周旺旺 劉德穩(wěn) 趙潔 陳李昊 劉陽(yáng) 萬(wàn)鋒
摘要:
實(shí)際地震具有多維特性,只考慮水平向作用往往不夠真實(shí)全面,而且遠(yuǎn)場(chǎng)長(zhǎng)周期地震動(dòng)不同于普通地震動(dòng),具有周期長(zhǎng)、持時(shí)長(zhǎng)、低頻成份豐富等特征,對(duì)周期較大的隔震類結(jié)構(gòu)會(huì)產(chǎn)生不利影響,在考慮SSI效應(yīng)(soil-structure interaction,SSI)中尤為復(fù)雜,需深入探討?;诖?,建立大底盤層間隔震結(jié)構(gòu),在三維地震動(dòng)激勵(lì)下,探討普通地震與遠(yuǎn)場(chǎng)長(zhǎng)周期地震對(duì)層間隔震結(jié)構(gòu)的不同影響,并分析考慮SSI效應(yīng)對(duì)結(jié)構(gòu)的不同程度影響。結(jié)果表明:三維地震下,遠(yuǎn)場(chǎng)長(zhǎng)周期對(duì)層間隔震結(jié)構(gòu)產(chǎn)生的地震響應(yīng)遠(yuǎn)大于普通地震;考慮SSI效應(yīng)時(shí),隨著土體變軟,結(jié)構(gòu)響應(yīng)增大;針對(duì)傳統(tǒng)水平隔震支座,在三維遠(yuǎn)場(chǎng)長(zhǎng)周期地震下出現(xiàn)層間位移角和支座位移超限問(wèn)題,設(shè)置三維隔震支座,解決了超限問(wèn)題,分析結(jié)果表明其隔減震效果明顯優(yōu)于傳統(tǒng)水平隔震支座。
關(guān)鍵詞:
層間隔震; 三維地震動(dòng); 遠(yuǎn)場(chǎng)長(zhǎng)周期; SSI效應(yīng); 隔震支座; 地震響應(yīng)
中圖分類號(hào): TU352.1????? 文獻(xiàn)標(biāo)志碼:A?? 文章編號(hào): 1000-0844(2023)02-0362-10
DOI:10.20000/j.1000-0844.20210802001
Seismic response analysis of inter-story isolation structures considering
SSI under three-dimensional far-field long-period ground motions
ZHOU Wangwang1, LIU Dewen1,2, ZHAO Jie1, CHEN Lihao1, LIU Yang3, WAN Feng1
(1. College of Civil Engineering, Southwest Forestry University, Kunming 650000, Yunnan, China;
2. Postdoctoral Research Station, Southwest Forestry University, Kunming 650000, Yunnan, China;
3. College of Civil Engineering, Tongji University, Shanghai 200123, China)
Abstract:
Earthquake excitation is a kind of complicated multi-dimensional motion, so it is not safe and accurate enough to only consider horizontal earthquake excitation. Unlike ordinary ground motions, far-field long-period ground motions have characteristics such as long period, long duration, and rich low-frequency components. They will have adverse effects on structures with large isolation periods. The soil-structure interaction (SSI) is particularly complicated and needs further discussion. Therefore, a large chassis inter-story isolation structure was established in this paper. Under the excitation of three-dimensional ground motion, the different effects of ordinary earthquakes and far-field long-period earthquakes on the inter-story isolation structure were discussed, and the different effects of SSI on the structure were analyzed. The results show that the seismic response of three-dimensional long-period far-field ground motion on the inter-story isolated structure is far greater than that of ordinary ground motion. When the SSI effect is considered, the structural response increases with increasing soil softness. Three-dimensional isolation bearings were set to solve the problems of traditional horizontal isolation bearing under three-dimensional far-field long-period ground motion, i.e., story drift ratio and bearing displacement beyond limits. The analysis results show that the isolation effect of three-dimensional isolation bearings is better than that of traditional horizontal isolation bearings.
