Slab Deformation Research Articles

The Moho, slab and tomography of the East Japan forearc derived from seafloor S-net data

We investigate the 3-D P and S wave velocity structure of the East Japan forearc using a large number of high-quality arrival-time data of local earthquakes recorded by a permanent seafloor seismic network (S-net) and the land-based Kiban seismic network. Geometries of the subducting slab boundary and the Conrad and Moho discontinuities under the forearc are refined by referring to results of previous studies including active-source seismic soundings and seismicity located by the S-net. The obtained P and S wave velocity images are quite similar to each other, suggesting that they reflect robust features of the 3-D seismic structure. The subducting Pacific slab exhibits high velocities, whereas significant low-velocity (low-V) anomalies are revealed in the overlying Okhotsk plate beneath the forearc, which may reflect accretionary materials containing abundant fluids. The subducting oceanic crust atop the Pacific slab is revealed clearly as a thin low-V layer extending from the trench axis down to ~100 km depth under the volcanic front. Our results of earthquake relocation using the 3-D velocity model indicate that the double seismic zone in the subducting Pacific slab occurs from the trench axis down to ~180 km depth. The occurrence and focal mechanisms of the double seismic zone are caused by slab deformation during its subduction, such as slab bending or unbending, as well as other processes including hydration, dehydration, compositional variations, and phase changes in the subducting slab.

Study on the nonlinear bending behavior of soft slabs subjected to vertical compressions

Finite bending of soft materials exists in large deformation and great curvature, which correspond to high nonlinearity. It is challenging to investigate such a bending problem using the traditional three-point or four-point bending tests due to giant deflections. This paper provides a new way to study the large bending deformation of a soft slab subjected to vertical compression between two rigid plates. We fabricated three types of PDMS slabs with different stiffnesses and then placed them vertically between two rigid plates. By decreasing the distance between the plates, we can induce bending deformation in soft slabs. The compressive force between the plates is measured with a force transducer while a camera calibrates the deformation with the assistance of CAD software. We used two effective sizes of soft slabs, and each size corresponds to three different ratios of base material and curing agent material. We find that the slab’s deformed inner and outer radii only depend on the slab size rather than the stiffness, and the stretches are independent of both the size and stiffness. A simple linear model and finite element analysis are developed to explain the experimental data. They agree well with each other at finite bending. We, therefore, find that the center portion of the compressive soft slabs is approximately in pure bending. This paper provides an effective way to induce bending deformation in soft slabs and study the nonlinear behaviors.

Relating Slip Behavior to Off‐Fault Deformation Using Physical Models

AbstractDeformation in transform systems is accommodated by discrete fault slip and distributed off‐fault deformation. Here, we consider how a change in slip behavior along a fault can influence the distribution between on‐ and off‐fault deformation. We use a physical experiment to simplify the geometry, material properties, boundary conditions, and slip history along a strike‐slip fault to directly observe patterns of off‐fault deformation. We document deformation of a silicone slab on a simple shear apparatus using particle image velocimetry (2D) and photogrammetry (3D). The experimental results show regions of topographic highs and lows on either side of the slip transition that grow, evolve, and are displaced with progressive strain. The experimental dilatation field shares similarities with strain fields in central California along the San Andreas fault, which suggests that a change in slip behavior may explain some of the real‐world patterns in short‐ and long‐term deformation.

Non-Uniform Deformation of Slab during Heavy Reduction Process

The bulge deformation of slab narrow face can cause surface defects of hot rolled steel plate. A three-dimensional bulging model, was proposed to simulate the evolution of deformation behavior of the continuous casting slab during heavy reduction (HR). The model was taken to investigate the non-uniform deformation of slab during HR process. The bulging deformation behavior of the slab was then calculated in one segment included seven pairs of rollers. To improve the edge defect on hot-rolled steel plates, the relationship between the reduction amount and bulge deformation of slab narrow face has been investigated.

