Force on Slab End?

[WpgKarl]

Lets say I have a slab cantilevering 16" from the C.L. of a steel beam. The architect wants to support brick cladding a further 12" beyond the end of the slab, by use of 6"x6" HSS vertical tube hangers + 4"x4" HSS spacers welded to the hangers + a 4"x4" contin. shelf angle, supporting the brick.

The moment from the 12" eccentricity is taken into the floor system thru a couple formed by a weld plate on the face of the slab (where the 6"x6" tube hangers are welded) and an HSS horiz. strut running to the bottom of the steel support beam (between the 6"x6" vert tube + the steel beam).

If there is a tributary 3.6 kip vertical load acting down at the shelf angle location (per each 6"x6" hanger), then for the design of the slab end would I use the same 3.6 kip load placed at the tip, or would I need to magnify the load on the slab end up by 3.6*(16"+12")/16"? Not sure if I explained very well - maybe I should add a sketch?

 

[271828]

Hard to follow, but I think you have that extra moment from the extra 12", so need to magnify as you suggested.

 

[WpgKarl]

How do I cut & paste a sketch into this thread? I want to add a sketch to make my ? a little clearer....

 

[Lion06]

I don't see any reason you would magnifiy your vertical load (other than traditional load factors). You will have to account for the moment, though. The tip of the slab should be loaded with a 3.6K vertical force and a 3.6K-ft moment.

 

[lkjh345]

Might be wrong, but I believe that both magnifing the load, as 271828 has it, or placing a load plus a moment at the edge of the slab, as StructuralEIT has it, yeilds the same design forces for the slab design.

FWIW: Hit this problem a lot as brick cladding (supported off the edge of a floor slab) is a popular architectural look in my part of the world. Typically use TS6x2 tubes as the hangers at 4'-0" o.c with 6" light gage studs between. Your case may be different, but usually there is not much need to go a TS6x6. The width doesn't do much. Have seen other engineers us a C6 in these cases, but loading the hanger off of its shear center bothers me just a little bit.

 

[DaveAtkins]

Just do the statics. You will end up with a vertical load of 3.6 kips at the tip of the slab, and a horizontal force (equal to the 3.6 kf moment divided by the moment arm) at the tip of the slab and at the beam bottom flange. There will be no moment at the tip of the slab. Don't forget to kick the force at the bottom flange back up to the slab.

DaveAtkins

 

[csd72]

As stated by the last 3 posts, you either have

1. a shear and a moment
or
2. an amplified shear reaction

not both.

I would believe that 1. is more applicable in this case.

csd

 

[WpgKarl]

Thanks all who replied. Was having a brain fart last night - I looked it over again this morning and since I have a couple formed from the horizontal reactions in the slab and horiz strut, if I sum forces in y-dir - Fy has to equal 3.6 kips, and the horiz forces take care of the moment.