Loading and Transport of Steel Coils in ISO Containers Capt Kaps

Prof. Kapt. Hermann Kaps

Loading and Transport of Steel Coils in ISO-Containers

Not like this!

Abstract

The main problems found with the carriage of steel coils in Standard ISO-containers are: Permissible transverse load to the container bottom, Permissible longitudinal load to the entire container, Longitudinal and transverse securing of coils within the container.

Up to coil masses of 49 % of the container-payload the first problem prevails. The solution is to distribute the weight of each coil to a sufficient number of transverse bottom girders of the container by means of two longitudinal beams. In doing so, the necessary length t of these beams is not only depending on the relative weight of the coil, but also on their mutual distance s (spread). The greater the spread, the shorter the beams may be. To this purpose, chapter 3.3 provides a diagram that enables to determine the necessary length of beams in a simple manner. It is important with this solution that the area of the container bottom between the beams must not be loaded.

If the relative coil mass is above 49 % of the container-payload, only one coil may be loaded, which must be placed at half the length of the container. This is where the second problem comes to the fore, because the limits of longitudinal strength of the container require a minimum length of the longitudinal beams, which is independent from their spread. Also for this problem the above mentioned diagram provides the solution.

Besides the length of those beams for longitudinal load spreading, also their strength, or in technical terms, their section modulus is of importance. The necessary section modules of longitudinal beams for coils upwards from about 65 % of the container-payload, make the use of steel beams compulsory. In chapter 4.3 diagrams are presented that supply the required section modules for timber beams and steel beams in a simple manner.

The securing arrangement of coils in containers, which are underway by multimodal transport on road or rail and on a seagoing vessel, must resist longitudinal accelerations of 1 g and transverse accelerations of 0.8 g. Since the lashing points inside the containers are limited in number and strength, any lashing can only have a supportive function. In all cases, the main share of securing must be provided by friction to the bottom and by square timber bracing to the side and end walls or to the corner posts of the container.

Friction supplies a share of securing that covers between 0.3 g and 0.4 g. The residual bracing with timber presents a technically demanding task. The considerable securing forces must not only be transferred from the coil to the side and end walls or corner posts, but they must also be distributed by appropriate cross-beams in order to avoid local deformation of the container. Additionally, the braces or shores must be stabilised against coming loose during the transport. One should always remember that the container will generally be opened not until arrival at the consignee. Until then, everything must stay in good order.

For checking the securing arrangement, chapter 5.3 presents a simple securing balance, which is carried out in accordance to the Annex 13 of the CSS-Code* issued by the IMO** . However, this balance cannot safeguard against mistakes in workmanship. Advice on good workmanship is found in the five attached examples and in the Container Handbook by GdV.

* Code of Safe Practice for Cargo Stowage and Securing, 2003** International Maritime Organization

1. IntroductionUsual multi purpose containers are principally designed in a way, that they can accommodate and carry their full payload, if the latter completely fills the available space. Thereby, the weight of the load is equally transferred from

the bottom cross beams to the side frames and finally to the lower corner fittings. Also the securing of the goods filling the entire container is ensured by mutual form closure up to the container boarders in a simple manner.

However, the loading and transport of heavy steel coils in ISO-containers with high point loads and large free spaces, imposes great demands on the quality of load distribution and securing measures in the container.

Regrettably, these demands are often not complied with. Heavy and extra heavy coils are often pushed into a container with brutal force and then poorly blocked and secured. After the doors are closed, nobody may become aware of the time bomb ticking inside (Figure 1).

Figure 1: Coil of 16 t in a container without bedding, fixed poorly by wedges and timbers and secured by soft iron wire

The consequences, in the less spectacular case, are containers loosing their approval due to twisted bottom girders and being taken out of service for repairs (Figure 2). In the worst case, while lifting and handling the container, a heavy coil breaks through the bottom and smashes people at work on the factory premises or on board ship.

Figure 2: Container from Figure 1 with extinct approval due to twisted bottom girders

The appropriate stowage and securing of steel coils in standard containers requires the consideration of the transverse strength of the container bottom and of the longitudinal strength of the whole container, as well as the careful securing of the coils against accelerations in longitudinal and transverse direction.

In view of different weights and dimensions of steel coils there is a variety of solutions of this problem. Therefore, in this guidance steel coils are divided into several classes of weight (mass) and adequate examples of stowage and securing options are presented.

However, in order to offer the user the opportunity to find and verify own solutions, the strength capacity of containers in longitudinal and transverse direction as well as the utilisation of timber and steel beams is presented in detail. Simple rules and diagrams for the correct arrangement and dimensioning are given.

The securing of coils against longitudinal and transverse loads during transport is also highlighted in the loading examples. Securing can be implemented rather uniformly by timber shoring (bracing) and lashing, and checked with a simple balance of forces.

2. General conditions2.1 Containers

2.2 Steel coils

2.3 Classes of weight (mass)

2.4 Stowage arrangements

2.4.1 Arrangement "Eye to sky"

2.4.2 Arrangement "Eye to side"

2.4.3 Arrangement "Eye fore and aft"

2.1 Containers

Only containers of the types 1CC or 1C are used. These are ordinary 20' Standard-Containers with the heights 8' 6" (1CC) respectively 8' (1C). Containers specially fitted with bottom trays for the transport of steel coils are not regarded in this paper.

The payloads P of the mentioned containers amount to between 21 and 30 t, depending on their structural design. It is recommended to use container types with higher payloads in the range of at least 28 t, if heavy coils are to be carried.

Roughly can be distinguished:

Hot rolled steel sheet of several millimetres thickness. The coils are not covered and less sensible against mechanical damage. Shipping in containers is less common.