Simulation of concrete structures deformation affected by alkali–silica reaction considering environmental conditions and multiaxial stress state

In this study, the expansion and deformation of alkali–silica reaction (ASR)-affected concrete structures under natural environment and multiaxial stress state are predicted. The performance of the ASR model proposed in previous research is quantitatively investigated in terms of relative humidity, multiaxial stress, and temperature dependencies based on experimental results. The simulation results indicate that the relative humidity-dependent expansion caused by the ASR can be simulated effectively by slightly modifying the relative humidity threshold in the model. In a simulation focusing on stress dependency, the insufficient consideration of the relationship between compressive stress and ASR gel absorption into pores in the model by previous research resulted in discrepancies between the simulation and experimental results. The performance of the model by previous research in simulating temperature dependency is improved by referring to the relationship between the expansion rate and temperature recorded from specimens exposed to the real environment. An exposure experiment of reinforced concrete (RC) slab on steel girders is simulated using the modified model. The results show that the modified model can reproduce the tendency of three-dimensional deformation of RC slab, while model improvement considering time-dependent and stress-dependent phenomena should be needed for long-term quantitative predictions.

Optimal Design of Mix Proportion of Hot-Mix Epoxy Asphalt Mixture for Steel Bridge Decks and Its Anti-Slip Performance

To solve the problem of the insufficient anti-slip performance of steel bridge deck wear layers, a kind of new epoxy asphalt mixture FAC-10 (Full Epoxy Asphalt Content is shortened to FAC) is proposed in this paper based on the design method of an asphalt-rich mix proportion. The FAC-10 pavement layer was tracked and tested using a pavement texture tester to study the change in its skid resistance under traffic load from a macroscopic and microscopic perspective. The influence of traffic load on the deformation of the FAC-10 wearing layer was also simulated and analyzed via lab tests. The results show that the new FAC-10 epoxy asphalt mixture is superior to the traditional EA-10 epoxy asphalt mixture in terms of skid resistance. During the monitoring and testing period, the three-dimensional (3D) structure depth of the pavement surface showed a decreasing trend followed by an increasing trend, while the density of microtexture distribution showed the opposite trend. After a wheel pressure rutting test, the rutted slab showed slight deformation and a certain degree of reduction in 3D structure depth; the deformation of the rutted slab mainly occured in the surface layer, and the internal deformation was negligible.

Deep mass redistribution prior to the 2010 Mw 8.8 Maule (Chile) Earthquake revealed by GRACE satellite gravity

Subduction zones megathrust faults constitute a considerable hazard as they produce most of the world's largest earthquakes. However, the role in megathrust earthquake generation exerted by deeper subduction processes remains poorly understood. Here, we analyze the 2003 – 2014 space-time variations of the Earth's gravity gradients derived from three datasets of GRACE geoid models over a large region surrounding the rupture zone of the Mw 8.8 Maule earthquake. In all these datasets, our analysis reveals a large-amplitude gravity gradient signal, progressively increasing in the three months before the earthquake, North of the epicentral area. We show that such signals are equivalent to a 60km3 water storage decrease over 2 months and cannot be explained by hydrological sources nor artefacts, but rather find origin from mass redistributions within the solid Earth on the continental side of the subduction zone. These gravity gradient variations could be explained by an extensional deformation of the slab around 150-km depth along the Nazca Plate subduction direction, associated with large-scale fluid release. Furthermore, the lateral migration of the gravity signal towards the surface from a low coupling segment around −32.5∘ North to the high coupling one in the South suggests that the Mw 8.8 earthquake may have originated from the propagation up to the trench of this deeper slab deformation. Our results highlight the importance of observations of the Earth's time-varying gravity field from satellites in order to probe slow mass redistributions in-depth major plate boundaries and provide new information on dynamic processes in the subduction system, essential to better understand the seismic cycle as a whole.

Vertical Nonlinear Temperature Gradient and Temperature Load Mode of Ballastless Track in China

In the process of heat exchange with the external environment, the internal temperature of ballastless track structure presents a nonlinear distribution. The vertical temperature gradient will cause repeated warping and deformation of track slab, resulting in mortar layer separation, which will affect driving comfort and track durability. The traditional temperature field analysis method of concrete structure based on thermodynamics has the disadvantages of too many assumptions, difficult parameter selection and too much calculation of energy consumption. In this paper, based on the finite element software ANSYS, the heat exchange was transformed into the boundary condition of heat flux, which was applied to the thermodynamic analysis model to study the nonlinear temperature distribution law of ballastless track. The accuracy of the analysis method was verified by the measured data. On this basis, the regional distribution law of temperature gradient of ballastless track under different geographical coordinates and climatic conditions was studied. By adding a regional adjustment coefficient, the vertical temperature load model of ballastless track suitable for typical areas in China was proposed. The proposed temperature load model makes up for the lack of refinement of climate division and temperature load model in relevant specifications, and has strong engineering application and popularization value.

