哈工大地震工程工程地震部分第五章強(qiáng)地課件

1、Engineering Seismology (3)Main Characteristics and Attenuation of Ground Motionhttp:/www.cen.bris.ac.uk/civil/students/eqteach97/glossary.htmhttp:/www.cen.bris.ac.uk/civil/students/eqteach97/earth4.htm強(qiáng)地震動(dòng)相當(dāng)復(fù)雜，只能選擇其主要的特征，地震動(dòng)三要素：幅值(amplitude)，最大值PGA、PGV、PGD，有效值EPA、EPV，均方根值A(chǔ)rms、Vrms、Drms，SI等；頻譜特征：富氏譜(

2、Fourier spectrum)、反應(yīng)譜(response spectrum)和功率譜(power spectrum)等；持續(xù)時(shí)間(duration)，絕對(duì)持時(shí)(0.05g或0.1g)、相對(duì)持時(shí)(5%-95%)等。 The strongest earthquake motions that have been recorded to date have peak accelerations between 1 g and 3 g, where 1 g (= 980 cm/sec2) is the acceleration of the Earths gravity field, althou

3、gh records with such large peak values are rare. It is less clear what threshold of ground motion needs to be exceeded to be considered “strong motion”. Probably a logical level to choose would be about 10 cm/sec2, as the older strong-motion instruments (accelerographs) that traditionally defined th

4、e field are not able to resolve ground accelerations with amplitudes smaller than this. Modern digital accelerographs are much more sensitive, able to resolve peak accelerations to 0.1 cm/sec2 or smaller. People at rest are able to feel motions as small as 1 cm/sec2. In moderate magnitude earthquake

5、s, damage to structures that are not designed for earthquake resistance appears at accelerations of about 100 cm/sec2. 最大增量速度（IV）、最大增量位移（ID） 增量速度：加速度脈沖下的面積，實(shí)際上代表速度變化的增量，它與質(zhì)量的乘積代表結(jié)構(gòu)的動(dòng)量或者相當(dāng)于地震左右的沖量作用 增量位移：速度脈沖下的面積 可用來(lái)刻畫(huà)近斷層區(qū)域的地震動(dòng)破壞勢(shì) RMSA 、RMSV、RMSD 均方根加速度、均方根速度和均方根位移定義為:其中：x(t)為地震動(dòng)的加速度、速度或位移， Td為地震動(dòng)的持時(shí)

6、。對(duì)于量度地震動(dòng)的能量方面更為有效一些 AI阿里亞斯（Arias）烈度譜烈度(Spectrum Intensity) Sv為對(duì)應(yīng)阻尼比為的相對(duì)速度反應(yīng)譜，T為周期，常取為0或0.2，是一個(gè)客觀的物理量，并不涉及任何宏觀現(xiàn)象。 譜烈度也是一個(gè)從能量的角度表征地震動(dòng)潛在破壞勢(shì)的參數(shù)，因?yàn)镾v反映了彈性單自由度體系的能量需要，但譜烈度一個(gè)明顯的缺點(diǎn)就是它沒(méi)有考慮持時(shí)的影響，而持時(shí)對(duì)結(jié)構(gòu)的累積損傷是很重要的。地震動(dòng)反應(yīng)譜(response spectrum)單自由度彈性系統(tǒng)在地震動(dòng)作用下最大反應(yīng)的絕對(duì)值與體系的自振特征(自振周期或頻率和阻尼比)之間的函數(shù)關(guān)系 （日）大崎順彥著，呂敏申、謝禮立譯，地震動(dòng)

7、的譜分析入門(mén)，地震出版社，1980反應(yīng)譜的算法Response spectra describe peak time-domain response of a suite of single-degree of freedom oscillators to the seismic excitation. Response spectra play an important role in the development of engineering designs. The pseudo-relative velocity, PSV, is obtained from Sd by PSV =

8、(2/ To) Sd. The pseudo-relative acceleration, PSA, is obtained from Sd by PSA = (2/ To) 2 Sd. In general, PSA Sa and PSV Sv, although these different spectra can have different asymptotic properties at high and low frequencies. The spectra are usually computed for a range of damping, from h = 0% (un

