商業(yè)結構外文翻譯

1、<p><b>　　譯文</b></p><p>　　1989年10月17日,Loma Prieta地震</p><p><b>　　1989年10月</b></p><p><b>　　商業(yè)結構</b></p><p>　　Loma Prieta地震和它的余震導致了

2、一系列商業(yè)結構的大面積順壞損壞.正如這個量級的典型地震一樣,有一大批地理范圍受到了影響.被波及的地區(qū)包括8個郡,從南部的Monterey和San Benito,到北部的San Francisco, Alameda, 和 Contra Costa .總共有大約3000平方英里面積的建筑結構遭受到了破壞.</p><p>　　盡管地震帶來的破壞面積很廣,但是這些破壞很零散.據(jù)估計,最接近震中的地區(qū),包括Hollist

3、er, Los Gatos, Santa Cruz, 和 Watsonville 經(jīng)歷了最集中的破壞.再遠一點,僅僅是那些地基建在松軟的土質上的質量非常差的建筑物遭到了嚴重的破壞,這些土質在地震的運動中中被破壞和坍塌.這和1985年的墨西哥地震產(chǎn)生的影響是相似的.</p><p>　　地震的影響是具有很強的方向性的.大多數(shù)破壞發(fā)生在從西北向東南方向延伸的狹窄地段,大約與San Andreas Fault平行.因此

4、沿著 San Francisco 灣的許多地區(qū)逃脫了這場截難.</p><p><b>　　不穩(wěn)固的石質建筑物</b></p><p>　　正如在過去的California 地震中所發(fā)現(xiàn)的那樣,最集中和嚴重的建筑物結構破壞發(fā)生在不穩(wěn)固的石質建筑物結構中.不穩(wěn)固的石質建筑物結構包括木頭框架的屋頂和地板,這些屋頂和地板是由很厚的不穩(wěn)固的墻磚支撐的,這種結構在Califor

5、nia一直流行到30年代,那時抗震材料在建筑上的應用阻止了它進一步的發(fā)展.因此,不穩(wěn)固的石質建筑物結構通常在 California 的老城區(qū)中的集中商業(yè)地段被發(fā)現(xiàn).</p><p>　　不穩(wěn)固的石質建筑物結構的失敗之處在于,屋頂和地板的隔離膜的磚墻拋錨點不夠,還有就是基礎建筑材料的承重和柔韌性的限制,以及低質的建筑技術.由于天氣頻繁的作用導致了灰泥和木質框的變質和低質.</p><p>　

6、　California 近來頒布了法令(SB 547)要求鑒別城市中的不穩(wěn)固的石質建筑物結構,然后制訂計劃減少它們所帶來的風險.</p><p>　　在Loma Prieta地震中導致的不穩(wěn)固的石質建筑物的破壞,從在震中大的坍塌,到70英里以外的.Martinez的欄桿的倒塌.在Hollister, Los Gatos, Oakland, 和 San Francisco的商業(yè)區(qū) 也 發(fā)生了危及生命的倒塌.許多建筑

7、物中的屋頂和地板以及倒塌的墻壁在失去支撐時仍然保持直立,似乎否定了萬有引力的作用.一般說來,在屋頂和地板之間有連通拋錨點的建筑物比沒有這個結構的建筑物的性能要好得多.</p><p>　　在這個地區(qū)的大多數(shù)不穩(wěn)固的石質建筑物在地震中沒有倒塌或者有明顯的損壞.但是,地質調查顯示,大多數(shù)這種結構的建筑物被過度地拉扯和破裂,因此被削弱了質量.如果不修理,這些建筑物有可能在以后的地震中倒塌.有超過3,4層不穩(wěn)固的石質建筑

8、物一般是通過鋼筋框架來承重的.在這些建筑物中的石墻是用來為建筑分層的,給結構增加側面抵抗性.這些鋼筋框架填充的建筑物在California 過去的地震中一般比小一些的</p><p>　　墻磚結構的建筑物的性能要好.但是,這些建筑物在California 的立法中被歸為不穩(wěn)固石質建筑.在Loma Prieta 地震中,許多石墻鋼筋框架的建筑性能很差,盡管它們沒有倒塌.在San Francisco 和 Oaklan

