Showing papers on "Slab published in 1982"

Punching Shear Behavior of Reinforced Slab-Column ConnectionsMade with Steel Fiber Concrete

Abstract: Punching shear failures occur suddenly and produce catastrophic results. The effect of fiber reinforcement on the deformation and strength characteristics of punching shear failures is discussed in this paper. The fibers were used throughout the slab or in the punching shear zone of the column head, and comparative tests were carried out on connections with bent-up steel bars. The results show that fibers reduce deformations at all stages of loading, increase ultimate punching shear loads, and produce ductile shear failures. Substantial increases in ductility and energy absorption can be obtained by using fiber concrete. Fibers can not only produce flexural failures for the same load capacity in shear but can achieve it with considerable saving in flexural steel. Bent-up bars are clearly more effecti•·e than fiber reinforcement but are very labor-imensive.

Thermal modeling of the geometry of subduction with implications for the tectonics of the overriding plate

Abstract: The path which subducting lithosphere follows can be broken into three zones: zone I, a subhorizontal region of nearly constant dip near the trench; zone II, a region of rapidly increasing dip; and zone III, a region generally deeper than 125 km, again of nearly constant dip. We have modeled the thermal evolution of slabs as they pass through these three zones using the method of lines, a numerical technique well suited to the solution of time dependent partial differential equations. By use of appropriate initial conditions and time dependent boundary conditions we can simulate subduction with variations in age of subducting lithosphere, slab velocities, and paths followed by the slab. Thermal modeling results indicate that the geometry of the slab in region II can be empirically related directly to the thermal structure of the slab in that region and thus indirectly to age and velocity. It follows that low angle subduction can extend several hundred kilometers inland only in cases of high convergent velocities (>15 cm yr−1) and old (>120 m.y.) lithosphere. We further suggest that rapid variations in the convergence velocities can provide an enabling mechanism for back arc spreading while slow changes in convergence velocities and/or age variations in the subducting lithosphere lead to migration of volcanic arcs.

Experiments on continuous composite beams.

Abstract: Tests are presented of six continuous composite beams of 9M length and having compact steel section. Two beams had limited rotation capacity and were tested under severe sagging rotation conditions; the other four were loaded symmetrically and included cases where local buckling contributed to failure. It is proposed that beams having a ductility parameter greater than 1.4 can be designed using simple plastic theory, without regard to loading and span configuration. An assessment is made of the vertical shear resistance of the slab at interior supports. It is concluded that simple plastic design incorporating full plastic moment values may be confidently used in continuous composite beams having compact steel section, adequate slab and shear connection, even under conditions of severe rotation requirement. (Author/TRRL)

Prefabricated building panel

Abstract: A prefabricated load-bearing wall panel has a layer of concrete attached to a plurality of spaced apart parallel metal wall studs. The slab support is achieved by flexible bolsters secured at spaced locations to each stud and fastened to a reinforcing mesh embedded in the concrete slab. The bolsters, which are partially embedded in the slab, provide compressive and tensile support for the slab on the studs in a direction generally perpendicular to the general plane of the slab. In addition, the wall panel exhibits a synergistic effect in terms of composite design, wind load strength and shear strength.

Optimization techniques and inverse problems: Reconstruction of conductivity profiles in the time domain

Abstract: The iterative probing of an inhomogeneous lossy dielectric slab, whose conductivity is unknown, is discussed. The probing is done in the time domain from the measurements of the field on the interface when this slab is illuminated by a known field. An exact integral formulation is used. Minimization of a cost function, characteristic of the discrepancy between the measured field and the field which would be scattered by a known slab, is specified by the optimization theory. The notion of the adjoint state of the field is introduced. The influence of some parameters of this minimization is studied. Great importance is given to the sensitivity of the probing as function of the amplitude of errors in the data. Such an iterative probing appears fast, accurate, and efficient, even in the case of large errors.

Thermal stresses in subducting lithosphere can explain double seismic zones

Abstract: The discovery of double-planed zones of intermediate-depth seismicity associated with subducting oceanic lithosphere (refs 1–7 and L.S.H. and K.H.J., in preparation) has generated much interest in the origin and distribution of stresses in descending plates. Several mechanisms have been proposed to explain why double zones occur8. Here we investigate the role of thermal stresses for the state of stress in a descending plate and test whether they can account for the observed characteristics of double seismic zones. By modelling the descending slab as a thin elastic plate and using the temperatures in the slab estimated by Toksoz et al.9, we find that the polarities of thermally generated stresses agree with those obtained from the focal mechanisms of earthquakes in the two zones. Thermal stresses also can explain the separation between the two zones of seismicity at shallow depths and their gradual merging at greater depth.