Keywords:
inter-story isolation; three-dimensional ground motion; far-field long period; SSI effect; isolation bearing; seismic response
0 引言
層間隔震結(jié)構(gòu)是在基礎(chǔ)隔震結(jié)構(gòu)的基礎(chǔ)上發(fā)展而來(lái)的一種新型隔震結(jié)構(gòu),近年來(lái)成為防災(zāi)減災(zāi)領(lǐng)域的研究熱點(diǎn)之一,兩種隔震結(jié)構(gòu)的對(duì)比如圖1所示。
Wang等[1-2]對(duì)基礎(chǔ)隔震與層間隔震建筑的動(dòng)力性能差異進(jìn)行了試驗(yàn)研究。Skandalos K等[3]利用算法對(duì)層間隔震進(jìn)行了多目標(biāo)優(yōu)化設(shè)計(jì)。Tsuneki Y等[4]指出相對(duì)于基礎(chǔ)隔震,高層建筑層間隔震結(jié)構(gòu)在中間設(shè)置隔震層,上部結(jié)構(gòu)具有較高的抗震能力體系的物理性能。Kim等[5]對(duì)某高層建筑結(jié)構(gòu)進(jìn)行了智能中層隔離控制系統(tǒng)的優(yōu)化設(shè)計(jì),該系統(tǒng)由橡膠軸承和磁流變阻尼器組成,結(jié)果表明該方法能有效地減少地震引起的層間和隔震體位移。目前,層間隔震研究主要集中在普通地震以及少部分的近斷層地震研究[6-8],對(duì)遠(yuǎn)場(chǎng)長(zhǎng)周期地震的研究偏少。周福霖等[9]在中日聯(lián)合考察中記錄了一些典型的長(zhǎng)周期地震,分析指出長(zhǎng)周期地震對(duì)高層建筑的破壞不容忽視,應(yīng)進(jìn)行專項(xiàng)研究。與普通地震動(dòng)作用不同,遠(yuǎn)場(chǎng)長(zhǎng)周期地震易與自振周期大的結(jié)構(gòu)發(fā)生共振,產(chǎn)生不利影響[10-12]。
在考慮土與結(jié)構(gòu)相互作用(soil-structure interaction,簡(jiǎn)寫SSI)的隔震研究體系中,研究主要集中在普通地震,對(duì)于遠(yuǎn)場(chǎng)長(zhǎng)周期地震的研究較少。于旭等[13-14]、朱超等[15]提出了SSI效應(yīng)的能量反應(yīng)平衡方程,基于軟土層地基進(jìn)行了振動(dòng)臺(tái)試驗(yàn)。寶鑫等[16]考慮SSI效應(yīng)對(duì)儲(chǔ)液結(jié)構(gòu)動(dòng)力反應(yīng)的地震影響。李昌平等[17]基于集總參數(shù)模型,建立了考慮SSI的隔震結(jié)構(gòu)模型,并推導(dǎo)出模型動(dòng)力特性參數(shù)的計(jì)算公式。張尚榮等[18]、吳應(yīng)雄等[19]針對(duì)土-結(jié)構(gòu)相互作用對(duì)層間隔震結(jié)構(gòu)進(jìn)行影響分析。
