Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations KootK on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

stability of the haunch in a rafter 1

Status
Not open for further replies.
Bubik

Bubik

Structural
Mar 15, 2016
103
Hi everyone,

I am designing a pitched portal frame elastically and need to check the stability of the haunched section of a rafter. As I don't have an option to use software , I have to do it by hand. I know how to conduct checks (lateral torsional buckling,combined lateral and axial,bending ,etc) if a section is uniform but in the case of a haunch, the section is non- uniform so I wonder how others would approach the problem. I heard that it is possible to divide the section into five sub-sections but I still don't know which 'end' of a subsection should consider.By the way I design to British Standards but input based on any other code would also be greatly welcomed.

Thanks in advance!
 
Replies continue below

Recommended for you

Sort by date Sort by votes
The picture depicts the stability zones for pitched portal frame with eaves and apex haunches ..and ofcourse valid for only gravity loading. In case of uplift loading the zones will change...

I want to remind also, EC 3 Clause 6.3.5.2 requires that, all plastic hinges laterally and torsionally restrained. You may add purlin stays from purlins to inner flange to provide such restraint.

I will suggest you to look to the worked example at appendix C of the following doc. published by SCI ,free of charge.


Haunch_stability_zones_irylxd.png
 
Upvote 0 Downvote
Thank you for your answer. The provided document describes plastic analysis however , I will be designing elastically
The approach is to consider different modes of failure in order to validate the haunch section, just the way a member in compersion and bending would be checked

Mode_of_failure_checks_y8nfdy.png



Because the cross-section varies along the haunch, I don't know what cross-section I should apply in order to calculate plastic modulus of the section.
 
Upvote 0 Downvote
The BS EN 1993 1-1 EC 3 is silent for t he elastic verification of buckling resistance of haunched member. There are two aapproaches, the first , the stability of haunch is verified by considering an equivalent compression flange ,see clause 6.3.2.4 . The second approach is , the haunched length containinng platic hinge , which assumes will be adequate for elastic case also.

I hope this explanation makes sense .
 
Upvote 0 Downvote
HTURKAK

It makes perfect sense, thank you
 
Upvote 0 Downvote
Upvote 0 Downvote
HTURKAK
Extremely helpful!! once again thanks
 
Upvote 0 Downvote
Be careful. We were involved in a failure of an entire PEMB frame whose "rafter stays" were not adequately strong or stiff. The roof loading was far below the design load.

Stability can be a house of cards and you just don't know how close to the edge you are.

 
Upvote 0 Downvote
JLNJ,

Could you elaborate on the failure? What bracing elements failed, and what was their strength and stiffness compared to normal design practice?
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

XR250
  • Question
Haunch Capacity
Replies
9
Views
920
XR250
XR250
IlliniPE
  • Locked
  • Question
Rafter Ties in Utility Buildings Necessary? 2
Replies
10
Views
208
phamENG
phamENG
HDStructural
  • Question
Foundation Stability Factors of Safety 3
2
Replies
23
Views
352
hardbutmild
hardbutmild
STrctPono
  • Locked
  • Question
Large Notch at Rafter End
Replies
10
Views
122
Greenalleycat
Greenalleycat
SHEAR_FORCE
  • Locked
  • Question
Rafter Notch at Supports in Snow Country 2
2
Replies
23
Views
270
XR250
XR250

Part and Inventory Search

Sponsor

Back
Top Bottom