This program provides a complete and detailed analysis of rectangular footings subjected to axial, horizontal shear and moment loads about one or both axes. The program can also handle:

 

A column pedestal and equivalent column dimensions can be entered to identify location of shear transfer to footing and dimensions used to calculate beam and punching shear stresses.

 

The user can select whether the analysis should be performed by applying lateral and moments separately about both axes, or if a full biaxial soil pressure/shear/moment analysis is required. When a biaxial analysis if performed, skew bending theory is correlated with Esling's equations to generate a neutral axis and soil pressure matrix at 2,500 points under the footing. This pressure grid is then used to calculate maximum shears and moments.

 

Final calculations give results for ACI load factor combination equations 9-1, 9-2, and 9-3 simultaneously. One way shears, two-way shears, bending moments, reinforcing requirements at all four sides, and overturning stability ratios about both axes are given.

 

 

 

Basic Usage

 

 

Unique Features

 

Assumptions & Limitations

 

 

Example

The data entry for this example is shown in the screen captures that accompany the Data Entry Tabs and Results & Graphics Tabs sections to follow.

 

Data Entry Tabs

This set of tabs provides entries for all input in this calculation. While you are entering data and switching between these tabs you can view the desired resulting information on the tabs on the right-hand side of the screen (calculated values, sketches, diagrams, etc.). A recalculation is performed after any entry data is changed. After each data entry you can view the results on the right-hand set of tabs.

 

General Tab

 

 

Allowable Soil Pressure

Enter the maximum allowable soil bearing pressure for static (not short term) loading.

 

Short Term Increase

If a short term increase in soil pressure will be allowed, enter the multiplier here.

 

Seismic Zone

This entry is used to control overall ACI load factoring. When wind loads generate the short-term forces, enter a 0" here. When seismic loads generate the short-term loads, enter 1" through 4" here to indicate the UBC seismic zone. When zone 3 or 4 is used, the special load factoring provisions of the UBC section 2625 are applied.

 

Biaxial Analysis

This YES/NO flag instructs the program whether or not to combine all loads and moments simultaneously about each axis when performing the analysis. If you answer NO, the moments and shears about each axis are applied separately to produce maximum soil bearing pressures.

 

Combine LL & ST

This entry instructs the program when to include live load with short-term loads. Typically, wind load analysis will include live load, while short-term loads due to seismic forces are usually not combined with live loads.

 

Concrete Weight

By entering a non-zero number here, the weight of the footing will be included in soil bearing pressure, shear, and bending calculations.

 

f'c

Allowable compressive stress for the concrete.

 

Fy

Allowable yield stress of the reinforcing steel

 

Rebar CL to Soil

Enter the distance from the bottom of the footing to the centerline of the reinforcing. This will be subtracted from the footing thickness to calculate rebar d distance when determining required reinforcing and shear depths/distances.

 

Minimum Steel %

Enter the minimum percentage of steel reinforcing that you wish to use when determining required reinforcing area. See As Required for a discussion of how this item is used.

 

 

Loads Tab

 

 

Axial Loads

You can apply a dead, live, and short-term axial load to the footing. These loads will be DL+LL and DL+ST+[LL] combinations when calculating maximum bearing pressures.

 

Eccentricity

This eccentricity specifies the distance the column is shifted from the center of the footing. These eccentricities will cause the axial loads to induce moments onto the footing.

 

Overburden Weight

This represents an applied uniform surcharge load over the footing. It can be from soil, concrete slab, or storage loads.

 

Moments

This program allows you to apply dead, live, and short-term moments at the footing centerline. Positive moments will cause higher soil pressures at the top and right side of the footing. This corresponds to the +Y and +X directions.

 

Shear

You can also apply horizontal dead, live, and short-term shears at the plane of the top of the footing. To calculate the actual overturning moments due to these loads, the shears are multiplied by the Footing Thickness + Base Height. Positive shears will cause higher soil pressures at the top and right side of the footing. This corresponds to the +Y and +X directions.

 

 

ACI Factors Tab

This tab specifies the load factors to be used by the program when calculation the factored dead, live, and short term loads to be used in the internal load combinations for determining Mu & Vu.

 

 

Results & Graphics Tabs

This set of tabs provides the calculated values resulting from your input on the "Data Entry Tabs". Because a recalculation is performed with each data entry, the information on these tabs always reflects the accurate and current results, problem sketch, or stress/deflection diagram.

 

 

Summary Tab

This section summarizes the results of the analysis. For each loading direction, the maximum service and factored soil pressures are given for both static and short term loading. Notice that for service load bearing pressure, only DL+LL and DL+[LL]+ST are used as load combinations. For factored load pressures, ACI equations C-1, C-2, and C-3 are used. When a biaxial analysis is used, the pressures at left, right, top, and bottom reflect all loads applied at once. For non-biaxial analysis, the loads are applied about each axis separately to give separate maximum Left/Right and Top/Bottom pressures.

 

 

 

 

Max. & Allow Pressure

This is the absolute maximum service load soil pressure for both load conditions as presented in the area titled Service Load Pressure within the summary box.

 

X Ecc. &Y Ecc.

These eccentricities are the location of the total vertical force resultant considering axial load eccentricity, and applied moments and lateral shears. This eccentricity is measured from the footing centerline.

 

Mu

Maximum factored moments created about all four sides of the footing from factored soil pressures generated by ACI equation 9-1, 9-2, and 9-3.

 

Vu: 1 Way

By using the Column Dimension values to determine the shear plane for one-way bending, this is the maximum shear by checking all four sides of the footing and all three ACI equations.

 

Vu:2 Way

By using the Column Dimension values to determine the punching shear perimeter area, this is the maximum punching from checking all three ACI equations.

 

Overturning Stability

Factor of safety against overturning by applying the loads and moments about each axis. Biaxial analysis has no effect on this number. 999" indicates there is no overturning.

 

Service Load Pressures

This table shows the actual service load soil pressures at all four sides of the footing due to static and short-term load combinations.

 

Factored Load Pressure

This table shows the actual factored load soil pressures at all four sides of the footing by combining all loads into ACI load combinations 9-1,9-2, and 9-3.

 

Sketch Tab

This tab provides a sketch of the beam with loads and resulting values shown. Using the [Print Sketch] button will print the sketch in large scale on a single sheet of paper.

 

 

 

Printing Tab

This tab allows you to control which areas of the calculation to print. Checking a box will signal that the information described by the item will be printed. However, if there is no information in for a particular selection it will not be printed. So these checkboxes are best described as "If this particular area of the calculations contains data then print it".

 

 

 

Sample Printout