Dock Door Foundation Wall Best Practices 1

[azogr]

I am probably opening up a can of worms here but I am re-evaluating how I am doing my foundations around dock doors. I am curious about details that performed well and not-so-well for you guys, your design approaches, and any other comments/suggestions you may have. For instance...

1) Do you pour the slab over top of the wall or pour flush with the top of the wall?

2) Do you tie the wall to the slab with dowels?

3) Do you have a minimum wall thickness that you use? For instance an 8" poured wall may work fine structurally but do you use something thicker for durability and unknown impact forces?

4) Are you designing the wall for impact forces or do you assume that this force would go directly into the back-fill or slab?

5) If you are designing for impact forces how did you determine them?

6) What surcharge loading are you using behind the wall? ...are you using a surcharge loading behind the wall?

7) What do you do if a geotech report is not available at the time permit drawings are being created? In other words do you find that you have a typical design that works everytime and you are not really re-inventing the wheel with each project?

I haven't had any problems with the ones I have designed but this is a high traffic area and there is a lot going on in these locations so I thought it was worth a conversation. Look forward to hearing from you. Thank you!

 

[phamENG]

1) Usually over the top. If it's flush, the foundation wall becomes a surcharged cantilever retaining wall. It also makes it easier to create the necessary recesses for dock and truck levelers, minimizes differential settlement that could adversely impact forklift ops, etc.

2) Usually. Again, I usually use the slab to tie back the foundation wall. Positive connection required to do that.

3) I'd say 8" is the minimum. I don't worry much about impact forces. Most of the loading docks I've done have rubber fenders that take care of this, and the force is usually transferred back up to the slab.

4) See #3.

5) If I did do it, I would look at the AASHTO weights for the design truck, and assume it's backing up at maybe 3mph for flat/shallow ramps - faster if it's a steep ramp. That'll give me the kinetic energy of the truck at impact, and I can use energy methods to determine the effect on the structure.

6) Floor live load and slab dead load. Maybe 125psf for a light storage warehouse, maybe 500psf for a machine shop that's building and shipping aircraft engines.

7) What I described above. Note all of the "usually"s. Every case is somehow unique, and while this is where I start I look at each "typical detail" and make sure it makes sense for the application.

 

[azogr]

phamENG,

Thank you for the response. One more question if you don't mind. I am in the Northeast US where frost is a concern. Do you know if it is common to put insulation behind the wall in frost susceptible areas?

Thanks

 

[phamENG]

You're quite welcome. I think that'll depend on the use of the space. Most of the new ones I've designed have been more-or-less open air warehouses (Mid-Atlantic, gets chilly in winter but our frost depth is still only 8-12") and insulation wasn't a concern. If I had been designing a conditioned storage space I could see it making sense. I usually discuss those details with the architect/mechanical engineer as they're managing energy flow through the building.