外文翻譯--現(xiàn)有的建筑物上增加的雪荷載和風(fēng)荷載效應(yīng)挪威建筑物可靠性分析

1、<p><b>　　外文翻譯一：</b></p><p>　　外文原文一出處：DOL: 10.1061/(ASCE)0733-9445(2006)132:11(1831)</p><p>　　現(xiàn)有的建筑物上增加的雪荷載和風(fēng)荷載效應(yīng)：挪威建筑物可靠性分析</p><p>　　Vivian Meloysund, Ph.D. ; Kim R

2、obert Liso, Ph.D. ; Jan Siem ; and Kristoffer Apeland</p><p>　　摘要：對來自在挪威的20個現(xiàn)有建筑物上的一個雪荷載和風(fēng)荷載效應(yīng)的調(diào)查結(jié)果分析。由于存在雪荷載或風(fēng)荷載，所以需要調(diào)查在哪些范圍內(nèi)的現(xiàn)有的建筑物會與現(xiàn)有的規(guī)范要求或者抵抗倒塌的安全度有關(guān)。十八個建筑物在現(xiàn)在的規(guī)范之下有一個超過1.0的利用比。新的設(shè)計(jì)規(guī)范已經(jīng)開始應(yīng)用到大部分的建筑上，與現(xiàn)在規(guī)

3、范，對于雪荷載和風(fēng)荷載效應(yīng)，對于減少坍陷的安全性有較好的安全度。當(dāng)評估一個國家的規(guī)劃具有哪些可能結(jié)果的時候，建筑物的大部分的數(shù)據(jù)依照現(xiàn)行的房屋建筑規(guī)范來評估，那么可靠性是很低的。對未來的氣候變化的研究表明雪荷載和風(fēng)荷載在很大程度上會有增加的趨勢，大面積的屋頂也會在強(qiáng)烈的風(fēng)荷載下需要承受更多的危險。因此，在將來這些建筑物的可靠性將會降低。</p><p>　　關(guān)鍵字: 承載力； 建筑物； 氣候上的變化； 挪威； 可

4、靠性； 雪載重； 結(jié)構(gòu)設(shè)計(jì)； 結(jié)構(gòu)的安全性； 風(fēng)荷載</p><p><b>　　緒論</b></p><p><b>　　背景</b></p><p>　　在1999/2000年的冬天，挪威北部的巨大雪載導(dǎo)致部分建筑物倒塌。在Bardufoss社區(qū)活動中心的意外事件中，屋頂塌陷甚至造成三人死亡,這是所有這類性質(zhì)的意外事件

5、中最嚴(yán)重的（圖1）。當(dāng)該建筑物建成后，屋頂上的雪載就超過其原來設(shè)計(jì)當(dāng)初的標(biāo)準(zhǔn)荷載，而且此坍陷的最重要的因素之一是在屋頂上有一個構(gòu)造過失。</p><p><b>　　圖1</b></p><p><b>　　主要目標(biāo)和定界線</b></p><p>　　調(diào)查的主要目標(biāo)是獲得關(guān)于雪荷載或/和風(fēng)荷載的作用下，以及在現(xiàn)行的規(guī)范標(biāo)

6、準(zhǔn)約束下，挪威現(xiàn)有建筑抵抗塌陷的可靠性研究調(diào)查。以及，在未來挪威氣候改變的條件下，如何分析并建立一個原理和模型。本次調(diào)查分析包括設(shè)計(jì)文件，20座曾經(jīng)經(jīng)歷過五次較大雪載作用的，五次強(qiáng)風(fēng)荷載作用的，至今仍然存在的建筑物。統(tǒng)計(jì)資料包括了大約三百七十萬在挪威注冊登記建筑物的建筑類型，建筑年限，地質(zhì)資料。特別需要注意的是那些無遮掩，完全暴露在風(fēng)荷載或者雪荷載作用下的建筑物。評定是否合理那要決定于規(guī)范中的一些數(shù)據(jù)在設(shè)計(jì)中使用是否準(zhǔn)確，理論上的參數(shù)是

7、否包括在正常范圍之內(nèi)。調(diào)查把重心集中在評估建筑物的主要負(fù)荷-支承結(jié)構(gòu),或者更小的范圍甚至可以僅是副載重-支承結(jié)構(gòu)。表1列舉了各年份挪威各地區(qū)所發(fā)生塌陷事故的建筑。</p><p>　　表1 主要由雪載引起的塌陷事故</p><p><b>　　房屋建筑設(shè)計(jì)規(guī)范</b></p><p>　　關(guān)于雪荷載和風(fēng)荷載效應(yīng)的荷載規(guī)范</p>

