1、Review of assessment and repair of fire-damaged RC highway bridgesAbstract：This paper presents a review of the progress of the research and engineering practice of assessment and repair of fire-damaged RC highway bridges，based on which existing and pressing problems of the evaluation method are poin

2、ted outAt last，Prospect for the development of assessment and repair of fire-damaged highway bridges is also proposedKey words：fire damage；assessment；repair techniques；RC structure；bridge1 PrefaceFires can cause great structural damage to bridges and major disruption to highway operationsThese incid

3、ents stem primarily from vehicle accident (often oil tanker) fires， bridges might also be damaged by fires in adjacent facilities and from other causesQuite a few of them，though rarely happened，lead to severe structural damage or collapse and casualtyOn June 2，2008，fire disaster broke out under the

4、18th span of Nanjing Yangtze River Bridge and lasted for approximate 75min During the fires development and extinguishment，the structure experienced the sharp rise and fall in temperature causing severe damage to fire- stricken segmentsOn April 29，2007，a gasoline tanker overturned on the connector f

5、rom Interstate 8O to Interstate 880 in CaliforniaThe intense heat from the subsequent fuel spill and fire weakened the stee1 underbelly of the elevated roadway ,collapsing approximately 165 feet of this elevated roadway onto a section of I880belowOn March 25，2004，Connecticut，United States，a tanker t

6、ruck carrying fuel swerved to avoid a car and overturned，dumping 8000 gallons of home heating oil onto the Howard Avenue overpass The consequent towering inferno melted the bridge structure and caused the southbound lanes to sag several feetUndocumented number of bridge fires occurring throughout th

7、e world each year cause varying degrees of disruption，repair actions，and maintenance costAlthough fires caused damage to the bridge structures ,some bridges continue to function after proper repair and retrofitStill in some situations they have to be repaired for the cause of traffic pressure even t

8、hough supposed to be dismantled and reconstructedHowever ,in other cases， structures are severely damaged in the fire disaster and fail to function even after repair，or the costs of repair and retrofit overweigh their reconstruction costs overwhelmingly even if they are repairable， under which situa

9、tion reconstruction serves as a preferable optionTherefore insitu investigation and necessary tests and analyses should be conducted to make comprehensive assessment of the residual mechanical properties and working statuses after fire and to evaluate the degrees of damage of members and structures

10、, in reference to which decisions are made to determine whether Fire damaged structures should be repaired or dismantled and reconstructedUrgent need from engineering practice highlighted the necessity to understand the susceptibility and severity of these incidents as wel1 as to review available in

11、formation on mitigation strategies，damage assessments，and repair techniques.2 Progress in Research and Engineering Practice2.1 Processes of Assessment and Repair of Fire damaged Bridge StructureIn China and most countries in the world，most highway bridges are built in RC structureAnd the practice of

12、 the assessment and repair techniques of bridge structure after fire directly refer to that of RC structure，which，to date，domestic and foreign scholars have made great amount of research on，with their theories and practices being increasingly mature .As for the assessment and repair of fire-damaged

13、reinforced concrete structures， there are two mainstream assessment processes in worldCountries including United States，United Kingdom and Japan adopt the assessment process stipulated by The British Concrete Society .This process grates the severity of fire damage of concrete structure into four de

14、grees according to the deflection， damage depth，cracking width, color， and loading capacity variation of fire-damaged structures and adopt four corresponding strategies (including demolish，strengthen after safety measures，strengthen. and strengthen in damaged segments) to deal with them accordingly

15、In general，this process is a qualitative method and considered，however，not quantity enough.In Chinese Mainland and Taiwan ，the prevailing as assessment and repair process of fire damaged incorporates following steps：In comparison this process is more detailed(1)Conduct In-situ inspections，measuremen

16、ts，and tests including color observation，concrete observation，degree of rebar exposure observation， cracking measurement， deflection measurement， various destructive and nondestructive test methods as grounds for assessment of firedamaged structures In assessment of the post -fire mechanical propert

17、ies of firedamaged structures，historical highest temperature and temperature distribution of structure during the fire serve as decisive factors The common methods to determine them incorporate petrographic analysis， ultrasonic method， Rebound method，Ignition Loss method，core test，and color observat

18、ion method(2)calculate to determine whether the fire-damaged structure can meet the demand of strength and deflection under working loads after fire using mechanical properties of rebar and concrete before and after fire based on the historical highest and temperature distribution of structures obta

19、ined from step one There are two main methods to evaluate the post -fire performance of fire-damaged structures：FEM method and Revised Classic Method(3)On the basis of test and calculation results obtained from step two，take corresponding repair strategies and particular methods to strengthen the fi

20、re-damaged structures.22 Repair TechniquesFor the repair of firedamaged bridge，proper repair methods should be taken according to the degree and range of the structures damageMeanwhile the safety and economy of the repair methods should be concerned with by avoiding destructing the original structur

