Slab-on-ground foundation design method

Abstract

This disclosure describes the invention of an improved WRI slab-on-ground foundation design method. The improved rational design method integrates any combination of rebar, wire mesh, and post-tensioned cable reinforcements into the foundation design. According to the method, cantilever lengths are derived for at least one rectangular section of a foundation for a structure. Foundation design loads typically consist of uniformly distributed loads. The invention adds the capability to include line loads representing loads transmitted to the foundation. Foundation design quantities such as moments, shears, and deflections are calculated from uniformly distributed loads. Moments, shears, and deflections from line loads are added to these design quantities. A deflection multiplier for the foundation deflections from line loads is employed for compatibility with WRI design procedures. A cracking potential of a foundation was formulated as a function of tensile stresses.

1 . A slab-on-ground foundation design method, comprising the steps of: 
 specifying a preliminary design for a foundation, the preliminary design defining at least a shape and dimensions of said foundation and at least one reinforcing element selected from a group consisting of rebar, and post-tensioned cable and design loads on said foundation including design line loads due to a structure to be built on said foundation;    identifying soil conditions for a given construction site;    deriving, based on said soil conditions, at least one cantilever length for at least one rectangular section of said foundation;    calculating a uniformly distributed unit weight for said foundation as well as its design loads based on said preliminary design;    calculating an all-in structural weight including said design loads of said structure;    calculating design moments, shears, and deflections based on said cantilever lengths, said uniformly distributed unit weight of the foundation, and said design loads on the foundation;    applying corrections to said design moments, shears, and deflections based on said design line loads and any loads attributable to post-tensioned cable to obtain corrected design moments, shears, and deflections for all loads on the foundation; and    evaluating said preliminary design in view of said design moments, shears, and deflections and said corrected design moments, shears, and deflections.    
   
   
       2 . The method of  claim 1 , wherein, in applying corrections to said deflections, a deflection multiplier is used for compatibility with WRI deflection formulas.  
   
   
       3 . The method of  claim 1 , wherein said line loads represent loads transferred to said foundation through exterior walls of said structure.  
   
   
       4 . The method of  claim 1 , wherein said line loads represent loads transferred to said foundation though interior walls of said structure.  
   
   
       5 . The method of  claim 1 , further comprising the step of calculating foundation bearing loads based on said all-in structural weight and said cantilever lengths that are used to evaluate if the soil bearing capacity is adequate to carry the vertical loads.  
   
   
       6 . The method of  claim 1 , further comprising the step of using said design moments, shears, and deflections, and said corrected design moments, shears, and deflections, to determine design properties for a slab-on-ground foundation.  
   
   
       7 . The method of  claim 6 , wherein said design properties are used to evaluate a number and width of beams of said preliminary foundation design.  
   
   
       8 . The method of  claim 6 , wherein said design properties are used to evaluate an amount of steel reinforcement of said preliminary foundation design.  
   
   
       9 . The method of  claim 6 , wherein said design properties are used to evaluate an amount of post-tensioned cable reinforcement of said preliminary foundation design.  
   
   
       10 . The method of  claim 6 , wherein said design properties are used to evaluate an amount of both steel reinforcement and post-tensioned cable reinforcement of said preliminary foundation design.  
   
   
       11 . The method of  claim 1 , further comprising the step of evaluating any combination of steel reinforcement elements and post-tensioned cable reinforcement elements in a slab-on-ground foundation design to satisfy strength and deflection requirements compatible with said design moments, shears, and deflections, and said corrected design moments, shears, and deflections.  
   