Cold rolled steel sheet of generally less than a millimetre thickness, often galvanised or otherwise refined. These coils are wrapped up by sheet metal and very sensible against mechanical damage and corrosion. Shipping in containers is increasingly observed and offers the usual advantages of multimodal transport.

The following shipping recommendations are given on the assumption of cold rolled steel coils, but may as well be used for hot rolled coils.

2.3 Classes of weight (mass)

For the shipping recommendations in this paper the following classes of weight (mass) are appointed:

Class L: Coils up to 32 % of the payload P of the containerClass M: Coils from 32 % to 49 % of the payload P of the containerClass H: Coils from 49 % to 65 % of the payload P of the containerClass XH: Coils above 65 % of the payload P of the container

Coils of class L (light) may be loaded three or more in number with largely utilising the container payload. The layout of stowage must primarily regard to the transverse strength of the container.

Coils of class M (medium) may only be loaded two per container. Also in this case, the transverse strength of the container places substantial demands on the layout of the stowage.

Coils of the classes H (heavy) and XH (extra heavy) may only be loaded one per container. The layout of stowage must take the transverse strength as well as the longitudinal strength of the container into account. For coils of the class XH the safeguarding of longitudinal strength requires a bedding of steel beams, because timber cannot spread the load with reasonable expense.

The correlation between weight (mass) and size of a coil cannot clearly be defined, because the three dimensions breadth b, outer diameter d and eye diameter di are mutually variable to a certain extent. If the dimensions are known, the mass m may be calculated under the assumption of an effective density of ρ = 7.6 t/m³.

m = 7.6 · b · (d² - di²) · /4 [t] with the dimensions in metres

2.4 Stowage arrangements

Three general stowage arrangements may be distinguished, which are associated with corresponding loading procedures.

2.4.1 Arrangement "Eye to sky"

"Eye to sky" means that the coils rest in the container with vertical coiling axis. This arrangement is only used with small and narrow coils, i.e. with so-called split coils where b < d. These split coils are generally delivered on wooden pallets and may simply be moved into the container and set down by a forklift.

This stowage arrangement does generally not present problems with the structural strength of the container, provided the bottom is fairly evenly loaded over its full width and length. However, the securing time and effort by carefully adjusted square timbers and lashings if necessary, is quite formidable (see Container Handbook chapter 5.2.14.6).

2.4.2 Arrangement "Eye to side"

The arrangement "Eye to side", where the coils rest in the container with transverse coiling axis, is used with coils of all sizes, in particular, if stuffing by crane and C-hook is not envisaged (see Container Handbook, chapter 5.2.14.4).

For this arrangement the coils are placed in front of the open container door on a bedding made from two longitudinal square timbers, fastened to them and then pushed into the container by an accordingly strong forklift. Since the forklift may generally not enter the container, the coils are moved the last end by means of adapted timber scantlings, together with their bedding. As a stuffing example of this method, Figures 3 and 4 show the positioning of a heavy cable drum into a container.

Coils which are fastened to solid skids (Figure 5), are placed into a container in the same manner.

Furthermore, it is possible to roll a coil on top of longitudinal beddings into the container and stabilise it in the desired position by means of cross-timbers.

Figure 3: Timber structure for bedding a cable drum in front of a container

Figure 4: Cable drum on its bedding in the container

Figure 5: Steel coil on a solid skid

2.4.3 Arrangement "Eye fore and aft"

The arrangement "Eye fore and aft", where the coils rest with their coiling axis longitudinally in the container, is applied with light to medium coils, loaded by crane and C-hook. Small coils may also be entered and positioned in this arrangement by means of a forklift with special adapter, e.g. a round bar. Coils on skids must be placed on extra longitudinal beams, in order to distribute the weight onto a sufficient number of bottom girders of the container.

Coils without skids are placed in this arrangement with a C-hook into pre-arranged beddings, consisting mainly of parallel longitudinal beams with bevelled upper edges (see Container Handbook Vol. II, pages 240 to 245). The coil bellies shall not touch the container bottom. However, with small coils in this arrangement, the spread of the longitudinal beams becomes often so narrow that the full payload of the container may not be utilised.

3. Strength capacity of containers

3.1 Loading the bottom in transverse direction

3.2 Loading the container longitudinally

3.3 Bedding-diagram

Containers are designed by manufacturers according to the standard ISO 1496-1 in such a way that the permissible payload P, if homogeneously distributed over the entire loading floor, can safely be transferred to the four corner posts under all conditions of carriage.

This quality of a container implies sufficiently large section modules in longitudinal and transverse direction, for accepting the acting bending moments and the resulting tensile and compression stresses. For the tare-weight T of the container and for additional loads from accelerations during handling and transport, the ISO standard provides strength allowances, which are also reflected in test conditions.

If a load is not homogeneously distributed over the loading floor, suitable means for load distribution must be used and/or the load has to be reduced compared to the maximum permissible payload.

3.1 Loading the bottom in transverse direction

The minimum inner dimensions of a 20'-container are 5.867 x 2.330 m. So the permissible load in tonnes per metre bottom length P1 = P / 5.867 [t].

The transverse distance of the centres of the corner fittings is 2.26 m. When loaded homogeneously, the bottom of the container has to bear shear forces and bending moments as shown in Figure 6.

Figure 6: Shear forces and bending moments in the container bottom from a homogeneous load

The maximum bending moment from the load P1 (for one metre) is calculated as:

For a longer or shorter distance t in longitudinal direction the moment is obtained as:

This expression serves as limiting value for inhomogeneous loads, which may appear when loading steel coils.

