Steel beam supported by timber column?

[red22]

A colleague of mine and I have different views on support of steel beams on timber, and I was hoping for some additional insight. I was always taught that steel beams should never be supported on timber. My colleague disagrees and says he does this all the time in residential projects. I could not find any code specific language about this, and it seems like everyone I ask has a differnet opinion. Any thoughts?

 

[tdawgui]

We support wood with steel. Why not support steel with wood? As long as the supporting member can resist the loads there shouldn't be a problem. Usually, I see steel used in residential projects for clearance issues anyway so its not really because of a super high load... just to minimize depth and not have a deflection issue.

 

[ronster]

The problems with supporting steel beams on wood beams are
1.) Making a connection to transfer any lateral or uplift loads. Often the beam is flush in a floor and does not any lateral or uplift forces and this is not a problem.
2.) Shrinkage in the wood post. PSL posts have negligable shrinkage and should be used.
3.) Building inspector will not let you do it. No solution to this one aside from seeing if he will accept a sealed letter from the engineer. This is the #1 reason why I do not sit steel beams on wood posts. Not worth the hassle.

 

[msquared48]

As long as the loads are light, the column can handle the load , and the connection of the beam to the columnn is well detailed, I have no concerns.

The use of the wood column will reduce the effect of differential shrinkage in the story a little (guessing about 5 to 10%) over using the steel column, but the vast majority of any shrinkage will still occur in the sawn wood beam/joist/blocking/sill plate areas.

Mike McCann
MMC Engineering

 

[youngstructural]

Depends on the climate in my honest opinion. I would not support steel with timber in a garage in Canada (where you'd have the potential for pretty large differences in temperature over time, as well as lots of cyclical wet/dry and high to low moisture levels in addition to chemical attack possibilities), but often do so here in New Zealand. The combination of climate and climate specific timber treatment options here permit this type of construction.

Just as an aside, when detailing steel posts for steel beams you can create problems with differential shrinkage , just like Mike talked about, as well as the different coefficients of thermal expansion. Detailing can solve much of these, and essentially I use pin connections and ensure that my detailing permits some rotation.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[csd72]

Why not?

The only things that should not be supported on timber are masonry walls and chimneys, other than that its a free country.

 

[SlideRuleEra]

During the Great Depression (1930's) some State Highway Departments had very little money. In South Carolina they designed what are called "Upside-Down Bridges" which used low cost materials:
Creosoted timber piling
Poured-in-place reinforced concrete caps
Structural steel beams
Poured-in-place reinforced concrete superstructure

In the 1970's many of these bridges were widened (not replaced, overhauled, or strengthened) using more modern designs for the additions (prestressed concrete piling, for example). So, today, the now 70+ year old center core of these bridges are still is service, carrying 21st century traffic. (It is probably time for them to be replaced, now).

Although this is not exactly what you have asked, the principle is the same - weak columns, strong beams.

Based on my experiences with these elderly structures, I have no problem using PROPERLY designed wood columns to support steel beams.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[MiketheEngineer]

I use wood all the time and just as Msquared48 said, I do it so that all wall sections shrink or expand at the same rate.

With so much residential construction using 10' or 12' walls and 20' foyers - you want everything to move together. Steel columns do not move.

If your walls are steel - use steel columns - if walls are wood - use wood columns - Assuming loads and connections are OK