板柱-剪力墙结构的动力特性分析

采用有限元方法，改变结构的跨度和层数，对无边梁的板柱-剪力墙结构、带边梁的板柱-剪力墙结构和框架-剪力墙结构的动力特性进行对比分析。指出水平荷载作用下无边梁的板柱-剪力墙结构的侧移曲线是弯曲型的，而带边梁的板柱-剪力墙结构的侧移曲线是弯剪型，并且边梁可以有效提高板柱-剪力墙结构侧向刚度。     

基于典型工程实例对剪力墙抗震性能动力时程分析的提高研究

为提升剪力墙抗震性能分析精度,以某高层建筑工程楼体剪力墙为背景,将静力弹塑性分析方法与能量等效准则相结合,确定房屋剪力墙结构沿2个主轴方向的三线性恢复力参数,通过参数构建房屋剪力墙相近层模型。使用三维有限元模型模拟房屋剪力墙工程楼体,并采用相近层模型模拟该楼体三维有限元模型抗震性能的动力时程。结果表明,随着地震水平和楼层的增加,房屋剪力墙层间侧移角包络值和顶点侧移角包络值都在明显增加。设置黏滞流体阻尼器可改善房屋剪力墙受两种地震波的作用,在Ⅸ度罕见地震作用下,房屋剪力墙结构的X向减震效果比Y向好,房屋剪力墙X向和Y向层间位移角的最大减震率分别约为38%与18%。     

钢框架-带缝钢板剪力墙结构受力性能分析

本文对4种钢框架、6种带缝(两排)钢板剪力墙片(四周与构件无连接)和6种固接的钢框架-带缝钢板剪力墙结构在3种不同竖向荷载作用下的抗侧能力和往复荷载下的滞回性能进行了研究,并对比分析。结果表明:前两种结构的侧移刚度、抗侧能力相对较低,屈曲后刚度退化快;钢框架-带缝钢板剪力墙结构的侧移刚度、抗侧能力和耗能能力比前两种结构有明显的提高,说明钢框架与带缝钢板剪力墙片固接后工作协调性能良好。带缝钢板剪力墙片与钢框架-带缝钢板剪力墙结构的整体设计参数宽高比W/H,开缝设计参数开缝墙肢的高宽比h/b、宽厚比b/t、开缝墙肢与剪力墙的高宽比h/H对结构的抗侧能力和滞回性能有很大影响。W/H增大,结构的抗侧能力增强,滞回性能降低;h/b、b/t、h/H增大,结构的抗侧能力降低,滞回性能提高。     

方钢管混凝土框架-十字加劲薄钢板剪力墙的力学性能研究

采用大型通用非线性有限元软件ABAQUS 6.10分别对方钢管混凝土框架-十字加劲薄钢板剪力墙和非加劲薄钢板剪力墙进行了数值分析,对二者的受力特征、刚度、极限承载力、剪力分配及柱子的受力特征进行了研究.结果表明:当肋板刚度比为30时,十字加劲肋能够提高钢板剪力墙结构的弹性屈曲荷载、极限承载力、初始刚度,降低柱子轴压比对剪力初始分配的影响;在加载的初始阶段(顶点侧移角小于0.2％),钢板剪力墙承担了大部分剪力,随后墙板承担剪力的比例逐渐下降,框架承担的比例逐渐上升,当顶点侧移角达到1％时,框架和钢板剪力墙承担剪力的比例保持不变;方钢管混凝土框架-薄钢板剪力墙的滞回环饱满,滞回性能稳定.由于薄钢板墙拉力场作用,方钢管混凝土柱壁易与混凝土发生分离,在设计时应予以注意.     

剪力墙结构层间位移计算方法探讨

规范对高层剪力墙结构层间位移进行限制时,没有考虑结构体系侧移模式不同的影响,这对以弯曲变形为主的结构会造成很大的误差,甚至得出一些与实际情况完全不相符的结论。针对这一问题,本文根据剪力墙结构的受力特点,将楼层位移分为有害位移和无害位移,将层间位移分为名义层间位移Δui和有害层间位移Δui~,用倒三角形分布水平荷载的等截面悬臂杆件的弯曲变形曲线作为剪力墙结构的近似侧移曲线,从理论上分析了剪力墙结构的名义层间位移、有害层间位移、层间相对转角以及截面的弯曲曲率之间的关系,给出有害层间位移的实用计算公式。最后,对比分析了控制剪力墙层间变形的几种不同方法,并通过算例分析验证了本文方法实用可行,与实际情况符合较好。     

钢结构抗侧力体系抗震性能对比

常见的钢结构抗侧力体系包括抗弯钢框架、偏心支撑钢框架和钢板剪力墙结构,它们的耗能构件分别为框架梁、耗能梁段以及内填钢板。现行规范采用基于强度的设计方法,不能保证结构的整体破坏模式,无法对各抗侧力体系进行横向比较。采用近年来的性态设计方法,设计了3组10层抗弯框架、偏心支撑钢框架和钢板剪力墙模型,进行了静力弹塑性分析和动力弹塑性分析,对比了各抗侧力体系的承载能力、抗侧刚度、延性、层间侧移分布、破坏模式以及用钢量。对比结果表明:抗弯钢框架承载力和刚度最小,偏心支撑钢框架的延性最好,钢板剪力墙虽然承载力最高,但是延性却是最低。     