21、e，preserving the valuable structural members， and minimizing unnecessary demolishment and reconstruction。Common repair techniques are listed as follows(1)Fire-damaged concrete ReplacementThe replacement of firedamaged concrete is the most common technique in damaged concrete repairIf the concrete st

22、ructure is damaged only within the concrete cover，it is preferable to remove the firedamaged concrete from the structure making the rebar exposed and to make up the removed part by means of recasting or concrete spraying If the displacement of the structure exceeds the controlled value or the embedd

23、ed rebar is buckled，the damaged structure should be otherwise handled。(2)CFRP strengtheningCFRP materials have strong tensile strength and elasticity as well as excellent workability and durability and are widely applied in engineering practice in recent years CFRP materials are used to boost the lo

24、ading capacity by adhering them to the edge of tensile region to replace the reinforced rebar .CFRP are especially suitable for the projects calling for boost of loading capacity while no extra weight is allowed(3)Structural member ReplacementFor slab bridges and girder bridges ,the decks of the bri

25、dge are made of parallel girders or thick slabs .On condition that part of structural member is severely damaged in the fire so that its beyond repair or the repair cost over weigh a new one，it is preferable to replace thedamaged spans with new girders or slabsThough appears to be relatively high in

26、 cost, this method serves as reliable and effective way in engineering practice23 Case Study of Assessment and Repair Techniques of fire- damaged bridgesSome domestic and foreign scholars have conducted a series of studies on the inspection，assessment，and repair techniques of fire damaged bridges in

27、 the engineering practice by different assessment standards and processes on the casebycase basis using a variety of field andlaboratory evaluation methods， including both destructive and nondestructive testingLiterature employed visual inspection and material testing including compressive strength

28、testing and petrographic analysis(paste depth， micro cracking，color change)on a fire-damaged bridge，based on which 1oad rating analysis was performed using reduced girder and deck sectionsLiterature made qualitative safety evaluation on two fire-damaged bridge structures using the rebound method，cor

29、e tests，carbonization depth measurement， concrete cover measurement，deflection measurement，and appearance observation Literature use the combination of ultrasonic method and rebound method to determine the historical highest temperature of structures in fire，based on which stiffness and strength of

30、two fire damaged structures are determined to make safety evaluations on them And then CFRP and structural adhensive are used to strengthen the firedamaged segments respectivelyLiterature made a safety evaluation on a prestressed reinforced concrete slab bridge， the firedirectlystricken segments of

31、which are severely spalled and carbonized with embedded rebars and prestressed strands exposed Its rubber isolators were also highly carbonizedThe researcher took the core tests and inferred that local segments of the slabs were severely damaged and the prestress had been lostMeanwhile，the researche

32、r conducted a series of dynamic tests on the damaged bridge and presumed that the variation of the comprehensive performance of the bridge structure after fire was insignificant in reference to the results of the dynamic tests . The researcher proposed to replace the severely damaged slabs from the

33、perspective of durability and safetyLiterature made the damage assessment and repair work on a fire- damaged T- shaped prestressed beam bridge The fire disaster was derived from the leakage of a oil tanker and then the burning oil was spread to the underbelly of the bridge Several boundary and secon

34、dary boundary girders are consequently damaged in the fire. Judging by the fire duration，color change，and damage depth，the researcher concluded that the fire-damaged girders fell the category of severely-damaged structures and cannot be repaired for the prestress loss and material degradation Theref

35、ore five spans of boundary and secondary boundary girders are dismantled and reconstructedLiterature：1 Martha Davis，PE ，Paul Tremel，PE，Alex PedregoBill williams Bridge Fire AssessmentJStructure Magazine，2008，：3O一322 FENG Zhi-nan，CHEN AipingInspection and Assessment of an Expressway Underpass Bridge

36、After Fire DamageJWorld Bridges，2009，(2)：65673 LI Yi，XIANG Yiqiang，WANG JianjiangDamage Detection and Safety Assessment on Bridge Structure after Fire AccidentJChina MunicipalEngineering，2006，(5)：26274 LIU Qiwei，WANG Feng，XU Kaishun，CHEN Xiao qiangDetection Evaluation and Repairing of Fire Damaged B

37、ridgeJJournal of Highway and Transportation Research and Development，2005，22 (2)：71745 XI YongInspection and Evaluation of Fire Damaged BridgesJWorld Bridges，2007，(4)：62656 SUN Dasong，MIAO Changqing，LI Zhijun Examination and Evaluation of a Prestressed Concrete Slab Bridge after FireJMunicipal Engin

38、eering Technology，2007，25(3)：2462487 Zheng Jiguang，W ang Xing，Liu ZhongguAnalysis of Unforeseen Co nflagration Injury of Prestressed Concret Bridge StructureJNorthern Communieations，2007，(12)：54 57 對火災后鋼筋混凝土公路橋梁的評估和修復摘要:本文綜述了對火災后鋼筋混凝土公路橋梁的研究進展,工程實踐評估以及修復,并在此基礎上指出了現有的評估方法以及急需解決的問題.除此之外,還對火災后的公路橋梁的評估和

