I'm planning to remove a load bearing wall and place a 4500 beam. Steel is stronger than timber and I should be able to use a thinner steel beam than a timber beam. Does this make sense and how do I attach it to the timber posts and rafters?
Can you install a steel beam in timber posts
structural
Related Solutions
You've essentially got a column buckling problem here. Factors affecting the maximum load include the geometry of the beam cross section, its material properties, and the manner which its ends are constrained. You can read up on it here.
What makes it more complicated is a possible eccentric loading condition, as The Evil Greebo points out. Now you have to worry about compressive stress and normal stress. This eBook does a good job describing the loading conditions and resulting stress under the "Maximum Stress" section.
Since the current exact loading conditions are unknown, and in addition you're changing the location the load is applied in, I think it would seek professional engineering advice. (I would, and I'm a mechanical engineer - I just don't specialize in architecture.) Either that, or an experienced contractor may be able to give you a better answer. (Shirlock, where are you on this one, buddy?)
It depends on what kind of wood you're using. Different woods have different strength characteristics. You may want to swing by the local library and grab a copy of a "Timberframing: Design, Construction, Finishing" by Ted Benson, which has tables of wood characteristics.
Note: If you live in a town where a permit is required to do the work you're planning, you're going to have to get sign-off by a structural engineer - in which case, you might as well ask the engineer what dimensions you need for the wood you're planning to use.
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Best Answer
You have several issues to consider: 1) span of steel beam vrs. wood beam, 2) weight of steel beam vrs. wood beam, 3) connectors, 4) ease of connecting joists to wood beam vrs. steel beam, 5) ease of installing wood post vrs. steel post, 6) size of footing under posts.
1) Yes, steel beams can be smaller than wood beams when carrying the same load and spanning the same distance. However, if there is a headroom problem, you can move the beam up and have the joists frame into the side of the beam or reduce the span of the wood.
2) Physically moving the beam into place is going to be difficult. A steel beam may weigh less, but with a wood beam you can nail supports to the side of it to keep it level, aligned, stable, etc. Also, if the beam needs to be cut to fit, wood is easier.
3) Connectors from a steel beam to a wood post will need to be custom and probably designed by a structural engineer. However, a connector from a wood beam to a wood (or steel) post is readily available and standard through Simpson Strong Tie. (See Simpson LCC or CCOS connectors for wood to steel posts.) See here: https://www.fastenersplus.com/shop-by-product/simpson-connectors/post-bases-post-caps/lccccos-lally-column-caps
4) Connections from wood joists to steel beam is not standard and you’ll need a structural engineer to determine ledger size and bolting, plate size and bolting, etc. Whereas wood to wood Connection is standard.
5) When wood posts are cut to fit, they must be the perfect length. Fitting a wood post with a connector on it is very difficult to “pound” into place and fit tight. However, using a “Lally Column” allows adjusting in place.
6) If you are trying to span an extra long distance by using a steel beam, your footing will need to be extra large too. Make sure it’s sized properly.
Summary: Generally for ease of construction, the beam and posts are reversed: wood beam and steel posts.