Force - Deformation Curve - ASCE 41-17 1

[ENGJP22]

Hi, I'm trying to construct the force-deformation curve described in ASCE 41-17 in order to do a pushover analysis, but I'm finding trouble trying to understand how to calculate point C in the graph, could tell whats the correct approach?

 

[sticksandtriangles]

When I first got into ASCE 41, point C was very mysterious to me as well, I wish it was well defined! Pasted image from ASCE 41 for reference:

Here's what I've come to understand point C to be:

It is a function of the material you are trying to model and varies depending on the item you are modelling, it essentially represents the point at which strain hardening has stopped and you start to fail the material.

For example, let's say you are trying to do a pushover on a concrete shearwall. Point C would be the value at which the rebar reaches its expected yield strength, ~say 75ksi, for a nominal yield bar of 60ksi.

Point B is where you are essentially elastic:

 

[ENGJP22]

Allright! what would it be the case for W Shape, ASTM A992?

 

[sticksandtriangles]

What are you trying to do with the W shape? Is it a moment frame beam? Is it a column?

Ry (ratio of yield to tensile strength) for A992 steel is 1.1 from my memory. You could use this construct a similar diagram as shown with the concrete example.

S&T -

http://www.re-tug.com

 

[ENGJP22]

My bad, I didn't explain myself clearly, I'm using Etabs to construct a M3 for a moment frame, the value of scale factor that the use for point C is 1.27, at first I Thought it should be 1.10 like you said, but I dont know why they use that other value

 

[sticksandtriangles]

I bet this is what is happening:

Fy = 50 ksi, Fye = 1.1*50 = 55ksi
Ft = 65 ksi, Fte = 1.1*65 = 71.5ksi

C ~ Fte/Fye = 71.5/55 = 1.3

C is more the ratio of the tensile strength to yield strength.