目前,層間隔震技術(shù)在大底盤結(jié)構(gòu)中獲得了廣泛的應(yīng)用,以上均為水平向地震下的隔震結(jié)構(gòu)響應(yīng)研究,但實(shí)際地震具有多維特性,只考慮水平往往不夠真實(shí)全面,可能帶來(lái)安全隱患,而且遠(yuǎn)場(chǎng)長(zhǎng)周期地震動(dòng)不同于普通地震動(dòng),具有周期長(zhǎng)\,持時(shí)長(zhǎng)、低頻成分豐富等特征,對(duì)隔震類周期較大的結(jié)構(gòu)會(huì)產(chǎn)生不利影響,在考慮SSI效應(yīng)中尤為復(fù)雜,值得探討。本文就三維地震動(dòng)激勵(lì)下,選取了3條普通地震與6條遠(yuǎn)場(chǎng)長(zhǎng)周期地震,探討了不同種類地震下對(duì)結(jié)構(gòu)的地震響應(yīng),并分析了考慮SSI效應(yīng)對(duì)結(jié)構(gòu)的不同程度影響。基于此,本文建立了大底盤層間隔震結(jié)構(gòu)模型,進(jìn)行三維地震下考慮SSI層間隔震結(jié)構(gòu)的地震響應(yīng)分析。
1 有限元模型建立
1.1 工程概況
某9層大底盤框架層間隔震結(jié)構(gòu),總高度為34.8 m,跨度為30 m,下部底盤2層高均為4 m,上部塔樓層高均為3.6 m,在底盤與塔樓連接處設(shè)置1.6 m的隔震層。設(shè)防烈度8度,設(shè)計(jì)基本地震加速度值為0.20g,場(chǎng)地類別Ⅱ類,地震設(shè)計(jì)分組第二組。底盤柱尺寸為900 mm×900 mm,梁尺寸為350 mm×700 mm;塔樓柱尺寸為700 mm×700 mm,梁尺寸為300 mm×600 mm。底盤柱、塔樓柱配筋分別為12C32、12C25;底盤梁、塔樓梁配筋均為上部端部6C20、跨中4C20、下部4C20。柱、梁混凝土強(qiáng)度等級(jí)分別為C40、C30,混凝土保護(hù)層厚度為30 mm。大底盤層間隔震結(jié)構(gòu)的3D圖、立面圖如圖2所示。
1.2 模型建立
運(yùn)用有限元軟件ETABS建立大底盤層間隔震
結(jié)構(gòu)模型,隔震支座根據(jù)總水平屈服力為重力荷載標(biāo)準(zhǔn)值下基底豎向反力的2%來(lái)布置,結(jié)構(gòu)角柱隔震支座均使用LRB700鉛芯橡膠隔震支座,邊柱使用LRB600鉛芯橡膠隔震支座,其余柱子使用LNR500橡膠隔震支座,隔震支座參數(shù)如表1所列。梁柱采用空間梁柱單元,樓板采用殼單元,隔震支座采用Isolator單元,C40、C30混凝土采用Takeda滯回類型,HPB300和HRB400鋼筋均采用Kinematic滯回類型??蚣苤捎美w維P-M2-M3鉸,框架梁和連梁兩端采用M3鉸。
1.3 SSI效應(yīng)的實(shí)現(xiàn)
地基土體采用點(diǎn)彈簧進(jìn)行非線性模擬,點(diǎn)彈簧的剛度隨著土的剪切波速及密度的增大而增大,點(diǎn)彈簧的剛度越大,土體越硬,以此模擬不同性質(zhì)的土體。地基土的平動(dòng)剛度kT、平動(dòng)阻尼cT、轉(zhuǎn)動(dòng)剛度k、轉(zhuǎn)動(dòng)系數(shù)c可以按下式計(jì)算[20]:
點(diǎn)彈簧模擬的四種土體參數(shù)如表2所列。
1.4 地震波選取
根據(jù)規(guī)范選取的每類3條地震波,時(shí)程曲線計(jì)算所得的結(jié)構(gòu)底部剪力平均值大于振型分解反應(yīng)譜法計(jì)算結(jié)果的80%。從美國(guó)太平洋地震中心選取6條臺(tái)灣集集遠(yuǎn)場(chǎng)長(zhǎng)周期地震,根據(jù)文獻(xiàn)[21]判別遠(yuǎn)場(chǎng)長(zhǎng)周期地震,其中3條遠(yuǎn)場(chǎng)類諧和長(zhǎng)周期地震波CHY092、ILA004、TCU006,3條遠(yuǎn)場(chǎng)非類諧和長(zhǎng)周期地震波TTN008、KAU015、TAP012,以及三條普通地震遷安波、上海人工波和天津波,三向地震分量的加速度比值按1∶0.85∶0.65比例調(diào)整,遠(yuǎn)場(chǎng)長(zhǎng)周期三向地震波信息如表3所列。將地震的加速度峰值調(diào)整至罕遇地震400 cm·s-2,分別得到加速度時(shí)程、加速度反應(yīng)譜如圖3~4所示。
