Here we will take a quick look at how steel beams can be used in commercial construction to extend the span between the outside walls of a building.
Commercial Construction is often very different then residential construction.
First many of the loads are different since the buildings are often taller and larger.
For the most part the safety aspects of construction are the same but in each type of construction there may be reasons for doing the same thing differently.
The most important part of construction is the ability of the engineer or architect to design their building within the well established guidelines of dead and live loads so that the building contractor can follow their plans and endup with a safe place for business or habitation.
Here we are looking at a single story building that has a 12 foot ceiling. This is not a normal situation for residential building but it is within the acceptable guidelines. If for some reason you wanted to build a Great Room or maybe an enclosed swimming pool off of the back of your home you can probably implement some of these design features.
When we take a look at the wall structure we can see that the base of the wall is sitting on a slab. This is where the 2×12 foot long studs are used to form the wall structure. In residential construction if you wanted a wall this high you would probably build a block or concrete knee wall for the first 4 feet of height and then use 2x 8 foot tall studs to build the remainder.
Also if you look closely at the wall you will see that many extra studs have been added around window and door openings. This is to increase the stability in that area. This is required because of the extended height of the wall. Horizontal blocking is also used for attaching drywall, stability and also for fire-blocking.
The bottom plate is attached to the slab with all thread and nuts and washers.
So far with the exception of a little extra blocking and a few more studs we have basically just built a residential Stud Wall but now we will get into the differences.
As we can see our outside walls do not need steel beams for top plate headers because this is only a single story building but the span between the outside walls of the building is well over the distance that a normal 2 point roof truss can span.
Normally in residential building you will see a triangular roof truss that is under or about 30 feet in distance between its bottom corners. Each corner usually sits directly on the outside wall top plate and the center of the span goes totally unsupported.
In this building the span is too great so the engineer has to design a point at the mid-span of the bottom part of the Roof truss that will take some of the load. This is where we need a center span beam.
Center span beams you should know from how they are used in residential basements for first floors. A steel beam is installed on posts and a wood sill-plate is attached to the top of the beam with carriage bolts to allow nailing to the metal beam.
If we look at the design of the steel you will also see that outriggers are used for stability and not for carrying the loads of the trusses.
Posts are located within our outside walls to accept the beams that are directed out from the center span beam. They are also used in areas where there will be a glass partition wall.
Between the posts on the outside walls at this corner you can see that a steel beam header has been installed. This will allow for a large opening of either a door or glass to be used in this area while safely supporting the roof structure.
If we take a look at where the trusses will attach on the outside wall you can see that there is a space between the outrigger beams and the place where the truss attaches to the top plate of the wall.
The outrigger beams do not support the truss system directly but they have wood studs attached for nailing and other uses.
If this was a 2 story building that has 12 foot tall first floors then additional steel would be needed. Instead of resting the outside ends of the trusses on stud walls with double headers it would be necessary to install perimeter steel beams to support a floor.
Buildings of this height and expanse will require a lot of additional engineering time and will often have second floors that are poured concrete.
The real difference in commercial is the distance things need to span and when you have to go a long distance it means steel.
Another option is timber framing as found in older homes and barns but designs that rely on large timbers are usually restricted to 3 stories or less.
Timber framing also takes a lot of technical knowledge and the costs of materials are extreme.
The use of steel in commercial or residential construction is nothing to be scared of and for the most part things like the planing of loads and the fabrication of the steel will be left to an architect and a fabrication plant that specializes in steel framing.
For a Contractor or a home owner that includes steel in their design you will basically follow standard building practices and then insert the steel into your work as shown on your plans.
So, the next time a new business is going up in your area stop by and take a look for a few minutes. You are sure to learn something and you might even thing about using it in your next project.