×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

#### Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
To Your Posts
• Keyword Search
• One-Click Access To Your
Favorite Forums
• Automated Signatures
On Your Posts
• Best Of All, It's Free!
• Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

# Etabs dynamic analysis (more understanding)

 Forum Search FAQs Links MVPs

## Etabs dynamic analysis (more understanding)

(OP)
Hi all

I have one 3 storey building project, ground floor, 1st, long span Steel roof truss. the steel roof is light weight compate to the rest floors. And the 1st to roof is 20m high. My Steel roof column is sitting on the 20m high RC column ( RC　column from　1st to roof)

Based on code, I run a dynamic analysis in etabs, my mass participation is 95% and Base shear for response spectrum (Rs)/ Static(E) is 85 percent.

I want to clarify the load combination 1.2DL+1.0LL+RSx+0.3RSy.....1.2DL+1.0LL+RSx-0.3RSy .... SO on for dynamic analysis load combination.

load combination 1.2DL+1.0LL+Ex+0.3Ey.....1.2DL+1.0LL+Ex-0.3Ey .... SO on for equvalent analysis load combination.

the analysis shows the steel roof column connect to RC column moment reaction is 3 times for the dynamic load combination and equvalent load combination. (equvalent method 3 times more than dynamic).

My question is， is this correct??? if so, can I use the dynamic analysis load combination reaction force to design my steel columns.

Thanks

### RE: Etabs dynamic analysis (more understanding)

Well Not sure if it is "correct" but depending of irregularities definitely could be expected, equivalent static analysis and dynamic Response spectrum analysis can not be scaled with one factor for all dynamic quantities, for RSA each demand is combined using modal load combination rules, so there is never correspondence between them, also static equilibrium does not apply to RSA.

### RE: Etabs dynamic analysis (more understanding)

(OP)
Thanks, my thinking it might be due to:

1) the roof structure is too light and siffness is too low so the Seismic load is lesser till the roof
2) the column grids is 14m from gound to 1st, and 28 m from 1st to roof
3) the column is too high 20m from 1st to roof

All these will cause the roof T period is high and acceleration is too low, so the shear force is low at roof.

It means the roof stiffness is low and too slender. So the below floor columns need to be further strengthen.

Is this correct?

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

### Reply To This Thread

#### Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

#### Resources

White Paper - How ESI is Helping Move New Medical Device Product to Market Quicker & More Cost Effic
Early Supplier Involvement has long been a strategy employed by manufacturers to produce innovative products. Now, it almost seems like a necessity. Because decisions made in the design phase can positively affect product quality and costs, this can help add value to OEM bottom lines. This white paper will discuss many facets of ESI, including why itâ€™s so valuable today, what challenges limit the benefits of ESI, how cost is impacted, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.