Regardless of the type of steel building, ideal foundation options should be considered simultaneously with the building design.
Durability and sustainability of the steel buildings are very much dependent on how well the foundation is designed and how well it is constructed. An ideal foundation should transfer the dead and service loads of the buildings effectively to the soil beneath without incurring any structural damage. This includes avoiding settlement and/or tilting of the walls and building frame.
2. Founding Considerations
Before initiating the selection process, below variables should be taken into consideration. There may be some additional considerations that your building expert will ask you about, but these are a good starting point:
- The type of soil and its bearing characteristics. As the soil having immediate contact with the footing would be bearing a greater share of stress. So ensure to excavate any dirt poor soil and replace it with a high-quality soil if required.
- The loading conditions depending on the type of usage. You must be clear about how many vehicles would be parked on the foundation and any other heavy items being stored on it.
- Wind, Snow, and Earthquake conditions. As the steel building would use anchoring, any lateral or uplifting load is directly transferred to the building. Because of this if you live in an area prone to earthquakes, then this is something to let your building rep. know. Also if you happen to be in an area with heavy winds, or snow loads then those need to be factored in since any pressure put on the building is transferred down to the foundation itself.
- The area of the building and the size of the plot: The land can be surveyed for grading and area. This may seem simple, but be sure to get the tape measure out at the very least and ensure you have enough space. Not only space for the building itself, but for a perimeter around it as well.
3. Steel Building Foundation Types
3.1 Slab Foundation
Slab foundations are also sometimes called floating slabs or floating foundations. This is because of the fact that it literally floats over the undisturbed soil. If large enough, it can span patches of poor bearing soils. This feature makes it an ideal choice for softer soils, like in coastal areas that could sink or settle unequally.
Figure 1 : Slab Foundation
If you’re working on a budget then a slab foundation is likely your best choice. As an economical solution, this floating type of slab foundation is very popular and common. It can be poured easily and quickly. If you’re planning to construct a shed, a garage or some extension work which is not wider than 15 meters, than this is the most suitable option. Unlike other types, it does not require any extensive excavation and also fewer labours are adequate.
Often, on the exterior perimeter of the slab foundation, a thickened reinforced edge beam is added. It’s referred to as a grade beam. The thickness of the slab would be decided by the engineer of record, keeping in view the above-stated inputs. Typically a slab in between 12-18 cm would be enough.
Reinforcements are embedded in the concrete. If you intend to store a particularly heavy load on the steel building foundation then you must use concrete of high compressive strength i.e. about 4000 psi. For normal usage, 2500 psi could do the job.
If you have a problem fixing the reinforcement mesh in the concrete slab; you can use fiber reinforced concrete which has considerable tensile strength when compared with that of un-reinforced concrete.
3.2 Pier Foundation
There are two main ways to go about a Pier Foundation. You can either build steel constructions directly on pile or pier, or you can embed the pier in the floating concrete slabs. It looks similar in style to the foundation of decks for the building. In slab foundation type, the top of concrete slab serves the purpose of the floor while in this type the floor is left as dirt or rough gravel.
Figure 2 Pier Foundation
This type of foundation is ideal for agricultural sheds and open pavilions where an enclosure is never a need. The most common type of pier foundation has a grade beam which ties together all the piers which help in resisting horizontal column reactions. Pier foundation is comparatively expensive than slab foundation but it offers resilience against wind uplift pressure and seismic stress reversals.
Figure 3 Pier Foundation -2
3.3 Perimeter Wall Foundation
Referred to as standard foundation, this type is used for steel buildings wider than 15 meters. You can also call it a T-wall foundation, perimeter wall foundation or frost wall foundation. The strip which is wider than the width of the perimeter wall provides stability by distributing the load over a larger area. The columns of the steel buildings are anchored trough embedded bolts in concrete pedestals in the strip wall. This type of footing should run below the maximum anticipated frost line.
Figure 4 Perimeter Wall Foundation
You can cast this foundation in three stages; first, the strip is cast followed by concreting the perimeter wall. After curing, the plinth of the building is backfilled and the floor is afterward cast. This type of foundation requires labour force and is time-consuming as you’d require fixing formwork and waiting for the curing of the concrete.
A local concrete engineer should be hired to design your steel building foundation. They will be best qualified to determine the specifics for using perimeter walls, piers, or a concrete slab for metal building foundations.
Novelty Steel provides the anchor bolt plans and technical information for your foundation engineer and contractor in order to plan the perfect foundation for your steel structure. This allows your foundation to be poured and cured in advance, so construction can begin immediately when your steel framing arrives.