Slab Theory Research Articles

Ultimate water level and deformation failures of the artificial dam in the coal mine underground reservoir

Coal mine underground reservoirs provide a new choice for the protection and utilization of water resources. This paper takes the underground reservoir of Wulanmulun Mine as the background, and takes the MB-1# artificial dam in the goaf of 31104–31116 working face of 3–1 coal seam as the research object. The theoretical model of artificial dam is established by elastic–plastic two-way slab theory, and the theoretical mechanical analysis and calculation are carried out. A similitude physical model for the coal mine underground reservoir was built by using the self-developed nested dual-dynamic-pressure similitude simulation testing system. Later, the mechanical response and deformation failure features of the artificial dam under different water pressure values were analyzed and the ultimate water pressure was determined. In addition, FLAC3D was used to determine the stress-seepage field-coupling model for the artificial dam. Using this model, the influence of water pressure on the multi-load coupling effect of the artificial dam and coal pillar dam was characterized. The dam form is optimized and the safety water level evaluation method of the dam body is proposed. The research results are as follows: (1) Based on the theory of elastic–plastic two-way slab, the theoretical analysis model of artificial dam is established, the expression of the ultimate water level function of artificial dam is derived, and the theoretical ultimate water head is determined to be 18.2 m (2) The seepage law of underground reservoir under different water pressures is obtained, and the ultimate water pressure of the model is determined to be 11.43 kPa. (3) It is clarified that the failure modes of the artificial dam are seepage failure and mechanical failure, and it is revealed that the groove area is the weakest position where the dam is most vulnerable to failure. In view of the failure modes of the dam, the I-shaped structure artificial dam is proposed. (4) A safe water level assessment method is proposed for the constructed artificial dam. According to the analysis of on-site monitoring data of MB-1# dam, the actual water level in the reservoir is within the allowable water level range of the artificial dam, and the whole reservoir is in a stable and relatively safe state at present. The reliability of this assessment method has been verified.

Orbital-free density-functional theory for metal slabs.

Orbital-Free Density-Functional Theory (OF-DFT) is known to represent a promising alternative to the standard Kohn-Sham (KS) DFT, as it relies on the electron density alone, without the need to calculate all KS single-particle orbitals and energies. Here, we investigate the behavior of the main ingredients of this theory, which are the non-interacting kinetic-energy density (KED) and the Pauli potential, for metal slabs. We derive explicit density functionals for these quantities in the quantum limit where all electrons are in the same slab discrete level of energy, and we present numerical calculations beyond this quantum limit for slabs of various widths. We have found the first explicit KED functional for a realistic many-particle fermionic system, which we prove to be generally valid with no assumption about the KS potential. We also discuss the total non-interacting kinetic energy and the corresponding enhancement factor, which represent basic quantities for the practical implementation of OF-DFT.

Estimating Load Transfer Efficiency for Jointed Pavements from TSD Deflection Velocity Measurements

Transverse joints are the weakest element of jointed pavements, and when these joints lack structural capacity, the onset of load-related distress is imminent. The most widespread measurement of the joints’ structural performance is the Load Transfer Efficiency Index (LTE), a ratio of the deflection of the two adjoining slabs. LTE can easily be assessed with a falling weight deflectometer, but this test procedure is not advisable for evaluation at the network level because of user safety concerns and because it can be excessively time-consuming. Traffic speed deflection devices like the traffic speed deflectometer (TSD) are suitable devices for network-level pavement structural evaluation. Yet, as of today, no interpretation technique to get structural health metrics for jointed pavements from TSD data has been published. In this paper, a backcalculation scheme based on slab theory is proposed to estimate the joints’ LTE from TSD deflection velocity measurements. The backcalculation problem formulation and its numerical solution using fast procedures are described in detail. The approach is tested with TSD data collected on the MnROAD test track. Overall, it was found that the backcalculation converges to reasonable estimates of the pavement structural properties and can furnish LTE estimates for most transverse joints from 5 cm-resolution TSD data, all at a reasonable computational cost. This allows for corridor-wide LTE assessment of a pavement’s joints using TSD measurements.

