Foundations For Commercial Metal Buildings
The construction of steel and metal buildings in Houston is very similar to that of other types of structures, and solid foundations are essential to the integrity and ability of the buildings to withstand inclement weather and other conditions. An experienced foundation contractor will have several choices available, but all of them use concrete as the primary material.
Preparing the Construction Site
The first step in the construction of metal buildings is for the foundation or concrete contractor to prepare the construction site. This begins with a survey of the land to designate the boundaries of the plot. After the survey, the ground can be leveled so that it conforms to the stakes marking the required heights for the foundation. The particular type and depth of excavation depends upon the foundation that will be used. Shallow excavation can be performed by hand to a depth of 3 inches while heavy construction equipment will be required for major excavation work.
Most of the problems that occur in metal buildings over time can be traced back to weak foundations, so choosing the proper type of foundation is vital to the job.
Nearly all foundations are made of concrete, which is a mixture of portland cement, sand, course aggregate and water. In addition, an admixture may be used to strengthen and cure the concrete after it is poured. When mixed properly, concrete sets in about 28 days, and after this time, it should have a compression strength of 3,000 psi. To increase the tensile strength, steel rebar may be inserted into the ground before the concrete is poured.
The three types of foundations most commonly used for steel buildings are as follows:
• Footing and grade beams – This type of foundation consists of square and rectangular footings that are supported by grade beams. The footings carry the weight of the vertical loads.
• Drilled piers – Drilled pier foundations are similar to footing and grade beam foundations except that the footings are replaced with vertical piers created by drilling deep holes into the ground.
Constructing the Foundation
Before pouring, forms are placed in the foundation area to support the liquid concrete before it dries. The forms determine the final shape of the foundation, and they are usually made of metal, wood or another material that is strong enough to bear the weight of the concrete.
Once the forms are set and drainage troughs have been dug for water runoff, the concrete can be poured. It must be poured evenly over the area to ensure that the aggregate does not settle to the bottom and that no air bubbles are inside the mixture. To help with this, the concrete should be constantly agitated in a rotating drum or a vibrating container.
After pouring, the concrete can then be leveled. In this process, excess concrete is pushed into areas that are underfilled, and the surface is made flat. The next step is finishing the concrete, which consists of using heavy floats to compress it and push some of the larger aggregate material lower into the mixture.
The final stage of laying the foundation is to cure the concrete. Ideally, the conditions outside should be warm and dry. The best temperatures are in the range of 50°F to 90°F, and this is an important requirement for at least the first 72 hours. Once the foundation is cured, the floor can be completed, and the rest of the building can be erected.