Tapered portal frame Analysis 2

[HawkOkeoJr]

hallo everyone,
My friend is working on a Portal Frame analysis and he was asking me some questions which i didn't know how to answer,it would be great if you can highlight me on some. so the question is:
How do you go about with Analytic solution for a Tapered portal frame?,and how is it different from the other portal frame analysis.
Another question is, which major significance will be noticed (calculation wise), if the frame is welded profile(but middle beam of the girder is rolled profile) and when the frame is entirely Rolled profile?.

Anybody with a worked example of a tapered portal frame would also help.
Thank you.

 

[normm]

Here are some points of difference :

You will need Area and Inertia values of members to analyse the portal frame. In standard rolled section the values are readily available from the manufacturere's tables. These values also remain constant within the length of a member.
But if you use a purpsely manufactured tapered section, you will have to calculate the properties at each section and how it changes along its length, as this will affect member stiffness. Computer analysis programs may have this facility built in. But if you are using hand methods, it will be a very laborious exercise unless you find some tables that give you this information. Sometimes people end up with a small number of stepped sections rather than continuously tapered section to keep the work load managable.

Having found the resulting bending moment, shear etc, the design codes will give you guidance on the design differences of built-up tapered sections and standard rolled section.The tapered sections will need additional checks for local buckling depending on the width and thickness of plates selected. The most critical section for checking is also not obviously clear in tapered members. It is much simpler using standard rolled sections.

 

[haynewp]

Look at getting AISC's design guide:

http://www.aisc.org/store/p-2116-design-guide-25-frame-design-using-webtapered-members.aspx

I would get simple frame software like RISA to do the analysis part. I don't think it goes through the design checks last time I inquired for web tapered and variable flange width frames, so you would have to export the analysis results to a spreadsheet to do all the AISC checks if you use RISA. Or look for a program that does it.

 

[SteveGregory]

Ram Elements will do the web-tapered analysis and member design following the new AISC Design Guide #25.

 

[JoshPlumSE]

FYI: In just a few weeks the new version 11 of RISA will incorporate code checks per AISC design guide 25. I am testing out the feature now.