9、damped) to h = 20% of critical. This range is used because most manmade structures are similarly lightly damped. A damping of h = 5% is the most likely to be reported. 擬反應(yīng)譜（pseudo response spectrum）三聯(lián)反應(yīng)譜標(biāo)準(zhǔn)反應(yīng)譜(normal response spectrum)動(dòng)力放大系數(shù) 、 和標(biāo)準(zhǔn)化形式的設(shè)計(jì)譜（規(guī)范） 將阻尼比為5的加速度反應(yīng)譜在周期0.10.5秒之間平均為一常值Sa，將阻尼比為5%的

10、速度反應(yīng)譜在周期1秒附近平均為一常值Sv，則有效峰值加速度、有效峰值速度的定義如下： EPA=Sa/2.5, EPV=Sv/2.5 這樣定義的有效峰值與真實(shí)峰值相關(guān)，但一般來(lái)說(shuō)，并不等于、甚至不比例于真實(shí)的峰值。常數(shù)2.5是一個(gè)經(jīng)驗(yàn)系數(shù)，其物理意義相當(dāng)于大量地震動(dòng)加速度反應(yīng)譜的平均放大倍數(shù)。 峰值加速度與地震動(dòng)過(guò)程中結(jié)構(gòu)的最大內(nèi)力無(wú)法直接聯(lián)系，而有效峰值加速度則彌補(bǔ)了這個(gè)缺點(diǎn)，DurationDefinitionbracket duration（relative or absolute）Energy durationEngineering durationEffect to seismic r

11、esponse of structures The simplest of these is peak acceleration, which is easily obtained from the accelerogram. After records are digitized, it is common to obtain several additional parameters. Time domain parameters often include peak velocity and peak displacement. Duration of the strong shakin

12、g is generally considered important, but there is not a unique definition of duration. One simple approach is to measure the interval between the times when the peak acceleration first and last exceeds some threshold, usually 0.05g. The alternative approach namely to define the amount of time in whi

13、ch 90% of the integral of the acceleration-squared takes place. These two definitions lead to opposite results as distance increases. At large distances the peak ground motions decrease so that the interval duration goes to zero even though the ground was moving. On the other hand, the energy become

14、s dispersed, resulting in an increase in the time interval over which 90% of the total energy in the seismogram arrives. In the frequency domain, the Fourier amplitude spectrum and a class of spectra known as response spectra are generally determined. 其它參數(shù)位移延性能量（輸入能量、滯回能量） 討 論 如何用地震動(dòng)的參數(shù)合理的表征地震動(dòng)的潛在破壞

15、勢(shì)（或?qū)Y(jié)構(gòu)的破壞能力）？ 評(píng)判的標(biāo)準(zhǔn)是什么？地震動(dòng)的衰減 (GM attenuation)最簡(jiǎn)單的預(yù)測(cè)地震動(dòng)的經(jīng)驗(yàn)關(guān)系，其中震源的影響用震級(jí)表示，地震波從震源到場(chǎng)地的傳播影響用距離來(lái)描寫(xiě)，場(chǎng)地的影響用場(chǎng)地分類(lèi)來(lái)描寫(xiě)；將距離項(xiàng)分解為幾何擴(kuò)散和非彈性衰減兩項(xiàng)。預(yù)測(cè)地震動(dòng)的三種方法？ The peak acceleration and other peak parameters can be described by a .ground motion prediction equation. as a function of the earthquake magnitude, distance f

16、rom the fault to the site, general site condition parameter, and sometimes other parameters. Peak acceleration is a commonly employed parameter for these regressions, but peak velocity, peak displacement, spectral amplitudes, and duration have also been modeled in this manner. Naturally the ground m

17、otion prediction equations do not exactly describe peaks of past earthquake ground motions. 地震動(dòng)衰減關(guān)系的統(tǒng)計(jì)數(shù)據(jù)地震數(shù)據(jù)，M或M0，類(lèi)型臺(tái)站數(shù)據(jù)，距離，場(chǎng)地條件地震動(dòng)觀測(cè)數(shù)據(jù)和常規(guī)數(shù)據(jù)處理的成果地震動(dòng)衰減關(guān)系的統(tǒng)計(jì)擬合方法 在確定衰減關(guān)系的系數(shù)時(shí)，最常用的統(tǒng)計(jì)分析方法是最小二乘法。由于數(shù)據(jù)的分布不可避免地存在病態(tài)，自變量之間總要有一定的相關(guān)性，在數(shù)據(jù)不很豐富時(shí)，一次個(gè)別地震中的數(shù)據(jù)占比例過(guò)大、一個(gè)場(chǎng)地的記錄占比例過(guò)大等，都要有些辦法處理。如加權(quán)最小二乘法、穩(wěn)健回歸法、一致加權(quán)最小二乘法。Boore和