8、<p>　　1949年12月15日發(fā)布的房屋建筑規(guī)范在對于雪荷載的設(shè)計(jì)時屋頂雪荷載大致在1.5KN/m左右。在單獨(dú)建設(shè)的房屋上，不管這個估算是減少了還是荷載增加了都需要由政府權(quán)威部門批準(zhǔn)才可以執(zhí)行。屋頂上的雪荷載與屋頂?shù)男螤钣嘘P(guān)，但是其荷載標(biāo)準(zhǔn)值大小卻以簡單的方法來計(jì)算。一般正常的建筑物設(shè)計(jì)中風(fēng)壓是等于1.0 KN/m，而無遮掩部分的面積，其風(fēng)載應(yīng)該要等于1.5 KN/m。完全暴露于風(fēng)壓作用下的建筑面積，建設(shè)的主管當(dāng)局可以批準(zhǔn)

9、增加這些風(fēng)壓荷載的大小。一個封閉建筑的迎風(fēng)和背風(fēng)的系數(shù)總和可以是1.2。</p><p>　　在1970年挪威建筑規(guī)范NS3052中，是由雪載圖來說明哪些區(qū)域雪載達(dá)到1.5 KN/m，哪些在1.5KN/m和2.5 KN/m之間, 哪些在2.5 KN/m以上。風(fēng)荷載則是由四種曲線把各區(qū)域分為A,B,C,D四種，在圖2中可以看到。規(guī)范應(yīng)用更多更詳細(xì)的標(biāo)準(zhǔn)數(shù)據(jù)來指出迎風(fēng)和背風(fēng)墻的系數(shù)也是1.2。與1949年的房屋建筑規(guī)

10、范相比，在NS 3052中，不同的是它更多的指明了在空曠地區(qū)的風(fēng)速壓力是相對較小的。同時，在NS3052中，也介紹了部分傳遞系數(shù)，當(dāng)風(fēng)壓作用時的部分傳遞因數(shù)被設(shè)定成1.5的時候，雪荷載的部分傳遞因數(shù)則要設(shè)定成1.6。</p><p>　　在2002a挪威標(biāo)準(zhǔn)規(guī)范中，整個國家的434個行政區(qū)域都被分區(qū)并詳細(xì)的說明了風(fēng)壓標(biāo)準(zhǔn)規(guī)范。由風(fēng)的參考速度來定義方位(在22 m/s和31 m/s之間變化)。在迎風(fēng)的10km區(qū)域，

11、地面的粗糙程度對風(fēng)壓是很重要的。在規(guī)范里成為速度風(fēng)壓，也有五個關(guān)于地形粗糙程度的定義。另外其它重要的因素包括風(fēng)向、建筑高度、地形也需要列在考慮范圍之內(nèi)。</p><p><b>　　圖2</b></p><p>　　在這個規(guī)范的修正方法中，挪威標(biāo)準(zhǔn)規(guī)范1999（NS 3490）則為環(huán)境的負(fù)荷規(guī)定一個50年的重現(xiàn)周期。環(huán)境負(fù)荷部分的傳遞系數(shù)被設(shè)定成1.5。部分的傳遞系數(shù)

12、要乘以一個縮減系數(shù)k。</p><p>　　規(guī)范的廣泛修訂已經(jīng)相當(dāng)大的增加了規(guī)范的詳細(xì)程度。目的是為了符合表2的要求，從而達(dá)到一個安全的水平。換句話說，目的是為建筑物能達(dá)到一個相對的可靠度要求而制定了一個比較統(tǒng)一的安全等級要求，即使建筑物在不同的區(qū)域建造,但如果有些結(jié)構(gòu)處于不同的可靠度等級，那么就具有不同的安全水平。</p><p>　　表2 可靠性等級、建筑類型、可靠性系數(shù)和塌陷概率&l

13、t;/p><p>　　meloysund等人詳細(xì)描述風(fēng)荷載效應(yīng)和雪荷載的設(shè)計(jì)荷載發(fā)展歷史。</p><p><b>　　選擇標(biāo)準(zhǔn)及方法</b></p><p><b>　　使用范圍</b></p><p>　　在人多的時候發(fā)生建筑塌頂?shù)暮蠊热松俚臅r候要嚴(yán)重的多,因此在公共建筑，如體育館，若是發(fā)生類似