If a coil of the mass mC placed on two longitudinal square timbers in the container with the transverse distance s (Figure 7), a bending moment results in the middle of the bottom:

Figure 7: Load on two longitudinal beams in the container

This bending moment must not exceed the limiting value presented by equation (1a). The mass mC must therefore be restricted to:

This equation is of restricted validity for values of s greater than 1.7 m. If the spread s comes close to the width of the container, the equation yields very large mC-figures, which may exceed the longitudinal strength of the container. Then the limiting value for mC is the coil mass determined by assuring the longitudinal strength. But concerns regarding the vertical shear loads in the bottom girders are unfounded.

Notice: The two dashed beams in Figure 7 between the two outer longitudinal beams are often found in skids supplied with the coil. They do not support the coil in the shown load case, because the container bottom deflects elastically, the coil, however, does not follow this deflection due to its greater stiffness. The inner beams are therefore not necessary, but also not harmful. If they would be bearing however, the bending moment in the container bottom would become greater than shown by equation (2).

A favourable option for shipping small coils on longitudinal beams is shown in Figure 8. Also for this case the equations (2) and (3) are valid with the corresponding value of s.

Figure 8: Two loads transverse in the container

3.2 Loading the container longitudinally

The longitudinal distance of the centres of the corner fittings is 5.853 m. This figure is only little less than the usable inner length of 5.867 m, so that the calculation of the maximum bending moment is based on a length of the homogeneous load and an equal distance of supports of both 5.86 m.

Figure 9: Shear forces and bending moments in the side walls from a homogeneous load

The homogeneous loading of a container produces shear forces and bending moments in the side walls of a container as shown in Figure 9. The maximum bending moment from the load P can be calculated as:

This expression serves as limiting value for inhomogeneous loads, which may appear when loading steel coils.

If a coil of the mass mC is placed on longitudinal beams of the length t in the container (Figure 10), a bending moment results at half the length of the container of:

Figure 10: Uniform load of length t longitudinally in a container

This bending moment must not exceed the limiting value presented by equation (4). The mass mC must therefore be restricted to:

This load case applies to usual bedding arrangements for coils of weight classes H and XH.

If two coils of the same mass are placed longitudinally into a container as shown in Figure 11, the full payload of the container may only be utilised, if the coils are not stowed closer to each other than at ¼ and ¾ of the container length, so that the distance t is at least 2.93 m. For a distance less than 2.93 m, the mass of both coils has to be reduced to:

Figure 11: Separated load longitudinally in a container

If three coils of the same mass are placed longitudinally into a container, they have to be stowed at 1/7, 1/2 and 6/7 of the container length for utilising the full payload of the container. That means the centres of the end coils have a distance to the end walls of only 84 cm.

If four coils of the same mass are placed longitudinally into a container, they have to be stowed at 1/8, 3/8, 5/8 and 7/8 of the container length for utilising the full payload of the container. That means the centres of the end coils have a distance to the end walls of only 73 cm.

3.3 Bedding-diagram

The equations (3) and (6) shown in this chapter may be transformed into a diagram that allows a fast decision on the correct bedding arrangement for coils in a container.

By entering with the "relative coil-mass mC/P" the diagram in Figure 13 delivers the necessary length of the beams, depending on their spread s (set of curves to the left). For coils of less than 0.5 P there is only the spread of importance.

For heavier coils, of which only one can be loaded at a time, the entry with the relative coil-mass first of all yields the minimum length t of beams necessary for safeguarding the longitudinal strength (limiting curve to the right). Only if the spread is so small that it demands longer beams, then of course the greater value applies (set of curves above the limiting curve).

Figure 12: Spread s and length t of bedding timbers or steel beams

Example 1: mC = 6 t; P = 28 t; mC/P = 0.214; spread of beams s = 1.0 m: Necessary length t of longitudinal beams per coil = 1.45 m.

Example 2: mC = 9 t; P = 26 t; mC/P = 0.346; spread of beams s = 1.2 m: Necessary length t of longitudinal beams per coil = 1.96 m.

Example 3: mC = 17 t; P = 28 t; mC/P = 0.607; s = 1.4 m: Necessary length t of longitudinal beams = 2.80 m. For longitudinal strength a length t = 2.06 m would have been sufficient (blue curve).

Example 4: mC = 20 t; P = 27 t; mC/P = 0.741; s = 1.8 m: Necessary length t of longitudinal beams = 3.81 m. For the transverse strength with s = 1.8 m a length t of just under 1.9 m would have been sufficient.

Figure 13: Diagram for the determination of necessary bedding dimensions

4. Load distribution with timber or steel beams

4.1 Section modules and permissible loads

4.2 Prevailing load case

4.3 Beam-diagrams

Timber beams or steel beams, which are used for load distribution when stowing coils into containers, must have such properties that they can resist the expected loads during transport by road, rail and sea as well as during handling. Important are the vertical accelerations, which may add up to ±1 g in unfavourable stowage positions on sea-going vessels (in addition to the gravity acceleration).

4.1 Section modules and permissible loads

The employed timber or steel beams are subject to bending and must therefore have a sufficient section modulus. The section modulus W of a timber beam with rectangular cross-section of the width b and the height h has the value:

Figure 14: Steel beam and timber beam

When applying timber beams it should be noted that the traded dimensions my fall short by the width of the saw cut and by shrinkage from drying of up to 4 %. If in doubt, the dimensions should be measured. The section modules of steel beams should be taken from tables used in the steel trade.

The following figures are only for reference and used in chapter 6.

dimensions in cm 10 x 10 12 x 12 15 x 15 20 x 20

section modulus in cm³ 152 263 513 1217

Table 1: Section modules of timber beams (with 3 % shrinkage)



Table 2: Typical section modules of IPB steel beams

For the purpose of transport bedding, the permissible tensile stress of conifer timber may be appointed to 1 kN/cm², the same for mild steel to 15 kN/cm².

