南京长江大桥桥头堡抗震加固受力性能研究

为研究南京长江大桥桥头堡填充墙加固对结构抗震性能的影响,提出考虑较高填充墙开裂的双斜撑模型,用于罕遇地震工况下桥头堡的抗震性能计算,同时提出考虑填充墙加固后刚度增强效应的建模方法。利用SAP2000建立了加固前后用于多遇地震工况、设防地震工况及罕遇地震工况的分析模型,并选取了桥头堡在1974年经历的实际地震激励时程及El-Centro地震激励时程作为激励进行了加固前后结构的抗震性能分析比较。研究发现,填充墙加固后桥头堡的抗震性能有了明显提升,其位移响应峰值约下降8%~23%,层间位移角响应峰值约下降12%~22%,而且桥头堡结构在设防地震情况下2个方向的层间位移角均满足了规范要求。另外,在罕遇地震工况下,未加固的填充墙开裂会使结构的扭转刚度下降,而填充墙加固可有效提升结构的扭转刚度,降低桥头堡在地震时发生扭转振动的概率。这2种地震荷载激励的分析结果差异约在3%~21%不等,且响应峰值出现的位置也有一些不同,故对桥头堡进行抗震时程分析时建议选取多条地震波输入综合分析。研究成果可为同类型的钢筋混凝土建筑遗产的抗震加固提供借鉴和参考。     

故宫太和殿二层斗拱竖向加载试验

为了更好地保护古建筑,采取静力试验方法,以故宫太和殿二层平身科、柱头科、角科斗拱为对象,研究了竖向荷载作用下斗拱的受力性能。基于上述3种斗拱构造特征,制作了1∶2比例模型,进行了竖向加载试验,讨论了不同斗拱在荷载作用下的破坏形式、内力及变形特征,归纳了斗拱的竖向刚度计算模型。结果表明:竖向荷载作用下,太和殿二层斗拱的坐斗及与之相交的头翘、正心瓜拱容易产生破坏,且模型倒置时下层构件受力要小于上层构件。对于不同斗拱而言,斗拱极限承载力:平身科角科柱头科;斗拱变形及残余变形量:柱头科角科平身科;斗拱延性:角科柱头科平身科。竖向荷载作用下,太和殿二层斗拱的竖向刚度计算模型可简化为三折线段形式。     

传统铁箍墩接法加固底部糟朽木柱轴压试验

铁箍墩接是古建木柱柱根糟朽的一种传统加固方法。为探讨该方法的有效性,以故宫内某古建木柱为例,进行了试验研究。制作了1根完好木柱、3根铁箍墩接法加固木柱,开展了轴压试验,获得了木柱加固前后的承载力-变形曲线,以及延性、应变、刚度等参数,讨论了铁箍墩接法的加固机理。结果表明:传统铁箍法加固底部糟朽木柱后,由于铁箍对木柱的侧向约束作用,木柱的极限承载力可恢复约91.8%,延性性能可恢复约95.2%,水平极限应变恢复率约97.2%,竖向极限应变恢复率约84.1%,且加固木柱的刚度要大于完好木柱。由于铁箍材料与木材强度差别较大,使得加固后木柱的整体性能要低于完好木柱,因而加固效果有限。结果可为古建筑木结构的保护与维修提供理论参考。     

故宫太和殿结构现状数值模拟研究

为保护故宫太和殿,采用数值模拟方法,研究了太和殿的结构现状特征。采用ANSYS有限元程序,考虑榫卯节点、斗拱连接等构造,建立了太和殿有限元模型。分别对模型进行自重作用、风荷载作用下的静力分析及8度常遇地震作用下的时程响应分析,获得了太和殿在不同荷载作用下的内力及变形分布特征,评价了太和殿的结构安全现状。结果表明:重力及风荷载作用下,太和殿结构的内力、变形均在容许范围内;地震作用下,结构保持稳定状态,且榫卯节点及斗拱构造有利于减震。因此,太和殿结构现状是安全的。     

民国钢筋混凝土结构中的梁构件计算方法研究

为研究民国时期混凝土梁构件的设计计算方法,从材料层面到构件层面,对民国时期混凝土设计与结构计算的相关历史文献进行研究,总结出民国时期混凝土梁构件的设计与计算方法,并结合案例分析,与现代混凝土梁构件的设计计算方法进行比较研究,包括钢筋混凝土梁的受弯承载力计算方法及受剪承载力计算方法。通过对比计算分析,不考虑地震荷载作用时,在1.0%~2.0%纵筋配筋率的范围内,采用现行规范计算的受弯承载力是采用民国规范计算的受弯承载力的3.6~4.0倍;在配箍率0.1%~1.0%范围内,采用现行规范计算的受剪承载力是采用民国规范计算的受剪承载力的1.6~2.4倍;在弯起钢筋配筋率0.5%~1.5%范围内,采用现行规范计算的受剪承载力是采用民国规范计算的受剪承载力的2.0~2.4倍。研究结果可为民国钢筋混凝土梁的结构安全评估提供科学依据。     