18、Joyner（1981）提出了兩步法，既將震級(jí)項(xiàng)和距離項(xiàng)分兩步統(tǒng)計(jì)，以減少兩者間的相關(guān)性對(duì)歸結(jié)果的影響。 相對(duì)持時(shí)，隨距離的增加而增大Because ground motion prediction equations are a key component of probabilistic seismic hazard analyses, it is clear that their development will be an important part of seismological research for some time to come.Until 1999, for lar

19、ge magnitudes and short distances the estimates from these equations were based more on extrapolation than on extensive amounts of data.In 1999, there were two significant earthquakes that contributed very important data at short distances. One was the Izmit, Turkey earthquake (August 17, 1999, Mw =

20、 7.6). In this earthquake, Anderson et al. (2000a) find that the peak accelerations on rock at near-fault distances were significantly below four different ground motion prediction equations. The other was the Chi-Chi, Taiwan, earthquake (September 21, 1999, Mw = 7.6). Peak accelerations from this e

21、arthquake were significantly below three different recent ground motion prediction equations developed primarily from North American data but presumed to apply to the same tectonic environment. 缺乏強(qiáng)震記錄地區(qū)的地震動(dòng)衰減關(guān)系 從宏觀烈度分析或者從地震臺(tái)網(wǎng)導(dǎo)出的地震參數(shù)評(píng)定所考慮地區(qū)的地震震源和地震波傳播 (衰減)特性，與已經(jīng)提出經(jīng)驗(yàn)的和理論的強(qiáng)運(yùn)動(dòng)衰減關(guān)系的世界其它地區(qū)加以比較辨別所考慮地區(qū)的構(gòu)造環(huán)境

22、類(lèi)型和發(fā)生的地震震源的斷裂形式(即，板緣、板內(nèi)，淺地殼、俯沖消減帶、走滑等)從地震震源與所考慮地區(qū)最相似的地理地區(qū)選擇若干衰減關(guān)系式若需要，根據(jù)與地區(qū)中有限的強(qiáng)運(yùn)動(dòng)數(shù)據(jù)的比較，調(diào)整選擇的衰減關(guān)系式，評(píng)價(jià)和/或理論計(jì)算。利用現(xiàn)有可供使用的地震數(shù)據(jù)，可以研究理論衰減關(guān)系式。 最近幾次大地震中強(qiáng)地震動(dòng)表現(xiàn)的一些新特征 幾十年間，研究人員發(fā)表了大量的地震動(dòng)三要素，幅值、持時(shí)和譜特征的統(tǒng)計(jì)關(guān)系。隨著記錄的不斷積累、研究的深入，發(fā)現(xiàn)這些地震動(dòng)主要特征的變化相當(dāng)復(fù)雜，受許多因素的影響。 震害經(jīng)常顯示出比用簡(jiǎn)單經(jīng)驗(yàn)?zāi)Ｐ皖A(yù)測(cè)的大得多的不規(guī)律性，與地震震源過(guò)程、從震源到場(chǎng)地的地震波的傳播和場(chǎng)地反應(yīng)等方面有關(guān)。 在

