基于地脉动单点谱比的场地特征参数测定方法适用性研究

通过克拉玛依、浙江46个场地的地脉动单点三分向记录和两次地震的强震记录,对比了戈壁荒漠地区地脉动与地震动的H/V谱比,分析了地脉动H/V谱比卓越频率与覆盖层厚度、不同深度等效剪切波速以及特征周期之间的相关性,研究了基于地脉动单点谱比的场地特征参数测定方法在戈壁荒漠等覆盖层较薄以及东部沿海等覆盖层较厚地区的适用性,对该方法的高频、低频部分进行修正,扩展了适用频带范围。结果表明,在戈壁砂砾地区,地震动与地脉动H/V谱比的卓越频率具有很高的一致性;基于地脉动单点谱比的场地特征参数测定方法在计算场地覆盖层厚度、覆盖层等效周期时,对于东部沿海等深厚覆盖层场地会低估,对于戈壁荒漠等浅覆盖层场地会高估;对该方法修正后,适用频带范围扩展到了0.58～12.5 Hz,计算的场地覆盖层厚度、覆盖层等效周期与实测值的平均相对误差提高到了22%和27%;在0.58～12.5 Hz频带,场地V_(s20)、V_(s30)、T_(s20)、T_(s30)、T_s与地脉动卓越频率也体现出了明显的相关性,V_(s30),T_(s30)与地脉动卓越频率的相关性要大于V_(s20),T_(s20)。     

钢管混凝土拱桥台阵试验研究:场地条件的影响

为了研究不同场地条件对钢管混凝土拱桥地震响应的影响规律,以某钢管混凝土拱桥为原型,设计制作1/16缩尺比例模型,依据NEHRP场地分类标准,选取符合不同场地条件的ChiChi地震波,利用多子台积木式振动台台阵系统,完成了纵向、横向、竖向、横向+纵向和横向+竖向一致地震动输入的对比试验。研究结果表明:场地条件对此类钢管混凝土拱桥响应的影响较为显著,结构响应由A类至E类场地逐类递增,结构在E类场地下的响应为A类场地的1.6倍~4.1倍;相对于水平向加速度响应,拱顶竖向加速度响应对场地条件更为敏感,场地条件对竖向加速度的放大作用要高于水平向加速度,在确定设计加速度反应谱时,如果竖向设计加速度反应谱与水平设计加速度反应谱采用相同的场地系数会使竖向加速度反应谱最大值偏小。     

松软场地上桩筏基础AP1000核岛结构的三维非线性地震反应特性

松软场地上核岛结构的地震安全正成为一个挑战性的重大工程问题。选取代表性的近场强震、中远场强震和远场大震记录作为基岩地震动,考虑场地工程地质特性、土体非线性和人工边界条件,对松软场地-桩筏基础-AP1000核岛结构三维体系进行非线性地震反应分析,结果表明:核岛结构谱加速度的卓越周期与基岩地震动的基本相同,对与核岛主体结构基本频率相近的地震动分量的反应更为强烈,冷却系统水箱“晃动水”的地震反应对核岛结构的影响类似于鞭梢效应;核岛结构的峰值加速度放大系数随结构高度增大,近场和远场强震作用时,该放大效应主要取决于核岛结构自身特性及基岩地震动经土层到核岛底部的传播;核岛结构相对其底部的峰值相对位移随结构高度增大,且远场大震作用时的反应更为强烈;随基岩峰值加速度的增大,核岛结构的峰值加速度放大效应减弱、峰值相对位移反应增大。地基柔性及土-结构相互作用的耦合效应对输入地震动具有高频过滤、低频放大效应,从而使核岛结构下部的峰值加速度显著放大、中上部的峰值加速度显著减小。     

不同深度与倾角断层破碎带对Rayleigh波传播及场地地震动反应的影响研究

采用Rayleigh波时域波动输入方法,对Rayleigh波作用下的场地地震动反应进行动力时程反应分析,重点研究了断层破碎带深度与倾角对Rayleigh波传播以及场地地震动反应的影响。结果表明:断层破碎带对Rayleigh波传播及场地地震动反应影响显著。在Rayleigh波入射一侧的断层角点以及距角点较近处,峰值位移反应随着断层深度的增大而增大并趋于稳定,而随着断层倾角的增大其峰值位移反应明显减小;在Rayleigh波入射一侧的中远场地表面,断层深度与倾角对地面峰值位移反应影响很小;在另一侧中远场地面的峰值位移反应随着断层深度的增大而减小,而断层倾角的变化对该侧地面的峰值位移反应影响很小。最后通过改变场地条件进行了适用性分析,结果表明该结论具有较好的适用性。     

水平层状饱和场地地震响应分析的等效线性化方法

采用饱和土层和半空间精确的动力刚度矩阵,建立了求解P波、SV波斜入射情况下水平层状饱和场地地震响应的一维等效线性化分析方法。将饱和场地退化至干土场地进行方法验证,并将该文结果与二维有限元程序FLUSH结果进行对比,验证了该文方法的准确性。以天津市区某典型饱和场地为例,分别比较了P波和SV波入射情况下饱和场地线性、非线性地震响应之间的差别,以及饱和场地、干土场地非线性地震响应之间的差别,并讨论了入射角度和透水条件等因素对地面运动加速度峰值的影响,总结了饱和场地非线性地震响应的一些基本规律。     

