焊接板梁外文翻譯

1、<p><b>　　畢業(yè)設(shè)計(jì)（論文）</b></p><p><b>　　譯文及原稿</b></p><p>　　譯文題目 5-6 焊接板梁 </p><p>　　原稿題目 5-6 Welded Plate Girders

2、 </p><p>　　原稿出處 Leonard Spiegel, George F.Limbrunner. Applied Structural Steel Design (Fourth Edition) </p><p&g

3、t;<b>　　焊接板梁</b></p><p>　　板梁腹板和翼緣的初步選擇</p><p>　　ASDS，B10部分聲明，在一般情況下，板梁應(yīng)該由慣性矩比例的方法確定。這種方法要求選擇一個(gè)適當(dāng)?shù)脑囼?yàn)截面，然后用慣性矩比例檢查。</p><p>　　如前所述，總梁深度范圍大致為跨度的1/8到1/12，取決于負(fù)載和跨度的要求。因此,腹板深度范圍

4、可能為減去2到4。假設(shè)小于梁總深度,那么腹板厚度可以在ASDS中允許的深度厚度比基礎(chǔ)上選出。這些比率是基于屈曲的考慮，腹板必須有足夠的厚度抵抗梁在荷載作用下產(chǎn)生的屈曲。由于腹板的垂直壓縮和在翼緣的組成部分上偏轉(zhuǎn)的梁作用應(yīng)力,使主梁,垂直壓縮腹板構(gòu)成擠壓作用。腹板屈曲強(qiáng)度須能抵抗這些擠壓作用。這是ASDS標(biāo)準(zhǔn)(Gl節(jié)) 腹板高厚比不超過規(guī)定的翼緣最低的屈服應(yīng)力的基礎(chǔ)。</p><p>　　h/t>14000/

5、 ADSD EP.(G1-1)</p><p><b>　　注:</b></p><p><b>　　h=翼緣之間的距離</b></p><p><b>　　t=腹板厚度</b></p><p>　　=指定的翼緣最低的屈服應(yīng)力</p><p>　

6、　在翼緣之間，如果橫向中間加強(qiáng)板的間隔距離不超過腹板高度的1.5倍，那么這一比率是允許超出的。最大的h/ t比率則變?yōu)?lt;/p><p>　　最大h/t=2000/ ASDS EP.(G1-2)</p><p><b>　　5-6節(jié) 焊接板梁</b></p><p>　　表格5-4 最大h/ t比率</p>

7、<p>　　表5-4中，前面兩個(gè)表達(dá)式的值可作為各個(gè)的值。</p><p>　　此外,考慮到腹板屈曲，可能需要減少在壓縮翼緣允許彎曲應(yīng)力。根據(jù)ASDS，G2部分,當(dāng)腹板深度-厚比超過760/,在壓縮翼緣上的最大彎曲應(yīng)力必須降低到一個(gè)值,這個(gè)值可以從ASDS方程計(jì)算(G2-l)。</p><p>　　在ASDS，G3部分中，梁腹板依靠的拉力場(chǎng)作用（以短期內(nèi)定義）必須勻稱，在平面的

8、時(shí)候腹板彎曲拉應(yīng)力不超過0.60或</p><p>　?。?.825-0.375f/） ASDS EP.(G5-1)</p><p><b>　　注：</b></p><p>　　f=計(jì)算腹板平均剪切應(yīng)力(總剪力除以腹板面積)</p><p>　　=根據(jù)ASDS方程允許的腹板剪應(yīng)力（G

9、3-1）（KSI）</p><p>　　實(shí)際上，彎曲和剪切應(yīng)力的相互作用導(dǎo)致了容許彎曲應(yīng)力的減少（ASDS，G5節(jié)）。</p><p>　　經(jīng)初步選定腹板尺寸，所需的翼緣面可使用如下近似的方法決定。參考圖5-21，總截面的慣性矩軸x-x</p><p><b>　　I=I+I </b></p><p>　　當(dāng)忽略翼緣面

10、自身形心軸的慣性，可假設(shè)h（d-t），近似慣性總值可表示為</p><p>　　I= th/12+2A(h/2) </p><p>　　截面模數(shù)（S）表示，并假設(shè)hd</p><p>　　S= th/12/h/2+2A(h/2)/h/2</p><p><b>　　= th/6+Ah</b></p><

