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1.
Viscous and other damping devices are often used as elements of seismic isolation systems. Despite the widespread application of nonlinear viscous systems particularly in Japan (with fewer applications in the USA and Taiwan), the application of viscous damping devices in isolation systems in the USA progressed intentionally toward the use of supplementary linear viscous devices due to the advantages offered by these devices. This paper presents experimental results on the behavior of seismically isolated structures with low damping elastomeric (LDE) and single friction pendulum (SFP) bearings with and without linear and nonlinear viscous dampers. The isolation systems are tested within a six‐story structure configured as moment frame and then again as braced frame. Emphasis is placed both on the acquisition of data related to the structural system (drifts, story shear forces, and isolator displacements) and on non‐structural systems (floor accelerations, floor spectral accelerations, and floor velocities). Moreover, the accuracy of analytical prediction of response is investigated based on the results of a total of 227 experiments, using 14 historic ground motions of far‐fault and near‐fault characteristics, on flexible moment frame and stiff braced frame structures isolated with LDE or SFP bearings and linear or nonlinear viscous dampers. It is concluded that when damping is needed to reduce displacement demands in the isolation system, linear viscous damping results in the least detrimental effect on the isolated structure. Moreover, the study concludes that the analytical prediction of peak floor accelerations and floor response spectra may contain errors that need to be considered when designing secondary systems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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The Chichontepec volcano is a Plio-Pleistocene composite volcano that erupted lavas ranging from high-alumina basalts to dacites. It experienced a caldera-forming paroxysmal eruption during the early Pleistocene. Pre-caldera lavas are mildly tholeiitic and they evolved mainly by low pressure crystal fractionation, notwithstanding the fact that most mafic lavas (low-MgO high-alumina basalts) retain traces of polybaric evolution. Conversely, post-caldera lavas, which are mainly pyroxene andesites, are clearly calc-alkaline, having evolved by open-system crystal fractionation. Sr–Nd isotopic data and trace elements characteristics indicate that the same mantle source was involved in the petrogenesis of these series. Modelling the AFC process showed that it did not play any role in the petrogenesis of these rocks; a crystal fractionation model is considered to be more relevant. A slight variation in the fractionating assemblage could have caused the transition from an early mildly tholeiitic trend to a late calc-alkaline one. Mineralogical evidence, mass-balance calculations and elemental chemistry support this hypothesis, assuming that the greater amount of pyroxene on the liquidus is at the expense of plagioclase; this would have prevented the trend in iron enrichment. 相似文献
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The seismic performance of a steel framed structure equipped with (i) friction damping devices and (ii) base isolators is compared. A parametric study based on energy concepts is performed first using time-history dynamic analysis to determine the optimum properties of the two systems when excited by an earthquake whose energy is distributed over a relatively broad frequency band (1940 El Centro, N-S). Using these same properties, the responses of the two structural systems are then examined when excited by earthquakes whose power content essentially is concentrated at the low frequency end of the energy spectrum (1977 Romania, Bucharest, N-S and 1985 Mexico, SCT E-W). The results of the study show that, while both systems similarly reduce the response of conventional structures to the California earthquake, the friction damped structure exhibits a superior performance under the low frequency earthquakes. Very large shear forces and displacements are observed when the Romania and Mexico earthquakes are applied to the base isolated structure, indicating that the performance of a base isolated structure depends on the characteristics of the site earthquake. By comparison, friction damped structures are shown to behave favourably under the three earthquakes studied; this suggests that friction damping devices offer a more consistent way of protecting structures during earthquakes. 相似文献
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The upper part of the Deccan Traps sequence (Bushe to Mahabaleshwar Formations) shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials. This is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation (AFC). The observed correlations (e.g. between Mg-number and Sr isotope initial ratios) are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence, while contaminant availability declines in the upper part. It is probable, however, that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes, a process during which fractional crystallisation is suppressed by magmatic turbulence. The absence of AFC relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber. Other continental flood basalt provinces such as the Parana and Etendeka do show AFC relationships, and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent. 相似文献
6.