9、d的一些這種類型的大型建筑經(jīng)歷了過度的破壞,包括失去部分外墻,內(nèi)部黏土層脫落,以及陶瓦板的散裂.</p><p><b>　　混凝土建筑</b></p><p>　　許多加強型的老式混凝土建筑在抗震方面是非常有限的.這些建筑物非常沉重,導致巨大的地震力量.另外,混凝土本身十分易碎,它要求大量的加強的鋼筋在地震中發(fā)揮作用.在70年代中期以前設計的大多數(shù)混凝土結構沒有足夠

10、堅固的鋼筋來保證其良好的性能.由工程師設計的沒有延展性的混凝土結構,在過去的地震中倒塌了.倒塌了的Cypress Viaduct 結構就是一個沒有延展性的混凝土結構.</p><p>　　幸運的是,在這個地區(qū)的沒有延展性的混凝土結構建筑物相對較少,所以這種類型的建筑物沒有倒塌的.然而,很多中期興起的混凝土結構建筑物沒有經(jīng)歷過過度的破壞.主要的破壞包括承重墻的斜方向的拉裂,有時伴有從建筑物上落下來的大塊的混凝土碎片

11、.一個在Oakland中心的15層的混凝土結構被嚴重的破壞了.在第一層的輕質混凝土墻逐步破裂,露出了加強鋼筋.在建筑物中的額外的鋼筋框架可以阻止這種結構的建筑物的倒塌.</p><p>　　在San Francisco的一個6層高的混凝土支撐墻建筑也受到了一定的破壞。這座建筑近來被加以防震措施，在它周圍加上了鋼筋帶。由于設計和建筑工藝處理得不好，建筑物得邊框不適當，大多數(shù)都垮了。建筑的偏差引起了邊框的倒塌，使得內(nèi)

12、部的柱子打穿了地板的厚板。在門戶上的承重墻也受到了普遍的破壞。</p><p><b>　　上傾斜建筑物</b></p><p>　　混凝土上傾斜建筑是貫穿整個 California的低層工業(yè)商業(yè)結構中最普遍的形式。他們通常是由蓋著木頭框架的屋頂?shù)膴A板構成，周圍是由混凝土支撐的。它們被稱為上傾斜，因為它的圍墻是平的，而地板是傾斜的，在整個建筑物周圍都是斜的。在過去的地

13、震中，像1987年的Whittier 和1971年的 San Fernando地震。</p><p>　　上千棟上傾斜建筑物位于受影響的地區(qū)。盡管一些嚴重的破壞是在震中發(fā)生的，大多數(shù)這種結構的建筑是位于受到微震的地區(qū)。因此大多數(shù)這種建筑物幾乎沒有遭到破壞。</p><p>　　我們對Hollister 的一些建筑進行了調查。在地震時，由于裝著番茄的罐子對墻進行壓迫，一些上傾斜建筑物倒塌了。

14、這強調了和地震有關的設備和內(nèi)容的話題的重要性，還有建筑設計的重要性。這些建筑是在60年代晚期或者70年代早期建造的，因此一般沒有屋頂?shù)綁Φ腻^。這些錨導致了1971年San Fernando 地震中上傾斜建筑物的崩潰。有一個建筑物，它一半的屋頂都居住著人的，也倒塌了，引起了內(nèi)部的廣泛的破壞。</p><p>　　在Watsonville，有一個食品包裝商的大型的上傾斜建筑，它的一些面板在中間向前方拱出，差一點就倒塌

15、了。柱子上的混凝土碎片脫落了，露出了加固鋼，一些被扣住了。另外，一些新近建成的上傾斜建筑物，在歪斜處的的內(nèi)部連接也遭到破壞，屋頂也被嚴重地扯壞了。</p><p><b>　　鋼鐵建筑物</b></p><p>　　現(xiàn)代鋼架建筑物在這次地震中表現(xiàn)得很出色，正如它們在過去的地震中的表現(xiàn)一樣。這些建筑遭到的破壞非常有限，僅僅限于覆蓋層和內(nèi)部區(qū)間的破裂，以及建筑物中物品的混