11、;p>　　圖5-21 主梁命名</p><p>　　所需的S=M/F，因此，</p><p>　　M/F=th/6+Ah</p><p><b>　　以及</b></p><p>　　所要求的A=M/Fh-th/6</p><p><b>　　注：</b><

12、/p><p>　　A=一個(gè)主梁翼緣的面積</p><p><b>　　h=梁腹板的深度</b></p><p>　　F=壓縮翼緣的允許彎曲應(yīng)力</p><p>　　M=繞X-X軸的最大彎矩</p><p>　　在此表達(dá)式M/（Fh）中，假設(shè)無(wú)梁腹板的作用，所需的第一部分翼緣面必要能抵抗彎矩M。但是由于

13、腹板提供一些彎矩阻力，在第二個(gè)部分（th/6）也要包含在內(nèi)。</p><p>　　根據(jù)計(jì)算確定所需的翼緣面，翼緣的實(shí)際比例要考慮額外的ASDS標(biāo)準(zhǔn)確定。</p><p>　　為了防止ASDS，B5部分和表B5.1受壓翼緣的局部屈曲，規(guī)定翼緣寬厚比為上限。此I形板梁的翼緣上限是在非緊湊形狀列表B5.l中。非緊湊分類是不太可能使用在緊湊部分產(chǎn)生的梁尺寸。因此，在一般情況下，0.60F作為允許的

14、最大彎曲應(yīng)力。因?yàn)橐浞挚紤]到有效（沒有受到進(jìn)一步的許用應(yīng)力減少）翼緣，受壓翼緣寬度厚度比不得超過95.0。數(shù)學(xué)表達(dá)為：</p><p><b>　　b/t95/</b></p><p><b>　　注:</b></p><p>　　b=全部名義翼緣寬度的一半(b/2)</p><p>　　t=翼緣

15、厚度（TF）</p><p>　　F=規(guī)定的最小屈服應(yīng)力（KSI）(組合梁的屈服應(yīng)力,用有效翼緣的強(qiáng)度儲(chǔ)備F代替)</p><p>　　K=擠壓元素約束系數(shù)</p><p>　　如果h/ > 70年,可以確定為</p><p>　　K=4.05/（h/t）</p><p>　　否則，K取1.0。H定義為翼緣之間的

16、凈長(zhǎng)。</p><p>　　當(dāng)K=1.0，所有的95.0列于ADSD中表5的數(shù)值部分。根據(jù)b/t=b/2t=15.8</p><p>　　確定A36鋼最大主梁板寬度（充分有效的延伸段）</p><p><b>　　那么 </b></p><p>　　最大b=2（15.8t）=31.6t</p><p&

17、gt;　　正如前面提到的，腹板屈曲是必要的,如果腹板深厚比超過760/，那么壓縮翼緣允許的彎曲應(yīng)力應(yīng)減少。當(dāng)這種情況發(fā)生時(shí)，允許的翼緣應(yīng)力不得超過</p><p>　　’[1.0-0.0005A/A(h/t-760/)]R ASDS Ep(G2-1)</p><p><b>　　注：</b></p><p>　　=在ASDS，f章確定適

18、用的彎曲應(yīng)力</p><p><b>　　A=腹板的面積</b></p><p><b>　　A=壓縮翼緣面積 </b></p><p>　　’=由于大部分腹板的深厚比，在壓縮翼緣板梁允許減少的彎曲應(yīng)力</p><p>　　R=組合梁系數(shù)對(duì)非組合梁取1.0</p><p>　

19、　括號(hào)內(nèi)的[]是板梁的彎曲強(qiáng)度折減系數(shù)，指定的R在ASDS，部分G2中。</p><p>　　在完成梁腹板和翼緣的初步選定，由于考慮到橫向不支持的壓縮翼緣，必須計(jì)算慣性和截面模數(shù)。然后計(jì)算允許的彎曲應(yīng)力，并與實(shí)際的彎曲應(yīng)力比較。</p><p>　　翼緣板，在其最大彎矩的基礎(chǔ)上確定大小，這樣會(huì)延長(zhǎng)梁的全長(zhǎng)。這是不必要的，因?yàn)楫?dāng)彎矩明顯下降時(shí)，他們可能會(huì)減少。改變翼緣板是最好的方法，通過改變

