冲击荷载对埋地管道影响的试验与数值模拟研究

为了研究冲击荷载作用下埋地管道的动力响应,自制管道及土箱缩尺模型,开展埋地管道落锤冲击试验,并建立管道冲击模型对冲击荷载作用下埋地管道的动力响应过程进行数值模拟分析,探讨管道距振源水平距离、冲击能量以及管道埋深等参数对埋地管道动力响应的影响。试验测量得到管道纵向和环向的应变分布特性,同时对比冲击荷载作用下埋地管道数值模拟所得的结果与试验结果,二者较为吻合。研究结果表明：在冲击荷载作用下,管道受土压力的影响随管道距振源水平距离的增加而减小,并且管道受影响最大的位置因距振源水平距离的增加而发生偏移;随着冲击能量的增加,管道距离冲击中心点较近区域受到的影响随之明显增大,管道两端距离冲击中心点较远的区域受到的影响较小;管道覆土深度增加,土体缓冲作用随之增强,管道的应变峰值明显减小。研究结论可为埋地管道抗冲击设计规范制订、管道敷设及管道维护提供参考。     

单桩-土-结构振动台试验模型数值计算分析

为研究地震荷载作用下桩基-土-核电结构的抗震性能及土结动力反应规律,对拟开展的地震模拟振动试验模型进行数值计算分析。核电工程结构上部质量大和刚度大,试验模型不同于一般的工程结构,为检验振动台试验模型设计、传感器布设方案,对试验模型进行了数值模拟。数值模拟以单端承桩为研究对象,计算了上部结构质量和刚度变化时,在脉冲荷载及基于RG1.60谱人工合成地震动作用下桩身的地震反应规律。数值模拟表明:在水平地震动作用下,桩身剪力和弯矩包络线呈"X"状分布,桩底和顶处剪力弯矩较大;上部结构质量越大,桩身的剪力与弯矩越大;上部结构的刚度越大,桩身的剪力与弯矩越小;随着上部结构质量的增大和刚度的减小,反弯点逐渐向桩顶移动。桩顶发生最大位移时所对应的桩身挠度随着上部结构质量的增加而增大并且随着上部结构刚度的增大而减小。土层分界面处,桩身内力发生突变。此外,在脉冲荷载输入下,桩身反弯点位置与输入荷载的周期有关。计算结果为振动台试验模型设计提供了理论依据。     

强夯振动加速度的量测及现场试验研究

结合延安新区强夯加固地基工程,进行强夯振动加速度测试现场试验。选取填方区场地,结合地形设计监测方案,以测试强夯波沿水平方向和斜坡的传播规律。在选定试验段的某级填方场地上布置多组加速度传感器,运用多个8通道24位高速采集卡记录强夯振动加速度在平面和斜坡的传播和衰减过程,探讨强夯振动波沿水平面和斜坡的传播规律以及能级对振动加速度的影响。结果表明:径向和竖向加速度值均随与夯点距离的增大而减小;在与夯击点距离相同处,强夯振动波沿水平方向传播的径向和竖向加速度值要大于沿斜坡方向;随着能级的增大,强夯产生的夯击波增强,在与夯击点相同距离处产生的径向和竖向加速度均明显增大。     

墙体开洞影响下房屋砖砌体结构地震易损性分析

为获取可靠的墙体开洞影响下房屋砖砌体结构地震易损性分析结果,采用ABAQUS有限元分析软件构建房屋砖砌体结构墙体模型,设置合理的墙体模型参数和数值模拟参数;对比模拟数值与以往研究的测试值,证明所构建模型参数取值合理;将截取的峰值段江油地震波作为上述模型的地震动输入,根据测得的房屋砖砌体结构的力学变化数据,分析房屋砖砌体结构的地震易损性。分析结果表明:地震情况下,随着墙体开洞率的增加,墙体荷载能力下降、墙体水平承载力增长幅度降低、墙体相对刚度退化率增加;墙体开洞数量越多,房屋砖砌体结构侧向刚度下降越快。因此分析得出墙体开洞率大、墙体开洞数量多,房屋砖砌体结构的地震易损性越显著。     

