Slab Surface Research Articles

Full-scale fatigue simulation of the deterioration mechanism of reinforced concrete road bridge slabs under dry and wet conditions

This study investigates the deterioration process and mechanism of reinforced concrete (RC) slabs in road bridges under dry and stagnant water (wet) conditions. Previous studies used a simple-plate model (SPM) to predict the fatigue life of RC decks by considering conservative assumptions for safer assessment under different environmental processes. To obtain a more detailed analysis and clarify the deterioration result and mechanism, a full-scale superstructure of a realistic bridge is used in this study. The simulation results reveal differences between the full-scale model (FSM) and SPM due to size effects and boundary conditions. The findings also demonstrate that the failure mechanism in the FSM simulations differs between dry and wet conditions. In dry cases, damage easily occurs at the bottom surface of the bridge slab. However, in wet cases, horizontal cracks and disintegration occur below the top surface near the upper rebar layer of the slab during the early stage over a very short time period, which cannot be visually investigated according to current bridge slab inspection regulations. These results successfully reproduce the deterioration phenomenon that occurred on site, which indicates the credibility of the simulation. Then the effect of two wheel-loading on RC slabs is studied to assess the slab continuity at adjacent panels. This study provides a useful reference for more rational design and maintenance of RC slabs of road bridges.

Formation and evolution of fracture spacing on various geometric surfaces in layered materials

Fracture spacing as a widespread phenomenon in nature shows similar patterns on various geometric surfaces. To explore the similarities and differences between various geometric surfaces in the process of fracture spacing formation, numerical simulations are conducted on bi-layered three-dimensional models of three various geometric surfaces, including slab surface, cylindrical surface, and spherical surface by the finite element method (FEM). The fractures develop under a quasi-static loading condition with constant displacement increments. The progressive failure process from fracture initiation to saturation is researched, and the material heterogeneity is introduced by using a probability distribution, which acts as the main reason for failures generating randomly inception. An intuitive explanation is also provided for the phenomenon of fracture saturation. Then, as the loading condition varies, fracture patterns in both slab surface models and cylindrical surface models show a transition from parallel fractures, step-like fractures to regular polygonal fractures. However, in spherical surface models, only uniform polygonal fractures emerge under the condition of radial expansion. Furthermore, through quantitative analysis by statistical means, we find that, except for the fractured layer thickness, curvature also has a significant impact on the crack density.

Factors affecting slip and stress distribution of concrete slabs in composite beams

An experimental program is carried out to examine the effects of different factors on the slip and stress distribution of concrete slabs in composite beams. A total of ten steel–concrete composite beams with a span of 4.80 m are tested to find the effects of the type of shear connectors and the concrete slab reinforcement on the behaviour of composite beams. All beams consist of monosymmetric steel cross-sections connected to 120 cm wide concrete slabs. Welded shear connectors (angles or channels) spaced at 20 cm are used to connect the concrete slabs to the steel beams. The concrete slabs of eight beams are provided with a lower steel reinforcement only while two beams are provided with both lower and upper steel reinforcement. The results showed that the ultimate load capacity of composite beam with channel connectors is 14% higher than the counterpart beam with angle connectors and 30% stiffer in resisting the slip of the concrete slab. Moreover, composite beams with channel connectors tend to maintain strain compatibility at the interface between concrete slab and steel section better than the counterpart beams with angle connectors. It is also found that using upper steel reinforcement mesh enhances the stress distribution in the concrete slab until failure. It is found that increasing the reinforcement ratio of the concrete slab from 0.18% to 0.46% increases the flexural strength of the composite beams by 7.45%, while decreases the deflection values by 23%. Moreover, using upper steel reinforcement prevented the longitudinal cracking of the top surface of the concrete slab and allowed for full plastification of the steel cross-sections.

A Nanoplasmonic-Based Biosensing Approach for Wide-Range and Highly Sensitive Detection of Chemicals.

