Re-Entrant Corner Collector Design 2

[omoreno1]

I have a 7000 sq. ft U-shaped commerical wood building located in SDC "C" and in A 90 MPH wind speed zone. I have re-entrant corners exceeding the 15% requirement per ASCE 7-02 for plan structural irregularities. Although I am not in a SDC "D" to trigger the usuage of the special seismic load combinations, am I still required to design a collector element to transfer the forces? Or would it be adequate to design the shearwalls to take the loads entirely from one side? My gut feeling is to design a collector, but I am sure if this other method is a viable solution. Any ideas or references?

 

[OldPaperMaker]

1. If the shearwall is not continuous across the reentrant corner then a collector or drag-strut would have to be designed & detailed to transfer the load from the diaphragm to the shearwall.
2. But, it appears that section 12.10.2.1 of ASCE 7-05 has an Exception that sez "structures braced entirely by lightframe shearwalls need only be designed to resist forces in Section 12.10.1.1". I think that this is "ASCE-speak" for saying that one does not have to use the overstrength factor, omega in lightframe structures.

I hope that this helps.

 

[omoreno1]

I guess what I meant, was that if the shearwalls along the "wings" are designed to resist the horizontal wind loads, would a load transfer at the re-entrant corner to that shearwall be required?

 

[UcfSE]

It would be good to provide the drag strut each way at the re-entrant cornersso that you don't have incompatible deformation issues in the diaphragm when it tries to deflect. This may or may not be a big deal depending on building dimensions and loads, but at the least I would call it good practice.

 

[msquared48]

I fully agree with UcfSE. You are going to need drag links (struts) in each direction anyway for shear connectors to the exterior shear walls. Only makes good structure and good sense.

Mike McCann
McCann Engineering

 

[LGARG]

hi to all, i agree with all of you. I think that in some case you should check if the diaphram could take the shear force at that point or the tension/compression developed when the diaphram deflects.But i insisit that is a good practice to provide a drag at every reentrant corner.


LG

 

[omoreno1]

I appreciate all the good input from everyone on this. Thank you all!

 

[connect2]

If the architectural layout permits it cut off the 'U' not far up (less than 15%) the 2 legs of the 'U' with shear walls, bracing what ever. Cut off the re-entrant corner so to speak. Turn it into three seperate diaphragms joined at these shear walls or braces.

 

[faromic80]

This may be off topic so sorry, but what is a re-entrant corner?

 

[hokie66]

Look at a carpenter's framing square. At the corner of the square, and on the inside, is the reentrant corner. Reentrant corners are of great interest to structural engineers because they cause stress risers.

 

[gyroman10]

i would distribute the building in three regular shapes one rectangular and two squares, cut off the legs of U !, and detail the seismic joints between buildings. this makes thinks very simple, but offcoarse you would be in a better possition to judge whats the best. What are the dimensions of the building.