冲击荷载作用下干砂动力特性试验研究

对常规的霍普金森压杆装置进行改进,使其可以应用于干性砂土试样的冲击试验。针对干砂开展冲击试验,得到应变率在102~103 s-1范围内稳定的入射波、反射波和透射波的波形图,并用橡胶膜作为波形整形器以获得更明显的透射波信号。结果表明:在较高应变率荷载作用下干砂没有明显的应变率效应;对于等厚度砂土试样,应变率随着加载气压的增大而增大,且增大趋势明显;在同等加载条件下应变率随着砂土试样厚度的增大而减小。     

不平衡弯矩作用下板柱节点抗冲切性能非线性分析

通过研究不平衡弯矩作用下板柱节点变参数、刚度变化等受力性能的特点和规律,为弥补试验研究的局限性,全面认识板柱节点的受力特征、内力分布规律提供新的研究途径,同时也为工程设计与实践提供理论指导.应用OpenSees(Open System for Earthquake Engineering Simulation)有限元计算平台建立了与试验相同的三维网格梁数值模型,通过数值模拟结果与试验结果的对比分析,验证了有限元分析模型的可行性.对不同的板厚,以不平衡弯矩水平、配筋率及混凝土强度为变参数分别进行了数值模拟.结果表明:数值模拟结果与试验结果吻合较好,不同的不平衡弯矩水平对节点抗冲切性能影响显著,配筋率的变化对构件开裂荷载、极限承载力以及延性影响显著.因此,合理地建立有限元模型可较好地模拟不平衡弯矩作用下板柱节点的受力性能;随着不平衡弯矩水平的增大,极限承载力显著降低,随着配筋率的增大,极限承载力显著增大、延性降低.     

地震作用下承台桩-土动力相互作用数值模拟分析

基于已开展的非液化场地-群桩基础-结构体系动力响应大型振动台模型试验,进行三维全时程动力数值模拟分析。采用修正的Davidenkov模型反映土体在地震反应过程中的模量衰减,通过“捆绑边界”模拟模型箱的层状剪切运动。通过对比试验中土-结构体系加速度响应时程、土体位移和桩基内力等,验证数值模型的有效性。利用已验证的数值模型,开展承台尺寸对桩-土-上部结构动力响应影响研究。结果表明,承台厚度的增大会导致上部结构和桩顶惯性效应减小;地震作用下沿激振方向前桩大于后桩,随着承台厚度的增大,前桩与后桩峰值弯矩差值率为16.1%～32.1%,群桩效应影响增大;随着承台厚度的增大,承台-土动土压力增大了3～6倍,承台与桩基水平荷载分担比增大,桩基弯矩反弯点位置上移了0.50 m;承台-土的相互摩擦作用会降低结构整体动力响应。     

锈蚀钢筋混凝土构件反复荷载下性能退化研究

为研究地震作用下钢筋锈蚀对试件性能退化影响的规律,对6个锈蚀钢筋混凝土受弯构件进行低周反复荷载试验,得到不同锈蚀程度试件的滞回曲线及骨架曲线,分析了钢筋锈蚀对试件强度和刚度的影响。试验发现,随着钢筋锈蚀程度的增大,各试件强度退化基本呈增大趋势;低锈蚀率试件由于锈胀内力的存在,强度退化相对比未锈蚀试件和高锈蚀试件大;随着锈蚀率的增大,试件加载和卸载刚度总体上逐渐减小,且随着位移的增大而持续减小。此外,还分析了锈蚀钢筋混凝土结构刚度退化机理。成果可供锈蚀钢筋混凝土结构抗震性能研究参考。     

活性粉末混凝土板抗冲击性能试验研究

为了研究常温养护条件下活性粉末混凝土(RPC)板的抗冲击性能,对3块RPC板和3块普通钢筋混凝土(RC)板进行14 m高度下的落锤冲击试验,利用高速动态采集系统对落锤冲击过程中动态加速度和动态支座反力、混凝土板的应变进行采集,通过记录数据并对比分析了RPC板和RC板抗冲击性能的差异。试验结果表明:与普通RC板相比,RPC板的落锤冲击持续时间明显延长,冲击速度增大,冲量明显增加;冲击加速度峰值、平均冲击力及最大冲击力均减小;RPC板四角所承受的动态反力幅值明显大于RC板;RPC板的最大应变均大于RC板。分析混凝土板的破坏情况,发现RPC板正面接触冲击部位只出现较小的冲击坑,未出现RC板的穿透性破坏,且RPC板背面的裂缝数量均少于RC板,宽度也明显小于RC板。试验结果,表明常温养护条件下RPC板的抗冲击性能明显高于RC板,且随着钢纤维掺量的增加,RPC板的抗冲击性能逐渐增强,相比较于普通混凝土,RPC材料更加适用于受落石冲击危害的地区。     

