Analysis on the Securing of Steel Coils in Container Transportation

Abstract: Aiming at the common securing methods of steel coils shipped in ordinary containers, the inertial force of 6 t steel coils is calculated by using the ship acceleration formula, and the securing form of 4 steel wire ropes is set according to the actual condition of the container's fastening bolts , and the securing mode is determined. Carry out balance checks, and propose check methods and securing suggestions for container steel coil transportation.
Keywords : acceleration ; inertial force ; balance

fastening methods such as cargo hold stacking , special brackets or special bases. Due to the lack of standard lifting devices , the steel coils are stacked at the wharf for a long time and difficult to load and unload. Tied, resulting in longer shipping times and higher shipping costs . In view of the superiority of containers in hoisting and road, rail and water transport, many companies are trying to transport steel coils in containers without supports to increase circulation efficiency and reduce transportation costs . This method requires that the steel coil must be effectively secured in the container to ensure the safety of the ship and personnel . At present, the fastening method of steel coils shipped in containers is generally based on the practice of railway and road transportation [ 1-2 ] and some transportation experience of shipping companies . There are few studies on the calculation and analysis of securing of steel coils transported in containers for ships . Therefore, taking a container ship with a mainstream ship type of 1 100 TEU as an example, the acceleration of a steel coil with a weight of 6 t is calculated , combined with the current common wire rope lashing methods , the lashing force of the steel wire rope is calculated and the turning and moving of the steel coil is checked. possibility , Provide a certain theoretical basis for container steel coil securing .
1 basic situation
1) There are usually two ways to place steel coils in the container: vertical and horizontal . There are two types of horizontal placement, the axis of the steel coil is parallel to the longitudinal direction of the container and perpendicular to the longitudinal direction. Due to the difficulty of vertical loading and unloading and the difficulty of determining the securing point, it is only used for steel coils below 3 t ; the common one is horizontal placement, and its typical Securing condition .

Figure 1 Typical Situation of Steel Coil Securing in Containers
2) The main parameters of a 1 100 TEU container ship are shown in Table 1
Table 1 Ship type parameters of 1100TEU container

captain L / m	Type width B ／ m	Type deep draft D / md / m	initial stability altitude		Square system Number C b
			V / kn	GM/m
140.3	23.25	11.568 7.3	19	4.9	0.6

Acceleration calculation
Under the action of waves, the ship produces vertical , longitudinal , and transverse accelerations in three directions . It is considered that the lashing between the container and the ship is good , and the container and the ship have the same angular acceleration . Considering the steel coil in the container as a moving particle , considering the stacking of 8 layers of boxes on the deck (the ISO standard container stacking design capacity can only reach 8 layers ) and the dangerous situation at the stern 02L and the bow 0.2L , according to China Classification Society " Code for Classification of Sea-going Steel Ships " [ 3 ] , the acceleration can be calculated by the following method .
1) The rocking period T R when the ship is in motion is :
T R = 2k r A/GMs
where: k r radius of roll rotation , m ;
High initial stability under GM calculation conditions , m .
2 ) The maximum roll angle when the ship is in motion • m o
 

In the formula: : —coefficient, generally set to 1 respectively according to the presence or absence of bilge keels and anti-rolling devices . 2 , 1 . 0 and 0 . 8 .

1. Pitch period T P .

T p -1.80 JTTw

1. The maximum pitch angle must not be greater than 0.14 .

blood =0. 25a ) /Cb formula: C b square factor ;
a acceleration coefficient, oo=3sc/ L + C v V/~L,
where: C — wave coefficient ;
C v speed factor ;
C v = ZL/50 , take a value not greater than 0.2 .

1. Surge acceleration a ”, sway acceleration a y , heave acceleration %, roll angular acceleration a r , pitch angular acceleration a p .

a ” = 2 a) JC T a =3®
a =7ac/ JC b a = • (6.28/T r ) 2
a = (6.28/T p ) 2

1. Lateral synthetic acceleration at t .

a = Ja y + [a r (zz rp ) + lOsin^n ] 2 (1) where: —— the vertical distance from the calculated point to the baseline , m ;
z rp ——— the vertical distance from the roll rotation axis and pitch rotation axis to the baseline , in m .

1. Longitudinal synthetic acceleration a l .

a = " a 2 + [ a p (z — z rp ) + 10sin blood ] 2 (2)

1. The vertical composite acceleration a v takes the larger of the calculation results of the two formulas .

a. 2 = + a (x_0. 45l) 2 (4)
where: x is the longitudinal distance from the calculation point to the tail perpendicular , in m ;
y — the lateral distance from the calculation point to the longitudinal mid-section , m . According to formula ( 1 ), ( 2 ), ( 3 ), ( 4 ) and the ship type parameters in Table 1 , the maximum acceleration of steel coil is calculated in Table 2 .

	table 2	The maximum acceleration of the steel coil	m/s 2
acceleration	on deck layer 8 _	main deck	3 from bottom high place ( bilge )
horizontal a t	13.83	7.37	4.40
vertical a l	6.28	3.20/ 5.88①	1.74/ 5.88①
vertical a v	12.76	12.76	12.76

Note: ①Because the container is transported by road and water, according to the design standard of semi-trailer traction pin, the anti-collision acceleration of the traction pin is 0.6g, here the longitudinal acceleration is taken as 0.6g = 5.88 m/s 2 .

