A novel framework integrating downhole array data and site response analysis to extract dynamic soil behavior

Seismic site response analysis is commonly used to predict ground response due to local soil effects. An increasing number of downhole arrays are deployed to measure motions at the ground surface and within the soil profile and to provide a check on the accuracy of site response analysis models. Site response analysis models, however, cannot be readily calibrated to match field measurements. A novel inverse analysis framework, self-learning simulations (SelfSim), to integrate site response analysis and field measurements is introduced. This framework uses downhole array measurements to extract the underlying soil behavior and develops a neural network-based constitutive model of the soil. The resulting soil model, used in a site response analysis, provides correct ground response. The extracted cyclic soil behavior can be further enhanced using multiple earthquake events. The performance of the algorithm is successfully demonstrated using synthetically generated downhole array recordings.     

Changes in material fluxes from the Changjiang River and their implications on the adjoining continental shelf ecosystem

This study aims to examine the changing patterns of Changjiang material fluxes, which are influenced by anthropogenic activities, and the resultant modifications to the coastal and shelf oceanographic conditions, and to propose future research about the effect of these changes on the estuarine and shelf ecosystem. Within the catchment basin of the Changjiang River, the construction of more than 48,000 dams has caused significant sediment discharge reduction, together with modifications to the timing of seasonal freshwater discharge. In the future, the mean freshwater discharge will decrease following the completion of the water-diverting project for water supply to northern China. At the same time, the riverine nutrient loadings (N and P) have increased due to the extensive use of chemical fertilizers and the large discharge of industrial wastewater and domestic sewage. These changes are modifying the oceanographic conditions of the estuarine and shelf waters. The flushing time for the river water becomes longer in wet seasons but shorter in dry seasons. An increase in salinity can be expected after the completion of the water-diverting project. Nutrient concentrations will be enhanced in the shelf waters. In contrast to the decrease in the suspended sediment concentration of the river water, field measurements have not shown well-defined patterns of changes within the estuary; nevertheless, net sediment accumulation and carbon burial rates would be reduced in the deltaic areas because of the reduced sediment discharge. Finally, increase in the nutrient input appears to enhance the primary production in the East China Sea region, which, in turn, may enhance the fishery catch.     

A stochastic ground motion model with separable temporal and spectral nonstationarities

A fully nonstationary stochastic model for strong earthquake ground motion is developed. The model employs filtering of a discretized white‐noise process. Nonstationarity is achieved by modulating the intensity and varying the filter properties in time. The formulation has the important advantage of separating the temporal and spectral nonstationary characteristics of the process, thereby allowing flexibility and ease in modeling and parameter estimation. The model is fitted to target ground motions by matching a set of statistical characteristics, including the mean‐square intensity, the cumulative mean number of zero‐level up‐crossings and a measure of the bandwidth, all expressed as functions of time. Post‐processing by a second filter assures zero residual velocity and displacement, and improves the match to response spectral ordinates for long periods. Copyright © 2008 John Wiley & Sons, Ltd.     

底柱加强对高层混合结构地震能量反应的影响

近年来,能量分析方法在结构抗震设计中的应用问题受到国内外地震工程界的普遍关注,被认为是今后结构抗震设计理论的发展方向之一.以一钢框架-钢筋混凝土剪力墙混合结构为对象,通过逐渐增大框架底层柱截面,分析它们在不同类型地震波下的地震能量反应,结果表明,加强钢框架底层柱使结构总输入能基本不发生变化,结构滞回耗能在总输入能中的比例ν和底部剪力墙滞回耗能占结构总滞回耗能的比例μ均随结构刚度特征值λ的增大而减小,因此,加强钢框架底层柱能够提高外钢框架-内混凝土剪力墙结构体系的抗震能力,降低其在强震作用下的损伤程度.     

Key parameters governing the dynamic response of long-period structures

The present study describes the important factors (period, duration, and intensity) involved in evaluating input ground motion and structural response for the design of long-period structures such as high-rise buildings and base-isolated buildings. First, the fundamental dynamic properties of high-rise buildings are explained based on the results of newly introduced vibration observations programs. Next, the distribution of the predominant period and duration of seismic ground motion within the Nobi Plain, one of the largest sedimentary plains in Japan, is discussed with respect to the possibility of resonance of long-period structures. Finally, we introduce a recently developed long-stroke shaking table that is intended to convince structural engineers and building owners to take adequate countermeasures against large floor response in high-rise buildings because of resonance. Presented at the International Workshop on Long-Period Ground Motion Simulation and Velocity Structures Earthquake Research Institute, University of Tokyo, Tokyo, November 14–15, 2006.     

