塔式起重機(jī)預(yù)期壽命

1、塔式起重機(jī)預(yù)期壽命TOWER CRANE LIFE EXPECTANCY塔式起重機(jī)預(yù)期壽命AN EXAMINATION OF RECENT TRENDS TO ESTABLISH AGE LIMITS 對最近確定年齡限制的趨勢的研究Over the past decade there have been increased discussions and attempts around the world to set and/or legislate a maximum service life of tower cranes, and in some cases mobile cranes

2、 based solely on their age. As a result of the recent publication Crane Accidents: A Study of Causes and Trends to Create a Safer Work Environment, 1983-2013, Jim D. Wiethorn, P.E., the Specialized Carriers and Riggers Association (SC&RA) approached Haag Engineering Co. to evaluate and compare the b

3、asis of these claims to our experience in crane accident analyses and Crane Study results. SC&RA submitted questions which their membership wanted addressed that relate specifically relate to the ages of the cranes. As part of our analysis, we examined the Crane Study results with respect to the cra

4、ne ages at the time of the incidents to the actual causative factors of the accidents, with an emphasis on tower cranes. Additionally, we researched and addressed a variety of issues raised in support of and rebuttal to proposals for regulations in various parts of the world. The purpose of this ana

5、lysis was to determine if any correlation exists between crane accidents and ages of cranes, to evaluate whether basis for these claims would suggest an age limit for such equipment.在過去的十年里，世界范圍內(nèi)越來越多的討論和嘗試設(shè)定塔式起重機(jī)的最大使用壽命和/或 立法，在某些情況下，移動式起重機(jī)僅基于其年齡。根據(jù)最近出版的起重機(jī)事故：創(chuàng)造更 平安工作環(huán)境的原因和趨勢研究，Jim D.Wietorn , P.EO,專

6、業(yè)運(yùn)輸公司和起重工協(xié)會 (SC&RA)與哈格工程公司(Haag Engineering Co.)接洽，評估并比擬這些索賠的依據(jù) 與我們在起重機(jī)事故分析和起重機(jī)研究結(jié)果方面的經(jīng)驗(yàn)。SC&RA提交了他們的成員希 望解決的問題，這些問題與起重機(jī)的年齡有關(guān)。作為我們分析的一局部，我們檢查了起重機(jī) 研究結(jié)果，從事件發(fā)生時起重機(jī)的年齡到事故的實(shí)際原因，重點(diǎn)是塔式起重機(jī)。止匕外，我們 研究并處理了在世界各地支持和反駁監(jiān)管建議的各種問題。本分析的目的是確定起重機(jī)事故 與起重機(jī)使用年限之間是否存在任何相關(guān)性，以評估這些索賠的依據(jù)是否會建議此類設(shè)備的 使用期限。HISTORICAL RESEARCH歷史研究The

7、 earliest known policy to stipulate calendar ages of cranes as a limit to their service lives was enacted in Singapore during October 2006, although development of the regulation first began in April 2004. The guidelines address imported tower cranes with both current registration and those seeking

8、first time use in the country. The statutes governed the introduction of used tower cranes from other countries that met the following criteria.新加坡于2006年10月公布了最早的將起重機(jī)日歷年齡作為其使用壽命限制的政策，盡管該 法規(guī)的制定始于2004年4月。該指南針對的是目前注冊的進(jìn)口塔式起重機(jī)和首次在國內(nèi)使 用的塔式起重機(jī)。法規(guī)規(guī)定了從其他國家引進(jìn)符合以下標(biāo)準(zhǔn)的二手塔式起重機(jī)。1. First Time Use of A Tower Crane:1

9、首次使用塔式起重機(jī)：Model and type-approved for use in Singapore and accompanied by a recent (not more than 2 years) inspection certificate from the statutory authority from the country it was used.and have very tight clearances between moving parts. The hydraulic fluid lubricating film keeps moving parts wit

10、hin hydraulic components separated and reduces wear. Many hydraulic components have mechanical clearances of only a few thousandths of an inch. Such tight clearances between moving internal parts make them highly susceptible to damage caused by particulates in the hydraulic fluid. Failure to heed to

11、 manufacturer inspection and maintenance schedules for hydraulic systems can reduce greatly the service life of the hydraulic components. Even so, worn hydraulic components are replaceable, and accelerated hydraulic system wear may not reduce the overall service life of a crane.各種起重機(jī)部件的檢查要求和維護(hù)計劃差異很大