In a specific biosensing application, a nanoplasmonic sensor chip has been tested by an experimental setup based on an aluminum holder and two plastic optical fibers used to illuminate and collect the transmitted light. The studied plasmonic probe is based on gold nanograting, realized on the top of a Poly(methyl methacrylate) (PMMA) chip. The PMMA substrate could be considered as a transparent substrate and, in such a way, it has been already used in previous work. Alternatively, here it is regarded as a slab waveguide. In particular, we have deposited upon the slab surface, covered with a nanograting, a synthetic receptor specific for bovine serum albumin (BSA), to test the proposed biosensing approach. Exploiting this different experimental configuration, we have determined how the orientation of the nanostripes forming the grating pattern, with respect to the direction of the input light (longitudinal or orthogonal), influences the biosensing performances. For example, the best limit of detection (LOD) in the BSA detection that has been obtained is equal to 23 pM. Specifically, the longitudinal configuration is characterized by two observable plasmonic phenomena, each sensitive to a different BSA concentration range, ranging from pM to µM. This aspect plays a key role in several biochemical sensing applications, where a wide working range is required.

Differentiating induced versus spontaneous subduction initiation using thermomechanical models and metamorphic soles

Despite the critical role of subduction in plate tectonics, the dynamics of its initiation remains unclear. High-temperature low-pressure metamorphic soles are vestiges of subduction initiation, providing records of the pressure and temperature conditions along the subducting slab surface during subduction initiation that can possibly differentiate the two end-member subduction initiation modes: spontaneous and induced. Here, using numerical models, we show that the slab surface temperature reaches 800–900 °C at ~1 GPa over a wide range of parameter values for spontaneous subduction initiation whereas for induced subduction initiation, such conditions can be reached only if the age of the overriding plate is <5 Ma. These modeling results indicate that spontaneous subduction initiation would be more favorable for creating high-temperature conditions. However, the synthesis of our modeling results and geological observations indicate that the majority of the metamorphic soles likely formed during induced subduction initiation that involved a young overriding plate.

Mechanical behavior and fatigue failure analysis of standing seam aluminum alloy roof system under temperature effect

Standing seam metal roof systems with universal high-strength, lightweight, and thin-walled characteristics have been applied worldwide in massive large-span landmark buildings, such as gymnasiums, airports, and railway stations. The existing research focuses on the wind uplift design, but there are few studies on the mechanical properties under the temperature effect. In this paper, the temperature effect of the standing seam aluminum alloy roof (SSAAR) system was studied. To be familiar with the mechanical and deformation characteristics of the SSAAR system, the static loading tests under different temperatures and boundary constraints were carried out. Two specimens, one with anti-wind clips and the other without anti-wind clips, were further tested under cyclic loading to evaluate and quantify the fatigue failure characteristics of the roof system. The testing results indicate that the stress concentration, thermal expansion displacement, and wear of the SSAAR system are significant. The slab rib stress is the largest, accounting for about 83.7% of the yield strength, followed by the slab surface stress, and the slab bottom stress is the smallest. The horizontal displacement is greater than the vertical displacement, and the maximum is about 20.42 mm. The boundary constraint mainly affects the support stress and vertical displacement to increase by 47.2% and 79.3% respectively. The anti-wind clips mainly increase the wear thickness of the roof slab, which is increased by 67.5%.

Stress distribution in a plate containing a triaxial ellipsoidal cavity

This paper presents the three-dimensional analysis of the stress distribution arising in an isotropic infinite slab with a triaxial ellipsoidal cavity, the surface of which is subjected to the three principal stresses and . To satisfy both boundary conditions on the surface of slab and the cavity, harmonic functions in rectangular coordinates are used and double Fourier transform is applied. The problem is reduced to the solution of three integro-differential equations. The existence and uniqueness of the solution is investigated.

Longitudinal Crack Detection Approach Based on Principal Component Analysis and Support Vector Machine for Slab Continuous Casting

Longitudinal cracks are the typical surface defects of continuous casting slabs, resulting in additional processing or even casting interruption. Monitoring longitudinal crack defects is of great significance in stabilizing and improving the slab quality. Herein, a monitoring model is developed to recognize the longitudinal crack defect of continuous casting slabs using principal component analysis (PCA) and support vector machine (SVM). First, the typical characteristics of the temperature patterns corresponding to the longitudinal crack defect are extracted, including the normal casting temperature with small and large fluctuations, as well as the longitudinal crack temperature. Then, PCA is used to reduce the dimension of these characteristics for removing the redundancy and reducing the computational burden. Subsequently, an SVM is applied to identify normal and longitudinal crack temperature patterns for training the monitoring model PCA–SVM. The monitoring performance is verified by the test data, in which the training accuracy and test accuracy are 100% and 96%, respectively. It is worth mentioning that the model can successfully predict all the real longitudinal crack defects, showing excellent detection performance. The established model is expected to provide a theoretical basis and a reliable way for online monitoring of slab surface cracks.

