Timber Stair Design 6

[JAS34]

Looking at an architect's building plans and it shows the general location for timber stairs for a two story building on the plan views. Structural notes give basic dimensional details such as riser height, tread depth, handrail height, etc.

As far as being the structural engineer, is it common practice to specify the design loads for the contractor to select a supplier's product that meets my requirements? Or should I design each component (stringers, risers, and treads material thicknesses and nail and bolt connection details) for the contractor to construct? Or should I check the IRC for some typical stair designs and subsequent allowable load tables. As far as the IBC, I see spacial requirements but no design aids or tables.


Thanks,

JAS34

 

[jdgengineer]

I think it can vary depending on the job. For a lot of our residences we don't design anything for the stairs aside from checking that the beams where the stringers will frame into are adequate for the loading.

On some other jobs we'll design the stringers, landings etc., but don't typically design the treads and connection of the treads to the stringer. I would think if you are doing a residence (since you are quoting IRC) that there are conventional attachments of these components.

 

[JAS34]

It is a building.

I just considered looking in the IRC for relative information to point me in the right direction since the IBC had no design information.

 

[msquared48]

In most cases, residential wood stairs are pretty well cut and dried in their construction. Not true with steel though.

What material are you using?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAS34]

It is wood stairs and it is a commercial building.

 

[msquared48]

If the srory heignt is normal at 9 to 10 feet or so, normal stair construction is fine for 100 psf loads. For any greater span or higher load, I would check the stringers.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[woodman88]

I prefer to use LVL or PSL for stairs at they have no knots. See the attached for some LVL info.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[MiketheEngineer]

And I like at least three stingers - seen too many with only two that make me squeam.

Like when the paper delivery guy has about 4 boxes of paper on a dolly!!

 

[JAS34]

Got another similar question...

Looking now at the timber porch railing on this commercial building.

Looking for the standard construction practice for wood post and railing attached to concrete masonry.

It is a concrete masonry wall opening that is to have wood posts, hand rail, top and bottom rails, and struts.

I am thinking 4x4 timber post embedded in the grouted concrete masonry using post base-ties from Simpson Strong tie. Cap the post with a 2x6 hand rail. Then 2x4 top and bottom rails. Last, 2x2 vertical struts at 5" o.c.

Any design tables (like woodman88 presented for the stairs), engineering experience, etc. out there that gives me a "prescription" design approach for the timber porch detailing?

- JAS34

 

[shobroco]

The Ontario Building Code gives prescriptive requirements for residential railings but not many designers would want to build anything that looks like them. As far as stairs go, whether wood, steel, or precast I would give the design loads & state that the builder must supply shop drawings unless the architect has clearly given me an aesthetic that he/she wants to achieve. I don't design OWSJ, wood trusses, wood I's, etc. because the builder will use a different supplier & make the effort pointless.

 

[Ron]

Wood stairs and commercial building would generally imply that the structural engineer of record would design the stairs, since most wood stairs are site built, not prefabricated. As Mike noted, if steel you would delegate the design to the contractor's subcontractor and review the design for conformance to your engineering requirements.

 

[shobroco]

Ron, you must be in a different area than I am; I haven't seen site-built wood stairs in any kind of building in more than 20 years.

 

[jdgengineer]

For wood railings make sure whatever your design is, that you can meet the loading requirements shown in ASCE 7 live load chapter. For a handrail that is a 200# point load or 50 pounds per linear foot. To meet this requirement, we often use 4x4 posts @ 4'-0" with a stronger connection at the base than just your typical Simpson base.