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1.
Hsen‐Han Khoo Charles Clifton Gregory MacRae Hao Zhou Shahab Ramhormozian 《地震工程与结构动力学》2015,44(8):1309-1324
The Asymmetric Friction Connection (AFC) remains elastic during moderate earthquake shaking but slides and dissipates energy through friction during severe earthquake shaking. The sliding friction forces developed are dependent on the clamping force in the connection which is provided by fully tensioned bolts which pass through slotted holes. During sliding these bolts are subject to moment and shear as well as axial force. Moment–shear–axial force interaction reduces the clamping axial force on the sliding interfaces thereby reducing the sliding shear resistance (Vss). Two methods to evaluate the moment–shear–axial force interaction have been proposed so that the sliding shear strength can be quantified, but as yet, these methods are not robust. This paper describes the results of 60 tests undertaken to improve the two methods, namely the moment–shear–axial force bolt model and the effective coefficient of friction method, for AFCs with high hardness steel shims. The bolts were M16 to M30 bolts and cleat thicknesses ranged from 12 mm to 25 mm. It is shown that either method may be used in design as the results obtained are similar. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
The widespread use of sliding bearings for the seismic isolation of structures
requires detailed knowledge of their behavior and improved modeling capability under seismic conditions. The paper summarizes the results of a large experimental investigation on steel–PTFE interfaces, aimed at evaluating the effects of sliding velocity, contact pressure, air temperature and state of lubrication on the mechanical behavior of steel-PTFE sliding bearings. Based on the experimental outcomes, two different mathematical models have been calibrated, which are capable of accounting for the investigated parameters in the evaluation of the sliding friction coefficient. The first model is basically an extension of the model proposed by Constantinou et al. (1990)Journal of Earthquake Engineering, 116(2), 455–472, while the second model is derived from the one proposed by Changet al. (1990)Journal of Engineering Mechanics, 116, 2749–2763. Expressions of the model parameters as a function of bearing pressure and air temperature are presented for lubricated and non-lubricated sliding surfaces. Predicted and experimental results are finally compared. 相似文献
3.
The attenuation of technically induced surface waves is studied theoretically and experimentally.In this paper, nineteen measurements of ground vibrations induced by eight different technical sources including road and rail traffic, vibratory and impulsive construction work or pile driving, explosions, hammer impulses and mass drops are described, and it is shown that the technically induced ground vibrations exhibit a power-law attenuation v～r-q where the exponents q are in the range of 0.5 to 2.0 and depend on the source types.Comparisons performed demonstrate that the measured exponents are considerably higher than theoretically expected.Some potential effects on ground vibration attenuation are theoretically analyzed.The most important effect is due to the material or scattering damping.Each frequency component is attenuated exponentially as exp(-kr), but for a broad-band excitation, the sum of the exponential laws also yields a power law but with a high exponent.Additional effects are discussed, for example the dispersion of the Rayleigh wave due to soil layering, which yields an additional exponent of 0.5 in cases of impulsive loading. 相似文献
4.
花管土钉已被广泛应用于基坑工程中,但其抗拔承载机理尚不明确。根据花管土钉的支护原理,分析其三种破坏形式,提出花管土钉的四个受力阶段;基于库仑土压力理论,将滑动土体上方看作均布荷载,推导出花管土钉极限抗拔承载力的计算公式;结合兰州某基坑实例,将《建筑基坑支护技术规程》中的花管土钉极限抗拔承载力计算方法与本文计算方法进行拉拔试验,并对结果进行对比分析。研究表明：花管土钉的破坏模式主要为花管杆体被拉断、出浆锚固体被剪断及出浆锚固体前端土体变形过大;花管土钉的四个受力阶段包括静止阶段、塑性区产生阶段、塑性区扩张阶段和破坏阶段;在花管土钉极限抗拔承载力的组成中,出浆锚固体提供的抗拔力所占比重随花管埋深的增大而显著增大,是花管土钉极限抗拔承载力的重要组成部分。 相似文献
5.
摩擦-碟簧三维复合隔震支座的性能试验研究 总被引：2，自引：0，他引：2
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。 相似文献
6.
