摘要: 考慮帶支撐六參數(shù)黏彈性阻尼器耗能隔震結(jié)構(gòu)在李鴻晶譜激勵(lì)下求解地震響應(yīng)較為復(fù)雜,提出了一種能夠獲得隨機(jī)地震響應(yīng)的簡(jiǎn)明解法。采用帶支撐六參數(shù)黏彈性阻尼器分析模型,以微分本構(gòu)方程實(shí)現(xiàn)黏彈性阻尼器隔震結(jié)構(gòu)的數(shù)學(xué)建模,結(jié)合復(fù)模態(tài)法與虛擬激勵(lì)法,獲得了隔減震體系系列響應(yīng)(位移、速度以及阻尼器受力)頻域解的統(tǒng)一表達(dá)式;以李鴻晶譜作為激勵(lì)功率譜,將激勵(lì)功率譜與結(jié)構(gòu)頻率響應(yīng)特征值函數(shù)進(jìn)行簡(jiǎn)化,獲得了該隨機(jī)激勵(lì)下系統(tǒng)響應(yīng)功率譜、響應(yīng)譜矩及響應(yīng)方差的簡(jiǎn)明解;給出算例,與此類問(wèn)題傳統(tǒng)的常用分析方法進(jìn)行對(duì)比,驗(yàn)證所提方法在該系統(tǒng)下分析動(dòng)力響應(yīng)的合理性和高效性,并討論了不同支撐剛度對(duì)阻尼器減震效果的影響。
關(guān)鍵詞:"隔減震體系;"帶支撐六參數(shù)黏彈性阻尼器;"李鴻晶譜;"響應(yīng)譜矩;"響應(yīng)方差
中圖分類號(hào): TU352.1;TU311.3 """文獻(xiàn)標(biāo)志碼: A """文章編號(hào): 1004-4523(2024)08-1397-12
DOI:10.16385/j.cnki.issn.1004-4523.2024.08.014
引""言
減隔震作為一種有效的被動(dòng)控制手段已廣泛應(yīng)用于橋梁、鐵路、建筑結(jié)構(gòu)等土木工程領(lǐng)域[1?3]。隔震技術(shù)是在建筑物底部或者層間設(shè)置隔震裝置[4](由隔震器、阻尼器裝置等組成),延長(zhǎng)結(jié)構(gòu)的自振周期,從而進(jìn)一步減小結(jié)構(gòu)的動(dòng)力響應(yīng)。阻尼器安裝在不同位置,可以達(dá)到設(shè)計(jì)的不同目的[5?7]。在基礎(chǔ)隔震層設(shè)置黏彈性阻尼器,依靠黏彈性材料的滯回耗能特性,阻尼器能夠充分發(fā)揮耗能作用為結(jié)構(gòu)提供附加剛度和阻尼,消耗了輸入到結(jié)構(gòu)中的大部分地震能量,能夠有效地保護(hù)結(jié)構(gòu)主體,起到減小地震響應(yīng)的目的[8?9]。
為能夠精確描述黏彈性阻尼器的力學(xué)關(guān)系,許多學(xué)者提出了多種恢復(fù)力模型,這其中包括:Maxwell模型[7]、Kelvin模型[10?11]、分?jǐn)?shù)導(dǎo)數(shù)模型[12]、標(biāo)準(zhǔn)線性固體模型[13]、廣義Maxwell模型[14],以及Mazza等[15]提出的六參數(shù)黏彈性阻尼器模型等。而六參數(shù)黏彈性阻尼器模型本構(gòu)方程易于擴(kuò)階,模型計(jì)算參數(shù)便于與實(shí)驗(yàn)數(shù)據(jù)擬合,更具有普適性。阻尼器常通過(guò)消能支撐連接于建筑結(jié)構(gòu),支撐是保證結(jié)構(gòu)有效耗能的重要構(gòu)件,隨著阻尼器在結(jié)構(gòu)抗風(fēng)、抗震等項(xiàng)目上應(yīng)用的發(fā)展,在很多結(jié)構(gòu)上已經(jīng)采用了不同安裝方式以組成不同類型的安置模型,有對(duì)角支撐、人字型支撐、剪刀式支撐等,阻尼器和支撐裝置起到了很好的消能減震作用[16?17]。
在隨機(jī)振動(dòng)分析中一般以功率譜密度函數(shù)作為分析地震地面運(yùn)動(dòng)的隨機(jī)模型[18?19]。工程中常用的地震動(dòng)隨機(jī)激勵(lì)模型有白噪聲模型[19]、Kanai?Tajimi模型[20]、李鴻晶模型[21]等。白噪聲模型不考慮場(chǎng)地類別等其他因素的影響,數(shù)學(xué)表達(dá)式簡(jiǎn)潔,容易獲得協(xié)方差函數(shù),但將譜參數(shù)值恒等于一個(gè)常數(shù),并不能準(zhǔn)確反映地震動(dòng)的頻譜特征。Kanai?Tajimi模型在零頻處無(wú)界且低頻段夸大了頻域能量分布,導(dǎo)出的均方速度和均方位移無(wú)界,只適用于中高頻結(jié)構(gòu)地震響應(yīng)分析[22]。李鴻晶等提出了一種改進(jìn)的功率譜模型,修正了金井清模型在零頻處存在的奇異點(diǎn),既能夠控制低頻又能夠抑制高頻的能量分布,且滿足兩次可積的條件,導(dǎo)出的均方速度和均方位移均有界[21],故以該譜分析隨機(jī)地震響應(yīng)具有很好的工程應(yīng)用價(jià)值。