14、的事件，后果是非常嚴(yán)重的。但是要是在倉庫里發(fā)生類似的倒塌事件，那后果的嚴(yán)重性將會減少很多，這在規(guī)范中也有表述。在現(xiàn)行的規(guī)范下，對于易產(chǎn)生嚴(yán)重后果的公共建筑則有更強(qiáng)硬的強(qiáng)制性。</p><p><b>　　材料使用與截面尺寸</b></p><p>　　相對于雪荷載來說，輕型屋頂?shù)谋戎厥呛苄〉模允且惺茏⊙┖奢d的作用。如果當(dāng)雪荷載標(biāo)準(zhǔn)值超過設(shè)計(jì)標(biāo)準(zhǔn)值時，那么承受荷載

15、的能力要隨著雪荷載增大而增加相同的百分比。如果特定的承載力已經(jīng)很高了，那么相應(yīng)的增長可以相對少。因此，輕型結(jié)構(gòu)相對于重型結(jié)構(gòu)來說，前者更適用于積雪量超過負(fù)荷而設(shè)計(jì)的結(jié)構(gòu)，而后者則比較困難。換句話說，重型結(jié)構(gòu)有較大的內(nèi)置的安全，當(dāng)負(fù)荷增加超出本身的承載能力時，則還要考慮其內(nèi)置的安全。</p><p>　　另一個選擇的標(biāo)準(zhǔn)是建筑物跨度的大小，一幢建筑物若是跨度很大，那它往往容易倒塌。</p><p

16、>　　很多類型的工程對不平衡受荷是相當(dāng)敏感的。當(dāng)結(jié)構(gòu)在清理積雪的時候，那就是前面所講的結(jié)構(gòu)所承受的荷載大于清理前的情形。而且有很多清除積雪的時候?qū)е陆ㄖ锏顾睦右彩谴嬖诘?。因此，重要的是要知道在清理積雪期間，建筑物是否可以承受不平衡的荷載。</p><p>　　工程年限、荷載、地質(zhì)情況</p><p>　　從1949年到今天，建筑荷載設(shè)計(jì)已經(jīng)有很大的變化。因此，建設(shè)工程的時間可能

17、會告訴我們建筑物的安全水平。一般來說，在高降雪地區(qū)老的建筑物比同樣地區(qū)新的建筑物安全水平要低一些。至于風(fēng)荷載，不同安全等級的建筑也稍微是不同的。</p><p>　　在遭受嚴(yán)重的環(huán)境荷載的區(qū)域中安全水平或許已經(jīng)被影響而下降,現(xiàn)在的雪荷載和風(fēng)荷載效應(yīng)的設(shè)計(jì)已經(jīng)從過去適用于整個國家區(qū)域，調(diào)整到挪威真實(shí)的環(huán)境荷載變化，從而一般情況下荷載標(biāo)準(zhǔn)值都是需要增加的。因此，在挪威西北部的北方海岸區(qū)域，風(fēng)荷載設(shè)計(jì)中大多比別的區(qū)域都

18、是較大的。建筑物地方性以及所在地方的地質(zhì)粗糙程度也是研究雪荷載和風(fēng)荷載的重要數(shù)據(jù)資料。</p><p><b>　　構(gòu)造方法</b></p><p>　　預(yù)制結(jié)構(gòu)現(xiàn)在仍然在使用中，它的結(jié)構(gòu)設(shè)計(jì)計(jì)算也不一定按照設(shè)計(jì)的標(biāo)準(zhǔn)，許多結(jié)構(gòu)都是按照挪威實(shí)際的雪荷載來設(shè)計(jì)的。許多需要進(jìn)行雪荷載設(shè)計(jì)的結(jié)構(gòu)也可以請國外關(guān)于雪荷載設(shè)計(jì)比較有成就的國家來做，比如像丹麥。</p>

19、<p><b>　　選中的建筑物</b></p><p>　　基于以上的調(diào)查評估，從所有建筑物中挑選20座建筑物，說明了建筑物所在的地區(qū)，建筑物的類型和建筑所在地方的參考風(fēng)速度及常遇的雪荷載。如表3所示，這些已經(jīng)被挑選的建筑物都是不向外泄露的。而問題是如何獲得這些必要的文件。</p><p>　　其中三座建筑物是1970年以前建造的，八座建筑物是1970