20、板的厚度，寬度，或兩者都改變，在兩個(gè)翼緣板的兩端加入下降槽的對(duì)接焊縫。只有當(dāng)節(jié)省翼緣材料的成本多于在過渡位置對(duì)接焊縫的額外費(fèi)用，才可以減小任何板的尺寸。</p><p>　　翼緣板理論過渡點(diǎn)的測(cè)定與板梁蓋板理論截止點(diǎn)的測(cè)定類似。這是在第5-3中討論。</p><p><b>　　橫向中間加勁肋</b></p><p>　　橫向中間加勁肋的作用主

21、要是對(duì)屈曲深，薄梁腹板加勁的目的。然而，在ASDS，允許梁腹板進(jìn)入屈曲范圍，因?yàn)橛醒芯勘砻鳎咏畹男「拱寮羟忻?，它仍然可以繼續(xù)抵制不斷增加的負(fù)載。當(dāng)這種情況發(fā)生時(shí)，屈曲的腹板承受著對(duì)角線的張力和中間加勁肋壓力。這種行為被稱為張力場(chǎng)作用，并且加筋肋的設(shè)計(jì)必須考慮到增加的壓縮荷載。</p><p>　　如果腹板的h/t比率是小于260（以及比在表5-4中規(guī)定的限制少）并且最大的腹板剪應(yīng)力小于ASDS方程（F4-2）所

22、允許的，那么可以不考慮中間加筋肋和張力場(chǎng)的作用，注</p><p><b>　　最大=V/h t</b></p><p><b>　　允許剪應(yīng)力</b></p><p>　　=(C)/2.890.40 ASDS方程（F4-2）</p><p><b>　　注:</b&g

23、t;</p><p>　　C=45000k/ (h/ t) 當(dāng)C<0.8</p><p>　　=190 /( h/ t) 當(dāng)C>0.8</p><p>　　k=4.0+5.34/(a/h) 當(dāng)a/h<1.0</p><p>　　=5.34+4.00/(a/h)

24、當(dāng)a/h>1.0</p><p><b>　　注：</b></p><p><b>　　t=腹板厚度</b></p><p>　　a=中間加勁肋之間的距離</p><p><b>　　h=翼緣之間的距離</b></p><p>　　36KSI屈服應(yīng)

25、力鋼和50KSI屈服應(yīng)力鋼各自允許的剪切應(yīng)力，在ASDS方程（F4-2）的基礎(chǔ)上，可能從ASDM的第2部分，表1-36和表1-50中得到。這些值是基于張力場(chǎng)作用沒有發(fā)生。當(dāng)存在張力場(chǎng)的作用，梁以外的混合梁（假設(shè)提供適當(dāng)?shù)闹虚g加勁肋），36KSI屈服應(yīng)力鋼和50KSI屈服應(yīng)力鋼各自允許剪應(yīng)力可能取自ASDS方程（G3-L），或ASDM的第2部分，表2-36和2-50中。</p><p>　　當(dāng)需要中間加勁肋，間距必

26、須符合腹板實(shí)際的剪應(yīng)力不超過ASDS方程（F4- 2）或（G3-1）(如適用)的值。a/h（有時(shí)也被稱為長(zhǎng)寬比）的比例不得超過所給出的值</p><p>　　a/h(260/h/t) ASDS方程（F5-1）</p><p>　　最大間距為梁腹板高度H的三倍。</p><p>　　當(dāng)要求有中間加勁肋時(shí)，設(shè)計(jì)過程需找到支撐梁第一中間加筋肋的相對(duì)

27、端支承加勁肋。這必須根據(jù)ASDS公式（F4- 2）或表1-36和1-50的ASDM的第2部分，因?yàn)檫@個(gè)面板必須在沒有任何張力場(chǎng)作用下設(shè)計(jì)（ASDS 部分G4）。</p><p>　　剩余中間加勁肋的間距計(jì)算可能是基于傳統(tǒng)的設(shè)計(jì)方法。ASDS方程（F4-2）或表l-36和1-50，可用于確定允許設(shè)計(jì)剪應(yīng)力，或根據(jù)設(shè)計(jì)的張力場(chǎng)作用，ASDS方程（G3-1）或，ASDM第2部分的表2-36，表2-50基礎(chǔ)上來(lái)確定。注意

28、表的使用，結(jié)合梁的最大剪應(yīng)力圖，有助于加勁肋間距的快速選擇。</p><p>　　然后確定加勁肋的大小，一般而言，焊接板梁的加勁肋交替焊接在腹板的每一側(cè)。</p><p>　　當(dāng)需要加勁肋時(shí)，他們必須滿足最低慣性彎矩的要求，是否有張力場(chǎng)的作用。為了提供足夠的側(cè)向支撐腹板，ASDS，G部分4要求所有中間加勁肋（不管是一對(duì)或一個(gè)）參考腹板平面軸I的慣性矩，如：</p><p