目前,國(guó)內(nèi)外應(yīng)用的結(jié)構(gòu)抗震設(shè)計(jì)方法是基于振型疊加的反應(yīng)譜法。對(duì)于設(shè)置了阻尼器的隔震結(jié)構(gòu),由于隔震體系阻尼分布具有明顯的非比例特征,得到的耗能隔減震結(jié)構(gòu)的振型不正交,用現(xiàn)有方法無(wú)法將結(jié)構(gòu)響應(yīng)精確分解為各響應(yīng)模態(tài)的線性組合,因此無(wú)法建立精確的設(shè)計(jì)反應(yīng)譜[23]。而復(fù)模態(tài)法作為時(shí)域分析地震響應(yīng)的常用方法可以將非比例系統(tǒng)精確解耦為獨(dú)立的復(fù)模態(tài)變量方程[19,24],虛擬激勵(lì)法[25]和傳遞函數(shù)法[7]作為頻域分析的兩種代表性方法,計(jì)算所得響應(yīng)譜矩表達(dá)式含積分項(xiàng),需逐步積分計(jì)算確定響應(yīng)譜矩值,導(dǎo)致計(jì)算結(jié)果不穩(wěn)定。
無(wú)論是時(shí)域法還是頻域法,以李鴻晶譜作為結(jié)構(gòu)響應(yīng)分析的激勵(lì)功率譜,均較難獲得響應(yīng)譜矩解。因此,本文提出了一種簡(jiǎn)明的算法:首先,構(gòu)建帶支撐阻尼器隔震結(jié)構(gòu)的運(yùn)動(dòng)方程,利用復(fù)模態(tài)法、虛擬激勵(lì)法得到系統(tǒng)響應(yīng)頻域解的統(tǒng)一表達(dá)式;其次,通過(guò)簡(jiǎn)化李鴻晶譜與結(jié)構(gòu)頻率響應(yīng)特征值函數(shù)獲得響應(yīng)功率譜、響應(yīng)譜矩和響應(yīng)方差的解析表達(dá)式,將其與傳統(tǒng)的響應(yīng)分析方法如虛擬激勵(lì)法進(jìn)行對(duì)比,驗(yàn)證了系統(tǒng)響應(yīng)功率譜及0~2階譜矩公式推導(dǎo)的合理性。
1 隔減震體系運(yùn)動(dòng)方程
1.1 結(jié)構(gòu)運(yùn)動(dòng)方程
1.2 "帶支撐六參數(shù)黏彈性阻尼器的等效本構(gòu)關(guān)系
六參數(shù)黏彈性阻尼器由彈簧單元、黏壺單元和2支標(biāo)準(zhǔn)Maxwell阻尼器并聯(lián)組成,該模型能夠反映材料的應(yīng)力松弛規(guī)律和蠕變特性,本構(gòu)方程易于擴(kuò)階,模型計(jì)算參數(shù)便于與實(shí)驗(yàn)數(shù)據(jù)進(jìn)行擬合。在實(shí)際工程中,阻尼器往往需要與支撐串聯(lián)安裝,支撐剛度對(duì)結(jié)構(gòu)減震效果有著明顯的影響,因此考慮支撐剛度更加符合實(shí)際。將阻尼器與支撐串聯(lián)設(shè)置在隔震層,建立等效阻尼器計(jì)算模型[17]如圖2所示。
2 隔減震系統(tǒng)響應(yīng)的頻域統(tǒng)一解
2.1 復(fù)模態(tài)解耦
2.2 響應(yīng)頻域解的統(tǒng)一表達(dá)式
3 功率譜二次分解
3.1 李鴻晶譜分解
從數(shù)理角度對(duì)式(32)進(jìn)行了簡(jiǎn)化處理,將其分解為頻率變量與譜參數(shù)平方和的線性組合。且從式(36)中可以直觀地看出隨著頻率變量ω的逐漸變大,李鴻晶譜的能量分布逐漸減小,而它與式(32)的區(qū)別僅是表達(dá)形式的不同。
3.2 頻率響應(yīng)特征值函數(shù)分解
功率譜分析是隨機(jī)振動(dòng)理論在工程應(yīng)用中最常用的方式,即由輸入功率譜(激勵(lì)功率譜)求出結(jié)構(gòu)響應(yīng)功率譜[19]。由式(31),根據(jù)虛擬激勵(lì)法知,結(jié)構(gòu)系統(tǒng)響應(yīng)功率譜為:
3.3 響應(yīng)功率譜
4 響應(yīng)譜矩與響應(yīng)方差
5 算""例
5.1 功率譜驗(yàn)證分析
5.3 帶支撐阻尼器減震效果分析
6 結(jié)""論
針對(duì)帶支撐六參黏彈性阻尼器基礎(chǔ)耗能隔震結(jié)構(gòu),基于李鴻晶譜的響應(yīng)解析算法進(jìn)行了研究,給出了隔減震體系較為簡(jiǎn)明的響應(yīng)解。結(jié)果表明:
(1)將復(fù)雜的李鴻晶激勵(lì)功率譜與結(jié)構(gòu)頻率響應(yīng)特征值函數(shù)簡(jiǎn)化處理,分解的激勵(lì)功率譜與李鴻晶譜的曲線吻合,說(shuō)明了分解李鴻晶譜的合理性。而通過(guò)代入不同的響應(yīng)模態(tài)系數(shù)得到對(duì)應(yīng)的系統(tǒng)系列響應(yīng)功率譜的曲線圖吻合程度較高,充分說(shuō)明了本文方法推導(dǎo)頻率響應(yīng)特征值函數(shù)的合理性。
(2)本文方法不僅得到了結(jié)構(gòu)響應(yīng)(隔減震系統(tǒng)位移、速度等)的簡(jiǎn)明解,還獲得了阻尼器響應(yīng)(阻尼器受力、阻尼器位移、支撐位移等)的簡(jiǎn)明解,通過(guò)與傳統(tǒng)的此類問(wèn)題的常用分析方法如虛擬激勵(lì)法進(jìn)行對(duì)比分析,本文方法無(wú)論是計(jì)算精度還是計(jì)算效率,均有極大的提高。因此可以為隔震結(jié)構(gòu)的隔震層參數(shù)選取、阻尼器的優(yōu)化等提供理論依據(jù),也有利于工程應(yīng)用。