由圖3可知:對(duì)比三種地震波的加速度時(shí)程曲線,可以看出,相對(duì)于普通地震動(dòng),遠(yuǎn)場(chǎng)長(zhǎng)周期地震動(dòng)具有周期大,持時(shí)長(zhǎng)等特性,其中遠(yuǎn)場(chǎng)類諧和地震波ILA004具有明顯的諧波時(shí)程成份,易對(duì)結(jié)構(gòu)產(chǎn)生不利影響。
由圖4可知:普通地震波加速度反應(yīng)譜峰值主要出現(xiàn)在0~1 s區(qū)間,隨后快速下降;遠(yuǎn)場(chǎng)非類諧和地震波加速度峰值主要出現(xiàn)在0~2 s區(qū)間,且1 s之后的加速度峰值大于普通地震波,并有雙峰現(xiàn)象出現(xiàn);遠(yuǎn)場(chǎng)類諧和地震波峰值主要出現(xiàn)在0~2 s區(qū)間,加速度峰值大于普通地震波,并在4~6 s區(qū)間出現(xiàn)雙峰。因此,遠(yuǎn)場(chǎng)類諧和地震波會(huì)對(duì)隔震類周期大的結(jié)構(gòu)產(chǎn)生更不利影響。
2 三維地震下考慮SSI層間隔震結(jié)構(gòu)響應(yīng)分析
2.1 結(jié)構(gòu)周期變化
基底采用不同性質(zhì)土(考慮SSI)模擬時(shí)層間隔震結(jié)構(gòu)周期對(duì)比如表4所列。
由表4可知:剛性地基的層間隔震結(jié)構(gòu)第1階周期為3.079 s,考慮SSI效應(yīng)時(shí),隨著土體性質(zhì)變軟周期增幅越大,軟土層地基時(shí)周期最大為3.809 s,這是由于土與結(jié)構(gòu)相互作用(SSI效應(yīng))使結(jié)構(gòu)剛度軟化,結(jié)構(gòu)變得更柔,土體越軟越明顯。周期的增大容易使層間隔震結(jié)構(gòu)在遠(yuǎn)場(chǎng)類諧和地震激勵(lì)下發(fā)生共振,對(duì)結(jié)構(gòu)產(chǎn)生更不利影響。
2.2 結(jié)構(gòu)響應(yīng)分析
輸入三維地震動(dòng),并將地震波峰值調(diào)幅至400 cm·s-2,在Ⅷ度罕遇地震下對(duì)不同土體性質(zhì)下的層間隔震結(jié)構(gòu)進(jìn)行動(dòng)力彈塑性分析,取每類地震波的包絡(luò)值,得出結(jié)構(gòu)的層間位移角對(duì)比如圖5,基底剪力對(duì)比如圖6。
由圖5可知:三維地震動(dòng)下,遠(yuǎn)場(chǎng)長(zhǎng)周期地震產(chǎn)生的層間位移角遠(yuǎn)大于普通地震,尤其是長(zhǎng)周期產(chǎn)生的層間位移角是普通地震動(dòng)的20倍,主要原因是遠(yuǎn)場(chǎng)類長(zhǎng)周期地震與層間隔震結(jié)構(gòu)產(chǎn)生共振。