Maybe not "cool details," but cold storage foundation details. OK, a corny title.
We recently had the opportunity to work on a project for an ice manufacturer. As you can imagine, the facility had proposed large areas for storage that were to remain below freezing throughout the year.
Required Frost Depth?
The building code requires certain frost depths for footings. This depth is dependent upon where the project is located and is a function of the area's climate. If minimum frost depths are not provided for footings, then there is the possibility of the soil below the footings freezing during winter months. This leads to frost heave--a condition that causes the foundation to rise above the elevation at which it was constructed. When the footing elevation changes, this can cause stress in the structural members and distress in finish materials. In general, it's something to avoid.
Frost depth in our area of the country is to protect footings from heave for relatively short periods of cold weather exposure. But what if the interior of the structure is kept below freezing 24/7, 365 days a year?
Increase the frost/footing depth? How far?
We realized this could be a serious potential issue. As it turns out, other food storage facilities in our area had detrimental problems at their structural columns due to this exact issue. The steel columns transferred heat from the footings and soils below into the cold storage area above. In simpler terms, the cold columns caused the footings to become very cold, and the moisture in the soil below said footings eventually froze. Over time, this lead to severe frost heave and serious cracking of the floor slab above. So much so that some remediation had to be performed in the past at these facilities.
To help control this phenomenon in our proposed ice storage facility, a thermal break was provided between the base of the steel columns and foundation below. These thermal breaks below the steel columns are called thermal blocks and help reduce heat transfer between the warmer foundation and cooler interior of the building. These were specified to have a strength to resist the vertical loads of the columns without failing. On the detail to the right, taken from our project plans, you can see how this all came together.
This facility had a fairly light column design load of approximately 50,000 lbs. As such, thermal blocks were designed to be rated at a compressive strength of 1,000 psi (pounds per square inch). Around this bearing block is a total of 6 inches of rigid insulation with a final 6-inch reinforced concrete slab over the insulation.
McKnight & Associates acted as General Contractor for the project and did a terrific job executing our design. We all agreed it was a deceptively intricate project with slabs at different elevations, insulation thicknesses, a tie-in to an existing building, and many details to incorporate.