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RE: Nonlinear Static Analysis of RC buildings

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Nonlinear Static Analysis of RC buildings
• From: "Terangue Gillham" <tiger(--nospam--at)palaunet.com>
• Date: Mon, 15 May 2006 11:38:13 +0900

Carlos:

Try looking to ATC-40  (Applied Technology Council) - this document is specifically set up to guide the process of analyzing existing structures for seismic loading, but it can be used for new buildings as well.

For text references, I recommend Paulay and Priestley's book on reinforced concrete design for seismic resistance (also includes a chapter on CMU).  This is a VERY comprehensive book, so you'll need to spend some time on it.

IMO, it is essential that the fundamentals outlined in these two references (or others, since there are a number of them) BEFORE attempting to use a nonlinear analysis program, since assumptions have to be made, and an understanding of the assumptions is needed for interpretation of the results.

As far as using a pushover analysis for R/C, this is a standard approach based on my experience.  You need to assume a hinge length, say double the depth of the member, and all plastic action is confined to that length.  Of course, for an existing structure, this can be a bit difficult under certain circumstances with regard to development lengths, extra bars etc.  You'll need to have a section analysis program or spreadsheet that will let you get the moment-curvature relationship for each member, which can get complicated for columns that take a fair amount of load from overturning.

In fact, I prefer pushover to dynamic, since dynamic requires an assuption for ground motion - which ground motion record should be used (unless you are doing a forensic job and happen to have the ground motion records) - this applies doubly to design of a new building.  A pushover analysis tells a lot about the sequence of hinge formation, and I have used it to drive a certain, preferred, sequence since I can double check whether the sequence will be followed or not.  With a good section analysis utility, distribution of reinforcement (even for walls) can be adequately accounted for.

Regarding your question on linear code forces versus nonlinear response, refer to Paulay and Priestley as they have a good discussion on this.  Numerous books have been written on this subject, and it would take a very long email to explain that sufficiently (at least IMO).

-Tiger

Terangue *Tiger* Gillham, PE
GK2, Inc.
PO Box 8061, Koror, Palau 96940
Phone: (680) 488-7282 office
779-6051 cellular
tiger(--nospam--at)palaunet.com <mailto:tiger(--nospam--at)palaunet.com>

-----Original Message-----
From: Carlos Avila [mailto:cavila67(--nospam--at)yahoo.com]
Sent: Saturday, May 13, 2006 2:51 PM
To: seaint(--nospam--at)seaint.org
Subject: Nonlinear Static Analysis of RC buildings

Dear friends
I have a question regarding the Nonlinear Analysis of RC buildings.

Is there any structural analysis software performing Nonlinear Static Analysis of RC buildings?
I know that Etabs or SAP2000 are able to run a Pushover based analysis, but in my opinion this type of analysis is suitable for steel structures, since  plasticity and fracture in concrete are !some how! distributed over an element rather than located on an specific section (plastic hinge).

If the softare exists is it able to account for the 3D distribution of reinforcement and its contribution in the nonlinear response of the structure?

On the other hand, codes allows a static linear analysis but a design based in the nonlinear material response. How this two things are made compatible?
For a lateral force procedure, the amplification of the elastic acceleration response spectrum by the  seismic response Importance factor (Ie) and the reduction by the response modification factor(R) can represent approximately the inelastic structural response.

If lateral loads are not considere what kind of factor(s) should be included in the analysis of RC buildings to make it compatible linear analysis vs nonlinear design?

I have some reserach interest in this matters, I am so sorry if it is out of focus of the professional practice.

Any explanation is really welcome, many thanks in advance.
Best regards,
Carlos

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