Study on the Stability Principle of Mechanical Structure of Roadway with Composite Roof

With the typical composite roof roadway and roof fall accidents in the Guizhou Province of China as the research background, the expression of damage parameters of composite roof was deduced according to Weibull statistical distribution, generalized Hooke’s law and Mises yield criterion, and the influence of shape and scale parameters of Weibull on damage characteristic was discussed. Based on the infinite slab theory, the expressions of deflection and layer separation of each layer of the composite roof were obtained, the critical load expression of each delamination was determined, and the influence of roadway width, overlying strata load, elastic modulus, shape parameters and scale parameters on the stability of composite roof was explored. The research shows that the bolt support can effectively reduce the layer separation between the composite roofs and enhance the stability of the composite roof. On this basis, it is proposed that for the surrounding rock control problem of roadways with composite roof, the active support technology with bolts as the core should be adopted.

Dynamic stability evaluation of underground cavern sidewalls against flexural toppling considering excavation-induced damage

Flexural toppling is a crucial engineering issue for high sidewalls of underground powerhouse caverns in low stress regions, when a small angle between cavern axis and bedding planes is formed. In this study, a novel dynamic method is proposed for stability evaluation of a high sidewall subjected to flexural-toppling, by integrating our derived criterion, continuum modelling and microseismic (MS) data. First, by virtue of cantilever slab theory, a geo-mechanical model is defined for analysing the toppling rock strata exposed on the high sidewalls of underground caverns. The Rayleigh-Ritz method is then adopted to deduce the equation for potential energies of toppling rock strata. A criterion for assessing the stability of high sidewalls considering a secondary stress field can thus be derived from catastrophe theory. Subsequently, stresses acting on the bedding planes are numerically obtained by continuum modelling coupled with MS data. Finally, a quantitative stability evaluation methodology is presented for flexural-toppling in view of progressive failure, considering the influence of fractures along bedding planes. A practical case of flexural toppling failure is analysed to verify our proposed approach. Good agreements indicate that our proposed approach is reliable for quantitatively evaluating the stability of larger underground powerhouse caverns against flexural toppling.

Construction and failure analysis of ultra-light GFRP fluted-core sandwich protective structures

Pultruded glass fiber reinforced polymer (GFRP) fluted-core sandwich panel is easily made and is a lightweight construction for protective structures. Blast-resistant doors are designed and constructed through combining three pultruded fluted-core sandwich panels framed by steel beams. With weight of 98.34 kg, the composite door is much lighter compared with traditional steel and concrete protective doors. Blast resistances of the composite protective doors are investigated by explosion testing. In current research, when the scaled distance is not smaller than 1.494 m/kg1/3, the door panel exhibits excellent anti-blast ability without any damage. When the scaled distance is less than 1.357 m/kg1/3, the structure damage is firstly characterized by the fluted-core shear and finally featured by the flexural failure of the delaminated sandwich panel. Including the deflection induced by the shear deformation of the fluted-core, dynamic one-way sandwich slab theory is proposed to predict the dynamic responses. The predictions are in agreement with the experimental results with acceptable errors. The dynamic theory can predict the critical scaled distance for the composite door based on core-shear failure criterion and the prediction is well consistent with the experiments. An equivalent static load model is suggested. Through the research, it is concluded that constructing protective door through pultruded GFRP fluted-core sandwich panels is a convenient, weight-saving and cost-saving way.

Structural performance of recycled aggregates concrete sourced from low strength concrete

Although much research has been carried out using recycled aggregates sourced from normal strength concrete, most of the buildings to be demolished are constructed with low strength concrete. Therefore, the properties of the concrete incorporating recycled aggregates, sourced from the waste of structural elements cast with low strength concrete, were investigated in this study. Four different concrete mixtures were designed incorporating natural and recycled aggregates with and without fly ash. The results of the mechanical and durability tests of the concrete mixtures are presented. Additionally, full-scale one-way reinforced concrete slabs were cast, using these concrete mixtures, and subjected to bending test. The feasibility of using conventional reinforced concrete theory for the slabs made with structural concrete incorporating recycled aggregates was investigated.

