Steel post and timber beam

[mocon11]

Hi All,

I have a question about an addition to the second story of a house only, leaving the bottom story open to the back yard. I had initially thought of using a moment frame or strong walls in the corners of this rectangular addition to transfer seismic loads, but another engineer told me to just used a steel post and timber beam and that would transfer the seismic loads to the foundation. We are only talking 500-600 sf of addition here.

Is it appropriate to use the steel post and beam? I imagine the seismic forces are transferred in tension and compression from the wood shear walls to the beam then to post and foundation.

 

[msquared48]

That can be done in one of two three ways:

1. Tne steel posts are designed as cantilevered columns, and are anchored directly to the concrete foundation, being fixed to it with afterset bolts.

2. The connection between the steel coumn and woodbeam is designed as a fixed or rigid connection, with the steel posts pinned at the connection to the founation, or

3. A combination of 1 and 2.




Mike McCann
MMC Engineering

 

[mocon11]

The cantilever column makes sense. So the lateral force that comes out of the floor diaphragm is applied to the columns, correct?

What kind of connectors provide rigid connections between timber beam and steel post? I thought this connection was typically thought of as a pinned connection.

 

[msquared48]

Typically it is. It would have to be specially designed to be rigid. There are ways to do that with steel plates and a lot of bolts, depending on the size of the wood beam.

Mike McCann
MMC Engineering

 

[csd72]

Be careful with the cantilevered column method, it amplified your loads at the top of the existing shear walls as it acts as a propped cantilever.