topic Re: Manual seismic combination in Robot Structural Analysis Forum

Manual seismic combination

nilsarne — Sat, 09 Jan 2021 10:57:08 GMT

Hi everyone!

I am doing a project where I was given the seismic horizontal load. I have used linear load on edges to simulate the seismic actions. (See the attached document for screenshot). I have made one load case for X-direction and one for Y-direction. I want to use automatic combination so that Robot can generate load combinations for ULS, SLS and ACC:SEI. My goal for the ACC:SEI load combination is to get combinations on the form like this: 1*X + 0,3*Y +0,3*Live +0,2*Snow

I have tried many things, but I haven`t been able to do this when I create a manual seismic load case.

After trying many different load combinations and cases, I noticed that the automatic load case generator made excessive load case groups (Se the attached document). How do I get rid of load group EI, E2, E3 & E5?

My last questions is if it is possible to have Robot calculate seismic actions if you have ground type S1 or S2? I have the parameters for these ground types (S, T_b, T_c and T_d)

Re: Manual seismic combination

Simau — Sat, 09 Jan 2021 18:14:20 GMT

Hi @nilsarne

Before using automatic combination, create Newmark combinations then run automatic comb:

Select Newmark comb you create before

When you generate the comb, you'll get what you are looking for

What seismic code are you talking about?

Re: Manual seismic combination

nilsarne — Sat, 09 Jan 2021 19:29:44 GMT

Hi!

I dont understand how you create Newmark combinations.

I am using Eurocode 1998 for seismic analysis.

Re: Manual seismic combination

Simau — Sat, 09 Jan 2021 19:57:08 GMT

Manually.

With Seism X and Y, create 4 Newmark Comb and 4 opposites. In my example i created only the 4 positives to show you the method.

Re: Manual seismic combination

Simau — Sat, 09 Jan 2021 20:02:48 GMT

Re: Manual seismic combination

nilsarne — Sat, 09 Jan 2021 20:28:55 GMT

I dont know how you create those 4 Newmark combinations.

Re: Manual seismic combination

Simau — Sat, 09 Jan 2021 20:57:23 GMT

Newmark comb are created manually (automatically)

Re: Manual seismic combination

nilsarne — Sun, 10 Jan 2021 17:44:43 GMT

Thank you for your explanation. I have a few more questions:

1. Could you explain to me what "Newmark" is and what it does? From what I understand I make manual combinations on this form : 1*X + 0,3* Y and name this combination "Newmark" , but why do I name it by that name?

2. Then you say I can do a regular automatic combination and make "or (excl)" relations between the Newmark cases, right?

3. How do I get rid of empty groups?? (E1, E2,E3,E4)

Re: Manual seismic combination

Simau — Sun, 10 Jan 2021 19:18:52 GMT

@nilsarne

Q1:

If you look at EC8 &4.3.3.5.1 (3) you'll find these combinations. They are called Newmark Combinations

(Google Newmark Combinations)

Q2:

Correct

Q3:

Not easy to answer without the model

Re: Manual seismic combination

nilsarne — Mon, 11 Jan 2021 10:08:57 GMT

Q1: So I could have just called these manual combination something else if I wanted? I dont need to call them "Newmark" for Robot to understand how they will be combined?

Q3: Attached is the model.

Again, thank you so much for your help!

Re: Manual seismic combination

Simau — Mon, 11 Jan 2021 10:54:26 GMT

@nilsarne

Q1: Correct

Q3: What is the kind of load in cases 7 8 9 10 ?

Re: Manual seismic combination

nilsarne — Mon, 11 Jan 2021 11:07:08 GMT

Q3: In cases 7 8 9 10 I have notional loads (geometric imperfections).

Re: Manual seismic combination

Simau — Mon, 11 Jan 2021 12:43:07 GMT

@nilsarne

When generating automatic comb, ignore E(1) to E(4), and select E(7).

I made some modifications to your model:

case 16 Newmark 4: 1x12 -03x11

case 7 to 10 36 set as DL

Renumbering of load cases

Please check if load types (DL, LL, ?) are correct

model attached

Re: Manual seismic combination

nilsarne — Tue, 12 Jan 2021 07:15:58 GMT

Thank you for your help! I have a few more questions:

Q1: I can see you have grouped Snowload and windload into or(incl) category? I thought it should be or(excl)?

Q2: How do you renumber the load cases in a quick way?

Q3: What do you mean that the load cases 7to10 is set as DL ? It has always been dead load. Load combination 36 I deleted.

Q4: Why do you prefer making "manual combinations - generate" instead of the "full automatic combinations." How do you check ULS+ for bending moments, normal forces, deformation etc when making manual combinations? Do you first select the components as shown below, then Robot automatically give you the max and min value?

Q5: If I want to delete these "manual combinations", how do I do this? And if I make some changes to these load cases, will the combinations automatically update? I dont need to first delete them and then make new ones for the changes to take place?

Re: Manual seismic combination

Simau — Tue, 12 Jan 2021 11:41:02 GMT

@nilsarne

Q1:

Yes you are right, but here we have only 1 wind and 1 snow load case so (or) and (or excl) will give same result.

Q2:

No quick way, manually

Q3:

Want only a confirmation from your side.

Q4:

Only my preference, because i want to check combination generated, so i could delete trivial comb i don't need before running generation, and saving calculation time.

Q5:

If I want to delete these "manual combinations", how do I do this?

See attached screenshot

if I make some changes to these load cases, will the combinations automatically update?

Yes

Re: Manual seismic combination

nilsarne — Thu, 14 Jan 2021 11:13:46 GMT

Thank you for your help! I know we have been drifting off a little bit from the original question, but there are many things with Robot that is not so easy to understand in the beginning. So again thank you!

When it comes to question 1 (Q1), its always been hard for me to understand how Robot thinks. I want to make sure it is correct so I would like you to help me understand:

A) If I have both a live load and a snow load on the same panel, but I dont want the live load and the snow load to be in the same combination how do I define the relation between the live load and snow load?

B) If I want both live and snow to be in the same combination, but also a combination where they are not in the same combination.

I would really appreciate it if you could explain to me how these relations works. Thanks in advance!

Re: Manual seismic combination

Simau — Thu, 14 Jan 2021 12:13:55 GMT

When you create a load case be sure to specify the correct nature

Then follow the differente steps in automatic combination, and choose the correct operator.

In Wind, Snow, Seismic categories the operator is Or(excl)

In live loads category the operator may be Or(incl) or And

In Dead loads category it’s always And

Screenshots and a model attached

Re: Manual seismic combination

nilsarne — Mon, 18 Jan 2021 10:47:14 GMT

Thank you! I think I understand now.

Do I always need to create the Newmark combinations manually, or will Robot do this for me when I generate seismic loads in Robot?

Re: Manual seismic combination

Simau — Mon, 18 Jan 2021 11:55:08 GMT

will Robot do this for me when I generate seismic loads in Robot?

Yes, Newmark comb will be created automatically