open access

https://doi.org/10.14943/doctoral.k12462

https://hdl.handle.net/2115/63436

積雪寒冷地における低温時免震橋梁の地震応答性状に関する研究

英語

2016-09-26

Hokkaido University

100

tures from damages in earthquakes. It has been extensively used worldwide inrecent years, considering the increasing threat of great earthquakes. The basic strategyof base isolation system is that a structure can be uncoupled from the damagingeffects of the ground movement in a strong earthquake, by taking advantage of theflexibility of base isolation devices, which provides flexibility through its ability todeform and move but return to its original position, i.e., restoring ability.Base isolation devices, which are mainly made of material rubber, havetemperature dependence behavior due to its material characteristics as an elastomertype of polymer. The thermal effect, when applied to polymers, induce a transitionfrom a elastomeric, rubbery phase to a brittle, glassy solid amorphous phase oncooling. Consequently, the stiffness of polymer trends to increase with the decreasingtemperature. With the increment of stiffness of rubber material, the flexibility of baseisolation devices is deteriorated and therefore its seismic protection capability will beweakened.For engineering purposes, cold regions are defined as any region where coldtemperatures, unique terrain, and snowfall significantly affect engineering structuresfor one month or more each year. About one quarter of the earth's land mass may betermed severely cold. Since the area of cold regions unavoidably overlap with seismiczone, i.e. Hokkaido Island of Japan, it is necessary to take account of the lowtemperature effect on base isolation system in seismic response analysis.This study conducts a three-dimensional non-linear numerical analysis toevaluate the seismic performance of curved grillage girder viaducts equipping baseisolation system when it is applied in severe cold environment. For this purpose, afinite element modeling is adopted to examine the seismic response of bridge systemin detail under the action of near-fault earthquake ground motions. Various baseisolation systems which represent various temperature conditions are systematicallycompared and discussed. Temperature effect and temperature variation is taken intoaccount particularly. And for the practicability and preciseness, a dynamic bearingproperty definition method is introduced to carry out the temperature and performancevariation process of base isolation system during earthquake.The temperature effect on lead rubber bearing (LRB) base isolation system is themain focus of this study, since it has been widely applied. Anylytical cases ofhigh-damping bearing (HDR) bearings are also added as comparison. For practice andaccuracy, the parameters of commercial products are adopted, which have beenproved to be proper design under room temperature in previous studied. Nonlineardynamic analysis is performed to obtain structural responses of the viaducts under theinput earthquake waves which are obtained from 1995 Kobe earthquake whichsupposed an inflection point in seismic design of highway bridges in Japan, and 2003Tokachi-oki earthquake which has a much longer duration to raise the temperature ofbearings higher.The main object of this study is to confirm the necessity of considering lowtemperature effect of base isolation system in seismic response analysis. In order toachieve this, a series of numerical results are carried out. Base-isolation bearings withenergy dissipation capacity, demonstrate to be very effective in suppressing excessiveforce responses acting on bridge piers when subjected to strong earthquakes. Based onthe dynamic analysis results, it is found that these types of bearing systems mayprevent structural damage during a seismic event, because their demand-reductionfeatures provide a significant reduction in the seismic forces that the bridge structuremust resist. Moreover, due to an appropriate selection of the design parameters ofthese bearing systems, moderate deformations of isolator devices are observed. Thisresult is significant in that it indicates that LRB base-isolation systems are capable ofcontrolling peak deck displacement response. Whereas cold region factorsconspicuously weaken this base isolation function, which is the main conclusion ofthis study. In this study, by adopting dynamic bearing property definition method andexamining the numerical results, the necessity of considering low temperature effect,not only in a short-duration earthquake, but also in a long-duration earthquake, hasbeen clearly indicated.On the other hand, high damping rubber (HDR) bearing system, which areexpected to be an improvement of LRB system, still keep relatively large area ofhysteresis loops under low temperature. This is because the yield force of HDR ismuch lower than LRB with a lead plug inside. Then HDR could take more advantageof stiffness after yield stage, achieving an overall low stiffness.Temperature dependence performance of base-isolation systems of highwayviaducts offers many possibilities for further research. In the present study, additionalinvestigation has been conducted to study the response of variable performance ofbase isolation system, which is time and temperature dependence. In particular,application of heat conduction technology to different types of base isolation systems,acquiring the accurate temperature value in specified time and finally putting adynamic properties definition of base isolation systems into use in the seismicanalysis.A further area for research concerns more detailed evaluation of HDR bearingsystem in cold region, which has better performance than LRB system in this study.As mentioned above, seismic protection capacity should be balanced withdeformation, which may be the main problem of application of HDR bearing system.It is also suggested to develop more temperature independence isolator devices.Since additional constant temperature equipment for base isolation systems isobviously inefficient, temperature independence materials and structures could be abetter idea. And this is actually being studied by several manufacturers.

2016-09-26

甲第12462号

博士(工学)

(主査) 教授 松本 高志, 教授 上田 多門, 教授 蟹江 俊仁, 教授 菊地 優

工学院（北方圏環境政策工学専攻）

博士論文

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