29、>　　I(h/50)ASDS方程（G4-1）</p><p>　　加強(qiáng)板，還必須滿足ASDS方程（G4-2）規(guī)定的最小截面積。中間加勁肋的總面積（平方英寸），間距必須不小于ASDS方程（G3-1）的要求。 </p><p>　　A=1-C/2[a/h-(a/h) /]YDhtASDS方程（G4-2）</p><p><b>　　注：</b&

30、gt;</p><p>　　C，a，h和t如先前定義</p><p>　　Y=腹板鋼的屈服應(yīng)力與加筋鋼的屈服應(yīng)力比</p><p>　　D=1.0成對(duì)布置加勁肋</p><p>　　=1.8單側(cè)角鋼加勁肋</p><p><b>　　=2.4單側(cè)加勁肋</b></p><p&g

31、t;　　當(dāng)加勁肋成對(duì)布置，如何確定該區(qū)域的總面積。此區(qū)域的要求，是張力場(chǎng)作用過程中的中間加勁肋能提供足夠的抗壓能力。因此，在設(shè)計(jì)時(shí)只需根據(jù)張力場(chǎng)的作用。</p><p>　　要求的A，在大多數(shù)情況下從ASDM，第2部分，使用斜體表列值的表2-36或2-50得到。當(dāng)f<面板中的,要求的總面積可能因?yàn)楸壤齠v/而減?。ˋSDS，G4部分）。</p><p>　　此外，在ASDS，B5部分

32、，表B5.1中，主梁加勁肋寬厚比不得超過95/。</p><p>　　一般來(lái)說，中間加筋肋在梁受拉翼緣的截?cái)喔鶕?jù)ASDS要求，加勁肋產(chǎn)生附加焊縫的最小長(zhǎng)度，（ASDS，第G4）。</p><p>　　最小長(zhǎng)度=腹板深度-6（腹板厚度）-翼緣與腹板間的焊縫尺寸</p><p><b>　　支承加勁肋</b></p><p>

33、;　　成對(duì)支承加勁肋一般放置在板梁的腹板兩端和在非框架集中荷載作用點(diǎn)。除了使反作用力或集中荷載轉(zhuǎn)移到腹板，支承加勁肋還可以防止腹板局部屈服，以及一般的腹板損壞和側(cè)移腹板屈曲，在這篇課文的第4章討論。支承加勁肋是否需要在集中荷載下或反作用力的測(cè)定，使用相同的標(biāo)準(zhǔn)：ASDS方程（K1-2）和（K1-3）為腹板屈服（K1-4）和（K1-5）為腹板損壞。k維，在腹板屈服方程，（K1-2）和（K1-3）中使用，采取從外表面的翼緣角焊縫和梁腹板交界

34、處的距離。（參見圖5-22。）如果提供加勁肋并延長(zhǎng)了至少h/2，ASDS方程（K1-4）和（K1-5）就需要檢查。</p><p>　　對(duì)于第三個(gè)考慮，側(cè)移腹板的屈曲，當(dāng)其中翼緣對(duì)相對(duì)水平運(yùn)動(dòng)不受限制則適用。當(dāng)壓縮載荷超過下列值，就需要支承加勁肋時(shí)。</p><p><b>　　第5-6焊接板梁</b></p><p>　　圖5-22 支承

35、加勁肋</p><p>　　如果加載的翼緣受限制于偏轉(zhuǎn)以及該值的</p><p><b>　　然后</b></p><p>　　注意：這種情況下，相對(duì)于腹板的歪曲，假定翼緣保持相互平行。</p><p>　　如果加載的翼緣不受制于偏轉(zhuǎn)以及該值</p><p><b>　　然后</b

36、></p><p><b>　　在這里</b></p><p>　　R=最大反力或集中荷載（K）</p><p>　　L=最大的側(cè)向無(wú)支撐長(zhǎng)度沿任意翼緣的負(fù)載點(diǎn)（英寸）</p><p>　　B=翼緣寬度（英寸）</p><p>　　d=d-2k=腹板角焊縫（英寸）凈高</p>