On the basis of about 300 earthquake wave forms observed in the Shidian M S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3, the seismic moments are 1010–1016 N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×105–20×105Pa. Through the statistical analyses of variation of corner frequency f c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and stress drops before and after the main shock have index significance to the precursory information before a strong earthquake. The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of lower stresses. 相似文献
7.
This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2D?, which can capture with fidelity the sliding, rocking, and slide‐rocking response of rigid‐body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in‐house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g‐value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes Mw=6.0–7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in‐between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
8.
Brittle fractures occurring at the beam–column connections of welded steel moment frames, such as those observed following the Mw 6.7 1994 Northridge earthquake, result in sudden decreases in connection strength and stiffness. These changes lead to various types of transient dynamic behavior at the local and global levels. The effects on global acceleration include highly transient, high‐frequency waveforms that occur immediately following fracture and decay quickly. The theoretical basis for the occurrence of these transient waveforms is examined and their presence in structural analysis results is demonstrated. Results from shaking table experiments on a simple steel moment frame with fracturing connections show that transient accelerations are consistently observed following fracture. These experiments and analyses show that, due to their short duration, the transient acceleration waveforms do not cause any sudden changes in the global lateral displacement response of typical building structures. Therefore, these global acceleration transients have relatively benign effects on overall system behavior despite their relatively large amplitudes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
9.
The stationary response of base-isolated buildings subjected to earthquake excitation is studied. The frequency content of earthquake input is described by the Clough-Penzien spectral model. The response parameters of interest are (1) the root-mean-square (RMS) displacement σx of the basement relative to the foundation (i.e. shear deformation of the isolation system) and (2) the ratio (σa/σa0) of the RMS value of the absolute acceleration at the roof of the isolated structure over the corresponding value when the isolation system is locked. The variation of these response parameters with the effective frequency f0 of the base-isolated structure is investigated. As input, earthquakes with moment magnitudes M = 7-3 and M = 6-0 are considered. The acceleration spectra corresponding to these two earthquake sizes have pronouncedly different frequency content over the frequency range 0–1-1–0 Hz which is of primary importance for base-isolated structures. An important conclusion that comes from these analyses is that confidence in the effectiveness of a base-isolated system should be based primarily on its capacity to absorb/dissipate energy and less on its influence in shifting the fundamental period of the structure out of the range of dominant earthquake energy. 相似文献
10.
Coulomb damping can be utilized effectively to reduce the dynamic response of structures subjected to seismic ground motions. To activate this damping, some parts of a vibrating structure are allowed to slide at rough interfaces. The dynamic response of structures provided with sliding interfaces at the base, between a floor slab and frame and in the cross bracings of a frame has been examined recently. In this paper, a simple slab sliding system provided with a spring to introduce a recovery mechanism and to reduce the sliding displacement requirement for low frequency structures has been examined. The equations of motion for this system are developed. An approach is presented to solve these coupled equations for earthquake induced ground motions. Structures with varying frequency and friction characterisics are considered and the numerical results are presented in response spectrum form. It is observed that, in low frequency structures, provision of a rather weak spring can reduce the sliding displacement requirements without significantly increasing the forces in the supporting frame and the acceleration input to supported secondary systems. 相似文献
11.
Based on the seismic response characteristics of space frame structures,a new type of seismic isolation bearing defined as a three-dimensional seismic isolation bearing(3DSIB) is developed in this paper.The bearing offers excellent properties such as multi-dimensional seismic isolation,reasonable rotation capability,good ability to resist lifting load,uncoupled stiffness in horizontal and vertical directions,etc.In the 3DSIB,the horizontal dimension is designed by combining the Teflon sliding device and helical spring,while the vertical dimension is developed by introducing disk springs or helical springs.The mathematical model of the 3DSIB was established and its performance with the critical parameters was tested on a shaking table.Furthermore,the 3DSIB was applied in a 120 m span hangar structure and simulated using SAP2000 software to evaluate its performance in practical structures.The performance of the structures with and without 3DSIB was compared.It is shown that the hangar structure with 3D bearings achieves a better performance.The axial force and acceleration response of the structures with 3DSIB are effectively reduced,while the displacement response of the bearing is within the predetermined range. 相似文献
12.