12、。例如，制造商要求維護(hù)人員通過每天檢查 過濾器、過濾器指示器和液壓儲油器，定期對液壓系統(tǒng)進(jìn)行檢查。制造商通常要求每兩年更 換一次液壓油，或者在起重機(jī)重新運(yùn)到另一個工作地點(diǎn)時更換液壓油，因?yàn)橐簤河偷奈⒘Ｎ?染會導(dǎo)致液壓元件過早損壞。液壓油中的微粒污染是一個明顯的問題，因?yàn)橐簤涸?jīng)過精 密加工，運(yùn)動部件之間的間隙非常小。液壓油潤滑膜使液壓元件內(nèi)的運(yùn)動部件保持別離，并 減少磨損。許多液壓元件的機(jī)械間隙只有千分之幾英寸。運(yùn)動內(nèi)部零件之間的間隙如此之小, 使得它們極易受到液壓油中微粒的損壞。不遵守制造商對液壓系統(tǒng)的檢查和維護(hù)計劃會大大 縮短液壓元件的使用壽命。即便如此，磨損的液壓元件是可更換的，液壓系

13、統(tǒng)的加速磨損不 會降低起重機(jī)的整體使用壽命。Components of cranes that endure regular movement through crane operations, cylinders, winches, motors, pumps, and other components, wear with use. Typically, these components operate for long periods before either rebuilding or replacement becomes necessary. These components h

14、ave a combination of bearings, bushings, seals, and/or piston (wear) rings that require replacement. Winch brake systems have brake linings and/or friction discs that also need replacement. Excessive wear of these crane components causes losses in performance and efficiency. In other words, these co

15、mponents lose responsiveness and tend to develop sluggish movements, sloppy movements, slower speeds, increased vibrations, and slippage during crane operation. These are indications that crane component maintenance is needed. Manufacturer service manuals address these performance inefficiencies wit

16、hin the trouble-shooting sections of their manual, as well as required actions to eliminate ineffectiveness of these components. Following these manufacturer recommendations will maximize component life. Manufacturers usually provide lists of replacement parts within their manuals to facilitate regu

17、lar maintenance practices. If some component is worn excessively and cannot be rebuilt, replacement of the Original Equipment Manufacturer (OEM) component will not reduce overall service life of the crane.在起重機(jī)操作過程中能夠承受定期移動的起重機(jī)部件、油缸、絞車、電機(jī)、泵和其他部件, 在使用過程中會磨損。通常，這些組件在需要重建或更換之前會運(yùn)行很長一段時間。這些部 件有需要更換的軸承、襯套、

18、密封件和/或活塞(磨損)環(huán)的組合。絞車制動系統(tǒng)的制動襯 片和/或摩擦片也需要更換。這些起重機(jī)部件的過度磨損會導(dǎo)致性能和效率的損失。換言之， 這些部件會失去響應(yīng)能力，在起重機(jī)運(yùn)行過程中會出現(xiàn)緩慢移動、草率移動、速度減慢、振 動增加和滑動。這些都說明需要對起重機(jī)部件進(jìn)行維護(hù)。制造商維修手冊在其手冊的故障排 除局部解決了這些性能低下的問題，以及消除這些部件失效所需的措施。遵循這些制造商的 建議將最大限度地延長部件壽命。制造商通常在其手冊中提供替換零件清單，以便于定期維 護(hù)。如果某些部件過度磨損而無法修復(fù)，更換原始設(shè)備制造商(OEM)部件不會降低起重機(jī) 的整體使用壽命。Structural deter

19、ioration is very long term issue. Design codes and historical performance typically result in structures being exceedingly robust. American Welding Society (AWS) design criteria assume that welded connections are flawed from the onset of fabrication and that fatigue crack initiation life is gone fro

20、m first use. (Total fatigue life is the sum of initiation life plus propagation life.) These design criteria for dynamic structures assume that fatigue cracks evolve from entrained flaws and that service life is governed solely by crack propagation. Inspection criteria usually are defined such that

21、multiple inspections are done during that period while crack growth is in the subcritical region. That is, if an existing structural crack is not detected during one inspection, there will be several subsequent inspections at later dates which should detect the crack long before it becomes catastrop

22、hic. Often, no catastrophic failure occurs even with a sizable crack present within a structure. Fatigue cracks which form in structural members should be visually obvious during routine inspections. In critical applications, inspection intervals are specified such that multiple inspections occur pr