37、<p>　　如果分別超過2.3或1.7，或腹板是受均勻分布負(fù)載，方程（K1-6）和（K1-7）不需要檢查。</p><p>　　如果板梁是連接在板兩端的列和/或角度，端支承加勁肋通常是不必要的。</p><p>　　圖5-23 列支承加勁肋</p><p>　　支承加勁肋應(yīng)緊密接觸，大約延伸到翼緣邊緣，如圖5-22所示。</p><

38、p>　　雖然不是ASDS所要求，建議所有支承加勁肋應(yīng)全面深入并且成列設(shè)計(jì)，假定成列部分將組成雙加勁肋和位于中心地帶的腹板，當(dāng)加勁肋位于腹板兩端，其寬度不超過厚度的12倍或當(dāng)加勁肋在位于內(nèi)部負(fù)荷，其寬度不超過厚度的25倍（見圖5-23）。有效列的長(zhǎng)度不應(yīng)小于計(jì)算長(zhǎng)細(xì)比加勁肋長(zhǎng)度的四分之三（ASDS，K1.8節(jié)）。加強(qiáng)板也必須檢查局部承載的壓力。只有腹板翼緣焊縫以內(nèi)的加勁肋被視為有效的支承，支承的應(yīng)力不應(yīng)超過允許值0.90fy（ASD

39、S，J8）。</p><p><b>　　梁的連接</b></p><p>　　中間加筋肋到腹板的連接：ASDS，G4部分，估計(jì)由于張力場(chǎng)的變化，每線性英寸的總剪切力（f）必須在中間加勁肋和腹板之間轉(zhuǎn)移。下面表示提供的最低值</p><p>　　如果實(shí)際的腹板剪切力基于</p><p>　　小于ASDS方程（G3-1）允

40、許剪切力的基礎(chǔ)上，然而，轉(zhuǎn)移的剪切力（f）可能會(huì)成正比減少。</p><p>　　一般來(lái)說，這個(gè)連接是間歇角焊縫,焊縫之間的凈距離不能超過腹板厚度的16倍或10英寸。</p><p>　　支承加勁肋到腹板的連接：</p><p>　　由于支承加勁肋是承載的要素，連接焊縫通常是一個(gè)在每個(gè)加筋板兩側(cè)的連續(xù)角焊縫。焊縫設(shè)計(jì)是用來(lái)傳輸總反應(yīng)力或腹板的集中荷載。</p&

41、gt;<p>　　翼緣板到腹板的連接：</p><p>　　翼緣板到腹板的連接為了防止產(chǎn)生總水平剪切梁的彎曲力。此外，焊縫必須勻稱傳輸任何直接荷載作用到腹板的翼緣，除非提供傳輸有直接影響，例如負(fù)荷通過支承加勁肋。</p><p>　　這焊縫可設(shè)計(jì)為間歇性的角焊縫，支承加勁肋到腹板的焊縫應(yīng)是連續(xù)的，腹板翼緣到腹板的焊縫也應(yīng)是連續(xù)的。這些都是作者的論點(diǎn)。</p>&

42、lt;p>　　總水平剪切力（千磅每線性英寸）可從下列表達(dá)式（任何材料的強(qiáng)度）得出</p><p><b>　　注：</b></p><p>　　=翼緣相對(duì)梁中性軸的靜矩（IN.3）</p><p>　　V=最大剪力（KI）</p><p>　　I=梁截面的總慣性矩（IN.3）</p><p>

43、;　　當(dāng)負(fù)載直接作用于翼緣（無(wú)支承加勁肋存在），可考慮每英寸的垂直剪切力和矢量的水平剪力，以確定腹板和翼緣之間產(chǎn)生的剪切力。</p><p>　　使用v=w/12（其中W是分布負(fù)載千磅每英尺或磅每英尺）作為直接應(yīng)用于翼緣每線性英寸剪切力，</p><p>　　連接必須能夠傳輸剪切力V。</p><p>　　ASDM的第2部分，提供一般說明，從45到92英寸的名義深度

44、，設(shè)計(jì)實(shí)例和焊接板梁屬性表是一個(gè)范圍廣泛的部分，此表作為選擇經(jīng)濟(jì)比例焊接板梁的指導(dǎo)。由于在ASDM板梁的設(shè)計(jì)范圍，包括四個(gè)不同的設(shè)計(jì)，而進(jìn)一步的設(shè)計(jì)指導(dǎo)不包括在此文中。</p><p>　　Preliminary Selection of Plate Girder Webs and Flanges</p><p>　　The ASDS, Section B10, states that,

