Yield line theory_steel plate 1

[vhengr]

thread507-210553

Hi

I am new to this forum; and it is my first post.
While browsing the above thread, few doubts came in my mind;

As per chas10 calc sheet; if the bolt load is 277 Kn per bolt; what will happen at rib/stiffener area? Resultant Hogging moments (due to either side of bolts load)will get nil?

I feel; Internal work done (D) will get reduced to 10.55m to 6.33m (in more than one bolt case); and accordingly it will ask for more thickness of plate of 33.8mm for increased moment demand occur due to other side of bolt load.

Seniors Pls. correct me; if my assumptions goes wrong.

 

[BAretired]

I don't follow your reasoning. The plate is welded to the stiffener, so there will be a hogging moment each side of the stiffener.

BA

 

[vhengr]

There will be a hogging moment each side of the stiffener....that is why I am got confused here..

Shall I assume ... the hogging moment at each side(actually total will be m1+m1) will be carry by support (i.e stiffener)itself. If this is the case, this moment should not to considered for determining the reqd plate thickness... what I feel.
But on the contrary; we are considering the moment (at one side only) for deciding the plate thickness. then why not the additional Other side hogging moment?

Bit confused. Your insights are much appreciated!

 

[BAretired]

Shall I assume ... the hogging moment at each side(actually total will be m1+m1) will be carry by support (i.e stiffener)itself. If this is the case, this moment should not to considered for determining the reqd plate thickness... what I feel.
But on the contrary; we are considering the moment (at one side only) for deciding the plate thickness. then why not the additional Other side hogging moment?

They are two separate yield lines, one each side of the stiffener and separated by the thickness of the stiffener. They act in opposite directions, one clockwise, the other counter clockwise so the stiffener does not take m1+m1; it takes m1-m1=0.

There could, however, be some concern about the effect of the plate bending on the weld. I'm not sure whether or not that is something which needs to be addressed. I suspect it is okay if the weld is designed for its share of the applied load.

BA

 

[vhengr]

Thanks BA

Agreed! Weld shall be designed for additional other side shear. (since applied load is twice)

Can we say; if weld is strong enough to transfer the moments to the stiffener plate, then one can further optimize the plate thickness here.


Best Regards_ VH

 

[BAretired]

There are a few items which deserve comment in the referenced thread (which is now closed):

1. The internal energy expression for the two diagonals is incorrect. Work done is m.L.θ; if L is taken as 78, θ is not 1/67.5. It is simpler to take L = 78sin45 = 55 mm and θ = 1/67.5

2. When equating internal and external work, factored loads should be used and yield stress should be used, modified by uncertainty factor φ = 0.9.

3. Plastic modulus bd[sup]2[/sup]/4 should be used in determining required thickness, not section modulus bd[sup]2[/sup]/6.

4. The final value of m obtained by equating internal and external work should be increased to account for possible corner effects not considered in the analysis. An increase of 10% is usual.

5. One poster in the original thread argued that it is not necessary to deduct for the holes, but when holes are large compared to the other dimensions, it would seem prudent to make the deduction. 34mm is quite a large hole.

BA

 

[vhengr]

Thanks BA for the details!

Actually was concerned/confused about continuous beam static problem.

Thxs again!

Best Regards_ VH