【正文】 emoval intensity g(t) as percentages of the annual load turnover. The removal data fisted in Table 1 is considered as expected values for any crane, which can be 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 per one month, but to establish these data without special statistical investigation is difficult. Besides, to solve the problem of life prediction a knowledge of future loads is required, which we take as expected values on cranes with similar operation conditions. The distribution of removal value Q(t) per month performed by the relative intensity q(t) is written as where Q is the annual load turnover 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 400,000 m3 per year, and A=10%, the volumes of loads transferred by the crane are obtained, which are listed in Table 2, with the total volume being 560,000 m3 for one year using K,. . Number of loading blocks The set of operations such as clamping, hoisting, transferring, lowering, and getting rid of a load can be considered as one operation cycle (loading block) of the crane. As a result to investigations, the operation time of a cycle can be modeled by the normal variable with mean equal to min and standard deviation to min. unfortunately, this characteristic cannot be simply used for the definition of the number of operation cycles for any work period as the local processing is extremely irregular. Using a total operation time of the crane and evaluations of cycle durations, it is easy to make large errors and increase the number of cycles pared with the real one. Therefore, it is preferred to act as follows. The volume of a unit load can be modeled by a random variable with a distribution function(t) having mean22 m3 and standard deviation 6。 the height of the piles is considered to be a maximum。 Fatigue assessment。 Strain gauging 1. Introduction Fatigue failures of elements of the metalwork of traveling gantry cranes LT62B are observed frequently in operation. Failures as fatigue cracks initiate and propagate in welded joints of the crane bridge and supports in threefour years. Such cranes are used in the forest industry at log yards for transferring fulllength and sawn logs to road trains, having a loadfitting capacity of 32 tons. More than 1000 cranes of this type work at the enterprises of the Russian forest industry. The problem was stated to find the weakest elements limiting the cranes39。when processing exceeds the log removal from the forest, the crane expects work above an operational pile close to the saw mill with the grab lowered on the pile。 一 3 m3, with the nominal volume of one pack being 25 m3. Then, knowing the total volume of a processed load for a month or year, it is possible to determine distribution parameters of the number of operation cycles for these periods to take advantage of the methods of renewal theory [1]. According to these methods, a random renewal process as shown in Fig. 2 is considered, where the random volume of loads forms a flow of renewals: In renewal theory, realizations of random:， having a distribution function F(t), are understoodas moments of recovery of failed units or request receipts. The value of a processed load:， after}th operation is adopted here as the renewal moment. Let F(t)=P﹛ n? ＜ t﹜ . The function F(t) is defined recurrently, Let v(t) be the number of operation cycles for a transferred volume t. In practice, the total volume of a transferred load is essentially greater than a unit load, and it is useful therefore totake advantage of asymptotic properties of the renewal process. As follows from an appropriate limit renewal theorem, the random number of cycles v required to transfer the large volume t hasthe normal distribution asymptotically with mean and variance. without dependence on the form of the distribution function 月 t) of a unit load (the restriction is imposed only on nonlattice of the distribution). Equation (4) using Table 2 for each averaged operation month,function of number of load cycles with parameters m,. and 6,., which normal distribution in Table 3. Figure 3 shows the average numbers of cycles with 95 % confidence intervals. The values of these parameters for a year are accordingly 12,719 and 420 cycles. 3. Strain measurements In order to reveal the most loaded elements of the metalwork and to determine a range of stresses, static strain measurements were carried out beforehand. Vertical loading was applied by hoisting measured loads, and skew loading was formed with a tractor winch equipped with a dynamometer. The allocation schemes of the bonded strain gauges are shown in Figs 4 and 5. As was expected, the largest tension stresses in the bridge take place in the bottom chord of the truss (gauge 1145 MPa). The top chord of the truss is subjected to the la