高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)研究評(píng)析

李?lèi)?ài)群, 瞿偉廉, 丁幼亮, 周廣東

(1.北京建筑大學(xué) 土木與交通工程學(xué)院, 北京 100044; 2.東南大學(xué) 土木工程學(xué)院, 江蘇 南京 210096;3.武漢理工大學(xué) 道路橋梁與結(jié)構(gòu)工程湖北省重點(diǎn)實(shí)驗(yàn)室, 湖北 武漢 430070; 4.河海大學(xué) 土木與交通學(xué)院, 江蘇 南京 210098)

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高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)研究評(píng)析

李?lèi)?ài)群1,2, 瞿偉廉3, 丁幼亮2, 周廣東4

(1.北京建筑大學(xué) 土木與交通工程學(xué)院, 北京 100044; 2.東南大學(xué) 土木工程學(xué)院, 江蘇 南京 210096;3.武漢理工大學(xué) 道路橋梁與結(jié)構(gòu)工程湖北省重點(diǎn)實(shí)驗(yàn)室, 湖北 武漢 430070; 4.河海大學(xué) 土木與交通學(xué)院, 江蘇 南京 210098)

高聳高層鋼結(jié)構(gòu)焊縫在風(fēng)和地震作用下的疲勞裂紋萌生和擴(kuò)展是一種危及結(jié)構(gòu)安全甚至引起結(jié)構(gòu)倒塌的鋼結(jié)構(gòu)重要破壞形式，已經(jīng)引起國(guó)際土木工程領(lǐng)域的關(guān)心和重視. 高聳高層鋼結(jié)構(gòu)焊縫多軸高周彈性應(yīng)力疲勞和多軸低周塑性應(yīng)變疲勞劣化機(jī)理和壽命預(yù)測(cè)的研究現(xiàn)狀是：1)焊縫應(yīng)力和應(yīng)變演化過(guò)程分析；2)焊縫疲勞損傷表征；3)焊縫疲勞壽命預(yù)測(cè)與設(shè)計(jì)方法. 在此基礎(chǔ)上指出未來(lái)的主要研究方向，包括：1)焊縫多尺度應(yīng)力和應(yīng)變狀態(tài)模擬方法；2)焊接殘余應(yīng)力場(chǎng)的產(chǎn)生機(jī)理、分布模式和松弛規(guī)律；3)焊縫等效疲勞損傷參量的數(shù)力學(xué)表征；4)焊縫疲勞劣化機(jī)理；5)焊縫疲勞壽命預(yù)測(cè)方法. 研究結(jié)果可為高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)研究提供參考.

高聳高層鋼結(jié)構(gòu)； 焊縫疲勞； 強(qiáng)風(fēng)； 強(qiáng)震； 壽命預(yù)測(cè)

鋼結(jié)構(gòu)由于其高強(qiáng)、輕質(zhì)特性而廣泛應(yīng)用于高聳高層結(jié)構(gòu). 風(fēng)和地震是作用在高聳高層鋼結(jié)構(gòu)上的主要?jiǎng)恿奢d，焊接連接是高聳高層鋼結(jié)構(gòu)桿件的主要連接形式. 然而，在風(fēng)力作用下，數(shù)座高聳鋼結(jié)構(gòu)都發(fā)生了焊縫開(kāi)裂進(jìn)而導(dǎo)致結(jié)點(diǎn)破壞和結(jié)構(gòu)倒塌的事故. 如298 m高的德國(guó)Bielstein桅桿、386 m高的英國(guó)Emley Moor桅桿及143 m高的中國(guó)昆明501中波臺(tái)的桅桿等都發(fā)生了因脈動(dòng)風(fēng)動(dòng)力作用引起拉耳結(jié)點(diǎn)的焊縫開(kāi)裂，直至拉耳節(jié)點(diǎn)板的破壞和桅桿結(jié)構(gòu)的倒塌. 又如中國(guó)220 kV的舟山大跨越輸電線塔發(fā)生了因長(zhǎng)期微風(fēng)渦激動(dòng)力作用引起的頂部地線支架焊接結(jié)點(diǎn)斷裂破壞. 再如美國(guó)10余座高速公路的高聳鋼管燈桿發(fā)生了因底部鋼管與法蘭之間焊縫風(fēng)致開(kāi)裂引起法蘭節(jié)點(diǎn)破壞和結(jié)構(gòu)倒塌的風(fēng)致災(zāi)害[1-2]. 同樣，強(qiáng)烈地震作用造成高層鋼框架建筑梁柱焊縫的裂紋萌生、并向梁和柱內(nèi)擴(kuò)展、進(jìn)而引起焊接結(jié)點(diǎn)破壞的災(zāi)害案例也屢見(jiàn)不鮮. 美國(guó)北嶺大地震、日本阪神大地震中的許多高層鋼框架建筑上的梁柱焊接結(jié)點(diǎn)都發(fā)生了焊縫開(kāi)裂和擴(kuò)展造成的結(jié)點(diǎn)破壞甚至結(jié)構(gòu)倒塌[3-6]. 可見(jiàn)，在風(fēng)和強(qiáng)震作用下，高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)的焊縫處都可能發(fā)生明顯的疲勞裂紋，進(jìn)而造成結(jié)構(gòu)焊接結(jié)點(diǎn)的破壞，甚至引起結(jié)構(gòu)的倒塌. 風(fēng)和強(qiáng)震作用引起的高聳高層鋼結(jié)構(gòu)焊縫處的疲勞開(kāi)裂已成為一種危及鋼結(jié)構(gòu)安全的重要破壞形式.

