Seismic behavior of single‐story asymmetric‐plan buildings under uniaxial excitation

The critical parameters that influence the nonlinear seismic response of asymmetric‐plan buildings are identified by evaluating the effects of different asymmetries that may characterize the structure of a building as well as exploring the influence of the ground motion features. First, the main findings reported in the literature on both the linear and nonlinear dynamic response of asymmetric‐plan buildings are presented. The common findings and the conflicting conclusions reached in different investigations are pointed out. Then, the results of comprehensive nonlinear dynamic analyses performed for evaluating the seismic response of systems characterized by different strength and stiffness configurations, representative of a large class of asymmetric‐plan buildings, are reported. Findings from the study indicate that the building response changes when moving from the linear to the nonlinear range, so that the seismic behavior of asymmetric‐plan buildings, apart from the source of asymmetry, can be always classified as irregular. Additionally, it was observed that as the seismic demands cause amplification of system nonlinearity with increasing earthquake intensity, the maximum displacement demand in the different resisting elements tends to be reached with the same deformed configuration of the system. The resultant of the seismic forces producing such a maximum demand is located at the center of resistance and corresponds to the collapse mechanism of the system that provides the maximum lateral strength in the exciting direction of the seismic action. Copyright © 2008 John Wiley & Sons, Ltd.     

Approximate analysis methods for asymmetric plan base‐isolated buildings

An approximate method for linear analysis of asymmetric‐plan, multistorey buildings is specialized for a single‐storey, base‐isolated structure. To find the mode shapes of the torsionally coupled system, the Rayleigh–Ritz procedure is applied using the torsionally uncoupled modes as Ritz vectors. This approach reduces to analysis of two single‐storey systems, each with vibration properties and eccentricities (labelled ‘effective eccentricities’) similar to corresponding properties of the isolation system or the fixed‐base structure. With certain assumptions, the vibration properties of the coupled system can be expressed explicitly in terms of these single‐storey system properties. Three different methods are developed: the first is a direct application of the Rayleigh–Ritz procedure; the second and third use simplifications for the effective eccentricities, assuming a relatively stiff superstructure. The accuracy of these proposed methods and the rigid structure method in determining responses are assessed for a range of system parameters including eccentricity and structure flexibility. For a subset of systems with equal isolation and structural eccentricities, two of the methods are exact and the third is sufficiently accurate; all three are preferred to the rigid structure method. For systems with zero isolation eccentricity, however, all approximate methods considered are inconsistent and should be applied with caution, only to systems with small structural eccentricities or stiff structures. Copyright © 2001 John Wiley & Sons, Ltd.     

考虑空间效应的非线性结构主共振分析

本文针对考虑空间效应非对称刚度的单层结构，利用能量法得到了结构水平侧移和扭转相耦合的振动方程，采用多尺度法研究了侧移刚度和扭转刚度之间有某一关系时的主共振，分析了结构主共振的定常解并且讨论了其稳定性，通过算例分析得到了考虑空间效应时结构的一些有益的结论。     

内蒙古察哈尔右翼中旗大清河金矿地质特征及成因探讨

内蒙古察哈尔右翼中旗大清河金矿床类型属于变质-热液型中低温矿床,产出于太古代乌拉山群,矿石类型主要为含金硫化物石英脉和蚀变岩型金矿石。本次工作总结了矿体地质特征及分布规律;结合相关元素测试分析及相邻典型矿床地质特征,综合研究认为区内金元素的物源区主要为太古代乌拉山群,其次为岩浆岩;矿床整体形成于古生代末期至二叠纪中晚期,早期成岩成矿作用形成原始矿床或初始矿源层,晚期受二叠纪中晚期多期次热液流体影响,萃取、活化、迁移金元素形成含金热液流体,并在有利成矿部位充填沉淀,成矿严格受二叠纪花岗闪长岩中NE向及NEE向压扭性构造裂隙控制,矿体具有隐伏再现和雁列式侧伏展布特征。     