Static and Dynamic Characteristics of Steel‐Concrete Composite Track Beam of Straddle Monorail with Cluster‐Distributed Studs

Because the transportation mode of straddle monorail is that the vehicle runs in the state of hugging the track, its track beam is usually a narrow‐high cross section. In order to study the static and dynamic characteristics and variation law of prefabricated steel‐concrete composite beam of straddle monorail with “cluster‐distributed studs” (CDS), a full bridge test model with a scale ratio of 1 : 3 was made. Relevant theoretical analysis, numerical simulation, and model test were carried out, and the data of structural frequency and damping, load‐deflection curve, and section height‐strain curve were obtained. The results show the following: (1) the equivalent vertical bending stiffness of the composite track beam of straddle monorail is nonlinear. The greater the load, the faster the stiffness decrease, and the greater the difference with the theory of composite beam with “uniformly distributed studs” (UDS). (2) At the same section, the deformation of steel beam and concrete slab is not coordinated along the height direction. The strain value of concrete slab is significantly larger than that of the upper edge of steel beam, so it is difficult to apply the plane‐section assumption. (3) Compared with all the measured results of the track beam test, the results of the detailed shell‐solid FEM model based on the load‐slip curve obtained by push‐out test are close to them, and the maximum error is 11.4% difference in stress. (4) Compared with the results obtained by the theoretical formula of the UDS, the results obtained by the theoretical formulas of the CDS based on a “correction coefficient of vertical bending stiffness” proposed in this paper show less deviation comparing to the measured results of the track beam test and are more resilient. When the correction coefficient is 0.9, the maximum error is 23.8% difference in stress. In the design of this kind of structure, the proposed formula can be used for early scheme comparison and later size optimization. Compared with the detailed shell‐solid FEM model, the proposed formula significantly reduces the design workload.

Mechanical Mechanism Analysis of Warping and Bulging Of Track Slab of High-Speed Railway in Service

Due to warpage and ballooning of high-speed rail track slab caused by debonding and environmental temperature changes during the deterioration of CA mortar layer being extremely concerned in practical engineering, it is based on numerical simulation of typical working conditions and analysis of test model that the deformation dynamics mechanism of track slab of high-speed rail in service is studied in this paper. Firstly, three kinds of damage conditions of CA mortar layer are designed to simulate the partial stress state of track slab under normal, warping and bulging conditions, and the results of model test are compared with those of finite element analysis so that the accuracy and credibility of the numerical simulation method and results are verified. Then, through finite element numerical simulation, the dynamical mechanism of actual full-scale high-speed rail track slab under vibration load is studied. The results show that the warping deformation around the track slab and the bulging deformation in the middle part under the action of positive and negative temperature gradient load caused by environmental temperature change will have a great impact on the structural performance of itself and CA mortar layer; Bulging deformation of track slab is more destructive to its structure than warping deformation. It is of great practical significance to further study the critical position of track plate warpage and bulging deformation, and to optimize and strengthen the structure of this part; The research results are of great significance to further study the deterioration.

Numerical Analysis of the Influence of Deep Foundation Pit Construction on Adjacent Subway Stations in Soft Soil Areas