已有的調(diào)查和研究表明，高聳高層結(jié)構(gòu)焊縫疲勞開(kāi)裂發(fā)生的原因主要是由于缺乏可靠的焊接結(jié)點(diǎn)區(qū)焊縫處累積疲勞效應(yīng)計(jì)算和評(píng)估方法，使得建造的高聳高層鋼結(jié)構(gòu)結(jié)點(diǎn)抵抗風(fēng)力和強(qiáng)震作用產(chǎn)生的累積疲勞損傷的能力不足. 因此，風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)是鋼結(jié)構(gòu)領(lǐng)域的重要研究方向. 本文綜述了高聳高層鋼結(jié)構(gòu)焊縫疲勞的國(guó)內(nèi)外研究現(xiàn)狀，包括焊縫應(yīng)力和應(yīng)變演化過(guò)程分析、焊縫疲勞損傷表征和焊縫疲勞壽命預(yù)測(cè)與設(shè)計(jì)方法；指出了高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)研究存在問(wèn)題、面臨挑戰(zhàn)及主要研究方向.

1 國(guó)內(nèi)外研究現(xiàn)狀

在強(qiáng)風(fēng)(強(qiáng)臺(tái)風(fēng)和強(qiáng)下?lián)舯┝?和強(qiáng)震(多維且不完全相關(guān)的)作用下，高聳高層鋼結(jié)構(gòu)焊縫均處于復(fù)雜多軸應(yīng)力狀態(tài)，其失效多為多軸疲勞破壞. 根據(jù)應(yīng)力水平的大小，可以將疲勞破壞分為兩種類(lèi)型. 當(dāng)焊縫應(yīng)力水平相對(duì)較低，使焊接結(jié)點(diǎn)區(qū)保持在彈性范圍內(nèi)工作，屬于多軸高周彈性應(yīng)力疲勞；當(dāng)焊縫應(yīng)力水平相對(duì)較高，使焊接結(jié)點(diǎn)區(qū)進(jìn)入到彈塑性的多軸應(yīng)變狀態(tài)，屬于多軸低周塑性應(yīng)變疲勞. 目前，對(duì)于風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊縫的多軸高周彈性應(yīng)力疲勞和多軸低周塑性應(yīng)變疲勞，國(guó)內(nèi)外已有一些研究.

1.1 焊縫應(yīng)力和應(yīng)變演化過(guò)程分析

高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)在焊接過(guò)程中會(huì)產(chǎn)生明顯的焊接殘余應(yīng)力場(chǎng)，焊接殘余應(yīng)力場(chǎng)在風(fēng)和強(qiáng)震引起的交變應(yīng)力作用下會(huì)有一定程度的松弛，松弛后的殘余應(yīng)力場(chǎng)與外荷載引起的應(yīng)力和應(yīng)變時(shí)程疊加形成焊接結(jié)點(diǎn)的實(shí)際應(yīng)力和應(yīng)變時(shí)程，此全過(guò)程稱(chēng)為應(yīng)力和應(yīng)變演化過(guò)程. 當(dāng)風(fēng)和地震作用引起的焊接結(jié)點(diǎn)焊縫危險(xiǎn)點(diǎn)的應(yīng)力超過(guò)屈服強(qiáng)度后，該點(diǎn)焊接殘余應(yīng)力完全松弛. 如強(qiáng)震作用下結(jié)點(diǎn)焊縫危險(xiǎn)點(diǎn)的應(yīng)變超過(guò)屈服應(yīng)變，這時(shí)就無(wú)需考慮焊接殘余應(yīng)力的影響. 可見(jiàn)，除了考慮風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)多尺度應(yīng)力、應(yīng)變狀態(tài)計(jì)算和焊接結(jié)點(diǎn)焊接殘余應(yīng)力場(chǎng)的產(chǎn)生機(jī)理、分布模式之外，還必須充分認(rèn)識(shí)焊接殘余應(yīng)力的松弛規(guī)律.