基于能量方法的江浙地区抬梁式及穿斗式传统民居木构件重要性分析

为研究中国传统木构建筑的结构构件重要性排序问题,以江浙地区抬梁式和穿斗式两种典型的传统民居木结构类型为研究对象,基于能量方法采用构件属性改变后对结构整体应变能的单位体积改变率作为构件重要性的评价指标,运用有限元软件Ansys(16.0)开发了基于生死单元法和改变弹性模量法的构件重要性评价程序。分析结果表明,改变弹性模量法更适用于中国传统木构建筑的结构构件重要性分析。通过对抬梁式和穿斗式的单榀框架和整体框架在竖向荷载、水平地震荷载两种工况下的结构构件重要性的计算分析,得到了构件的重要性系数和排序,并提取出了抬梁式和穿斗式传统木构的关键构件。研究结果可以为确定传统木构建筑遗产在修缮施工、维护以及结构健康监测过程中需要重点关注的构件提供科学合理的理论依据。     

基于荷载修正的传统木构建筑构件重要性分析方法研究

传统木构建筑的构件重要性对于整体结构状态的评估具有重要意义,为弄清楚传统木构建筑的构件重要性,开发了一种基于荷载修正的传统木构建筑构件重要性评价程序,基于荷载工况修正与荷载重分布修正重构了荷载分布矩阵,基于荷载施加构件修正改进了构件重要性计算方法。以典型传统木构建筑——保国寺大殿为例进行了数值模拟分析,并基于广义刚度评价了构件重要性,分析了各项修正对构件重要性的影响情况以及最终修正对构件重要性的结果变化率。结果表明:柱类构件的修正变化为-0.526%~2.192%;梁栿类构件的修正变化为-2.638%~50.598%;铺作类构件的修正变化为-12.763%~9.989%;槫类构件的修正变化为-7.586%~6.918%。保国寺大殿构件重要性排序:柱类>槫类>梁栿类>铺作类;修正后柱类、梁栿类重要性提高,铺作类、槫类重要性降低。可为传统木构建筑的结构状态评估和预防性保护提供参考。     

清式木建筑透榫节点加固方法的试验研究

我国传统木结构建筑的各构件间主要采用榫卯连接,这种节点形式在较大水平地震作用下容易出现局部拔榫、节点松脱现象,不利于结构的稳定和承载。为此针对榫卯节点的抗震性能及加固进行试验研究。依据清工部《工程做法则例》设计制作了4个足尺透榫节点试件,其中3个试件分别采用竹斜撑、角钢和碳纤维(简称CFRP)布进行加固。在改进榫卯节点拟静力试验装置的基础上完成了低周反复荷载试验,分析了对比节点和加固节点的破坏机理、承载力、延性、刚度退化、耗能和榫头拔出过程。试验结果表明,竹斜撑、角钢和CFRP布加固节点的正向峰值荷载较对比节点分别提高了92.4%、54.6%和63.0%,反向峰值荷载则分别提高了61.5%、75.7%和39.0%。对比节点和角钢加固节点初期刚度基本相同,且随转角增加出现先增大后减小的过程;竹斜撑加固和碳纤维布加固节点的初始刚度显著大于对比节点,随着转角的增加呈单调减少。此外,竹斜撑和角钢加固节点的榫头拔出长度明显小于相同转角下对比节点的榫头拔出长度,表明竹斜撑和角钢均起到了延缓榫头拔出的作用。     

白居塔塔体结构稳定性分析研究

在对白居塔建筑形制调查研究基础上,区分塔体内嵌高山体和内嵌低山体两种情况,确定重力作用以及重力和地震耦合作用两种工况。基于采用岩土摩尔—库伦本构模型的有限元分析技术,对白居塔和山体的耦合结构进行稳定性分析。得出以下结论:自重作用下,整体结构稳定性满足,且有较高的安全稳定系数;白居塔整体结构的刚度较大,整个结构体系属于抗震有利体系;白居寺整体结构基频模态以侧倾为主;在7°(基本加速度0.15 g)多遇地震作用下,两个模型整体结构的抗震稳定性较好,结构不会产生整体性失稳破坏;在8°(基本加速度0.3 g)多遇地震作用下,较高山体模型主体结构基本处于安全状态,较低山体模型主体结构不满足稳定要求;较高山体的模型相对于较低山体的模型,安全稳定性要高。     

