Distribution of steel beam load to masonry wall

[todh]

I am designing a load bearing CMU wall that is 22 feet in total height. At the 11 foot elevation, the roof on the west side of the wall is connected to the CMU wall by means of a steel beam every 20 feet. This steel beam is supposed to be supported by 4 anchor bolts embedded in the CMU wall. On the east side of the wall, there is a steel frame that the wall obtains lateral resistance from at the 20-foot height with a 2-foot parapet above that.

The design of the anchor bolts is straight forward enough, but my question is the distribution of the load transferred from the beam to the wall. If the beam were sitting on a bearing plate, I could transfer the load over the length of the bearing plate plus four times the wall thickness. Can I make the same assumption for designing the wall under the anchor bolts, but just use the spacing of the anchor bolts for my bearing plate width?

Also, since I am asking questions, since the wall is exposed to wind loads from the 11-foot to 22-foot elevation and a horizontal reaction at the 11-foot elevation, should I really consider this as a simply supported wall at 0 and 20 feet or as a 2 span structure supported at 0, 11, and 20 feet?

Thanks for any help you can provide.

 

[youngstructural]

Technically speaking the load distributes as point loads from each anchor bolt, however you can simplify this by considering the bolt spacing to be similar to a bearing plate. This simplification is not exactly right, however it is close enough to be acceptable.

I am more concerned that the connection not have flexural stiffness unless the wall is designed for this bending strength. If you are fixing the beam to the wall with the end plate flat against, or packed out solid to, the wall, you're going to impart bending loads. If you want to keep a similar detail, back the beam off 15mm and insert a rocker plate, which is essentially a long strip washer which allows the beam to rotate about the support. This also makes the beam easier to install.

Regarding your span question, this depends on how the wall is supported and built. Is there strength & stiffness in the system providing support at the 11 foot elevation? If so, then it is two span(s). The next question is whether or not there is continuity accross the 11 foot elevation. If there is continuity, it is a single two span continuous beam; If there isn't continuity (ie: flexural strength) the wall behaves as two simply supported beams.

Good luck and regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[jike]

Sounds like the wall currently is only braced at the 11 foot elevation at discrete points 20 feet apart (at beam locations). I would suggest that you continuously connect your diaphragm at the 11 foot level to brace the wall.

 

[civilperson]

The anchor bolts should be inserted into a horizontal bond beam which will act like the missing base plate.