topic Re: Combinations and envelops in Robot Structural Analysis Forum

Combinations and envelops

ypsilspy — Mon, 12 Mar 2018 11:16:31 GMT

Hi,

I've made the design of a connection and as I can see from the forces in the node of the selected connection, robot takes in account only these from a common combination, so it doesn't solve the connection with the envelope of forces in this node. So, it doesn't take in account the max-min for each (N, My,Mz,Vy,Vz) from all combinations to design? Is that right?

Thank you in advance.

Re: Combinations and envelops

Romanich — Mon, 12 Mar 2018 12:12:27 GMT

Hi @ypsilspy,

I would recommend to filter/collect and analyze loads by yourself and then use the worst cases with manual input.

Re: Combinations and envelops

Mohammed_Ata — Mon, 12 Mar 2018 13:15:15 GMT

@ypsilspy

I think what you have listed is not reliable ! We, as STR. designers, don't take the max each straining actions from all combinations! It is so fictitious!

We regularly design according to all combinations, then take the combination that give us the maximum section at the end ! Not collect the max N and the Max M and the Max Q and so on !

If We have

Comb 1: M=20 t.m , N= 30t

Comb 2: M = 15 t.m, N= 40t

We don't design on M=20t.m and N=40t, because this is not reliable !

You can group all of combinations and RSA can design according to all of them and give you the relevant section, see the tutorial below.

Re: Combinations and envelops

ypsilspy — Tue, 20 Mar 2018 23:13:57 GMT

So, Mohammed you don't accept the design with the maximum and minimum forces acting on a member.In the tutorial you've post, we can see the way we can make this envelope, but why to do this if you don't use it for the design?Furthermore, why Robot gives to the results table the max and min N,Q,M for every single mumber from all the combinations?

Also, I have to mention that other programms make design with envelops, such as Sofistik, with the module "Maxima".

However, thanks a lot for your concern to answer to my question.