Numerical analysis of the discontinuities in slab dielectric waveguides

Abstract: We propose an approximate method, of general applicability, for analyzing the discontinuities in slab dielectric waveguides. The method is based on replacing the unbounded configuration by a corresponding periodic multilayer structure. Hence the entire spectrum becomes discrete, and this makes the problem easier. The characteristic equation for the modal solution in a periodical multilayer dielectric waveguide is expressed in a matrix form which can be readily solved with a computer. In order to solve the discontinuity problems of slab waveguides, we expressed the reflected and transmitted fields by truncated modal expansions. The unknown amplitudes of the reflected and transmitted modes are determined by the boundary conditions. Numerical results are graphically shown including the cases which have been difficult to analyze by other methods. The accuracy of our results is checked by evaluating the relative errors and comparing with other available results.

Tension-field action in composite plate girders.

Abstract: The article reports on tests to failure carried out on negative-moment sections of five composite plate girders and a steel plate girder with slender stiffened webs. The study examines the interaction between tension-field action in web panels and the shear connection to the slab above for girders with relatively light steel top flages. The ultimate strength of all six girders exceeded by 30 per cent or more that given by the design method of the bridge code to BS5400. Details are given of a method of analysis, developed from other studies, that accurately predicts observed ultimate strengths. (Author/TRRL)

Coastal ocean current response to storm winds

Abstract: Design of offshore structures requires knowledge of the appropriate current profile to be used in conjunction with the design wave. Accurate determination of the current profile will depend on reliable current models. Vertical transfer of momentum in storm-driven current models is commonly treated either by using eddy viscosity or by assuming ‘slab-like’ mixed layer flow. These two fundamentally different approaches predict different current speeds and profiles during severe storms. The existing data base is inadequate to determine which approach is better, but most existing data sets are subject to one or more of four limitations that can lead one improperly to interpret the data as supporting the existence of current velocity shear in otherwise uniform mixed layers. One-dimensional slab models are found to compare favorably with observed wind-driven currents at the Ocean Test Structure in the Gulf of Mexico (deployed in 20 m deep water). By using some reasonably simple assumptions, these slab models are able to replicate many of the significant features of a wide range of different responses. The character of the response appears to depend on an interaction of stratification and topography. Barotropic responses are characteristic of typical coastal responses; currents are oriented longshore and are in phase with the wind. Baroclinic responses are dominantly inertial as might be expected in the deep sea, but with an additional near-bottom cross-shore counter flow. The structure of one observed barotropic response is compared in detail to predictions of both slab and eddy viscosity models and found consistent with a slab model and inconsistent with eddy viscosity models. Shear observed during this event was not significantly different from zero, but was significantly below estimated shear predictions of four eddy viscosity models given the peak 0.4 N/m2 wind stress.

Scattering from an inhomogeneity inside a dielectric-slab waveguide

Abstract: Scattering from cylindrical inhomogeneities immersed inside a dielectric-slab waveguide is investigated analytically. A volume integral equation technique based on Green’s function theory in regions with planar boundaries is used to formulate the problem. For the case of circularly inhomogeneous shapes, an analytical solution is developed when |b(k1 − k2) < 1, where k1 − k2 is the difference between the wave numbers of the slab and the circular inhomogeneity whose radius is b. Analytical expressions for the reflection and transmission coefficients in the slab, when a guided surface mode is incident upon the inhomogeneity from the left, are derived up to order [b(k1 − k2)]3. Numerical results are computed and plotted for several cases.

Dowel for pavement joints

Abstract: A device for transferring vertical shear stress and bending moments across transverse joints in concrete pavement slabs and the like, and for simultaneously controlling the joint gap width A dowel is formed from a continuous length of steel bar, treated to cause its outer ends to bond to concrete and its central portion treated to prevent bonding to concrete The outer ends of each bar is formed to permit the center portion to be disposed near either the top surface or bottom surface of the slab sections and the outer ends along the neutral axis of the slab sections The bars are used in pairs with one center portion adjacent the top surface and the other one adjacent the bottom surface A multiplicity of such dowels is embedded in the concrete of a continuously-poured concrete slab aligned with the roadway and in a spaced relationship across the slab The concrete is grooved before curing across the slab and over the central portions of the dowels As the concrete cures, the outer ends of the dowels bond to the concrete while the central portions remain unbonded causing a joint crack and strain produced in the concrete due to shrinkage which is partially transferred to the unbonded steel which acts as a latent spring to subsequently control the gap width The dowels additionally serve to transfer bending moments and vertical shear stresses from live loads across the pavement joint

Method of handling slabs by an overhead traveling crane provided with a slab grip lifter

Abstract: A method of handling slabs by an overhead traveling crane having a slab grip lifter comprises disengaging a brake for a lifter swinging motor and a brake for a crab moving motor in the beginning, causing the position of the lifter to be adjusted by a reaction force from a slab when the lifter grips the slab, and causing the lifter to return to its original position after it has gripped the slab.

