In addition, the tensile samples at 890–1350 °C have good hot ductility, indicating the dynamic recrystallization of deformed austenite can trigger grain boundaries migration away from cracks and avoid the side effect of the Ti (C,N) particles on hot ductility. The first brittle temperature range of 1350 °C‐melting point is mainly ascribed to the partial melting of the grain boundaries with element segregation of sulfur and phosphorus, and microporosity loose among dendrites.

Structural Behavior of Reinforced Concrete Hollow Core Slabs Cast with Self-Compacting Concrete Containing Recycled Concrete as Coarse Aggregate

This paper investigates the possibility of recycled aggregate use in concrete slabs with hollow cores. The main variables considered in the experimental study for the slabs were the recycled aggregate percentage and the hollow core number. Six slabs with dimensions of (1000 × 500 × 120) mm was fabricated and tested. The results showed that the addition of recycled aggregate in the concrete slabs affected the ultimate strength, ductility, and energy absorption of the concrete members. An increase of the recycled aggregate percentage to 25 % decreased the ultimate strength capacity by 3.54 %, but the increase of recycled aggregate to 50 % led to a decrease in the ultimate strength of about 6.64%. The existence of a hollow core reduced the cracking and ultimate load capacity of the RCA slabs, and this reduction was according to the core number which the fabrication of more cores caused more decrement. The ductility and energy absorption were decreased when the replacement ratio of the recycled aggregate increased. Also, the core number affected the ductility and energy absorption. The energy absorption was the most property affected by the core number increase which caused an average reduction of 71.5 % when the core number increased from two to three hollow cores.

Experimental and analytical study on steel-concrete-ECC composite frames with URSP-S connectors

To improve the slab crack resistance in the hogging moment region of steel-concrete composite frames, this paper proposes using Engineered Cementitious Composite (ECC) and Uplift-Restricted and Slip-Permitted Screw-type (URSP-S) connectors near the columns of the frames, the structural behavior of the innovative steel-concrete-ECC composite frames were experimentally and numerically investigated. Firstly, five 1/2-scaled steel-concrete composite frames were experimentally studied under vertical uniform slab loading and horizontal low cyclic loading. The failure mode and cracking, load-displacement relationship, stiffness and strength degradation, energy dissipating, and strain of composite frames with ECC and URSP-S connectors were analyzed, and good cooperative behavior and overall seismic performance were found. Then, it was compared with the results of the other four specimens with different slab materials and shear connector types. The experimental results showed that the use of ECC and URSP-S connectors improved slab crack resistance 55% in terms of crack width, and rarely influenced the structural performance of the composite frames. ECC played a major role in controlling the crack width while URSP-S connector played a major role in controlling the crack number. In addition, based on the test specimen with ECC and URSP-S connectors, an elaborate finite element (FE) model was developed and validated by the test results in terms of cyclic curves and failure mode. Moreover, supplementary modeling analyses with various parameters on the influence of the frame capacity were performed, where steel beam height was the most influential parameter.

Cracking Behavior and High-Temperature Thermoplastic Analysis of 09CrCuSb Steel Billets

This paper characterizes the surface crack morphology and elements of 09CrCuSb steel continuous casting slabs and studies the high-temperature thermo-plasticity of continuous casting slabs using a Gleeble 3500 thermal simulator. Combining the macro/micro fracture morphology and microstructure characteristics, the formation rules of slab cracks are discussed. The research results show that the increase in Ae3 temperature caused by changes in alloy elements results in the precipitation of a thin, film-like coexisting ferrite along the grain boundaries at a certain temperature, as well as the element segregation behavior of low-melting-point alloy elements at the original austenite grain boundaries, which are the main factors inducing cracks in 09CrCuSb steel continuous casting billets. The plasticity of 09CrCuSb steel at high temperatures is poor at 800~900 °C. In continuous casting process control, it is necessary to try to avoid long-term stay of the billet at this temperature range.