16、亂。鋼架建筑物的非結構性損壞很大一部分歸結于它們的彈性，可以允許大范圍內(nèi)的移位。</p><p>　　在Hollister的一個鋼架建筑，周圍是皺起的金屬，它是一個食品公司的倉庫。由于它和在Hollister的上傾斜建筑是一起的，這個番茄加工公司的鋼架結構和遭受了嚴重的破壞，貨物也受到了嚴重損失。放在30英尺高的標準貨價上的番茄聽裝罐在地震中被震落下來。大多數(shù)罐子都落下來，打穿了金屬墻。</p>&

17、lt;p>　　沖擊的力量是如此之大，以至于好幾個錐形鋼柱和梁被嚴重破壞。這些被扭曲，彎曲和打碎的鋼制物件占據(jù)了建筑物的整個部分。這次事故強調了在地震中，存放的貨物可能對整個建筑物造成的影響。</p><p><b>　　摘要</b></p><p>　　在這次地震中，離震中較遠的地區(qū)，如San Francisco 灣地區(qū)，倒塌的建筑物相對較少。除了震中的建筑物，

18、大多數(shù)嚴重的的損壞發(fā)生 在幾乎沒有抗震能力和土質極為疏松的建筑物上。有的結構不適當?shù)慕ㄖ镏詻]有遭受嚴重破壞，是因為它們所在的大多數(shù)地區(qū)地殼的運動都不是很劇烈。盡管如此，大多數(shù)商業(yè)活動至少停滯了一周，有的還遭受了巨大的損失。許多商業(yè)活動被迫搬遷地方，知道它們的建筑修理好或者是重建。在以后更強的地震中，或者地震發(fā)生更為接近人口集中區(qū)域時，更廣的破壞和更大的商業(yè)損失可能會發(fā)生。</p><p>　　住宅結構在受到

19、影響的地區(qū)的大多數(shù)住宅樓是木質框架結構。這樣的建筑物一般在過去的地震中表現(xiàn)較好，因為它們很輕，可以減小內(nèi)部壓力。由于它們相對較為僵硬，可以減小諸如變形之類的損壞，例如內(nèi)墻的破裂。但是無論如何，也存在一些反例。老住宅樓（尤其是40年代以前的），由于它們?nèi)狈εc地基的正確連接，或者它們的地板上升，這些地板是由相對較脆弱的跛墻支撐的。</p><p>　　一些形狀更為不規(guī)則的新樓，由于復雜的幾何形狀而缺乏清楚的負重路徑，

20、或者沒有建造足夠的墻來抵抗地震的壓力。低層有停車場的多層建筑，停車場的門大多數(shù)是由堅固的墻來代替的。</p><p><b>　　震中地區(qū)</b></p><p>　　在震中地區(qū)的住宅樓的損壞是很廣泛的，這種損壞也非常大，盡管許多新房子的性能非常好。許多使用木板墻的建筑，它們遭受了嚴重的內(nèi)部非建筑性損壞。對于石膏板內(nèi)墻的損壞要小的多。煙囪的損壞從破裂到彎曲，在整個震中

21、區(qū)域都可見倒塌的煙囪。這樣的損壞在Watsonville的老城區(qū)中30％到40％的面積的建筑物中都可以發(fā)現(xiàn)。在 Santa Cruz 的煙囪損壞沒有那么頻繁，主要限制在舊的，不牢固的煙囪上。</p><p>　　對住宅樓的嚴重結構性損壞可以歸結為跛墻的不牢固，以及基石的缺乏。這些跛墻是短的木頭框架，位于地基和的一層地板之間。由于它們沒有覆蓋石膏，正如生活區(qū)的墻壁一樣，它們非常脆弱，是一個經(jīng)常破損的區(qū)域。這樣的損壞