脉冲地震动缩放水平对结构非线性位移反应影响的分析

研究缩放速度脉冲型地震动强度水平引起的单自由度(SDOF)体系非线性位移反应的偏差。采用30条速度脉冲地震记录,通过SDOF的体系动力时程分析,分析了速度脉冲型地震动分别缩放到不同目标谱加速度(Sa)、峰值加速度(PGA)、峰值速度(PGV)、峰值位移(PGD)水平时,SDOF体系非线性位移反应偏差随系统自振周期和强度折减系数变化的规律;通过对散点数据的对数线性回归确定了位移反应偏差的变化趋势,并比较了不同地面运动强度表征参数下位移偏差的稳定性。分析结果表明：位移偏差对地震动缩放系数、系统的基阶自振周期和系统的强度有一定的依赖性,合理选用缩放系数和地面运动强度表征参数能有效减小估算结构地震位移响应的偏差。     

地震波斜入射下层状TI饱和场地地震反应分析

滨海地区的天然土体在长期的风化和沉积作用下,其水平模量往往会大于其竖向模量,表现出明显的横观各向同性（TI）饱和特性,目前还很少有针对地震波斜入射下TI饱和场地动力响应问题的研究。将HaskellThomson传递矩阵方法拓展到层状TI饱和半空间,求解了直角坐标系下两相介质的Biot动力平衡方程及孔隙流体运动方程,建立了层状TI饱和半空间传递矩阵,并结合地表边界条件求解了地震波斜入射下层状TI饱和场地自由场的时域反应。该文验证了提出方法的正确性,进而以CNTEWGXE波（0.3 g）作为输入地震动,研究了土体TI性质及饱和特性对场地加速度时程及反应谱的影响。结果表明:层状TI饱和场地和各向同性饱和场地地表的动力响应存在一定差异,TI参数的改变使得场地对地震波产生不同的滤波和放大效应;场地的饱和特性对地表的动力响应有重要影响,饱和多孔介质固液耦合作用对地震波具有削弱作用;地震波斜入射时地表加速度时程及反应谱响应小于其垂直入射时的响应,且入射角度对qP1波入射时的场地影响更明显。     

长周期结构相对位移反应谱研究

在对长周期结构进行抗震设计时,或采用基于位移的性能设计方法进行结构设计时,或采用各种结构控制技术对结构进行减隔震设计时,需要用到相对位移反应谱,而目前各国规范给出的一般都是某种标准化的绝对加速度反应谱。本文指出了国内外目前在用的部分规范提出的长周期反应谱存在的问题,采用80条高通低截止频率（0.025~0.125 Hz）、加速度峰值≥0.10 g的水平向强震记录,计算了周期0~10 s、阻尼比0.10~0.40的相对位移反应谱,研究了位移谱的影响因素及控制参数,建立了考虑震源参数、地震动幅值特性、场地条件、谱控制参数、阻尼比调整系数的可供长周期结构设计使用的弹性相对位移谱,给出了实用化计算公式及地震动位移峰值。结果表明,相对位移谱卓越周期是控制位移谱谱值及形状的重要参数;本文研究得到的相对位移谱能较好地拟合实际相对位移谱。     

基于弹塑性谱位移的钢筋混凝土框架概率地震需求分析

地震动参数的选择是影响概率地震需求分析中输入地震动的选择和调整以及分析结果可靠性的重要因素。开展概率地震需求分析时,常采用的地震动参数主要有峰值加速度和对应于结构基本周期的加速度反应谱值。但是,一方面,结构响应与地震动峰值加速度的相关性较差。另一方面,对应于结构基本周期的加速度反应谱值不能体现结构基本周期之外的地震动频率成分对结构地震反应的影响。以弹塑性谱位移作为地震动参数开展RC框架结构的概率地震需求分析研究。基于模态Pushover分析提出了弹塑性谱位移的计算方法;借助云图法和改进的增量动力法开展典型框架结构的概率地震需求分析,基于回归拟合及残差分析研究了弹塑性谱位移的充分有效性,并与弹性谱位移进行了比较。研究表明:弹塑性谱位移能够反映大于结构基本周期的地震动频率成分对结构弹塑性地震反应的影响,改善了弹性谱位移仅反映单一地震动频率成分对结构反应影响的不足,可以较合理地揭示由于结构软化导致自振周期延长后地震动的破坏作用。     

地震动频谱特性对隔震结构响应及损伤影响研究

针对地震动复杂频谱特性对隔震结构响应及损伤影响进行研究,用加速度反应谱平均周期Tr表征地震动周期特性,用Bouc-Wen模型及刚度退化的Bouc-Wen模型分别描述隔震层与上部楼层的滞变特性,建立隔震结构的质点系非线性分析模型,考虑隔震支座压剪相关性与拉压性能差异建立隔震体系损伤指数模型,分析不同地震动输入加速度幅值及不同Tr与对隔震结构地震反应、损伤影响规律。分析表明,在地震动高频范围内隔震结构响应随输入加速度峰值增加而增加,但对长周期地震动,输入加速度峰值对隔震结构地震反应影响较小,地震反应呈较大离散性、无规律性;在相同加速度幅值输入下隔震层地震反应、损伤的离散性远大于上部结构,在共振区内虽出现最大地震反应,但也会出现较小地震反应,表明隔震结构瞬时共振为非常复杂的过程。研究可为揭示地震动特性与隔震结构地震反应及损伤的关联性提供分析依据。     