F(x, y, z) acting on the steel coil is :
F (x,y,z) ma ( x, y,z) IF w(x, y) IF s(x, y) ( 5 )
Where: a ( x, y, z) longitudinal, transverse and vertical accelerations ;
F w(x,y) ——longitudinal and lateral force caused by wind pressure ;
F s(x,y) —— longitudinal and lateral forces caused by the beating of waves . Since the steel coil is inside the container , Wind pressure and wave slap force should be zero , Therefore , Formula (5) can be written as :
F (x,y,z) = m • a ( x,y,z) (6)
It can be seen that only the inertial force is considered for the external force on the steel coil in the container .
4 balance criteria
According to China Classification Society’s “ Guidelines for Compilation of Cargo Securing Manual ” [4] , the balance calculation of force and moment should include the following contents: ①Lateral sliding to left and starboard ; ②Lateral rollover to starboard and starboard ; The longitudinal sliding in the front-to-back direction occurs instead . It is worth noting that each side beam in a 20 t container usually has 4 fastening bolts, and the design tensile strength of each fastening bolt is 1. 5 kN .

1. The condition of lateral sliding equilibrium .

F y W( Mmg +14.7cosai + 14.7cosa +…+ 14.7cosa) (7)

1. Flip the balance condition laterally .

F y aWbmg + 14.7li +14.7/2 +…+ 14.71 ” (8)

1. Longitudinal sliding equilibrium condition .

F x W"(mg — F z ) + 14.7cosU +
14.7cosB + ... + 14.7cosB ” (9)
In the formula: " take 0.3; see Figure 2 and Figure 3 for a and B.

Figure 3 Horizontal Schematic of Container Securing
6 t steel coils in the container is shown in Figure 4 , which adopts the fastening method of wrapping 4 steel wire ropes and placing two steel coils in each container . Calculate the steel coil balance in the box on the 8th floor of the main deck according to formulas (6) ~ (9) , see Table 3 .

Table 3 Securing Balance Calculation of 6t Steel Coil

direction	inertial force F/kN	rope tension F 1 /kN	friction F 2 /kN	Balance Criteria
				Criteria items	Resistance	Criteria results
				horizontal slide F 1 + F 2 — F Lateral rollover anti-rollover moment	—16.18kN	Insufficient lateral tension
horizontal	82.98	49.12	17.66		28.97 kN • m	satisfy
portrait	37.68	50.57	0	Swipe vertically F 1 + F 2 — F Longitudinal rollover anti-rollover moment	12.89 kN 26.89 kN•m	satisfy satisfy

Fig . 4 Fastening method of 4 steel wire ropes
From the calculation results in Table 3 , it can be seen that when the 6 t steel coil is secured by four steel wire ropes , the steel wire ropes can provide sufficient resistance to lateral turning , longitudinal sliding , and longitudinal turning . However, the resistance generated by lateral sliding is insufficient . In this case , limited by the number and design strength of the solid cargo bolts in the container , It is impossible to increase the number of wire ropes and the breaking load of wire ropes , The most effective way is to reduce the stacking height of container steel coils on the deck . The calculation in Table 3 is to consider the 8th layer of containers on the deck . During the stowage process of the actual container on the deck , Usually empty containers are placed on the upper layer . If it is considered that the container with steel coils is placed on the first layer of the main deck , As shown in Table 2 , when the lateral acceleration is only 7.37 m/s 2 , the lateral sliding resistance will reach 22.56 kN, which is enough to ensure that the steel coil will not slide laterally . However, in the actual installation process , There is no guarantee that the container will not be placed on the top deck . As a conservative consideration , it is usually necessary to install horizontal triangular timbers and horizontal brackets as shown in Figure 1 to increase the lateral sliding resistance , although this experience has received good results in operation , but attention should also be paid to the effectiveness of the bracket during the rough course of the ship .
5 Conclusion

1. to the limitation of container fastening bolts , two 6t steel coils are shipped in each container , and each steel coil is shipped with 4 steel wire ropes . There is insufficient resistance to lateral sliding . It should be reduced by reducing the deck stacking height of the steel coil container or using Solve it in an empirical way to ensure the safety of fastening .
2. For the securing of steel coils shipped in containers, the acceleration of the ship shall be calculated according to the ship type , To determine the inertial force of the steel coil and perform a balance check , Then determine the fastening method of the steel coil to ensure the effectiveness of the fastening. references
3. Yu Hua·Scheme and practice of loading reinforcement without support for coil steel transportation [J] · Railway Transportation and Economy , 2004(6):23-24.
4. Wang Mingqiang , Cen Binkui . Research on loading reinforcement methods for railway transportation coils

[J]. Baotou Steel Technology , 2002(1). 92-95.

1. China Classification Society • Rules for Classification of Sea-going Steel Ships [S] Beijing : People's Communications Publishing House , 2006.
2. China Classification Society • Guidelines for Compilation of Cargo Securing Manual [M]. Beijing: People's Communications Publishing House , 1998.

Securing Analysis of Steel Coil in the Transportation of
F reight Containers
PAN Wen-huan 1 , SUN Shu _ xia 2
(1.Wuhan Rule and Regulation Research Institute , China Classification Society , Wuhan 430022 , China ;
2.Wuchang Shipyard，Wuhan 430064，China)
Abstract： For the common securing methods of f reight containers carrying steel coil，t he inertia force of six ton steel coil w as calculated by means of ship acceleration f orm ulas.Four securing types of wire ropes w ere set according to t he act ual lashing rings'arrangement in t he container，t hen the stability of securing types w ere checked. Finally，the paper presented t he checking methods and securing suggestion of steel coil in the containers't ransportation .
Key words： acceleration；inertia f o rce；st abilit y

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