Post-tensioned, below-grade concrete foundation system

Abstract

A below grade, post-tensioned concrete foundation system for use in the construction of residential dwellings and other structures is described. The foundation includes a post-tensioned concrete floor slab formed on the soil base of a below grade excavation. Concrete foundation walls are formed on the perimeter of the post-tensioned floor slab. The weight of the superstructure of dwelling as well as the weight of foundation itself is distributed across the post-tensioned floor slab, thereby resisting the detrimental effects of expansive soils on the foundation.

What is claimed is:  
     
         1 . A structure with a basement comprising: 
 at least one first post-tensioned concrete slab below grade; and    at least one exterior concrete basement wall supported on a perimeter edge of said first post-tensioned concrete slab.    
     
     
         2 . The structure of  claim 1  further comprising: 
 a plurality of beams; and  
 a high load bearing floor supported by said plurality of beams spanning a first portion of said exterior concrete basement wall and a second portion of said exterior concrete basement wall.  
 
     
     
         3 . The structure of  claim 1  further comprising 
 a plurality of beams; and  
 an interior concrete basement wall;  
 wherein said high load bearing floor is supported by said plurality of beams spanning said interior concrete basement wall and said exterior concrete basement wall.  
 
     
     
         4 . The structure of  claim 3  further comprising 
 at least one interior concrete buttress,  
 wherein at least one of said plurality of beams spans said at least one interior concrete buttress and said interior concrete basement wall.  
 
     
     
         5 . The structure of  claim 2  wherein said high load bearing floor is a garage floor.  
     
     
         6 . The structure of  claim 1  further comprising: 
 a concrete sub-beam extending underneath and supporting said first post-tensioned concrete slab; and  
 at least one tendon; and  
 wherein at least a first portion of said at least one tendon extends within said first post-tensioned concrete slab, and at least a second portion of said at least one tendon extends within said concrete sub-beam.  
 
     
     
         7 . The structure of  claim 1  further comprising: 
 a second post-tensioned concrete slab adjacent said exterior concrete basement wall; and  
 at least one tendon; and  
 wherein at least a first portion of said at least one tendon extends within said second post-tensioned concrete slab, and at least a second portion of at least one tendon extends within said exterior concrete basement wall.  
 
     
     
         8 . The structure of  claim 7  wherein at least a third portion of said at least one tendon extends within said first post-tensioned concrete slab.  
     
     
         9 . The structure of  claim 7  further comprising 
 a concrete sub-beam extending underneath and supporting said first post-tensioned concrete slab,  
 wherein at least a third portion of said at least one tendon extends within said first concrete sub-beam.  
 
     
     
         10 . The structure of  claim 9  wherein at least a fourth portion of said at least one tendon extends within said concrete sub-beam.  
     
     
         11 . The structure of  claim 7  wherein said second post-tensioned concrete slab is a garage floor.  
     
     
         12 . The structure of  claim 1  wherein said at least one exterior concrete basement wall is post-tensioned.  
     
     
         13 . The structure of  claim 1  further comprising: 
 a second post-tensioned concrete slab adjacent said exterior concrete basement wall;  
 an interior concrete basement wall;  
 at least one tendon; and  
 wherein at least a first portion of said at least one tendon extends within said second post-tensioned concrete slab, at least a second portion of said at least one tendon extends within said exterior concrete basement wall, and at least a third portion of said at least one tendon extends within said interior concrete basement wall.  
 
     
     
         14 . The structure of  claim 13  wherein at least a fourth portion of said at least one tendon extends within said first post-tensioned concrete slab.  
     
     
         15 . The structure of  claim 13  wherein said second post-tensioned concrete slab is a garage floor.  
     
     
         16 . The structure of  claim 1  further comprising at least one tendon, wherein at least a first portion of said at least one tendon extends within said first post-tensioned concrete slab and at least a second portion of said at least one tendon extends within said exterior concrete basement wall.  
     
     
         17 . The structure of  claim 1  further comprising: 
 an extension of first said post-tensioned concrete slab beyond said exterior concrete basement wall; and  
 at least one counterfort defined by a concrete member formed upon and generally normal to said extension of said first post-tensioned concrete slab.  
 
     
     
         18 . The structure of  claim 17  wherein a portion of a tendon from said first post-tensioned concrete slab extends within said at least one counterfort.  
     
     
         19 . The structure of  claim 17  further comprising a window opening located in said exterior concrete basement wall, and wherein said at least one counterfort defines a window well around said window opening.  
     
     
         20 . The structure of  claim 17  further comprising a sump pump opening in said extension of said first post-tensioned concrete slab, wherein said at least one counterfort defines a sump pump well around said sump pump opening.  
     
     
         21 . The structure of  claim 1  wherein said first post-tensioned concrete slab is supported by at least one post-tensioned concrete beam.  
     
     
         22 . A method of constructing a foundation resistive to effects of expansive soil, the foundation having a first concrete slab and an exterior concrete wall, the method comprising: 
 excavating a below grade level in soil;    placing a plurality of tendons in said below grade level;    pouring a cement mixture over said plurality of tendons in said below grade level;    at least partially curing said cement mixture to form said first concrete slab;    post-tensioning said concrete slab by applying tensile forces to said plurality of tendons; and    forming said exterior concrete wall on a perimeter of said first concrete slab.    
     
     
         23 . The method of  claim 22  wherein the step of placing further comprises placing at least one of said plurality of tendons such that a portion of said at least one of said plurality of tendons extends within said exterior concrete wall.  
     
     
         24 . The method of  claim 22  further comprising the step of supporting a high load bearing floor by said foundation.  
     