針對(duì)風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)多尺度應(yīng)力、應(yīng)變狀態(tài)的計(jì)算，國(guó)內(nèi)外目前的研究主要集中在整體結(jié)構(gòu)尺度和構(gòu)件尺度層面. 20世紀(jì)60年代，Davenport[7-9]在LiePmann抖振理論的基礎(chǔ)上建立了用于估算高聳結(jié)構(gòu)和高層建筑順風(fēng)向風(fēng)振響應(yīng)的陣風(fēng)荷載因子法，同時(shí)提出了等效靜力風(fēng)荷載的概念. 此后十年內(nèi)，Velotzz[10]、Viekery[11]和Simiu[12]等學(xué)者根據(jù)Davenport的理論，用數(shù)值計(jì)算的方法對(duì)結(jié)構(gòu)的風(fēng)振響應(yīng)進(jìn)行了研究. 80年代，Solari[13-14]在陣風(fēng)因子法的基礎(chǔ)上，提出了高聳結(jié)構(gòu)順風(fēng)向風(fēng)振響應(yīng)的閉合解. 90年代，Kasperski[15-17]指出定義為位移等效的靜力風(fēng)荷載法在計(jì)算彎矩、剪力等響應(yīng)時(shí)誤差過(guò)大，并對(duì)此提出了用荷載響應(yīng)相關(guān)法計(jì)算背景等效風(fēng)荷載. Holmes[18-20]在此基礎(chǔ)上定義了新的陣風(fēng)作用因子概念，并給出了計(jì)算格構(gòu)式自立塔架最大位移、彎矩和剪力的閉合公式. Loredo-Souza、DavenPort[21-22]還將背景響應(yīng)與共振響應(yīng)的概念直接應(yīng)用于塔線體系的風(fēng)振響應(yīng)分析. 國(guó)內(nèi)，張相庭等對(duì)高聳結(jié)構(gòu)順風(fēng)向響應(yīng)、橫風(fēng)向響應(yīng)以及風(fēng)與結(jié)構(gòu)的耦合作用進(jìn)行了研究[23-24]；樓文娟、孫炳楠[25]對(duì)大跨越輸電塔進(jìn)行了數(shù)值計(jì)算分析.

針對(duì)焊接結(jié)點(diǎn)焊接殘余應(yīng)力場(chǎng)的產(chǎn)生機(jī)理、分布模式和松弛規(guī)律，國(guó)際上其他學(xué)科的學(xué)者已有部分的研究成果. L. Karlsson[26]提出的將焊接過(guò)程分解成熱力學(xué)、力學(xué)、金相學(xué)的相互耦合過(guò)程. 在此基礎(chǔ)上，許多學(xué)者[27-39]從焊接的溫度場(chǎng)計(jì)算出發(fā)，來(lái)建立焊接殘余應(yīng)力場(chǎng)的計(jì)算方法. 還有部分學(xué)者[40-41]通過(guò)理論和試驗(yàn)研究了循環(huán)荷載下焊接殘余應(yīng)力場(chǎng)的松弛原理和數(shù)值模擬計(jì)算方法. 應(yīng)該看到他們的研究有助于我們掌握焊接殘余應(yīng)力場(chǎng)的數(shù)值計(jì)算及建立考慮焊接殘余應(yīng)力松弛的實(shí)際“焊接—風(fēng)致”應(yīng)力場(chǎng)計(jì)算方法.

