Title Stacking and transverse racking tests
Name Admin Date 2022-05-04
File
 So as to enhance both stacking  / transverse racking value; this is for logical suggestion on the basis of engineering calculation for an optimum invested cost without overkill under maximized efficacy and design;

                         Transverse Racking :



l   to know the condition of the container stacked on deck when the vessel encounters swell with rolling as per trans verse testing procedure:

 

l  Test Load : 20,000 kgs ( ISO : 15,240 kgs )

l  Pressure Calculation:

Cylinder dia: D = 150 mm,    d: 80 mm

+ Effective Area:

( Push ) : S¹ = π D² / 4 = 17662.5 mm²             

( Pull )  : S² = S¹ - πd² /4 = 12638.5 mm²

Pressure Required:

( Push ) : 2,000,000 / S¹ = 113.2 kgs/ =11.1 Mpa

( Pull )  : 2,000,000 / S² = 158.2 kgs/ = 15.5 Mpa

 

Check Points:

            + Rear / Front : Diagonal deflection.

             + Acceptable Limit: During : A + B = 60 mm, Final tolerance: 10 mm

l  A : Changed length, B : Changed length


Diagonal A + B
  

Note: Anti-racking rings' role is very important for the transverse racking test, being helpful for doors' deflection minimized during testing because the large bearing brackets are being grasped tightly by the anti-rings considerably during the test.




 3482 : Before, 3459 : during , 3479 : after ( PUSH )

 3504 : during, 3483 ( after )  ( Pull )

 

During: 23 mm + 22 mm = 45 mm ( within tolerance )

   Final: 3 mm + 1 mm = 4 mm ( Within tolerance )

 

Why 15,240 kgs against 150 Kn stipulated in ISO ?

 

    a) region by latitude: gravity  to be applied: 9.84

    b) by height ( center between south pole & north pole ) :

                           gravity to be applied : 9.807                                   

                   In general, while 1 Kgf=9.81 N

   However:

           It applies a) : 150Kn / 9.84 x 1,000= 15,243.902 : 15,240 kgs

               Whereas,

          It applies b) : 150 / 9.807 x1,000 = 15,295.197 kgs.


 

Note: during the testing; we can find gaps between the jointing center parts of RH/LH doors;

      In case of PUSH:  gap  noted  at gasket join parts of the bottom center twisted.(A)

      In case of PULL :  gap noted at gasket join parts  of the top center twisted. (B)

 

So as to minimize the gap; we have to pay special attention during doors assembly stage under bisection gaps between cams & keepers, anti-rings attached on the locking bars and large bearing brackets and hinge blade & hinge lugs as per correct assembly SOP as noted in the next page:

 

ܡTo improve the test result of Transverse racking test; as afore-mentioned; bisected gaps at the join-parts; cams & keepers, anti-rings attached on the locking bars and large bearing brackets and hinge blade & hinge lugs, are basically essential during the sub-assembly as below:

 

                    Betw anti-rings / Large bearing brackets         cam and keepers


                  
                   
bisected gaps betw cam/keeper                    Hinge blade / hinge lug

By means of this performance, it is absolute that transverse rack test result can be improved by reducing diagonal different of RH / LH doors.

Actually, during the test, if the margin gaps at each contact component, especially for the anti-racking rings and large bearing brackets are bisected, doors' diagonal force can be grasped by anti-racking ring strongly, consequently, transverse racking test result can be enhanced considerably.

 

In addition;

I've deeply reviewed / calculated raw material strength and rear corner castings connected / supported by the corner post of structural condition as explained in detail as follows:

a) corner casting mechanism:

 

Container corner fitting

 As the most critical component of container, corner fittings plays a very important role in ensuring the safety of container as well as human life. On one hand, overall strength of corner fitting shall be guaranteed. On the other hand, it shall not be too heavy. Therefore, corner fitting shall be designed in such a way that most important faces shall have largest thickness while least important faces shall have the thinnest thickness. 
 

CORNER FITTING

 

Corner fitting is cubic object with six faces: 1 top face, 4 vertical walls and 1 bottom plate (we take top corner fitting for an example). The first step we must take is to figure out for the strength as to which one is most important, which one is second important and which one is least important.

 
 

Top Face

Nobody can deny that top face is most critical since all stacking and lifting loads are directly applied on it. That is why top face has a largest thickness. (28.5mm+0-1.5mm) 


             

VERTICAL WALL VS BOTTOM PLATE

Vertical walls are more important and critical than bottom plate due to the below reason:

 

-As we all know, corner fitting mainly withstands lifting load (tensile load upward) and stacking load (pressure downward) and most of the load is transferred by four corner posts. As shown in below picture, front or rear corner posts are welded to corner fitting along those edges and right below the vertical walls.

 

-without many critical components connected in the middle area, bottom plate withstands less load.

 

Hence, we mainly rely on vertical walls rather than bottom plate for load transfer.

