normm
Structural
- Jan 29, 2008
- 74
Although this problem has been discussed before, I will much appreciate your response to the attached example.
The associated diagram shows 2 pairs of internal secondary beams 420 mm deeep in a roof layout.
The columns below are braced in both directions.
The right-hand pair of beams are cross-braced by trimmer beams 300 mm deep which also extend another bay to connect with the vertical bracing system. Thus these secondary beams can be considered braced in position as well as in torsion at trimmer beam positions and so the effective length of secondary beams is the distance between trimmer beams l1.
The left hand pair of beams are cross-connected by trimmer beams but not connected to vertical bracing system. Thus the secondary beams can be cosidered torsionally restrained but not restrained against sidesway.
What should be the effective length of the left hand pair of beams. Should it be the full length L ie the trimmer beams play no part in restraining the secondary beams at all or the effective length should be an intermediate value between l1 and L.
For this purpose consider the roof decking plays no part restraining the beams and there is no plan bracing in roof. Please ignore the red equipment boxes The trimmer and secondary beam connections to be welded and fully fixed.
Your thoughts and comments will be much appreciated specially if backed up with any reference to any AISC or BS Code. clauses.
The associated diagram shows 2 pairs of internal secondary beams 420 mm deeep in a roof layout.
The columns below are braced in both directions.
The right-hand pair of beams are cross-braced by trimmer beams 300 mm deep which also extend another bay to connect with the vertical bracing system. Thus these secondary beams can be considered braced in position as well as in torsion at trimmer beam positions and so the effective length of secondary beams is the distance between trimmer beams l1.
The left hand pair of beams are cross-connected by trimmer beams but not connected to vertical bracing system. Thus the secondary beams can be cosidered torsionally restrained but not restrained against sidesway.
What should be the effective length of the left hand pair of beams. Should it be the full length L ie the trimmer beams play no part in restraining the secondary beams at all or the effective length should be an intermediate value between l1 and L.
For this purpose consider the roof decking plays no part restraining the beams and there is no plan bracing in roof. Please ignore the red equipment boxes The trimmer and secondary beam connections to be welded and fully fixed.
Your thoughts and comments will be much appreciated specially if backed up with any reference to any AISC or BS Code. clauses.