45、in general, plate girders should be proportioned by the moment-of-inertia method. This approach requires the selection of a suitable trial cross section that would then be checked by the moment-of-inertia method.</p&g

46、t;<p>　　As was mentioned previously, the total girder depth should generally range from 1/8 to 1/12 of the span length, depending on load and span requirements. Therefore, the web depth may be estimated to be from

47、 2 to 4 in. less than the assumed girder total depth. The web thickness may then be selected on the basis of permissible depth-thickness ratios as established in the ASDS. These ratios are based on buckling consideration

48、s. The web must have sufficient thickness to resist buckling tendencies tha</p><p>　　h/t>14000/ ADSD EP.(G1-1)</p><p>　　where </p><p>　　h =

49、clear distance between flanges</p><p>　　t= web thickness</p><p>　　F= specified minimum yield stress of the flange (ksi)</p><p>　　It is allowed for this ratio to be exceeded if trans

50、verse intermediate stiffeners are provided</p><p>　　with a spacing not in excess of l.5 times the distance between flanges. The maximum permissible 0 ratio then becomes</p><p>　　maximum h/ t=2

51、000/ ASDS EP.(G1-2)</p><p>　　TABLE5-4 Maximum h/ t Rations</p><p>　　Resulting values for the preceding two expressions, as functions of various F values, are shown in Table 5-4.<

52、/p><p>　　In addition, web buckling considerations may require a reduction of the allowable bending stress in the compression flange. According to the ASDS, Section G2, when the web depth-thickness ratio exceeds

53、 760/, the maximum bending stress in the compression flange must be reduced to a value that may be computed from ASDS Equation (G2-l).</p><p>　　Plate girder webs that depend on tension field action (to be de

54、fined shortly), as discussed in ASDS. Section G3, must be proportioned so that the web bending tensile stress due to moment in the plane of the web does not exceed O.60For</p><p>　　（0.825-0.375f/F）F

55、 ASDS Ep(G5-1)</p><p><b>　　where</b></p><p>　　f=computed average web shear stress (total shear divided by web area) (ksi)</p><p>　　F=allowable web shear stress accordin

56、g to ASDS Equation (G3-l) (ksi)</p><p>　　This expression in effect constitutes an allowable bending stress reduction due to the interaction of concurrent bending and shear stress (ASDS, Section G5).</p>

57、;<p>　　After preliminary web dimensions are selected, the required flange area may be deter-mined by using an approximate approach as follows. With reference to Figure 5-21, the moment of inertia of the total sect

58、ion with respect to axis x-x is</p><p><b>　　I=I+I</b></p><p>　　Neglecting the moment of inertia of the flange areas about their own centroidal axes and assuming that h=(d-t),an appro

59、ximate gross moment of inertia may be expressed as</p><p>　　I= th/12+2A(h/2) </p><p>　　Expressing this in terms of the section modulus (S) and also assuming that hd:</p><p>　　S= th/

60、12/h/2+2A(h/2)/h/2</p><p><b>　　= th/6+Ah</b></p><p>　　FIGURE 5-21 Girder nomenclature.</p><p>　　The required S = M/F; therefore,</p><p>　　M/F=th/6+Ah</p&

61、gt;<p><b>　　and</b></p><p>　　required A=M/Fh-th/6</p><p><b>　　where</b></p><p>　　A= area of one girder flange</p><p>　　h = depth of the g

62、irder web</p><p>　　F=- allowable bending stress for the compression flange</p><p>　　M= maximum bending moment with respect to x-x axis</p><p>　　The first portion of this expression

63、M/(Fh) represents the required flange area necessary to resist the bending moment M, assuming no contribution by the girder web. Since the web does furnish some bending moment resistance, however, the second term (th/6)

64、is included.</p><p>　　Based on the computed required flange area, actual proportions of the flange can be determined by taking into account additional ASDS criteria.</p><p>　　To prevent a locali

65、zed buckling of the compression flange, the ASDS, Section B5 and Table B5.1, places an upper limit on the width-thickness ratio of the flange. This upper limit for the flange of an I-shaped plate girder is that tabulated

66、 for a noncompact shape in Table B5.l. The noncompact classification is used, since it is not likely that girder dimensions will be such that a compact section is produced. Therefore, in general, the maximum allowable be

