If there was a part of a building that could be deemed as “the most important”, it would inevitably be the foundation. A properly founded structure is fundamental to the success and longevity of that structure. In any design, the foundation should be thought about in the early stages of schematic design. For this particular Crop Stop we will be doing a majority of the fabrication on site. The intent of the studio, however, is to design a crop stop model that can be used across the whole south east U.S. region, and with a few adaptations, across the nation. So a factory controlled pre-built unit is possible for future Crop Stop projects. Additionally the crop stop needs to have the ability to be lifted onto a truck and moved to a new location if necessary. Those two design intents are immediately suggesting a very specific foundation design that needs to be integrated into the design during the schematic stages of the process. There are several regional parameters that need to be taken into consideration such as, soil bearing capacity, frost zones, flood zone, wind loads, seismic areas, snow loads, and termite threat. A great resource for learning about basic foundation design principles this foundation design guide which was prepared by the Manufactured Housing Research Alliance for the U.S. Department of Housing and Urban Development.
A Pier and ground anchored support system is most appropriate for our design initiative. The pier system is one of the most widely specified foundation systems for manufactured mobile structures because it can adapt to local sight parameters and requires minimal time and dimensional precision during installation. Of the pier foundation systems, the most commonly used is stacked CMU piers or jack stands on bearing pads. Both require tie-downs to compensate for uplift forces. These methods are the most economical because they are both nonproprietary commodity products that can be purchased at any hardware store. A couple of engineered foundation systems that are under consideration is the Diamond Pier system and the helical pier system.
The helical pier system is simply a pole with a screw on one end and is installed with a hydraulic screw drive. The Diamond Pier is a pin foundation system in which a precast concrete pier holds four steel pins in a strategically configured position to distribute loads to the soil in a highly effective manner. The precast concrete unit in this case is simply acting as a key to hold the four pins in place and the pins are distributing the structures’ loads to the soil. This is a foundation system that the Architecture + Community Build team has used before.
In the spring semester of 2014, a team of students (several of which are now on the Crop Stop team) designed and built a series of pedestrian bridges in the South Carolina Botanical Garden after a flood had washed away several poorly founded bridges in the garden. The diamond piers were a great solution for the new bridge foundations as they had a low impact to the site and could be built upon immediately after installation. Both the helical pier and the diamond pier are designed to handle down loads and up lift and, opposed to a poured concrete foundation, can be put into use as soon as they are installed. This all makes them a convenient solution, but convenience comes at a premium.