Apparatus for cutting stone panels

Abstract: Apparatus for cutting thin laminae of stone, e.g. marble, comprising a saw having two disc blades, a bogie movable beneath the saw and having a pair of vacuum-operated slab-gripping devices each of which is adapted to support a slab upwardly on its edge, and a second bogie movable in a direction transverse to the first bogie and carrying structure for tumbling a slab supported on one longitudinal edge, through 180°, so that it rests on its opposite longitudinal edge.

Multi slab gel casting electrophoresis apparatus

Abstract: An electrophoresis system which provides enhanced resolution and ability to identify nucleases through use of a two-dimensional technique involving isoelectric focussing of tube gels followed by the electrophoresis of second-dimension slab gels formed by the use of a holder allowing slab gels to be cast directly on the sides of the tube gels. DNA is employed as the enzyme substrate within the slab gels. The slab gels are electrophoresed for the second dimension in a chamber wherein the rack containing a stack of slab gels forms the partition between the anolyte and catholyte compartments. After the second-dimension electrophoresis, the slab gels are incubated in incubation buffer and placed in Pyronin Y to stain the unhydrolized DNA. After staining, they are destained in acetic acid. The DNAses are then visible as colorless spots in a reddish-colored gel.

The earthquake cycle in subduction zones

Abstract: A simplified model of a subduction zone is presented, which incorporates the mechanical asymmetry induced by the subducted slab to anchor the subducting plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the trench moves with respect to the deep mantle toward the subducting plate at a velocity equal to one-half of the convergence rate. A strong extensional pulse is propagated into the overthrust plate shortly after the earthquake, and although this extension changes into compression before the next earthquake in the cycle, the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back-arc region.

On a mixed boundary value problem of diffusion type

Abstract: Fluid arriving at the surface of an unevenly heated solid (such as a reactor rod) may initially be converted to steam on the higher temperature portion of the surface; and the extent of the steam covered portion shrinks when there is a continual supply of cooling fluid. A two-dimensional model diffusion problem, involving linear specifications and intended for a determination of the steady advance of the (quench) front which separates the fluid and steam covered parts of a slab face, is resolved in exact fashion and the estimates of a prior approximate calculation (Caflisch and Keller, 1981) are thereby extended.

Reflection and transmission of electromagnetic waves by a linearly accelerated dielectric slab

Abstract: The reflection and transmission of electromagnetic waves by a dielectric slab which performs a given accelerated motion is investigated theoretically. Rigorous expressions for the reflected and transmitted waves are obtained by making use of the covariant properties of Maxwell's equations under the arbitrary coordinate transformations. It is found that there exists a small Doppler shift in frequency for the transmitted wave due to the drag effect of the moving medium. It is shown that this frequency shift depends on the acceleration, the index of refraction, and the width of the slab and is independent of the velocity of the slab.

Diffusion of radon through cracks in a concrete slab.

Abstract: A mathematical model is developed to describe diffusion of radon through cracks or gaps in concrete slabs which are used in building foundations. As radon approaches the soil surface from underlying soil, it encounters a concrete slab. The radon will diffuse toward any air-filled cracks. The rate of exhalation through a portion of a cracked slab is determined and compared to the rate of exhalation from the same surface area of bare soil. In a typical case, this ratio is approx. 0.25. This is about a 20-fold increase to the ratio found when the concrete slab has no cracks. Therefore crack pathways are potentially a major source of indoor radon.

Strength of Composite Beams at Web Openings

Abstract: A model for the strength of steel-concrete composite beams with unreinforced, rectangular web openings is presented. The model includes the contribution of the concrete slab to shear strength, as well as flexural strength. Steel is represented as an elasto-plastic material with no strain hardening. Openings may be concentric or eccentric with respect to the steel section. Comparisons are made with test results. The model provides realistic, and generally conservative, predictions of the strength for the test beams. The contribution of the concrete slab to shear strength at an opening must be included to obtain a realistic model.