These figures already include safety margins that are required for vertical accelerations during sea transport, where it has been taken into account that the aforementioned extreme value of 1 g only scarcely occurs. Also the restricted duration of the sea transport justifies the mentioned figures.

The relation between maximum tensile stress σ, bending moment M and section modulus W reads:

Equation (9) shows, when using steel beams as bedding material, the section modulus may be smaller because the permissible tensile stress σ of steel is greater than that of timber by the factor 15.

4.2 Prevailing load case

In the applicable load case the beam rests on the internal bottom of the container with its entire length t and carries a symmetrical homogeneous load m over the length r (Figure 15). Under the assumption of a homogeneous load distribution from below and from the top the beam is subject to a bending moment of the magnitude:

Figure 15: Beam with linear load and linear support

The required section modulus results

for timber beams:

for steel beams:

In this load case the effective length t must be limited against r, because a too long beam would lift its ends off the ground and would no longer transfer the load fairly evenly to the ground. For this limitation the following rules of thumb are given:

Timber beams 10 x 10 cm: tmax = (1.2 · r + 0.8) m, but not more than (r + 1.0) m



Steel beams 12 x 12 cm: tmax = (1.2 · r + 3.0) m, but not more than (r + 4.0) m




4.3 Beam-diagrams

The solutions of equation (11) for timber beams are presented graphically in Figure 16. The load m varies between 1 and 12 t, and the extension of the beam (t - r) varies between 0 and 400 cm. With these entries all relevant cases may be covered.

It becomes clear however, that for coils of the weight class XH, where the beam length t must be greater than 2.7 m according to Figure 13 and hence the expected beam extension (t - r) greater than 1.5 m, a proper load distribution with timber beams cannot be obtained with reasonable expense. Therefore, a similar diagram in Figure 17 shows the solutions of equation (12) for steel beams.

Figure 16: Required section modulus for timber beam bedding

Example 1: A coil of 6 t mass on skids of 0.9 m length of timbers is placed on two longitudinal beams of 1.6 m length. The beam extension (t - r) is 70 cm. Each beam is loaded with 3 t. The diagram in Figure 16 shows a required section modulus of about 260 cm³. Hence, beams of 12 x 12 cm are necessary (see Table 1).

Example 2: A coil of 10 t mass on skids of 1.0 m length of timbers is placed on two longitudinal beams of 1.8 m length. The beam extension (t - r) is 80 cm. Each beam is loaded with 5 t. The diagram in Figure 16 shows a required section modulus of about 490 cm³. Hence, beams of 15 x 15 cm are just sufficient (see Table 1).

Example 3: A coil of 21 t mass and mC/P = 0.75 requires for safeguarding the longitudinal strength of the container two beams of 3.8 m length according to Figure 13. The load of 10.5 t is transferred to each of the beams over a length of about 1.3 m. So the beam extension (t - r) is about 260 cm. With this entry, the diagram in Figure 17 shows a required section modulus of about 225 cm³. With this, steel beams of 14 x 14 cm are just not sufficient (see Table 2). Stronger ones should be used.

Figure 17: Required section modulus for steel beam bedding

5. Securing principles

5.1 Securing effort

5.2 Securing methods

5.3 Securing balance

5.1 Securing effort

Steel coils in a container should at least be secured against longitudinal accelerations of 1.0 g (road/rail) and against transverse accelerations of 0.8 g (sea transport). With this, also a transverse stowage position on a ship would be covered.

Coils fastened to wooden skids exhibit, apart from friction locking, also a certain form locking to the skid (see Figure 5). Therefore, a friction coefficient of 0.4 may be attributed to the connection coil to skid. The same coefficient is valid, according to Annex 13 to the CSS-Code, for the boundary between the wooden skid and the wooden floor of the container. Thus a residual securing demand remains against accelerations of 0.6 g longitudinally and 0.4 g transversely.

However, if the coils rest on timber beams or with wooden liners on steel beams, the applicable friction coefficient is only 0.3. Then the residual securing effort must be directed against accelerations of 0.7 g longitudinally and 0.5 g transversely.

5.2 Securing methods

When coils are stowed "Eye to side", lashings taken as half loops through the eyes of the coils act only longitudinally in the container. Since the securing points in the bottom area of the container have an MSL of about 1000 kg (about 10 kN) only, and not all securing points can be put into effect simultaneously, additional pressure elements to the end walls and corner posts must be applied in general and also the coils stiffened to each other with timber.

Figure 18: Longitudinal securing of coils by means of half loops

The remaining transverse securing with that arrangement should exclusively be realised by pressure elements. Care should be taken that the transverse shores are not set directly against the side walls of the container (Figure 19), but transfer their securing load through longitudinal cross-beams onto as many corrugations of the container wall as possible (Figure 20). Additionally, the actual shores must be stabilised by nailed-on longitudinal scantlings in a way, that they retain their function after occasionally falling slack.

Figure 19: Improper transfer of pressure to the container walls and poor stabilising of shores

Figure 20: Sound transfer of pressure to the container walls and reliable stabilising of shores

With coils stowed "Eye fore and aft", simple half loops through the eyes of the coils will only act transversely in the container. But also here, additional pressure elements must be set in the transverse direction. The remaining longitudinal securing should solely be effected by pressure elements, which must be appropriately stronger. This securing concept is described in detail in the Container Handbook, chapter 5.2.14.4.

5.3 Securing balance

A securing balance may give an indication on whether a planned or implemented cargo securing arrangement has a sufficient level of strength. However, a balance cannot reveal deficiencies of workmanship. Hence, the application of a balance and the confidence placed into it are only justified if all securing elements considered, here including the container walls, corner posts and securing points, are able to transfer the forces appointed to them in the balance.

