Particularities regarding the design and conception of a bodywork superstructure intended for the transportation of perishable goods

The aim of this paper is to present the characteristics of the design and construction of a vehicle body superstructure intended for the transportation of perishable goods. In the first phase, the design of the superstructure was conceived, followed by its design. Then, the calculation of the mass distribution on the truck axles, as well as the calculation of the truck’s cornering, was carried out, and finally, the superstructure was made, which was mounted on the truck.


Introduction
At present, the transportation of perishable goods is one of the most demanding sectors in freight transportation, but also with a few regulations that must be followed to ensure that goods arrive at their destination in the best possible condition and do not endanger the health of the final consumer.According to statistical data, in 2010, there were 4 million refrigerated vehicles worldwide, and this number is expected to grow by 2.5% per year by 2030.To limit the growth in the number of refrigerated vehicles, and especially the pollution they generate, it is necessary to improve the superstructure or the materials of the insulation walls, which will lead to a reduction in energy consumption for achieving low temperatures.
Perishable food goods represent a very large proportion of the total goods transported nationally and internationally, making this segment one of the most attractive in transportation.
In Romania and Europe, this matter is generally carried out by road, as delivery times are shorter.In addition, the goods arrive from the loading point to the destination without changing means of transport, so perishable products such as meat, fish, vegetables, fruits, and dairy products must be kept cold or frozen throughout the supply chain [1].
Refrigeration or freezing, food quality and food waste are closely linked [2].Due to the fact that perishable goods must reach the final consumer safely, it is very important that the vehicle body superstructures used for transportation be constructed in such a way that the heat transfer between the interior of the vehicle body superstructure and the external environment is as small as possible.

Aspects regarding "Agreement on the International Carriage of Perishable Foodstuffs (ATP)"
The United Nations estimates that approximately 1/3 of all food produced for human consumption is wasted annually, while other sources indicate that food waste is as high as 40% of production [1].In 1970, the United Nations adopted the "Agreement on the International Transport of Perishable Foodstuffs (ATP)".This agreement contains all regulations for almost all types of refrigerated vehicles used in the transport of perishable goods [3].
Annex 1 of the ATP Agreement provides definitions and standards for special means of transport for the transport of perishable products:

Isotherm transport means
An isotherm transport means is a vehicle with a bodywork superstructure that is constructed with insulating walls, including doors, floors, and roofs, to limit heat exchange between the interior and exterior of the bodywork superstructure.This is achieved by ensuring that the global coefficient of heat transfer (K coefficient) allows the transport means to be classified into one of the following categories: -IN = normally insulated equipment specified by a global coefficient of heat transfer (K coefficient) equal to or less than 0.7 W/m 2 •K; -IR = heavily insulated equipment specified by a K coefficient equal to or less than 0.4 W/m 2 •K and by side-walls with a thickness of at least 45 mm for transport equipment of a width greater than 2.50 m.

Aspects regarding Annex 1, Appendix 2 of "Agreement on the International Carriage of Perishable Foodstuffs (ATP)"
In Annex 1, Appendix 2, of the ATP Agreement, are presented the methods and procedures for measuring and verifying the insulation capacity (isothermia) and the efficiency of cooling or heating devices of special means of transport for the transport of perishable goods.
The global coefficient of heat transfer (K coefficient), which characterizes the isothermia of special means of transport, is defined by the equation: (1): (1) where: -W [W]the heating power or the cooling capacity, as the case may be, required to maintain a constant absolute temperature difference ΔT between the mean inside temperature Ti and the mean outside temperature Te, during continuous operation, when the mean outside temperature Te is constant for a body of mean surface area S; -S [m 2 ]the mean surface of the bodywork superstructure = geometric mean of the inside surface area Si and the outside surface area Se of the bodywork superstructure.
(2) With respect to the classification of bodywork superstructures, the superstructure in the category of mechanically refrigerated superstructures can be considered (Annex 1): -thermal insulated bodywork superstructure, equipped either with its own refrigeration unit, or served, together with other transport equipment, by such a unit (compressor, absorption unit, etc.).The unit must be capable, at an average external temperature of +30°C, to lower the temperature inside the bodywork to a value Ti, and to maintain it continuously.