Fast Standing Modes in Transversley Nonuniform Solar Coronal Slabs: The Effects of a Finite Plasma Beta

Abstract We examine the dispersive properties of linear fast standing modes in transversely nonuniform solar coronal slabs with finite gas pressure, or, equivalently, finite plasma beta. We derive a generic dispersion relation governing fast waves in coronal slabs, for which the continuous transverse distributions of the physical parameters comprise a uniform core, a uniform external medium, and a transition layer (TL) in between. The profiles in the TL are allowed to be essentially arbitrary. Restricting ourselves to the first several branches of fast modes, which are mostly interesting from an observational standpoint, we find that a finite plasma beta plays an at most marginal role in influencing the periods (P), damping times (τ), and critical longitudinal wavenumbers ( ), when both P and τ are measured in units of the transverse fast time. However, these parameters are in general significantly affected by how the TL profiles are described. We conclude that, for typical coronal structures, the dispersive properties of the first several branches of fast standing modes can be evaluated with the much simpler theory for cold slabs, provided that the transverse profiles are properly addressed and the transverse Alfvén time in cold MHD is replaced with the transverse fast time.

Experimental Study on the Shear Performance of Shallow Hinge Joints for Prefabricated Hollow Slab Bridges

To investigate whether shallow hinge joint fracture was caused by shear stress or flexural stress, during the demolition and reconstruction of Xiaojiang River bridge, two original girders were collected and shipped to the lab, and the shallow hinge joint between the two girders was rebuilt. Tests were performed to investigate the cracking load, failure mode, and force transmission performance of the hollow slab girder and shallow hinge joint under vehicle load. The test result shows that under eccentric load, when the load increases to 365 kN, the midspan bottom slab of the testing girder starts to fracture; as the load increases to 560 kN, the roof slab of the testing girder starts to fracture; the hinge joint has a maximum horizontal opening of 0.153 mm and vertical relative displacement of 0.201 mm; during the entire test loading process, the shallow hinge joint structure does not develop fracture and shear failure; and the shallow hinge structure demonstrates excellent shear stress transmission performance. In addition, based on hinge slab theory, the hinge joint internal force under vehicle load was calculated. Based on ACI 318‐05 specification, CAN/CSA‐S6‐00, and JTG D61‐2005, the hinge joint shear bearing capacity was calculated. Hinge joint stress resistances calculated from the three specifications all exceed the internal force. Among them, the calculation results from ACI 318‐05 and CAN/CSA‐S6‐00 are similar, while the result from JTG D61‐2005 specification significantly exceeds the internal force, which is mainly because the designed concrete direct shear strength fvd in the Chinese specification does not consider factors such as bonding surface coarseness, concrete pouring sequence, and material properties. Theoretical calculations and tests show that the actual failure mode of the shallow hinge joint in prefabricated hollow slab girder bridges is not caused by shear stress.

Design and modelling of pre-cast steel-concrete composites for resilient railway track slabs