Deep foundation pit construction adjacent to a subway station in a soft soil area was numerically simulated with Midas GTS NX calculation software. The influence of the deep foundation pit construction on the deformation and stress of the subway station structure was studied, and the influence of the foundation pit retaining structure on the station was analyzed. The results show that during the foundation pit excavation process, the subway station slab rose as a whole and was greatly affected by the deformation of the common ground connecting wall, with the most unfavorable position changing as the excavation area changed. The excavation of foundation pits in different zones had a considerable influence on the east‐to‐west displacement of the common diaphragm wall outside the foundation pit. The maximum positive bending moment of the common diaphragm wall changed little, while the negative bending moment increased greatly during construction. Overall, the foundation pit excavation had a great impact on the negative moment of the common diaphragm wall. During the foundation pit excavation process, the subway station column lifted upward, and the maximum displacement, which was located at the west end of the station near the foundation pit, gradually weakened from west to east. As the foundation pit excavation process continued, the maximum axial force of the station column increased by 10.38%, and the pressure was the largest in the middle column. As the thickness of the diaphragm wall increased, the stiffness of the foundation pit retaining structure increased. After earthwork excavation and unloading, the locations in the retaining structure with high stiffnesses could resist deformations. The whole foundation pit was offset due to the high stiffness of the foundation pit retaining structure, which increased the horizontal deformation of the existing station structure. With increasing thickness, the relative horizontal deformation of the station slab gradually increased, mainly because the difference between the depths of the old and new diaphragm walls caused the embedded soil of the two same deep foundation pits to differ. Furthermore, there were great differences in the Earth pressure behind the wall. As the depth of the diaphragm wall increased, the active Earth pressure behind the diaphragm wall increased.

Wireless Monitoring of Ballastless Track Slab Deformation for High-Speed Railway

Ballastless slab track is the main form of ballastless track for the high-speed railway in the world. Deformation overrun of the track slab will seriously affect the smoothness of the track, and even lead to train safety accidents. The current practice mainly relies on manual periodic inspection, which is inefficient and cannot achieve continuous monitoring. Therefore, it is urgent to develop a real-time deformation monitoring solution for high-speed railway track slabs. This paper, based on multiple MEMs sensors, presents a multi-source sensor fusion and dynamic response analysis algorithm to identify the deformation mode of the track slab. Harvesting the vibration energy of the slab track instead of an electrochemical battery-only strategy could contribute to the achievement of carbon neutrality goals in the field of rail transit. Therefore, a self-contained system approach is developed for wireless monitoring of the track slab deformation. The deformation value of the track slab can be obtained with a monitoring resolution of <=1.5 mm, compliant with maintenance specifications for ballastless slab track deformation assessment (i.e., 1.5 mm for grade I threshold and 2 mm for grade II threshold). This work offers a new means for the safe operation and maintenance of high-speed railways and could also contribute to the realization of the strategic goal of the “dual-carbon project” in China.

Analysis of Fiber-Reinforced Concrete Slabs under Centric and Eccentric Load.

Research on the interaction between slabs and subsoil involves the field of materials engineering, concrete structures, and geotechnics. In the vast majority of cases, research focuses on only one of these areas, whereas for advanced study and computer simulations, detailed knowledge of the whole task is required. Among the new knowledge and information upon which this article focuses is the evaluation of subsoil stress using specialized pressure cells, along with detailed measurements of the deformation of a fiber-reinforced concrete slab. From a design point of view, this research is focused on the issue of the center of the cross section and the influence of eccentricity. Knowledge in this area is not yet comprehensively available for fiber-reinforced concrete slabs, where 2D deformation sections of the slab and 3D deformation surfaces of the slab are used in experiments. The experimental program includes a centrically and eccentrically loaded slab. These are structural elements that were tested on a specialized device. Both slabs had the same concrete recipe, with a dispersed reinforcement content of 25 kg/m3. The dimensions of the slab were 2000 × 2000 × 150 mm. Laboratory tests assessed compressive strength, the modulus of elasticity, splitting tensile strength, and bending tensile strength. Based on approximate data from the 3D deformation surfaces, an evaluation of the load-displacement diagrams for the center of the slab and for the center of eccentricity was performed. In conclusion, an overall evaluation and discussion of the results relies on experiments and the mechanical properties of fiber-reinforced concrete.

