Wall Footing Definitions

Wall footings consider soil loading and exterior loads to design both the wall stem and footing for concrete design, and consider overturning and sliding serviceability considerations.

Here we will explain the Wall Footing Definitions editor and spreadsheets, found on the Data Entry toolbar or the Spreadsheets drop-down list. Note that you can have multiple wall footings in a given project that may require multiple definitions.

The Wall Footing Definitions spreadsheet and editor are always synchronized. Making changes from one will update the other.

Here we will explain what each of these options mean.

Note:

General Tab

Here are some general considerations for wall footings:

Label

This label provides a unique name for each wall footing definition. Note that there is a red arrow that is available to click on. Clicking this arrow will open the Wall Footing Definition Editor. See below for more information on this dialog.

Wall Type

This allows you to choose between a retaining wall element and a strip footing element. See the Wall Footings - Modeling topic for more information on this.

Wall Const

This allows you to choose between a concrete or a masonry retaining wall.

Wall Material

This is the wall material for the wall. If a concrete wall is selected the concrete materials will be available. Similar with masonry.

Foot Material

This is the concrete material for the footing.

Wall Height

This is the wall height from the top of footing.

Soil Height

This is the height of the backfill behind the wall taken from the top of the footing for a retaining wall. This is the soil height on both sides of the wall above the footing for a wall footing.

Water Height*

This is the height of water behind the wall taken from the base of the footing. If this is input as zero (fully drained condition), then the water table will be assumed to occur below the bottom of footing or shear key.

Propped?*

This defines whether the top of the wall is propped. If the wall is propped it is assumed the base is also restrained laterally and sliding and overturning checks for the wall are omitted.

Foot Restrained?*

This defines whether the bottom of the footing is restrained laterally (i.e. a basement slab is poured adjacent to the wall). If so then the sliding check will be omitted.

Wall/Foot Continuity?*

This defines whether the wall and footing are assumed to be monolithic. If the wall and footing are monolithic (the Yes option) then we will not do a shear friction check for the dowels from the footing to the wall. If the wall and footing are not monolithic, then we will do a shear friction check. Smooth versus rough defines whether the footing at the location where the wall is poured has been intentionally roughened or not. This affects the shear friction calculation. For more information see the shear friction check section in the Wall Footings - Design topic.

Foot Dowels*

The number of layers defines whether there are dowels in both faces of the wall, or only the interior face (soil face). This input is only required if the footing and wall are NOT monolithic. If that is the case then the shear friction check at the base of the wall requires an area of steel for the dowel bars. The program assumes that the dowels from the footing into the wall will match the wall reinforcement and calculates Avf accordingly.

Geometry Tab

Here are some geometry inputs.

Wall Thickness

For concrete walls it is possible to batter the wall. This thickness excludes the battered portion and would be the thickness at the top of the wall.

For masonry this field is the block nominal thickness and must be set to 4, 6, 8, 10 or 12 inches. The program will subtract 3/8" from this value to get the actual thickness. This value is used, along with the value of grout / bar spacing, to determine the effective thickness of the wall. The effective thickness is based on table B3 of the Reinforced Masonry Engineering Handbook, by Amrhein, Copyright 1998.

Note:

Foot Thickness

This is the footing thickness.

Toe/Heel Length

This is the length of the footing from the outer/inner face of the wall.

Note:

Key Width/Depth*

These are the dimensions of the shear key if there is one. If either of these dimensions is zero then no key will be considered.

Key Offset*

This is the offset of the key from the inside (soil) face of the wall. A positive dimension will move the key in the heel direction. A negative dimension will move the key in the toe direction.

Wall Batter?

This allows you to slope the toe face of the wall, the heel face, or both.

Note:

Toe/Heel Batter

If you've chosen to batter the wall from the Wall Batter? section then this is where you can define the batter dimension. This value is an additional thickness from the Wall Thick entry, at the base of the wall.

Soil Tab

Here are the soil parameters.