由(a) (b) (c)可知考慮SSI效應(yīng)時(shí),隨著土體變軟,層間隔震上部結(jié)構(gòu)層間位移角幾乎不受影響,表現(xiàn)為軟土層地基略大于剛性地基;層間隔震下部結(jié)構(gòu)放大效應(yīng)尤為明顯,下部結(jié)構(gòu)層間位移角放大的主要原因是考慮SSI效應(yīng)后,土體性質(zhì)變軟,下部結(jié)構(gòu)剛度變?nèi)?,且隔震層?duì)下部結(jié)構(gòu)的反作用力使層間位移角變大,說(shuō)明考慮SSI效應(yīng)對(duì)層間隔震下部結(jié)構(gòu)的作用不容忽視,在軟土層進(jìn)行層間隔震下部結(jié)構(gòu)設(shè)計(jì)中應(yīng)格外關(guān)注。三維普通地震、三維遠(yuǎn)場(chǎng)非類諧和地震、三維遠(yuǎn)場(chǎng)類諧和地震分別作用下,剛性地基上部層間位移角最大值分別為0.000 24、0.002 2、0.009 8,考慮SSI效應(yīng)后,隨著土體性質(zhì)變軟,層間位移角也隨著變大,最大層間位移角分別為0.002 34、0.004 6、0.016,分別是剛性地基的9.8倍、2.1倍、1.6倍,根據(jù)規(guī)范[22]罕遇地震下隔震結(jié)構(gòu)的上部層間位移角限值為0.005,遠(yuǎn)場(chǎng)類諧和地震下層間位移角超出限值的3.2倍。
由圖6可知:三維地震動(dòng)下,剛性地基時(shí)普通地震、遠(yuǎn)場(chǎng)非類諧和地震、遠(yuǎn)場(chǎng)類諧和地震下的最大剪力分別為10 527 kN、27 246 kN、53 434 kN,遠(yuǎn)場(chǎng)長(zhǎng)周期地震產(chǎn)生的剪力遠(yuǎn)大于普通地震,尤其是遠(yuǎn)場(chǎng)類諧和地震是普通地震剪力的5.1倍。三維地震動(dòng)下,考慮SSI效應(yīng)對(duì)層間隔震結(jié)構(gòu)的剪力差值均在5%以內(nèi),無(wú)明顯影響。
2.3 結(jié)構(gòu)的塑性鉸和應(yīng)力結(jié)果
輸入三維地震動(dòng),進(jìn)行罕遇地震下的動(dòng)力彈塑性分析,取具有代表性的普通遷安波、遠(yuǎn)場(chǎng)非類諧和地震波TAP012、遠(yuǎn)場(chǎng)類諧和地震波ILA004的塑性鉸結(jié)果如圖7所示,應(yīng)力結(jié)果如圖8所示。
由圖7出鉸結(jié)果可知:三維地震動(dòng)下,遠(yuǎn)場(chǎng)長(zhǎng)周期地震產(chǎn)生的塑性鉸遠(yuǎn)多于普通地震,尤其是柱子處也出現(xiàn)少量塑性鉸??紤]SSI效應(yīng)時(shí),硬土層產(chǎn)生的塑性鉸與剛性地基接近,軟土層塑性鉸略多于硬土層和剛性地基,其中遠(yuǎn)場(chǎng)類諧和地震動(dòng)中的諧波成份與長(zhǎng)周期特性易于結(jié)構(gòu)產(chǎn)生共振,造成嚴(yán)重破壞,結(jié)構(gòu)布滿塑性鉸,考慮SSI,相對(duì)于共振影響表現(xiàn)較弱,塑性鉸結(jié)果幾乎不變。
由圖8可知:三維地震動(dòng)下,遠(yuǎn)場(chǎng)長(zhǎng)周期的應(yīng)力值大于普通地震;考慮SSI效應(yīng)時(shí),剛性地基與硬土層地基產(chǎn)生的應(yīng)力接近相等,遷安波、TAP012、ILA004產(chǎn)生應(yīng)力值范圍分別為0~0.21 MPa、0~0.22 MPa、0~0.43 MPa,軟土層地基產(chǎn)生的應(yīng)力值大于剛性地基和硬土層地基分別為0~0.59 MPa、0~0.60 MPa、0~0.71 MPa,放大倍數(shù)最大達(dá)3倍,說(shuō)明軟土層對(duì)層間隔震結(jié)構(gòu)的影響較大。
