(No.7, year 2010)
Transportation of natural stone slabs on “A”-frames
“Everything that happens once can never happen again.
But everything that happens twice will surely happen a third time.”.
Paulo Coelho “The Alchemist”
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We keep saying to our clients that the recurrent unsafe transportation indicates the logistics faults and should not be considered as insured event because damage to the cargo and other consequences are inevitable. I decided to begin with the most frequent cargo types we are to survey. They are equipment, metal and concrete.
One more cargo type sustaining damages during the transportation is natural stone. The transportation of such cargo is always hazardous, and accidents are spectacular and significant. Vehicles usually become severely deformed. Cargo often falls out of the vehicle. The great hazard the unsafe transportation of such cargo poses to people’s life and health is clearly seen on the photographs, taken in the center of Pskov:
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In this article we will consider the natural stone plates, or, as it is often referred to in stone milling, slabs. The slabs are rectangular plates of marble, granite, onyx, shale, etc. the dimensions are usually as follows:
Length 2500 – 3000 mm;
Width 1500 – 1800 mm;
Thickness 20 – 30 mm.
Gross weight of the cargo is usually 20 000 – 21 000 kg.
Standard consignment consists of 2 cargo units 10 000 – 11 000 kg each.
Country of origin: Italy or Greece.
Accident site: CIS.
One may only guess how many similar accidents occur before the cargo would crossed the CIS border, however, in the view of the fact that road conditions in CIS differ from those in EEC, the accidents, like the mentioned above, are inevitable.
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First, let us try to determine the causes of accidents and even the parties’ liability.
The Internet gives the following definition for Packing.
PACKING is a full range of protection measures and material resources applied to prepare the cargo for transporting and storing, and to ensure its safety.
The party, responsible for packing, is Shipper/Seller.
At the moment of loading, an aggregated cargo transport unit is formed inside a trailer, thus an “A”-shaped frame the mean of aggregation.
The dimensions given below were taken from one of our reports as an example. Every case is different, but the result of transportation was one and the same.
Cargo transport unit forming
The cargo transport unit of natural stone slabs is formed on two “A”- shaped frames, provided by a Shipper. On “A”- frames the slabs can be transported on butt ends.
The height of the frame from the floor to the upper lath is 1500 mm.
The length of the frame along the lower lath is 2000 mm.
The lower lath is made of steel “П” – shaped profile, 6 mm thick.
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The vertical component “A” is made of steel “Н”- shaped profile, 5,5 mm thick.
The intermediate reinforcing distance rod is made of steel “П”- shaped profile 20 х 10mm.
The packing frames with slabs loading
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90×18 mm wooden bars were put under the “A”-frames as lining material.
Tightening of the transport package
After the slabs were placed onto the frames, they were tightened with two sections of short-link chains around the entire package and jacketed with turnbuckle screws.
Cardboard linings were put under the chains in the areas where the chains contacted the marble slabs.
Characteristics of chain:
– Caliber: 7 mm;
– Length/width: 51 / 31 mm.
Characteristic of turnbuckle screw:
– Diameter: 16mm.
In the course of the survey the shift of rear “A”-frame in the sound cargo unit was reveled: the frame was inclined with its left leg pointing forward. The distance between the frames’ legs inside the packing was 1620 mm on the left, and 1800 mm on the right. The front “A”-frame had no lining material.
Securing
Our surveyors have never seen the linings increasing the friction ratio.
The maximum of 4 tightening belts per transport unit were used.
No other securing measures were applied.
Nearly all Shippers in Italy and Greece use similar methods of packing and securing, often claiming them to have been used for over 100 years. Therefore, it is asserted that such packing is conventional and standard for this type of cargo.
In our opinion, such transport packing is insufficient, and does not secure the cargo properly during the transportation at the territory of the Russian Federation.
Forces influencing the cargo
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In the course of the transportation at the EU territory cargo experiences the effect of inertial forces. The minimum coefficients are regulated by European standards. I would like to highlight the word “European”, because estimating the methods of cargo securing for transportation at the territory of Russian, one has to consider additional factors, besides the given in IMO/ILO/EU ECE or EN 12195-1. In order to ensure the safety of the cargo during its delivery under peculiar Russia’s transit conditions:
– long-term transportation under various climate conditions;
– severe vibrations which often impact the cargo and the securing.