20、-79年之間建造的，九座建筑物是1979年以后建造的，這表示這三座建筑物的荷載是由1949年建筑規(guī)范決定，而八座建筑物是1970年建筑規(guī)范決定，最后那九座建筑物是由1979年建筑規(guī)范決定的。</p><p>　　工程文件研究以及現(xiàn)場研究</p><p>　　經(jīng)對建筑物在建造的時候使用的計(jì)算模型、荷載、荷載影響力、解決方案的調(diào)查研究。荷載影響效應(yīng)是與新的荷載要求相一致，承載力也與新荷載的要求

21、相一致。經(jīng)過這些分析，結(jié)構(gòu)的利用比已經(jīng)與新的計(jì)算規(guī)范相一致，同時要加強(qiáng)利用比。</p><p>　　表3 挑選建筑的數(shù)據(jù)概要</p><p><b>　　結(jié)果</b></p><p><b>　　截面尺寸與材料數(shù)據(jù)</b></p><p>　　外部尺寸，最大跨度，主體結(jié)構(gòu)的材料見表3。建筑物的外部尺

22、寸包括寬度、長度、高度和屋頂斜坡。高度為建筑物房屋屋頂檐口到地面的高度，所有超出的或者是延伸的都不是尺寸范圍之內(nèi)。</p><p>　　正如表中的估算所所呈現(xiàn)出的，選定的建筑物大多是中型跨度建筑。坡屋頂?shù)慕嵌冉橛?和26度之間，所有建筑物高度都與其寬度和長度相關(guān)。實(shí)質(zhì)上，建筑物都列入輕質(zhì)結(jié)構(gòu)的調(diào)查之列，因?yàn)轭A(yù)計(jì)這些類型的大廈是最為脆弱的。</p><p><b>　　文件的可用性

23、和等級</b></p><p>　　根據(jù)市政府提供的資料，共有20座建筑物被挑選出來，具有可利用文件的建筑擁有優(yōu)先權(quán)。因此早期結(jié)構(gòu)上有內(nèi)置的建筑結(jié)構(gòu)是不公開的而且也是不允許被調(diào)查研究的。但是獲得這些文件是很有必要的，這樣可以從文件中知道內(nèi)置結(jié)構(gòu)的特點(diǎn)。如果能提供文件資料，這種建筑物是肯定要進(jìn)行廣泛的調(diào)查研究。即使建筑物有詳細(xì)設(shè)計(jì)資料，那也是有缺陷的，所以在這項(xiàng)調(diào)查的范圍內(nèi)我們不會去評估這方面的意義。&

24、lt;/p><p>　　選中的建筑物缺乏重要文件肯定會影響調(diào)查結(jié)果，接著計(jì)算必須根據(jù)自己的假設(shè)和估算，這可能不同于構(gòu)造的(提高的資料可供結(jié)構(gòu)計(jì)算)。隱蔽資料導(dǎo)致結(jié)構(gòu)性措施可能會增多，在缺少文件的情況下，就難以查明原因，最終不能明確的選擇結(jié)構(gòu)設(shè)計(jì)方案。</p><p>　　設(shè)計(jì)雪荷載和選定建筑的風(fēng)荷載的更改</p><p>　　表3列出了當(dāng)前要求下那些被選擇的建筑在特定范

25、圍內(nèi)其典型的雪荷載，以及速度特性的風(fēng)壓力。在所選建筑物資料中Andoy 2、Frana1和 Nittedal1一起引述成"a"和"b"。在這里, "a"意思是最初的建筑物，而"b"是指，之后增加的建筑(或延長建筑年限的建筑)。此外，這些資料也顯示了建筑設(shè)計(jì)中荷載的變化，這里的荷載設(shè)計(jì)要求是與當(dāng)時的規(guī)范相一致。表3說明了雪荷載在0.8和2.7之間更改設(shè)計(jì)的差別

26、，其均值等于1.6。在建筑物之間風(fēng)壓變化設(shè)計(jì)相應(yīng)處差別有0.4、1.4和均值0.9。換句話說, 平均雪荷載設(shè)計(jì)在增加，同時，風(fēng)壓平均設(shè)計(jì)值在下降。</p><p>　　正如所選建筑物的資料所示，在兩個不同行政區(qū)域的兩座建筑讓人體驗(yàn)到減少積雪負(fù)荷的設(shè)計(jì)。一種是積雪負(fù)荷水準(zhǔn)不變，然而另外一種是積雪負(fù)荷遞增。在對大部分關(guān)于積雪負(fù)荷設(shè)計(jì)建筑的調(diào)查中，我們發(fā)現(xiàn)對積雪負(fù)荷設(shè)計(jì)的變化已經(jīng)成為一項(xiàng)主要的要求。在調(diào)查的建筑中低坡度