67、nding stress is taken as 0.60F. For the f</p><p><b>　　b/t95/</b></p><p><b>　　where</b></p><p>　　b= half the full nominal flange width (t//z)</p><p

68、>　　t= the flange thickness (t)</p><p>　　F=the specified minimum yield stress (ksi) (for a hybrid girder, use the yield strength of the flange F instead of F)</p><p>　　k = a compressive elemen

69、t restraint coefficient</p><p>　　If h/t>70, k is determined from</p><p>　　K=4.05/（h/t）</p><p>　　Otherwise, k is taken as 1.0. h is defined as the clear distance between flanges.&

70、lt;/p><p>　　Values of 95.0 are tabulated in Table 5 of the Numerical Values section of the ASDS for the case where k=1.0. For A36 steel the maximum flange plate width (for a fully effective flange) is determine

71、d from</p><p><b>　　b/t=b/2t</b></p><p>　　from which</p><p>　　maximum b=2（15.8 t）=31.6 t</p><p>　　As was mentioned previously, a reduction of the allowable b

72、ending stress in the compression flange due to web buckling will be necessary if the web depth-thickness ratio exceeds</p><p>　　760/. When this occurs, the allowable flange stress may not exceed</p>&

73、lt;p>　　F’F [1.0-0.0005Aw/Af(h/t-760/)] Re ASDS Ep(G2-1) Modified</p><p><b>　　where</b></p><p>　　F= applicable bending stress as established by the ASDS, Chapter F (ksi)</p>

74、;<p>　　A= area of web (in.)</p><p>　　A=area of compression flange (in.)</p><p>　　F’= allowable bending stress in compression flange of plate girders as reduced because of large web depth-

75、thickness ratio (ksi)</p><p>　　R= a hybrid gilder factor that is taken as 1.0 for nonhybrid girders</p><p>　　The term within the brackets [ ] is a plate girder bending strength reduction factor

76、and is designated R in ASDS, Section G2.</p><p>　　After completing the preliminary selection of the girder web and flanges, the actual moment of inertia and section modulus must be calculated. The actual ben

77、ding stress should then be calculated and compared with the allowable bending stress. Due consideration must be given to a laterally unsupported compression flange.</p><p>　　The flange plates whose sizes are

78、 determined on the basis of the maximum bending moment may extend the full length of the girder. That is not necessary, however, and they may be reduced in size when the applied moment has decreased appreciably. Changes

79、in flange plates are best achieved by changing plate thickness, width, or both, with the ends of the two flange plates being joined by a fall-penetration groove butt weld. Any such reduction in plate size should be made

80、only if the saving in the c</p><p>　　The determination of the theoretical transition points for the flange plates is similar to the determination of the theoretical cutoff points for the cover plates of cove

81、r-plated beams. This was discussed in Section 5-3.</p><p>　　Transverse Intermediate Stiffeners</p><p>　　Transverse intermediate stiffeners primarily serve the purpose of stiffening the deep, thi

82、n girder webs against buckling. The ASDS, however, permits the girder web to go into the postbuckling range, since research has shown that after a stiffened thin web panel buckles in shear, it can still continue to resis

83、t increasing load. When this occurs, the buckled web is subject to a diagonal tension and the intermediate stiffeners to a compressive force. This behavior is termed tension field action, an</p><p>　　No inte

84、rmediate stiffeners are required, and tension field action is not considered, if the ratio h/tw for the web is less than 260 (as well as being less than the limit stipulated in Table 5-4) and the maximum web shear stress

85、 fv is less than that permitted by ASDS Equation (F4-2), where</p><p>　　maximum f=V/ht</p><p>　　and the allowable shear stress is</p><p>　　F=F(C)/2.890.40F ASDS Ep（F4-2）<

86、/p><p><b>　　Where </b></p><p>　　C=45000k/ Fy(h/t) 當(dāng)C<0.8</p><p>　　=190/(h/t) 當(dāng)C>0.8</p><p>　　k=4.0+5.34/(a/h) 當(dāng)a/h<1.0</p>&

87、lt;p>　　=5.34+4.00/(a/h) 當(dāng)a/h>1.0</p><p><b>　　where </b></p><p>　　t= web thickness</p><p>　　a= clear distance between intermediate stiffeners</p>

88、<p>　　h= clear distance between flanges</p><p>　　The allowable shear stress Fy, based on ASDS Equation (F4-2), may also be obtained from the ASDM, Part 2, Tables 1-36 and 1-50, for 36 ksi yield stress