1.2 焊縫疲勞損傷表征

目前，有學(xué)者針對(duì)高周彈性應(yīng)力疲勞問(wèn)題研究了多軸非比例加載條件的損傷表征方法，提出了以疲勞損傷臨界面上的應(yīng)力或應(yīng)力幅為損傷參量的臨界面法. 歸納起來(lái)，可分為二類(lèi). 其中，F(xiàn)indley[42]、Stulen和Cumnings[43]、McDiarmid[44-46]、Matake[47]、Macha[48]和Robert[49]的準(zhǔn)則可歸納為第1類(lèi)臨界面準(zhǔn)則. 這類(lèi)臨界面準(zhǔn)則認(rèn)為，臨界面上最大剪應(yīng)力(幅)和法向最大正應(yīng)力(幅)的線性組合達(dá)到最大值時(shí)，材料在臨界面上產(chǎn)生損傷. 在建立該類(lèi)臨界面準(zhǔn)則時(shí)，研究者引入了與材料及與單軸疲勞極限有關(guān)的系數(shù)，這些系數(shù)(k，B，K，a1，a2)對(duì)于構(gòu)建的臨界面準(zhǔn)則具有重要的意義. Dang Van[50-51]和Papadopoulos[52-54]基于材料微觀尺度提出的臨界面準(zhǔn)則為第2類(lèi)臨界面準(zhǔn)則，它利用剪應(yīng)力參數(shù)和靜水壓力的線性組合來(lái)構(gòu)建臨界面.

針對(duì)焊接結(jié)點(diǎn)區(qū)的多軸低周塑性應(yīng)變疲勞壽命預(yù)測(cè)，機(jī)械、航空、航天及金屬材料等學(xué)科已開(kāi)展了較多的研究. 對(duì)于塑性應(yīng)變疲勞損傷參量的表征，國(guó)際上已提出了等效應(yīng)變幅、耗散能量幅和疲勞損傷臨界面上應(yīng)變幅三種指標(biāo). 對(duì)于以等效應(yīng)變幅來(lái)表征損傷參量的等效應(yīng)變法，F(xiàn)atemi和Socie[55]通過(guò)比較指出：基于Tresca準(zhǔn)則和Mises準(zhǔn)則的等效應(yīng)變法，對(duì)于多軸低周非比例加載的塑性應(yīng)變疲勞壽命預(yù)測(cè)，誤差可達(dá)到3.5～5倍，且結(jié)果偏于不安全. 對(duì)于以耗散的能量幅來(lái)表征損傷參量的能量法，F(xiàn)atemi和Socie[55]、Jordan和Brown等[56]也指出，它的不足在于：塑性功判據(jù)是個(gè)標(biāo)量，不能反映多軸疲勞的破壞面；同時(shí)，它還需要一個(gè)精確的本構(gòu)方程，這在目前是很難做到的. 而對(duì)于以疲勞損傷臨界面上的應(yīng)變幅來(lái)表征損傷參量的臨界面法，由于它要求確定疲勞破壞面，即臨界面，及關(guān)于這個(gè)面上的應(yīng)變，因此具有一定的物理意義，是目前較廣泛應(yīng)用的一種方法. Brown和Miller[57-58]提出了疲勞損傷臨界面應(yīng)為最大剪應(yīng)變平面，并認(rèn)為損傷參量為此面上的最大剪應(yīng)變幅和法向正應(yīng)變幅. 其中前者控制裂紋的萌生，而后者控制裂紋的擴(kuò)展. Fash等[59]利用單軸疲勞試驗(yàn)數(shù)據(jù)給出了臨界面上低周疲勞破壞的判據(jù). Chu[60]、Kanazawad等[61]、Kandil等[62]和Socie等[63]都對(duì)Brown和Miller提出的方法進(jìn)行了修正. 特別地，Socie[64]及Morel[65-66]等指出將臨界面法應(yīng)用于多軸非比例加載時(shí)需考慮主軸旋轉(zhuǎn)所產(chǎn)生的附加強(qiáng)化. 因此，他們既用臨界面上的法向應(yīng)力代替法向應(yīng)變，又導(dǎo)出了考慮非比例加載時(shí)附加強(qiáng)化的低周疲勞壽命判據(jù).