各向异性介质中扭转波分裂的实验观测

实验室可以产生两种振动模式的横波,一种是剪切振动,另一种是扭转振动,在各向同性介质中两模式的横波速度是相同的,但它们的振动特性不一样,前者表现出很强的偏振特性,后者为无偏振特性.实验测试表明无偏振特性的扭转波在各向异性介质中传播时也会出现两种速度不同的扭转波,速度值与剪切横波的快慢横波速度值一致.用扭转波换能器接收时,这快慢扭转波的波形振幅不受各向异性方位影响.通过两块均匀的各向异性样品,用实验观测揭示了各向异性介质中扭转波的一些传播特征.     

绳索取心钻杆的瞬间液相扩散连接

采用瞬间液相扩散连接方法焊接绳索取心钻杆。试验表明, 瞬间液相扩散连接接头拉伸时断在45MnMoB杆体侧, 面弯和背弯180°未开裂, 且焊缝内外表面无余高, 成形美观, 满足绳索取心钻杆焊接接头的技术要求。扭转试验中, 管体首先开裂, 焊缝未开裂, 扭转强度远远高于螺纹连接扭转强度。表明瞬间液相扩散连接技术是满足绳索取心钻杆焊接要求的一种先进方法。     

Modified consecutive modal pushover procedure for seismic investigation of one-way asymmetric-plan tall buildings

The effects of higher modes and torsion have a significant impact on the seismic responses of asymmetric-plan tall buildings.A consecutive modal pushover(CMP) procedure is one of the pushover methods that have been developed to consider these effects.The aim of this paper is to modify the(CMP) analysis procedure to estimate the seismic demands of one-way asymmetric-plan tall buildings with dual systems.An analysis of 10-,15-and 20-story asymmetric-plan buildings is carried out,and the results from the modified consecutive modal pushover(MCMP) procedure are compared with those obtained from the modal pushover analysis(MPA) procedure and the nonlinear time history analysis(NLTHA).The MCMP estimates of the seismic demands of one-way asymmetric-plan buildings demonstrate a reasonable accuracy,compared to the results obtained from the NLTHA.Furthermore,the accuracy of the MCMP procedure in the prediction of plastic hinge rotations is better than the MPA procedure.The new pushover procedure is also more accurate than the FEMA load distribution and the MPA procedure.     

Fracture analysis for torsion problems of a gravity platform column with cracks under wind load

Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The column was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was reduced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion problem of the gravity platform column with a straight crack under various wind loads was calculated. The obtained results were compared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.     

Effects of torsion factors on simple non-linear systems using fully-bidirectional analyses

An ensemble of earthquake records is used to carry out non-linear analyses of simple torsionally unbalanced systems considering both resisting elements and earthquake components along two perpendicular directions. These fully bidirectional analyses are focused to study the effect of the following factors: (i) seismic-force reduction factor; (ii) factors α and δ used to compute the design eccentricity; (iii) initial lateral period; and (iv) initial stiffness eccentricity. Results indicate that the amplification factor α can be specified as a function of the force reduction factor, the lateral uncoupled period, and the stiffness eccentricity. It is concluded that the coefficient δ depends on the lateral period, the stiffness eccentricity, and the geometrical eccentricity. It was observed that negative shears caused by torsion should be neglected in the design of the stiff element, particularly in the case of systems with large stiffness eccentricity. Results suggest that additional studies should be performed to verify the assumed (partial) equivalence between unidirectional (resisting elements and earthquake components along one direction only) and fully bidirectional analyses to study building torsion problems. Copyright © 1999 John Wiley & Sons, Ltd.     

岳阳洞庭湖大桥斜拉桥索塔变形观测方

对岳阳洞庭湖大桥三塔斜拉桥三塔的位移和扭转变形 ,提出了布网方案、观测方法和计算方法 ;按相关平差的理论严密估算了变形观测的精度 ;得出的一些结论可作为以后实际变形观测的借鉴