Footing Design Sub-tab

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Footing Design Sub-tab

Footing Size & Materials

 

Toe Width: This is the width of the Toe of the footing, and is measured from the front edge of the footing to the front face of the stem. Can be set to 0.00 for a property line condition. All overturning and resisting moments are taken about the bottom-front edge of the toe.

 

Heel Width: Distance from front face of stem to back of heel projection. If a dimension is entered that is less than the stem width at the base, the program will automatically reset the heel dimension to at least the stem width. For a property line at the rear face of the stem, set this dimension to be equal to the stem width.

 

Total Footing Width: The calculated width of the footing, Toe Width + Heel Width.

 

Thickness: Total footing thickness, NOT including the key depth (if used). For bending and shear design of the footing, the rebar depth "d" is taken as Footing Depth - Rebar Cover - ½" (the additional 1/2" is to account for the rebar radius). If footing thickness is inadequate for shear capacity a red warning indicator will appear.
 
The footing thickness must be greater than the hooked rebar embedment length required for the bottom stem reinforcing + rebar cover. The program adds the calculated hooked bar embedment from the Stem screen and adds it to the rebar cover you have chosen for the bottom of the footing (usually 3"). If the specified thickness is inadequate, increase the thickness, or change the stem dowels.

 

Center Stem on Footing: Clicking this bar will adjust the toe and heel widths you have entered so the stem is centered on the footing but the overall footing width remains the same.

 

Automatic Width Design: Clicking this button will cause the program to iterate footing widths until the soil pressure and footing strength are acceptable. (Note:  This function does not optimize for overturning stability or sliding stability, so those will need to be checked after using this option.)  You can select either a fixed toe or heel distance, or balance the toe and heel dimensions. You can also select whether the resultant must be within the middle third of the footing. After clicking “Design,” the widths required will be displayed. Automatic footing design is not available for Restrained Walls, Gravity Walls, or Segmental Walls.

 

f'c: Enter concrete compressive stress for footing.

 

Fy: Allowable rebar yield stress to be used for design of footing bending reinforcement.

 

Rebar Cover in Heel/Toe: Distance from the face of concrete to edge of rebar. The program will add 1/2" to this value and subtract the result from the footing thickness to determine the bending "d" distance.

 

Minimum Temperature & Shrinkage As Percentage: Enter the minimum steel percentage to address temperature and shrinkage requirements in the footing (commonly 0.0018 Ag for Fy= 60,000 psi). If the % steel required by stress analysis is less than 200/Fy, the minimum of (200/Fy -or- 1.333 * bending percentage required) is calculated and compared with the Minimum Temperature & Shrinkage As% entered here, and the greater of the two is used to calculate rebar spacing requirements.

 

Neglect Upward Pressure at Heel: For heel calculations you may choose to neglect the upward soil pressure, typically resulting in greater heel moment. If this box is checked the Mu for upward loads will be zero.

 

 

Footing Rebar Requirements

 

Rebar at Stem Base: This is a reminder of the size and spacing of the reinforcing used at the bottom of the stem, to make it easier to select toe reinforcing to match (toe reinforcing is usually the bottom stem dowel bars bent toward the toe).

 

Toe Reinforcing Options: This list provides options for reinforcing sizes and spacing for the toe bars (located in the bottom of the footing). Typically the toe bars are extensions of the stem dowels, which are bent out toward the toe. Therefore, you will probably just want to verify that the stem dowel bar size and spacing would also be adequate for use in the toe.
NOTE: If “No reinf’ req’d” message appears, it means the flexural capacity of the footing (modulus of rupture times the section modulus, with 2” deducted from the thickness for crack allowance per code) is adequate to resist the applied moment. However, the designer in some cases may consider it prudent to add reinforcing regardless of the theoretical flexural capacity.  For plain concrete per ACI 22.5.1, Fr = Φ5λ(f’c)1/2.

 

Heel Reinforcing Options: This list provides options for acceptable sizes and spacing for heel bars (located in the top of the footing). It is desirable to select a spacing that is modular with the stem dowel bars for ease of construction. Note: The program does not calculate the heel bar development length inward from the back face of the stem (where the moment is maximum). You can refer to Appendix B for development lengths in concrete, which can be adjusted for the stress level in the heel bars. When detailing footing reinforcing it is important to consider and specify development lengths for both toe and heel bars.
 
NOTE: If “No reinf’ req’d” message appears, it means the flexural capacity of the footing (modulus of rupture times the section modulus, with 2” deducted from the thickness for crack allowance per code) is adequate to resist the applied moment. However, the designer in some cases may consider it prudent to add reinforcing regardless of the theoretical flexural capacity.

 

Rebar Selections: Use these three size and spacing entries to select your toe, heel, and if applicable, key reinforcing. The "Max @" message tells you the maximum spacing allowed for the bar selected.