Method (Rankine or Coulomb)*

Here you have the choice of how you want lateral earth pressures calculated. Note that if you want seismic forces applied to your retaining wall Coulomb must be selected.

Note:

Gamma Heel/Gamma Toe

These are the soil densities on both the heel and toe sides of the wall for a retaining wall. For a strip footing the Gamma Heel value is used for both the heel and toe.

Phi Heel/Phi Toe*

This is the internal angle of friction of the soil on both the heel and the toe sides of the wall. This is used, along with the backfill angle, in determining the lateral force coefficient (K). Note that there is a K input field. If this field is input then we will override the calculation and simply use the input K value. For more information on this see Soil Considerations in the Wall Footings - Design topic.

K Lat Heel/K Lat Toe*

This allows you to directly input the soil lateral force coefficient, K, for the soil on the heel and toe sides. You can leave this blank and the program will calculate K for you, using the Phi and Backfill Angle values. For more information on this see Soil Considerations in the Wall Footings - Design topic.

Delta Wall*

This is the wall friction angle. It is used only if Coulomb is set for the Lateral Pressure Method. For more information on how this is used see Soil Considerations in the Wall Footings - Design topic.

Note:

Backfill Angle*

This is the slope angle of the backfill on the heel side from horizontal. A negative slope is not allowed.

Heel Surcharge*

This is a vertical surcharge pressure on the soil adjacent to the heel side of the wall and is always considered in the LL load category.

Toe Depth*

This is the soil depth above the top of footing on the toe side of the wall. If this is set to zero, then the soil level will be assumed at the bottom of footing elevation. Thus, if there is a shear key, you can consider the passive pressure only on the key.

EQ Max*

This is used for seismic loading and, if input, would define the maximum earlhquake pressure at the top of an inverted earthquake pressure diagram. If this value is blank the program will use Kh and calculate the seismic forces per the Mononobe-Okabe formulation. Seismic forces are described in the Wall Footings - Design topic.

Note:

Kh*

This is the design horizontal ground acceleration (in units of g). This is an input into the Mononobe-Okabe seismic force calculation method. For more information on this procedure see the Wall Footings - Design topic.

Note:

Gamma Sat/Phi Sat Heel/K Lat Sat Heel*

These inputs are only considered if the water height is greater than zero. These are the soil parameters in the saturated portion of soil. If K Lat Sat Heel is left blank, the program will use the Phi Sat Heel and the Backfill Angle to calculate K. For more information on this see Soil Considerations in the Wall Footings - Design topic.

Wall Tab (Conc)

This tab is only used if your wall is made of concrete to define reinforcement parameters.

Location

This defines whether you have a single layer of reinforcement or bars each face.

Int Bar and Ext Bar

This defines the vertical bar on the interior (soil) and exterior faces of the wall. If you have defined a single layer of reinforcement then the Ext Bar field will not be used.

Min/Max Int and Ext Bar Space

The program will design the vertical reinforcement spacing based on these guidelines. If you want the reinforcement to be at an exact spacing, enter that spacing as both the min and max in order to force this spacing.

Note:

Bar Inc

This is the spacing change increment that the program will use for design. If the maximum spacing does not work, the spacing will drop by this increment and be checked again. The program will work its way down until it reaches a spacing that meets all reinforcement requirements.

Int and Ext Cover

These are cover dimensions for the interior (soil) and exterior faces of the wall. If you have defined a single layer of reinforcement then the exterior cover will not be used.

Hor Bar Size and Hor Bar Spacing

This defines the bar size and spacing of the horizontal bars in the wall. The program will check that these bars meet minimum requirements.

Note:

Outer Bars

This defines whether the vertical or horizontal bars in the wall are nearest the faces of the wall. This affects the "d" calculation for the wall. If you have defined a single layer of reinforcement then this field will not be used and it will be assumed that the vertical bar is nearest the inside (soil) face.

The images below are a section cutting horizontally through the wall.

Horizontal

Vertical

Wall Tab (Masonry)

This tab is only used if your wall is made of masonry to define reinforcement and design parameters.

