C-Store Design: A Blend of Structural Steel and CMU Construction
The type of foundation utilized for C-Stores is dependent upon the results of the site-specific geotechnical report, however due to the light loading from the superstructure the foundation will not necessitate deep foundations (drilled piers, auger cast piles, etc.). For foundations on non-expansive soil, continuous spread footings with a non-structural slab are commong. For foundations on expansive soils, stiffened slab-on-ground foundations are typically utilized since the controlling loading will be the active soil and not the superstructure loading.
Typical C-Stores are constructed with CMU (concrete masonry unit) walls and structural steel open-web roof joists. The CMU walls serve as the load bearing element for both gravity loading (dead, live, snow, wind uplift, etc.) and as shear walls for lateral loading (wind, seismic). Open-web steel roof joists are a practical option for the roof framing due to their truss configuration which allows them to span large distances at a relatively low cost. The front of the C-Store is typically framed with structural steel columns and beams due to the large storefront windows that preclude the use of CMU walls.
Fuel tanks present a special condition for C-Store design as they can become buoyant during flooding events. For example, the self-weight of a 20,000 gallon fuel tank is approximately 10,000 pounds. Assuming that the soil has become saturated and the fuel tank is empty, the buoyant force will be approximately 165,000 pounds. To overcome this buoyant force, deadmen anchors are employed to provide additional restraint.
The fuel canopy structure typically consists of HSS (Hollow-Structural Section) steel columns with “carry” wide-flange steel beams directly above spanning the short dimension of the canopy which then support the “purlin” wide-flange steel beam spanning the short direction. The metal roof deck is fastened to the soffit (bottom) of the steel beams. The HSS columns are typically founded on deep foundation elements.