SMA负刚度双曲面减震装置的优化及抗震性能研究

SMA负刚度双曲面隔震装置的试验结果表明：绕支座布置的SMA索在支座转弯处不能自由滑动,导致SMA索的受力与设计目标严重不符。为解决上述问题,拟提出一种优化升级的SMA负刚度双曲面减震装置。基于某一连续梁桥,比较研究了正刚度、零刚度与该负刚度装置的抗震性能。结果表明：该优化装置具有良好的耗能能力、自恢复性能以及强震下的限位能力。与正刚度装置及零刚度装置相比,该装置具有更好的抗震性能。     

Numerical simulations of a highway bridge structure employing passive negative stiffness device for seismic protection

A new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd.     

数字化气氡在井（泉）地震监测中的研究进展

氡是地下流体预报地震的灵敏组分之一,数字化气氡观测已经成为地震监测的一种重要手段。近年来,一些地震台站能够观测到气氡测值出现的震前异常、震后效应以及同震效应等变化,本文对这些异常变化研究进行总结并展开讨论;另外,对于在数字化气氡观测过程中可能产生干扰的影响因素,分别从自然环境、仪器系统、人为干扰不同方面进行分析归纳。      

Performance of a guideway seismic isolator with magnetic springs for precision machinery

This paper proposes the use of the nonlinear restoring force in an isolation system to improve the performance of a seismic isolator. Nonlinear magnetic springs applied to guideway sliding isolators (GSI) that protect precision machinery against seismic motion were studied. The magnetic springs use a non‐contact magnetic repulsion force to achieve a nonlinear property. A numerical simulation model of the GSI system using step‐by‐step integration in the time domain was developed. A full‐scale shaking table test was performed to verify the accuracy of the numerical model. Simulation and experimental results show that the GSI system with magnetic springs has good performance when subjected to floor vibrations during earthquakes. A parametric analysis of the magnetic springs in the GSI system under seismic motion was theoretically investigated. It was found that sufficient magnetic forces can diminish the system relative displacements. Copyright © 2008 John Wiley & Sons, Ltd.     

摩擦-碟簧三维复合隔震支座的性能试验研究

对适用于大跨结构的摩擦-碟簧三维复合隔震支座进行了振动台试验研究,该支座在水平向和竖向分别采用摩擦滑移装置和碟型弹簧隔震。在水平向,试验重点测试了简谐激励和地震动激励下支座的滞回性能,考察了竖向荷载变化及地震动强度对隔震性能的影响,以期为建立水平隔震理论模型提供依据;在竖向,对碟型弹簧的等效阻尼比和等效刚度进行了测试,研究了竖向预压荷载和动力荷载对竖向滞回性能的影响。结果表明,复合隔震支座在水平向和竖向均具有较好的滞回性能,竖向等效阻尼比在0.10～0.15间,且随着预压荷载的增加而增大。     

A macro‐model with nonlinear springs for seismic analysis of URM buildings

Seismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading; thus, these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in‐plane cyclic loading, which can be used for practical and accurate seismic assessment of masonry buildings. According to the proposed strategy, generic masonry perforated walls are modelled using an equivalent frame approach, where each masonry component is described utilising multi‐spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure. Copyright © 2016 John Wiley & Sons, Ltd.     

Ground viscosity and stiffness measurements for near surface seismic velocity

In land surveys, the weathering layer can often distort the seismic signal due to it passing through rapid velocity and density changes, dispersion, scattering and inelastic absorption. In a simple spring‐dashpot model for the earth response, an equivalent medium groups these complex phenomena into two parameters only; these are called ground viscosity and ground stiffness. The most recent controllers for vibrators can estimate both parameters. To validate these measurements, Saudi Aramco conducted an experiment measuring ground viscosity and stiffness from two different vibrator control systems over an area of varying terrain conditions, including unconsolidated sand and limestone outcrop. The two systems measured different values, but detected similar trends that correlated well with weathering conditions and surface geology, e.g. lower viscosity values on the outcrop than on the sand. The ratio of ground viscosity to ground stiffness can approximate the shallow S‐wave velocity, which we converted into P‐wave velocity through calibration with sparse uphole data. Static corrections incorporating this velocity information somewhat improved the focusing of seismic time sections. This new approach does not require additional acquisition efforts, and can model shallow complex formations in arid areas where classical static methods often fail.     