A review of research on seismic behaviour of irregular building structures since 2002

The paper presents an overview of the progress in research regarding seismic response of plan and vertically irregular building structures. Three areas of research are surveyed. The first is the study of the effects of plan-irregularity by means of single-storey and multi-storey building models. The second area encompasses passive control as a strategy to mitigate torsional effects, by means of base isolation and other types of devices. Lastly, the third area concerns vertically irregular structures and setback buildings. Although fewer papers have been published in this last area with respect to the former ones, this state-of-the-art reports extensively on research efforts and progress into the seismic behaviour of irregular buildings in elevation to show the growing interest among specialists in the field.     

流体饱和两相多孔介质动力反应计算分析

基于流体饱和两相多孔介质的弹性波动方程组,运用显式逐步积分格式与局部透射人工边界相结合的时域显式有限元方法对该波动方程组进行求解,对两相介质在输入地震波作用下的弹性动力反应进行计算和分析;对在是否考虑孔隙流体渗流的两种情况下计算得到的两相介质弹性动力反应结果的差异进行对比研究,从而揭示孔隙流体渗流对两相介质动力反应性质的影响。计算结果表明：两相介质弹性动力反应时程的波形与入射地震波的波形相同,且弹性动力反应的峰值出现的时刻对应于入射地震波的峰值出现的时刻;孔隙流体的渗流将对两相介质的弹性动力反应性质产生显著的影响。数值计算同时表明,时域显式有限元方法是进行流体饱和两相多孔介质弹性动力反应计算分析的一种有效的方法。     

含饱和土的层状场地的动力响应

利用精确的土层和半空间动力刚度矩阵求解了含饱和土的层状场地的动力响应,给出了含饱和土层状场地的自由场（入射P波、SV波）、动力Green函数及刚性条形基础动力刚度的计算方法,由此建立的场地模型更接近实际情况。建议方法的退化结果与单相场地结果一致。研究了界面不同透水条件对基础动力刚度的影响,并与相应单相场地结果进行了对比。研究表明：界面透水条件对竖向弹簧系数影响最大,饱和土体中孔隙水对场地动力响应具有不可忽视的影响。     

长江三峡地区全新世环境演变及其古文化响应

依据长江三峡地区大九湖和玉溪剖面AMS14C测年数据(校正为日历年)建立了约9.3～2ka BP高分辨率多环境代用指标(δ13C、K、腐殖化度、抱粉总浓度、Rb、Sr及Rb/Sr)的变化曲线,并在此基础上与研究区周边反映全新世气候环境变化的不同沉积记录进行综合对比分析.与此同时,本文还通过对研究区古遗址和古洪水层的统计分析,获取了本区新石器以来古文化兴衰变迁和古洪水发生的完整信息.研究结果表明:(1)本区全新世大暖期约出现在7.6～4 ka BP.9.3～7.6 ka BP,本区气候极不稳定,波动幅度大,总体上冷湿,多次出现显著的降温或干旱事件(9.1、8.2和7.7 ka BP前后);4～2 ka BP,本区气候较此前偏干凉,且波动频繁.(2)7.6～ka BP的大暖期分为三个演变阶段:即6～5 ka BP为大暖期的鼎盛期,气候稳定,温暖湿润,植被及生态条件优越,洪水发生频率低;7.6～6 ka BP和5～4 ka BP为大暖期中具有不稳定特征的过渡期,其中5～4 ka BP及4 ka BP前后的降温事件仍较显著,且多发洪水.(3)本区史前古文化的主要形成发展期与大暖期持续阶段相对应,其中耕作业相对发达的大溪文化繁荣期出现在大暖期中的鼎盛阶段(约6～5 ka BP),大溪文化前后处于低潮及表现为衰退现象的古文化则对应气候环境的不稳定期,总体上,研究区古文化响应气候环境变化的主要方式是通过改变其生业结构的途径来实现的.     

陕西省耕地资源数量与经济发展关系的计量分析

基于1978-2005年陕西省耕地资源数量与经济发展的统计数据,运用协整分析、误差修正模型、脉冲响应函数和方差分解等方法分析了陕西省耕地资源数量与经济发展之间的互动关系,结果显示:1)陕西省耕地资源数量与经济发展之间存在长期均衡关系,但短期内却存在失衡,短期波动向长期均衡趋近的调整幅度为4.23%,调整力度非常小;2)经济发展的冲击可以部分解释耕地资源数量的变化,解释水平为12%以下,耕地资源数量的冲击对经济发展的解释水平在18%以下;3)耕地资源数量、经济发展均显著地受其自身波动的影响.建议从提升经济发展质量和耕地利用效率等方面采取长期性、综合性的政府干预措施.