23、ior to the crack growing to critical size. Likewise, large structural displacements during operation should alert crane personnel that a structure is failing. Large deflections and progressive buckling symptoms often occur prior to catastrophic collapse.結(jié)構(gòu)惡化是一個長期的問題。設(shè)計規(guī)范和歷史性能通常導(dǎo)致結(jié)構(gòu)非常堅固。美國焊接協(xié)會 (AWS)的

24、設(shè)計標(biāo)準(zhǔn)假定焊接接頭從制造開始就有缺陷，并且疲勞裂紋起始壽命從首次使用 開始就消失了。(總疲勞壽命是起始壽命加上擴(kuò)展壽命的總和。)這些動態(tài)結(jié)構(gòu)的設(shè)計標(biāo)準(zhǔn)假 定疲勞裂紋是由夾帶缺陷演變而來的，使用壽命僅由裂紋擴(kuò)展決定。檢驗(yàn)標(biāo)準(zhǔn)的定義通常是 在裂紋擴(kuò)展處于亞臨界區(qū)時，在該期間進(jìn)行屢次檢驗(yàn)。也就是說，如果在一次檢查中沒有檢 測到現(xiàn)有的結(jié)構(gòu)裂縫，那么在以后的幾次后續(xù)檢查中，這些檢查應(yīng)在裂縫變得災(zāi)難性之前檢 測到。通常，即使在結(jié)構(gòu)中存在較大的裂縫，也不會發(fā)生災(zāi)難性的破壞。在常規(guī)檢查過程中， 結(jié)構(gòu)構(gòu)件中形成的疲勞裂紋應(yīng)明顯可見。在關(guān)鍵應(yīng)用中，規(guī)定了檢查間隔，以便在裂紋擴(kuò)展 到臨界尺寸之前進(jìn)行屢次檢查。同樣

25、，在操作過程中，較大的結(jié)構(gòu)位移應(yīng)提醒起重機(jī)人員， 結(jié)構(gòu)正在發(fā)生故障。大撓度和漸進(jìn)屈曲病癥通常發(fā)生在災(zāi)難性倒塌之前。Common commercial inspection techniques (mag particle, fluorescent particle, dye penetrant) readily detect surface cracks at sizes much smaller than critical size. However, quality inspections cannot be conducted on structures encrusted with d

26、irt, grime and thick layers of paint. Inadequate inspection procedures and improper surface cleaning are the greatest causes of cracks reaching critical size and causing structural failures. Even when inspection practices are inadequate, opening, closing and rubbing of crack surfaces causes spalling

27、 or cracking of the paint, dislodges grime and forms readily visible rust stains.比普通的磁粉探傷技術(shù)更容易檢測出顆粒尺寸更小的外表裂紋。但是，不能對有污垢、污垢 和厚漆層的結(jié)構(gòu)進(jìn)行質(zhì)量檢查。不適當(dāng)?shù)臋z查程序和不當(dāng)?shù)耐獗砬鍧嵤橇鸭y到達(dá)臨界尺寸并 導(dǎo)致結(jié)構(gòu)失效的最大原因。即使在檢驗(yàn)實(shí)踐不充分的情況下，裂紋外表的翻開、閉合和摩擦 也會導(dǎo)致油漆剝落或開裂，去除污垢，并形成容易看到的銹跡。Inspection requirements can increase due to environmental conditions

28、. Cranes operated in coastal regions, even for short durations, can experience deleterious corrosion attack. Chlorine from salt water and fog is particularly insidious to structural components. Cranes close to the shoreline need more frequent inspections of its structural components. Corrosion rates

29、 for metals increase the closer metals are to the shoreline, since the amount of salt in the air is greatest near the ocean. Winds carry salt air and moisture inland and provide an environment in which salt accumulations form on metal surfaces of cranes. Salt accumulation on metal surfaces, along wi

30、th high humidity, accelerate the reactions which cause corrosion. Corrosion rates are higher when high humidity keeps the surfaces damp longer. Over time, and even beneath paint films, chlorine corrosion will degrade steel members into dust. Therefore, more frequent periodic inspections and regular

31、maintenance of crane structural components are necessary to prolong the service lives of these cranes operating near a shoreline.由于環(huán)境條件，檢查要求可能會增加。在沿海地區(qū)作業(yè)的起重機(jī)，即使持續(xù)時間很短，也會 受到有害的腐蝕。來自鹽水和霧的氯對結(jié)構(gòu)構(gòu)件特別危險?？拷０毒€的起重機(jī)需要更頻繁 地檢查其結(jié)構(gòu)部件。金屬的腐蝕速率隨著金屬離海岸線越近而增加，因?yàn)楹Ｑ蟾浇諝庵械?鹽含量最多。風(fēng)把咸空氣和濕氣帶到內(nèi)陸，為起重機(jī)的金屬外表形成鹽積聚提供了環(huán)境。鹽 在金屬外表的積