约束混凝土梁的升降温全过程弯矩分析

利用SAFIR程序,开展了约束混凝土梁的升降温全过程梁端弯矩分析;考察了转动约束刚度比、轴向约束刚度比、截面尺寸、荷载比、全截面配筋率和升温时间等参数对梁端弯矩的影响规律,并与单调升温时的相应规律进行对比,给出了梁端弯矩的实用计算方法。研究结果表明：对于先升温、后降温的约束混凝土梁梁端弯矩的变化,总体表现出与单调升温类似的特征,主要区别在于后期因降温作用而呈现出缓慢降低的趋势;转动约束刚度比对梁端弯矩的影响集中在升温前期,在此时段内,梁端弯矩随着转动约束刚度比的增加而增大,但增幅逐渐趋缓;升温后30min以内,轴向约束刚度比的改变对梁端弯矩几乎没有影响;之后,梁端弯矩随着轴向约束刚度比的增加而逐渐减小。     

An investigation of earthquake induced pounding between adjacent buildings

The response of adjacent buildings in city blocks to several strong earthquakes is analysed, taking into account the mutual collisions, or pounding, resulting from insufficient or non-existing separation distances. The buildings are idealized as lumped-mass, shear beam type, multi-degree-of-freedom (MDOF) systems with bilinear force-deformation characteristics and with bases supported on translational and rocking spring-dashpots. Collisions between adjacent masses can occur at any level and are simulated by means of viscoelastic impact elements. Using five real earthquake motions the effects of the following factors are investigated: building configuration and relative size, seismic separation distance and impact element properties. It is found that pounding can cause high overstresses, mainly when the colliding buildings have significantly different heights, periods or masses. This suggests a possibility for introducing a set of conditions into the codes, combined with some special measures, as an alternative to the seismic separation requirement.     

基于遥感影像技术对普兰店农居建筑物的普查分析

房屋结构特征是评估地震灾害损失的重要影响因素之一,其中城市和农村房屋结构类型和抗震性能也有较大差异,城市建筑以砖混和框架结构为主,抗震性能较好,农村房屋主要以石木、砖木及砖混三种结构形式为主,抗震性能较差.对大连普兰店农居建筑物进行调研,通过无人机的航摄影像对建筑物结构的目视判读,并采用计算房屋误差矩阵和Kappa系数...     

南北地震带川滇甘陕地区竖向与水平向加速度反应谱比的统计分析

本文收集了从南北地震带川滇甘陕地区263个有详细场地资料的强震台站获得的802组强震动记录,按照场地、震级和震中距等因素统计分析了竖向与水平向加速度反应谱比的形状以及不同场地、震级和震中距下不同周期段内的谱比平均值,并与建筑抗震规范GB50011—2010规定的0.65进行了比较。结果表明:竖向与水平向加速度反应谱比受场地、震级和震中距等因素的影响; Ⅰ类和Ⅱ类场地在全周期段的谱比均值基本上大于0.65;无论何种分组情况谱比均值在0.1—1.0 s周期范围内基本低于定值0.65,周期大于1.0 s的谱比均值基本上远高于0.65。因此对于大部分抗震规范直接把竖向地震作用取为水平向地震作用的0.65倍,有待商榷。本文建议根据水平向反应谱的标定方式来确定现有竖向强震动记录的竖向地震作用。      

Evaluation of Vapor Intrusion Risk from Ethylene Dibromide Using the Vertical Screening Distance Approach