(3)支撐剛度的選取影響著阻尼器的減震效果。支撐剛度取值越大,阻尼器減震效果越好,但支撐剛度大到一定程度時(shí),響應(yīng)方差值基本趨于緩和,阻尼器減震效果提高不明顯。因此,在結(jié)構(gòu)變形滿足抗震規(guī)范要求的情況下,適當(dāng)選取合理支撐剛度以提高經(jīng)濟(jì)效益。
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A concise solution method for the seismic isolation structure of the supported six-parameter damper based on Li Hongjing spectrum
Han Hong,"ZOU Wan-jie,"Li Chuang-di,"Ge Xin-guang,"Jing Cheng-gui
(School of Civil Engineering,"Guangxi University of Science and Technology,"Liuzhou 545006,"China)
Abstract: Considering the complexity of solving the seismic response of the energy-dissipated isolated structure with six-parameter viscoelastic damper under the excitation of Li Hongjing spectrum,"a concise solution that can obtain random seismic response is proposed. The analysis model of six-parameter viscoelastic damper with support is adopted,"and the mathematical modeling of energy dissipation and isolation structure with viscoelastic damper is realized by differential constitutive equation. Combined with complex mode method and the pseudo excitation method (PEM),"the unified expression of frequency domain solution for system series response (displacement,"velocity and damper force)"of vibration isolation system is obtained. Taking Li Hongjing spectrum as the excitation power spectrum,"the excitation power spectrum and the eigenvalue function of structural frequency response are simplified,"and the concise analytical solutions of the system response power spectrum,"response spectral moment and response variance under the random excitation are obtained. An example is given to verify the accuracy and efficiency of the proposed method in analyzing the dynamic response of the system compared with the traditional response analysis method such as the PEM,"and the influence of different support stiffness on the vibration reduction effect of the damper is discussed.
Key words: vibration isolation system;"six-parameter viscoelastic damper with support;Li Hongjing spectrum;"response spectral moment;"response variance
作者簡(jiǎn)介: 韓""紅(1996—),女,碩士研究生。E-mail:"2845389539@qq.com。
通訊作者: 鄒萬(wàn)杰(1974—),男,博士,副教授。E-mail:"705450818@qq.com。