27、的建筑占了優(yōu)勢，由于屋頂受積雪負(fù)荷在背風(fēng)面因素的影響下，屋頂?shù)膬A斜度已經(jīng)在15度到60度之間增減。在一座7幢建筑的屋頂中傾斜度大于15度，負(fù)荷設(shè)計(jì)的增長平均為1.4。這個數(shù)據(jù)低于整體建筑的普通平均值。</p><p>　　風(fēng)荷載規(guī)范方面變化還不像雪荷載規(guī)范那樣有了很大的差別，但是風(fēng)荷載規(guī)范所產(chǎn)生的改變也是需要進(jìn)行研究調(diào)查。就像所選建筑物資料所列出的，規(guī)范上的改變往往導(dǎo)致Andoy和Frana兩個海邊地方的建筑所受

28、風(fēng)荷載變化。在被調(diào)查的建筑物中，風(fēng)荷載與建筑物的寬度、長度都沒有太大的聯(lián)系。這個形式的建筑物，迎風(fēng)和背風(fēng)的墻壁形狀因素的總數(shù)在NS3491-4上等于0.85 ，當(dāng)換成是高層建筑時，這個系數(shù)就變成了1.5。在較早的規(guī)范中，不管是什么建筑，對應(yīng)的形狀系數(shù)都是1.2。換句話說，形狀系數(shù)在被選擇的建筑物中都是比較小的，同時，若是這建筑物的寬度和長度更大，那么其形狀系數(shù)會變的更小了。減少建筑物設(shè)計(jì)風(fēng)荷載，在多高層建筑中是不允許的。</p&g

29、t;<p><b>　　討論</b></p><p>　　如前所述，大部分挪威建筑物的無遮擋面積有5%，是總建筑面積的11%，因此選定調(diào)查建筑物類型是認(rèn)為以后是要暴露在雪荷載和風(fēng)荷載下來建設(shè)的建筑，具有典型的意義。</p><p>　　在調(diào)查的建筑物中，90%的建筑的荷載設(shè)計(jì)與現(xiàn)行的荷載規(guī)范相比都是較低的。因此，在整個挪威可能有4.5%的建筑結(jié)構(gòu)設(shè)計(jì)都是

30、可能或者完全過低于現(xiàn)行的荷載設(shè)計(jì)標(biāo)準(zhǔn)。在95%的被調(diào)查的建筑物中，雪荷載的增加表明挪威現(xiàn)在有4.7%的建筑物在設(shè)計(jì)雪荷載時也增大了其標(biāo)準(zhǔn)值。被調(diào)查的55%被指出錯誤的建筑物有了更高的利用比，或者因?yàn)橛辛隋e誤的雪荷載值而重新進(jìn)行設(shè)計(jì)建造。因此，在挪威的建筑物可能有超過荷2.8%的建筑有較高的利用比。但是調(diào)查的只有20幢，這是個不足。不過，也是具有可信度的。</p><p><b>　　結(jié)論</b&g

31、t;</p><p>　　此項(xiàng)調(diào)查研究的主要目的是獲得可靠度的指標(biāo), 挪威現(xiàn)有建筑物是否符合當(dāng)前安全監(jiān)管的關(guān)于抵抗塌陷是由于雪荷載和/或風(fēng)荷載效應(yīng)造成的要求。從調(diào)查的結(jié)果表明這些方面應(yīng)該是以后建筑物設(shè)計(jì)建造的發(fā)展趨勢的典型代表。</p><p>　　因?yàn)閯倓偛砰_始建造這類的建筑，所以20幢建筑中有18幢建筑的利用比超過1.0（是調(diào)查建筑的90%），我想以后還會增加的。盡管如此，假設(shè)一幢建筑

32、有內(nèi)置安全結(jié)構(gòu)，那么這類建筑的利用比是很少超過1.0的。</p><p>　　未來氣候變化情況表明冬天的降水量的增多以及溫度的上升，會導(dǎo)致各地的屋面雪荷載的增加。根據(jù)這些情況,估計(jì)今后建筑物的可靠性還會降低。</p><p><b>　　認(rèn)證</b></p><p>　　本文寫在正在進(jìn)行研究和發(fā)展的SINTEF計(jì)劃， "一個更加嚴(yán)峻的