22、最早是在早于40年代的平行木頂住宅樓上發(fā)現(xiàn)的。這些建筑從幾個英寸向一個英尺側移，直到跛墻變得不穩(wěn)固和倒塌。由于這種運動造成的損壞非常頻繁。在Watsonville，在整個地區(qū)，大約有10％至20％的40年代以前的住宅樓的跛墻被損壞，許多街區(qū)100％的住宅樓都被損壞。在 Santa Cruz，損壞發(fā)生在土質較差的地方。在南太平洋公園街的太平洋街，幾乎所有的住宅樓都被破壞了。</p><p>　　在Myrtle大街，

23、Neary Lagoon的廢水處理廠附近，也發(fā)生了嚴重的損壞。在有一個街區(qū)，五分之一的住所的跛墻都被破壞。在這條街上，一些關于維護質量和震前情況的關聯(lián)性損壞也有發(fā)生。顯然，一些經(jīng)過結構性修復的老房子可以有結構上的升級。在下一頁的表格中顯示出，凡是有良好的防震條件的建筑都沒有被嚴重損壞，只有那些防震條件差的建筑受到了輕程度的損壞。在Watsonville 的一個街區(qū)，只有一個房子沒有從它的地基上脫落。它剛剛被升級，有一個新的地基。它的內(nèi)部

24、也沒有損壞，甚至夾板都沒有破裂。</p><p>　　San Francisco Marina街區(qū)</p><p>　　在 San Francisco遭受破壞最嚴重的地區(qū)是Marina街區(qū)。這個街區(qū)的土壤主要是由松軟的，滲透性的泥沙組成，其中一些是自然形成的，但是大多數(shù)都是在大約1915年的巴拿馬－太平洋博覽會時填充進去的。</p><p>　　在 Marina地區(qū)

25、的大多數(shù)建筑是木質框架結構的公寓房和單間房，2至5層高，在20年代時建成的。這些建筑大多數(shù)在第一層都有停車場。 Marina街區(qū)的大量建筑都受到了破壞。盡管在 Marina街區(qū)的所有的建筑物中都可以發(fā)現(xiàn)石膏和灰泥的破裂，最嚴重的破壞發(fā)生在中層（4至5層）。這些建造很多都完全崩潰了，更多的已經(jīng)完全不能修理了。</p><p>　　這些建筑物被破壞的主要原因有兩個。第一，建筑的聚集度和僵硬度可能會導致基本振動，這種基

26、本振動與支配性振動相近，都是由這個地區(qū)的松軟的土壤加強的。第二，幾乎所有的倒塌和幾乎倒塌的建筑物有相同的配置：這些建筑的第一層都有很多停車場的入口，缺乏切變強度或者稱為軟層。許多被嚴重損壞的建筑物都是建造在角落上的，因此它們的四個外墻中有兩個都作為停車場的入口。這些角落上的建筑也會彎曲，進一步使得它們的性能惡化。</p><p>　　地理上的塌陷和液化導致了在 Marina街區(qū)的街道和人行道的破裂。土壤的劣質不是

27、導致建筑物倒塌的直接原因，然而它們毫無疑問的對整個事件產(chǎn)生了影響。</p><p><b>　　地震和地質</b></p><p>　　里氏7.1級地震的震中位于Santa Cruz 的東南部10英里處，沿著San Andreas Fault，在Santa Cruz山接近 Loma Prieta 的地方。震深達到了11英里。這是非常深的，就連典型的Californi

28、a 地震的震深也只有4至6英里深。</p><p>　　一個5.2級的余震在主震之后發(fā)生了，持續(xù)了大約2。5分鐘，自從那次以后，上千次余震被紀錄。在地震以后的那個星期里，有大約300個余震達到2.5級，還有大約20個達到4。0級。余震區(qū)從接近Highway 17的 Los Gatos北部延伸到 接近 Highway 101的 Watsonville南部 ，跨越了25英里。這個區(qū)域是受到最嚴重破壞的地區(qū)。在深度上，

