Smart questions
Smart people
 Find A ForumFind An Expert
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Remember Me

Are you an
Engineering professional?
Join Eng-Tips now!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

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

Just copy and paste the

#### Feedback

"...I just wanted to say how much I have enjoyed these forums. I am a new user and have a lot of elementary questions. I get quick answers with a friendly attitude..."

#### Geography

Where in the world do Eng-Tips members come from?

# SAP2000 3-hinge arch buckling

 Forum Search FAQs Links Jobs Whitepapers MVPs
 catenaryworks (Structural) 1 Jun 12 20:08
 Hello,I am trying to analyze a 3-hinge arch to find the buckling load. I have attached the SAP file here, which has the modeling done correctly. I suspect I am not doing to P-delta analysis correctly. My objective is to apply equal value point loads at the two knees and the top ridge, starting with P1=P2=P3 =36 kips and trying to determine at what equal value load the arch would buckle. The answer should be P1=P2=P3 = 43.1 kips. Other checks can be:1. At P1 (left knee) = P2 (at ridge) = P3 (right knee)=36 kips, the downward deflection at the ridge should be 1.8189 in.1. At P1 = P2 = P3 =40 kips, the downward deflection at the ridge should be 3.1909 in.May I ask if someone could take a look and tell me what is not being done correctly? Thanks.
 catenaryworks (Structural) 1 Jun 12 20:58
 I am unsure if I attachment is uploaded. Here are the geometry and material properties. Left support : 0,0Left knee : 50 ft, 30 ftRidge (hinge) : 100 ft, 40 ftRight knee : 150 ft, 30 ftRight support : 200 ft, 0Cross-section of the arch member: 5.5" x 30.25"E = 1800 ksi
 catenaryworks (Structural) 17 Jul 12 20:41
 Hi, Attached is the 3-hinged arch I want to analyze to determine at what value of P, the arch will buckle. Cross-section of the arch member: 5.5" x 30.25", E = 1800 ksi I have been using non-linear P-delta analysis and applying P in small increments. Is there an easier way to obtain Pcr? Thanks. http://files.engineering.com/getfile.aspx?folder=b640a789-2570-41b9-9f16-4d
 catenaryworks (Structural) 17 Jul 12 20:51
 What would be the suggested procedure in SAP2000 for determining the buckling load Pcr for this particular 3-hinged arch with loads as indicated in my previous message?
 catenaryworks (Structural) 17 Jul 12 21:21
 Here's my SAP file. I will appreciate any help. http://files.engineering.com/getfile.aspx?folder=9f01e3be-5859-4b91-9ac3-4c
 stressed (Civil/Environmental) 19 Jul 12 8:09
 catenary, first, you have a 2D model, so set analysis options parameters to run as a 2D with XZ plane unless you are able to change the supports/restraints to fixed.. in which case you could run as 3D. Second, you do not have a buckling load case defined, only a P-delta case. Buckling case is eigen buckling which, unless you add a small imposed displacement or load to perturb the structure to simulate construction tolerance imperfections (out of plumbness), it will otherwise assume an idealized perfectly symetrical structure and may therefore calculate a theoretical buckling load that is an artificially high critical buckling load. In buckling analysis, as with modal analysis, in some cases you will want to base the buckling analysis on a "prestressed" nonlinear p-delta load case instead of assuming Unstressed state which is the default. There is also an option to run large deformation snap through buckling analysis, but you would need to change the P-Delta case option to P-Delta plus large displacements and switch 'Results saved' to Multiple steps

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!