Scheduling railway traffic at a construction site

We consider the problem of rescheduling trains in the case where one track of a railway section consisting of two tracks in opposing directions is closed due to construction activities. After presenting an appropriate model for this situation we derive a polynomial algorithm for the subproblem of finding an optimal schedule with minimal latenesss if the subsequences of trains for both directions outside the construction site are fixed. Based on this algorithm we propose a local search procedure for the general problem of finding good schedules and report test results for some real world instances. Received: December 8, 1999 / Accepted: May 2, 2001     

Strain gauge installation in a civil engineering site

Installurion of resistance strain gauges is described for field tests under conditions of high humidity and in water in the intake area of a water power plant in New Zealand.     

The decontamination of a disused gas works site

This paper describes work carried out at a site which was to be cleared prior to its use for erection of a large retail superstore together with its adjacent car park. A preliminary site investigation indicated that contamination, especially by tar, was widespread and that numerous underground pipes and tanks were also present. During site clearance approximately 10,000 m³ of contaminated solid material was removed and deposited in two licensed landfill sites 25 km and 40 km from the gas works. Liquid tar was adsorbed onto contaminated solids prior to disposal. A below-ground gas holder was used as a holding tank for contaminated aqueous liquids to enable suspended solids and immiscible organics to separate. After removal of contaminated material the site was covered with clean, crushed and compacted stone having known geotechnical characteristics.     

Prediction of blast wave effects on a developed site

The guidelines for protecting against and mitigating explosion hazards require knowledge and either the experimental or theoretical evaluation of blast wave parameters. To this end, this article proposes a numerical method for simulating blast wave propagation in complex geometries. This method permits an on-the-ground TNT-like explosion and the subsequent blast wave to be simulated, with the possibility of modifying the ground topology by adding a number of obstacles. The numerical model is explored from both a qualitative and quantitative point of view by comparing it to experimental data, with a correct determination of the wave amplitude and phase signature at different key-positions. The pressure and Mach number distributions deduced from simulations in complex congested areas highlight various fluid–solid interactions, such as regular reflections and diffractions. The iso-damage diagrams of different obstacle layouts are also presented and discussed.     

Adsorption site heterogeneity in silicalite: a calorimetric study

Differential heats of adsorption have been determined calorimetrically for benzene, n-, iso- and cyclo-alkanes and alcohols on silicalite. It is shown that for small molecules, as well as for the flexible straight chain paraffins and n-alcohols, silicalite may be regarded as an energetically homogeneous adsorbent, whereas molecules with sizes very close to the pore diameters of silicalite reveal energetically different adsorption sites.     

某场平工程现场混装铵油炸药配比优化研究

以遵义市新火车站场平工程为背景,进行了混装多孔粒状铵油炸药的组分配比优化现场试验。分析了不同直径下现场混装铵油炸药的柴油配比与爆速关系,对比了不同配比炸药的爆炸性能。结合理论研究和现场试验结果确定了炸药爆速最高、能量释放最为充分的最佳炸药配比:多孔粒状硝酸铵与柴油的配比为95∶5。现场工程试验表明,优化配比后的炸药在保证爆破效果的同时,炸药单耗降低了8%。     

Evaluation of natural attenuation rate at a gasoline spill site

Contamination of groundwater by gasoline and other petroleum-derived hydrocarbons released from underground storage tanks (USTs) is a serious and widespread environmental problem. Natural attenuation is a passive remedial approach that depends upon natural processes to degrade and dissipate contaminants in soil and groundwater. Currently, in situ column technique, microcosm, and computer modeling have been applied for the natural attenuation rate calculation. However, the subsurface heterogeneity reduces the applicability of these techniques. In this study, a mass flux approach was used to calculate the contaminant mass reduction and field-scale decay rate at a gasoline spill site. The mass flux technique is a simplified mass balance procedure, which is accomplished using the differences in total contaminant mass flux across two cross-sections of the contaminant plume. The mass flux calculation shows that up to 87% of the dissolved total benzene, toluene, ethylbenzene, and xylene (BTEX) isomers removal was observed via natural attenuation at this site. The efficiency of natural biodegradation was evaluated by the in situ tracer method, and the first-order decay model was applied for the natural attenuation/biodegradation rate calculation. Results reveal that natural biodegradation was the major cause of the BTEX mass reduction among the natural attenuation processes, and approximately 88% of the BTEX removal was due to the natural biodegradation process. The calculated total BTEX first-order attenuation and biodegradation rates were 0.036 and 0.025% per day, respectively. Results suggest that the natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the occurrence and efficiency of the natural attenuation process.