2.4 層間隔震支座位移
三維地震下激勵(lì)下,考慮SSI效應(yīng)的隔震位移結(jié)果如表5所列。
由表5可知:三維地震下,遠(yuǎn)場(chǎng)長(zhǎng)周期地震的隔震支座位移遠(yuǎn)大于普通地震,在考慮SSI效應(yīng)時(shí),隨著土體變軟,隔震支座位移有所增大。根據(jù)規(guī)范隔震支座水平位移限值,不超過(guò)0.55倍有效直徑和3.0倍橡膠總厚度的最小值,最小值為0.55×700 mm=385 mm。三維普通地震動(dòng)下,隔震支座最大位移為136.2 mm,滿足規(guī)范要求;三維遠(yuǎn)場(chǎng)非類諧和地震下,最大位移為490.7 mm,超過(guò)規(guī)范要求;三維遠(yuǎn)場(chǎng)類諧和地震下,最大位移為830.2 mm,超過(guò)規(guī)范限值的2.16倍,結(jié)果不容忽視。
3 三維隔震支座與傳統(tǒng)水平隔震支座減震效果對(duì)比
層間隔震結(jié)構(gòu)中隔震層支座一旦發(fā)生破壞,會(huì)引起隔震層減震作用失效,造成更嚴(yán)重的結(jié)構(gòu)破壞。針對(duì)出現(xiàn)的隔震支座位移超限與上部結(jié)構(gòu)層間位移角超限,將傳統(tǒng)水平隔震支座替換為三維隔震支座,三維隔震支座分為水平隔震部分與豎直隔震部分,水平隔震部分布置相同的LRB700、LRB600和LNR500隔震支座,并且配合黏滯阻尼器,消耗地震能量,達(dá)到減震效果。黏滯阻尼器在ETABS中通過(guò)Damping單元進(jìn)行模擬,該單元可模擬一種無(wú)剛度、速度相關(guān)型耗能器,其阻尼力公式如下為:
F=CdVα (5)
式中:Cd為阻尼系數(shù);V為阻尼器速度;α為速度指數(shù)。
豎直隔震部分設(shè)置碟形彈簧支座,并且配合黏滯阻尼器,碟形彈簧采用高強(qiáng)度鋼材60Si2MnA,材料參數(shù)為:彈性模量2.05×105 MPa、屈服強(qiáng)度1 500 MPa、切線模量75 MPa和泊松比0.3;黏滯阻尼器的阻尼系數(shù)為1 200 kN·s/m,速度指數(shù)為0.3,并與傳統(tǒng)水平隔震支座進(jìn)行罕遇地震下動(dòng)力彈塑性分析對(duì)比。
3.1 結(jié)構(gòu)減震效果對(duì)比
針對(duì)出現(xiàn)的超限問(wèn)題進(jìn)行特值分析,輸入三維地震動(dòng),取遠(yuǎn)場(chǎng)類諧和地震結(jié)果的包絡(luò)值,并考慮SSI效應(yīng)作用,上部結(jié)構(gòu)的最大層間位移角結(jié)果對(duì)比如圖9所示。取每類地震結(jié)果的包絡(luò)值,并考慮SSI效應(yīng)作用,基底剪力對(duì)比如圖10所示。
由圖9~10可知:相對(duì)于傳統(tǒng)水平隔震支座,三維隔震支座能顯著減少遠(yuǎn)場(chǎng)類諧和地震動(dòng)產(chǎn)生的層間位移角和基底剪力,在不同土體性質(zhì)下均具有良好減震效果,層間位移角減少了約60%~70%,基底剪力減少了約30%~40%。除軟土層外最大層間位移角均在規(guī)范的0.005以下,其中軟土層上部結(jié)構(gòu)最大層間位移角為0.005 2,與規(guī)范限值的0.005相差在5%以內(nèi),屬于可控范圍。
3.2 支座位移對(duì)比