29、區(qū)域從2至11英里延伸，我們有理由相信，破裂的長度是和主震相聯(lián)系的。</p><p><b>　　表面影響</b></p><p>　　沿著一個20英里的區(qū)域，產(chǎn)生3到4英寸的表面位移，這是通常伴隨著這個級數(shù)的地震的。但是我們在不間斷的模糊區(qū)域發(fā)現(xiàn)許多的裂縫。對于這些清楚的表面特征的缺乏，有一些可能的解釋。地震相當深，使得巖床破裂至地表變得困難。崎嶇地形，厚土壤，森林

30、覆蓋也使得地表顯得不是那么明顯。國家委員會1906年地震的報告描述了沿著San Andreas Fault的Santa Cruz山的非常相似的地表破裂特征。</p><p><b>　　歷史地震</b></p><p>　　San Andreas Fault是朝著西北方向延伸的，從California 灣向San Francisco北部的Cape Mendocino

31、延伸了800英里。它是許多大地震的源頭，包括1865年Santa Cruz東北部的地震，以及著名的1906年8.3級San Francisco地震。Loma Prieta地震實際上是重復了1865年的地震，是從1906年以來沿著San Andreas 的第一次大規(guī)模的破裂。fault的破裂長度通常是從1906年破裂的楠端伸展，因此從那時起，就有山脈開始聚集形成。由于這段斷層運動的缺乏， 還有在前二年發(fā)生的幾次5.0級的地震，使得地質學家

32、預測到這次地震。</p><p>　　在Santa Cruz地區(qū)的最近的一次破壞性強的地震包括一個1964年11月15日發(fā)生的5.2級地震，導致了煙囪的破壞；還有1988年6月發(fā)生的5.3級地震和這一年8月發(fā)生的5.4級地震，都和Loma Prieta地震發(fā)生在幾乎相同的區(qū)域。</p><p>　　近來在San Andreas 斷層的破裂對地震來說是不平常的。過去的地震的發(fā)生是由于兩邊斷層

33、的水平位移，西南端向西北端相對東北端運動。在近來的Loma Prieta地震的破裂中，不僅僅包括這種水平成分的位移，也包括一個西南和東北方向的上推，斷層陡峭地插入這個地區(qū)的西南端。</p><p><b>　　地殼運動紀錄</b></p><p>　　我們從數(shù)百個儀器中得到強烈的運動紀錄，允許通過一整個受到影響的地區(qū)的細節(jié)理解。初步結果表明，峰地的搖晃達到0.5g，(

34、g是重力加速度),這在震中的地區(qū)的水平和垂直方向都得到記錄。相對低的加速度在震中和Oakland 以及San Francisco之間的地方</p><p>　　被記錄到。在0.2g到0.33g的加速度在沿著San Francisco 和 Oakland 地區(qū)的周圍，內(nèi)部被記錄。在這些遙遠地區(qū)的更為強烈的地殼運動反映了土壤震動密度的影響。</p><p><b>　　土壤</

35、b></p><p>　　液化（一種現(xiàn)象，當被嚴重震動時，沙子被地下水滲透，暫時表現(xiàn)的像流沙的現(xiàn)象）調查的發(fā)生表明，受到最嚴重擠壓的地點是在San Francisco 和 Oakland邊緣，還有沿著Santa Cruz東部和南部的Pajaro 和Salinas河的沖積平原。液化影響在受到最嚴重破壞的區(qū)域San Francisco的Marina 地區(qū)被廣泛注意。在Oakland機場的高速公路上，在沿著Paj

36、aro and Salinas和的橋上，在Moss Landing 的San Jose State Marine站都被液化破壞了。</p><p>　　與在San Francisco 和 Oakland 的與液化和土壤因素有關的的破壞的類型與1906年的相似。在1906年的Oakland，液化和沉降導致對碼頭的水的破壞，這些碼頭位于現(xiàn)在的倒塌了的Cypress結構的南端。在San Francisco，先前的液化破