应县木塔横纹承压构件GFRP棒增强加固试验研究

应县木塔建造于1056年,高达67.31m,而当时对木材横纹承压受力性能缺乏应有的知识,致使木塔下部1～3层柱顶水平木构件横纹承压应力严重超过设计值,产生不可恢复的承压变形,部分构件已严重劈裂。本文提出用玻璃纤维增强塑料(GFRP)棒局部增强横纹承压技术,短期荷载试验结果表明,组合木构件的横纹承压强度大幅度提高,刚度有所增加,其延性性能得到大的改善。在深入研究GFRP棒增强机理的基础上,提出了GFRP增强木材组合构件横纹承压承载力的简化计算公式。     

Seismic Retrofitting of Columns with Lap Spliced Smooth Bars Through FRP or Concrete Jackets

The effectiveness of RC jacketing or FRP wrapping for seismic retrofitting of rectangular columns having smooth (plain) bars with 180° hooks lap-spliced at floor level is experimentally investigated. The relatively low deformation capacity and energy dissipation of five unretrofitted columns is found not to depend on lap length, if lapping is not less than 15 bar-diameters. Six columns cyclically tested up to ultimate deformation after RC concrete jacketing demonstrate force and deformation capacity and energy dissipation sufficient for earthquake resistance, regardless of the presence or length of lap splicing in the original column. Another ten columns cyclically tested to ultimate deformation after wrapping of the plastic hinge region with CFRP show that FRP wrapping of the splice region is more effective than concrete jackets for enhancement of the deformation and energy dissipation capacity of old-type columns with smooth bars lap-spliced at floor level, provided that wrapping extends over the member length sufficiently to preclude plastic hinging and early member failure outside the FRP-wrapped length of the column.     

AUTOMATIC MINIMIZATION OF THE RIGIDITY ECCENTRICITY OF 3D REINFORCED CONCRETE BUILDINGS

The objective of this paper is to obtain the optimum design of 3D reinforced concrete buildings in terms of their performance under earthquake loading. This goal is achieved by considering the minimisation of the eccentricity between the mass centre and the rigidity centre of each storey layout as the optimisation objective in order to produce torsionally balanced structures. This problem is considered as a combined topology and sizing optimisation problem. The location and the size of the columns and the shear walls of the structure of each storey layout constitute the design variables. Apart from the constraints imposed by the seismic and reinforced concrete structure design codes, architectural restrictions are also taken into account. The test examples showed that a reduction in the structural cost of the building is achieved by minimising the eccentricity between the mass centre and the rigidity centre of each storey layout. Evolutionary optimisation algorithms and in particular a specially tailored algorithm based on Evolution Strategies is implemented for the solution of this type of structural optimisation problems.     

Shaking Table Model Test of a Steel-Concrete Composite High-Rise Building

Shaking table tests were conducted on a 1/20 scaled-model of a 25-story steel-concrete composite high-rise building, composed of steel frame (SF) and concrete tube (CT). The seismic behavior of the model was investigated with the increasing of table-input acceleration amplitudes. It has been found that the seismic failure of the model concentrated on the shear walls and corner columns at the lowest story of the CT as well as the joints between the SF and the CT. Even subjected to extremely strong earthquakes, due to effective composite action, the composite model was able to support its weight to prevent collapse.     

Seismic Overstrength of Shear Walls in Parking Structures with Flexible Diaphragms

The objective in current design practice for parking structures is that energy is dissipated through the formation of plastic hinges at the base of shear walls while floor diaphragms remain elastic and are vertically supported by a combination of shear walls and gravity resisting columns. Unfortunately, this objective is not always achieved due to inaccuracies in current methods for calculating demands on shear walls and in calculating the capacity of shear walls (IBC 2003 International Building Code. International Conference of Building Officials. Whittier, CA.  [Google Scholar], ACI code). When demands are overestimated and capacity underestimated, then diaphragm can fail prior to flexural yield of shear walls as was observed in several parking structures in the 1994 Northridge earthquake.

Eigenvalue and inelastic dynamic response analyses were performed in order to investigate the effects of diaphragm flexibility on wall responses and of wall overstrength on diaphragm responses. The elongated periods of parking structures due to diaphragm flexibility were found to significantly decrease seismic force demand on shear walls relative to what is calculated using codes of practice in which diaphragms are assumed to be rigid. This leads to the over design of shear walls, which further compounds the problem by preventing the flexural yielding of these walls and thereby driving inelastic response to diaphragms. Various degrees of diaphragm flexibility, shear wall layout, seismic zone, and the number of stories were considered in these analyses.

