Response prediction,experimental characterization and P‐spectra design of frames with viscoelastic–plastic dampers          下载免费PDF全文

Jack Wen Wei Guo  Constantin Christopoulos 《地震工程与结构动力学》2016,45(11):1855-1874

Viscoelastic–plastic (VEP) dampers are hybrid passive damping devices that combine the advantages of viscoelastic and hysteretic damping. This paper first formulates a semi‐analytical procedure for predicting the peak response of nonlinear SDOF systems equipped with VEP dampers, which forms the basis for the generation of Performance Spectra that can then be used for direct performance assessment and optimization of VEP damped structures. This procedure is first verified against extensive nonlinear time‐history analyses based on a Kelvin viscoelastic model of the dampers, and then against a more advanced evolutionary model that is calibrated to characterization tests of VEP damper specimens built from commercially available viscoelastic damping devices, and an adjustable friction device. The results show that the proposed procedure is sufficiently accurate for predicting the response of VEP systems without iterative dynamic analysis for preliminary design purposes. A design method based on the Performance Spectra framework is then proposed for systems equipped with passive VEP dampers and is applied to enhance the seismic response of a six‐storey steel moment frame. The numerical simulation results on the damped structure confirm the use of the Performance Spectra as a convenient and accurate platform for the optimization of VEP systems, particularly during the initial design stage. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A cantilever beam analogy for quantifying higher mode effects in multistorey buildings          下载免费PDF全文

Lydell Wiebe  Constantin Christopoulos 《地震工程与结构动力学》2015,44(11):1697-1716

This paper examines higher mode effects in systems where the ductile mechanism for seismic design is the base moment‐rotation response. The modal properties of flexural and shear beams with uniform mass and elasticity and with a variable amount of base rotational restraint are derived. As the base fixity is released, the first mode becomes the rigid body rotation of the beam about the base, but the higher modes change much less, particularly for the shear beam model. Most response quantities that are of interest in the seismic design of typical mid‐rise buildings are controlled by the first two lateral modes, except at locations along the height where the second mode contributes little. However, the third and higher lateral modes are more significant for high‐rise buildings. Based on the theory of uniform cantilever shear beams, expressions are developed to avoid the need for a modal analysis to estimate the overturning moment, storey shear, and floor acceleration envelopes. Considering the measured response from the shake table testing of a large‐scale eight‐storey controlled rocking steel braced frame, the proposed expressions are shown to be of similar or better accuracy to a modified modal superposition technique, which combines the higher mode response from an elastic modal analysis with the response associated with achieving the maximum base overturning moment according to an inverted triangular load distribution. Because the proposed method uses only parameters that are available at the initial design stage, avoiding the analysis of a structural model, it is likely to be especially useful for preliminary design. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Diagnosing Non-Meteorically Induced Variations in the Chemistry of Saline Springs of the Vrancea Seismic Area (Romania)     

Horia Mitrofan  Constantin Marin  Alin Tudorache  Mădălina Vişan 《Pure and Applied Geophysics》2014,171(9):2315-2338

A monitoring operation conducted over more than seven years has been addressing chemical fluctuations displayed by several cool, low-discharge springs located close to the highly seismic Vrancea area (Romania). Those outflows compositions proved to be strongly controlled by binary, essentially isochemical mixing between a deep-origin brine and meteoric freshwater. By taking advantage of this particular setting, there have been constructed diagrams aimed at investigating how the groundwater-discharges Na–K–Mg geothermometric parameters fluctuated as a function of the chloride content (taken to be an estimator of the freshwater-induced dilution). We made use of the reciprocal algebraic relationships existing between the equations describing the Na–K–Mg geothermometric parameters “Na–K temperature” and “K–Mg temperature” on the one hand, and the so-called “maturity index” (MI) on the other. In an accordingly derived plot of MI against the logarithm of the chloride concentration, a series of data-points being quite uniformly off-set from the MI dilution-curve constructed for an apparently “regular” period, suggested that, episodically, all concerned springwaters were simultaneously subject to some similar changes in the controlling geochemical processes. One such modification intervened 3–4 months before the occurrence of the strongest earthquake ( \(M_{\text{w}} = 5.8\) ) of the hydrochemical monitoring period. The consequently derived interpretation was that then, the numerical values of certain geothermometric coefficients were likely altered: such a process could be consistent with changes in the alkali feldspars solubility relationships, possibly in response to episodic Al–Si complexing which might develop within a hypothesised, still active, exhumation-channel.  相似文献   