The influence of flexible sound insulation layers on the seismic performance of cross laminated timber walls

This paper presents the results of an experimental campaign investigating the seismic behaviour of full-size cross laminated timber (CLT) wall systems with sound-insulated shear-tension angle brackets. The main aim of the study was to investigate the influence of more and less flexible soundproofing bedding under the CLT wall. The paper shows a comparison of lateral load-bearing capacity, displacement capacity, ductility and stiffness obtained from racking tests on uninsulated specimens and specimens with various types of bedding insulation and levels of vertical load. Moreover, an analytical procedure to estimate the lateral load-displacement response of CLT walls with bedding insulation is proposed. This model is verified by direct comparison to the experimentally determined lateral load-displacement backbone curves. The results show that the elastomeric bedding does not have a significant effect on the bearing capacity of the wall system tested, but it reduces the stiffness and increases the displacement capacity. Due to the large decrease in stiffness, the insulation causes an overall reduction in ductility. The analytical estimation proposed was able to capture the reduction in lateral stiffness and adequately predict the load-bearing capacity. • Monotonic and cyclic shear tests of walls, analytical model. • The insulation does not significantly influence the lateral load-bearing capacity. • The insulation reduces the lateral stiffness of the wall and overall ductility. • High vertical load can cause irreversible deformation of the CLT slab and insulation. • The analytical model adequately predicted the lateral load displacement response.

CURLING BEHAVIOR MECHANISM OF CEMENT CONCRETE PAVEMENT AT EARLY AGE

In order to understand the behavior and formation mechanism of cement concrete pavement curling at its early age, vibrating wire sensors with a large range were designed to monitor the vertical displacement of slabs, and the whole vertical deformation in the first 14 days of slabs under summer conditions was continuously monitored. The behavior and formation mechanism of early-age curling were numerically analyzed by the special early-age character simulation program. The results show that: the evolution behavior of the early-age curling has three stages, namely, flat slab to corner curling, corner curling to intermediate curling with slab uplift at 1/4 positions, and corner curling to intermediate curling to curling at the middle of a slab. There are several curling modes and asymmetric phenomena in the early age of slab deformation. Early-age curling is significantly correlated with an environmental field, with concrete modulus, with creep and with structural restraint. Creep has a significant dissipation effect on the early-age behavior of a slab. In the combination case of insufficient constraint and insufficient driving of temperature deformation, the solidification shape of 1/4 diagonal slab uplift and will be produced, resulting in local unevenness and the void in corresponding position of a slab. It is suggested that the action characteristics of early-age built-in deformation and basis parameters should be distinguished, and the effect of built-in deformation can be equivalently reflected by support states.

Study and Modeling of Slab Deformation Processes in the Roughing Stands of Severstal’s Mill-2000 Hot-Rolling Line

Study and Modeling of Slab Deformation Processes in the Roughing Stands of Severstal’s Mill-2000 Hot-Rolling Line

Experimental investigation on hysteretic performance and deformation patterns of single-side yielding precast concrete beam–column connection with energy dissipation bars

With the aim of achieving high construction efficiency, satisfactory seismic performance, and rapid restoration of structural functionality after an earthquake, this study proposes an innovative single-side yielding beam–column connection with replaceable energy dissipation bars (REDB-SYBC) for precast concrete moment-resisting frames (PCMF). During assembly, the concrete beam is attached to a column via the connection function of a non-slipping threaded sleeve assembly (NSTSA) and the support action of the shear keys (SKs) in the REDB-SYBC. This reduces the need for temporary supports for the precast beams on site. Five large-scale tests on precast concrete connections considering the partial flange effect of a slab subjected to quasi-static cyclic loading were conducted to investigate the mechanical behavior, deformation patterns, and energy dissipation (ED) capacity. The primary experimental variables included different loading protocols, restrainer forms, ED segment areas, and whether to replace the ED bars. This paper presents the assembly construction and load-carrying mechanism, and the analysis of the experimental results, including the observations, hysteretic performance, and deformation patterns. The single-side yielding deformation pattern of the REDB-SYBC connection minimized the deformation of the adjacent floor slabs and magnified the deformation of the ED bars at the bottom of a beam, thus facilitating deformation compatibility with the floor system and causing the damage to be focused on the ED bars. Consequently, the five specimens exhibited similar failure patterns via the fracture of the ED bars due to low-cycle fatigue failure, which was attributed to extensive yielding in both tension and compression. The REDB-SYBC connections exhibited a distinct beam end yielding mechanism, which demonstrated a failure pattern that was consistent with the desired “strong column and weak beam” design philosophy. The test results indicated that the proposed REDB-SYBC connection exhibited a dependable decoupled moment and shear load transfer mechanism, stable hysteretic behavior, negligible beam elongation, and reduced floor damage. The performance of a repaired specimen was nearly the same as its counterpart before repair, indicating that replacement was effective. The impact on the REDB-SYBC connection in response to a strong aftershock was also estimated by reloading an unrepaired specimen.