Activating Both Basal Plane and Edge Sites of Layered Cobalt Oxides for Boosted Water Oxidation

AbstractLayered AxCoO2 materials built by stacking layers of CoO2 slabs and inserting alkali ions in between them have shown a promising activity of oxygen evolution reaction (OER) due to their active edge sites. However, the large basal plane areas of the CoO2 slabs show too strong adsorption energy to the reaction intermediates, which is unfavorable for the release of O2. Here, a simple cation‐exchange strategy based on Fe3+ and alkali ions is proposed to simultaneously activate both the basal plane and edge sites of AxCoO2 for the OER. X‐ray absorption spectroscopy has revealed that the Fe3+ ions deposit both on the surface and edge sites of the CoO2 slabs and enter the interlayer. The cation‐exchanged AxCoO2 electrodes show a boosted activity compared to their pristine and conventional Fe‐doped AxCoO2 counterparts. This phenomenon is mainly ascribed to the abundant edge‐sharing Co–Fe motifs at the edge sites and the charge redistribution in the basal plane sites induced by the insertion of Fe3+ ions. This work provides a novel method to fully exploit layer‐structured materials for efficient energy conversion.

Collapse testing of steel-concrete composite floor systems under an exterior-column-removal scenario

To evaluate the influence of openings in floor slabs on the collapse performance of steel-concrete composite floor (SCCF) systems, 2 one-third scale 1 × 2 bay SCCF substructures were fabricated and tested under static load up to final collapse in an exterior-column-removal scenario. The experimental results indicated that arch-shaped and radial cracks emerged on the top and bottom surfaces of the floor slab, respectively, for the SCCF substructure without openings in the floor slabs. Meanwhile, local buckling of the steel girders at the beam ends successively occurred during the loading procedure. As for the SCCF system with openings in the floor slabs, the crack distribution appeared more irregular, and torsion of the spandrel beam became prominent because of the discontinuity of the floor slab. The ultimate collapse resistance and the corresponding displacement of the failed column for the substructure with openings in the floor slabs were about 0.85 and 0.55 times as large as those of the substructure without openings. Owing to the existence of the openings, the tensile membrane action in the floor slab was weakened prominently, which further decreased the collapse resistance capacity of the SCCF system. After the removal of the exterior column, load was redistributed among the columns around the failed column and much more load was assigned to the adjacent exterior column. The flexural action and catenary action of the composite beams, as well as the tensile membrane action of the floor slabs worked together to resist collapse load at the large deformation stage.

Slab Folding and Surface Deformation of the Iran Mobile Belt

AbstractBack‐arc regions are usually punctuated by pulses of tectonic deformation, lasting for few tens of millions of years. Yet, the origin of those short‐lived deformation episodes is disputed. Here, we compile structural, stratigraphic, geochemical, and geochronological data from Iran and we combine them with a kinematic reconstruction to show that the back‐arc region of the Central Neotethys subduction zone was affected by alternating pulses of extension and compression, linked to episodes of trench retreat and advance, respectively. To back‐up these observations and investigate the causes of such a trench behavior, we run 2D numerical models exploring (i) the dynamics of subduction into a viscously stratified mantle, and (ii) the deep slab deformation induced by mineral phase changes at the mantle transition zone. Our results indicate that episodes of trench retreat and trench advance, like those observed in the Central Neotethys domain, emerge spontaneously by slab folding, and penetration into the mantle transition zone. We propose a coupled mantle‐surface tectonic evolution model of the Central Neotethys slab that reconciles back‐arc deformation and short‐lived pulses of upper‐plate vertical motion in a unique, dynamically self‐consistent model of deep mantle subduction.