32、聚，再加上高濕度，會加速引起腐蝕的反響。當(dāng)高濕度使外表潮濕的時間更 長時，腐蝕速率更高。隨著時間的推移，甚至在漆膜下面，氯腐蝕會使鋼構(gòu)件退化成灰塵。 因此，有必要對起重機(jī)結(jié)構(gòu)部件進(jìn)行更頻繁的定期檢查和定期維護(hù)，以延長在海岸線附近運(yùn) 行的起重機(jī)的使用壽命。National consensus standards address inspection and maintenance emphasizing the importance of these requirements. ASME B30-Safety Standard for Cableways, Cranes, Derricks, H

33、oists, Hooks, Jacks, and Slings, includes in all its volumes INSPECTION, TESTING, AND MAINTENANCE as part of the requirements for the use of that equipment. ASME B30.3-2012 expanded its requirements to include a new category, 3-2.1.5-MAJOR INSPECTIONS which addresses nondestructive testing and disas

34、sembly of specific components on a five-year schedule for more thorough examination normally not included in other inspections. Cal/OSHA referenced ASME B30.3 in their decision not to implement age restrictions. Cal/OSHA decided proper maintenance, inspection and testing would suffice to assure cran

35、e integrity. If proper maintenance and testing protocol is established and performed on a crane as recommended by the manufacturers and by national standards, the economic service life of a crane will end when the costs of inspection, testing and maintenance exceed the income the machine can produce

36、. Certainly, proper inspections, testing and maintenance are the cornerstones of proper crane operations and equipment longevity.國家共識標(biāo)準(zhǔn)涉及檢查和維護(hù)，強(qiáng)調(diào)這些要求的重要性。ASMEB30纜道、起重機(jī)、吊桿、 起重機(jī)、吊鉤、千斤頂和吊索的平安標(biāo)準(zhǔn)在其所有卷中包括檢驗(yàn)、測試和維護(hù)，作為該設(shè) 備使用要求的一局部。ASMEB30.3-2012擴(kuò)展了其要求，包括一個新的類別，主要檢 查，該類檢查在五年計劃中對特定部件進(jìn)行無損檢測和拆卸，以便進(jìn)行更徹底的檢查，通常 不包括

37、在其他檢查中。Cal/OSHA在決定不實(shí)施年齡限制時參考了 ASME B30.3。Cal/OSHA認(rèn) 為適當(dāng)?shù)木S護(hù)、檢查和測試足以確保起重機(jī)的完整性。如果按照制造商的建議和國家標(biāo)準(zhǔn), 在起重機(jī)上建立和執(zhí)行適當(dāng)?shù)木S護(hù)和測試協(xié)議，當(dāng)檢查、測試和維護(hù)的本錢超過機(jī)器的收入 時，起重機(jī)的經(jīng)濟(jì)使用壽命將結(jié)束。當(dāng)然，正確的檢查、測試和維護(hù)是起重機(jī)正常運(yùn)行和設(shè) 備壽命的基石。Some jurisdictions, including the City of New York, want to incorporate service life cycle-counters on cranes. Life cyc

38、le analysis and prediction becomes much more complicated when loading events do not have equal or symmetric magnitudes per cycle. Asymmetric loading events probably is why crane manufacturers currently provide no end of service life definitions for their equipment. However, attempts are continuing i

39、n other critical applications to devise methods and instruments which count and predict accumulated fatigue damage. Earliest applications included data recorders for strain gages applied at critical locations in military aircraft. Systems continued to evolve which utilized instruments which discrimi

40、nated between damaging and non-damaging events. Other systems with greater sophistication calculated the relative damage per event and predicted residual life. Part of the challenge has been to identify which locations were most effective to monitor. In aircraft, critical locations are known as the

41、result of very sophisticated design and analyses procedures. In other equipment, usually designed based on historical performance behavior or from the use of accepted design manuals (e.g. AISC Steel Design Manual), critical locations are not known specifically.包括紐約市在內(nèi)的一些司法管轄區(qū)希望在起重機(jī)上安裝使用壽命周期計數(shù)器。當(dāng)加載事件