This study proposes two types of shape memory alloy (SMA)‐based devices, the tension‐SMA device (TSD) and the scissor‐SMA device (SSD), for the increase of stiffness. Both devices employ superelastic NiTi wires with a diameter of 1.2 mm. Performance tests to study pseudoelastic behavior of NiTi wires find that NiTi wire's pseudoelastic property is insensitive to loading frequency within the meaningful frequency range of most structures in civil engineering. The detailed design of TSD and SSD using NiTi wire is then presented accordingly. Shaking table tests of a scaled 5‐story steel frame incorporated with TSDs and SSDs, respectively, in the first story are carried out. The experimental results indicate that both SMA devices can effectively reduce building seismic response. SSDs achieve greater response reduction than TSDs due to their displacement magnification configuration. The seismic response of the building model with and without SMA devices is numerically simulated and the simulation results demonstrate that they are in good agreement with the experimental results. Finally, it is identified that by using the wavelet transform method the structures incorporated with SMA devices exhibit nonlinear behavior and the time‐dependent characteristics of natural frequency during earthquake excitation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Hydraulic characterization and hydrological behaviour of a pilot permeable pavement in an urban centre,Brazil 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Artur Paiva Coutinho Laurent Lassabatere Suzana Montenegro Antônio Celso Dantas Antonino Rafael Angulo‐Jaramillo Jaime J. S. P. Cabral 《水文研究》2016,30(23):4242-4254
Considering all the alterations on hydrology and water quality that urbanization process brings, permeable pavement (PP) is an alternative to traditional impermeable asphalt and concrete pavement. The goal of the PP and other low impact development devices is to increase infiltration and reduce peak runoff flows. These structures are barely used in Brazil aiming stormwater management, one of the big hydrological issues in cities throughout the country, with increasing urbanization rates. The main objective of this paper is the hydraulic characterization of a PP and the assessment of its hydrological efficiency from the point of view of the infiltration process. The study focuses on a pilot area in a parking lot in an urban area (Recife, Brazil). Soil elements filling the voids between concrete elements were sampled (particle size density, water contents) and tested with water infiltration experiments at several points of the 3 m × 1.5 m surface pilot area. Beerkan Estimation of Soil Transfer parameters algorithm was applied to the infiltration experiment data to obtain the hydraulic characteristics of the soil composing the PP surface layer, the concrete grid pavers (with internal voids filled with natural soil) permeability being neglected. Results show that the soil hydraulic characteristics vary spatially within the pilot area and that the soil samples have different hydraulic behaviours. The hydraulic characteristics derived from Beerkan Estimation of Soil Transfer parameters analysis were implemented into Hydrus code to simulate runoff, infiltration and water balance over a year. The numerical simulation showed the good potential of the PP for rainfall–runoff management, which demonstrates that PP can be used to retrofit existing parking infrastructure and to promote hydrological behaviour close to natural soils. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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《Journal of Volcanology and Geothermal Research》2004,129(1-3):155-172
When a hot basaltic magma is emplaced into continental crust or a pre-existing silicic magma chamber, the processes of assimilation with fractional crystallization (AFC) are likely to control the liquid line of descent of the magma. These processes are particularly important at the floor of the magma chamber because evolved light liquids generated by floor melting readily mix with the overlying basaltic magma. In order to clarify the effects of temperature and composition of the floor on the AFC processes, we experimentally investigated simultaneous melting and crystallization of a NH4Cl–H2O binary eutectic system. In the experiments, evolution of temperature and compositional profiles of a hot solution overlying a cold solid mixture of variable initial temperatures and compositions were measured. The initial NH4Cl concentrations of solid and liquid are chosen to be higher than the eutectic composition, such that the density change of the experimental material by crystallization and melting is qualitatively the same as that of natural magmas and crusts. The results show that a mushy layer forms at the floor due to simultaneous crystallization and (partial) melting and that the liquid evolves due to mixing with liquids released by crystallization and melting. The ratio of melting mass to crystallization mass (M/C ratio) depends on the initial floor temperature and composition. As the initial floor temperature decreases, the rate of melting largely decreases, so that the M/C ratio becomes smaller. As the initial NH4Cl concentration of the solid floor decreases, the degree of partial melting of the floor increases; however, it does not necessarily result in an increase in the M/C ratio. The higher melt fraction of the mushy layer increases permeability within the mushy layer, so that vertical exchange between the liquid in the mushy layer and the more concentrated overlying liquid is enhanced. This effect promotes crystallization in the mushy layer, and decreases the M/C ratio. It is suggested that the M/C ratio during AFC processes depends on details of the mixing process in the liquid layer such as spacing and meandering of buoyant plumes. 相似文献
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Triangular-plate added damping and stiffness(TADAS) devices are reliable metallic energy dissipaters for seismic upgrading used in design and retrofitting of civil structures. Conventional TADAS devices are designed with closedended slots. In this study, a modified form of the TADAS device is proposed with open-ended slots in order to reduce the manufacture cost, facilitate the assembling and avoid abrupt stiffness increase. Cyclic and monotonic loading tests are then conducted to investigate the mechanical characteristics of the modified TADAS devices with regular Q345 steel and lowyield point LY160 steel triangular plates. The test results show that although the hysteresis performances are stable, the cyclic hardening behavior is different between the TADAS specimens with different grades of steel. The TADAS specimen with LY160 triangular plates exhibits more significant overstrength behavior than the one with Q345 triangular plates in cyclic loading, which is unsuitable to be described by the classic Bouc-Wen model. Therefore, a modified Bouc-Wen model is proposed to describe such overstrength behavior. It is shown that the modified model is able to simulate different extent of overstrength behavior in cyclic loading, based on which the cyclic hardening behavior of the TADAS specimen with LY160 triangular plates can be well described. 相似文献
10.
