Joist connection to masonry wall--eccentricity 2

[rholder98]

If attaching a joist to the side of a CMU wall, via a shelf angle, what is the eccentricity? In other words, how far from the vertical face of wall is it to the effective point load of the joist reaction? Assume I'm using a 4" horizontal leg: do I assume the reaction to be centered (2" out)? I've heard of people assuming a triangular stress distribution, which would move it out to 2/3 the horizontal dimension. Specifically, I'm trying to select anchors for the joist support, and I'm analyzing the shear/tension interaction. Thank you in advance.

 

[archeng59]

determine where the center of the joist seat is located along the horizontal leg. if you are checking the horizontal leg of the angle for flexural stresses, the eccentricity is the horizontal distance from the seat center to beginning of the fillet between the two legs. the triangular stress distribution is between the vertical leg of the angle and the wall.

 

[Lutfi]

First of all, according to SJI, all you need is 2.5 inches of joist bearing on steel and 4 inches on concrete or masonry. I have been following this for over 23 years.

Secondly, I think your analysis seems reasonable. I would take the centroid of the reaction at the 2 inch from the face of the masonry wall. This would make your eccentricity (e) = 1/2 CMU block width plus 2 inches. I do not think you find much argument from anyone.

Third, make sure to consider the overturning on the wall due to this eccentricity.

Fourth, I agree with archeng59 regarding the flexure in the angle leg.

Good luck


Regards,
Lutfi

 

[RareBugTX]

There is an excellent book with examples of masonry connections like the one you are talking about. The book is called "Masonry Designers Guide". I have a few year's old edition but I know there is a newer one. It is published by TMS, ASCE and ACI.


Highly recommended.


Hopefully it helps you


Rarebug