Investigation on interfacial anti-sliding behavior of high strength steel-UHPC composite beams

This paper investigates the anti-sliding behavior of high-strength steel (HSS)-to-ultra-high performance concrete (UHPC) composite beams with perfobond strip connectors (PBLs). The experimental program is comprised of two test series. The first series of push-out tests were performed on six PBLs fabricated using HSS and UHPC. For each PBL, the load-slip curve, load-uplift displacement relationship, strain history, shear stiffness, ultimate resistance, failure modes, and ductility were recorded and discussed. For the second series, three HSS-UHPC composite beams were designed and manufactured. Based on the structural responses of the composite beams under four-point flexural loadings, the interfacial sliding behavior was presented and analyzed. By employing the theory of beams-on-elastic-foundation, expressions for calculating the anti-sliding stiffness of the composite beams were deduced. Experimental results indicate that the uneven load distribution among the multiple PBLs significantly reduced the shear performance of an individual PBL. Compared to a single-hole PBL, providing double holes in the perforated plate reduced the stiffness and strength of the individual PBL by 43% and 18%, respectively, while the corresponding stiffness and strength reductions for the PBL with triple holes were 51% and 19%, respectively. The perforated plates’ end-bearing effect improved the anti-sliding stiffness of the composite beam; however, the early cracking of the UHPC slab caused by the end-bearing led to a reduced yield load of the steel beam. The anti-sliding stiffness calculated from the proposed analytical formulas correlated well with experimental results. The proposed method is anticipated to provide a reference for the anti-sliding design of HSS-UHPC composite beams in practical applications.

Experimental and numerical studies on the dynamic response of precast concrete slabs under blast load

The blast resistance of precast concrete (PC) slabs was studied by field blast test and numerical simulation. A field blast test of PC slabs under different scaled distances (1, 0.8, and 0.6 m/kg1/3) was conducted, and the incident and reflected overpressures, displacement, and damage distribution of the PC slabs were measured. The results were compared with the test results of ordinary reinforced concrete (RC) slabs at the same scaled distance. The incident and reflected overpressures were consistent with the CONWEP empirical formula, which verified the effectiveness of the blast load in the test. Under the same working condition, the maximum displacement of the PC slabs was greater than that of the RC slabs. Both slab types exhibited bending failure, but their crack distributions were obviously different. The number of cracks of the PC slabs was large, the width was narrow, and the distribution was more uniform. The PC slabs could dissipate the blast shock wave evenly. No obvious cracks were observed in the laminated surface of the PC slabs, thereby meeting the shear resistance requirements. The dynamic response of the PC slabs under blast load was studied using the CONWEP method, and the validity of the finite element (FE) model was verified with the LS-DYNA software.

Progressive Failure Characteristics and Failure Symptoms of Straight-Walled Arched Sandstone Tunnels

In order to investigate the development process of crack formation in shallow-buried sandstone tunnel, biaxial compression tests were conducted on a similar model of the real straight-walled arched sandstone tunnel. The results indicate that the initial crack appeared at the arch line on both sides of the tunnel and propagated downwards, eventually leading to spalling of the rock mass on the surface of the tunnel, forming a V-shaped groove. Additionally, slab cracks were observed in the straight wall on the right side of the tunnel, which were approximately parallel to the vertical load. The failure characteristics of the tunnel were closely related to the fractal dimension of the crack geometry distribution. During the tunnel compaction and elastic deformation stage, the fractal dimension of the cracks in the tunnel surface increased linearly, while during the crack propagation stage, the fractal dimension increased gradually, with a sudden increase occurring just before the rock mass reached its peak load. The acoustic emission results revealed that AE ringing counts and amplitude were inactive during the first 4239 seconds of the test. And they only increased during the crack propagation stage. The continuous decrease of the b-value and the sudden increase of the fractal dimension of cracks can serve as a reliable precursor of tunnel failure.

Analysis of Uneven Wear Mechanism of Narrow-Face Copper Wall of Funnel Mold

In thin-slab continuous casting, due to the influence of the special shape of the funnel mold, cracks at the corner of the slab shell are more likely to occur than those in conventional slab shells, and a serious wear phenomenon also appears on the narrow face of the copper wall of the mold. Aimed at the corner cracks of thin slabs and the wear phenomenon of the copper wall, a new 3D stress analysis model in a funnel mold has been developed to simulate the stress-–train behavior of the slab shell under high-speed continuous casting. The results show that at the position 600 mm below the meniscus, the gap begins to appear at the corner of the slab; the maximum value of the first principal stress appears at the corner. The shell is squeezed by the copper wall during the downward movement in the funnel mold, and the slab shell in the funnel area moves towards the narrow face. The displacement causes the deformation of the slab shell to extend to the corners, the deformed shell is pressed against the corner of the copper wall. A new type of copper wall was designed for production, and it was found that the cracks at the corner of the slab shell were greatly reduced.