SHM deformation monitoring for high-speed rail track slabs and Bayesian change point detection for the measurements

Fiber Bragg grating (FBG) technology has significant advantages in anti-electromagnetic interference and is suitable for structural health monitoring (SHM) in high-speed rail (HSR). In this paper, a deformation monitoring system based on FBG technology is designed for HSR track slab. Regarding to the possible large deformation of the track slab, a Bayesian change point detection (CPD) method is adopted to detect change points of the monitoring data sequence and the posterior probability distribution of change points can also be derived. The Bayesian CPD algorithm can directly sample and simulate from the posterior probability distribution of change point to determine corresponding parameters of regression model, as well as yielding uncertainty evaluation. The designed SHM system was implemented on a segment of HSR track on the Lanzhou-Xinjiang line in China to carry out the measurement of track slab deformation. Results shows that the designed SHM can resist strong electromagnetic interference in the operation environment of high-speed rail and versine deformation monitoring data over two months for the target track segment can be extracted based on SHM measurement. Through posterior distribution information of the Bayesian CPD method, change points which have the highest posterior probability can be identified for the versine deformation of HSR track slabs, which is essential for investigating the cause of the change point and providing maintenance plan in time.

NUMERICAL ANALYSIS OF FIRE BEHAVIOR OF CONCRETE SLABS IN FULL-SCALE STEEL-FRAME STRUCTURE

The influence of the position and quantity of fire span on the fire behavior of concrete floor in the structure is studied. Based on Vulcan software, using thick plate element and beam-column element, combined with EC2 material high temperature constitutive model, the temperature and deformation of fire top floor (corner and middle) and second floor (four) in a steel frame structure are simulated numerically. The influence of concrete expansion strain on the deformation of floor slab under fire is analyzed, and the membrane mechanism, crack distribution and internal force development of steel beam are investigated. The results show that: the predicted results of floor temperature and deformation are in a good agreement with the experimental results, and the concrete expansion strain has a decisive influence on the mid-span deformation of the fire zone in the structure, that is, when the expansion strain is larger, the predicted deformation is larger; the boundary conditions have a decisive influence on the membrane mechanism and crack distribution of the heated plate, and the heated plates have three kinds of membrane mechanisms: ring type, opposite-edge U type and diagonal U type. The bending moment and axial force of the steel beam near the heated grid gradually increase, and the increase of the axial force of the steel beam is relatively large.

Numerical simulation of slab deformation process with different reduction values in vertical rolls of mill 2000 roughing stands

Perfection of rolled stock production processes at continuous wide-strip hot rolling mill (CWHRM) aimed at minimization of metal consumption, is an effective mean to decrease its cost. In the process of slabs rolling at CWHRM, the metal consumption is stipulated first of all by complicated workpiece forming in roughing stands during consecutive reduction by vertical and horizontal rolls. Results of the numerical study of slab deformation with different values of reduction in vertical rolls of roughing stands of mill 2000 are presented. The implementation of rolling process model based on application of DEFORM-3D program of finiteelement analysis described for evaluation of metal shifting from the edges of slab in the direction of the middle of the width. The convergence of the simulation results with the measurements data of workpiece forming during roughing rolling at Severstal mill 2000 was experimentally confirmed. It was found that an increase of reduction in vertical rolls has no significant effect on the metal shifting from a narrow edge to a wide one. Increase the total reduction in vertical rolls leads to an unfavorable stress-strain state of the edge region and the Cockcroft–Latham criterion rises by 20–30%. It was proposed to reduce the total reduction in the vertical rolls of the roughing stands of mill 2000 down to 40–50 mm. It was shown that increase of time of slab moving from the heating furnace to the scale breaker causes growth the Cockcroft-Latham criterion and does not affect the amount of metal shifting from a narrow face to a wide one. The proposed method of simulation the process of slab deformation in the roughing group of the mill 2000 proved by results of industrial rolling can to be used for further study of the effect of rolls profiling and forming of surface defects with the provision of minimal metal shifting onto a wide face.