设置负刚度装置的大跨长联连续梁桥地震反应分析

为完善大跨长联连续梁桥的减震和隔震技术,提出将负刚度装置引入某带有摩擦摆支座隔震的大跨长联连续梁桥中组成新型减震和隔震系统。基于CSIBridge软件建立全桥有限元模型,负刚度装置采用弹性多段线模拟,摩擦摆支座采用双线性恢复力模型,输入7条地震波进行了非线性时程分析,考查了新型减震和隔震系统下桥梁结构的地震反应,探究了负刚度系统对大跨长联隔震连续梁桥地震反应的影响。研究结果表明：在大跨长联隔震连续梁桥上布置负刚度装置后,梁体加速度及支座位移可被有效降低,近场地震动下的墩底内力也有明显减小。负刚度装置可有效提高大跨长联摩擦摆支座连续梁桥的抗震性能,负刚度装置也适用于大跨长联隔震连续梁桥。     

Dynamic loading tests and seismic response analysis of a stud-type damper composed of multiple friction units with disc springs

This paper presents an experimental study on the performance of a shear-sliding stud-type damper composed of multiple friction units with high-tension bolts and disc springs. A numerical evaluation of the response reduction effects achieved by the stud-type damper is also presented. In dynamic loading tests, the behavior of stud-type multiunit friction damper specimens was investigated. Three different full-scale damper specimens, which were composed of five, six, or seven friction units with two or four sliding surfaces, were incorporated into loading devices for testing. The stud-type friction dampers demonstrated stable rigid-plastic hysteresis loops without any remarkable decrease in the sliding force even when subjected to repetitive loading, in addition to showing no unstable behavior such as lateral buckling. The damper produced a total sliding force approximately proportional to the number of sliding surfaces and friction units. The total sliding force of the stud-type damper can thus be estimated by summing the contributions of each friction unit. In an earthquake response simulation, the control effects achieved by stud-type dampers incorporated into an analytical high-rise building model under various input waves, including long-period, long-duration and pulse-like ground motions, were evaluated. A satisfactory response reduction was obtained by installing the developed stud-type dampers into the main frame without negatively impacting usability and convenience in terms of building planning.     

Operating principles and technical characteristics of a small-sized molecular-electronic seismic sensor with negative feedback

The results of analysis of the output parameters of small-sized seismic motion sensors based on molecular electronics are presented. These devices feature a molecular-electronic transducer with negative feedback the introduction of which makes it possible to improve the sensor performance (specifically, to broaden the frequency range, reduce the amplitude-frequency characteristic (AFC) unevenness, and reduce the nonlinear distortion factor (NDF) value). The operating principle of these devices is outlined. The basic characteristics such as AFC, NDF, and the inherent noise level are determined experimentally, and the methods of their determination are described. The obtained data are analyzed and compared to the data on similar foreign devices. Principal lines of further research aimed not only at improving the technical characteristics but also at establishing a serial production process are specified.     

Wall building stiffness and strength effect on content sliding in Wellington seismic conditions

A numerical study of unobstructed content sliding within several low‐to‐midrise reinforced concrete cantilever wall buildings designed to Wellington conditions in New Zealand is performed to validate the belief that increasing a building's strength and/or stiffness would result in more severe sliding response. It was shown that contents within stronger buildings experienced larger sliding response. If the building was designed to be strong, the sliding response of contents with a friction coefficient of 0.1 was smaller in stiffer buildings compared with those in flexible buildings. However, the trends start reversing with an increase in friction coefficient or a decrease in building strength. Overall, content sliding is not necessarily more severe in stiffer buildings, and in many cases, the opposite is true. This study's findings were compared against an existing parametric equation for estimating the maximum sliding displacement. This equation, which was originally derived for contents located within elastic frame buildings, was found to be more efficient than considering total floor accelerations alone but was underconservative by a mean of 17% for yielding multistorey buildings. A design procedure considering content sliding using the parametric equation and an example are provided. Copyright © 2016 John Wiley & Sons, Ltd.     