   
       12 . A computer program product comprising a computer-usable medium having computer-readable program code embodied thereon, the computer-readable program code including computer instructions for: 
 inputting preliminary design properties of a preliminary design for a foundation, the preliminary design defining at least a shape and dimensions of said foundation and design loads on said foundation including line loads due to a structure to be built on said foundation;    identifying soil conditions for a given construction site;    calculating, based on said soil conditions, and displaying at least one cantilever length for at least one rectangular section of said foundation;    calculating a uniformly distributed unit weight for said foundation based on said preliminary design;    calculating an all-in structural weight including said design loads of said structure;    calculating and displaying design moments, shears, and deflections based on said cantilever length, said uniformly distributed unit weight of the foundation, and said design loads on the foundation;    applying corrections to said design moments, shears, and deflections based on said design line loads to obtain corrected design moments, shears, and deflections for all loads on the foundation; and    displaying said corrected design moments, shears, and deflections.    
   
   
       13 . The computer program product of  claim 12 , wherein said computer-readable program code further comprises computer instructions for deriving an equivalent Plasticity Index from said soil conditions.  
   
   
       14 . The computer program product of  claim 12 , wherein said computer-readable program code further comprises computer instructions for deriving a Potential Vertical Rise from said soil conditions.  
   
   
       15 . The computer program product of  claim 12 , wherein said computer-readable program code further comprises computer instructions for: 
 computing a total load on soils supporting said foundation and said structure from a combination of at least the weight of the structure including its foundation and said design loads to compute soil bearing stresses; and    displaying factors of safety for said bearing stresses with respect to the soil bearing capacity.    
   
   
       16 . The computer program product of  claim 12 , wherein said line loads include loads on said foundation due to exterior walls and loads supported by the exterior walls of said structure.  
   
   
       17 . The computer program product of  claim 12 , wherein said line loads include loads on said foundation due to interior walls and loads supported by the interior walls of said structure.  
   
   
       18 . The computer program product of  claim 12 , wherein said computer-readable program code further comprises computer instructions for using said design moments, shears, and deflections, and said corrected design moments, shears, and deflections, to evaluate the design properties of the preliminary (ribbed) slab-on-ground concrete foundation design.  
   
   
       19 . The computer program product of  claim 18 , wherein said preliminary design properties specify a number and width of beams in said foundation.  
   
   
       20 . The computer program product of  claim 18 , wherein said preliminary design properties specify an amount of steel reinforcement in said foundation.  
   
   
       21 . The computer program product of  claim 18 , wherein said preliminary design properties specify an amount of post-tensioned cable reinforcement in said foundation.  
   
   
       22 . The computer program product of  claim 18 , wherein said design properties describe a foundation design that includes at least one reinforcement element selected from a group consisting of steel reinforcement elements and post-tensioned cable reinforcement elements.  
   
   
       23 . The method of  claim 12 , wherein said computer-readable program code further comprises computer instructions for applying a combination of at least one reinforcement element, selected from a group consisting of steel reinforcement elements and post-tensioned cable reinforcement elements, in a (ribbed) slab-on-ground foundation design to indicate that strength and ductility and deflection requirements according to said design moments, shears, and deflections are satisfied.  
   
   
       24 . The method of  claim 12 , wherein said computer-readable program code further comprises computer instructions for using said design moments, shears, and deflections to evaluate said preliminary foundation design.  
   
   
       25 . A method of evaluating the cracking potential of a concrete slab-on-ground foundation, comprising the steps of: 
 computing an extreme tensile fiber stress caused by loading and support of said foundation;    computing at least one threshold as a function of the compressive strength of concrete (f′ c );    comparing the extreme tensile fiber stress to said least one threshold (f′ c ).    
   
   
       26 . The method of  claim 25 , wherein said at least one threshold includes a lower threshold and an upper threshold.  
   
   
       27 . The method of  claim 26 , wherein said cracking potential is determined to be low if said extreme tensile fiber stress is less than said lower threshold.  
   
   
       28 . The method of  claim 26 , wherein said cracking potential is determined to be medium if said extreme tensile fiber stress is between said lower and upper thresholds.  
   
   
       29 . The method of  claim 26 , wherein said cracking potential is determined to be high if said extreme tensile fiber stress is greater than said upper threshold.