Expert: Dan Griffin - 7/23/2009

Question
I plan to construct a building inside a manufacturing facility.  The building will measure 48' deep by 60' wide and have 10' ceiling.  I would like to use 2x12x16 on 16" centers for a load bearing ceiling and support each end of the 2x12x16 on top of a steel "I" beam supported by 4" schedule 80 pipe welded to the "I" beam with welded flanged bottom plate bolted to a concrete floor with an adjoining row of 2x12x16's to span another section until I reach the size of structure I need in terms of the 60' width.  
The entire load bearing ceiling surface will be sheathed with 3/4 plywood.  The perimiter of the structure will be 2x4x10' and have an additional 2x4x6' added to the top to form the perimiter around the load bearing ceiling section where there will be storage.  
The entire load bearing ceiling will be supported by steel "I" beam and pipe for which I plan to use for storage of heavy shelving and supplies.  I plan to keep most of the shelving near or on top of the steel "I" beams for long term safety and to keep most of the weight off the 2x12x16's if possible.
The perimiter structure will be attached to the steel "I" beams in some way but will not be used in conjunction with the steel "I" beams as load bearing walls.

Question:  What size steel "I" beam would be sufficient to support "X" lbs/ft ?  4x8 5/16" thick ?  4x10?  Thickness?

What centerline should the support pipes be placed at for 48' length of steel "I" beam considering the "I" beam may be welded lengths measuring maybe 12' in length and having 4 pieces per section being welded together to form 48' long ?  One support pipe every 6 feet?  Every 12 feet where the ends of the "I" beam are welded together?

How much weight can I put on this load bearing ceiling?

Thank You,

Doug Williams


Answer
Doug, I cannot design this for you.  I am not a structural engineer.  Here are some guidelines:

I prefer using this span table for the wood information:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

The two strongest woods are Southern Pine and Douglas Fir.  This choice would have to do with your location and availability.  The actual grade of lumber is critical in the table.  Often going to closer centers is cheaper than using higher grade lumber.
Code requires a minimum of L/360 deflection.  I would probably go for L/480.  This number is the amount the joists are allowed to sag at mid span.
Only you know the potential loading.  Your local code enforcement may have a minimum in your circumstance.  I would use 100#/SF live load to accommodate paper storage (one of the highest)


This table will let you do some figuring on steel loading:
http://www.toolbase.org/Design-Construction-Guides/Exterior-Walls/flitch-plate-b...
scroll to the very bottom for pound/ft information on steel beams.  I see no reason for schedule 80 pipe columns, though if you do, the floor will not be able to take the loads.

You will need to decide about floor loading on the existing slab.  Point loads from the steel columns can easily exceed the ability of the floor.  It would be best to cut the floor and create footings as required for the columns.

The outside edge will require fall protection, and will probably require some provision for fork lift access.  This will require 200# loadings on the rail which will probably require an engineer's stamp for your code/permit people.

I hope this has been helpful.