西安清真寺木牌楼结构特性与抗震性能分析

研究木结构古建筑的结构特性对保护和维修古建筑遗产具有重大意义.文中以西安清真寺木牌楼为研究对象,用弹簧单元模拟榫卯连接的半刚接特性,对其进行有限元数值分析.通过对榫卯连接的非线性接触分析得到了其各方向刚度值;在竖向荷载作用下结构的实际内力远小于其强度设计值,其安全裕度在60％以上;给出了结构的运动微分方程,结构模态分析...     

木结构节点摩擦耗能及抗震研究

对木结构节点建立了等效摩擦阻尼系统,依据能量等效原理将榫卯节点干摩擦耗散的能量等效为阻尼力做功,推导了节点关于干摩擦耗能的等效阻尼系数,以应用比较广泛的燕尾榫为例,通过有限元模拟得到了等效阻尼系数的大小。通过建立木框架结构,并在榫卯节点处引入MATRIX27单元模拟榫卯之间的干摩擦阻尼,选取兰州波和El Centro波,分别在结构考虑摩擦阻尼和不考虑摩擦阻尼的情况下进行了罕遇地震作用下的时程对比分析,引入无量纲的减震系数β来表示减震效果,得到榫卯节点在考虑摩擦阻尼的情况下,其节点位移和相对位移将会减小,而且荷载越大,减震效果越明显,说明榫卯节点的摩擦滑移在地震作用下具有较好的减震作用。     

基于有限元数值分析的木结构抗震性能分析及其在建筑中的应用

为了提高木结构抗震性能分析的精度,采用多尺度建模分析方法对木结构进行抗震分析。利用多点约束方法分别将榫卯节点和梁柱构件设定为关键区域和非关键区域。采用多尺度的建模思想,对关键区域采用实体单元进行精细尺度建模,而非关键区域则采用梁单元进行普通尺度建模,再通过不同尺度实现宏观结构模型和局部微观模型的相互协调,比较不同尺度下的实体单元和梁单元建模在抗震中的性能。实验结果表明,多尺度的有限元数值分析能够模拟木结构的整体动力响应和精确分析边界条件。通过多尺度、大范围的分级建模能够构建局部和全局的抗震性能分析的过程,精度较高,可提升抗震分析的效率。     

单围柱重檐攒尖木结构动力特性试验及地震响应分析

为研究单围柱重檐攒尖木结构的动力特性及地震响应,以西安兴庆宫五龙坛木结构建筑为例,对其进行原位动力试验,采用峰值拾取法与随机子空间法,分析了结构的前6阶自振频率、空间振型及阻尼比。考虑单围柱、榫卯连接、斗栱铺作、抹角梁架空间构造的特征,建立了单围柱重檐攒尖木结构有限元分析模型,计算得到结构的前6阶频率、振型及五龙坛原位试验结果吻合较好。结果表明：单围柱重檐攒尖木结构一阶自振频率在1.924～1.975 Hz之间,二阶自振频率在2.146～2.15 Hz之间,一、二阶振型分别为南北平动与东西平动;三阶自振频率在2.775～2.841 Hz之间,振型为扭转振动。输入不同幅值的El Centro波、Taft波及兰州波地震激励,在罕遇地震作用下底层最大层间位移角为1/83,童柱层最大层间位移角为1/87。     

明清木结构榫卯节点拟静力试验研究

以西安城永宁门箭楼为研究对象,通过对3个带雀替木构架模型在低周水平反复荷载作用下的试验研究,分析了半榫榫卯节点的受力变形特征及其破坏形式,得到了相应的弯矩-转角滞回曲线、骨架曲线、节点特征参数和恢复力模型,确定了半刚性榫卯节点的延性系数范围在1.58~3.99之间变化。研究结果可为木结构古建筑的抗震性能研究和修缮加固提供参考。     

考虑残损的古建木结构地震易损性分析

现役古建木结构普遍存在残损现象,这将影响结构的抗震性能。本文以北京故宫的咸福宫西配殿为研究对象,通过简化其屋顶、斗拱、榫卯和柱脚节点建立结构的理想模型,并在此基础上考虑材料老化和节点性能降低等因素建立其残损现状模型。通过地震易损性分析,得到古建木结构的地震易损性曲线并进行理想和残损结构的震害等级及其发生概率对比。研究结果表明:残损现象降低了咸福宫西配殿的刚度和自振频率;相比于理想结构,咸福宫西配殿残损结构在小震作用下发生轻微损坏的概率增大21.1%,在中震作用下发生中等破坏的概率增大3.7%,大震作用下发生严重破坏的概率增大10.6%;咸福宫西配殿在大震作用下发生倒塌的概率很小,体现了木结构具有良好的抗震性能。     