33、2000年的建筑氣候條件"(2000-2006),戰(zhàn)略研究所項(xiàng)目"氣候變化給建筑環(huán)境帶來的沖擊"。(2005Liso等人著)。作者致謝所有挪威建筑業(yè)研究委員會的委員。特別感謝Jan Vincent教授，也很感謝Karl Vincent Hioseth教授和Tore Kvande教授為文章寫的評論。</p><p><b>　　參考文獻(xiàn)</b></p>

34、<p>　　Karl, T. R., and Trenberth, K.E. (2003). “Modern global climate change.” Science, 302 1719-1723</p><p>　　National office of Buildings Techolgy and Administration. (1993). “Orkan 1992.” Norwegian

35、 Building Research Insititue, Oslo, Norway (in Norwegian).</p><p>　　Standards Norway. (1970). Beregninger av belasninger, NS 3052, 1st Ed., Standard Norway, Oslo, Norway (in Norwegian).</p><p>

36、;　　Standards Norway. (1970). Prosjektering av bygningskonstruksjoner Dimensjonerende laster, NS 3479, 1st Ed., Standard Norway, Oslo, Norway (in Norwegian).</p><p>　　Standards Norway. (1999). Design of str

37、uctures Requirements to reliability, NS 3490, 1st Ed., Standard Norway, Oslo, Norway (in Norwegian).</p><p>　　Standards Norway. (2002a). Design of structures Design actions1st Ed., Standard Norway, Oslo, N

38、orway (in Norwegian).</p><p>　　McCarthy, J.J., Canziani, O.F., Leary, N.A., Dokken, D.J., and White, K.S., eds. (2001). Climate change 2001: Impacts, adaptation and vulnerability, Cambrige University Press,

39、 Cambriged, U.K.</p><p><b>　　外文原文一：</b></p><p>　　Increased Snow Loads and Wind Actions on Existing Buildings: Reliability of the Norwegian Building Stock</p><p>　　Vivia

40、n Meloysund, Ph.D. ; Kim Robert Liso, Ph.D. ; Jan Siem ; and Kristoffer Apeland</p><p>　　Abstract: Results from an investigation of snow loads and wind actions on 20 existing buildings in Norway are presente

41、d. The objective has been to investigate to what extent existing buildings meet current regulatory requirements relating to safety against collapse owing to snow loads or wind actions. Eighteen buildings have a utilizati

42、on ratio of more than 1.0 under current regulations. The new design rules have led to most of the buildings investigated having reduced safety against collapse ow</p><p>　　DOL: 10.1061/(ASCE)0733-9445(2006)1

43、32:11(1831)</p><p>　　CE Database subject headings: Bearing capacity; Buildings; Climatic changes; Norway; Reliability; Snow loads; Structural design; Structural safety; Wind loads.</p><p>　　Intr

44、oduction</p><p>　　Background</p><p>　　Large snow loads on during the winter of 1999/2000 led to the collapse of several buildings in northern Norway. The accident at Bardufoss Community Centre,

45、where the roof caved in and claimed three lives, was the most serious of these accidents (Fig.1). The most important causes of this collapse were a faulty construction of the roof when the building was erected and larger

46、 snow loads on the roof than it was designed for.</p><p>　　Principal Objectives and Delimitations</p><p>　　The principal objective of the investigation has been to obtain a reliable indicator as

47、 to whether existing buildings in Norway meet current regulatory requirements concerning safety against collapse owing to snow loads and/or wind actions, and also to establish a basis for the analysis of future climate c

48、hange impacts on the Norwegian building stock. The analysis encompasses design documentation investigations and field studies of 20 existing buildings in five high-snowfall and five high-wind m</p><p>　　Buil

49、ding Regulations and Design Codes</p><p>　　Development of Design Codes for Snow Loads and Wind Actions</p><p>　　The building regulations of December 15, 1949 referred to a general snow load on r

50、oofs corresponding to 1.5KN/m. This value could be reduced or increased by the individual building authority with the Ministry’s approval. The importance of the shape of the roof for the size of the snow load on the roof

51、 was calculated in a simple way. Structures should normally be designed for a wind pressure equal to 1.0 KN/m, while a wind pressure equal to 1.5 KN/m should be used in exposed areas. In heavily exp</p><p>　