Australian railway networks possess a large amount of aging timber components and need to replace them in excess of 280 thousands m3 per year. The relatively high turnover of timber sleepers (crossties in a plain track), bearers (skeleton ties in a turnout), and transoms (bridge cross beams) is responsible for producing greenhouse gas emissions 6 times greater than an equivalent reinforced concrete counterparts. This paper presents an innovative solution for the replacement of aging timber transoms installed on existing railway bridges along with the incorporation of a continuous walkway platform, which is proven to provide environmental, safety and financial benefits. Recent developments for alternative composite materials to replace timber components in railway infrastructure construction and maintenance demonstrate some compatibility issues with track stiffness as well as structural and geometrical track systems. Structural concrete are generally used for new railway bridges where the comparatively thicker and heavier fixed slab track systems can be accommodated. This study firstly demonstrates a novel and resilient alterative by incorporating steel-concrete composite slab theory and combines the capabilities of being precast and modulated, in order to reduce the depth, weight and required installation time relative to conventional concrete direct-fixation track slab systems. Clear benefits of the new steel-concrete composites are the maintainability and constructability, especially for existing railway bridges (or brown fields). Critical considerations in the design and finite element modelling for performance benchmarking of composite structures and their failure modes are highlighted in this paper, altogether with risks, compatibilities and compliances.

Fast Numerical Simulation of Symmetric Flat Rolling Processes for Inhomogeneous Materials Using a Layer Model − Part I: Basic Theory

In the first part, a brief introduction to a general non‐isothermal layer model for symmetric but inhomogeneous rolling conditions is presented. The model is based on an extended slab theory. Additional to conventional approaches, a phenomenological layer thickness model for NS‐layers and its application to several rolling conditions is briefly described in part I. Within the course of computation for the stress and strain state internal stresses at the entrance and exit of the roll gap are predicted as a closing condition for the derived set of kinematic and kinetic equations. They transform elastically outside the roll gap to residual stresses. In this part, first comparisons are given to finite element solutions and experimental investigations. The results of an extensive case study will be given in part II. Due to the used coupling between kinematics and kinetics, a significant improvement of the slab theory in relation to a local description of an inhomogeneous plane strain deformation and stress state is found.

3-D LUMPED MASS METHOD OF DYNAMIC ANALYSIS FOR HIGH-RISE BUILDING

This study is related to decreasing size of stiffness matrix of high-rise building by using floor diaphragm constraints. The combined actions of horizontal structural members such as slab and beams produce structural response that is much stiffer than vertical elements such as columns. In structural analysis of high-rise building model, absolute rigid slab and vertical structure are working together for lumped mass method. Each lumped mass node has 6 degree of freedoms which is very suitable for high-rise building calculation. The lumped mass is consisted of slab and beams, on the other hand the system’s stiffness matrix is only assembly of columns and braces. High-rise building lumped mass model’s stiffness matrix size is n=6 x m (n; total size of stiffness matrix, m; total floor number). In the step by step calculation, total unknown number is decrease enough which means we can easily calculate high-rise building structures for dynamic analysis also nonlinear step by step calculation using simple personal computer. If building model has large span and short height, in this case rigid slab theory will not satisfied. This idea is more suitable for high-rise building calculation.

Comparation of Numerical Methods for Calculation of Thin Slabs

The purpose of this paper is to compare calculation of internal forces and deformations of slabs for two calculation methods: the finite element method and the finite difference method. Two concrete slabs have been analysed. In the case of the finite element method, different element mesh are used, providing, thus, solutions in different variants. The calculation and algorithms is based on a thin slab theory. Variants calculate in program Scia Engineer effects of shearing forces by means of the Midlins theory or thin slab theory. Algorithms for the calculation were developed in Matlab.

The Precise Prediction of Rolling Forces in Heavy Plate Rolling Based on Inverse Modeling Techniques

© 2014 Wiley-VCH Verlag GmbH & Co. KGaA. The industry scale production of heavy steel plates is performed in plate mills using reversing mill stands and roll schedules with 30 or more passes. Ideal pass scheduling is dependent on a precise prediction of the roll force in each pass. To obtain these forces process models based on the slab theory together with semi-empirical material models are most frequently used. The material parameters necessary to calibrate the models for a specific steel grade are conventionally generated on a lab scale via time-consuming and expensive compression tests. This paper will introduce a concept that allows obtaining the material model parameters directly from the rolling process on an industrial scale by an inverse modeling technique. In this context, the parameters of the material model are adjusted according to the current offset between measured and calculated roll forces. The adjustment is enabled by a non-linear optimization that aims for a minimum deviation between measured and calculated roll forces for each pass. Several results gathered in an optimization run with industrial data of about 2650 produced plates are presented. The concurrence between measurement and prediction using the optimal parameters is in detail shown for three different schedules. In summary, inverse modeling seems to allow utilizing data of past rolling processes to determine material model parameters with high accuracy.