The balance is carried out in accordance with the Annex 13 to the IMO CSS-Code. The approach of the balance reads:

External force ≤ friction + sum of forces from lashing and shoring

The external forces in Kilo-Newton (kN) result from a longitudinal acceleration of 1 g and a transverse acceleration of 0.8 g, multiplied with the cargo mass m in tonnes.

The friction force in kN is the product of the applicable friction coefficient and the cargo weight, also in kN, calculated from mass multiplied with gravity acceleration m · g.

The securing forces from lashing and shoring in kN are the sum of MSL-values of the lashings and shores, divided by 1.5. The latter is requested by the CSS-Code as an extra safety factor, because it cannot be supposed that all securing devices carry with their MSL simultaneously.

The MSL of lashings in a container is generally limited by the securing points to 10 kN. Longitudinal or transverse lashings should not deviate from their assigned effective direction by more than 30°. Lashing running steeper than 60° should not be counted or at least only partially included in the calculation. The MSL of timber shores for bracing is 0.3 kN per cm² cross-section transverse to the timber grain and 1 kN per cm² along the grain (see Container Handbook, Vol. I, chapters 4.3 and 4.4).

Example: A coil of 19 t mass on a skid is placed into a container. Longitudinal securing is accomplished

by two half loops to fore and aft with two loaded ends each (similar to Figure 18), and by three timber shores fore and aft of 12 x 12 cm (similar to Figure 20). Transverse securing is achieved by four timber shores of 10 x 10 cm to each side. Care has been taken that all timber shores can transfer the desired forces evenly into the container walls respectively corner posts. The balance in kN then reads:

Longitudinally: 1 · 9.81 · 19 ≤ 0.4 · 19 · 9.81 + (4 · 10 + 3 · 144 · 0.3) / 1.5 186 ≤ 75 + 113 186 < 188 Balance is just met!

Transversely: 0.8 · 9.81 · 19 ≤ 0.4 · 19 · 9.81 + (4 · 100 · 0.3) / 1.5 149 ≤ 75 + 80 149 < 155 Balance is just met!

Notice: Other than in the Annex 13 to the CSS-Code, this balance does not presume that the friction in the bottom of the container is reduced by vertical accelerations, simultaneously appearing with maximum longitudinal forces. This phenomenon is only encountered at sea, where, however, the longitudinal acceleration is only about 0.3 g. In the above balance the acceleration applicable for road or rail transport of 1 g is used, requiring greater securing forces. In this way, also the Annex 13 requirement for sea transport is satisfied.

6. Stowage examples

6.1 Weight class L

6.1.1 Checking transverse and longitudinal loads to the container

6.1.2 Checking the loads to the timber beams

6.1.3 Securing of the coils

6.2 Weight class L(max)




6.3 Weight class M(max)




6.4 Weight class H



6.4.3 Securing of the coil

6.5 Weight class XH


6.5.2 Checking the loads to the steel beams


6.6 Alternative solution for all weight classes

6.1 Weight class L

Weight class L covers coils with a mass of up to 32 % of the container payload. Depending on the payload the upper mass limit is therefore between about 6 t and 9 t per coil.

In this example coils of 4 t each shall be loaded into a container of P = 28.230 t. Thus each coil has a mass of 14.2 % of the payload. The diameter is d = 0.84 m and the breadth is b = 1.26 m. The coils are tendered on skids of three longitudinal timbers of 10 x 10 cm cross-section and 0.90 m length. The distance of the middles of the outer timber is 1.10 m.

In order to fully exploit the payload of the container, the coils are arranged as shown in Figure 21 with about 36 cm free space at the door end. This arrangement is sufficiently symmetric in the transverse and the longitudinal direction. The longitudinal centre of gravity is only about 18 cm off the half length of the container.

The coils, which are stowed at the fore and aft ends of the container must be set on extra longitudinal timbers for distributing the load onto a sufficiently large number of bottom girders of the container. These coils are stowed tightly against the container sides.


The coils stowed transversely in the middle of the container rest on longitudinal beams of a spread s = 1.10 m. With

this, the diagram in Figure 13 displays with an entry of mC/P = 0.142 a minimum length of the longitudinal beams of t = 0.90 m. This requirement is just met.

The coil couples of 2 x 4 = 8 t stowed longitudinally at the ends of the container keep a distance (middle to middle) of s = 1.40 m. With this, the diagram in Figure 13 displays with an entry of mC/P = 0.284 a minimum length of the longitudinal beams of t = 1.35 m. This requirement is met with 1.40 m.

The longitudinal bending moment in the container will actually be smaller than with a homogeneous load due to the heavier loaded ends of the container. A check by calculation may therefore be omitted.

Figure 21: Stowage of "light" coils with full payload


The coils stowed at the container ends rest on two beams of 10 x 10 cm cross-section and a length of t = 140 cm.

The loaded length from the coil is r = 120 cm. With a beam extension of (t - r) = 20 cm and a load of 2 t, the necessary section modulus for each beam is taken from the diagram in Figure 16 with about 50 cm³. The beams have a section modulus of 152 cm³ (Table 1). Also the extension is well within permissible limits.

The coils stowed transversely in the middle of the container rest on three longitudinal timbers of 10 x 10 cm cross-section, of which the middle one does not bear due to the deflection of the container bottom. The outer timbers of t = 90 cm are loaded fairly evenly over a length of r = 63 cm. With the extension of (t - r) = 27 cm and the load of 2 t the necessary section modulus for each beam is taken from the diagram in Figure 16 with about 65 cm³. Also this value is less than the existing section modulus of 152 cm³. Also the extension of 27 cm is well within permissible limits.



The coils are secured according to the principles in chapter 5. The friction coefficient is taken as 0.4 due to the form locking to the skids. Thus, a residual securing demand remains against longitudinal accelerations of 0.6 g and transverse accelerations of 0.4 g.