52、　In NS 3052 (Standard Norway 1970) snow maps were introduced showing zones with roof snow loads values of up to 1.5 KN/m, between 1.5 KN/mand 2.5 KN/m, and above 2.5 KN/m. Four curves for the wind pressure were introduce

53、d: Curves A, B, C, and D, as seen in Fig.2. The code quoted many more-detailed rules for the wind shape factors for the lee and windward walls was in the code also set to 1.2. Compared to the building regulations of 1949

54、, the changes in NS 3052 largely implied a reduction in the w</p><p>　　In NS 3497-4 (Standards Norway 2002a), a classification of the whole country has been carried out so that wind exposure for all 434 muni

55、cipalities is defined. Exposure is defined by means of a reference wind velocity (varies between 22 m/s and 31 m/s). Roughness of the terrain in an area 10 km against the wind direction is important for the wind pressure

56、 (in the code called the gust velocity pressure). The code defines five such categories of terrain roughness. Other parameters of importance for</p><p>　　In this regulation amendment process, NS 3490 (standa

57、rds Norway 1999) prescribes a 50-year return period for environmental loads. The partial factors for environmental loads are set to 1.5. A reduction factor kby which the partial factor must be multiplied is introduced.&l

58、t;/p><p>　　The extensive revisions of the codes have increased the level of detail in the regulations considerably. The objective is to achieve a safety level in accordance with Table 2. In other words, the int

59、ention is to achieve a more uniform safety level for buildings that have the same reliability class even if they are built in different places, and also to obtain different safety levels for structures classified in diff

60、erent reliability classes.</p><p>　　A thorough description of the historical development of design loads for wind actions and snow loads is presented by Meloysund et al.(2004).</p><p>　　Selectio

61、n Criteria and Methodology</p><p>　　Limits of Use</p><p>　　The consequences of a collapse are greater in buildings in which many people are present than in buildings with few people. A collapse

62、in public buildings such as sports halls, and the like has. Therefore, greater consequences than, for example, in storage facilities in which it is less probable that people will be present. This is also apparent from th

63、e reliability approach set out in numbers in Table 2 in which, under current rules, more stringent requirements are imposed on structures whose c</p><p>　　Material Use and Geometry</p><p>　　For

64、light roofs, the specific weight is open low compared to the snow load that the roof is required to withstand. If the snow load exceeds the design value, the load has increased virtually the same percentage as the snow l

65、oad. If the specific weight had been high, the percentage increase would have been much smaller. Lightweight structures are, therefore, more vulnerable to an increase in snow load above the load for which the structure i

66、s designed than heavy structures. In other words, heavy </p><p>　　Another selection criterion is the maximum span of a building. The consequences of a collapse in buildings with large spans are usually great

67、.</p><p>　　A number of types of construction may be sensitive to unbalanced loads. When the structures are being cleared of snow, this may in the worst case make the stresses in the structure larger than bef

68、ore the snow clearance started. There are many examples of snow clearing leading to the collapse of structures. It is, therefore, important to know whether the structure can carry the unbalanced load that arises during s

69、now clearance.</p><p>　　Year of Construction, Loads, and Geographical Location</p><p>　　Design loads on buildings have changed considerably in the period from 1949 to today. The year of construc

70、tion may, therefore, tell something about the building’s safety level. In general, older buildings in high-snowfall areas may have a lower safety with respect to snow loads than newer buildings. The difference in safety

71、level with respect to wind action is probably somewhat less.</p><p>　　The safety level is probably affected mostly in areas that are heavily exposed to the environmental loads, when snow loads and wind actio

72、ns in the regulation are increased from general loads that have applied to the entire country to differentiated loads that are adjusted to the actual environmental load variation in Norway. Increased wind actions, theref

73、ore, probably have the greatest consequences for coastal areas from northwest Norway northward. Locally roughness of terrain and topography and</p><p>　　Construction Process</p><p>　　Prefabricat

74、ed structures are often imported. It has been claimed that design calculations do not always meet the design rules set out in Norwegian codes and that many structures have been designed for relatively small snow loads co

75、mpared to Norwegian requirements. Structures have been imported from countries such as Denmark that are designed for snow loads well below those required in Norway.</p><p>　　Selected Buildings</p><

76、;p>　　Based on the assessments above, 20 buildings were selected Table 3 lists the municipality in which the buildings were selected, the building type, and the requirement that currently applies to characteristic snow

