fatigue life prediction of the metalwork of a travelling gantry crane

1、?PERGAMON Engineering Failure Analysis 5 “0888# 020Ð0300249Ð5296:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[PII] S 0 2 4 9 Ð 5 2 9 6 “ 8 7 # 9 9 9 3 0 Ð 6Fatigue lif

2、e prediction of the metalwork of a travelling gantry craneV[A[ KopnovP[O[ Box 53\ Ekaterinbur` 519096\ RussiaReceived 2 April 0887^ accepted 18 September 0887AbstractIntrinsic fatigue curves are applied to a fatigue life

3、 prediction problem of the metalwork of a travelling gantry crane[ A crane\ used in the forest industry\ was studied in working conditions at a log yard\ and strain measurements were made[ For the calculations of the num

4、ber of loading cycles\ the rain~ow cycle counting technique is used[ The operations of a sample of such cranes were observed for a year for the average number of operation cycles to be obtained[ The fatigue failure analy

5、sis has shown that failures of some elements are systematic in nature and cannot be explained by random causes[ Þ 0888 Elsevier Science Ltd[ All rights reserved[Keywords] Cranes^ Fatigue assessment^ Strain gauging0[

6、 IntroductionFatigue failures of elements of the metalwork of travelling gantry cranes LT51B are observed frequently in operation[ Failures as fatigue cracks initiate and propagate in welded joints of the crane bridge an

7、d supports in threeÐfour years[ Such cranes are used in the forest industry at log yards for transferring full!length and sawn logs to road trains\ having a load!lifting capacity of 21 tons[ More than 0999 cranes of

8、 this type work at the enterprises of the Russian forest industry[ The problem was stated to _nd the weakest elements limiting the cranes| lives\ predict their fatigue behaviour\ and give recommendations to the manufactu

9、rers for enhancing the lives of the cranes[1[ Analysis of the crane operationFor the analysis\ a travelling gantry crane LT51B installed at log yard in the Ekaterinburg region was chosen[ The crane serves two saw mills\

10、creates a log store\ and transfers logs to or out of road trains[ A road passes along the log store[ The saw mills are installed so that the reception sites are under the crane span[ A schematic view of the crane is show

11、n in Fig[ 0[V[A[ Kopnov : En`ineerin` Failure Analysis 5 “0888# 020Ð030 022Table 0 Removal intensity “)#Month 0 1 2 3 4 5 6 7 8 09 00 01q“t# 9[14 9[13 9[21 ?9[97 ?9[06 ?9[03 ?9[02 ?9[01 ?9[04 ?9[04 ?9[95 9[08Table 1

12、 The amount of transferred load “0999 m2#Month 0 1 2 3 4 5 6 7 8 09 00 01Q“t# 59[5 59[0 53[1 31[1 26[0 27[7 28[3 28[8 27[1 27[1 33[4 44[9data listed in Table 0 is considered as expected values for any crane\ which can be

13、 applied to the estimation of fatigue life\ and\ particularly\ for an inspected crane with which strain measurement was carried out “see later#[ It would be possible for each crane to take advantage of its load turnover

14、per one month\ but to establish these data without special statistical investigation is di.cult[ Besides\ to solve the problem of life prediction a knowledge of future loads is required\ which we take as expected values

15、on cranes with similar operation conditions[ The distribution of removal value Q“t# per month performed by the relative intensity q“t# is written asQ“t# ? Q“Aq“t#¦7[22#:099“m2#\ “0#where Q is the annual load turnove

16、r of a log store\ A is the maximal designed store of logs in percent of Q[ Substituting the value Q\ which for the inspected crane equals 399\999 m2 per year\ and A ? 09)\ the volumes of loads transferred by the crane ar

17、e obtained\ which are listed in Table 1\ with the total volume being 459\999 m2 for one year using Kl[1[1[ Number of loading blocksThe set of operations such as clamping\ hoisting\ transferring\ lowering\ and getting rid

18、 of a load can be considered as one operation cycle “l(fā)oading block# of the crane[ As a result of investigations\ the operation time of a cycle can be modelled by the normal variable with mean equal to 00[4 min and standa

19、rd deviation to 0[4 min[ Unfortunately\ this characteristic cannot be simply used for the de_nition of the number of operation cycles for any work period as the load processing is extremely irregular[ Using a total opera

20、tion time of the crane and evaluations of cycle durations\ it is easy to make large errors and increase the number of cycles compared with the real one[ Therefore\ it is preferred to act as follows[ The volume of a unit