     
         25 . The method of  claim 24  further comprising the step of hanging a plurality of beams between a first portion of said exterior concrete wall and a second portion of said exterior concrete wall; and 
 constructing said high load bearing floor on said plurality of beams.  
 
     
     
         26 . The method of  claim 25  wherein the step of forming further comprises forming an interior concrete wall; and 
 he step of hanging further comprises hanging at least one of said plurality of beams between said exterior concrete wall and said interior concrete wall.  
 
     
     
         27 . The method of  claim 26  further comprising forming an interior concrete buttress, and wherein the step of hanging further comprises hanging at least one of said plurality of beams between said interior concrete buttress and said interior concrete wall.  
     
     
         28 . The method of  claim 24  wherein said high load bearing floor is a garage floor.  
     
     
         29 . The method of  claim 22  further comprising the step of structurally integrating a second concrete slab with said foundation.  
     
     
         30 . The method of  claim 29  wherein said second concrete slab is adjacent to said exterior concrete wall, and wherein the step of structurally integrating said second concrete slab to said foundation further comprises connecting said second concrete slab with said exterior concrete wall with at least one tendon.  
     
     
         31 . The method of  claim 30  wherein the step of connecting further comprises connecting said exterior concrete wall and said first concrete slab with said at least one tendon.  
     
     
         32 . The method of  claim 30  further comprising forming an interior concrete buttress, and wherein the step of connecting further comprises connecting said interior concrete buttress and said exterior concrete wall with said at least one tendon.  
     
     
         33 . The method of  claim 31  wherein the step of connecting further comprises connecting said interior concrete buttress and said first concrete slab with said at least one tendon.  
     
     
         34 . The method of  claim 29  wherein said second concrete slab is a garage floor.  
     
     
         35 . A below grade foundation for a structure comprising: 
 a concrete slab;    an exterior concrete basement wall on a perimeter edge of said concrete slab; and    a means for post-tensioning said concrete slab.    
     
     
         36 . The below grade foundation of  claim 35  further comprising a means for structurally integrating said concrete slab with said exterior concrete basement wall.  
     
     
         37 . A multi-level foundation for a structure comprising: 
 a first level further comprising a first concrete slab, an exterior concrete basement wall on a perimeter edge of said first concrete slab, and a means for post-tensioning said first concrete slab;    at least one additional level further comprising a second concrete slab;    a means for structurally integrating said first level with said at least one additional level to form a unitary structure; and    wherein at least one of said levels is below grade.    
     
     
         38 . The multi-level foundation of  claim 37  wherein said at least one additional level supports a garage.  
     
     
         39 . A structure comprising: 
 a below-grade concrete foundation; and    a means for post-tensioning said foundation;    wherein effects of expansive soil on said foundation are mitigated by said foundation by a combined force of said structure and said below-grade foundation counter to the expansive soil.    
     
     
         40 . A foundation system for a structure comprising: 
 a post-tensioned concrete slab seated directly on soil below grade;    an exterior concrete foundation wall positioned on a perimeter edge of said post-tensioned concrete slab; and    wherein said foundation system counteracts forces created by expansion of the soil.    
     
     
         41 . The foundation system of  claim 40  further comprising at least one post-tensioning cable, wherein at least a first portion of said at least one post-tensioning cable extends within said exterior concrete foundation wall and at least a second portion of said at least one post-tensioning cable extends within said post-tensioned concrete slab.  
     
     
         42 . The foundation system of  claim 40  further comprising at least one internal concrete buttress generally normal to said exterior concrete foundation wall.  
     
     
         43 . The foundation system of  claim 40  further comprising: 
 an extension of said post-tensioned concrete slab; and  
 at least one counterfort defined by a concrete member formed upon and generally normal to said extension of said post-tensioned concrete slab.  
 
     
     
         44 . The foundation system of  claim 43  further comprising a window opening located in said exterior concrete basement wall, wherein said counterfort defines a window well around said window opening.  
     
     
         45 . The foundation system of  claim 43  further comprising a sump pump opening in said extension of said post-tensioned concrete slab, wherein said counterfort defines a sump pump well around said sump pump opening.  
     
     
         46 . The foundation system of  claim 40  further comprising at least a second concrete slab structurally integrated with said post-tensioned concrete slab.  
     
     
         47 . A counterfort comprising: 
 an extension of a post-tensioned concrete slab beyond a wall of a foundation supported by said post-tensioned concrete slab, wherein said extension of said post-tensioned concrete slab is poured directly on soil of a basement excavation; and    a concrete member formed upon and generally normal to said extension of said post-tensioned concrete slab.    
     
     
         48 . The counterfort of  claim 47 , further comprising an opening in said extension of said post-tensioned slab for housing a sump pump.  
     
     
         49 . The counterfort of  claim 47 , wherein said concrete member forms a window well.  
     
     
         50 . The counterfort of  claim 49 , further comprising an opening in said extension of said post-tensioned slab for housing a sump pump.  
     
     
         51 . A foundation beam for a structure comprising: 
 a concrete sub-beam;    a concrete slab formed upon said concrete sub-beam;    a concrete wall formed upon said concrete slab; and    a tendon of which a first portion extends within said concrete sub-beam, a second portion extends within said concrete slab, and a third portion extends within said concrete wall; wherein    when tensioned, said tendon structurally integrates said concrete sub-beam, said concrete slab, and said concrete wall into said foundation beam.    
     
     
         52 . The foundation beam of  claim 51 , wherein said concrete slab is post-tensioned.  
     
     
         53 . The foundation beam of  claim 51 , wherein said concrete sub-beam, said concrete slab, and at least a portion of said concrete wall all formed below grade.