The residual longitudinal securing effort of 28 · 0.6 · 9.81 = 165 kN should be partly achieved by lashings, because securing by pressure elements alone would overcharge the end walls, as they are rated for 0.4 g only.

Figure 22 shows the arrangement of such lashings in a container with 10 securing points in the bottom area. Due to the layout of the securing points only four of them are loaded simultaneously to fore or aft in this example.

Figure 22: Longitudinal lashing of the coils

Figure 23 shows the additional longitudinal pressure elements. They consist of three upright timbers of 10 x 10 cm in the space between the coils in the middle, secured against falling loose. To the end wall on the left, the coils are braced by means of two cross beams in a height of 0.5 and 1 m. At the door end this is done by 8 short scantlings of 10 x 10 cm cross-section being braced to the corner posts.

Figure 23: Longitudinal and transverse bracing of the coils

The residual transverse securing effort of 28 · 0.4 · 9.81 = 110 kN is exclusively achieved by pressure elements of four timbers of 10 x 10 cm cross-section to each side wall with the coils in the middle. The coils resting side by side at the ends of the container are braced against each other by two scantlings of 10 x 10 cm cross-section.

The arrangement is checked by a balance:

Longitudinally: 1 · 9.81 · 28 ≤ 0.4 · 28 · 9.81 + (4 · 10 + 8 · 100 · 0.3) / 1.5(to the door end) 275 ≤ 110 + 187 275 < 297 Balance is met!

Transversely: 0.8 · 9.81 · 12 ≤ 0.4 · 12 · 9.81 + (4 · 100 · 0.3) / 1.5(3 middle coils) 94 ≤ 47 + 80 94 < 127 Balance is well met!

Transversely: 0.8 · 9.81 · 4 ≤ 0.4 · 4 · 9.81 + (2 · 100 · 0.3) / 1.5(each 1 Coil at the ends) 31 ≤ 16 + 40 31 < 56 Balance is well met!

Notice: The bracing between the coils stowed longitudinally at the ends of the container must transfer the load from one coil only at a time.

The shown securing effort may appear rather extensive. But it must be necessarily installed because in a case of failure the damage may become immense and may also impact neighbouring containers on a sea going vessel.

6.2 Weight class L(max)

In this example three coils of 9 t each shall be loaded into a container of P = 28.230 t. Thus, each coil has a mass of 31.9 % of the payload. The diameter is d = 1.10 m and the breadth is b = 1.66 m. The coils are tendered without skids. If the coils were stowed longitudinally using a C-hook, the longitudinal beams underneath would have a spread s = 0.75 m (Figure 24). Consequently, the beams needed to have a length of 2.60 m according to the diagram in Figure 13, in order not to overload the container bottom. But then only two of these coil could be loaded because 3 x 2.60 exceeds the length of the container.

Figure 24: Narrow spread with a stowage "Eye fore and aft"

Thus the coils are stowed transversely into the container as shown in Figure 25 and arranged according to the rule (1/7, 1/2, 6/7), mentioned in chapter 3.2. This arrangement is symmetrical in longitudinal and transverse direction.

Figure 25: Stowage of "light" coils with full payload (limit weight)


The transversely stowed coils rest on longitudinal beams with a spread of = 1.50 m. Using this, the diagram in Figure

13 provides a minimum length of the beams of t = 1.30 m with the entry mC/P = 0.319. This requirement is met with t = 1.40 m.

The longitudinal strength of the container is safeguarded by observing the aforementioned stowage rule. A calculated check is therefore not necessary.



The coils rest on two beams of 15 x 15 cm cross-section and a length of t = 140 cm. The loaded length from each coil is r = 90 cm. With the extension of (t - r) = 50 cm and the load of 4.5 t the necessary section modulus for each beam is taken from the diagram in Figure 16 with about 280 cm³.

The beams have a section modulus of 513 cm³ (Table 1). Also the extension of 50 cm is well within permissible limits.






The coils are secured according to the principles in chapter 5. The friction coefficient is taken as 0.3 due to non-existing form fit. Thus, a residual securing demand remains against longitudinal accelerations of 0.7 g and transverse accelerations of 0.5 g.

The residual longitudinal securing effort of 27 · 0.7 · 9.81 = 185 kN is achieved by lashings and additional pressure elements to the end walls and corner posts. Also among each other the coils are longitudinally braced with timbers. These timbers consist of three scantlings of 15 x 15 cm cross-section in each intermediate space, secured against falling loose. At the end walls, strong cross beams are inserted, which are jammed against the corner posts and also have contact to the end walls.

Due to the arrangement of the securing points, only 8 of them are loaded simultaneously. Considering the securing situation in the intermediate spaces, only four of the securing points are found to bear simultaneously to fore or aft.



The residual transverse securing effort of 27 · 0.5 · 9.81 = 132 kN is exclusively realised by 9 timber braces of 10 x 10 cm cross-section to each side.


Longitudinally: (between the coils with 15 x 15 cm timbers)

1 · 9.81 · 18 ≤ 0.3 · 18 · 9.81 + (4 · 10 + 3 · 225 · 0.3) / 1.5 177 ≤ 53 + 162 177 < 215 Balance is well met!

Transversely: (all coils with 10 x 10 cm timbers)

0.8 · 9.81 · 27 ≤ 0.3 · 27 · 9.81 + (9 · 100 · 0.3) / 1.5 212 ≤ 79 + 180 212 < 259 Balance is well met!

The securing effort is comparable to that of the previous example. The quality, however, is more important due to the greater masses.