A framework for addressing health disparities in vulnerable populations with the help of Esri Community Analyst     

Camelia Maria Kantor  Veronica Constantin 《GeoJournal》2017,82(1):1-8

Increasingly, health outcomes are tied to nutritional opportunities based on the availability of foods and cultural patterns of consumption. This paper demonstrates how Esri Community Analyst can help in identifying at-risk communities. The methodology that results argues a means by which national data made available by Esri in a “one-stop shop” can be utilized in a simplified, user-friendly way to identify specific populations with higher prevalence of certain diseases and areas where nutritional needs are likely unmet. For demonstration purposes, this paper presents a case study for South Carolina, USA.  相似文献   

Comparison of aquifer vulnerability assessment techniques. Application to the Néblon river basin (Belgium)     

Radu?Constantin?GoguEmail author  Vincent?Hallet  Alain?Dassargues 《Environmental Geology》2003,44(8):881-892

Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of Belgium. The basin covers about 65 km² and the karst aquifer provides a water-supply of about 28,000 m³d^-1. The methods tested were: EPIK (Doerfliger et al. 1999), DRASTIC (Aller et al. 1987), 'German method' (von Hoyer and Söfner 1998), GOD (Foster 1987) and ISIS (Civita and De Regibus 1995). The results are compared and critically examined. From the analysis, it seems that reducing the number of parameters is unsatisfactory, due to the variety of geological conditions. The various methods produce very different results at any given site. As only physically-based methods can be checked for their reliability, it is clear that future vulnerability mapping techniques must incorporate such methods.  相似文献   

The Holocene vegetation history of the Khibiny Mountains: implications for the post‐glacial expansion of spruce and alder on the Kola Peninsula,northwestern Russia     

Constantin Kremenetski  Tatiana Vaschalova  Leopold Sulerzhitsky 《第四纪科学杂志》1999,14(1):29-43

Pollen and peat botanical investigations of the Lutnermayok peat bog, Kola Peninsula, northwestern Russia, were carried out, and 21 surface pollen samples were studied. Combined with previous studies our data form the basis for the vegetation history over the last 7000 yr of the Khibiny Mountains. Pinus sylvestris was the dominant species between 7000 and 5000 yr BP and Picea obovata penetrated to the Khibiny Mountains ca. 5500/5300 yr BP. Since 4500 yr BP, Picea replaced Pinus in major parts of the area and dominated the forest cover. Picea immigrated to the Kola Peninsula after 7000 yr BP. There were two paths of spruce migration: from the southeast and the southwest. Grey alder, Alnusincana, immigrated to the Kola Peninsula from the southwest and northwest about ca. 8000 yr BP. Grey alder has been restricted to its modern range since 4000 yr BP. The range of vertical movement of the treeline in Khibiny Mountains during the last 700 yr was 240–260 m, which corresponds to an amplitude of summer temperature change of 2°C. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Contrasting volcanic-tectonic processes during the past 2 Ma on the Mid-Atlantic Ridge: submersible mapping,petrological and magnetic results at lat. 34°52′ N and 33°55′ N     

Bideau  Daniel  Hékinian  Roger  Sichler  Bertrand  Gràcia  Eulàlia  Bollinger  Claire  Constantin  Marc  Guivel  Christelle 《Marine Geophysical Researches》1998,20(5):425-458

In August–September of 1995, 20 Nautile dives and detailed magnetic surveys (spaced every 1.8 km) were undertaken on two segments of the Mid-Atlantic Ridge between the Oceanographer and Hayes fractures zones. These two segments are only 65 km apart and show strong morphology and gravity contrasts. OH1 is shallower and has a large mantle Bouguer anomaly (MBA) bull's eye, whereas OH3 is deeper and has a smaller MBA bull's eye.Thirteen dives were devoted to segment OH1. The Median Ridge (MR) located on the central high (1700 m deep) is topped by 100 to 300 m high circular volcanoes. The volcanics consists mainly of porphyritic and/or vesicular pillows and volcaniclastics. The NVZ (2200 m deep), located in the valley floor east of the MR, consists of near aphyric fluid lava flows. A chain of off-axis volcanoes, displaying a magnetic continuity with surroundings, extends on both sides of the axis. Three volcanoes on the east side and one on the west side of the axis were explored and sampled by submersible. The off-axis increase of weathering, Fe-Mn coating and magnetic signature suggest that the volcanoes were built at or near the ridge axis. The spacing of NS elongated hills bearing circular volcanoes and separated large magnetic signature (2 to 4 km) depressions suggests that several similar volcanic events occured during the past 2 Ma. The last 1 Ma episode involves (1) the construction of an axial ridge (MR) by fissure eruptions and the formation of circular summit volcanoes by focused volcanism, and (2) the extrusion of fluid magma in the depressions formed by further fissuring and faulting of the MR.  相似文献   

