Analyze for residual stress in steel column section

[gopaladhikari]

Hi all,

I am carrying out a second order analysis of a wharf with lots of steel H-piles. I was thinking of using Steel02 material with initial stress parameter to include the effect of residual stress pattern. However, the approach would be quite cumbersome since the wharf has about 40 piles. I am wondering whether there is a smarter way to include the residual stress pattern in the second order analysis.

Thanks for your help.

Gopal

[mhscott]

Are all the piles the same H-section, or maybe the same few sections? You don't have to define a section for each pile and you can define a function to impose the residual stress pattern.

I'm not sure if this helps, so reply if you have more details.

[gopaladhikari]

Dear Professor,

There are a few number of steel sections, not all 40 piles are different. I will assign the residual stress pattern only to four sections. However, I am not sure how to define this stress pattern. I understand Steel02 can be defined with initial stress value.
My plan now is to define a function to generate residual stress values at each fiber and then define a set Steel02 material with initial stress. Afterwards, I can analyse for gravity and lateral loads. Does that sound like I'm heading towards right direction or is there any smarter way to define the effect of residual stress pattern.
If you share a sample script that would be super helpful.

Thanks

[selimgunay]

Your approach of assigning the actual initial stress to each fiber sounds like the most realistic approach. An approximate way would be to consider a nonlinear stress strain relation for the whole section that on average represents the change of the stress strain relation from actual steel stress strain to a nonlinear one with reduced Fy due to the presence of the initial stresses

[mhscott]

Here's what I used for the Lehigh pattern in this post: https://wp.me/pbejzW-Bh

It's 2D, but can be adapted for 3D if needed.

Code: Select all

    ops.uniaxialMaterial('Hardening',1,E,Fy,0.005*E,0)
    Fr0 = -2*(Frc+Frt)*bf/2/(dw*tw)
    ops.uniaxialMaterial('InitStressMaterial',2,1,Frt)
    ops.section('Fiber',1)
    y1 = bf/2
    z1= d/2
    Nfw = 20
    ops.patch('rect',2,Nfw,1,-tw/2,-z1+tf,tw/2,z1-tf) # web
    Nff = 8
    dbf = bf/Nff
    Af = dbf*tf
    for j in range(int(Nff/2)):
        Fri = Frc + (j+0.5)/Nff*(Frt-Frc)
        matTag = 3+j
        ops.uniaxialMaterial('InitStressMaterial',matTag,1,Fri)
        ops.fiber(-bf/2+(j+0.5)*dbf, d/2-tf/2,2*Af,matTag)
        ops.fiber( bf/2-(j+0.5)*dbf, d/2-tf/2,2*Af,matTag) 

[gopaladhikari]

Thanks Michael and Selim.

Appreciate your help. I will try the script and let you know how it goes.

thanks,
Gopal