古建筑木结构震害分析及加固研究

近年来,随着国家对古文物建筑的重视,科学合理地对其进行修缮保护已越来越有必要。主要根据四川雅安地震后,笔者对古建筑木结构的现场震害调查,通过系统归纳和分类统计,对古建筑木结构的地基基础、梁柱和枓栱等构件、榫卯节点、整体稳定性以及围护结构在地震作用下的破坏情况及破坏原因进行了详细的分析和探讨;并针对结构不同的破坏情况,提出了相应的抗震加固措施。分析结果可为古建筑木结构的修缮加固提供参考。     

木结构榫卯节点抗震性能及其加固试验研究

为研究木结构榫卯节点的抗震性能及其加固后性能的变化,进行了6个榫卯节点的拟静力试验,并对试验后的榫卯节点分别采用扒钉、碳纤维、钢销、U型铁箍、角钢、弧形钢板进行加固。对比研究加固前后榫卯节点的破坏形态、滞回曲线、骨架曲线、耗能能力及刚度退化等抗震性能参数。试验结果表明:加固前节点滞回曲线有明显的捏缩现象,木结构良好的抗震性能正是依赖于节点的滑移摩擦耗能;加固后榫卯节点的抗震性能良好,可以达到破坏前的抗震性能;其中弧形钢板加固后的节点初始刚度较大,滞回环饱满,累计耗能为加固前的3倍,承载力提高70%,加固效果明显。根据试验结果给出了基于转角的震损榫卯节点加固设计方法。     

节点刚度对单层柱面网壳地震响应及内力的影响分析

论文首先采用壳单元Shell163建立了单层柱面网壳模型,同时利用壳单元模拟了焊接空心球节点,并通过计算验证了模拟方法的合理性。然后,通过调节空心球节点的厚度,考察了节点刚度变化对单层柱面网壳地震响应的影响,分析结果表明,在强震作用下节点刚度变化对网壳节点响应与杆件内力的影响均较大,建议在进行此类结构的动力分析时考虑节点刚度的影响。     

基于能量耗散的多层木结构古建筑的地震破坏评估

以西安城墙永宁门箭楼为研究对象,评估震后多层木结构古建筑的破坏程度,根据各主要耗能构件在低周水平反复荷载作用下的滞回耗能特性,计算其构件破坏总耗能;根据地震模拟振动台试验,计算不同地震工况下各耗能构件所耗散的能量,在此基础上建立主要耗能构件相应的破坏模型。对三个主要耗能部位:柱架榫卯节点、斗栱结构层和柱础进行地震破坏状态评估;引入能量分配系数建立主要耗能构件破坏状态与整体结构破坏状态之间的关系,继而得出整体结构的破坏系数以反映整体结构在不同地震作用下的破坏状态,研究结果可为多层木结构古建筑的抗震加固提供参考借鉴。     

A zone of columnar joints beneath the roof of a granitic pluton: The Okueyama granite,southwestern Japan

Igneous rocks are fractured during cooling from magma to form cooling joints, which are typically columnar joints in volcanic rocks, while orthogonal joints are considered typical for plutonic rocks. We performed a 3D study of joint systems in a granitic batholith of the Okueyama granite in western Japan, which has its roof and its internal structures from the roof to 1000 m downward exposed. We used an unmanned aerial vehicle (UAV) to observe the joints in outcrops from various angles. Based on our study, we propose a schematic model for joint systems in a granitic pluton. A granitic pluton has zones of rock columns below the roof and next to the wall. The rock column zone below the roof is as thick as 300 m, and its higher portions form steep cliffs, probably because of increased resistance to weathering. The axes of the rock columns are nearly vertical below the roof and gently plunge next to the walls, with high intersection angles with the wall. The distribution of columnar joints near only the roof and walls suggests that the granite cooled more rapidly near the roof and walls than in the core of the pluton. When the granite was jointed by parallel joints during cooling, the rock slabs between the parallel joints near the roof and the walls are subdivided into columns with polygonal cross-sections. This suggests that the granite was fractured by parallel joints at a temperature immediately below the solidus, after which the rock slabs were subdivided into rock columns during further cooling.     

钢筋混凝土框架角节点抗剪强度试验研究

通过对6个钢筋混凝土框架梁柱角节点在低周反复荷载作用下的试验,调查了高强度节点箍筋、双向加载等对节点强度的影响。试验结果证明,节点强度试验值为规范设计值的85%左右,设计式应导入强度降低系数。高强度箍筋对节点强度提高影响很小,在节点强度设计时可忽略不计。双向加载的节点强度只有单向加载时的80%,节点抗震设计时角节点应作为所有边节点中最不利情况考虑。楼板虽然可以提高梁的强度及刚度,但对角节点强度及最大荷载后的节点延性有不利影响。     