Inelastic static pushover analyses were preformed to investigate the design and capacity evaluation of shear walls. The results illustrate that the shear capacity of walls may be close to twice that calculated by codes of practice. The largest overstrengths were observed in shear walls with low height-to-length ratios in which a significant portion of the lateral load was taken by direct strut action to the foundation and without placing demands on the longitudinal tension reinforcement in the shear walls. The article concludes that methods in codes of practice for calculating shear wall demands and capacities need to be improved if good seismic performance of parking structures is to be achieved.     

Controlled Rocking CLT Walls for Buildings in Regions of Moderate Seismicity: Design Procedure and Numerical Collapse Assessment

Controlled rocking heavy timber walls are designed to rock on their foundations in response to earthquakes. For regions of moderate seismicity, it is proposed that this rocking behaviour can be adequately controlled using only post-tensioning, even with a large force-reduction factor and no supplemental energy dissipation. This article presents a force-based design procedure for controlled rocking cross-laminated timber walls without supplemental energy dissipation, including a method for estimating higher mode effects. Fragility analyses of three prototype walls demonstrate that the procedure can limit the probability of collapse to <10% during a maximum considered earthquake in a region of moderate seismicity.     

汶川地震导致的壁画文物震害研究——以广元市觉苑寺大雄宝殿壁画为例

为保护壁画文物,以四川省广元市剑阁县大雄宝殿为例,对汶川地震作用下殿内壁画的震害进行了研究.根据震后勘查结果,讨论了大雄宝殿壁画的典型震害症状,分析了古建筑侧脚构造对壁画抗震的有利影响.根据大雄宝殿壁画加固工艺作法及古建筑榫卯连接特点,建立了大雄宗殿的震前有限元模型.为研究汶川地震作用下壁画的震害特征,首先对其进行了模态分析,然后将模拟汶川地震波进行调幅,然后作用于大雄宝殿进行地震反应分析.通过采用时程分析法,获得了地震作用下不同时刻壁画整体的内力与变形响应峰值,并获得了典型节点的地震响应曲线.结果表明:大雄宝殿壁画开裂与空鼓的主要原因是面层与墙体粘结不牢导致的受拉破坏;地震作用下壁画保持稳定的振动状态;为提高壁画的抗震性能,壁画木框与外墙板间应加强连接,并在空隙处填塞隔震材料,同时应加强壁画本身保养工作.     

Archaeological Observation on the Layout of the Three Courts and Five Gates of the Daming Palace of the Tang Dynasty

The system of Three Courts and Five Gates is an essential content of the designs of the capitals and palaces of ancient China. The Three Courts and Five Gates planning of the Daming Palace is the adoption of this rule and the application to the spatial designing of the palace city. The archaeological fieldwork revealed that within the Daming Palace, the Three Courts pattern with three walls as the borders, and Hanyuan Hall, Xuanzheng Hall, and Zichen Hall as the centers formed the outer court, middle court, and inner court plan, which was the embodiment of the new interpretation of the Tang Dynasty to the traditional Three Courts and Five Gates ritual system. Through the trimming of the archaeological data fetched in the past 60 years about the southern part, which is the official affair zone, of the Daming Palace, this paper discusses the spatial structure of the Three Courts and Five Gates pattern of the Daming Palace, and analyzes the substantial relationship between this pattern and the political demands of the ruling class.     

隋唐长安城东北角夹城及十王宅遗址2021年度发掘简报

隋唐长安城东北角夹城及十王宅遗址位于隋唐长安城遗址东北部,位置十分重要。2021年对遗址整体向西发掘10米,清理了隋唐长安城东郭夹城墙所在区域。该段夹城墙是兴庆宫通往大明宫的夹城墙仅存的一段,为唐玄宗开元年间修筑。本文即是对2021年度发掘工作主要收获的简报。     

MODELLING OF RC BEAM-COLUMN JOINTS AND STRUCTURAL WALLS

The deformation of beam-column joints may contribute significantly to drift of reinforced concrete (RC) frames. In addition, failure may occur in the joints due to cumulative concrete crushing from applied beam and column moments, bond slip of embedded bars or shear failure as in the case of existing frames with nonductile detailing. When subjected to earthquake loading, failure in RC structural wall is similar to failure of frame joints as it may occur due to cumulative crushing from high flexural stresses, bond slip failure of lap splice, shear failure or a combination of various mechanisms of failure. It is important to include these behavioural characteristics in a simple model that can be used in the analysis of RC frames and RC walls to predict their response under earthquake loading and determine their failure modes.

Global macro models for the beam-column joint and for RC structural walls are developed. The proposed models represent shear and bond slip deformations as well as flexural deformations in the plastic hinge regions. The models are capable of idealising the potential failure mechanism due to crushing of concrete, bond slip or shear with allowance for the simultaneous progress in each mode. The model predictions are compared with available experimental data and good correlation is observed between analytical results and the test measurements.