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RE: Geometry of haunch for moment connection

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As far as I understand there are two basic reasons for a haunch:


1)       Increase depth of beam at connection, to reduce bolt forces and localised effects applied to support

2)       Reduce size of main beam


For the latter the required geometry and length of the haunch and its depth, are determined from the applied bending moment and the resistance of the main beam section. The geometric limitations are largely practical:


1)                           cutting a standard I-Section into a T-section, or cutting and building up from plates. Too sharp an angle and impractical to cut.

2)                           Too sharp an angle and maybe impractical to weld at the sharp end. May pose a fatigue problem.


Not sure I follow your dimensions. A haunch with a length less than the depth  doesn’t seem much benefit (0.6*depth). Whilst a length of haunch equal to depth, may be suitable for increasing beam depth for connection purposes only.


Also not sure which angle referring to. Cutting I-section at 45 degrees, would produce haunch with length approx. equal to depth. If the angle given is between column and haunch flange, then suitability of 45 degrees would be dependent on elevation of the beam (eg. roof rafter, cf. floor beam), and the resultant angle between beam and haunch. For a level floor beam, maybe acceptable, for a rafter it may not be acceptable.


If it achieves its function, and is practical to make, then otherwise not aware of any code restrictions.




Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust



South Australia