Vapor intrusion (VI) occurs when volatile contaminants in the subsurface migrate through the vadose zone into overlying buildings. The 2015 U.S. EPA petroleum VI guidance recommends that additional investigation of the VI risk from gasoline hydrocarbons at the underground storage tank (UST) sites is not necessary where the vertical distance between a building and a vapor source exceeds a recommended vertical screening distance. However, due to the lack of soil-gas data on the attenuation of ethylene dibromide (EDB), additional VI investigations to evaluate VI risk from EDB are recommended at UST sites with leaded gasoline releases containing EDB. We analyzed soil-gas and groundwater concentrations of EDB from eight petroleum UST sites using a new analytical method with soil-gas detection limit <0.16 μg/m³ EDB (VI screening level at the 10⁻⁶ risk level). The analysis included (1) assessing the frequency of EDB detections ≤0.16 μg/m³ at various vertical separation distances and (2) predicting vertical screening distances for EDB using the U.S. EPA PVIScreen model for different soil types in the vadose zone above dissolved-phase and LNAPL sources. Ranges of estimated aerobic biodegradation rate constants for EDB, air exchange rates for residential buildings, and source vapor concentrations for other constituents were combined with conservative estimates of EDB source concentrations as model inputs. Concentrations of EDB in soil-gas indicated that the U.S. EPA recommended vertical screening distances are protective of VI risk from EDB. Conversely, vertical screening distances predicted by modeling were >6 ft (1.8 m) for sites with sand and loam soil above dissolved phase sources and >15 ft (4.6 m) for sites with sand soil above LNAPL sources. This predicted dependence on the vapor source type and soil type in the vadose zone highlights the importance of soil characterization for VI screening at sites with EDB sources.     

Vertical acceleration demands on column lines of steel moment‐resisting frames

In this paper, vertical peak floor acceleration (PFA_v) demands on elastic multistory buildings are statistically evaluated using recorded ground motions. These demands are applicable to the assessment of nonstructural components that are rigid in the vertical direction and located at column lines or next to columns. Hence, PFA_v demands of the floor system away from column lines and their effects on nonstructural components are not addressed. This study is motivated by the questionable general assumption that typical buildings are considered to be relatively flexible in the horizontal (lateral) direction but relatively rigid in the vertical (longitudinal) direction. Consequently, only few papers address the evaluation of vertical component acceleration demands throughout a building, and there is no consensus on the relevance of vertical accelerations in buildings. The results presented in this study show that the vertical ground acceleration demands are amplified throughout the column line of a steel frame structure. This amplification is in many cases significant, depending on the vertical stiffness of the load‐bearing system, damping ratio, and the location of the nonstructural component in the building. From these outcomes it can be concluded that the perception of a rigid‐body response of the column lines in the vertical direction is highly questionable, and further research on this topic is required. Copyright © 2016 John Wiley & Sons, Ltd.     

强震动台站周边地面建筑物对观测结果的影响分析

强震动观测是获取地震地面运动最基本的手段,但其观测质量会受到观测台站周边环境的影响。本文针对不同场地条件的观测台站和附近不同高度建筑物,开展建筑物对观测场地地震动影响的模拟分析,探讨其对强震动观测的影响规律。基于ABAQUS有限元分析软件以及粘弹性边界方法,建立了8个场地-建筑物体系计算模型,分别考虑了4种不同剪切波速的场地和4种不同层数的框架结构建筑物,计算分析了建筑物高度、观测点与建筑之间的距离对强震动观测及场地土波速变化的影响。结果表明:强震动台站附近地面建筑物的存在对观测结果将产生明显的影响,近距离建筑物影响的相对误差可高达20%以上;建筑物高度的变化并没有明显改变其影响程度和影响较大的地震动周期范围,但较高建筑物的影响程度会随距离增加衰减速度减慢;场地土越软,周边建筑物对观测带来的影响越大。建议:对于较软弱场地（土层平均剪切波速低至210m/s）,强震动台站避让建筑物的距离应不小于40m,对于较坚硬场地（土层平均剪切波速大于250m/s）,强震动台站避让建筑物的距离应不小于25m。同时还认为,如果强震动观测要求较高精度,需进一步增加避让距离,且应具体考虑建筑物高度等因素的影响。     

黏滞阻尼器用于层间位移角超限的既有建筑的优化研究

在水平地震作用下,结构产生较大的层间变形或者结构底部地震剪力较大导致了很多建筑发生破坏.对于既有建筑,可采用安装黏滞阻尼器的加固方法减小其层间位移角,而结构层间位移角和基底剪力等均受阻尼器的位置与参数影响.因此,阻尼器的位置及参数优化的研究有重要意义.对于层间位移角超过现行规范限值的既有建筑结构,文中综合考虑结构变形与...     