37、壞發(fā)生在Ft. Mason附近，與在Marina 區(qū)域的當前的破壞的位置相近，還有就是沿著waterfront的商業(yè)區(qū)，在那里Embarcadero高速公路和許許多多的古老的磚石建筑都受到了破壞。很有可能的是，1906年最廣泛的液化發(fā)生在 Market的南部，和 China Basin東部，在那里，發(fā)生了對建筑物和I-280航線的嚴重的損壞。 </p><p>　　地震導致了成百上千的沿著陡峭斜坡的滑坡，從震中

38、地區(qū)的山上到至少遠至在San Francisco南部的太平洋彼岸。在 Santa Cruz山脈的一些居民區(qū)被這些滑坡嚴重地損壞了。在Highway 17二條小路被一個在山頂西部發(fā)生的巨大的滑坡堵死。由于沉降，整個Bay地區(qū)，在路上產(chǎn)生了巨大的裂縫。</p><p>　　這個San Andreas Fault 30英里長的裂縫并沒有改變在未來30年里再次發(fā)生一個或者幾個7.0級地震的可能性，這個可能性是50％。19

39、06年8.3級地震的重復發(fā)生的可能性仍然是存在的。</p><p>　　The October 17, 1989 Loma Prieta Earthquake</p><p>　　October 1989 </p><p>　　Commercial Structures</p><p>　　The Loma Prieta Earthquake

40、 and its subsequent aftershocks resulted in widespread damage to a variety of commercial structures. A large geographical area was affected, as is typical for an earthquake of this magnitude. The affected area encompasse

41、s eight counties, from Monterey and San Benito in the south to San Francisco, Alameda, and Contra Costa in the north. In total, building structures experienced damage over an area of approximately 3,000 square miles.<

42、/p><p>　　Although damage was widespread, it was also quite sporadic. As would be expected, areas closest to the epicenter including Hollister, Los Gatos, Santa Cruz, and Watsonville experienced the most concent

43、rated damage. Farther away, heavy damage was generally limited to buildings of very poor construction founded on soft soils that failed or amplified the earthquake ground motions. This is similar to the effects noted in

44、the 1985 Mexico City Earthquake.</p><p>　　Earthquake effects also tended to be highly directional. Most damage occurred within a narrow band that extends northwest to southeast, approximately paralleling the

45、 San Andreas Fault. Thus many communities along the margins of San Francisco Bay escaped serious damage.</p><p>　　Unreinforced Masonry Buildings</p><p>　　As has been observed in past California

46、earthquakes, the most concentrated and severe damage to building structures occurred in unreinforced masonry (URM) bearing-wall buildings. URM buildings, constructed of wood-frame roof and floor systems supported by thic

47、k unreinforced brick walls, were commonly constructed throughout California until the 1930s, when the adoption of building codes with seismic-resistive provisions prevented their further development. As a result, URM bui

48、ldings are typically</p><p>　　Failures of URM buildings result from inadequate anchorage of the masonry walls to roof and floor diaphragms, as well as the limited strength and ductility of the basic building

49、 materials and poor construction workmanship. Deterioration of the sand-lime mortar and wood framing due to weather exposure frequently contributes to poor performance. California has recently enacted legislation (SB 547

50、) requiring cities to identify URM buildings and develop plans to reduce the risk they present.</p><p>　　Damage to URM buildings in the Loma Prieta Earthquake ranged from dramatic collapses near the epicente

51、r to fallen parapets in Martinez, more than 70 miles away. Life-threatening collapses also occurred in Hollister, Los Gatos, Oakland, and the San Francisco financial district. The roofs and floors in many buildings with

52、collapsed walls seemingly defied gravity by continuing to stand after losing their load-bearing support. Generally, buildings with through-wall anchorage to floor and roof framin</p><p>　　Most URM buildings

53、in the region survived the earthquake without collapse or obvious substantial damage. However, field investigations show that many of these structures have experienced extensive cracking of the masonry and are therefore

54、weakened. If not repaired, some of these buildings are likely to collapse in future earthquakes.</p><p>　　URM buildings with more than three or four stories were generally constructed with steel frames to ca

