10/22/12: Foundation Engineering

At my mentorship with Bowman Engineering, Inc., I'm learning the fundamentals and even some details of structural engineering. Bowman mostly works with foundation plans, which are CAD drawings drawn as if you were one inch above a floor looking down. This way, you can see what is supporting you, better known as your foundation.

I'm learning about rebar standards (rebar is used to help concrete structures maintain their shape and strength), standard sizes for I-beams, standards for steel railing, and much more. In my most recent project, I designed the foundation plan for a water tank at SAPA in Gainesville. The structure is made up of a foundation in the ground, a water tank, a floor above the water tank that is supported by four beams on its four corners, and a water tank on top of the floor. This requires us to look at soil conditions, the loads we expect the structure to carry (weight of the tanks when filled with water), and how we expect the structure to perform.

The same happens for all structures, and those three criteria are the most important part to anything staying up. I read an article published on A-1 Engineering's website about foundation design. Here is my synopsis:

Foundation Engineering
In order to create a building, a foundation is required. To build a foundation, important data must be acquired. A geotechnical engineer will perform soil tests on a site to determine the type of soil present. The structural engineer in charge of the project will then review International Residential Codes and International Building Codes to determine the types of footings, slabs, and beams used in the project. The Codes contain lists of available books and resources that not only tell how to build the structure, but also acceptable standards for its construction. This is done to ensure that the structure does not collapse.

Soil
Structural engineers need to know the type of soil they are building on in order to avoid catastrophes. For example, building on fertile soil such as in the Midwest requires larger foundations so that water can't get inside buildings. Engineers building on the red clay of North Georgia have to consider the thickness of the clay to avoid a heavy load resting on a layer of limestone. Acid rain causes sinkholes because it dissolves the limestone, so if limestone must be built on, a load-bearing support does not need to be there.

Loads
After determining that the soil is good for building, a structural engineer must determine to what degree something can be built. For example, a building that needs 2,500 pounds per square foot (psf) of support shouldn't be built on top of limestone or thin clay, but a building that only has to support 500 psf can be built on nearly anything. The psf requirement is calculated by adding the weight of all of the walls, the floors, the roof, and the maximum weight of potential furniture and people. That number is multiplied by 25, then divided by 2. The final number tells the requirement for how many pounds per square foot that the soil can support.

Performance
Plain and simple, if a structure is going to be frequently used (like an apartment complex), then the support structures will need to be strong overall. For something like a house, then normal-strength 2x4 boards are strong enough. And for something like a shed (where equipment sits in the same place for extended periods of time), the support below those objects will need to be stronger, and the rest of the shed doesn't have to be strong at all.

Overall
In conclusion, soil, expected loads, and building performance are the three major parts to determining how a building is created, and if International Codes are followed, the building will be a great structure for many years.

Source
A-1 Engineering. "Foundation Engineering Design." A-1engineering.com. A-1 Engineering, n.d. Web. 29 Oct. 2012. <http://www.a-1engineering.com/foundationengineering.htm>.