77、 load on the ground and to the reference wind velocity. As shown in Table 3, attempts have been made to keep the selected buildings as anonymous as possible. Problems in obtaining the necessary documentation implied that

78、 an investigation of only one building was conducted in two of the m</p><p>　　Three of the buildings were constructed in the period before 1970, eight were built in the period 1970-79, and nine were built in

79、 the period after 1979. This implies that the loads are determined by the 1949 building regulations for three of the buildings, by NS 3052 for the buildings, and by NS 3479 for nine of the buildings.</p><p>

80、　　Project Documentation Investigation and Field Study</p><p>　　Calculation models, loads, forces, and solutions used when the buildings were constructed have been investigated. The forces in the structure we

81、re then determined in accordance with new load requirements, and the capacities checked in accordance with new load requirements. In light of these analyses, the structure’s utilization ratio has been determined in accor

82、dance with new calculation rules, and the need for reinforcement assessed.</p><p>　　On site, whether the structures have defects or deficiencies that are not apparent from the project documentation of whethe

83、r or not the construction was in accordance with the documentation, and whether or not there were weaknesses in the structure owing to reduced durability or due to reconstruction.</p><p><b>　　Results&l

84、t;/b></p><p>　　Geometry and Material Data</p><p>　　External dimensions, maximum spans, and the material of the main load-bearing structures are shown in Table 3. The building’s external dimen

85、sions are quoted as width, length, height, and roof slope. The height indicates the cornice height for buildings with other roof shapes. Additions or extensions that are not included in the assessments have not been incl

86、uded in the dimensions.</p><p>　　As is apparent from the values in the table, the buildings selected can be characterized as medium-sized buildings with medium spans. The roof slope varies between 0 and 26&#

87、176;. All the buildings are of low height relative to their width and length. Essentially, the buildings included in the investigation are light-weight constructions, because buildings of this type are empirically expect

88、ed to be most vulnerable.</p><p>　　Availability and Scale of the Documentation</p><p>　　When the investigations started, the writers were prepared for the fact that it might be difficult to obta

89、in full documentation on the load-bearing structures in the buildings, which in this context have been defined as design calculations and structural drawings. Although there were requirements in the building regulations

90、up to 1997 that design calculations should form part of the building licence application, it is well known that many municipalities have not enforced this requirement.</p><p>　　In light of the information su

91、pplied by the municipalities, a total of 20 buildings were selected. Buildings with available documentation were given priority. It was decided at an early stage that built-in structures would not be opened and investiga

92、ted. It was therefore necessary to obtain the best possible documentation so that built-in structures were known from the documentation. If there were links between available documentation, such selection criteria would

93、lead to the buildings most ext</p><p>　　A lack of important documentation for buildings included in the investigation can affect the results. The calculations must then be based on our own assumptions and as

94、sessments, which may be different from the constructor’s (see Table 3 for information on available structural calculations). Deficient information on hidden, structural measures may then be significant. A lack of documen

95、tation makes it difficult to uncover the reason for chosen structural designs unambiguously.</p><p>　　Changes in Design Snow Loads and Wind Actions for Selected Buildings</p><p>　　Current requir

96、ements for characteristic snow loads on the ground and characteristic gust velocity pressure against the selected buildings are presented in Table 3. In Table 3, Andoy 2, Frana 1, and Nittedal 1 are quoted with “a” and “

97、b” versions. Here, “a” means the original building and “b” means additional (or extensions). Furthermore, the changes in design loads on the buildings are shown, where current requirements are compared with the requireme

98、nts that applied when the building was being d</p><p>　　As Table 3 indicates, only two buildings in two municipalities experienced reduced design snow loads, one experienced an unaltered load level, while th

99、e rest experienced increased snow loads. The changes in the rules for snow loads have, therefore, been of major importance to the requirement concerning design snow loads on most of the buildings that have been investiga

100、ted. Buildings with a low roof slope dominate the investigation. Pitched roofs slopes of between 15 and 60°have been given reduce</p><p>　　The changes in wind action rules have not been as important as

101、the change in the snow load rules for the design loads on the buildings in investigated. As Table 3 shows, the changes in the rules have only resulted in a significant increase in the wind action on the buildings in the

102、coastal municipalities of Andoy and Frana. The buildings included in the investigation were low in height relative to their width and length. For buildings with this form, the sum of the shape factors against the wind<