山地与平原地形对地震动影响的对比分析

山地和平原地形在破坏性地震中对震害和地震动有很大影响,不同地形对地震动有不同的地形效应。为研究山地和平原地形对地震动的影响规律,基于集集地震后续M L6.6余震的强震观测记录,对位于不同地形且与震中位于同一直线上的四个强震台记录处理计算,从波形特征、频谱分析、加速度反应谱计算、与规范谱比较等方面进行对比分析,完成长周期地震动反应谱分布的计算。研究表明,山地地形对地震动的高频成分有地形放大效应,沉积平原对地震动的低频长周期部分有放大作用,并且长周期反应谱的峰值区域始终位于沉积平原中部。平原上强震记录产生的长周期放大系数谱已超出规范谱,沉积平原上长周期建筑的抗震设防应引起重视。     

Response based design metocean conditions for a permanently moored FPSO during tropical cyclones: Estimation of greenwater risk

Response based analysis (RBA) is used to establish the design metocean conditions (DMCs) of a generic weather-vaning FPSO off the North West Shelf (NWS) of Australia for determining greenwater severity. A vessel heading prediction tool, an essential component of the RBA analysis for weather-vaning vessels, is developed and evaluated by comparing with full-scale measurements from an operating FPSO. Locations at the bow, amidships and the stern of the vessel are found to be susceptible to greenwater risks and the vessel is often exposed to oblique waves during tropical cyclones. Long-term extrapolation is performed to estimate 1 in. N-year return relative wave-vessel motions represented by both the most probable maximum relative wave-vessel motion within a storm r_mp, and the maximum individual relative wave-vessel motion r_Max. It is observed that r_Max ˜ (1.1–1.2) r_mp. The use of r_Max allows for the variability of the short term maxima per storm and also the fact that the peak in response might not come in the most severe sea-state. Given the focus on greenwater rather than wave severity, the slightly larger value of r_Max at a given return period is used for assessment of greenwater risk. The sea-states that lead to r_Max at a 1 in 100 year level are identified and subsequently used for characterising the wave groups causing maximum relative wave-vessel motion at various locations around the vessel. For a given location, the shapes of the wave time histories which give rise to extreme relative wave-vessel motions in a set of design metocean conditions are similar, indicating that a ‘design wave’, derived within the framework of linear wave theory, may be a useful approach to tackle highly nonlinear and complex greenwater overtopping problems.     

近场问题的研究现状与发展方向

在过去的20年里,近场问题受到了地震学家和土木工程师的共同关注,一方面原因旨在阐明地震本身的机理,解释新现象;另一方面是由于地震动作为一种主要的输入荷载,在某些情况下将对整个结构设计的最终结果起到控制作用. 同时试验和评估等其它领域的相关研究也均以指定的荷载形式为前提,荷载形式的变化直接影响了土木工程中的诸多方面,所以希望研究这种荷载的规律并获得其与结构反应之间的关系. 本文回顾了近场问题研究的历史,介绍了近年来国内外针对近场地震动所展开的相关研究工作,其中包括近场地震动本身的特性与近场地震动对土木工程结构的影响等方面,指出了目前存在的问题和进一步应该研究的方向,对于近场问题的深入研究具有一定的参考价值.      

Progress and trend on near-field problems in civil engineering

Introduction The characteristics of ground motions recorded near the fault of an earthquake are quite dif- ferent from the usual far-field ground motions. After the original recognition of their differences in the Port Hueneme earthquake in 1957, a great lot of inhabited structures and lifeline systems were damaged in the major earthquakes happened in the following years. The damages were beyond minds of seismologists and engineers. A quite rational reason is the lack of enough knowledge of t…     

Seismic response of slender rigid structures with foundation uplifting

The rocking of rigid structures uplifting from their support under strong earthquake shaking is investigated. The structure is resting on the surface of either a rigid base or a linearly elastic continuum. A large-displacement approach is adopted to extract the governing equations of motion allowing for a rigorous calculation of the nonlinear response even under near-overturning conditions. Directivity-affected near-fault ground motions, idealized as Ricker wavelets or trigonometric pulses, are used as excitation. The conditions under which uplifting leads to large angles of rotation and eventually to overturning are investigated. A profoundly nonlinear rocking behavior is revealed for both rigid and elastic soil conditions. This geometrically nonlinear response is further amplified by unfavorable sequences of long-duration pulses in the excitation. Moreover, through the overturning response of a toppled tombstone, it is concluded that the practice of estimating ground accelerations from overturning observations is rather misleading and meaningless.     

Propagation and attenuation characteristics of various ground vibrations

In order to effectively control vibration related problems, the development of a reliable vibration monitoring system and the proper assessment of attenuation characteristics of various vibrations are essential. Various ground vibrations caused by train loading, blasting, friction pile driving and hydraulic hammer compaction were measured using 3D geophones inside of the borehole as well as on the ground surface, and the propagation and attenuation characteristics of various source generated vibrations were investigated by analyzing particle motions. For the geometric modeling of various vibrations, the types of various sources and their induced waves were characterized and the geometric damping coefficients were determined. The measured attenuation data matched well with the predicted data when using the suggested geometric damping coefficient, and the estimated soil damping ratios were quite reasonable taking soil type of the site and experiencing strain level into consideration.     

海南岛南渡江三角洲海岸演变的波浪作用分析

本文应用白沙门1984年波浪统计资料,通过对南渡江三角洲北部近岸海底泥沙活动特性与东部废弃海岸泥沙沿岸输移方式及其岸外沙坝、堡岛响应波浪动力而具有的形状进行分析,揭示了波浪在南渡江三角洲北部沿岸演变中的重要作用。     

Large-scale motion of solar filaments

Precise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.     

Periodic orbits of the Sitnikov problem via a Poincaré map

In this paper by means of a Poincaré map, we prove the existence of symmetric periodic orbits of the elliptic Sitnikov problem. Furthermore, using the presence of the Bernoulli shift as a subsystem of that Poincaré map, we prove that not all the periodic orbits of the Sitnikov problem are symmetric periodic orbits.This revised version was published online in October 2005 with corrections to the Cover Date.     

乌恰5.1级地震强震动加速度记录初步分析

对新疆数字强震台网记录的2010年06月10日乌恰Ms5.1地震10组三分量加速度记录进行处理和初步分析.在分析前对原始加速度记录进行整理,转换数据格式,进行零线校正,计算校正加速度、速度、位移时程谱、傅立叶振幅谱、加速度反应谱.在对本次地震的强震动特性进行分析后发现,较大的加速度峰值沿发震断层分布,集中在靠近断层的狭...