Shaking‐table tests of a full‐scale single‐story masonry veneer wood‐frame structure

This paper presents the findings of shaking‐table experiments conducted to examine the seismic performance of a full‐scale, one‐story, wood‐framed structure with masonry veneer. The structure was designed and constructed in accordance with current U.S. code provisions. The veneer was attached to the wood backing with two kinds of metal anchors, corrugated ties fastened with 8d nails and rigid ties fastened with #8 screws. The tests have shown that the use of nails to fasten veneer anchors to the wood studs is highly unreliable due to the high variation of the nail extraction capacity, which can be influenced by the moisture content of the wood. Other than this, both the wood frame and the masonry veneer performed well under severe ground motions far exceeding a design level earthquake for Seismic Design Category D. Good performance was observed for the rigid veneer ties, which were attached to the wood studs with screws. The results have shown that the veneer walls parallel to the direction of shaking helped to restrain the motion of the wood structure and therefore should not be simply treated as added mass. The detailing of wood roof diaphragms requires special attention in consideration of the out‐of‐plane inertia force of the veneer that can be transmitted through the top plate of the wood‐stud wall to the rim joist. Copyright © 2010 John Wiley & Sons, Ltd.     

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Stability of L4 for radiated rigid primaries in resonant cases

The non-linear stability of the triangular libration point L₄ of the restricted three-body problem is studied under the presence of third- and fourth-order resonances, when the more massive primary is a triaxial rigid body and source of radiation. In this study, Markeev's theorems are applied with the help of Moser's theorem. It is found that the stability of the triangular libration point is unstable in the third-order resonance case and in the fourth-order resonance case, this is stable or unstable depending on A₁ and A₂, and a source of radiation parameter α, where A₁, A₂ depend upon the lengths of the semi-axes of the triaxial rigid body.     

Motion of a Rigid Body in a Tidal Field

We investigate the motion, near the equilibrium configurations, of an initially spinless rigid body subject to an external tidal field. Two cases are considered: when the center of mass of the body is at rest at the equilibrium point of the field generated by a generic mass distribution, and when it is placed on a circular orbit subject to a spherically symmetric potential. A complete analysis of the equilibrium configurations is carried out for both cases. First, we derive the conditions for the stable equilibria, and then we analyze the frequencies of oscillations around the equilibrium positions. In view of these results, we consider the problem of alignment of galaxies in clusters. After estimating the period of the oscillations induced on the galaxies by the tidal field of the cluster, we discuss the possible effect of resonances between stellar orbits inside the galaxy and the oscillations of the galaxy as a whole; this may be a mechanism responsible for producing an intracluster stellar population. This revised version was published online in July 2006 with corrections to the Cover Date.     

坚硬顶板煤层一次采全高顶板支护管理研究

大采高综采技术是厚煤层开采工艺的重要发展方向,越来越多地被采用,顶板事故在矿山生产安全事故中占有较大比例,有效控制顶板,合理对顶板进行支护是采矿过程中必须认真考虑的问题。大采高综采工作面采场顶板跨度大、高度高,矿山压力复杂,管理难道大,本文针对某矿9、10号煤层大采高综采工作面顶板坚硬特性,通过理论计算出了不同工作条件下支架工作阻力和顶板支护强度参数,结合对本矿区所做的相似模拟实验结论,对顶板管理中支护强度进行了分析研究,就矿区特定顶板条件选定和提出了具体支护要求。     

Constraints on rigid zones and other distinct layers at the top of the outer core using CMB underside reflected PKKP waves

Clear PKKP, a P wave reflects off the core-mantle boundary on the core side, is recorded by the transcontinental USArray from two deep earthquakes occurred in South America and Tonga, and one intermediate-depth earthquake in the Hindu Kush region. We compare the PKKP waveforms with the direct P waves to investigate the fine structures near the core-mantle boundary, with a primary focus on the core side. We find no evidence for the existence of a sedimentary layer of lighter elements with a thickness above a few hundreds of meters beneath the reflection points of the two deep events, which are located at the Ninety-East Ridge and South Africa. On the other hand the PKKP wave duration of the Hindu Kush event is almost twice as long as that of the P wave, suggesting that multiple reflections may be occurring at the core-mantle boundary located beneath the Antarctic, which is located inside the so-called tangent cylinder of the outer core. The tangent cylinder is an imaginary cylindrical region suggested by geodynamics studies, which has different flow pattern and may have a higher concentration in lighter elements as compared to the rest of the outer core. One possible explanation of the elongated PKKP is a thin distinct layer with a thickness of a few kilometers at the top of the outer core, suggesting that precipitation of lighter elements may occur at the core-mantle boundary. Our data also indicate an extremely low Q_P of 312, approximately 40% of the PREM average (~780), within the large-scale low-velocity anomaly in the lowermost mantle beneath Pacific.     