6.3 Weight class M(max)

In this example two coils of 13.6 t each shall be loaded into a container of P = 27.780 t. Thus, each coil has a mass of 49 % of the payload. The diameter is d = 1.40 m and the breadth is b = 1.42 m. The coils are tendered on skids. The bottom scantlings of these skids have a cross-section of 15 x 15 cm and a length of 1.40 m.

The coils are stowed transversely into the container. With a spread of the outer scantlings of 1.25 m, the bedding length must be extended by longitudinal beams of at least 2.64 m length, according to the diagram in Figure 13. The coils are arranged as shown in Figure 28, according to the rule (1/4, 3/4) in chapter 3.2. This arrangement is symmetric in longitudinal and transverse direction.

Figure 28: Stowage of "medium" coils with full payload (limit weight)


The spread of the longitudinal beams underneath is s = 1.25 m. The chosen length t = 2.70 m, according to the diagram in Figure 13 with an entry of mC/P = 0.49, satisfies the transverse strength requirements of the container.

The longitudinal strength of the container is safeguarded by observing the (1/4, 3/4) stowage rule. A calculated check is therefore not necessary.


The coils rest on timbers of 20 x 20 cm cross-section with a length of t = 270 cm. The loaded length from each coil is r = 140 cm. With the extension of (t - r) = 130 cm and the load of 6.8 t the necessary section modulus for each beam is taken from the diagram in Figure 16 with about 1100 cm³.

The beams have a section modulus of 1217 cm³ (Table 1). Also the extension of 130 cm is well within permissible limits.dimensions in cm

10 x 10

12 x 12

15 x 15

20 x 20




The coils are secured according to the principles in chapter 5. The friction coefficient is taken as 0.4 due to form fit with the skids and the contact timber/timber below. Thus, a residual securing demand remains against longitudinal accelerations of 0.6 g and transverse accelerations of 0.4 g.

The residual longitudinal securing effort of 27.2 · 0.6 · 9.81 = 160 kN is achieved by lashings and additional pressure elements to the end walls and corner posts. Also between the coils there are longitudinal braces. These pressure elements consist of four timbers of 15 x 15 cm cross-section at the end walls and three timbers of 15 x 15 cm cross-section in the intermediate space, secured against falling loose. Due to the arrangement of the securing points, only six of them bear simultaneously.

The residual transverse securing effort of 27.2 · 0.4 · 9.81 = 107 kN is exclusively realised by 4 timber braces of 12 x 12 cm cross-section to each side.




Longitudinally: 1 · 9.81 · 27.2 ≤ 0.4 · 27.2 · 9.81 + (6 · 10 + 4 · 255 · 0.3) / 1.5 267 ≤ 107 + 220 267 < 327 Balance is well met! Transversely: 0.8 · 9.81 · 27.2 ≤ 0.4 · 27.2 · 9.81 + (4 · 144 · 0.3) / 1.5 213 ≤ 107 + 115 213 < 222 Balance is just met!

The securing effort is similar to that of the previous example. The quality, however, is even more important due to the greater masses.

6.4 Weight class H

In this example one coil of 17 t shall be loaded into a container of P = 28.230 t. Thus, the coil has a mass of 60 % of the payload. The diameter is d = 1.86 m and the breadth is b = 1.00 m. The coil is tendered without skid and shall be

placed "Eye fore and aft". For bedding the coil, square timbers of 20 x 20 cm cross-section are allocated, on which the coils is pushed into the container by means of soft soap.

The section modulus of these timbers is 1217 cm³. The diagram in Figure 16 shows, with a load of 8.5 t per beam, a permissible extension of about 1.1 m and hence a length of the beam of t = 2.1 m. This particular length requires a

spread of the longitudinal beams of 1.6 m, according to the diagram in Figure 13.

This spread cannot be realised with a coil diameter of 1.86 m. The maximum possible spread of 70 % of that diameter is 1.30 m. This however, requires a beam length t = 3.10 m.

Eventually, a spread of s = 1.25 m with a length of beams t = 3.20 m is selected according to the diagram in Figure 13. The permissible extension of 1.1 m is maintained by laying shorter beams of 2.1 m length in between. The

arrangement is shown in Figure 31.

Figure 31: Longitudinal stowage of a "heavy" coil


The spread of the longitudinal beams is s = 1.25 m. The selected length of beams t = 3.20 m, obtained by entering the diagram in Figure 13 with mC/P = 0.60, satisfies the requirements of the transverse strength of the container.

For safeguarding the longitudinal strength of the container, a length of beams t = 2.00 m would have been sufficient, according to the diagram in Figure 13.



The coil rests on two lower beams of 20 x 20 cm cross-section and a length t = 320 cm. The loaded length from each beam on top is r = 210 cm. With the extension of (t - r) = 110 cm and the load of 8.5 t the necessary section modulus for each beam of about 1150 cm³ is obtained from the diagram in Figure 16. The same situation applies to the upper beams loaded directly by the coil with r = 100 cm.

The beams have a section modulus of 1217 cm³ (Table 1). Also the extension of 110 cm is well within permissible limits.





The coil is secured according to the principles in chapter 5. The friction coefficient is taken transversely as 0.4 due to form fit and the contact timber/timber, but longitudinally as 0.3 due to the contact steel/timber. The effect of the soft soap should be compensated by subsequently connecting the upper with the lower beams by cramps, bolts or angle joints. Thus, a residual securing demand remains against longitudinal accelerations of 0.7 g and transverse accelerations of 0.4 g.

The residual longitudinal securing effort of 17 · 0.7 · 9.81 = 117 kN is achieved by lashings and by pressure elements to the end walls and corner posts. The pressure elements consist of two timbers of 15 x 15 cm cross-section, secured against falling loose and against buckling due to their length. Only four of the securing points bear simultaneously to fore or aft. The lashings also have a transverse effect.

