Building Homes or Extensions/Supporting and Straightening a Steel Ibeam
QUESTION: Dear Stephen,
I have a two-and-a-half storey house built in 1936. A steel ibeam runs east-west the length of the house in the middle of the basement, a span of about 30 feet. I've provided its dimensions in the table below.
Height (d) 9 7/8
Width (bf) 5 7/8
Web Thickness (tw) 3/8
Flange Thickness (tf) 1/4"
I think it must be somewhere between W10x22 and W10x12.
The beam is supported by the east and west walls of the house and by one post located a distance of 5' 8 from the east wall. The span between the post and the west wall is about 22.5'. The beam is bolted to the post and sits on the walls.
The beam twists downward towards the centre of the 22.5' span about 3/8 and also sags about 5/8 at that point. The total drop at the lower (south) edge of the bottom flange is about 7/8 to 1 from horizontal. The joists to the south are resting inside the web on the lower flange. Those to the north have lifted off it. They are floating above it, cantilevered on a partition located about 3' to the north of the beam. The joists are all 2 x 10 with 16 centres. Both those to the north and those to the south are 13' 10 long. None are attached to the beam.
I'm wondering if I can straighten out the twist in the beam by putting a permanent jack post under it and slowly raising it up. Will I be able to take the twist out at the same time as I get rid of the sag? Alternatively, Alternatively, I wonder if I should raise the beam using jacks and place a lally post under it, though I prefer to use a jack post for ease of installation.
I want to position the second post 11.5 feet to the west of the first post and 11 feet east of the west wall in order to locate it opposite the midpoint of the space between two basement windows on the south wall.
This project started when my wife asked for a new kitchen floor. Once I've finished with the beam, I'll decide whether to sister the joists to the south or block them to take the sag out of the kitchen floor and reduce its flexibility. (The joists sag, too.)
I've enjoyed reading your advice to others and would be very thankful for your help with my problem.
It appears that the beam is covering a span that is too great for it's intended use. The sag plus the twist are consequences of this. Do you know if there was a post or column elsewhere along the span, that has been taken out? This even may include an old chimney structure.
Without knowing the loads involved, I can't make a recommendation regarding the spacing of any permanent posts that you may install. However, for a 22' span, I would intuitively place two new columns at 7.5' and 15'. It is safest to use a house (screw) jack (see attached) to slowly lift the beam, coupled with a stout timber post like a knot-free 4x4 or 6x6 with straight grain. Prior to lifting the beam, you need to install proper footings to take the load. At a minimum, I would cut out 2' square sections of the existing concrete floor, excavate down about 8" to 10" below the floor surface, install a rebar grid (three #5 rebar each way), and pour concrete on stable firm soil. Float and finish level with the floor and damp cure for at least a week prior to loading. Placing a load-bearing column on a concrete floor (without footings) is a bad option.
Lastly, use actual columns, often called FHA columns well connected top and bottom. These have a short screw section built in, but this is for adjustment only, not active lifting (see attached).
Goo luck and let me know if you have any additional questions.
---------- FOLLOW-UP ----------
QUESTION: Dear Stephen,
Thanks for your quick and very helpful reply.
You asked whether there had been a post or column elsewhere along the span. No, there has always been just the one post. I have the blueprints for the house showing only the one. The room is labelled Billiard Room on the blueprint, so I assume the owner/designer wanted space to wield a cue. The blueprint, in fact, shows the beam ending at the post, but the builder extended it another 5.5' so that it would also rest on the second foundation wall.
I discovered a local supplier willing to build a 3.5-inch diameter custom post, cut to length, with a rating of 42,000 lbs. I'm wondering whether it would provide sufficient support at 11.5 feet along the 22-foot span. I'd rather one post than two, and then, there's also a drain tile that runs diagonally under the basement floor, crossing below the beam near the 15-foot mark. I'm concerned about digging down over top of it were I to excavate a footing for a second post.
In the end, we would have supports at the east wall, at the first post 5.5' along the span, at the second post 17' along it, and at the west wall. The distance between the east wall and the first post would be 5.5', between the first and second post, 11.5', and between the second post and the west wall, 11'. The total span, from wall to wall, is 28'
Also, can I ask you what you think about setting the top of the footing 3 to 4 below the floor and securing the base of the post with 3 to 4 of cement, instead of bolts and anchors?
Lastly I wonder what support you recommend I use on the basement floor under the house jack when I raise the beam, and whether you know where I can purchase a house jack. I'm having a bit of trouble finding one. Could I use a bottle jack, instead?
Adding a post as you describe will certainly help with the sag and twist in the beam. But again, without knowing more about the loads from above, it is difficult to recommend a correct fix.
From your description it sounds like the designer chose the I-beam with that large span in mind. It is, by the way, quite a large section beam for typical residential use. But, as sometimes happens, the beam turned out to be a bit undersized for the actual loading conditions.
Your plan to bury the post base in concrete is good, just be sure that the footing is thick and wide, and reinforced as I described in the first response.
The 3.5" dia. post should do the trick.
Don't buy a house jack, just rent it. They are a common rental item. If you can't do that, then a large bottle jack is OK, but much trickier to use. They can lose pressure slowly, and the jacking post can fall unexpectedly. Go slowly and have a competent helper or two.