 

VERTICAL WALL VS BOTTOM PLATE

From these photos, we can see that, even if bottom plate is removed, water may leak into container and cause cargo damage. But in terms of strength, container is still OK. It can still be stacked, lifted and handled, which means the bottom plate except for edges welded with the corner posts is not so critical for the strength.



VERTICAL WALL
VS BOTTOM PLATE

-Unlike vertical wall, bottom plates are protected and not exposed. Let’s take ISO dry cargo container for example, from outside, your almost can not see bottom plate except for rear corner fitting (You can see a small area of rear corner fitting.) As a result, it is less likely for bottom plate to bear direct foreign collision and impact.
 

VERTICAL WALL VS BOTTOM PLATE

Based on our previous comparison, we can conclude that vertical walls are more critical and important than bottom plate in terms of strength.

 

Vertical walls shall be thicker than bottom plate in order to ensure sufficient strength.

 

Currently, the thickness of vertical walls are controlled around 12mm in most corner fitting manufacturers. It is unjustifiable to reduce the minimum thickness to 10mm. It is good for manufacturer since cost can be saved but it is bad for container owner since strength is reduced.




IMPROPER DIMENSION CHAIN

It is very obvious that, if minimum thickness is set to 10mm, the overall height will be more than 118mm+0-1mm which is existing nominal height for corner fitting. Without any doubt, this is a improper dimension chain unless minimum thickness of bottom plate is changed to 9mm or ever below.

 

VERTICAL WALL VS BOTTOM PLATE

We admit that there are some factories that can produce corner fittings with minimum thickness of bottom plate more than or equal to 10mm. However, internal height are often sacrificed in order to keep bottom plate more than or equal to 10mm. Please see below photo, internal height is less than required value (79.5mm+1.5mm-0).



VERTICAL WALL VS BOTTOM PLATE

Please do not forget that heat number and manufacturer name are made about 2mm high above bottom plate. This further reduces internal height. We received some complaints from our client saying that internal height is too small for people to handle twist-lock.

 

VERTICAL WALL VS BOTTOM PLATE

The minimum thickness of bottom plate is still controlled at less than 10mm in many corner fitting factories. 



CONCLUSION for corner casting:

On the basis of the above data; it's OK for the corner fittings' design as it is unless its strength relating to chemical composition and mechanical properties during its analysis is violated against the standard.

However, we need to check / inspect and test the corner fittings frequently because we can't say enough about the importance of the corner fitting quality in terms of container basic structural conception.

 

In this connection;

I can find another technical point to be modified for the enhancing of the stacking load & transverse racking test values as under-explained:

 

ܡ Rear top side rail design recommendation:

 

Recently, all manufacturers are to standardize the design of the rear top side rail ( shape & material thickness, etc ) to save cost with less consideration of its strength:



As shown in above diagram; the rear top rail thickness is 4.0 mm t while that of rear bottom rail

is still by 4.5 mm t.

In this connection, we found that it's fact for the rear top corner fitting whose welding edge area with the rear corner post is so little in terms of design-wise than the front corner fitting & its post as shown in Diag.#1 that the top corner fitting for edge welding part is to be actually tilted down after having them stacking load tested because NO welding edge part of that ( inwards ) can't be supported by the corner post structure in terms of actual rear corner post design as (B) below:


Consequently, the rear top rail ( 4.0 mm t ) might be pressed by 2 top corner fittings during stacking load test / transverse racking tests,

Thus, there might be high possibility for more gasket tilting at the joint parts of both doors' center during voyage when vessel, she encounters with typhoon and rough swell with rolling & pitching. of course, rear corner posts are to be deform as well through the same bad weather condition during voyage.

through which likelihood of water ingress into container is highly inevitable.

 

In order to enhance this and improve this likely terrible happening; technically in engineering mind, I'd like recommend you to consider to modify design by less investment without over kill as below:



Conclusion of design change recommendation:

"U" typed rear top side rail:

material thickness is to be increased from 4.0 mm t to 4.5 mm t:

Cost increase: about $4.0 per unit as detailed below:

 

In addition:

As I reported / recommended you already;

In case of 109 ton stacking load like NYK, MSC : to apply a reinforcement into rear / front corner posts and rear top rail thickness increase. ( $17 +$4 per unit )

[(50 mm x 2301 mm x 4 mm x 2)x@7.85÷1,000,000]x0.9=$6.5x2( Rear/Front )=$13 ( steel )

welding wire + wage & etc:$4           Total:US$17.0 per unit


Plus, to increase the rear top rail thickness from 4.0 mm vs. 4.5 mm:

[(4 mm x 334 mm x 2338 mm)x@7.85÷1,000,000]X0.9=$22 for 4.0 mm rear top rail steel

[(4.5 mm x 334 mm x 2338 mm)x@7.85÷1,000,000x0.9=$24 for 4.5 mm rear top rail steel

$24-$22=$2 +$2 (shearing / bending & wages)=US$4 per unit






In case of up-to 102 tons of the stacking load, it seems to be enough for rear top rail thickness increase only to enhance both stacking load / transverse racking.

                                                      - The end-  

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