Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Temperature distribution in composite bridges

Abstract: Thermal stresses in composite concrete deck slab‐on‐steel beam bridges can be significant in comparison to dead or live load stresses. Specifications by AASHTO do not provide guidance for the vertical temperature distribution through the depth of the composite bridge, while the Ontario Highway Bridge Design Code does require the designer to account for the effects of temperature differentials, but is deficient in several aspects. Based on a synthesis of several theoretical and experimental studies on prototype bridges, a simple but realistic vertical temperature distribution through the section depth is proposed. Maximum and minimum values of temperature differentials, consistent with observed field measurements, are also presented. The proposed distribution is linear through the depth of the slab and uniform through the depth of the steel beam. This distribution also leads to simple formulas to estimate the thermal stresses in simple and continuous composite bridges.

Seismic anisotropy and heterogeneity in the Alaska subduction zone

Abstract: SUMMARY We determined P- and S-wave tomography and P-wave anisotropic structure of the Alaska subduction zone using 259 283 P- and 73 817 S-wave arrival times from 7268 local shallow and intermediate-depth earthquakes recorded by more than 400 seismic stations. The results show strong velocity heterogeneities in the crust and upper mantle. Low-velocity anomalies are revealed in the mantle wedge with significant along-arc variations under the active volcanoes. In the mantle wedge, the low-velocity zone extends down to 100–150 km depth under the backarc. The results indicate that H2O and fluids brought downwards by the subducting Pacific slab are released to the mantle wedge by dehydration and they are subsequently transported to the surface by the upwelling flow in the mantle wedge. Significant P-wave anisotropic anomalies are revealed under Alaska. The predominant fast velocity direction (FVD) is trench-parallel in the shallow part of the mantle wedge (<90 km depth) and in the subslab mantle, whereas the FVD is trench-normal within the subducting Pacific slab. The trench-parallel FVDs in the mantle wedge and subslab mantle may be caused by 3-D mantle flow that is induced by the complex geometry and strong curvature of the Pacific slab under Alaska. The flat and oblique subduction of the Pacific slab may play a key role in forming the trench-parallel FVD under the slab. The trench-normal FVD in the subducting Pacific slab may reflect the original fossil anisotropy when the Pacific Plate was produced at the mid-ocean ridge.

Lateral variation in slab orientation beneath Toba Caldera, northern Sumatra

Abstract: The Investigator Fracture Zone (IFZ) subducts beneath Toba Caldera, the Earth's largest Quaternary caldera, in northern Sumatra, suggesting a possible relationship between them. Locations of sub-crustal earthquakes based on arrival times of P and S waves at a seismograph network surrounding Toba reveal the geometry of the subducted slab and the IFZ beneath Toba. A vertical tear of less than 20 km in the slab across the IFZ, as previously suggested, cannot be ruled out but the large-scale geometry of the slab is dominated by a broad bend of slab contours parallel to the concaveseaward indentation of the trench. The slab shape is probably a response to the trench curvature, can explain the change in trend of the volcanic arc near Toba, and may cause shallowing of the forearc basin near Nias Island. The decrease in radius of curvature of the slab contours is not accompanied by an observable decrease in dip angle, possibly resulting in lateral compressive stress in the slab. The high rate of seismicity along the subducted Investigator Fracture Zone, that intersects the slab obliquely to its plunge direction, is uncommon at subducted fracture zones and is likely caused by such lateral stress in the slab.

Structure and method for coupling light between dissimilar waveguides

Abstract: A strip loaded waveguide comprises a slab and a strip, wherein the strip is separated from the slab. Nevertheless, a guiding region is provided for propagating an optical mode and this guiding region extends both within the strip and the slab. A layer of material having an index of refraction lower than that of the strip and the slab may be disposed between and separate the strip and the slab. In one embodiment, the slab comprises a crystalline silicon, the strip comprises polysilicon or crystalline silicon, and the layer of material therebetween comprises silicon dioxide. Such waveguides may be formed on the same substrate with transistors. These waveguides may also be electrically biased to alter the index of refraction and/or absorption of the waveguide.