55、rry the gravity loads. Masonry walls in these buildings were primarily provided for building closure and partitions and to add lateral shear-resistance to the structure. These steel-frame infill masonry buildings have ge

56、nerally performed better in past California earthquakes than the smaller bearing-wall buildings. Nonetheless, these buildings were included in California legislation addressing th</p><p>　　In the Loma Prieta

57、 Earthquake, many steel-frame buildings with infill masonry walls performed quite poorly, although no collapses occurred. Several major structures of this type in San Francisco and Oakland experienced extensive damage in

58、cluding partial loss of the exterior masonry walls, shattering of interior clay tile partitions, and cracking and spalling of terra-cotta veneers.</p><p>　　Concrete Buildings</p><p>　　Many older

59、 reinforced concrete structures have very limited seismic resistance. These buildings tend to be quite heavy, resulting in large seismic forces. In addition, concrete itself is quite brittle and requires extensive amount

60、s of reinforcing steel to perform properly in earthquakes. Most concrete structures designed prior to the mid-1970s do not have adequate reinforcing steel to ensure good performance. Termed non-ductile concrete structure

61、s by engineers, these structures have collapsed in</p><p>　　Fortunately, there are relatively few non-ductile concrete buildings in the region and no buildings of this type collapsed. Many mid-rise concrete

62、structures did experience extensive damage, however. Damage typically consisted of large diagonal cracking of shear walls, occasionally accompanied by spalling of large pieces of concrete from the building</p><

63、;p>　　A fifteen-story concrete shear-wall structure in downtown Oakland was extensively damaged. The lightweight concrete shear walls at the first story literally shattered, exposing the reinforcing steel to view. The

64、presence of a redundant steel frame within the building may have prevented the collapse of this structure.</p><p>　　A six-story concrete shear-wall building in San Francisco also experienced substantial dama

65、ge. This building had recently been seismically strengthened with the addition of steel braces on the building perimeter. Due to poor design and construction workmanship, the attachment of the braces to the building was

66、inadequate and most of the bolts failed. Building deflections following failure of the bracing caused an interior column to punch through a floor slab. Extensive damage to shear walls above</p><p>　　Tilt-up

67、Buildings</p><p>　　Concrete tilt-up buildings are the most common form of modern low-rise industrial and commercial construction throughout California. They usually are constructed with plywood sheathed wood

68、-frame roofs supported by perimeter concrete walls. They are called tilt-ups because the perimeter walls are constructed lying flat against the floor slab and then tilted-up into position around the building. Extensive d

69、amage to these buildings has been observed in past earthquakes, including the 1987 Whittier </p><p>　　Thousands of tilt-up buildings are present in the affected region. Although some significant damage was e

70、xperienced near the epicenter, the greatest concentrations of these buildings are located in areas that experienced very weak ground motion. Most of these buildings therefore had little damage.</p><p>　　Seve

71、ral buildings in Hollister were investigated. Several tilt-up building partially collapsed as the result of inventories of stacked cans containing tomato product impacting the walls during the earthquake. Damage was exte

72、nsive. Much of the inventory was lost or severely damaged. This underscores the importance of addressing seismic issues relating to equipment and contents, as well as structural designThe buildings appeared to be late 19

73、60s or early 1970s vintage and as such were observed not</p><p>　　In Watsonville, several panels of a large tilt-up owned by a food packager bowed outward at mid-height and approached collapse. Concrete spal

74、led off of several of the pilasters in the building wall, exposing the reinforcing steel, some of which buckled. In another, newly constructed Watsonville tilt-up, interpanel connections at a skewed corner were damaged a

75、nd roof sheathing was severely torn.</p><p>　　Steel Buildings</p><p>　　Modern steel-frame buildings performed excellently in this earthquake, as they have in the past. Damage to these structures

76、 was typically limited to cracking of cladding and interior partitions and widespread disarray of contents. The nonstructural damage sustained by steel-frame buildings may largely be attributed to their flexibility, whic

77、h results in very large displacements.</p><p>　　A steel-frame building with corrugated metal siding in Hollister serves as a warehouse for a food company. As with the concrete tilt-up buildings in Hollister,

78、 this tomato packing company experienced severe damage to its steel-frame building and significant loss of inventory. Canned tomato products stacked over 30 feet high on standard pallets were mobilized by the earthquake.

