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11.
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
12.
Direct displacement-based design of seismically isolated bridges 总被引：1，自引：1，他引：0
A Displacement-Based Design (DBD) procedure for bridges equipped with different seismic Isolation Systems (IS’s) is proposed.
It has been derived from the Direct DBD method recently developed by Priestley and co-workers. The key aspect of the proposed
procedure is the definition of a uniform target displacement of the deck, which is assigned by the designer to accomplish
a given performance level, expressed through limit values of the maximum IS displacement and of the pier drift, respectively.
The proposed design procedure has been developed for four different idealized force-displacement cyclic behaviours of IS’s,
which can be used to describe the response of a wide variety of IS’s, including: (i) Lead-Rubber Bearings (LRB), (ii) High-Damping
Rubber Bearings (HDRB), (iii) Friction Pendulum Bearings (FPB), (iv) Combinations of either Low-Damping Rubber Bearings (LDRB)
or FPB and Viscous Dampers (VD), (v) Combinations of lubricated Flat Sliding Bearings (FSB) and LDRB, (vi) Combinations of
FSB and Steel Yielding Devices (SYD), (vii) Combinations of FSB, Shape Memory Alloy (SMA)-based Re-centring Devices and VD.
In the paper, the background and implementation of the design procedure is presented first, then some validation studies through
nonlinear time-history analyses on different configurations of continuous deck and multi-span simply supported deck bridges
are illustrated. 相似文献
13.
Donatello Cardone Mauro Dolce Giuseppe Gesualdi 《Bulletin of Earthquake Engineering》2009,7(3):801-834
This paper presents a new approach for the evaluation of accurate lateral force distributions for the Linear Static Analysis
(LSA) of Base Isolated (BI-) buildings. In essence, the proposed lateral force distributions depend on a factor measuring
the degree of non- linearity of the Isolation System (IS) and on the ratio between the effective period of the BI-structure
(Tis) and the fundamental period of the Fixed Based (FB-) structure (Tfb). The proposed approach is fully compatible with the Direct Displacement-Based Design (DDBD) method, recently developed by
Priestley and co-workers. The proposed lateral force distributions have been derived from the results of a large number of
Nonlinear Time-History Analyses (NTHA), carried out on six numerical models of multi-storey buildings, differing in storey
number (3, 5 and 8, respectively) and fundamental period of vibration (from 0.25 to 0.8 s) in the fixed-base configuration.
A great variety of Isolation Systems (ISs), characterised by either Elasto-Plastic with Hardening (EPH) or Flag-Shaped (FS)
force-displacement behaviour, have been considered in the NTHA. The numerical parameters of the IS models have been varied
in such a way as to reproduce the actual mechanical behaviour of the main currently used ISs, including: (i) Lead Rubber Bearings
(LRB), (ii) High-Damping Rubber Bearings (HDRB), (iii) Friction Pendulum Bearings (FPB), (iv) combinations of flat Sliding
Bearings (SB) and Low-Damping Rubber Bearings (LDRB) and (v) Combinations of flat SB and re-centring devices based on Shape
Memory Alloys (SMA). Comparisons between the storey shear forces derived with the proposed method and those obtained from
NTHA clearly show the great improvements in the accuracy of LSA predictions, when using the proposed lateral force distributions. 相似文献
14.
We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in
the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the
non-linear one, for redshifts larger than one. 相似文献
15.
16.
Mauro Dolce Donatello Cardone Giuseppe Palermo 《Bulletin of Earthquake Engineering》2007,5(4):491-509
Three different isolation systems (IS’s) for bridges and viaducts are considered in the present study. All of them are made
of steel-PTFE sliding bearings (SB) to support the weight of the deck and auxiliary devices, based on different technologies
and materials (i.e. rubber, steel and shape memory alloys), to provide re-centring and/or additional energy dissipating capability.