39、修復提出了展望.關鍵字:火災損害；評估；修復技術；鋼筋混凝土結構；橋梁。1. 前言火災能夠對橋梁結構造成重大損害，并影響公路的正常使用功能。起因主要源自車輛交通事故（通常是指油罐車）造成的火災，周邊設施著火或者其他因素，都可能使橋梁結構發生損壞。盡管許多因素鮮有發生，但一旦產生就會造成橋梁嚴重損壞并帶來人員傷亡。2008年6月2日，18跨度的南京長江大橋發生了火災，火災持續了將近75分鐘。伴隨著大火持續燃燒和最終被撲滅，橋梁結構承受了急劇的溫差變化，并給火災影響到的橋段帶來了嚴重的損壞。2007 年 4月29日，一輛油罐車在加利福尼亞州80號公路與880號公路交匯處發生側翻，隨后燃油泄漏，大火

40、產生的強熱削弱了高架橋下不鋼材的強度，最終高約165英尺高架路橋I-880段發生倒塌。2004年3月25日，美國Connecticut州，一輛攜帶燃油的油罐車為了躲開與另外一輛車的相撞，左右轉彎時發生傾倒，8000加侖的家庭供暖燃油被傾倒在Howard Avenue 立交橋，隨后漫天火海融化了橋梁結構，導致立交橋南行線降低了幾英尺。世界各地還有許多未公布的橋梁火災事故，都給橋梁造成了不同程度的損壞，增加了修復和維護成本。雖然火災給橋梁結構造成了損害，但經過適當的維修和翻新，一些橋梁仍能繼續使用。但在某些情況下，即使有些橋梁該被拆除重建，但迫于交通壓力，他們不得不在被維修之后就投入使用。然而，在

41、某些情況下，橋梁在火災中損壞嚴重，即使被修復也無法正常使用。有時橋梁修復翻新的費用壓倒性地超過了重建的費用，在這種情況下，重建是一個較好的選擇。因此，應該對火災后橋梁殘余的力學性能和工作狀態進行深入現場調查，做必要的檢測分析，以準確檢測出結構構件的破壞程度，之后來判定是該修復被損毀的橋梁，還是將其拆了重建。實際工程的迫切需求，強調了很有必要去了解橋梁對事故發生的敏感性，嚴重性，以及重新審查減災戰略，損害評定和修復方法的相關信息。2. 研究與工程實踐的進展2.1 橋梁結構受火災損壞的評估以及修復進展在世界上許多國家包括中國,大部分的公路橋是鋼筋混凝土結構.實際當中我們會直接參照混凝土結構來對遭受

42、火災之后的橋梁進行評估和修復,如此一來,到目前為止,國內外的學者經過做了大量研究,這些理論和實踐正日益成熟.至于對火災后的橋梁結構進行評估和修復,世界上有兩種主流的評估流程.包括美國,英國和日本在內的許多國家都采用了由英國土木工程協會制定的評估流程.參照偏斜的大小,損傷深度,裂縫寬,顏色以及損毀結構承載力的變化,評估流程將混凝土結構受火災損壞程度劃分為四個等級,并采取相應措施(包括拆除,安全測量加固,加固受損段)對其進行處理.一般來說，這是一個定性的流程，而不單單定量就足夠了。中國大陸和臺灣，現行的評估和修復過程采用如下步驟：經比較這種流程更詳細。（1）進行現場調查，測量。顏色觀察，具體觀測鋼

43、筋暴露程度，開裂深度測量，撓度檢測以及各種破壞性和非破壞性的測試方法，是對火災損壞結構的評估依據。對火災損毀的結構進行災后力學性能分析，并對火災過程中，結構所達到的最高溫度以及溫度分布進行分析。常用的方法有巖相分析，超聲波法，核心測試和顏色觀察。（2）依據火災之后工作荷載下的鋼筋和混凝土力學性能，按照步驟一中火災前后結構所承受的最高溫以及溫度分布分析，通過計算來確定災后結構是否滿足強度和撓度的要求。有兩種主流的方法來判定結構遭受大火損壞之后其工作性能：FEM法和傳統修復法。（3）依據步驟二的結果統計和測試，采取相應的修復方案以及特定的方法，來加固受火災損毀的結構。2.2 修復技術修復火災損毀的橋梁，應依據結構損壞的程度和范圍來采取恰當的修復方案。同時應該關注修復方法的安全性和經濟型，盡量避免破壞原有結構，保留有價值的構件，減少不必要的拆遷和重建。常規修復技術如下。（1）更換火災損壞的混凝土用新混凝土代替火災損壞的混凝土，是最常用的修復技術。如