管國(guó)東 翟慕賽 張培杰 王春生
摘要:采用動(dòng)態(tài)稱重(WIM)技術(shù)對(duì)陜西省省道S305線崾峴中橋進(jìn)行交通荷載監(jiān)測(cè),分析得出了適合陜西省混凝土橋梁的標(biāo)準(zhǔn)疲勞車模型。采用動(dòng)應(yīng)變監(jiān)測(cè)技術(shù)對(duì)混凝土矮箱梁關(guān)鍵部位進(jìn)行長(zhǎng)期動(dòng)應(yīng)變監(jiān)測(cè),獲得了運(yùn)營(yíng)狀態(tài)下混凝土矮箱梁的實(shí)測(cè)應(yīng)力譜;運(yùn)用Miner線性準(zhǔn)則和應(yīng)力幅-循環(huán)次數(shù)曲線對(duì)結(jié)構(gòu)進(jìn)行疲勞壽命評(píng)估;對(duì)超載情況下混凝土矮箱梁的疲勞壽命進(jìn)行了分析。結(jié)果表明:在目前交通荷載作用下,混凝土矮箱梁的疲勞壽命為5 120年,考慮腐蝕疲勞的因素后疲勞壽命降至254年;當(dāng)超載車輛比例低于1%時(shí),超載對(duì)橋梁結(jié)構(gòu)的疲勞壽命影響很小;當(dāng)超載車輛比例達(dá)到10%時(shí),結(jié)構(gòu)的疲勞壽命隨著超載率的提高而顯著降低;該研究成果可為崾峴中橋未來(lái)維護(hù)管理提供技術(shù)支撐,同時(shí)為同類型其他橋梁的疲勞壽命評(píng)估提供參考。
關(guān)鍵詞:混凝土矮箱梁橋;疲勞性能;運(yùn)營(yíng)監(jiān)測(cè);交通荷載;超載
中圖分類號(hào):U448.21 文獻(xiàn)標(biāo)志碼:A
Fatigue Performance Monitoring and Assessment for Concrete Low-box Girder Bridge
GUAN Guo-dong1, ZHAI Mu-sai2, ZHANG Pei-jie2 , WANG Chun-sheng2
(1. Xian Highway Research Institute, Xian 710054, Shaanxi, China; 2. Institute of Bridge Engineering, Changan University, Xian 710064, Shaanxi, China)
Abstract: Weigh-in-motion (WIM) system was adopted to monitor the fatigue loads of Yaoxian medium bridge in Shaanxi provincial road S305, and standard fatigue vehicle model for concrete bridges in Shaanxi province was determined based on recorded data. Dynamic strain monitoring technique was adopted to conduct continuous strain monitoring of key positions on concrete low-box girder, acquiring the real stress spectrum under service situation. Moreover, the fatigue life assessment of structures was carried out by using Miner linear criterion and stress amplitude-cycle number curve. The results show that the fatigue life of concrete low-box birder is 5 120 years under the present traffic load, and the fatigue life decreases to 254 years when taking into consideration of fatigue corrosion. Under overload situation, when the ratio of overload vehicle belows 1%, the influence is little; when the ratio reaches 10%, the fatigue life of structures will decrease sharply with increasing of the overload ratio. Research achievement can provide technical support for the future management and maintenance of Yaoxian medium bridge, and provide reference for fatigue life assessment of other similar bridges.
Key words: concrete low-box girder bridge; fatigue performance; service monitoring; traffic load; overload
0引 言
在中國(guó)的公路與城市道路建設(shè)中,混凝土結(jié)構(gòu)橋梁使用廣泛,而混凝土矮箱梁橋以其整體性好、跨越能力相對(duì)較高等優(yōu)點(diǎn),在中小跨徑混凝土橋梁中占有很高比例。伴隨著交通運(yùn)輸行業(yè)的迅猛發(fā)展,交通量、軸載及車速都在不斷提高,超載現(xiàn)象也頻繁發(fā)生,由此造成的混凝土構(gòu)件疲勞損傷不容忽視。加上環(huán)境因素、材料性能的影響,混凝土橋梁在運(yùn)營(yíng)過(guò)程中梁體開裂、鋼筋銹蝕問(wèn)題日益突出。隨著車輛荷載及外部環(huán)境的影響,在運(yùn)營(yíng)期內(nèi)鋼筋混凝土橋梁的承載能力不斷降低,而實(shí)際交通的運(yùn)營(yíng)需求卻不斷增加。為了使混凝土矮箱梁橋在運(yùn)營(yíng)期內(nèi)能夠可靠、安全地完成其任務(wù),并為后期維護(hù)管理提供相應(yīng)技術(shù)依據(jù),解決混凝土矮箱梁橋的疲勞壽命評(píng)估問(wèn)題刻不容緩。
20世紀(jì)70年代以前,鋼筋混凝土結(jié)構(gòu)均是按照容許應(yīng)力法進(jìn)行設(shè)計(jì)的,因結(jié)構(gòu)的容許應(yīng)力較低,故運(yùn)營(yíng)期間因疲勞而破壞的工程實(shí)例較少[1]。因此,在以往混凝土結(jié)構(gòu)的疲勞斷裂問(wèn)題方面沒有給予足夠的重視,中國(guó)公路規(guī)范在疲勞斷裂問(wèn)題方面亦未給出具體要求。相比一些發(fā)達(dá)國(guó)家已經(jīng)著手研究混凝土結(jié)構(gòu)的疲勞斷裂問(wèn)題而言,中國(guó)的相關(guān)研究和探索還處于開始階段。近年來(lái),鋼筋混凝土結(jié)構(gòu)逐步采用高強(qiáng)混凝土及高強(qiáng)鋼筋,并且采用極限狀態(tài)設(shè)計(jì)理論以充分利用材料的強(qiáng)度,這也導(dǎo)致結(jié)構(gòu)中很多部位都處于高應(yīng)力狀態(tài)。隨著高強(qiáng)材料的廣泛應(yīng)用使得結(jié)構(gòu)的恒載不斷降低,從而動(dòng)載所占比例相對(duì)增大,動(dòng)載引起的疲勞損傷日益嚴(yán)重。疲勞斷裂引起的失效問(wèn)題在各種結(jié)構(gòu)構(gòu)件中越來(lái)越突出,并且這一問(wèn)題正在逐漸成為造成工程結(jié)構(gòu)和構(gòu)件失效的主要原因。在理論及設(shè)計(jì)方面,由于對(duì)結(jié)構(gòu)的分析越來(lái)越精確,對(duì)混凝土的力學(xué)性能了解越來(lái)越全面,這也使我們認(rèn)識(shí)到混凝土結(jié)構(gòu)的疲勞斷裂問(wèn)題是一個(gè)不容忽視的問(wèn)題,并已逐漸成為重要研究課題[2-5]。