Manufacture of anisotropic electrical steel plate with improved iron loss

Abstract: PURPOSE: To obtain industrially and stably a product with improved iron loss by subjecting a slab for an electrical steel plate contg. prescribed percentages of C, Si, Al, N, S, Mn and P to hot and mechanical working under prescribed conditions. CONSTITUTION: A slab consisting of 0.025W0.075% C, 3W4.5% Si, 0.01W0.06% acid-sol. Al, 0.003W0.013% N, ≤0.007% S, 0.08W0.45% Mn, 0.015W0.045% P and the balance Fe is cast. The slab is heated to ≤1,280°C and hot rolled. The hot rolled plate is annealed at 850W1,200°C for a short time and cold rolled at ≥80% draft. The cold rolled plate having the final thickness is subjected to continuous decarburization annealing in wet hydrogen, it is coated with a protective coating material for annealing, and finish annealing is carried out at a high temp. COPYRIGHT: (C)1984,JPO&Japio

Kinetic theory of neutrals in a bounded plasma slab with inhomogeneous temperature and density profile

Abstract: The transport of neutral hydrogen atoms in a hydrogen plasma slab is considered. The influence of the inhomogeneous ion temperature profile on the neutral density and distribution is discussed as well as the influence of the neutral edge energy, charge exchange, and ionization rates. The analytical solutions for the neutral density and distribution function are obtained and compared with the numerical results. The effects due to the inhomogeneous temperature profile are discussed. The recommen‐dations from the viewpoint of the effects mentioned previously for the purposes of the cold‐gas mantle system have been given.

Circular Voided Concrete Slab Stiffnesses

Abstract: Finite element procedures for determining the plate bending stiffnesses of a circular voided slab are presented and the results are compared with those obtained from tests on model elastic voided plates. Preliminary investigations showed that a simplified plane-strain formulation, rather than a more complex general plane-strain formulation, could be used to determine the transverse flexural stiffness. Torsional stiffnesses were obtained from an analysis using the Prandtl stress-function formulation of the torsion problems. Tests were carried out on four epoxy-resin model plates having different void sizes. Good agreement was obtained between the finite element and experimental results. For design purposes, charts are presented which enable a designer of a concrete voided slab, having a Poisson's ratio of 0.2, to determine the values of the plate bending stiffnesses required for a thin plate analysis of such a slab. It is also shown that simple calculations based upon replacing a circular void with an equivalent square void are often adequate for design purposes.

Implications of stress concentration on a strike-slip fault in an elastic plate subject to basal shear stress

Abstract: Summary. We consider a long strike-slip fault in a lithosphere modelled as an elastic slab. To the base of the slab a shear stress distribution is applied which simulates the viscous drag exerted by the asthenosphere. The resulant stress on the fault plane may directly fracture the lithosphere in its brittle upper portion; alternatively it may give rise at first to a stable aseismic sliding in the lower portion. In the latter case, stress concentration due to the deep aseismic slip is the relevant feature of the pre-seismic stress acting on the upper section of the lithosphere. The two cases are examined by use of dislocation theory and their observable effects compared. Different depths of the aseismic slip zone and the presence or absence of a uniform friction on the seismic fault are allowed for. If the model is applied to the San Andreas fault region, where a steady sliding condition actually seems to be present at shallow depth, it turns out that the slip amplitudes commonly associated with large earthquakes are consistent with average basal stress values which can be substantially lower than a few bars, a value often quoted as the steady state basal stress due to a velocity gradient in the upper asthenosphere.

Stiffening girder for a stayed cable bridge

Abstract: A stiffening girder for a stayed cable bridge, constructed of reinforced concrete or prestressed concrete, is formed by a closed multi-cell box extending in the long direction of the bridge. The upper part of the box is a substantially horizontally extending roadway slab. Webs extending downwardly from the roadway slab and in the long direction of the bridge combine with the roadway slab to form at least a part of the multi-cell box. The webs can be vertically arranged or obliquely inclined relative to the roadway slab. Further, a bottom slab spaced downwardly from the roadway slab may complete the box. The girder or box is supported by inclined cables extending in at least one support plane along the long direction of the bridge. The cables can be attached to the girder along its center line in the long direction or at symmetrical locations positioned outwardly from the center line.

Radiation from a dipole in the presence of a grounded gyromagnetic slab

Abstract: Radiation from dipoles in the presence of a grounded gyromagnetic slab is considered. The Green’s function for an arbitrarily oriented elementary dipole source is derived first, assuming that the static magnetic field applied to the gyromagnetic slab is either vertical or parallel to the slab surface. A plane‐wave Fourier representation is employed to expand the field in and out of the slab. Several symmetry relations are exploited to reduce the complexity of the solution. Radiation properties of the grounded slab, such as the surface wave launching and the far‐field behavior, are then investigated. It is shown that the far‐field amplitude and phase can be controlled by varying the external static magnetic field. Numerical results are presented for several cases.