罕遇地震下,考慮SSI效應(yīng),傳統(tǒng)水平隔震支座結(jié)構(gòu)與三維隔震支座結(jié)構(gòu)的支座位移對(duì)比如表6所列。
由表6可知:相對(duì)于傳統(tǒng)水平隔震支座,三維隔震支座具有良好的限制支座位移的效果,減少了約40%~55%,其中在遠(yuǎn)場(chǎng)類諧和地震作用下最大支座位移為373.6 mm,小于規(guī)范限值0.55D=385 mm,能保護(hù)支座不受到超限破壞,使層間隔震結(jié)構(gòu)發(fā)揮正常隔減震作用。
3.3 豎向減震性能對(duì)比
輸入三維地震動(dòng),取每類地震的包洛值,兩種不同隔震支座結(jié)構(gòu)對(duì)豎向地震力的減震能力對(duì)比表7所列。
由表7可知:考慮不同土體性質(zhì)(SSI),三維隔震支座對(duì)結(jié)構(gòu)的最大豎向位移均有明顯降低,由此表明,三維隔震支座比傳統(tǒng)水平隔震支座具有更好的豎向地震減震性能。
4 結(jié)論
本文建立了大底盤層間隔震結(jié)構(gòu)模型,在罕遇地震下,進(jìn)行了三維地震動(dòng)下,考慮SSI效應(yīng)的動(dòng)力彈塑性分析。針對(duì)上部結(jié)構(gòu)層間位移角和隔震支座位移超限問(wèn)題,設(shè)置三維隔震支座,并與設(shè)置傳統(tǒng)水平隔震支座結(jié)構(gòu)進(jìn)行了地震響應(yīng)分析對(duì)比,得到以下結(jié)論:
(1) 相對(duì)于普通地震動(dòng),遠(yuǎn)場(chǎng)長(zhǎng)周期地震動(dòng)具有周期長(zhǎng)、持時(shí)長(zhǎng)、豐富的低頻成份,造成的層間隔震結(jié)構(gòu)地震響應(yīng)遠(yuǎn)大于普通地震動(dòng),尤其是遠(yuǎn)場(chǎng)類諧和地震在4~6 s時(shí)會(huì)出現(xiàn)雙峰現(xiàn)象,地震后期階段具有諧波特性,對(duì)隔震類等周期大的結(jié)構(gòu)易產(chǎn)生共振,造成更不利影響。
(2) 三維地震動(dòng)下,相對(duì)于普通地震動(dòng),遠(yuǎn)場(chǎng)長(zhǎng)周期地震對(duì)層間隔震結(jié)構(gòu)產(chǎn)生的層間位移角、層間剪力、塑性鉸、應(yīng)力均大于普通地震,且遠(yuǎn)場(chǎng)類諧和地震產(chǎn)生的響應(yīng)最大;考慮SSI效應(yīng)時(shí),結(jié)構(gòu)自振周期有所延長(zhǎng),層間隔震下部結(jié)構(gòu)的層間位移角顯著增大,結(jié)構(gòu)均布滿塑性鉸,結(jié)構(gòu)軟土地基產(chǎn)生的應(yīng)力均大于剛性地基,土體越軟造成的響應(yīng)越大,因此在軟土層進(jìn)行結(jié)構(gòu)設(shè)計(jì)時(shí)應(yīng)予以充分注意。
(3) 采用三維隔震支座時(shí),考慮SSI效應(yīng),結(jié)構(gòu)基底剪力顯著減少,減震效果達(dá)30%~40%,并且解決了傳統(tǒng)水平隔震支座出現(xiàn)的上部結(jié)構(gòu)層間位移角和隔震支座位移超限問(wèn)題,減震效果分別為60%~70%、40%~55%,且在豎向方向的減震性能也表現(xiàn)良好,分析結(jié)果表明,在三維地震下考慮SSI效應(yīng),三維隔震支座表現(xiàn)出更好的隔減震效果。
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