刚性桩复合地基桩体抗震性能分析

建立三维有限模型,分别采用振型分解反应谱法和时程分析法研究刚性桩复合地基的抗震性能,并根据相似理论,建立刚性桩复合地基群桩模型,采用模型拟动力试验,对其进行了地震作用下桩体响应规律试验研究,并对其在不同方法下的结果进行了对比分析,结果表明：无论是弯矩值还是剪力值,都是角桩最大,其次是边桩,再次是中心桩;不同分析方法所得的位移值相差不大,位移分布比较均匀;而且通过观察试验现象、分析试验和理论数据可见刚性桩复合地基具有良好的抗震性能;模型动力试验方法用于研究刚性桩复合地基的抗震性能是可行的,并且可推广应用到类似性的其他复合地基的抗震性能试验研究。     

刚性桩复合地基地震反应机理分析

为研究刚性桩复合地基的抗震性能,用刚性桩复合地基振动台试验验证了所采用的等效线性方法及其参数取值,在此基础上针对实际问题进行了三维有限元分析,对地基分层、土体模量、桩径、桩长、垫层厚度和垫层模量等因素对复合地基地震反应的影响进行了分析讨论,对刚性桩复合地基在地震荷载作用下的工作机理进行了较详细的分析。结果表明,等效线性方法能较好地模拟结构-复合地基相互作用的特性;上部结构惯性力和自由场变形对复合地基桩身内力影响都较大;地基明显软硬分层的存在,会使桩身内力显著增大。     

Rigid‐plastic models for the seismic design and assessment of steel framed structures

This paper demonstrates the applicability of response history analysis based on rigid‐plastic models for the seismic assessment and design of steel buildings. The rigid‐plastic force–deformation relationship as applied in steel moment‐resisting frames (MRF) is re‐examined and new rigid‐plastic models are developed for concentrically‐braced frames and dual structural systems consisting of MRF coupled with braced systems. This paper demonstrates that such rigid‐plastic models are able to predict global seismic demands with reasonable accuracy. It is also shown that, the direct relationship that exists between peak displacement and the plastic capacity of rigid‐plastic oscillators can be used to define the level of seismic demand for a given performance target. Copyright© 2009 John Wiley & Sons, Ltd.     

Three-layer model for vertical velocity distribution in open channel flow with submerged rigid vegetation

Based on the detailed laboratory experiments and theoretical analysis, a new three-layer model is proposed to predict the vertical velocity distribution in an open channel flow with submerged vegetation. The time averaged velocity and turbulence behaviour of a steady uniform flow with fully submerged artificial rigid vegetation was measured using a 3D Micro ADV, and the vertical distribution of velocity and Reynolds shear stress at different vegetation height, vegetation density and measuring positions were obtained. The results show that the velocity profile consists of three hydrodynamic regimes (i.e. the upper non-vegetated layer, the outer and bottom layer within vegetation); accordingly different methods had been adopted to describe the vertical velocity distribution. For the upper non-vegetated layer, a modified mixing length theory combined with the concept of ‘the new vegetation boundary layer’ was adopted, and an analytical model was presented to predict the vertical velocity distribution in this region. For the bottom layer within vegetation, the depth average velocity was obtained by numerically solving the momentum equations. For the upper layer within vegetation, the analytical solution was presented by expressing the shear stress as a formula fitted to the experimental data. Finally, the analytical predictions of the vertical velocity over the whole flow depth were compared with the results obtained by other researchers, and the good agreement proved that the three-layer model can be used to predict the velocity distribution of the open channel flow with submerged rigid vegetation.