Analytical and empirical models for predicting the drift capacity of modern unreinforced masonry walls

Displacement‐based seismic assessment of buildings containing unreinforced masonry (URM) walls requires as input, among others, estimates of the in‐plane drift capacity at the considered limit states. Current codes assess the drift capacity of URM walls by means of empirical models with most codes relating the drift capacity to the failure mode and wall slenderness. Comparisons with experimental results show that such relationships result in large scatter and usually do not provide satisfactory predictions. The objective of this paper is to determine trends in drift capacities of modern URM walls from 61 experimental tests and to investigate whether analytical models could lead to more reliable estimates of the displacement capacity than the currently used empirical models. A recently developed analytical model for the prediction of the ultimate drift capacity for both shear and flexure controlled URM walls is introduced and simplified into an equation that is suitable for code implementation. The approach follows the idea of plastic hinge models for reinforced concrete or steel structures. It explicitly considers the influence of crushing due to flexural or shear failure in URM walls and takes into account the effect of kinematic and static boundary conditions on the drift capacity. Finally, the performance of the analytical model is benchmarked against the test data and other empirical formulations. It shows that it yields significantly better estimates than empirical models in current codes. The paper concludes with an investigation of the sensitivity of the ultimate drift capacity to the wall geometry, static, and kinematic boundary conditions.     

Assessing the ecosystem effects of the abalone Haliotis midae from its diet and foraging behaviour

The South African abalone Haliotis midae is commercially exploited and seriously threatened by overfishing. This not only affects the species itself but potentially the functioning of the ecosystem because of associated changes in community structure. The nature of effects that can follow the loss or reduction of a species depends in part on its position in the foodweb and its feeding behaviour. To assess the ecosystem effects of the adults and subadults of this previously abundant herbivore on the south-west coast of South Africa, we studied their diet and mode of food procurement by (a) in-field observations of adult and subadult abalone, (b) analysis of the gut contents of adults, (c) comparison of diet with the availability of algae, and (d) a mesocosm experiment on subadult feeding behaviour. Both field and dietary studies showed that adults subsist mainly by trapping drift kelp, but also occasionally graze on attached algae such as Plocamium spp., and feed in a manner that is highly selective, with drift kelp constituting 95–98% of the diet, and several species of common algae being avoided. In the mesocosm experiment, subadults preferentially fed on drift kelp, but emerged at night to a greater extent to graze on microflora if no drift material was available. Their propensity to emerge was, however, reduced if the rock lobster Jasus lalandii was present. Collectively, this evidence indicates that any ecosystem effects that subadults and adults of H. midae have as grazers will be weak because they feed mainly by trapping drift material, and the frequency of grazing and the incidence of consumption of attached algae are low.     

Analytical and experimental investigations on seismic performance of exterior beam–column subassemblages of existing RC‐framed building

Seismic performance of exterior beam–column subassemblages of reinforced concrete structure designed and detailed on the basis of the provisions of Eurocode and Indian Standards at different stages of their evolution is evaluated. Performance of the subassemblages designed and detailed according to the three different stages of codal evolution (gravity load design, ‘Nonductile’, and ‘Ductile’) is evaluated through analytical formulations and experimental investigations. In the ‘NonDuctile’ specimens, it has been observed that the shear distortion and degradation in stiffness and strength are significantly high. Performance of the ‘Ductile’ specimens based on Eurocode and Indian Standards is almost similar in terms of strength and stiffness degradation. Nevertheless, the specimen designed on the basis of Indian Standard shows higher energy dissipation at a given drift ratio. In the analytical study, shear and flexural failure of members of subassemblage and shear failure of the joint are considered as possible modes of failure of the beam–column subassemblage. For evaluating the shear strength of the joint region, a soften strut‐and‐tie model is used. Analytically obtained strengths based on the failure criteria of different components of the specimens have been first validated with experimental results and then used to determine the strength of the specimens. The investigation could indicate even the mode of failure at local level. It is utmost important to mention here that even the ductile specimens dissipate most of the energy through the development of damage in the joint region, which is neither desirable nor safe for the stability of whole structure. Copyright © 2013 John Wiley & Sons, Ltd.     

