Study For Steel Structure Reliability Of Tower Crane

With characteristics of high efficiency, large rotation radius and great lifting height, tower crane has been widely used in the area of industry and civil engineering etc and it has been indispensable construction equipment in construction industry. According to the statistics, many tower cranes used in the construction industry nationwide were designed in 1960s or 1970s, which were out-of-date machinery, and many tower cranes have been worked for a long time, part of which have been worked for 20 years even 30 years. As longer as it works, the tower cranes must have some hidden troubles which may cause severe safety accidents. Therefore, the issues of safety operation of old and out-of-date tower cranes and how long they can work for reliable and safety working have been greatly concerned by tower crane using company and higher level administration bureau. To make those tower cranes, which can continuously working safely to scrap compulsively, it would bring great economic losses for the enterprise, but also it would cause serious national resources waste. However, to keep those tower cranes, which cannot secure safety working to continuously work, it would bring severe hidden trouble to staffs safety, even cause the tragedy of casualty. Till to date, the consolidated national standards for reliability forecast of tower cranes scrap year limit and steel parts structure aren't available; therefore, the reliability of those old and out-of-date tower cranes which are still working is very important. Based on this background, this paper analyzed the reliability of tower cranes steel structure after worked for certain years; and to judge if it can safely work based on the reliability and to provide theory support for industrial supervisory bureau of tower crane scrap. Based on related theory of the reliability of structure and combing the actual situation of tower crane steel structure, the following studies have been developed: ①According to stress-strength interference model of structure reliability, that is only if the forces of structure stress is larger than the forces on strength, the structure could be safely working. Combining with the characteristics of loading alteration when tower crane steel structure works and as the steel structure material working longer and the stress lower, we can make the conclusion that the reliable mathematic model can be applied to tower crane steel structure. ②According to the actual situation of load change of tower crane steel structure, this paper customize a operating cycle, which contained various lifting operating mode of tower crane in actual working conditions and imitating the strength of steel structure in the actual production process. And also this paper deduced load of tower crane jib according a typical tower crane operating cycle. These steps were basis for finite element emulates stress-time of tower crane jib. ③Dynamic analysis has been done on building up the model of QTZ25 tower crane jib in finite element software ANSYS according to loading of tower crane jib. The stress-time of tower crane jib and danger section of tower crane jib was confirmed. Stress amplitude and stress cycle indexes of tower crane jib danger section were calculated by rain flow counting method. This paper hypothesised stress amplitude submitting logarithmic normal distribution, according to stress amplitude and stress cycle indexes. Finally, this paper testified the stress amplitude submitting logarithmic normal distribution by k-s method. ④This paper confirmed Q235 steel strength possible distribution, according to predecessor experimental result, and calculated reliability of tower crane steel structure after working several years. Through the result of reliability, it can define this tower crane which can continue work or not. ⑤This paper proved this way through an example calculation.