Support Beam - Residential

[dcStrucEng]

I work mainly on concrete and steel commercial office building design and haven't had too much experience with residential single family homes, but how hard could it be, right

So, I was asked by a friend to review some preliminary architectural drawings that he is planning on using (eventually) for his home addition/remodeling. Currently in the garage there is a existing steel pipe column supporting a two-span steel beam, 12'-2" +/- each span. The far ends are supported by exterior CMU bearing walls (mostly above grade). The steel beam supports the existing 2x10 floor joists for the kitchen.

My friend (and his architect) want to remove the pipe column and steel beam and replace with a stronger beam to span 24'-4", thereby having a column-free garage. Obviously, there will be temporary shoring issues to deal with, but that aside my question is this: if headroom is not an issue, is there much of a cost difference in going with a larger steel beam vs. an engineered wood product (glulam, LVL, I-joist, etc.)?

How does the decision of beam material effect the pocketing of the beam into the existing exterior CMU wall? By this I mean, do I need to recommend dampproofing/waterproofing around the ends of the beam or anything else to prevent deterioration?

Any advice would be appreciated.

 

[JAE]

A wood beam would slowly creep downward over time but for a garage roof probably negligible.

A wood beam would have to be supported on treated wood on the CMU to avoid moisture damage or rotting.

The removal of the column means that you will now be depositing around twice the original load on the CMU walls and thus on the footings below - could be a problem - you'd have to check both the wall stability, masonry bearing, and footing strength and sizes.

You'd have to price out steel vs. wood for your locale.

 

[BAretired]

You are asking a lot of questions in one thread. Wood beams are deeper than steel beams as a result of their lower modulus of elasticity. Cost difference varies with location and several other factors.

Removing the central column is possible only if the remaining supports have adequate support to receive the larger load.

On the dampproofing/waterproofing issue, you should follow recommended procedures.

BA

 

[hokie66]

Since you are supporting a floor, I would only consider replacing steel with steel. That's a long span for a wood floor beam, and creep deflection does affect floor serviceability. You should investigate the CMU walls at the bearings. I would want them to be grouted solid in the vicinity of the beam bearings.

 

[dcStrucEng]

Thanks. I agree that the existing masonry walls and their footings need to be checked. And I should recommend fully grouting walls under new beam if it is not already done (home was originally built in the 1930's, not sure if it was common practice back then).

But whether the beam winds up being steel or engineered wood, I think it should be designed with support only at each end. I have a hard time convincing myself that the 2x10s bearing on the beam will provide lateral bracing. Agree?

 

[ToadJones]

if the beam is supported on a pilaster on the inside of the structure, the moisture will likely not be a huge problem, but waterproofing will probably make all involved feel a little better.
There are wood beams resting on interior pilasters or pocketed into
CMU's all oer' the land. If the beam is not exposed to weather, moisture will not likely be a problem.

If the increased reaction on the wall is problem, you may consider constructing a new pilaster or post inside he existing wall ...this will also make erecting the new beam much easier.
This will require a footing check or pouring a new small footing.

 

[ToadJones]

if there is a head room problem, you could temporarily support the 2x10 joists on either side of the main beam and cut them short, slide your new beam up in such that top-of-beam = top-of-joists, then hang the 2x10's from the new beam.
This can be achieved with a wideflange by bolting ledgers to the web of the wideflange

 

[ToadJones]

....this will save you 9.25" of head room and provide better lateral stability to the beam.

Resting the 2x10s on the new beam should laterally brace the compression flange of the new beam.....doubt it will ever see uplift ...Unless the homeowner has a Blown Hemi and revs it up in the garage :-D

 

[msquared48]

Good idea Toad, and I have done that too. Depends on ducting and electrical too often though.

I agree with Hokie here to replace the steel with steel. If it was designed by an engineer (I realize that I am being idealistic here) the steel was used for a purpose initially, probably high loads, and deflections. Stay with it.

Could have also been that the framing contractor had a couple of old steel beams laying around and wanted to save some money. Seen that happen too.

As for the top flange lateral support issue, that has been discussed here in the forum many times. Personally, if the joists rest on and are are nailed to a wood sill plate that is bolted to the steel beam, considering the stiffness of the diaphragm, I believe that the required lateral support to the top flange can be provided at every joist.

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

 

[csd72]

dcsrtuceng,

You have learnt the important lesson about domestic building, it definately can be more complex than most commercial buildings as the structural systems are not as defined and they involve all the major materials.

Personally I would agree with the comment above that the steel would be a better job due to:

shallower depth therefore more headroom
Lower long term deflection
Less end bearing issues

Sometimes the up front costs are only part of the issue and I would expect that the cost differential would not be much.