水平加劲肋对刚性梁柱全焊节点力学性能的影响分析

梁柱节点是钢框架的关键连接部分,其连接性能直接影响框架结构在荷载作用下的整体行为。采用有限元法对刚性梁柱全焊节点的力学性能进行数值模拟,分析不同受力条件下全焊节点的力学行为,揭示不同弯矩作用时刚性梁沿长度方向的Mises应力变化特性,并对比分析有无水平加劲肋对全焊节点位移和Mises应力的影响规律。结果表明：有水平加劲肋的全焊节点总位移明显小于无水平加劲肋的,弯矩为65kN·m时,有水平加劲肋与无水平加劲肋全焊节点位移差值出现突变,且有水平加劲肋时,全焊节点转角随着所施弯矩的增大近似呈指数变化;无论有无水平加劲肋,Mises应力值从悬臂梁自由边缘到梁柱连接节点逐渐增大,梁与柱连接节点的Mises应力值较大,柱腹板节点域的Mises应力值最大。对比发现,有水平加劲肋时,悬臂梁及柱腹板节点域的Mises应力明显小于无水平加劲肋时的。由此可见,水平加劲肋可有效提高刚性梁柱全焊节点的承载能力,并有效防止节点处应力集中。     

Non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements

A comprehensive study of non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements has been conducted. A numerical model of contraction joint reinforcements is presented for optimization control of the joint opening. The objective of this control is to reduce the joint opening and expectantly to balance the sustained loads between the horizontal and the vertical components of the dam, thus avoiding an overstress in the cantilever while retaining the release of arch tensile stresses to some extent. Several parameter studies such as critical element size and required number of joints to be simulated for convergence are also performed. As an engineering application, a 292‐m high arch dam (the Xiaowan arch dam) and the Big Tujunga dam are analysed in detail. The results demonstrate that the joint opening and the corresponding load transfer from the arch to cantilever components of the dam during strong earthquakes are substantial. It is also evident that by providing sufficient strength and reinforcement flexibility, the joint opening can be controlled to some extent. However, the stress redistribution due to reinforcement control is not sufficient to avoid the overstress in the cantilever for the Xiaowan arch dam. Thus, alternative measures are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

梁柱组合节点的拟动力试验研究

本文主要介绍了所开展的梁柱组合节点的拟动力试验,梁柱连接采用高强度螺栓平端板形式。试验采用经过调幅的具有不同地震加速度峰值的Ispara地震动作为激励进行加载,对试件在地震作用下的加速度反应、位移反应、滞回性能、刚度和耗能进行分析,对试验现象和结果进行了比较详细的阐述和分析。     

Combination of EM and DC Measurements For Upper Crustal Studies

Joint use of electrical and electromagnetic techniques is found to be useful for better understanding of the subsurface electrical resistivity structure. Detection of thin buried layers (conductive or resistive), which may be difficult to identify by a single method alone, could possibly be identified by a combination of methods. Further, distortion or error in the observed data could be corrected, as both methods depend on the same physical parameter, namely electrical conductivity. Although these methods have been known for the last several decades, joint interpretation of data sets is increasingly being used in recent years, especially for complex geological problems. This review covers the main results of the combination of these methods, giving more emphasis to case histories.     

地球物理联合反演研究的现状与趋势分析

本文从回顾和分析地球物理联合反演的必要性、分类方式,以及基本原理入手,通过分析和总结前人的研究思路,讨论了联合反演研究和应用中的关键性问题,归纳出联合反演研究的三个基本环节,即模型参数化、目标函数构造和反演算法选择,并对其加以讨论, 同时指出非线性联合反演方法和模型参数化研究将成为未来联合反演研究的主流和热点.     

多层螺旋CT在踝关节外伤诊断中的应用

目的：探讨多层螺旋CT（MSCT）在踝关节外伤中的诊断价值。方法：回顾性分析21例踝关节扭伤后行X线平片（DR）及MSCT检查的患者影像资料。结果：确诊骨折20例,MSCT扫描检查共检出骨折46处,包括内踝13例,外踝17例,胫骨下端前结节4例,后踝12例,均可清晰显示骨折线走行及骨折块大小、移位情况。DR共检出骨折37处。结论：MSCT可准确对踝关节外伤所致骨折做出诊断,尤其可清晰显示胫骨下端前结节及后踝骨折情况。     

Combined effect of climate change and human activities on the hydrological processes of an urban river: case study of the Xiaoqing River,China

ABSTRACT

The aim of this study is to reveal statistical characteristics and exceedance probability of discharge under the combined effect of climate change and human activities. The study is conducted in the Xiaoqing River in Jinan, China, based on data of discharge, land-use types and precipitation from the period 1970–2016. A multivariate joint probability distribution of the data is established to test the univariable, bivariable and trivariable change points. These are then used to calculate and analyse the risk probability of discharge exceeding the specific values under different conditions of precipitation and land-use type. The results show that the change point calculated by trivariate joint distribution can reduce the disturbance of the change point obtained with the univariable or bivariable approach and reflect the changes of various factors in the hydrological processes more objectively. When the land-use type is taken into consideration, the trivariate distribution can reflect the variation of hydrological processes more reasonably.