42、的 每個周期的量級不相等或?qū)ΨQ時，生命周期分析和預(yù)測變得更加復(fù)雜。不對稱裝載事件可能 是起重機(jī)制造商目前沒有為其設(shè)備提供使用壽命終止定義的原因。然而，在其他關(guān)鍵應(yīng)用中， 仍在繼續(xù)嘗試設(shè)計方法和儀器，以計算和預(yù)測累積的疲勞損傷。最早的應(yīng)用包括用于軍用飛 機(jī)關(guān)鍵位置的應(yīng)變計的數(shù)據(jù)記錄儀。使用區(qū)分破壞性和非破壞性事件的工具的系統(tǒng)繼續(xù)開展。 其他更復(fù)雜的系統(tǒng)計算每個事件的相對損傷和預(yù)測的剩余壽命。挑戰(zhàn)的一局部是確定哪些地 點(diǎn)最有效地進(jìn)行監(jiān)測。在飛機(jī)上，關(guān)鍵位置是非常復(fù)雜的設(shè)計和分析程序的結(jié)果。在其他設(shè) 備中，通常根據(jù)歷史性能行為或使用公認(rèn)的設(shè)計手冊(如AISC鋼結(jié)構(gòu)設(shè)計手冊)進(jìn)行設(shè)計， 關(guān)鍵位置并不明

43、確。Likewise, older cranes which have been operating for many years present particular challenges because the extent of accumulated damage at any structural location is unknown and no load histories exist. Without knowing the extent of accumulated damage, no predictions or measurements of remaining se

44、rvice life are possible. This renders application of cycle counting in older cranes unrealistic. First, no data exists on prior use, so accumulated fatigue and overload damage is unknown. Second, maintenance during the life of a crane can vary substantially, particularly cranes operated under diverg

45、ent conditions, cranes owned by several different entities, and cranes operated by many different people. The current state of maintenance also is contingent on daily inspections, actions and lubrication performed by the company using the crane during any specific interval. During bare rentals, nati

46、onal standards designate the crane user (lessee) to be responsible for all inspections, maintenance and required testing. The crane owner has little or no control while the machine is in the possession and control of others. Timely and proper documentation by the user during a bare lease is mandator

47、y to ensure all inspections be conducted and conditions be evaluated properly. These records become part of the crane historical data and a basis for future maintenance and repair.同樣，運(yùn)行多年的老式起重機(jī)也面臨著特殊的挑戰(zhàn)，因?yàn)槿魏谓Y(jié)構(gòu)位置的累積損傷程度都是 未知的，并且不存在載荷歷史。如果不知道累積損壞的程度，就不可能預(yù)測或測量剩余使用 壽命。這使得在老式起重機(jī)上應(yīng)用循環(huán)計數(shù)是不現(xiàn)實(shí)的。首先，沒有關(guān)于先前使用的數(shù)

48、據(jù)， 因此累積的疲勞和過載損傷是未知的。其次，起重機(jī)使用壽命期間的維護(hù)可能會有很大的變 化，特別是在不同條件下運(yùn)行的起重機(jī)、由多個不同實(shí)體擁有的起重機(jī)以及由許多不同人員 操作的起重機(jī)。當(dāng)前的維護(hù)狀態(tài)還取決于公司在任何特定時間間隔內(nèi)使用起重機(jī)進(jìn)行的日常 檢查、操作和潤滑。在裸租期間，國家標(biāo)準(zhǔn)指定起重機(jī)使用者(承租人)負(fù)責(zé)所有檢查、維 護(hù)和所需的測試。當(dāng)機(jī)器由他人占有和控制時，起重機(jī)所有者幾乎沒有控制權(quán)。在裸租期內(nèi)， 用戶必須及時、適當(dāng)?shù)靥峁┪募源_保進(jìn)行所有檢查并正確評估條件。這些記錄將成為起 重機(jī)歷史數(shù)據(jù)的一局部，并作為未來維護(hù)和維修的基礎(chǔ)。Suggestions regarding the

49、 means by which to count cycles in cranes include counting the number of “picks and recording load line forces, strains on the boom, and tower strains. Although instrumentation can be devised which will measure forces, strains, accelerations and deflections, no consistent algorithm exists by which t

50、o convert reliably any of these factors into accumulated damage or residual life. In fact, installing such instrumentation into an older crane would result in erroneous data and instill false confidence. With no historical data to input, the instrumentation will consider an older crane to be a new w