Control devices incorporated with shape memory alloy 总被引：1，自引：1，他引：1
Shape Memory Alloy (SMA) is a type of material that offers some unique characteristics for use in devices for vibration control applications. Based on SMA's material properties, four types of control devices that incorporate NiTi SMA wires are introduced in this paper, which include three types of dampers (SMA damper, SMA-MR damper and SMA-friction damper) and one kind of isolation bearing (SMA-rubber bearing). Mechanical models of these devices and their experimental verifications are presented. To investigate the control performance of these devices, the SMA-MR damper and SMA-rubber bearing are applied to structures. The results show that the control devices could be effective in reducing the seismic response of structures. 相似文献
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In the present study, the seismic behavior of steel–concrete composite structures isolated by base-isolation devices under near-fault earthquake excitations is numerically investigated. The seismic analysis is performed by means of the static non-linear (pushover) analysis procedure conducted on two five-storey three-dimensional (3-D) buildings with steel columns and steel–concrete composite slabs and beams. The present 3-D building examples are assumed to be located at a near-fault area in order to take into account the effect of strong ground motion on the isolation devices. The results of this study allowed the verification of the adequacy of the attachment isolation system as well as the comparison of the behavior of the seismic-protected building with or without bracings to the unprotected buildings with or without bracings, showing the benefits of the application of the isolation devices, the limitations and the characteristics of their performance. 相似文献
13.
A 3D finite element (FE) model for the Sutong cable-stayed bridge (SCB) is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges. 相似文献
14.
斜拉桥在横桥向采用塔-梁、墩-梁固结的约束体系,导致其整体刚度增加,地震惯性力增大,给边墩及其基础的抗震设计造成困难。分别采用位移相关型(方案1)和速度相关型(方案2)两类减震装置对一座斜拉桥的横桥向进行了减震研究。方案1在边墩-主梁间设置位移相关型减震装置,并对其屈服荷载进行了参数分析;方案2对速度相关型减震装置的安装位置和数量进行了优化分析,并对其参数取值进行了参数分析;对横桥向固结体系和减震体系的地震反应进行了对比。结果表明:地震作用下两类减震装置发生滞回变形,延长了结构在横桥向的周期,有效降低了边墩的地震剪力和弯矩反应;横桥向墩-梁间的相对位移会增大,可通过减震装置参数的选取将其控制在合理的范围内;塔底的地震剪力和弯矩反应变化不明显。2种方案均可用于斜拉桥横向减震。 相似文献
15.
《地震工程与工程振动(英文版)》2015,(3)
A comparative analytical study of several control strategies for semi-active(SA) devices installed in baseisolated buildings aiming to reduce earthquake induced vibrations is presented.Three force tracking schemes comprising a linear controller plus a "clipped" algorithm and a nonlinear output feedback controller(NOFC) are considered to tackle this problem.Linear controllers include the integral controller(I),the linear quadratic regulator(LQR) and the model predictive controller(MPC).A single degree-of-freedom system subjected to input accelerograms representative of the Portuguese seismic actions are first used to validate and evaluate the feasibility of these strategies.The obtained results show that structural systems using SA devices can in general outperform those equipped with passive devices for lower fundamental frequency structural systems,namely base-isolated buildings.The effectiveness of the proposed strategies is also evaluated on a 10 storey base-isolated dual frame-wall building.The force tracking scheme with an integral controller outperforms the other three as well as the original structure and the structure equipped with passive devices. 相似文献
16.