1.3 焊縫疲勞壽命預(yù)測(cè)和設(shè)計(jì)方法

對(duì)于強(qiáng)風(fēng)作用下高聳鋼結(jié)構(gòu)焊接結(jié)點(diǎn)的風(fēng)致疲勞壽命預(yù)測(cè)，國(guó)際和國(guó)內(nèi)學(xué)者目前主要采用的方法是：以焊縫危險(xiǎn)點(diǎn)處的等效應(yīng)力幅為疲勞損傷參量，用雨流計(jì)數(shù)法求取損傷參量的響應(yīng)幅值譜，依據(jù)結(jié)構(gòu)焊縫材料疲勞壽命的S-N曲線和Miner線性累積疲勞損傷公式，來(lái)預(yù)測(cè)桿件和結(jié)點(diǎn)的疲勞壽命. 其中，國(guó)際學(xué)者Pile[67]進(jìn)行了開(kāi)創(chuàng)性的研究；Matsuishi和Endo[68]進(jìn)行了進(jìn)一步的拓展；Wirsching、Nagode和Fajdiga、Tovo、Rychli、Colombi和Anthes等[69-74]以及部分國(guó)內(nèi)學(xué)者以上述方法為核心，提出了高聳鋼結(jié)構(gòu)基于結(jié)構(gòu)確定性和隨機(jī)風(fēng)振響應(yīng)的風(fēng)致疲勞壽命和風(fēng)致疲勞可靠度的評(píng)定方法，探討了鋼桅桿的拉耳焊接結(jié)點(diǎn)及各類(lèi)自立式鋼塔架的焊接結(jié)點(diǎn)和構(gòu)件的風(fēng)致疲勞性能.

由于焊縫疲勞危險(xiǎn)點(diǎn)及疲勞裂紋路徑上的焊接殘余應(yīng)力場(chǎng)的確定十分困難，尚無(wú)可行的方法進(jìn)行評(píng)估，因此上述焊縫疲勞壽命預(yù)測(cè)方法均忽略了焊接殘余應(yīng)力場(chǎng)的影響[75]. 但是，由于焊縫處的焊接殘余應(yīng)力一般都較大(最大值可達(dá)到200～300 MPa)，且在交變外荷載的影響下存在焊接殘余應(yīng)力場(chǎng)的松弛效應(yīng)，它們對(duì)焊縫處實(shí)際的應(yīng)力場(chǎng)和應(yīng)變場(chǎng)及焊縫材料的疲勞壽命曲線都會(huì)有較大的影響，忽略它們會(huì)產(chǎn)生較大的誤差，因此在評(píng)估高聳鋼結(jié)構(gòu)焊接結(jié)點(diǎn)焊縫疲勞壽命時(shí)需充分考慮風(fēng)致應(yīng)力場(chǎng)、強(qiáng)震致應(yīng)變場(chǎng)、焊接殘余應(yīng)力場(chǎng)以及焊接殘余應(yīng)力場(chǎng)的松弛.

2 值得進(jìn)一步研究的問(wèn)題及面臨的挑戰(zhàn)

雖然鋼結(jié)構(gòu)的單軸、多軸、比例、非比例、低周和高周疲勞問(wèn)題已經(jīng)被廣泛探討，也取得了許多突破性成果. 但是對(duì)于風(fēng)和地震作用下高聳高層鋼結(jié)構(gòu)焊縫的疲勞劣化機(jī)理和壽命預(yù)測(cè)的研究，還存在許多問(wèn)題，致使土木工程界至今還不能對(duì)高聳高層鋼結(jié)構(gòu)焊縫的風(fēng)致和強(qiáng)震致疲勞損傷災(zāi)害做到較精確地預(yù)測(cè)和評(píng)估. 未來(lái)的主要研究方向有：

1)焊縫多尺度應(yīng)力和應(yīng)變狀態(tài)模擬方法. 由于缺乏可靠的動(dòng)力荷載下多尺度有限元模型的邊界切割和界面銜接方程，使得風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)的內(nèi)力分析尚不能達(dá)到焊縫尺度. 因此，應(yīng)進(jìn)一步研究非良態(tài)氣候條件風(fēng)荷載和不完全相關(guān)三維地震動(dòng)的隨機(jī)作用模型和數(shù)值模擬方法，提出動(dòng)力荷載下高聳高層鋼結(jié)構(gòu)整體尺度、結(jié)點(diǎn)尺度和焊縫尺度的多尺度三維非線性有限元模型的邊界切割和多尺度銜接方程，結(jié)合模型試驗(yàn)建立風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)多尺度彈性應(yīng)力響應(yīng)和塑性應(yīng)變響應(yīng)的模擬方法.

