Iso : Floor Calculation

[DUCRUY Jacques]

Good Morning,

I had problems for understanding the principle of floor calculation in load case 4 (cf ISO 12215 part 9 annex C).

If you take the worked exemple, you have :

Bending moment (M41) : 47212 N
Lq : 1.10 m L1 : 0.54mm and L2 : 0.56 m

How to calculate the vertical force in the floor ?

If I use the formula of Larsson & Eliasson, I have Fv = M41/Lq, or 42920 N.

But, in the exemple, Fv is the maximum force on the bolt (26365 N).

What is the explication ?


Thank you by advance

Have a nice day


Jacques

[Ad Hoc]

Originally Posted by DUCRUY Jacques

Bending moment (M41) : 47212 N

A moment has the units "Nm" not just "N"....so unless that is a typo, you need to multiply by a distance.

A bending moment shall be as a result of either a point load or uniformily distrubited laod. Either way, this bending moment can be resolved into a shear force, ie what is supporting that member that has the bending moment?

Then the shear force is simply BMmt/(L/2)..ie what is supporting it..half the frame at one end, and half the frame at the other end!

[DUCRUY Jacques]

Hello,

Sorry for my late answer.

You have right : the moment M41 is 47212 Nm.

But why the vertical force on floor is only the maximum force in bolt ?

Thank in advance



Jacques

[Ad Hoc]

Originally Posted by DUCRUY Jacques

But why the vertical force on floor is only the maximum force in bolt ?

Do you have a sketch, so i can understand your question better...as i want to avoid an assumption on my part.

[DUCRUY Jacques]

Hello,

You'll find attached a sketch of the calculation of vertical force in floor in case of grounding (as described by Larsson & Eliasson).

The exemple is take in annex C of ISO/DIS 12215-9 (2009 03 10).

The table C4 of annex C give the calculation of force in bolt (load case 4), with a maximum of 26366 N ... and the bending moment of the floor is calculated for this force ... et not for 42 920 N (see my sketch).

So, I dont unterstand the calculation of ISO.

Thank you in advance

Regards


Jacques

[Ad Hoc]

Your force of 42920N is correct, for the reaction on each bolt as F1 & F2.

However, you need to be careful, since how does the 26366N relate to the bending moment? Where does the 26366N come from? Is it exactly the same as your F1 & F2 calculation, but just a different result? And the bending moment, how is this calculated or assumed from the vertical reaction force?...since this reaction force, via the bolts, puts a bending moment into any member transversely (and/or longituidinally) that the bolt is atteched too....but nothing of that is provided such as spans fixity etc.

Also, you shall have Fi, as a horizontal force too, assuming the keel is stiff enough.

The total load on the bolt is the vertical and shear load combined.

[DUCRUY Jacques]

Hello,

Thank you very much for your answer.

You'll find attached an extract of the table C5 : the bending moment of the floor is 5253 N (with a force of 26366 N and a length of floor of 1.70 m, end fully fixed).

In other terms, it seems to me that the exemple of ISO take in account the vertical force on the bolt et not the vertical force on the floor ; Is it logical ?

Have a nice day


Jacques

[Ad Hoc]

Jacques

You are using incorrect units for bending moment again!

Without seeing the arrangement, i can't really comment on those values, it is just a string of numbers. But of what? Bending moments and reactions etc, require a basic arrangement to estbalish the value of each. Without seeing the GA of the structure/bolting, i have no idea whether those numbers are correct.

[DUCRUY Jacques]

Hello,

Sorry for the unit of BM ...

You'll find under a sketch of de G.A. I consider only the floor FL2, FL3 and FL4.

Thank you

Have a nice day



Jacques