An extensive numerical investigation has been carried out in order to (i) assess the reliability of different design approaches,
(ii) compare the response of different types of IS’s, (iii) evaluate the sensitivity of the structural response to friction
variability due to bearing pressure, air temperature and state of lubrication and (iv) identify the response variations caused
by changes in the ground motion, bridge and isolation characteristics. The nonlinear time-history analyses have been carried
out using a simplified pier-deck model, where the pier is modelled as an elastic cantilever beam and the mass of the deck
is connected to the pier through suitable nonlinear elements, simulating the behaviour of the IS. Both artificial and natural
seismic excitations have been used in the nonlinear dynamic analyses. 相似文献
17.
Displacement limits and performance displacement profiles in support of direct displacement‐based seismic assessment of bridges 
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下载免费PDF全文 Donatello Cardone 《地震工程与结构动力学》2014,43(8):1239-1263
Displacement limits and performance displacement profiles (PDPs) for the direct displacement‐based assessment of existing bridges are proposed. The PDPs are defined as the bridge inelastic deformed shapes associated with the attainment of selected damage states in some critical elements of the bridge. In the paper, displacement limits are provided for piers, abutments, joints, bearing devices and shear keys. Moreover, different approaches for the definition of the PDP are examined, including adaptive pushover analysis, effective modal analysis, and rational analysis of simplified bridge models. In the paper, the key aspects and modeling assumptions of the proposed direct displacement‐based assessment procedure are presented first. This is followed by some examples of application to typical Italian highway bridge configurations, differing in pier layout, deck type, and pier‐deck connections. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
High-damping response spectra are essential tools for the assessment and design methods based on the equivalent elastic structure
concept. They are also often used for the analysis and design of structures with seismic isolation or energy dissipation systems.
Many formulations of the reduction factors have been proposed and included in seismic codes to estimate high-damping response
spectra from their 5% damping representation. They are reviewed in the present paper. The accuracy of each of them in estimating
the maximum elastic response of structures with viscous damping ratios greater than 5% is assessed by comparing exact and
approximate displacement response spectra for three different damping levels, namely 10, 20 and 30%, respectively. The comparison
is referred to more than 120 ground motion records, relevant to earthquakes with magnitude between 6 and 8, epicentral distance
ranging from 1 to 100 km and Peak Ground Accelerations (PGA’s) greater than 0.1 g. The comparison between exact and approximate
response spectra is carried out for both single earthquakes and groups of earthquakes with similar magnitude and epicentral
distance. The drawbacks of using the same damping reduction factor to estimate both maximum displacement response and design
seismic forces are also addressed. 相似文献
19.
Two families of passive seismic control devices exploiting the peculiar properties of shape memory alloy (SMA) kernel components have been implemented and tested within the MANSIDE project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are special braces for framed structures and isolation devices for buildings and bridges. Their most important feature is their extreme versatility, i.e. the possibility to obtain a wide range of cyclic behaviour — from supplemental and fully re‐centring to highly dissipating — by simply varying the number and/or the characteristics of the SMA components. Other remarkable properties are their extraordinary fatigue resistance under large strain cycles and their great durability and reliability in the long run. In this paper, the working mechanisms of the SMA based devices are outlined and the experimental tests carried out to verify the above‐mentioned properties are extensively described. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
20.
Rossella Baldacconi Frine Cardone Caterina Longo Maria Mercurio Carlotta Nonnis Marzano Elda Gaino Giuseppe Corriero 《Marine Ecology》2010,31(2):309-317
The present study focuses on the reproductive success of transplants of the bath sponge Spongia officinalis Linnaeus, 1759, with the aim of investigating the possibility of restocking this species, one of the most endangered organisms of the Mediterranean sessile zoobenthos. Transplants of S. officinalis, collected from a wild population along the Apulian coasts (Ionian Sea, Italy), have been moved into an area where the species was present in the past. The transplants consisted both of specimens in toto and of fragments of different sizes, obtained after having cut the mother sponge into pieces. All transplanted sponges showed complete cicatrisation of the cut surfaces within a month of the initial manipulation and had a survival rate of 100% throughout the 12 months of the study. From the present investigation, it has emerged that the reproductive effort and the larval release by the transplants do not differ significantly from those shown by the source population. This successful technical approach supports its application as a strategy for restocking the population of this endangered species. 相似文献