The Predication Parameters of the Stress Distribution and Failure of the Roof of the Severely Inclined Coal Seam

By turning to the elastic thin slab theory, the present authors have established a model for the mechanical assessment of the roof failure for the severely inclined seam under long wall working in swith formulae deduced for the calculation of the stress distribution. When the roof stress distribution is characterized, a model for the roof breakage of the long wall coal seam under working, with failure assessment parameters deduced.

Calculation of Load Lateral Distribution for Hinged Slab Bridge with Different Stiffness between Outside Slabs and Inside Slabs

Based the hinged slab bridge theory and fundamental of structural mechanics, calculation formulas of load lateral distribution are deduced for hinged slab bridge with different rigidity between outside slabs and inside slabs, which make the hinged slab theory more perfect. Finally, a practical example is calculated and its results are compared with the results calculated by Equivalent Stiffness Method.

Some evaluations of basic nodal-like schemes for a selection of classical problems in particle transport theory

In order to provide some basic evaluations of elementary nodal techniques, as used in the general area of particle transport theory, critical and albedo problems for cylinders, spheres, and slabs are solved approximately in terms of averaged quantities and compared to exact results.

Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide

We propose a hybrid waveguide-plasmon system consisting of gold pillar arrays on top of a dielectric waveguide. The formation of extraordinary transmissions induced by the hybrid waveguide-plasmon resonances is investigated by rigorous coupled-wave analysis. The characteristics of the hybrid resonances can be predicted by introducing the photonic crystal slab theory. Extremely narrow absorption peaks and the electromagnetically induced transparency-like optical property are demonstrated in our hybrid system.

Effects of ether vs. ester linkage on lipid bilayer structure and water permeability

The structure and water permeability of bilayers composed of the ether-linked lipid, dihexadecylphosphatidylcholine (DHPC), were studied and compared with the ester-linked lipid, dipalmitoylphosphaditdylcholine (DPPC). Wide angle X-ray scattering on oriented bilayers in the fluid phase indicate that the area per lipid A is slightly larger for DHPC than for DPPC. Low angle X-ray scattering yields A=65.1A(2) for DHPC at 48 degrees C. LAXS data provide the bending modulus, K(C)=4.2x10(-13)erg, and the Hamaker parameter H=7.2x10(-14)erg for the van der Waals attractive interaction between neighboring bilayers. For the low temperature phases with ordered hydrocarbon chains, we confirm the transition from a tilted L(beta') gel phase to an untilted, interdigitated L(beta)I phase as the sample hydrates at 20 degrees C. Our measurement of water permeability, P(f)=0.022cm/s at 48 degrees C for fluid phase DHPC is slightly smaller than that of DPPC (P(f)=0.027cm/s) at 50 degrees C, consistent with our triple slab theory of permeability.

Reduction of Vibrations due to Foundation Slabs

This paper investigates the reduction of vibration due to the foundation slab both in horizontal and vertical directions. Similar reduction efficiency of the foundation slab was obtained among three-dimensional finite element analyses, field experiments, and the averaging scheme of the rigid slab theory. Then, two formulas fitted from numerical simulations were generated. Using those two simple formulas, one can estimate the reduction efficiency of horizontal and vertical vibrations due to foundation slabs. In summary, a suitable mat foundation can significantly reduce the horizontal vibration transformed from soil. The reduction efficiency depends on the size of the mat foundation over the soil wavelength. Enlarging the thickness of the foundation slab can decrease the vertical vibration transferred from soils. However, it is difficult to reduce vertical low-frequency vibrations for a reasonable slab thickness.