Uncoupled rocking and shear base-mechanisms for resilient reinforced concrete high-rise buildings     

Fei Tong  Constantin Christopoulos 《地震工程与结构动力学》2020,49(10):981-1006

High-rise buildings are an efficient solution to meet the housing challenges of global urbanization that is happening at an incredible pace. Code-based seismic design philosophies are aimed at achieving collapse-prevention under major earthquakes, implying extensive structural damage associated with important losses. A number of high-performance systems have been investigated for enhancing the resilience of high-rise buildings whose design is especially challenging due to higher-mode effects even when a flexural mechanism is formed at the base of the structure. To this end, this paper proposes a new concept consisting of a three-dimensional uncoupled rocking and shear mechanism system for high-rise buildings where reinforced concrete (RC) core walls are used as the lateral-force-resisting system. The proposed system provides a dual-mechanism at the base that independently limits both overturning moments (OTMs) and shear forces and thus more effectively mitigates higher-mode effects. The characteristic mechanics of the proposed system are first studied through an idealized model. A physical embodiment is then designed, detailed, and validated through advanced models and extensive nonlinear dynamic analyses. A 42-story RC core-wall building that is located in Los Angeles and was studied as part of the PEER Tall Buildings Initiative is used as a reference structure in this study. Results confirmed that the proposed system eliminates damage at the base of the walls and minimizes the inelastic demands over the height of the building. In a general sense, the proposed concept provides a framework in which the intended dual mechanism can be implemented to a wider range of high-rise structures.  相似文献   

Real-time hybrid simulation of structures equipped with viscoelastic-plastic dampers using a user-programmable computational platform     

Jack Wen Wei Guo  Ali Ashasi-Sorkhabi  Oya Mercan  Constantin Christopoulos 《地震工程与工程振动(英文版)》2017,16(4):693-711

A user-programmable computational/control platform was developed at the University of Toronto that offers real-time hybrid simulation (RTHS) capabilities. The platform was verified previously using several linear physical substructures. The study presented in this paper is focused on further validating the RTHS platform using a nonlinear viscoelastic-plastic damper that has displacement, frequency and temperature-dependent properties. The validation study includes damper component characterization tests, as well as RTHS of a series of single-degree-of-freedom (SDOF) systems equipped with viscoelastic-plastic dampers that represent different structural designs. From the component characterization tests, it was found that for a wide range of excitation frequencies and friction slip loads, the tracking errors are comparable to the errors in RTHS of linear spring systems. The hybrid SDOF results are compared to an independently validated thermalmechanical viscoelastic model to further validate the ability for the platform to test nonlinear systems. After the validation, as an application study, nonlinear SDOF hybrid tests were used to develop performance spectra to predict the response of structures equipped with damping systems that are more challenging to model analytically. The use of the experimental performance spectra is illustrated by comparing the predicted response to the hybrid test response of 2DOF systems equipped with viscoelastic-plastic dampers.  相似文献   

Sensitivity analysis for the EPIK method of vulnerability assessment in a small karstic aquifer, southern Belgium   总被引：5，自引：0，他引：5  

Radu Constantin Gogu  Alain Dassargues 《Hydrogeology Journal》2000,8(3):337-345

Applying the EPIK parametric method, a vulnerability assessment has been made for a small karstic groundwater system in southern Belgium. The aquifer is a karstified limestone of Devonian age. A map of intrinsic vulnerability of the aquifer and of the local water-supply system shows three vulnerability areas. A parameter-balance study and a sensitivity analysis were performed to evaluate the influence of single parameters on aquifer-vulnerability assessment using the EPIK method. This approach provides a methodology for the evaluation of vulnerability mapping and for more reliable interpretation of vulnerability indices for karst groundwater resources. Received, March 1999/Revised, December 1999, February 2000/Accepted, February 2000  相似文献