GPS系统硬件延迟估计方法及其在TEC计算中的应用

给出了用于估计GPS系统硬件延迟的卡尔曼滤波的状态方程和观测方程,在卫星和接收机相对硬件延迟计算方法的基础上,进一步给出了滤波器初值的计算方法,然后给出了GPS系统硬件延迟和卫星相对于平均值的硬件延迟的计算结果,并对GPS系统硬件延迟及卫星和接收机硬件延迟的稳定性进行了评价,结果表明,在两个半月的时间里,它们是非常稳定的,最后通过TEC的计算结果及其与滤波估计的比较证明了本文方法的正确性.     

铰接隅撑钢框架抗震性能研究

传统抗弯钢框架的梁柱节点通常设计为刚性连接,这种刚性节点具有很大的抗弯刚度,然而节点延性不足,罕遇地震作用导致节点脆性断裂.研究学者提出了多种解决该问题的思路,例如半刚性连接节点、节点加强或削弱方法使塑性铰外移等.本文提出了一种简化的梁柱节点连接方式-铰接连接,改变梁柱节点的传力方式,在节点处设置隅撑提供框架的抗侧刚度...     

中国2010年上海世博会场址区地质环境条件分析与评价

文章在简要介绍世博会场址地质条件的基础上，分别分析了场址区流砂、软土和地下水等不良地质现象对工程建设的影响，然后评价了场址区天然地基工程、桩基工程以及地下工程建设的适宜性，为世博会场址区工程建设提供必要的地质依据。     

徐州张集水源地浅层地下水动态及其对不同开采方案响应

张集水源地是徐州市一个拟建水源地。了解浅层地下水动态变化规律是设计水源地最优取水方案、满足当地居民生活及工农业生产需水和水源地环境保护的重要前提条件之一。分析了水源地在现状以及不同开采条件下浅层地下水动态影响因素,建立了三维等参有限元数学模型模拟水源地地下水运动规律,利用大型群孔抽水试验资料进行参数识别和模型校正,预报了不同开采方案对水源地浅层地下水动态的影响,结果表明:水源地开采后,水源地开采将成为浅层地下水动态的主要影响因素之一;水源地允许开采量为13.71万m³/d是适合的,它不会引起地下水位的持续下降,不仅可满足当地居民用水需求,而且可以向徐州市稳定供水。     

Dérive à la surface de l'océan sous l'effet des vagues

We model the drift velocity near the ocean surface separating the motion induced by the local current, itself influenced by winds and waves, and the motion induced by the waves, which are generated by local and remote winds. Application to the drift of ‘tar balls’, following the sinking of the oil tanker Prestige-Nassau in November 2002, shows that waves contribute at least one third of the drift for pollutants floating 1 m below the surface, with a mean direction about 30° to the right of the wind-sea direction. Although not new, this result was previously obtained with specific models, whereas the formalism used here combines classical wave and circulation forecasting models. To cite this article: F. Ardhuin et al., C. R. Geoscience 336 (2004).     

平极长期漂移与地球平均下地幔黏性估计

利用9个国际纬度观测站的平纬长期变化序列,重新讨论并估计了平极的长期漂移,得到漂移的平均速率为(3.356“±0.142”)×l0-3/a,方向为西经78.7°±2.5°.进一步基于最新的ICE-4G冰期后地壳反弹模型,采用地球上8个冰盖的冰融参数,估计了理论的平极长期漂移方向为西经74.8°.由观测的平极长期漂移速率为约束,基于1066B地球模型,估计得到地球平均下地幔的黏性为vLM=(0.5-1.7)×1022Pa^.s,表明vLM应具有近1022Pa^.s量级,并认为地球平极的长期漂移很可能是由最近的21000年以来冰期后的地壳反弹所致.     

Paleobiogeography of Cretaceous larger Foraminifera of Pakistan and the Caribbean region and their bearing on continental drift

The Cretaceous larger Foraminifera of Pakistan are restricted to the Upper Cretaceous belonging to the species of Orbitoides Lepidorbitoides, Omphalocyclus, and Siderolites. The species of these genera are quite distinct in comparison to other assemblages of the Tethys region. None of these species are identical in the Mediterranean or Caribbean regions, with the exception of few concordant species of Orbitoides recorded in the deep-sea cores of Bahama Island. The paleo-ecological factor is the most important consideration in paleogeographic distribution of the Upper Cretaceous larger Foraminifera.