Vibration
The transport vibration can become the cause of the shift of “A”-frames from the lining wooden bars, and, as a result, the loosening of the chain securing.
Drawbacks
1) A-frames are not stable. The elements of packing are not connected in a single rigid structure neither with one another, nor with the cargo. As a result, vibration causes the shift of A-frames from their initial position.
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2) A-frame inside the transport package can incline. As a result, the total height of the transport unit is decreases, and chain and tightening belts securing loosens.
3) A-frame can rotate around its axis inside the transport unit. As a result, the total height of the transport unit is decreases, and chain and tightening belts securing loosens.
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The driver is incapable of monitoring the chains and belts tightening inside a sealed trailer.
As a result of the chain and tightening belts securing loosening, a 10 tons transport unit becomes unsteady and shaky.
The pressing of the structure against the trailer floor will be useless, the break of the tightening belts is inevitable.
Recommendations on cargo securing
The majority of the securing recommendations state that:
1) А- frames should be connected in a single structure;
2) The structure should be rigidly connected to the trailer;
3) А- frames should be higher than the slabs on them.
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Undoubtedly, a single structure of two interconnected A-frames (see Fig. 25) would spare the Carrier a lot of troubles, but this is not our case.
A rigid connection with the trailer is as well impossible due to some design features of the A-frames. An Italian Shipper would hardly use high A-frames instead of those they have been using for 100 years already.
Transport Information Service of the German Marine provides the following recommendations regarding the concerned cargo type packing and securing inside a trailer:
1) “A”-frames are to be to each other, in a single structure. The cargo can be secured on these structures in advance, in order to avoid shifting of A-frames. The entire cargo transport unit will be secured inside the container.
2) In order to avoid longitudinal and lateral shift of the cargo it is recommended to use wooden buffer stops attached to the floor of a container.
3) Vertical braces are used to avoid inclining.
4) A sufficient number of tension belts should be used in order to avoid any lengthwise shift.
Fig. 27. Securing of А-frames inside container. Front view.
Fig. 28. Top view
Fig. 29. Enlarged top view
In spite of the intelligibility of the above recommendations, this is still not our case.
Recommendations made by the Transport Research Institute, Stockholm, 1998.
I did not come across any exact recommendation concerning the natural stone slabs road transportation, but let me quote the Swedish recommendations for the transportation of panels:
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1. Top-over lashings.
2. Protection securing linings.
3. Filling block.
Typical example:
- If the cargo is not load close enough to the front side of a trailer, a blocking is recommended, using a filling block (3) or springs.
- In some cases, the blocking, such as a filling block (3) or springs, is recommended in order to avoid backward shift.
- The slabs are to be put close to “A”-frames and pressed to the flooring by top-over lashings (1).
- If necessary, the space between the cargo units is filled with filling blocks (3).
- Protection linings (2) are used between the top-over lashings and the cargo.
Fig. 31.
According to the Table above, the 12 top-over lashings, clamping force of 400 daN, are the benchmark to secure a 10 tons consignment properly.
Our recommendations to the Carrier are as follows:
In the course of loading procedures:
1) Increase the number of fastening chains to 4 per cargo transport unit.
2) Increase the friction ratio both between “A”-frames and trailer floor and between the slabs and “A”-frames. The Carrier should have enough their own antiskid rubber mats.
3) Use blocking as a securing method, in particular, fill the empty space between the front side and the first transport unit by wooden pallets. Install front and rear springs.
4) Use top-over securing only to increase the friction ratio.
5) Use a sufficient number of loop-type fastenings to avoid lateral shift.
6) Use the belts protection to avoid their damage by slabs’ edges.
7) Increase significantly the number of securing measures for the rear transport unit, as this is the unit to experience the maximum load during the transportation.
Fig. 32.
Hold-down belts not shown in the diagram.
In the course of transportation:
1) Use every chance to check the condition of chains and lashings.
The Shipper might refuse to increase the number of securing means, as this cuold cause the damage to the cargo during the transportation, but a conscious Carrier should always remember that the cargo, fallen out of the vehicle, is a great hazard to other peoples’ health and life.
The control over the cargo securing sufficiency has to be at least doubled during the transportation at the territory of Russia, taking into consideration the state of the road surface and the increased vibration loads.
The author intentionally avoided using mathematical calculations of the number of securing means, based on the existing European standards.