5 story wood building - issues? 3

[jonny55]

I am designing a 5 story wood framed building. Are there any unique issues or special code requirements I need to consider when designing the 5 story building?

If vertical settlement of the wood framing is an issue, how do you prevent it or justify it is acceptable?

Thanks, Jonny

 

[boo1]

In tall wood structures consideration should be made for structural loading, durability and usability. Consider design loading, shear walls, diaphragms, lateral stability, shrinkage, water management, fire resistance and sound control.

Lateral stability can be an issue depending on your wind or seismic conditions. Building lateral drift/stiffness may limit the type of exterior cladding. Check the top plate compression. Compression perpendicular to grain may control stud size due to end-bearing requirements on the wall plates, or bearing plate sizing in beam and column design. Include the strength reduction for fire resistance. For exterior walls consider x by 6 lumber at 12 or 16 inches on-center and 3 by 4 lumber at 16 inches on-center for the interior wall studs.

The effects of cumulative shrinkage can affect the building envelope, such as the exterior cladding, windows and hold down system. Special consideration must be given to designs that allow for shrinkage. To minimize shrinkage consider selecting kiln dry plates, open web parallel-chord trusses for floor joist members and composite wood products. Simpson or ATS have hold down system you might consider that can take up the shrinkage. Horizontal sheathing gaps with flashing must be detailed.

Control strategies must be developed to effectively deal with each of these sources and mechanisms.
The two general strategies for rain penetration control:
• minimize the amount of rainwater contacting the building surfaces and assemblies
• manage the rainwater deposited on or within assemblies
Drainage planes must be detailed. Interior moisture source must be considered.

Consider fire-stopping and draft-stopping techniques, use fire retardant material and non-combustible stairs wells. Spatial separation to the property line maybe required. Automatic sprinklers requirement should be analyzed.

Sound transmission is an important non-structural design consideration for multi-story wall and floor construction.

Attached is a report SEA BC on the subject

 

[msquared48]

Pretty much hit it all there with the shrinkage and fire issues.

Additionally will be the size of the holddowns at the foundation, which, depending on the amount of shearwall, can get very large.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Don't forget that you should have some input on the type of claddding that will be used, as that can significantly affect the performance of your structure. Pay attention to waterproofing, flashing, and particularly, windows.

 

[JAE]

And don't let the architect put partial height brick veneer up to the undersides of windows. If the wood shrinks (which it will) the windows (which are attached to the wood) will come downward and be crushed by the brick below (which is only vertically attached to the footings).

 

[hokie66]

JAE,
Sounds like you have seen that happen. Darned architects!

 

[dik]

Don't splice sheathing joints at the floor lines... lap them over the stud wall plates.

Dik

 

[msquared48]

JAE:

The Arcitect needs to spec rubber bricks.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dik]

If using bricks for any height... bricks 'swell' over time and wood shrinks... (not longitudinally, so much)

Dik

 

[csd72]

You will possibly have to follow stud loads down the building to ensure they are distributed properly, particularly when doors or windows do not line up.

You will need to do more calculations than you would for a standard timber building.

 

[concretemasonry]

If you use brick veneer, you will need intermediate support angles (with flashing, etc.) and a soft exterior caulk below the ledger angle. The BIA will have some specific recommendations for the spacing of intermediate brick supports. Depending on the story heights, you will have 1 or 2 for a 5 story building unless there is a significant height of foundation exposed.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

Does anybody really hang brick veneer off a wood frame?

 

[concretemasonry]

Yes - Wood frame or wrinkled tin studs for apartments is very common in some areas.

A major problem with a 5 story wood frame building is the effect of long term shrinkage on the plumbing system unless measure are taken early.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[abusementpark]

Don't splice sheathing joints at the floor lines... lap them over the stud wall plates.

I'm assuming this is to ensure that you have a continuous lateral load path at the floor lines?

It seems like it could work with sheathing joints at the floor lines, but you would have to be more careful about detailing.

 

[boo1]

Additional resource:

 

[boo1]

Four story wood-frame structure over podium slab case study:

http://www.woodworks.org/files/PDF/publications/Case_Studies_and_Design_Examples/podium.pdf