The residual transverse securing effort of 17 · 0.4 · 9.81 = 67 kN is achieved by lashings and by pressure elements to each side. Only three securing points are loaded simultaneously. However, due to the unfavourable lashing angles only two points are considered in the transverse balance.

Figure 32: Longitudinal and transverse lashing of the coil

Figure 33: Longitudinal and transverse shoring of the coil


Longitudinally: 1 · 9.81 · 17 ≤ 0.3 · 17 · 9.81 + (4 · 10 + 2 · 225 · 0.3) / 1.5 167 ≤ 50 + 117 167 = 167 Balance is just met!

Transversely: 0.8 · 9.81 · 17 ≤ 0.4 · 17 · 9.81 + (2 · 10 + 3 · 100 · 0.3) / 1.5 133 ≤ 67 + 173 133 < 140 Balance is just met!

The securing effort is less than in the previous example. The quality however, is even more important due to the increased mass of the coil. Due to the marginal satisfaction of the balances, good workmanship is of particular concern.

6.5 Weight class XH

In this example one coil of 24 t shall be loaded into a container of P = 28.230 t. Thus, the coil has a mass of 85 % of the payload. The diameter is d = 1.66 m and the breadth is b = 1.84 m. The coil is tendered without skid and shall be placed "Eye to side". For loading, it is rolled into the container.

Safeguarding the longitudinal strength of the container requires a length of beams of just under 4.9 m. With the expected extension of nearly 4 m, timber for bedding is beyond question. Steel beams must be used.

Steel beams of 18 x 18 cm and a length of 5.00 m are selected with a spread s = 1.40 m. For stabilising, in particular for the process of loading, both beams are weld connected by cross beams. The arrangement is shown in Figure 34.

Figure 34: Transverse stowage of an "extra heavy" coil


The selected length of beams t = 5.00 m for safeguarding the longitudinal strength satisfies also the requirements of the transverse strength of the container. For the latter, also a spread of 1.20 m would have been sufficient.

6.5.2 Checking the loads to the steel beams

The coil rests on two steel beams of 18 x 18 cm and a length of t = 500 cm with intermediate layers of timber dunnage for increasing the friction. The loaded length from the coil is r = 100 cm. With the extension of (t - r) = 400 cm and the load of 12 t, the diagram in Figure 17 provides the necessary section modulus of just over 390 cm³.

Each beam has a section modulus of 426 cm³ (Table 2). Also the extension of 400 cm is well within permissible limits

of 480 cm in this case.

Figure 17: Required section modulus for steel beam bedding



Table 2: Typical section modules of IPB steel beams

.5.3 Securing of the coil

The coil is secured according to the principles in chapter 5. The friction coefficient is taken as 0.3 due to non-existing form fit and the contact surfaces steel/timber. Thus, a residual securing demand remains against longitudinal accelerations of 0.7 g and transverse accelerations of 0.5 g.

The residual longitudinal securing effort of 24 · 0.7 · 9.81 = 165 kN is achieved by lashings (red in Figure 35) and by pressure elements to the end walls and corner posts. Only four of the lashings are loaded simultaneously to fore or aft. The pressure elements consist of four timbers of 15 x 15 cm cross-section, secured against falling loose and against buckling due to their length (the latter not shown in Figure 36).

The residual transverse securing effort of 24 · 0.5 · 9.81 = 118 kN is achieved by lashings (green in Figure 35) and by pressure elements of four timbers of 12 x 12 cm cross-section to each side. Only three securing points are loaded simultaneously in the transverse direction.

Figure 35: Longitudinal and transverse lashing of the coil

Figure 36: Longitudinal and transverse shoring of the coil


Longitudinally: 1 · 9.81 · 24 ≤ 0.3 · 24 · 9.81 + (4 · 10 + 4 · 225 · 0.3) / 1.5 235 ≤ 71 + 207 235 = 278 Balance is well met!

Transversely: 0.8 · 9.81 · 24 ≤ 0.3 · 24 · 9.81 + (3 · 10 + 4 · 144 · 0.3) / 1.5 188 ≤ 71 + 135 188 < 206 Balance is met!

The securing effort is increased again with regard to the previous example. In particular the distribution of forces from transverse braces onto the container walls requires carefulness. Attention should be paid to introduce the load into the lower third of the side walls. The transverse lashings shall provide some relief to the side walls.

It stands out in all examples that the lashings, due to the low strength of the securing points, contribute only little to the overall securing arrangement. Nevertheless, they should be applied because they may, if given a good pre-tension, disburden the weaker end walls of the container and have an overall stabilising effect on the securing arrangement.

6.6 Alternative solution for all weight classes

As shown in all examples, the effort for stowage and securing is consistently expensive regarding labour and material, if carried out properly. A multiple use of the material will be scarcely possible, because it will be too expensive to have it collected and returned.

The logistics industry offers to that purpose an interesting alternative, in particular for the weight classes H and XH, which in fact creates cost for leasing and also cost for return transport, but therefore reduces the stowage and securing effort to a minimum, concurrent with a high level of safety. It is the Coil-TainerTM, a transport pallet for coils in a container.

The Coil-Tainer is offered in two sizes: Class I with 1.472 m length for coils up to 12 t mass (Figure 37), Class II with 2.930 m length for coils up to 25 t mass (Figure 38).

Figure 37: Two coils of 12 t each in Coil-TainerTMClass I - pallets

Figure 38: Coil of 25 t in a Coil-TainertTM Class I - pallet

With these pallets various combinations of loading are possible depending on the coil masses. The Coil-Tainer pallets are stackable for return transport.

More details may be obtained under www.coil-tainer.com.

http://www.coil-tainer.com/

Documents

Loading and Transport of Steel Coils in ISO Containers Capt Kaps