The simulation of high compressive stress and extrusion phenomenon for concrete face slabs in CFRDs under strong seismic loads

The evaluation of high compression zones for anti-seepage face slabs is an increasingly important task in the safety evaluation of high concrete faced rock-fill dams (CFRDs). This manuscript uses the scaled boundary finite element method (SBFEM) to construct a cross-scale model of the rockfill and bedrock in a high CFRD. Nonconforming elements are applied to independently refine the mesh locally in the concrete face slab, which allows an accurate modeling of the rotating and bending phenomenon experienced by the face slab zone. Meanwhile, the non-matching node interface is introduced to connect the locally refined face slab mesh to the rockfill zone and obtain the final cross-scale model for refined analysis. The generalized plastic constitutive model and a state-dependent elasto-plastic interface constitutive model are employed to capture the complex behaviors of rockfill and soil-structure interaction (SSI). Leveraging the above approaches, static and dynamic analyses of a high CFRD are conducted to identify high compressive stress zones and simulate the extrusion damage. The results indicate that self-weight, water pressure, friction force and seismic loads contribute to rotating and bending between face slabs, and can lead to significant local stress concentration within the surface of face slab near the longitudinal joints and may potentially extrusion damage.

A Multiscale-Based Approach to Understand Dendrite Deflection in Continuously Cast Steel Slab Samples

Dendrite bending angle measurements were conducted along two different directions on four steel slab samples collected from a conventional caster. The primary dendrites growing at the slab surface showed a transition in their growth direction as the distance from the surface increased. Numerical fluid flow simulation showed changes in the flow directions that might have caused the change in the growth direction. The bending angle measurements were also correlated with the casting process parameters. Thereafter, a multiscale approach was adopted to predict the dendrite deflection angles by correlating the macro-scale flow profile with the micro-scale bending angle formulation and subsequently corroborated with the industrial scale measurements.

Interrelation of CCM (Steel Billet Continuous Casting Machine) Tube Steel Casting Parameters and Hot-Rolled Plate Quality

The quality of the hot-rolled plate up to 36 mm thick was estimated by the percentage of rolled products, sorted due to the presence of a surface defect "Non-metallic inclusions", and internal defects, detected by ultrasonic plate control. The analysis of the data on the total sorting of hot-rolled plates demonstrated that the amount of sorting differs significantly on the melting from which each series of tubular metal casting commenced, compared to all the other melting in the series. The sorting of the sheets rolled from the metal of the first in a series of melting proved to be 1.9 times higher than that of the metal of all other melts. The main reason (in 68% of cases) of sorting is the presence of non-metallic inclusions on the surface of the plates. The effect of sorting of hot-rolled plates on non-metallic inclusions of various parameters has been studied: the duration of the intermediate ladle-heating; the length of time from the end of the heating of the intermediate ladle, prior to the beginning of the casting; lining temperatures of the intermediate ladle before the beginning of casting; duration of filling the intermediate ladle; the filling rate of the intermediate ladle with metal; mass of metal in the intermediate ladle before the beginning of casting into the crystallizer; chemical composition of metal; overheating of the metal over the liquidus point at the beginning, middle and end of the casting. On the sorting of flat products for non-metallic inclusions, of all the parameters considered, a statistically significant effect is due only to the overheating of the metal above the liquidus point, which varies in the range from 19 to 35 ° C. In order to obtain an acceptable quality of both the surface of slabs and the surface of hot-rolled plates for non-metallic inclusions, the first in a series of melts recommends overheating of the metal in the intermediate ladle above the liquidus temperature of 30-35 ° C.

Theory of light reflection and transmission by a plasmonic nanocomposite slab: emergence of broadband perfect absorption

A theory of light reflection and transmission by an optically thin nanocomposite slab that contains randomly distributed metal nanoparticles (NPs) is developed. The underlying model treats NPs as point dipoles and employs a dyadic Green’s function known analytically for a slab that allows one to obtain the refection and transmission coefficients in a fully analytical form. The model also takes into account the enhanced decay of localized surface plasmons in dense NP arrays and light scattering at the slab surface roughness. It is demonstrated that the first effect leads to broadband perfect absorption observed in such nanocomposites, whereas the second one is responsible for its omnidirectional character and polarization insensitivity. These findings open up new possibilities to engineer broadband perfect absorption in plasmonic nanocomposites.