2)焊接殘余應(yīng)力場(chǎng)的產(chǎn)生機(jī)理、分布模式和松弛規(guī)律. 焊接殘余應(yīng)力場(chǎng)的產(chǎn)生機(jī)理、分布模式和松弛規(guī)律對(duì)于焊縫疲勞裂紋的產(chǎn)生和發(fā)展至關(guān)重要，然而目前仍未能深入理解焊接殘余應(yīng)力場(chǎng)的產(chǎn)生和松弛過(guò)程. 因此，應(yīng)進(jìn)一步研究高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)焊接過(guò)程的隨機(jī)熱力學(xué)模型，提出高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)焊接殘余應(yīng)力場(chǎng)的分布模式，在此基礎(chǔ)上通過(guò)試驗(yàn)研究不同循環(huán)應(yīng)力水平下焊接結(jié)點(diǎn)焊接殘余應(yīng)力場(chǎng)的松弛特征，揭示焊接結(jié)點(diǎn)焊接殘余應(yīng)力場(chǎng)的松弛規(guī)律，進(jìn)而建立風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)應(yīng)力、應(yīng)變演化過(guò)程.

3)焊縫等效疲勞損傷參量的數(shù)力學(xué)表征. 第1類(lèi)和第2類(lèi)臨界面法準(zhǔn)則都是其它學(xué)科學(xué)者針對(duì)多維簡(jiǎn)諧激勵(lì)和彎扭或拉扭工況下高周應(yīng)力疲勞的臨界面法準(zhǔn)則，并不完全適用于風(fēng)和地震作用下高聳結(jié)構(gòu)焊縫處多軸隨機(jī)應(yīng)力疲勞的情況. 因此，應(yīng)進(jìn)一步研究焊接結(jié)點(diǎn)焊縫危險(xiǎn)點(diǎn)多軸高周彈性應(yīng)力疲勞和多軸低周塑性應(yīng)變疲勞臨界面確定方法，建立多維彈性應(yīng)力和塑性應(yīng)變條件下焊縫危險(xiǎn)點(diǎn)臨界面上損傷參量等效模型，研究采用等效統(tǒng)一臨界面代替時(shí)變臨界面所引起的附加強(qiáng)化效應(yīng)的數(shù)力學(xué)表征，進(jìn)而形成焊接結(jié)點(diǎn)焊縫危險(xiǎn)點(diǎn)等效統(tǒng)一臨界面和臨界面損傷參量的確定方法.

4)焊縫疲勞劣化機(jī)理. 針對(duì)焊縫疲勞劣化機(jī)理的研究，主要集中在單軸焊縫疲勞和比例加載條件下的疲勞. 由于多軸非比例疲勞與單軸比例疲勞存在本質(zhì)的差異，使得已有的研究成果并不能直接用于多軸非比例條件下的焊縫疲勞性能分析. 因此，應(yīng)結(jié)合疲勞試驗(yàn)分析風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)焊縫高周彈性應(yīng)力疲勞和低周塑性應(yīng)變疲勞破壞特征，研究多軸非比例加載路徑對(duì)焊縫疲勞破壞的影響規(guī)律，分析焊接結(jié)點(diǎn)疲勞損傷從細(xì)微觀尺度向宏觀尺度發(fā)展進(jìn)而破壞的劣化過(guò)程及其耦合特征，揭示風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)焊縫高周應(yīng)力疲勞和低周塑性應(yīng)變疲勞劣化機(jī)理.

5)焊縫疲勞壽命預(yù)測(cè)方法. 已有的高層高聳鋼結(jié)構(gòu)焊縫疲勞壽命預(yù)測(cè)研究主要集中在風(fēng)致高周應(yīng)力疲勞方面，而針對(duì)強(qiáng)震條件下的低周應(yīng)變疲勞則開(kāi)展較少. 雖然建立了高聳高層鋼結(jié)構(gòu)焊縫風(fēng)致疲勞壽命預(yù)測(cè)方法，但是其計(jì)算過(guò)程存在諸多不合理的簡(jiǎn)化，比如忽略焊接殘余應(yīng)力，使得計(jì)算結(jié)果與實(shí)際情況差異巨大. 因此，應(yīng)通過(guò)試驗(yàn)形成各類(lèi)焊接細(xì)節(jié)高周彈性應(yīng)力疲勞和低周塑性應(yīng)變疲勞S-N曲線，結(jié)合破壞機(jī)理建立臨界面上的修正S-N曲線數(shù)學(xué)模型，在此基礎(chǔ)上建立風(fēng)和強(qiáng)震作用下焊縫疲勞壽命的預(yù)測(cè)方法，形成風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)抗疲勞設(shè)計(jì)方法.