On the basis of about 300 earthquake wave forms observed in the Shidian M
S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to
estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3,
the seismic moments are 1010–1016 N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×105–20×105Pa. Through the statistical analyses of variation of corner frequency f
c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously
lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly
higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and
stress drops before and after the main shock have index significance to the precursory information before a strong earthquake.
The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main
shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of
lower stresses.
Foundation item: Scientific and Technological Key Project of Yunnan Province (2001NG46) 相似文献
13.
A shift approach is presented for evaluating and interpreting the response of rigid‐perfectly plastic single‐degree‐of‐freedom systems to dynamic loading. Scaling laws for such systems are, as the term suggests, multiplicative in nature, relating peak dynamic response to products of key problem parameters such as linear spectral coordinates, force reduction coefficient and peak values of the excitation and its time derivatives. Contrary to classical laws, the proposed approach is additive, imposing a shift in the ordinates and the abscissa of the excitation function by means of a set of parameters uniquely related to the yielding resistance of the system. The dynamic response is then obtained by integrating the modified excitation function in a linear‐like manner within a particular yielding branch, for the nonlinearity is incorporated into the forcing term. The mathematical validity of the approach is demonstrated analytically and its importance is highlighted for systems with symmetric yielding resistance subjected to near‐fault earthquake motions. The modified excitation function may be discontinuous between different yielding branches and relates uniquely to the development of plastic deformation. It is thereby referred to as Plastic Input Motion (PIM). It is shown that the ordinates and the duration of this function may be significantly (yet not necessarily) smaller than those of the original ground motion depending on yield strength. The relationship of the proposed approach to the existing methods and parameters of earthquake engineering such as Newmark's sliding block and relative ground acceleration, is discussed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
The response of a rigid block supported on a horizontally moving foundation through a dry‐friction contact is investigated to near‐fault ground motions. Such motions can be thought of as consisting of a coherent component (‘pulse’) and an incoherent component, which can be described as a band‐limited ‘random noise’. The equation of motion of this strongly nonlinear system is reduced to a normalized form that reveals important parameters of the problem such as the critical acceleration ratio. The response of the sliding block to a set of uniformly processed near‐fault motions, covering a sufficiently wide range of magnitudes, is evaluated numerically for selected discrete values of the acceleration ratio. For each value of the critical acceleration ratio, the numerically computed residual slips are fitted with a Weibull (Gumbel type III) extreme value probability distribution. This allows the establishment of regression equations that describe accurately design sliding curves corresponding to various levels of non‐exceedance probability. The analysis reveals that the coherent component of motion contributes significantly to the response of the sliding block. Furthermore, the relevant acceleration in specifying the critical acceleration ratio is the (normalized) amplitude, αH_pulse, of the pulse and not the (normalized) amplitude of the incoherent component αH. Finally, the incoherent component is described quantitatively in terms of the root‐mean‐square acceleration aRMS, and an attempt is made to understand its influence on the response of the sliding block. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
16.
A laboratory instrument was developed to investigate the electrical properties of rock samples with respect to changes of frequency, temperature and pressure. The instrument can be used to obtain general trends and typical values for geological media. It should be of particular interest in geothermal studies and research in the geophysical properties of rocks. The design intervals for quantities under investigation were 20–300°C, 105-4 × 107 Pa and 5 × 10?4-103 Hz. Certain limitations exist on the simultaneous use of the highest values of temperature and pressure. The main features of the instrument are: analog electrical outputs recorded by an x-y recorder or observed on a scope with an attached camera (according to the frequency range); pressures produced by an oil hydraulic system in order to ensure electrical insulation of the sample; temperatures obtained by placing the pressure vessel into a thermostatically controlled room. Thus the monitoring instrumentation is directly accessible during the experiment. Information is also given about calibration procedures and examples of rock sample data are given. 相似文献
17.
