Adding a steel i-beam in home.

Can you clarify a few items?

1. What is the other dimension of the garage?

2. What is above the garage: a living space and then a roof, or just a roof?

3. Are the existing columns such as to divide the span in equal parts?

4. What is your local snow load criterion?

5. Are you limited to 12" depth of the steel beam? (Don't want the bottom to be so low as to be a head-bumper.)

The actual dimension of the garage is 26 x 27. The existing beam is running the 27 feet. The living space is above the garage then the roof. The existing columns are equally spaced under the beam. It splits the garage in half two allow for two cars. The snow load is mostly zero. Worst case if a blizzard hits maybe 6 inches and we have had no snow for 15 years. More than 12 " would be fine but not much more.

Given the actual dimensions of four 2x12 are closer to 7 x 11.5 you could place three 2 x 10 or 2 x 12 I beams with additional sheets between them and have a far more rigid and stronger support system.

I would use 1/4 inch web beams and sheets if possible. Three beams with two sheets would give you a cross section of 1.25 inches. Thats more than strong enough for any house loads! I don't know the actual limits of defection but it would be far less than the four 2 x 12's you have now even at a 30 foot span.

You haven't considered that the columns will be taking additional load due to their new position. so the columns may not be adequate. What is the yield stress of the said columns? What is the foundation to the columns?

This should be thought through more carefully and would normally require a qualified, registered, insured engineer.

CR4 can give some basic advice for an initial understanding of the problem but cannot give you the fully thought out solution. Generally you should come away with more questions than answers.

GA. Definitely hire an engineer.

The original poster's assertion that the beam is supported by two columns appears incorrect. It sounds as if it is supported by two columns and two walls. There were probably good reasons for the two steel columns, and placing the entire load on just the walls would be unwise without a competent analysis.

The deflection of a beam is proportional to the cube of its length. If the 2x12s are supported at 10' intervals, the steel at 30' will need to be inherently 27 times as strong. This not insuperable, but it is sobering.

Hire a competent engineer to examine your structure and make the necessary recommendations.

Factors not known to you may arise in analysis and inspection which would influence the work to be done.

Liability is too great not to use prudence in this case. A collapse (even during construction) of the structure causing injury or death can bankrupt.

The most important thing to find is what load the two columns are actually supporting. This can be accomplished with hydraulic jacks placed alongside the columns and raised until a clearance is made at the column /beam interface. The pressure of the oil and active surface area of the rams will give you the supported load.

Then the structural engineer will calculate your beam or beams size taking into consideration safety factors and codes etc. This is not something that should be done through this forum.

Might not be a bad idea to get a copy of the local building code and understand it.

Hi 84V,

Welcome to CR4!

Very good point!

GA for you. And on your very first post!

Structural integrity is the starting point of interest—building site drawings would confirm?

In common with the other posters you will require significant documentation and on-site evaluation of architect/engineer or agent thereof.

What I will describe must not be taken as a fully informed design; rather, it is meant for illustration. As others have said, you should engage an engineer. This might help you to understand his/her calculations, though.

A typical residential floor loading is 40 psf. Typical snow loads vary by region, and are usually specified in local codes. Freak storms can screw this up, however. One year in Yakima, WA, USA (design snow load 40 psf, as I recall) there was an accumulation of a bit over a foot of snow. This was followed by rain. Instead of the rain draining off, the snow soaked it up like a sponge, resulting in a foot of water on many roofs. That's 62.4 psf, and many roofs caved. That's why I asked.

If we guess your snow load (roof) to be 30 psf and the floor load 40 psf, then your total load is 26 x 27 x 70 = 49,140 lb. Surprise!? The beam down the center supports half of this: 24,570 lb.

For a uniformly loaded beam (which might not be exactly true in your case--another reason to have an engineer) the deflection is D = 5 W L³/(384 E I). (W = weight, L = length, E = modulus of elasticity of the beam material, I = moment of inertia of the cross-sectional shape). For steel, E ≈ 29E6; i.e., 29,000,000. For your beam, L = 27 x 12 = 324 inches. A common deflection spec is L/360 (max); in this case 324/360 = 0.9 inches (max). Solving for I, we get I ≥ 417 in⁴.

From a steel table, some candidate shapes (with I) are: W14x120 (495), W12x152 (454), W14x109 (447), W27x146 (443), and W24x162 (443). The W14x109 is the least weight at 109 lb/ft, but maybe it will encroach into your headroom. The other decent choice is W12x152. The rest are head-knockers.

From experience, I suspect that deflection is the limiting factor here. You must also check ultimate strength, and some other factors....

There is a fair amount of complexity here (engineer again), and the hour grows late. More later.

A valiant effort for someone who is not a structural engineer.

However, you looked up the Iy values in the steel handbook instead of the Ix. A more appropriate beam size would be a W12x53.

In addition new steel columns will most likely be required in the walls and the existing footings under the walls which would support these columns would have to be increased is size.