79、 Most stacks collapsed, impacting and ripping through the corrugated metal side walls. </p><p>　　Impact forces were so great that several tapered steel columns and beams were severely damaged. These steel me

80、mbers twisted, bent, and failed, taking down an entire section of the building. Much of the inventory was lost or severely damaged. As with concrete tilt-up warehouses, this incident highlights the effect that stored inv

81、entory can have on the integrity of a building during an earthquake.</p><p><b>　　Summary</b></p><p>　　The remote epicentral location of this earthquake allowed the San Francisco Bay

82、Area to survive with relatively few instances of structural collapse. Except for buildings near the epicenter, most cases of severe damage occurred in older buildings with little seismic capacity and in areas of extremel

83、y weak soils. The fact that many inadequate structures in the region experienced little damage indicates that ground motion in most areas was not severe. Even so, most businesses experienced at least </p><p>

84、;　　Residential Structures</p><p>　　Most residential buildings in the affected area are of wood-frame construction. Such buildings have generally performed well in past earthquakes because they tend to be lig

85、ht, minimizing inertial forces; and because they are relatively rigid, minimizing damage associated with deformation, such as cracking of interior walls. There are, however, major exceptions to this generally good perfor

86、mance record. </p><p>　　Older (especially pre-1940s) homes, because they lack positive connections to their foundations or have raised floors supported by relatively weak cripple walls.</p><p>　

87、　Some of the more irregularly shaped newer homes, because they lack clear load paths due to complex geometry or are built without enough wall area to resist the seismic forces.</p><p>　　Multi-story apartment

88、 buildings or houses with garages on the ground floor, where garage doors have replaced most solid walls.</p><p>　　Except for areas of poor soils (soft, saturated sands and silts), which experienced severe d

89、amage as far away as San Francisco, damage to residences was generally limited to the epicentral area of Watsonville, Santa Cruz, and Los Gatos.</p><p>　　Epicentral Area</p><p>　　Residential bui

90、lding damage in the epicentral area was widespread and considerable, although most newer houses performed very well. Many buildings with wood-lath-and-plaster walls suffered severe interior nonstructural damage; damage t

91、o gypsum board interior walls appeared to be significantly less severe. Chimney damage ranging from cracking to twisting and collapse was observed throughout the epicentral area. Such damage was observed in as many as 30

92、% to 40% of the homes in the older areas of W</p><p>　　Severe structural damage to homes observed could mainly be attributed to failure of unbraced cripple walls and lack of sill anchorage. These cripple wal

93、ls are short wood stud framing present between the foundation and first floor of the building. Because they are not sheathed with plaster, as are walls in the living area, they are substantially weaker and a common locat

94、ion for failures.</p><p>　　Such damage was mainly observed in pre-1940s homes with horizontal wood sheathing. These homes moved laterally from several inches to a foot, until the cripple walls became unstabl

95、e and collapsed. Damage to utility lines due to this motion was frequent. In Watsonville, cripple wall failures were observed in approximately 10% to 20% of the pre-1940s residences throughout the area, with many blocks

96、suffering close to 100% failures. In Santa Cruz, damage appeared to occur mainly in the area of poor</p><p>　　Severe damage was also apparent on Myrtle Street, near the wastewater treatment plant at Neary La

97、goon. On one block, five of twenty-five homes had cripple wall failures. On this street, correlation of damage with quality of maintenance and general pre-earthquake condition was evident. Apparently, older homes that ha

98、d been restored architecturally often also had structural upgrades. The table on the following page shows none of the homes with "good" pre-earthquake condition to be severely damaged</p><p>　　San

99、Francisco Marina District</p><p>　　The most severely damaged area in San Francisco was the Marina district. The soils in this area consist mainly of soft, saturated sands and silts, some of which are natural