中国西部及邻区百年尺度周期的地震活动及其和太阳活动之间的负相关性

利用小波变换分析中国西部及邻区1700年以来M≥7级和M-T图分析1700年以来M≥7.8级地震活动,除了得到和其他学者研究基本一致的几个十年尺度周期结果外,还得到百年左右尺度的地震活动周期结果,再与太阳黑子活动进行比较,发现地震活动与太阳黑子数在百年左右尺度周期上具有负相关性,地震高活动时段对应太阳黑子低值时段.此外,从活动性分析中得到目前中国西部及邻区可能正处于强震活跃期间.     

Rectangular footing on soil with depth-degrading stiffness: Vertical and rocking impedances under conditional existence of surface waves

The response of rectangular rigid footings resting on an elastic soil of shear modulus decreasing monotonically with depth is studied. Such profiles are typically encountered after ground improvement. The propagation characteristics of SV/P surface waves are investigated, showing the appearance of cut-off frequencies above which surface waves do not exist. The semi-analytical method of the subdivision of the footing/soil contact area is then used for solving the boundary value problem, whereby the influence functions for the sub-regions are determined by integration of the corresponding surface-to-surface Green׳s functions. Impedance functions are presented over a wide range of frequencies for typical values of the non-homogeneity parameters, the Poisson׳s ratio and the foundation geometry. The salient features that are associated with the non-homogeneity and the appearance of cut-off frequencies are elucidated.     

滑动屋盖摩擦控制系统对地震频谱和结构刚度的鲁棒性

地震功率谱密度函数的频率范围和结构刚度变化对滑动屋盖摩擦控制系统减震效果的影响分析表明 :控制系统减震效果对地震功率谱的频域宽窄不敏感 ,而对功率谱所覆盖的结构自振频率敏感 ;结构刚度发生± 15 %的变化对减震效果的影响不大。分析还表明 ,滑动屋盖摩擦控制系统对于结构非线性地震反应有显著的减震作用     

Efficient analysis of pile-group effect on seismic stiffness and strength design of buildings

A new efficient method is developed for the analysis of pile-group effects on the seismic stiffness and strength design of buildings with pile foundations. An efficient continuum model consisting of a dynamic Winkler-type soil element and a pile is used to express the dynamic behavior of the structure-pile-soil system with only a small numerical error. The pile-group effect is taken into account through the influence coefficients among piles which are defined for interstory drifts and pile-head bending moments. It is shown that, while the pile-group effect reduces the interstory drift of buildings in general, it may increase the bending moment of piles at the head. This means that the treatment without the pile-group effect results in the conservative design for super-structures and requires a revised member design for piles.     

Nonstationary seismic responses of structure with nonlinear stiffness subject to modulated Kanai–Tajimi excitation

A simple structure under earthquake excitation is modeled as a single‐degree‐of‐freedom system with nonlinear stiffness subject to modulated Kanai–Tajimi excitation. The nonstationary responses including the nonstationary probability densities of the system responses and the statistical moments are obtained in semi‐analytical form. By applying the stochastic averaging method based on the generalized harmonic functions, the averaged Fokker–Planck–Kolmogorov(FPK) equation governing the nonstationary probability density of the amplitude is derived. Then, the solution of the FPK equation is approximately expressed by a series expansion in terms of a set of properly selected basis functions with time‐dependent coefficients. According to the Galerkin method, the time‐dependent coefficients are solved from a set of linear first‐order differential equations. Thus, the nonstationary probability densities of the amplitude and the state responses as well as the statistic moments of the amplitude are obtained. Finally, two types of the modulating functions, i.e. constant function and exponential function, are considered to give some semi‐analytical formulae. The proposed procedures are checked against the Monte Carlo simulation. The effects of the structure natural frequency and the intensity of the excitation as well as the ground stiffness on the system responses are discussed. It should be pointed out that the proposed method is good for broadband excitation and light damping. Copyright © 2011 John Wiley & Sons, Ltd.     