Specifics of the design and construction of a bodywork superstructure for a vehicle intended for the transport of perishable goods.
For illustrative purposes, the specifics of the design and construction of a bodywork superstructure for a vehicle intended for the transport of perishable goods, namely, for the transport of meat carcasses on hooks, will be presented.For the cooling and heating of the interior of the bodywork superstructure, a refrigeration unit was chosen, which was placed in the upper part of the front wall.
The bodywork superstructure for a truck with a maximum authorized total weight of 19000 kg was designed and constructed.
Taking into account the optimal distribution of masses on the truck's axles, the dimensional characteristics of the refrigeration unit, and the maximum total height of the truck (4 m -maximum total height allowed by current legislation [4]), a bodywork superstructure was designed with an external length of 7.207 m and an internal length of 7.03 m.The external width is 2.6 m (this being the maximum width allowed by current legislation), and the useful internal width is 2.47 m.The internal height of the bodywork superstructure is 2.505 m, and the total external height is 2.765 m.
In Figure 1, the main dimensions of the bodywork superstructure are presented: From the point of view of construction, the bodywork superstructure able to carry a payload of 9,500 kg was designed and constructed.It consists of the following components: -floor; -roof; -front wall; -side wall; -rear wall (rear doors); -perimeter frame.
The bodywork superstructure was modeled in 3D using the SolidWorks design software [5].The Figures 2, 3, 4 and 5 show some isometric 3D models of the bodywork superstructure:   In order for this bodywork superstructure to be able to transport meat carcasses, it is necessary to install hooks that slide on 5 eurobars with a diameter of ∅60 mm.These are fixed to the roof by means of 69 supports, which are made of steel and have a load capacity of 500 kg each (according to [6]).This is shown in Figure 6, which is a drawing of the supports.The eurobar supports are fixed to the roof with M10 screws, which have a grade of 10.9.This is shown in Figure 7, which is a drawing of the assembly of the eurobar supports and eurobars.According to [6], a hook has a load capacity of 750 kg of meat carcass, and its main dimensions are shown in Figure 8.

Calculation of load distribution on truck axles
The weight distribution simulation was performed using the Trailer Win software [7].
For the calculation of weight distribution, the useful load is considered to be uniformly distributed over the entire length of the bodywork superstructure.In Figure 10 are presented the overall dimensions of the truck, taken from the simulation performed using the Trailer Win software.The calculation of the carrying capacity distribution is described below: • Interior length of the bodywork superstructure= 7030 mm; (3) • Rear overhang = 2277 mm; (4) • M payload =M max -M truck =19000-9500=9500 kg. ( where: • M payloadtruck payload; • M max =19000 kg; (7) • M truck =M truck front axle +M truck rear axle =5177 + 4323 = 9500 kg; The truck payload on the front axle is determined by the following relationship: The truck payload on the rear axle is determined by the below relationship: M truck rear axle =M payload -M truck front axle =9500-3230=6270 kg (10) In Table 1 is described the weight distribution on the axles of the truck: The verification of the weight distribution is performed using the following relationships: M truck front axle =7500 kg ≤ M max.front axle =7500 kg (11) M truck rear axle =11500 kg ≤ M max.rear axle =11500 kg (12) The authorized weight on the driving axle must be 25% greater than the maximum authorized total weight, which is determined by the following relationship: M max rear axle =11500 > 25%M max truck =4750 kg (13) The authorized weight on the steering axle must be 20% greater than the weight of the truck when the rear axle is loaded to the maximum permissible weight, which is determined with the help of the relationship below: M max front axle =7500 > 20%M max truck =3800 kg (14)

Calculation of truck turning radius
Trucks must be built in such a way that, when they complete a full circle with a radius of 12.5 m, the covered circular crown must not be wider than 7.2 m, when the extreme outer point of the front console moves on the circle with a radius of 12.5 m [4].When entering the tangent on the circle, no part of the truck must exceed this tangent, outwards, by more than 0.8 m, as shown in Figure 12.X=0.17 m <0.8 m, the truck meets the conditions for entering the curve. (28)

Conclusion
The bodywork superstructure presented in the paper was designed, engineered, and built, falling within category IN, class C, being a refrigerated and heat-insulating transport vehicle.
The truck with the bodywork superstructure mounted is shown in Figure 14.Respecting [8], [9], [10] the truck was individually approved by the Romanian Road Authority for circulation on public roads.

Figure 1 .
Figure 1.The main dimensions of the bodywork superstructure.

Figure 2 . 4 Figure 3 .
Figure 2. Isometric view of the bodywork superstructure from the left front side.

Figure 4 .
Figure 4. Isometric view of the bodywork superstructure in longitudinal section.

Figure 5 .
Figure 5.A longitudinal section of the bodywork superstructure, showing the clearance dimensions.

Figure 7 .
Figure 7. Assembly of eurobars together with their supports.

Figure 8 .
Figure 8. Dimensions of a hook destinated for transporting meat carcasses.

Figure 10 .
Figure 10.The overall dimensions of the truck taken from the simulation performed using the Trailer Win software.The weight distribution diagram is presented in Figure 11.

8 Figure 12 .
Figure 12.Truck turning.The intermediate radii of the curve entry are represented in Figure 13.

Figure 14 .
Figure 14.Truck with the bodywork superstructure mounted.