A Review on experimental and numerical studies of Glass Fibre Reinforced Polymer (GFRP) strips strengthened Reinforced Concrete (RC) slab subjected to low velocity impact

This paper reviewed the previous research on experimental and numerical studies on the impact behaviour of fibre reinforced polymer (FRP) strips reinforced concrete (RC) slab with various (FRP) strips arrangement. This review focusses on the effect of thicknesses, arrangements of FRP strips and type of support layouts. Initially, a throughout investigation was made on the FRP and its properties. Experiments associated to impact resistance of RC slabs was also performed. Furthermore, numerous finite element model (FEM) of RC slabs externally strengthened with different arrangement FRP strips were developed with ABAQUS and ANSYS. The numerical simulations on impact resistance of RC slab models externally strengthened with different arrangement FRP strips were performed. Generally, the experimental results displayed the diagonal two-way arrangement FRP strips externally bonded on bottom surface of RC slabs and four hinge supports applied had improved the impact strength significantly. The experimental and numerical impact results obtained for RC slabs externally strengthened with FRP strips were better as compared to the control RC slabs without FRP strengthening. Afterwards, the results gained from numerical was validated with experimental results. Finally, the methods and results of experimental and numerical reviewed was reliable as a reference for the study of RC slab externally strengthened with GFRP strips subjected to low velocity impact.

Role of chromium in Cr–Fe oxide catalysts for high temperature water-gas shift reaction – A DFT study

Carcinogenic hexavalent Cr in the current iron oxide-based catalysts of high temperature water-gas shift (HT-WGS) reaction is great environmental concern. Interpreting the role of the Cr in this important industrial catalyst system is required. In the present study, we investigated substitution of Cr atoms into the most stable termination of Fe3O4 (111) slab surface by spin-polarized periodic DFT approach to comprehend the role of Cr. We applied the projector augmented-wave (PAW) method within the Perdew-Wang 1991 (PW91) form of the generalized gradient approximation (GGA) on the Vienna Ab-initio Simulation Package (VASP). The calculations point out that Cr atoms choose being below the surface FeO6 sites. Cr slightly affects the dissociative H2O adsorption. There is no effect on the CO adsorption. Oxygen vacancy is favored to form on the topmost layer with less vacancy formation energy. Substitution of Cr into the structure increases the oxygen vacancy formation energy. This indicates that Cr does not act as a chemical promoter and does not affect the catalytic activity positively, which is experimentally confirmed by the previous studies.

Spin-polarized two-dimensional electron/hole gases on LiCoO$_2$ layers.

First-principles calculations show the formation of a 2D spin polarized electron (hole) gas on the Li (CoO_22) terminated surfaces of finite slabs down to a monolayer, in remarkable contrast with the bulk band structure, which is stabilized by Li donating its electron to the CoO_22 layer forming a Co-d-t_{2g}^6d−t2g6 insulator. By mapping the first-principles computational results to a minimal tight-binding models corresponding to a non-chiral 3D generalization of the quadripartite Su-Schrieffer-Heeger (SSH4) model and symmetry analysis, we show that these surface states have topological origin.

Cooper pair trajectories in superconducting slab at self-field conditions

Dissipative-free electric current flow is one of the most fascinating and practically important properties of superconductors. Theoretical consideration of the charge carriers flow in infinitely long rectangular slab of superconductor in the absence of external magnetic field (so called, self-field) is based on an assumption that the charge carriers have rectilinear trajectories in the direction of the current flow whereas the current density and magnetic flux density are decaying towards superconducting slab with London penetration depth as characteristic length. Here, we calculate charge particle trajectories (as single electron/hole, as Cooper pair) at self-field conditions and find that charge carriers do not follow intuitive rectilinear trajectories along the slab surface, but instead ones have meander shape trajectories cross the whole thickness of the slab. Moreover, if the particle velocity is below some value, the charge moves in opposite direction to nominal current flow. This disturbance of the canonical magnetic flux density distribution and backward movement of Cooper pairs can be entire mechanism for power dissipation in superconductors.

Effectiveness Evaluation of Cellar Application with Controlled Temperature Mode in Low-Rise Buildings with Pile Foundations

Low-rise buildings made of light steel thin-walled structures (LSTS below) in the Arctic regions are considered by thermal protection destruction due to many heat-conducting elements and high air infiltration. Constructive measures have been recommended to increase thermal protection for buildings made of LSTS including thermally insulated cellar with a controlled temperature mode. A comparative assessment of the energy efficiency of the proposed measures has been carried out. A significant temperature improvement on the inner surface of the basement slab was obtained. The energy characteristics improvement of a building made of LSTS is shown in comparison with the indicators of a standard solution.