23、1994年美國(guó)北嶺地震、1995年日本阪神地震和1999年臺(tái)灣集集地震中觀測(cè)到的近斷層的方向性效應(yīng)、上盤(pán)效應(yīng)、地殼波導(dǎo)效應(yīng)、盆地邊緣反應(yīng)效應(yīng)等都對(duì)地震動(dòng)有重要的影響，又都牽涉到更復(fù)雜的震源機(jī)制、傳播途徑和場(chǎng)地條件的影響中的基礎(chǔ)理論問(wèn)題。近斷層地震動(dòng) 在近斷層區(qū)域地震動(dòng)幅值分布受斷裂的幾何形態(tài)影響很強(qiáng)烈。對(duì)于豎直的走滑斷裂，破裂方向性效應(yīng)對(duì)于給定的至斷裂最近距離處地震動(dòng)引起很強(qiáng)的空間變化。對(duì)于傾滑斷裂，有兩個(gè)主要的效應(yīng)：破裂方向性效應(yīng)和上盤(pán)效應(yīng)。上盤(pán)效應(yīng)主要是由斷裂對(duì)上盤(pán)場(chǎng)地的更近引起的。從上盤(pán)一側(cè)斷裂的頂部邊緣向更遠(yuǎn)處發(fā)生。破裂方向性效應(yīng)是由于破裂傳播和幅射模式效應(yīng)引起的。上盤(pán)效應(yīng) (hang

24、ing wall effect) 一個(gè)傾斜斷裂上盤(pán)的場(chǎng)地在總體上比下盤(pán)上最近距離相同的場(chǎng)地更靠近斷裂面。這引起了上盤(pán)短周期地震動(dòng)比下盤(pán)相同最近距離處更大。上盤(pán)對(duì)逆沖地震引起的短周期地震動(dòng)增加了斷裂因子的形式，一般比走滑地震的大1.3-1.4倍。 Abrahamson和Somerville發(fā)展了上盤(pán)效應(yīng)經(jīng)驗(yàn)型模型將上盤(pán)場(chǎng)地的地震動(dòng)與下盤(pán)的遠(yuǎn)離斷層破裂端部的區(qū)分開(kāi)來(lái)。上盤(pán)效應(yīng)在最近距離8-18千米處、周期范圍0-0.6秒是最大的（達(dá)到1.45），在5秒降為1.0。 近斷層方向性效應(yīng)(rupture directivity effect) 在斷層近場(chǎng)地區(qū)，影響地震動(dòng)特征的一個(gè)重要因素是斷層的破裂方向

25、。根據(jù)場(chǎng)地與斷層的相對(duì)位置，方向性效應(yīng)可以分為向前效應(yīng)（forward）、向后效應(yīng)（reverse）和中性效應(yīng)（neutral），如果斷層的破裂方向朝向場(chǎng)地或破裂方向與震源（hypocenter）和場(chǎng)地連線的夾角較小的話，場(chǎng)地的效應(yīng)稱為向前方向性效應(yīng)；如果斷層的破裂方向背離場(chǎng)地或破裂方向與震源和場(chǎng)地連線的夾角較小的話，稱為向后方向性效應(yīng)；如果場(chǎng)地與震源的連線幾乎垂直于斷層的破裂方向，稱為中性效應(yīng)。通常所說(shuō)的“方向性效應(yīng)”是指向前方向性效應(yīng)，因?yàn)橄蚯胺较蛐孕?yīng)產(chǎn)生的地震動(dòng)對(duì)工程結(jié)構(gòu)來(lái)說(shuō)更為不利。 近斷層方向性效應(yīng) 斷層破裂所產(chǎn)生的能量波在傳播介質(zhì)中以幾乎等于介質(zhì)剪切波速的速度向場(chǎng)地傳播，使得斷層產(chǎn)生的能量以非常短的時(shí)間到達(dá)場(chǎng)地，這樣，在場(chǎng)地的地震動(dòng)中將產(chǎn)生一個(gè)大的速度脈沖（通常發(fā)生在地震動(dòng)的開(kāi)始階段）。近斷層方向性效應(yīng) 斷裂上剪切位錯(cuò)的幅射模式使這個(gè)地震動(dòng)的大脈沖朝向垂直于斷裂方向，引起垂直于斷層分量的峰值速度比平行于斷層分量的峰值速度要大。近斷層運(yùn)動(dòng)巨大破壞性在1994年北嶺地震、1995年板神地震以及1999年集集地震中清楚地表現(xiàn)出來(lái)。在這兩個(gè)地震中，記錄到了大到175cm/秒，記錄到的近斷層脈沖的周期為1-2秒，大體相當(dāng)于橋梁和中高層建筑物的結(jié)構(gòu)自振周期，而許多這類(lèi)結(jié)構(gòu)在地震中破壞強(qiáng)烈。 地殼波導(dǎo)效應(yīng) (crustal w