shear collector beam connection

[shepherd]

I've got a 5 story steel frame building 50'x200'. Concentric braced frames (chevron braces) to resist longitudinal shear are at the corner bays of the building (exterior). In one corner, this is adjacent to a stair opening (only place architect will give it to me). There is no slab adjacent to this frame to transfer shear. I'm assuming this shear will need to be collected by adjacent exterior beams and transfered into the lateral frame. I'm looking for recommendations for the detailing of the connection of the collector beam to the lateral frame. Another thought -Has anyone ever connected rebar extended into the concrete diaphragm to the column and transfer the shear through the embedded rebar (connection to column may be impossible for required loading)? Thanks in advance.

Shepherd

 

[JAE]

Shepherd:
I guess I would say first off that all of your perimeter beams should be considered as collectcors...not just the beam extending past the stair opening. The floor diaphragm shear should be transferred into the collector beams down each side of the diaphragm.

As the shear is built up along the collector, you have an increasing axial tension/compression as the collectors approach the brace. Usually you can develop a drag force diagram (looks like a "bowtie" shear diagram) and determine the forces in each collector bay.

With these axial E forces (note that there are special provisions for collectors in the UBC and IBC) you include these with gravity loads in their appropriate combinations.

We usually detail a shear tab plate and try to combine the vertical gravity, vertical seismic (if any) and lateral forces into a bolt connection that will work. Usually end up with two vertical rows of bolts for larger forces. These have to be properly transferred through the column.

I have never heard of connecting a diaphragm to a column with rebar to transfer the lateral shears into the frame. Sounds kind of awkward to me.

 

[ishvaaag]

As long as the resulting analysis for the connection results valid, of course transfer through welded rebar taking what rebar is to take is a feasible option, again, if within the requirements for the kind of structure you are to project.

 

[JAE]

ishvaaag - only if you aren't in a high seismic area - I'm not sure that welded rebar qualifies for seismic - less ductility in the weld.

By the way - good to see you posting more these days....how's Spain?

 

[jike]

If the axial force is not too high, you can use clip angles with the thickness designed to resist the prying force. Another possible way is to use clip angles with small gussets to prevent the angles from opening up.

You could also have the fabricator's engineer size the connections by specifying the collector axial force to be combined with the beam (end shear) reaction.

When checking the stress interaction for the collectors, don't forget to add the bending due to the the shear coming into the beam at the top flange (eccentric to the beam by one half its depth). Also for the roof collector beams, you should add in the bending due to wind uplift.