钢框架-钢板剪力墙结构抗震性能研究

基于等效拉杆理论,对3组不同高度的钢框架-钢板剪力墙结构进行动力时程分析,研究了结构的层间侧移角、塑性铰出现顺序和外框架与支撑架的剪力分配等指标。结果表明:设计合理的钢框架-钢板剪力墙结构符合双层抗侧力体系设计原则。钢板剪力墙进入弹塑性状态后其支撑架的刚度并不明显退化,结构在各级地震下的外框架与支撑架的剪力分配比例较为稳定。另外,其剪力分配比例受其结构失稳类别的影响,一般情况下,外框架分配的剪力随结构高度的增加而增加。     

基于宏观模型的暗支撑短肢剪力墙非线性分析

建立了适合于带暗支撑短肢剪力墙非线性分析的宏观计算模型，分析推导了SAP程序中Link单元的刚度矩阵，明确了Link（单元中各弹簧的物理意义，给出了各单元等效刚度计算方法，选取了合适的单元力一位移关系。用由Link单元建立的宏观模型对3片普通短肢剪力墙和3片带暗支撑短肢剪力墙进行了静力弹塑性分析，试验和计算所得顶点力一位移骨架曲线符合良好，说明所建宏观模型合理，用由Link单元建立的宏观模型能较好的模拟带暗支撑短肢剪力墙的非线性行为。     

基于超级单元的钢-混凝土混合结构动力特性及地震反应研究

本文提出了基于超级单元的钢框架－混凝土剪力墙结构体系动力特性及地震反应分析的一种方法，该方法考虑了混合结构体系中钢框架部分的受力和变形特点，即节点柔性（半刚性）、梁柱效应（p-δ效应）及P－△效应（以下合称P－Delta效应），推导了考虑三种因素情况下，钢框架的层间侧移刚度及钢框架－混凝土剪力墙结构体系的超级单元刚度矩阵，采用刚度法求解钢框架－混凝土混合结构周期和振型。该方法物理概念清楚，计算简便。     

基于性能的联肢钢板剪力墙抗震设计与评估研究

联肢钢板剪力墙能通过连梁耗能实现多重抗侧体系,其优良的抗震性能被越来越多的学者研究论证。本文基于能量平衡原理和Chao和Goel提出的弹塑性层剪力分布模式,预设目标侧移及屈服机制等性能参数,归纳出完整的联肢钢板剪力墙结构塑性设计流程,并采用该方法基于8度(0.3g)抗震设防条件下设计了12个联肢钢板剪力墙结构算例。利用有限元分析软件ABAQUS对结构进行了Push-over分析,研究了刚度退化、构件屈服顺序和结构整体变形等方面的结果。结果表明：设计算例能够实现多重抗震机制,并满足预期性能目标。     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.     

Scenario predictions for potential near-field and far-field earthquakes affecting Hong Kong

Historical earthquakes noted in the written records of the South China region, including Hong Kong, are not well delineated along identified prominent fault sources. Despite the lack of any definitive, localised trend in the spatial distribution of seismic activity in the region, there does appear to be some major disparity in the seismic activity rates (especially for large magnitude earthquakes) between the near-field and the far-field regions of Hong Kong. Despite this observation, previous studies of the regional seismic activity and seismic ground motion hazard (the latter using a probabilistic seismic hazard assessment, PSHA) have considered very broad source zone regions, in which uniform levels of seismic activity have been assumed. The present paper further scrutinises this broad source zone (BSZ) approach by adopting a novel expanding circular disc (ECD) method to determine the rates of earthquake recurrence. Such a method is intended to counter-check previously developed models by determining earthquake scenario events in terms of magnitude–distance (M–R) pairs or combinations, having defined values of average return period. Unlike the BSZ approach, the ECD method specifically accounts for the supposed variations in the seismic activity rates between events in the near-field and the far-field of Hong Kong.The form of the developed method is particularly suited to the determination of design-level earthquake ground motions for bedrock sites, since it assumes a directionally-independent attenuation model as described in the companion paper. It is found that, whilst the BSZ approach may indicate the overall average levels of hazard that are representative of the South China region as a whole, it does not capture the large disparity in seismic activity rates between near-field and far-field events. This important feature is expected to have a significant impact upon engineering assessments of the seismic safety of structures in Hong Kong and elsewhere in the South China region. For example, it is found that for events with M≥6, the seismic activity rate (normalised by time and area) in the very far-field is around 3.5 times larger than in the near-field and medium-field of Hong Kong. The resulting design M-R combinations, covering a range of return periods from 70 to 2500 years, are limited, for very long return periods and for distant events, by the maximum credible earthquake (MCE) magnitude. Intensive research to determine this seismic hazard parameter is recommended, in order to refine further the results of the ECD analysis, which presently conservatively assumes the MCE to range between M=6 in the near-field of Hong Kong to M=8 in the very far-field, at distances greater than 280 km from Hong Kong.     

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.     

THEORETICAL APPROACH TO THE SOLUTION OF THE INFILTRATION PROBLEM

ABSTRACT

The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content.

Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data.

Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme.

Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate.     

Late Permian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust

Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO ₂ (67.8–71.0 wt%), Al ₂ O ₃ (14.9–17.1 wt%) and Na ₂ O (5.3–8.6 wt%), low K ₂ O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area.