You are here:

Civil Engineering/Rsponse History Analysis-Overstrength factor

Advertisement


Question
QUESTION: Hi
I would appreciate it if you could guide me through this two problems.
1.can you introduce me a reference to help me in step by step modeling and analyzing a 2d concrete frame(or 3d building) with nonlinear Response History Analysis (Especially modeling); I am using Etabs 2015.
2.Does ACI 318-11 consider over-strength factor (for example 3 for special moment resistance frames) in all earthquake concluded combinations or not.I do know it considers Sds in my combinations cause i can see its effect on dead load in load combinations forum but no sign of over-strength factor in earthquake    
thanks
Regards

ANSWER: Dear Mohsen

1- No way to perform nonlinear time history analysis in Etabs unless you model in every potential hinge a plastic link. Then it is crucial to recognize the potential hinge locations and introduce there the proper links. But you can perform a push over analysis with the member being assigned by elasto plastic behaviour.

2- The R factor in recent versions of ACI and UBC is considered without consideration of over strength. Then it is obvious that you have smaller reduction factors compared to older versions which are base on Rw ( and working stress method). This is done in the similar way for dead and live loads through loading and strength factors.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Thank you for sharing your precious experience, the following questions passed through my mind:
1. "No way to perform nonlinear time history analysis in Etabs unless you model in every potential hinge a plastic link". is there any need for plastic link even in "Direct Integration" type and not FNA?

2- "The R factor in recent versions of ACI and UBC is considered without consideration of over strength". Does it mean we must consider OMEGA factor in every earthquake concluded load combination? and my last question was about considering this factor,I said when you consider vertical effects of earthquake,Sds, in Etabs you can see its effect on dead load in "load combination" and when you consider OMEGA there is no sign of it in "load combination" (ACI 2011: special sway: omega=3 R=8 cds=5.5)

Answer
Dear Mohsen

1- The method of integration doesnt matter with the need to assign the hinge locations and links. The software doesnt recognize the real hinge location.

2- When you are working with recent codes which are based on ultimate deisgn method like LRFD and use lower lever of reduction factor , you dont need to consider the overstrength unless a special code item require it explicitly. For example when you are designing a non dutile system like connections the oversrength of the girder will influence the ultimate state of loading on connections.

Regards
BEH

Civil Engineering

All Answers


Answers by Expert:


Ask Experts

Volunteer


Babak Esmailzadeh Hakimi

Expertise

I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!

Experience

I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

Organizations
Sinam Consulting Engineers Co.

Education/Credentials
Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

©2016 About.com. All rights reserved.