Auroral precipitating electrons pass through an acceleration region before entering the atmosphere. Regardless of what produces it, a parallel electric field is assumed to cause the acceleration. It is well known that from kinetic theory an expression for the corresponding upward field-aligned current can be calculated, which under certain assumptions can be linearized to j = KV. The K constant, referred to as the Lyons-Evans-Lundin constant, depends on the source density and thermal energy of the magnetospheric electrons; it is an important parameter in magnetosphere-ionosphere coupling models. However, the K parameter is still rather unknown, and values are found in a wide range of 10–8–10–10Sim–2. In this study, we investigated how the type of auroral structure affects the K values. We look at onset and westwards-travelling surge (WTS) events and make comparisons with earlier results from observations of more stable auroral arcs. A new analysis technique for studying those magnetospheric parameters using ground-based measurements is introduced. Electron density measurements are taken with the EISCAT radar, and through an inversion technique the flux-energy spectra are calculated. Source densities, thermal energies and potential drops are estimated from fittings of accelerated Maxwellian distributions. With this radar technique we have the possibility to study the changes of the mentioned parameters during the development of onsets and the passage of surges over EISCAT. The study indicates that the linearization of the full Knight formulation holds even for the very high potential drops and thermal temperatures found in the dynamic onset and WTS events. The values of K are found to be very low, around 10–11Sm–2 in onset cases as well as WTS events. The results may establish a new technique where ionospheric measurements are used for studying the ionosphere-magnetosphere coupling processes. 相似文献
18.
The paper focuses on seismic sliding displacement calculations of gravity wall bridge abutments when subjected to passive condition during earthquakes. Pseudo-dynamic approach has been used for the calculation of the passive seismic earth pressure. A novel element of the present investigation is the computation of seismic passive earth pressure coefficients by considering the composite curved rupture surface behind the abutment wall in the framework of limit equilibrium method. Sliding failure along the wall base is considered in the new pseudo-dynamic method. The critical seismic acceleration coefficient for sliding and sliding component of the displacement, resulting from horizontal and vertical sinusoidal ground accelerations, are computed by using Newmark's sliding block method. The effect of sliding on the response of earth structures is evaluated and comparisons are made between sliding displacements calculated using planar and composite failure mechanisms. Results of the comparative study showed that the assumption of planar failure mechanism for rough soil–wall interfaces significantly overestimates the critical seismic accelerations for sliding and underestimates the sliding displacements. 相似文献
19.
Two of China's highest earth-core rock-fill dams (ECRDs) and concrete-faced rock-fill dams (CFRDs) were simulated by large-scale earthquake simulation shaking table tests in this work. A series of staged tests were performed, including white noise, different types of earthquake excitations with different magnitudes etc. The seismic performance of the ECRD and CFRD models were analyzed and investigated. The test results indicated that reservoir impoundment influenced the structure and seismic characteristics of the ECRD model much more than the CFRD model. The average fundamental frequency of the CFRD decreased less than the ECRD model when subjected to strong excitation. The acceleration amplification factors decreased as the input peak acceleration increased. The maximum acceleration occurred at the top of the ECRD model, while it occurred at 0.6–0.9 dam height of the CFRD model. Seismic residual deformations of the two models were very small. When subjected to strong earthquake excitation, the residual deformation of the CFRD model was smaller than that of the ECRD model. The dominant failure pattern of the two models was shallow sliding at the height of 3/4 on the downstream slope. The above analysis indicated that seismic performance of CFRD was superior to ECRD. 相似文献
20.
Artificial ground motion compatible with specified peak velocity and target spectrum 总被引：1，自引：0，他引：1
In this paper, a method, which synthesizes the artificial ground motion compatible with the specified peak velocity as well as the target acceleration response spectrum, was proposed. In this method, firstly, an initial acceleration time history α8^（0） （t）, which satisfies the prescribed peak ground acceleration, the target spectral acceleration ST（ω, ζ）,and the specified intensity envelope, is generated by the traditional method that generates the requency domain; secondly,α8^（0） （t）is further modulated by superimposing narrow-band time histories upon it in the time domain to make its peak velocity, approach the target peak ground velocity, and at the same time to improve its fitting precision to the target spectrum. Numerical examples show that this algorithm boasts high calculation precisions. 相似文献