Probabilistic evaluation of seismic performance of 3‐story 3D one‐ and two‐way steel moment‐frame structures

This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.     

基于有限元的弯矩计算中若干问题探讨

在岩土工程的数值计算中,除了将岩土材料本身划分为实体单元外,设置在岩土体中,与岩土材料相互作用的其他材料也常常划分为实体单元,比如桩基、堤坝防渗墙和面板等。由于对桩基、防渗墙等往往需要利用内力和弯矩进行设计,这就提出了如何利用有限元得到的应力和位移信息计算结构弯矩的问题。通过对一悬臂梁的计算分析就这一问题进行探讨,发现用应力计算弯矩为提高精度需要划分较多单元。用位移计算可以减少单元划分的工作量,但计算易出现振荡,结果不可靠。同时,对剪切闭锁现象等进行了探讨。     

钢筋混凝土梁在低速撞击下的动力响应

研究分析了在半无限粘弹性Winkler地基上的钢筋混凝土梁受低速刚性体撞击的塑性动力响应问题。认为低速撞击下梁的计算必须考虑撞击时局部损伤的影响,研究梁结构整体破坏,从而建立了局部损伤和整体变形的关系式,推导出了钢筋混凝土梁在低速中心撞击时弹塑性阶段撞击力和撞击处的横向位移的计算公式。     

自由边界形状与近边界裂纹相互作用模型研究

大量的研究表明, 岩爆发生条件与岩石的力学性能有关。岩体中微裂纹的形成、扩展和汇合对岩体的力学性能产生显著影响,可以导致材料的逐渐劣化直至破坏。对于单轴压缩的岩石试件,其破坏型式主要是微裂纹的摩擦滑移、自相似平面扩展和弯折扩展。基于断裂力学机制,对单轴压缩荷载下3种不同边界形状,即直边、凸形、凹形情况下近边界原生斜裂纹的扩展进行了理论研究,并运用FLAC数值模拟技术,建立了基于Interface界面单元的裂纹扩展数值模型。近直边界及凸形边界情况的裂纹扩展使用梁渐近模型来解析薄片岩层的屈曲断裂问题,对于近凹形边界情况给予简化,提出了裂纹－圆－椭圆相互作用的修正模型并进行理论分析。研究结果表明,基于Interface界面单元的裂纹扩展的数值模型正确,解析解与数值解吻合较好,相应的梁渐近模型及裂纹-圆-椭圆模型可以合理地分析应力调整过程中裂纹的扩展和裂纹与不同洞室表面形状的相互作用问题,为岩爆工程及理论研究提出了新的理论依据。     

Unsteady thermoelastic analysis of a circular disk with a hot central core and subjected to adiabatic conditions

The unsteady thermoelastic analysis of a cooling circular disk or cylinder which is originally at uniform temperature is a classical problem of the theory of thermal stresses. More recent studies consider the case of composite structural configurations. The present paper deals with a situation which, apparently, has not been previously considered: unsteady thermal stresses caused by the presence of a hot, central nucleus. The temperature field is obtained in terms of a Fourier–Bessel expansion and then, radial and tangential stresses are evaluated analytically. The problem is of basic interest in mechanical and naval engineering systems.     

电子束CT三维重建技术与颅颌面外科

目的 探讨电子束CT三维重建技术在颅颌面外科的适应症和应用价值。方法 采用美国Imatron公司的电子束CT(electron beam CT,以下简称EBCT)C-150,对76例严重颅颌面病人实行薄层CT容积扫描。将所获CT图象经数字接口传至加拿大ISG公司生产的Allegro工作站进行三维重建。结果EBCT成像技术能立体的、详尽和精确的显示机体组织三维解剖结构极其相互关系。其再现畸形或病体模型的程度可以达到近乎解剖学的精度,为准确了解和掌握病情并制定合理的手术治疗计划提供了极为重要的依据,提高了手术治疗效果。结论EBCT三维重建技术是现代颅颌面外科最主要的诊断方法之一并具有重要的临床应用价值。     

Cyclic tests on a hybrid coupled wall utilizing a rocking mechanism

A new type of hybrid coupled wall system, consisting of rolled steel coupling beams, reinforced concrete (RC) wall piers, and concrete‐filled tube (CFT) short columns, is introduced. In this new system, the bases of the wall piers are connected to the base beams only through CFT short columns, unlike conventional coupled walls. Yield occurs in the coupling beams and the short columns; hence, in the RC wall piers, only minimum cracking appears. A total of four subassembly specimens, designed to fail in various collapse mechanisms, were cyclically loaded under constant axial force. A benchmark specimen showed ductile behavior with large energy dissipation until fracture occurred in the coupling beam. In the specimen designed to fail in shear in its CFT, substantial axial shortening was observed, but the overall behavior was ductile. Behavior of specimens with small amounts of section steel in the wall panel fringe, or with thin wall panels, also showed ductile behavior, but the strength and energy dissipation were significantly smaller than other two specimens. An analytical model was proposed for a frame analysis program using fiber elements to simulate elastic–plastic behavior of the system. Design methods to prevent shear failure of CFT and RC panels are suggested using the analytical and test results. Copyright © 2008 John Wiley & Sons, Ltd.     

列车引起的地基动应力特性

为分析列车引起的地基动应力特性,用移动荷载作用下的弹性地基Euler-Bernoulli梁模型计算得到地基表面与路堤之间的反力。将其视为作用于地基表面的移动面荷载,以单位移动荷载引起的半空间地基内部应力解为基础,对反力在作用空间上进行积分,得到了列车速度小于地基中Rayleigh波速时列车荷载在地基中引起的稳态应力响应解答。给出了应力随空间坐标和时间的变化,分析了应力的特性及分布规律。发现列车经过时在地基中产生的动应力是循环应力,具有明显的偏移应力。竖向动应力的影响范围随着列车速度的增大而不断增大。     

不均匀性束内充塞效应对星载测雨雷达 反演算法的影响

星载雷达在地面的足印可达数公里,强降雨团的特征尺度也仅为几公里,加上波束内各部分对回波的贡献是非线性的,研究不均匀性束内充塞效应（Non Uniform Beam Filling,或简称NUBF）对星载测雨雷达反演雨强算法的影响就显得非常重要。利用TOGA/COARE期间Ku波段机载雷达实测资料提供的不同的降雨结构进行不均匀性束内充塞效应的研究。     

Statistical aspects of Tricomi's function and modified Bessel functions of the second kind

Some of the considerable statistical content of modified Bessel functions of the second kind and of Tricomi's confluent hypergeometric function is illustrated. Moment solutions for the parameters of exponential class distribution functions based on both are derived. Unlike the generalised inverse Gaussian, the Tricomi exponential distribution is little known but it emerges that it is of wide applicability, highly flexible and has the gamma distribution as a special case.