89、steel and 50 ksi yield stress steel, respectively. These values are based on tension field action not occurring. With tension field action included, for girders other than hybrid girders (and assuming that proper interme

90、diate stiffeners are provided), the allowable shear stress Fv may be obtained from ASDS Equation (G3-l), or the ASDM, Part 2, Ta</p><p>　　The spacing of intermediate stiffeners, where stiffeners are required

91、, must be such that the actual web shear stress does not exceed the value of Fv given by ASDS Equations (F4-2)or (G3-1) as applicable. The ratio a/h (sometimes called the aspect ratio) must not exceed the value given by&

92、lt;/p><p>　　a/h(260/h/t) ASDS Ep.（F5-1）</p><p>　　with a maximum spacing of three times the girder web depth h.</p><p>　　When intermediate stiffeners are required, the desig

93、n procedure is to locate the first intermediate stiffener relative to the end bearing stiffener at the girder support. This must be based on the use of ASDS Equation (F4-2) or Tables l-36 and l-50 of the ASDM, Part 2, si

94、nce this panel must be designed without any benefit of tension field action (ASDS, Section G4).</p><p>　　The spacing for the remaining intermediate stiffeneis must then be computed and may be based on the co

95、nventional design method. ASDS Equation (F4-2) or Tables l-36 and 1-50 may be used to determine the allowable design shear stress Fv or, if designing on the basis of tension field action, ASDS Equation (G3-1) or Tables 2

96、-36 and 2-50 of the ASDS, Part 2, may be used. Note that the use of the tables, in combination with a maximum shear stress diagram along the girder, assists in a rapid selection </p><p>　　The size of the sti

97、ffener is then determined. Generally, for welded plate girders, the stiffeners are plates welded alternately on each side of the web.</p><p>　　Whenever stiffeners are required, they must satisfy minimum mome

98、nt-of-inertia requirements, whether tension field action is counted upon or not. To provide adequate lateral support for the web, the ASDS, Section G4, requires that all intermediate stiffeners (whether a pair or single)

99、 have a moment of inertia Ist with reference to an axis in the plane of the web, as follows:</p><p>　　I(h/50) ASDS Eq. (G4-l)</p><p>　　The stiffeners must also satisfy a minimum

100、cross-sectional area requirement as provided by ASDS Equation (G4-2). The gross area (in.) of intermediate stiffeners, spaced as required for ASDS Equation (G3-1), must not be less than</p><p>　　A=1-C/2 [a/h

101、-(a/h)/] Y D ht ASDS Ep. (G4-2)</p><p>　　where </p><p>　　C, a,h, and t are as previously defined</p><p>　　Y = ratio of yield stress of w

102、eb steel to yield stress of stiffener steel</p><p>　　D = 1.0for stiffeners furnished in pairs</p><p>　　= 1.8 for single-angle stiffeners</p><p>　　= 2.4 for single-plate stiffeners&l

103、t;/p><p>　　When stiffeners are furnished in pairs, the area determined is total area. This area requirement is for the additional purpose of supplying adequate compression capacity for the intermediate stiffene

104、r during tension field action. Hence it should be used only when the design is based on tension field action.</p><p>　　The required As, may also be obtained in most cases from the ASDM, Part 2, Table 2-36 or

105、 2-50, using the italicized tabulated values. This gross area requirement may be reduced by the ratio f/F when f<F in a panel (ASDS, Section G4).</p><p>　　In addition, the ASDS, Section B5, Table B5.1, st

106、ates that the ratio of width to thickness for plate girder stiffeners must not exceed 95/.</p><p>　　Generally, intermediate stiffeners are stopped short of the girder tension flange. A minimum length of stif

107、fener, based on ASDS requirements for the attaching weld (ASDS,Section G4), may be taken as</p><p>　　minimum length = web depth - 6(web thickness) - web to flange weld size</p><p>　　Bearing Stif

108、feners</p><p>　　Bearing stiffeners are generally placed in pairs at unframed ends on the webs of plate girders and where required at points of concentrated toads. In addition to transferring reactions or con

109、centrated toads to the web, bearing sriffeners prevent localized web yielding as well as a more general web crippling and sidesway web budding, which were discussed in Chapter 4 of this text. The determination of whether

110、 bearing stiffeners are required under concentrated load or at reactions makes use of the</p><p>　　For the third consideration, sidesway web budding, the following applies where flanges are not restrained ag