3 結(jié) 論

對(duì)于風(fēng)力和強(qiáng)震作用下高聳高層建筑鋼結(jié)構(gòu)的焊接結(jié)點(diǎn)，無(wú)論是因脈動(dòng)風(fēng)或旋渦脫落引起的焊縫高周應(yīng)力疲勞，還是因強(qiáng)震引起的焊縫低周塑性應(yīng)變疲勞，已有的研究成果都無(wú)法可靠預(yù)測(cè)疲勞裂紋發(fā)生和發(fā)展過(guò)程，急需重新尋找準(zhǔn)確的焊縫疲勞壽命預(yù)測(cè)方法，使得高聳高層建筑鋼結(jié)構(gòu)焊接結(jié)點(diǎn)的設(shè)計(jì)更為可靠和安全.

針對(duì)高周彈性應(yīng)力疲勞和低周塑性應(yīng)變疲勞問(wèn)題，提出風(fēng)和強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊縫彈性應(yīng)力和塑性應(yīng)變的多尺度計(jì)算方法，揭示焊接結(jié)點(diǎn)焊縫焊接殘余應(yīng)力場(chǎng)產(chǎn)生機(jī)理、分布模式和松弛規(guī)律，建立風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)焊縫等效疲勞損傷參量的數(shù)力學(xué)模型，揭示風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)焊縫高周應(yīng)力疲勞和低周塑性應(yīng)變疲勞破壞機(jī)理，提出風(fēng)和強(qiáng)震作用下焊接結(jié)點(diǎn)高周應(yīng)力疲勞和低周塑性應(yīng)變疲勞壽命的預(yù)測(cè)公式和抗疲勞設(shè)計(jì)方法. 該方向的研究工作將為高聳高層鋼結(jié)構(gòu)焊接結(jié)點(diǎn)的抗震設(shè)計(jì)和抗風(fēng)設(shè)計(jì)提供依據(jù)，從而保證高聳和高層鋼結(jié)構(gòu)的抗震抗風(fēng)安全，具有重要的學(xué)術(shù)意義和工程應(yīng)用價(jià)值.

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[責(zé)任編輯：佟啟巾]

A Summary Review of Fatigue Deterioration Mechanism and Life Prediction of Welded Joints on Tall Steel Structures under Winds and Earthquakes

Li Aiqun1, 2, Qu Weilian3, Ding Youliang2, Zhou Guangdong4

(1.School of Civil and Traffic Engineering, Beijing University of Civil Engineering and Architecture, Beijing 100044;2.School of Civil Engineering, Southeast University, Nanjing 210096;3.Hubei Key laboratory of Roadway Bridge & Structure Engineering, Wuhan University of Technology, Wuhan, 430070;4.College of Civil and Transportation Engineering, Hohai University, Nanjing 210098)

Fatigue crack initiation and propagation of weld joints on tall steel structures under winds and earthquakes, which may reduce structural safety and cause structural collapse, is an important failure mode of steel structures and drawn attention of engineers and researchers in civil engineering throughout the world. In the paper, the stat-of-the-art of the multi-axial high-cycle stress fatigue and the multi-axial low-cycle plastic-strain fatigue in weld joints of tall steel structures, including: 1) the evolutionary process of stress/strain in weld joints; 2) the indicator of fatigue damage in weld joints; and 3) the fatigue life prediction and fatigue resistance design method of weld joints, is summarily reviewed. Based on this, the challenges and promising research fields, such as: 1) the simulation of multi-scale stress/strain in weld joints; 2) the generation, distribution, and relaxation of welding residual stress, 3) the mathematical and mechanical models of equivalent fatigue damage indexes; 4) the failure mechanism of welded joints, and 5) the fatigue life prediction methodology of welded joints, is presented. The results are expected to provide reference value for the research of fatigue deterioration mechanism and life prediction of welded joints on tall steel structures.

tall steel structures; welded joint fatigue; strong wind; strong earthquake; life prediction

1004-6011(2016)03-0029-07

2016-08-03

國(guó)家自然科學(xué)基金重點(diǎn)項(xiàng)目(51438002)

李?lèi)?ài)群(1962—)， 男， 教授， 博士生導(dǎo)師， 博士， 研究方向： 結(jié)構(gòu)健康監(jiān)測(cè)與振動(dòng)控制.

TU973+.13

A