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An on-grade mat foundation is an above-ground type of foundation used to provide load-bearing capacity in expansive, rocky or hydro collapsible soils. The foundation is created by connecting a series of thermal-grade heat resistant plastic forms or Insulated Concrete Forms ICF's often made from Expanded or extruded polystyrene, set directly on grade, and then monolithically pouring a post tension, rebar or Fiber reinforced concrete slab (usually 4” – 8”). No footings are required. The monolithic pour creates concrete beams running throughout the footprint and perimeter in one operation. The completed slab then sits on the ground like a raft, the void areas underneath the slab, or the low pressure areas formed by the placement of the forms allowing for expansive soil movement. The on-grade mat foundation possesses great stiffness, with strength to resist differential swelling resulting from landscaping practices, surface drainage, or flooding from any source. It does not require presoaking underlying soil pads, and there is no need for footings, meaning no earth spoils. And, since the slab section is typically 13” – 14” above grade, it requires little or no gravel, sand or moisture barrier. ==IBC and an on-grade mat foundation== On-grade foundations adhere to International Building Code requirements. By 2008, most states put into effect the changes adopted in the 2006 IBC and, in regards to foundations, the on-grade mat foundation has become a more attractive design because, as an engineered system, it already accommodates the 2008 design recommendations, and required no major modifications to bring it into compliance. The Post-Tensioning Institute, in June 2008, approved two key specifications of an on-grade mat foundation and immediately incorporated them into the PTI Manual, the publication used by municipalities around the world to determine building code regarding specifications and requirements of post tensioned foundations. First, in section 4.5.2.1, the PTI Manual was revised to permit rib spacing of less than 6 feet, and to clarify what spacing shall be used to compute moments and shears. Second, in section 4.5.2.3, the PTI Manual was revised to limit rib widths to a range of 6 to 14 inches (from the previous 8 to 14 inches). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「On-Grade Mat Foundation for Expansive Soils」の詳細全文を読む スポンサード リンク
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