带窗洞加强肋复合墙体抗震性能及抗侧刚度影响因素研究

进行了1榀开窗洞1:2比例的加强肋复合墙体模型的伪静力试验,通过对墙体中钢筋应变进行分析,研究墙体的受力性能和破坏模式,探究在低周反复荷载作用下带窗洞加强肋复合墙体的承载力、滞回及耗能能力、延性和刚度退化等抗震性能,并与不开洞墙体的抗震性能进行对比。在试验研究的基础上,建立具有不同窗洞参数的有限元数值模型,探究窗洞位置、大小、肋柱截面及肋柱配筋率的改变对加强肋复合墙体抗侧刚度的影响。结果表明:带窗洞加强肋复合墙体按照砌块-外框-肋梁的顺序依次破坏,破坏模式以弯剪型破坏为主;相比不开洞加强肋复合墙体,带窗洞墙体的抗侧刚度等抗震性能明显较差;相同窗洞尺寸情况下,窗洞居中时加强肋复合墙体的抗侧刚度相对较大;窗洞开洞率小于12.9%的墙体洞边可不设肋柱;洞边加强肋柱对开窗洞墙体的抗侧刚度提升作用显著,但其提升作用随着窗洞肋柱截面的增大而逐渐减弱;增大加强肋柱配筋率对墙体抗侧刚度的提高不明显。     

西南地区地震观测井泉水温动态特征研究

本文利用西南地区地震前兆台网记录的井泉水温数字观测资料,对水温各类动态特征进行研究,提取不同井水温各类观测动态及同井不同深度水温各类观测动态特征.收集整理了114个井泉水温观测台站的观测数据,结果表明,西南地区水温观测以中深非自流井为主,水温动态范围较大,热水和高温热水主要分布在川西和云南地区.西南井泉水温长期动态可大致分上升型、下降型和波动型三种,短期动态可大致分为短周期型、稳定型、固体潮型三种.研究区井水温的同震变化以下降居多,单个井水温对不同地震的同震响应存在优势响应方向,说明水温的同震特征更依赖于井孔自身观测条件的影响.通过对1966年以来西南地区36次MS≥5.9级震例总结的统计分析得出,西南地区水温前兆异常率达67％,上升型水温异常占比最大,且水温异常多属于短临异常.给出了Ms≥5.9地震震前水温异常井的最大震中距的大致范围,并根据异常震中距-震级的G-R关系给出其定量关系,为今后西南地区中强地震的发生提取有用的水温前兆信息提供基础资料.     

AVS/D半主动振动控制结构的抗震设计方法探讨

本文介绍了AVS／D半主动控制系统的工作原理,参照现行抗震设计规范的设计思想,提出了AVS／D半主动控振结构的抗震设计方法,并针对具体结构控制系统的工作性能,探讨了结构设计中关键参数：主体结构的地震力折减系数和薄弱层层间位移相对控制率的确定方法,最后通过实例分析验证了该方法的可行性。     

Laboratory-scale study of field of view and the seismic interpretation of fracture specific stiffness

The effects of the scale of measurement, i.e., the field of view, on the interpretation of fracture properties from seismic wave propagation was investigated using an acoustic lens system to produce a pseudo-collimated wavefront. The incident wavefront had a controllable beam diameter that set the field of view at 15 mm, 30 mm and 60 mm. On a smaller scale, traditional acoustic scans were used to probe the fracture in 2 mm increments. This laboratory approach was applied to two limestone samples, each containing a single induced fracture and compared to an acrylic control sample. From the analysis of the average coherent sum of the signals measured on each scale, we observed that the scale of the field of view affected the interpretation of the fracture specific stiffness. Many small-scale measurements of the seismic response of a fracture, when summed, did not predict the large-scale response of the fracture. The change from a frequency-independent to frequency-dependent fracture stiffness occurs when the scale of the field of view exceeds the spatial correlation length associated with fracture geometry. A frequency-independent fracture specific stiffness is not sufficient to classify a fracture as homogeneous. A nonuniform spatial distribution of fracture specific stiffness and overlapping geometric scales in a fracture cause a scale-dependent seismic response, which requires measurements at different field of views to fully characterize the fracture.