51、ith a full complement of service life left to be consumed. Reliance on such instrumentation would potentially supplant the use of vigorous and competent inspections and lead to missed opportunities to discover cracks and other mechanical damage.關(guān)于計算起重機(jī)循環(huán)次數(shù)的方法的建議包括計算“鎬”的數(shù)量，并記錄載重線力、吊桿上的 應(yīng)變和塔架應(yīng)變。雖然可以設(shè)計

52、出測量力、應(yīng)變、加速度和撓度的儀器，但沒有一致的算法 可以可靠地將這些因素轉(zhuǎn)換為累積損傷或剩余壽命。事實(shí)上，在老式起重機(jī)上安裝這種儀器 會導(dǎo)致錯誤的數(shù)據(jù)，并灌輸錯誤的信心。在沒有歷史數(shù)據(jù)可輸入的情況下，儀表將把舊的起 重機(jī)視為新的起重機(jī)，剩余的全部使用壽命將被消耗。依賴這種儀器可能會取代強(qiáng)有力的、 稱職的檢查，并導(dǎo)致錯過發(fā)現(xiàn)裂紋和其他機(jī)械損傷的機(jī)會。Ultimately, some end of life criteria must be defined. We have discussed this specific issue with multiple crane manufacture

53、rs and designers, and currently no ends of life definitions are available. Although sophisticated life-extension technologies exist for older equipment, implementation often includes extensive inspection, refurbishment and replacement of components. Life extension programs are cost effective for cap

54、ital-intensive equipment such as aircraft and power plants, but probably not for cranes.最終，必須確定一些“生命終結(jié)”標(biāo)準(zhǔn)。我們已經(jīng)與多個起重機(jī)制造商和設(shè)計師討論過這個 具體問題，目前還沒有壽命終止的定義。雖然對于較舊的設(shè)備存在復(fù)雜的延長壽命的技術(shù), 但實(shí)施通常包括廣泛的檢查、翻新和更換部件。延長壽命計劃對于資本密集型設(shè)備（如飛機(jī) 和發(fā)電廠）是具有本錢效益的，但對起重機(jī)來說可能不是。Finally, fatigue manifests as the result of cyclical loading, a

55、nd has no direct correlation with the calendar age of a crane or of any of its components. A recent example occurred in New York City when a boom hoist wire rope failed as a result of fatigue after only 6 months of use. The incident occurred as a result of the type of use, and was completely unrelat

56、ed to calendar age of the wire rope. Instead, it was the result of lifts resulting in high stress cyclical loading. Different crane components have different useful service lives, depending on how the crane is used and how well the crane is inspected and maintained. Twenty-five years is not only an

57、arbitrary “shelf-life” for a crane, it could very easily mislead crane users into a false sense of security with cranes under 25 years of age.最后，疲勞表現(xiàn)為周期性載荷的結(jié)果，與起重機(jī)或其任何部件的日歷壽命沒有直接關(guān)系。紐 約市最近一次鋼絲繩使用6個月后出現(xiàn)疲勞。事件的發(fā)生是由于使用的類型，與鋼絲繩的日 歷年齡完全無關(guān)。相反，這是導(dǎo)致高應(yīng)力循環(huán)載荷的提升的結(jié)果。不同的起重機(jī)部件有不同 的使用壽命，這取決于起重機(jī)的使用方式以及起重機(jī)的檢查和維護(hù)情況。25年

58、不僅是起重 機(jī)任意的“保質(zhì)期”，它很容易誤導(dǎo)起重機(jī)使用者對25年以下的起重機(jī)產(chǎn)生錯誤的平安感。 CRANE STUDY RESULTS 起重機(jī)研究結(jié)果During July 2014, we published the results of a study of crane accidents that dates back to 1983. Our analysis and experience was based on the evaluation of over 800 crane accidents since 1987. The study involved complete ana

59、lysis of 507 crane accidents at the time of publication. As part of our study, we identified the manufacturing date of the crane for each incident, as well as the age of the crane at the time of the incident in order to determine if there was a correlation. Of the accidents included in our study, we

60、 were able to identify the exact age of the crane 125 times. 2014年7月，我們公布了 1983年起重機(jī)事故研究結(jié)果。我們的分析和經(jīng)驗(yàn)是基于1987年 以來800多起起重機(jī)事故的評估。這項研究包括對出版時507起起重機(jī)事故的完整分析。作 為研究的一局部，我們確定了每起事故的起重機(jī)制造日期，以及事故發(fā)生時起重機(jī)的年齡, 以確定是否存在相關(guān)性。在我們研究的事故中，我們能夠確定起重機(jī)確實(shí)切年齡125次。 Our study indicated a range of crane ages from 0 to 92 years with th