Some Analyses on Effects of Site Classification on Ground Motion Characteristics in the Chi-Chi, Taiwan Earthquake

According to the epicenter distance and the site classification, the 404 groups of earthquake recordings of the main shock of the Chi-Chi, Taiwan China earthquake in 1999 are catalogued. Based on these data, we analyze the statistical features of duration, PGA, envelopes and the response spectra ratio of the horizontal and vertical components of the acceleration recordings. The results of these analyses show that the effect of site classification on the acceleration of various components is obvious; furthermore, fault direction also has certain effects on the characteristics of the horizontal components of ground motion. The detailed research results are as follows： （ 1 ） the duration of the horizontal components of acceleration records increases with the softening of the site; （2） the direction of fault slip has some effects on PGA＇s attenuation features; （3） the average envelopes of acceleration records at different distances and site dames are basically single peak functions of time and the envelopes of horizontal and vertical components of ground motion are obviously different; （4） with the same epicenter distance, EW/NS response spectrum ratios tend to approximate 1.0 as the site becomes softer and the period shorter. V/H response spectrum ratios in short periods （〈 0. 1s） increase with the softening of site, however, V/H ratios within the long-period range （ 〉 characteristic period） decrease with the softening of the site, and the decrease of V/EW ratio speeds up relatively.     

我国农村房屋的地震破坏分析与工程抗震处理对策

根据对我国农村建(构)筑物震害的调查结果,总结了农村房屋的震害特征,分析了建(构)筑物破坏的主要原因及农村房屋建(构)筑物在选址、施工、抗震设防等方面的教训,采用有限元分析比较了基础材料不同时基础部分的抗震差异。提出了提高农村房屋抗震能力的对策和建议。     

Unstructured mesh generation and landcover-based resistance for hydrodynamic modeling of urban flooding

Urban flood inundation modeling with a hydrodynamic flow solver is addressed in this paper, focusing on strategies to effectively integrate geospatial data for unstructured mesh generation, building representation and flow resistance parameterization. Data considered include Light Detection and Ranging (LiDAR) terrain height surveys, aerial imagery and vector datasets such as building footprint polygons. First, a unstructured mesh-generation technique we term the building-hole method (BH) is developed whereby building footprint data define interior domain boundaries or mesh holes. A wall boundary condition depicts the impact of buildings on flood hydrodynamics. BH provides an alternative to the more commonly used method of raising terrain heights where buildings coincide with the mesh. We term this the building-block method (BB). Application of BH and BB to a flooding site in Glasgow, Scotland identifies a number of tradeoffs to consider at resolutions ranging from 1 to 5 m. At fine resolution, BH is shown to be similarly accurate but execute faster than BB. And at coarse resolution, BH is shown to preserve the geometry of buildings and maintain better accuracy than BB, but requires a longer run time. Meshes that ignore buildings completely (no-building method or NB) also support surprisingly good flood inundation predictions at coarse resolution compared to BH and BB. NB also supports faster execution times than BH at coarse resolution because the latter uses localized refinements that mandate a greater number of computational cells. However, with mesh refinement, NB converges to a different (and presumably less-accurate) solution compared to BH and BB. Using the same test conditions, Hunter et al. [Hunter NM, Bates PD, Neelz S, Pender G, Villanueva I, Wright NG, Liang D, et al. Benchmarking 2D hydraulic models for urban flood simulations. ICE J Water Manage 2008;161(1):13–30] compared the performance of dynamic-wave and diffusive-wave models and reported that diffusive-wave models under-predicted the longitudinal penetration of the flood zone due to important inertial effects. Here, we find that a relatively coarse-mesh implementation of a dynamic-wave model suffers from the same drawback because of numerical diffusion. This shows that whether diffusion is achieved through the mathematics or numerics, the effect on flood extent is similar. Finally, several methods of distributing resistance parameters (e.g., Manning n) across the Glasgow site were evaluated including methods that utilize aerial imagery-based landcover classification data, MasterMap^® landcover classification data and LiDAR-based feature height data (e.g., height of shrubs or hedges). Results show that landcover data is more important than feature height data in this urban site, that shadows in aerial imagery can cause errors in landcover classification which degrade flood predictions, and that aerial imagery offers a more detailed mapping of trees and bushes than MasterMap^® which can locally impact depth predictions but has little impact on flood extent.