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Axle Load Determination of Truck for Wood Transportation

In Croatian Forestry wood transportation is usually carried out by trucks with trailer (forest truck unit) and trucks with two-axle semitrailer (forest semitrailer assembly). As they travel on public roads, they are subject to severe legal restrictions on allowable loads of axles and the whole vehicle. The basic legal regulation that defines some technical features is the »Regulation on Technical Conditions of Vehicles in Road Traffic« – (Official Gazette »Narodne novine«, No. 51/10). Based on the analysis of the said Regulation, it can be concluded that the maximum load of the forest truck with trailer is 26 t for the truck and 18 t for the trailer, and that the total mass of the truck and the trailer must not be more than 40 t. At the same time individual load of single-axles must not exceed 10 t, and of the dual axles 18 t in total (Fig. 2).Due to the above said legal restrictions of the total mass of loaded truck assemblies and allowable axle loads, need has arisen in forestry practice for measuring truck units during their loading, i.e. right before entering public roads.

    As a result of direct measurement of axle loads of forest truck units, no limit values would be exceeded in wood transportation. The transport of adequate load mass in accordance with legal restrictions and recommended load capacities of trucks and trailers (semitrailers) would reduce maintenance costs of forest roads and increase the life cycle of technical equipment.However, axle loads as well as total mass of forest truck units depend on the type of load (type of wood assortments, species of wood), wood moisture, way of piling wood assortments in the load space of the truck, trailer and semitrailer.The aim of this research is to establish the effect of load mass on axle loads of the truck with trailer and truck with semitrailer and determine the reliability and applicability of the new measurement system (portable measuring platform) used for carrying out the measurements.The first truck unit (Fig. 6) consists of the Iveco Trakker 440 truck and trailer. The truck is equipped with forestry accessories and crane Epsilon Palfinger E110Z Plus, the trailer is equipped with forestry accessories. The second truck unit consists of a MAN truck (Fig. 7), equipped with the crane Cranab 2190 and semitrailer equipped with forestry accessories. The axle loads were measured by a portable measuring platform (Fig. 4). The dimensions enable setting of all wheels of dual axles of trucks or semitrailers, which makes the measurement easier.The results of research show the measured values of axle loads and total masses of unloaded and loaded forest truck with trailer and truck with semi-trailer, and load mass. In measuring, the same load was used for the truck with trailer and truck with semitrailer. The total load volume was 22.61 m3. The load mass ranged between 20 460 kg and 22 140 kg, i.e. the average value of the load mass was 21 433 kg (Table 1). The load differences are only the result of differently piled wood assortments in the load space.The mass of the unloaded truck with semitrailer is 20 652 kg (Table 2). The mass on the wheels of the unloaded semitrailer is 4 208 kg and hence it only represents 20% of the total load of the unloaded unit (Fig. 9). The total mass of the truck with semitrailer with the load of 22.61 m3 is 42 345 kg (Table 3). Comparison between the measurement results of unloaded and loaded truck with semitrailer shows the relief of the front tuck axle (Fig. 10). The load mass is transferred to the wheels of the dual rear axles of the truck and dual axles of the semitrailer. The front axle of the truck accounts for 20% of the total axle load, while 40 % of the total load is on the rear axles of the truck and axles of the semitrailer.The mass of the unloaded truck with trailer is 19 960 kg (Table 4), of which the highest load is on dual rear axles of the truck (10 020 kg or 50% of the truck unit load, or 68% of the total truck load). The load of rear axles of unloaded truck is most highly affected by the installation of hydraulic crane on its rear part. The axle load of unloaded trailer is 2 430 kg and 2 820 kg, or 26% of the total load of the unloaded truck unit (Fig. 11).The total mass of the loaded truck with trailer is 40 980 kg (Table 5). The comparison between measuring results of the unloaded and loaded truck unit shows the increase of load on all axles. The highest load is on dual axles of the truck (Fig. 12).According to the measurement results, all dimensions of the truck with trailer and truck with semi trailer are in accordance with applicable laws and regulations. Both units were overloaded with the load of 22.61 m3. The truck with trailer was overloaded by 980 kg on average, and the truck with semi-trailer by 2 345 kg. However, no axle was overloaded.The measuring platform on which the measurements were carried out proved to be good for measuring axle loads because the measurement is precise enough, it is easy for handling and it can be transferred to different places. In this way, disturbance of production cycles is reduced.It can be seen that the starting mass of the truck with semi trailer is on average higher by approximately 700 kg than the mass of the truck with trailer. Based on this data it could be concluded that it would be better to use trucks with trailers for long-distance wood transportation, but it should be noted that the truck with semi trailer was purchased before and that the semitrailer was made of heavier materials than the trailer of the truck unit. Such data indicate the possible development trend of the semitrailer. The use of more modern materials for the construction of semitrailers and installation of a more modern and lighter crane of the same capabilities would decrease the starting total mass of the track with semitrailer, which would ultimately enable the transportation of a larger useful load.