From the Desk of Dylan Clemente,
Design of Concrete Foundations (Or A Building Is Only As Strong As Its Foundation)
Are you thinking about starting a new construction project? Are you looking to construct a new building, or add an extension to your home’s floorplan? If so then you are going to need a foundation designed for your project.
Many people don’t tend to think about the foundation of a structure, because as you can guess the foundation isn’t usually visible, “out of sight out of mind”. However, despite the fact that foundations are the least thought about, it is actually the most important part of your structure. The idea behind this is simple once you break it down. No matter how well you design the rest of the structure, if the foundation fails the rest of the structure fails with it. This is why it is important to have a foundation designed by a licensed professional, primarily a structural engineer.
So now the question is what goes into the design of a foundation? First, you need to consider the factors that can impact the foundation’s design. The most commonly talked about factor is the frost depth, however, in many cases, this tends to not be an issue because most structures include basements which require the bottom of the foundation to go well below the frost depth.
The second necessary piece of information is what is the strength of the soil? This information is typically derived from a geotechnical analysis. The strength of the soil allows us to determine several design parameters. First it will determine the type of foundation that will be used, whether it is supported by piles or by concrete. Second, it will determine the soil bearing capacity, or the loading in which the soil can support before failing. This allows the designer to determine the size that the footings need to be in order to properly transfer the loads for the structure into the soil.
The next question is how do we determine the loading or forces that will be placed on the foundation? The initial thought most people have is that the loading on the foundation is coming from the weight of the structure, the weight of people, appliances and snow. However, there are other loads that impact the design of a foundation. These loads are soil pressure, Lateral loads caused by wind, and water pressure. Soil pressure is caused by the soil that rests against the foundation wall. This can cause the wall to overturn if not properly designed. Lateral loads from wind are transferred from the structure above ground to the foundation, the pressure is then directed towards the soil which can be overburdened if not properly designed for. Water pressure can be present in locations that have high groundwater. This requires the foundation to be waterproofed as well as be designed to resist the additional forces that the water exerts on it.
Once we know the loading from the structure, the bearing capacity of the soil, and the dimension of our footings to not overburden the soil, we move onto determining the design of our footings and foundation walls. This step we determine the thickness and reinforcement of the footings and foundation walls. These are the factors that prevent a footing from cracking and failing.
Once these design elements are complete, we need to ensure that all is code compliant. Code requirements dictate the clearances of rebar, along with both the maximum and minimum requirements for reinforcement in a concrete structure.
A good designer understands all the necessary requirements and keeping a construction budget in check
I hope that you find this information useful in determining what is needed to design a concrete foundation. If you have any questions, including pricing and applicability, please don’t hesitate to contact us by phone at 631-234-2220 or send me an email at Dylan@holzmacher.com
J.R. Holzmacher P.E., LLC