Chang-Hwa Chen Setsuya Nakada Yuch-Ning Shieh Donald J. DePaolo 《Journal of Volcanology and Geothermal Research》1999,89(1-4)
The magma generation at Unzen volcano may be considered as the product of crustal material mixed with mantle magma accompanied by fractional crystallization (AFC). The magma in the Unzen volcano is estimated to consist of about 50–80% of residual magma (F) and about 30–70% assimilated crustal material (A) relative to the original magma. Concerning the 1991–1995 eruption, it is estimated that the magma formed as the result of mixing of about 50–60% crustal material and about 55–65% of residual magma. An alternative magma eruption model for the 1991–1995 eruption is proposed here. In the early stage, the isotopic characteristics of 1991 eruption are defined by AFC process in the deeper magma chamber. Later, the magma ascended through the conduit and quiescently stayed for a long time in a shallow reservoir before eruption. The minerals continuously crystallized as phenocrysts especially at the chilled top and outer margin in the shallow chamber. The crystallized phenocryst mush was reworked into the central part of the magma chamber by means of magma convection and rapid magma ascent. Therefore, the reaction between phenocrysts and melt occurs only in internal chemical disequilibrium in the magma chamber. In contrast, the isotopic compositions of the original magma shall be little influenced by the above processes throughout its eruptive history. The 1991–1995 eruptive rocks of the Unzen volcano show their characteristics in Sr and Nd isotopic values independent of their two previous eruptions. However, the isotopic values of early eruptive product could represent the original magma value. This result also supports the previous work of Chen et al. (1993) [Chen, C.H., DePaolo, D.J., Nakada, S., Shieh, Y.N., 1993. Relationship between eruption volume and neodymium isotopic composition at Unzen volcano. Nature 362, 831–834], that suggested the Nd of early or precursory eruptive products could be a qualitative indicator of the maximum size of a continuing or impending eruption. 相似文献
17.
Passive high force‐to‐volume (HF2V) dampers offer significant displacement reduction and energy dissipation, but cannot customise overall response. Semi‐active resettable devices offer adaptive, custom hysteresis loops that reduce displacement and base shear, but have limited dissipation. This paper presents a new, combined concept to maximise displacement reduction without increasing base shear – a net‐zero base‐shear concept. HF2V devices, up to a maximum of 10% structural weight, are combined with fixed stiffness resettable devices. Spectral analyses are run for the three SAC ground motion suites that iteratively size the HF2V device at each structural period to achieve maximum displacement reductions without increasing median base shear. HF2V velocity dependence and the need to scale HF2V capacity to spectral velocity are examined in terms of their impact on the results of these analyses. The net‐zero approach reduces base shear by up to 50% and displacements by 30–70% over all ground motions, exceeding reductions obtained by either device separately by 30–50% (relative). The net‐zero condition is not reached within the device limits defined, except at relatively long periods (>3.5 s) because of a virtuous circle of reduced displacement from the resettable and HF2V devices outweighing the increased base shear from the HF2V devices alone. These results are independent of HF2V device scaling, design and velocity dependence. The overall net‐zero concept offers a significant advantage in a combination that cannot be achieved by passive or semi‐active solutions alone. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Mafic enclaves in the rhyolitic products of Lipari historical eruptions; relationships with the coeval Vulcano magmas (Aeolian Islands, Italy) 总被引：1，自引：0，他引：1
The recent finding of mafic enclaves in the Rocche Rosse (RR) lava flow, the last magmatic product on Lipari (Aeolian Islands,
Italy) (AD 1230 ± 40), opens the possibility to investigate in detail the most recent magmatic system of the island, an important
issue for the volcanic hazard assessment of the area. The RR lava flow is an aphyric rhyolitic coulée consisting of grey and
black pumice and black and grey obsidian. Enclaves have ellipsoidal to spheroidal shape and vary from mm-sized in the central
portion of the flow, to cm-sized, at the top and in the flow front, where they are also more abundant. Enclaves are shoshonitic-latitic
(group A) and trachytic (group B) in composition. The mineralogy of group A consists of dominant clinopyroxene crystals with
minor abundance of feldspar (plagioclase > K-feldspar), olivine and biotite, while group B is composed of feldspar (K-feldspar > plagioclase)
with minor clinopyroxene, olivine and biotite. Geochemical modeling suggests that the host rhyolitic rocks could be the product
of AFC (Assimilation plus Fractional Crystallization) of a magma compositionally similar to the associated shoshonitic-latitic
enclaves, which, in turn, could be obtained, through an AFC process, from the primitive melts erupted as olivine hosted melt
inclusions during the last 15 ka at Vulcano. The already-known last 42 ka relationship between Lipari and Vulcano Islands
is here reinforced until historical time, especially for the last 1 ka. The geochemical and petrological overlap between Lipari
and Vulcano is interpreted to reflect the existence of a similar magmatic system underneath the two islands. The nearly aphyric
RR rhyolites are interpreted to be the products of a superheated (temperature far above the liquidus) and initially water-undersaturated
magma that underwent degassing close to the surface inhibiting microlite crystallization. 相似文献
20.
新型形状记忆合金阻尼器的试验研究 总被引：23，自引：5，他引：23
本文在对形状记忆合金(SMA)的力学性能研究的基础上，设计和制造出一种性能良好的SMA阻尼器，介绍了其工作原理及有关试验结果，将该阻尼器安装在斜拉桥模型上，进行了斜拉桥模型振动试验。试验结果表明该阻尼器的耗能效果明显，在工程结构振动控制方面具有比较好的应用前景。 相似文献