Block Grouting

This option defines how the wall is grouted. If "Partially Grouted" is chosen, then the spacing of grout will be based on the Bar Spacing Min/Max..

Reinforced

This defines whether the wall is reinforced or not. Note that if the wall is unreinforced the program will also consider the wall ungrouted.

Wall Area Method

This option defines where the wall area is taken from. The NCMA option pulls the An value from the NCMA TEK 141B document. The RMEH option pulls the "Equivalent Solid Thickness" value from Table B-3a and B-3b from the Reinforced Masonry Engineering Handbook, James Amrhein, 5th edition copyright 1998.

In doing research on these two methods of calculating the area for a masonry wall, the two methods produce very different results. The NCMA values assume face-shell mortar bedding and web bedding around grout-filled cells. The RMEH values assume full mortar bedding (both face-shells and all webs). The Amrhein values also appear to average in the area of horizontal bond beams as well. This would make the area conservative for a self-weight calculation, but unconservative for stress calculations. With these considerations in mind we are defaulting the behavior to use NCMA.

See the Masonry Wall - Design topic for the specific calculations regarding NCMA or RMEH.

Note:

Bar Size

This is the main vertical bar size that will be used for design.

Bar Space Min/Max

This allows you to give a maximum and minimum bar/grout spacing. If you give a range between the max and min, then the program will optimize the reinforcement spacing according to code check requirements.

Bar Placement

This defines how the reinforcement is placed in the wall.

Center will put a single bar centered in a given cell.

Non-Center will put a single bar non-centered in a given cell.

Each Face will put reinforcement on both faces of a given cell.

Staggered alternates the bars on either face along the length of the region.

Note:

Cover

Allows you to specify the distance from the exterior of the masonry block to the extreme fiber of the reinforcement. The default cover value is defined as Min. The Min input will use whichever governs between these two sections of the specification:

Thus, the Min term will create a cover equal to the maximum of tfaceshell + 1/2" OR 1-1/2".

For any other cover you wish to impose simply overwrite the Min value with your value. If using the Non-Center option then the cover will always be from the +z local axis face of the wall.

For example, let's assume the wall shown below is using the "Non-Centered" reinforcement and the cover is set to 2.5". The image below shows exactly where this bar is then located in the wall (d = 7.625" - 2.5" - 3/8" = 4.75").

 

The actual "d" used in design will depend on the governing direction of loading.  If load is applied in both out-of-plane directions to the wall then it is possible that a lower level of loading can produce a higher code check because the "d" is smaller in one direction than the other.

If a non-sensical value is defined (i.e. one where the bar does not fall inside of the block core then the program will give an error in the results and place the reinforcement just inside the faceshell of the block.

Note:

Mortar/Cement Types

Allows you to specify the type of mortar/cement in the wall. This affects the modulus of rupture (flexural tensile stresses) from Tables 8.2.4.2 and 9.1.9.2.

Footing Tab

Here are footing reinforcement parameters.

Location

This defines whether you have a single layer of reinforcement or bars both top and bottom.

Bot Bar and Top Bar

This defines the bottom and top bar sizes in the footing. If you have defined a single layer of reinforcement then the Top Bar field will not be used.

Min/Max Bot and Top Bar Space

The program will design the main footing reinforcement spacing based on these guidelines. If you want the reinforcement to be at an exact spacing, simply enter that spacing as both the min and max in order to force this spacing. If you have defined a single layer of reinforcement then the top min and max spacing will not be used.

Bar Inc

This is the spacing change increment that the program will use for design. If the maximum spacing does not work, the spacing will drop by this increment and be checked again. The program will work its way down until it reaches a spacing that meets all reinforcement requirements.

Top Cover and Bot Cover

These are cover dimensions for the footing. If you have defined a single layer of reinforcement then the top cover dimension will not be used.

Long Bar Size and Long Bar Spacing

This defines the bar size and spacing of the longitudinal bars in the footing. The program will check that these bars meet minimum requirements.

Note:

Wall Footing Definition Editor

The Wall Footing Definition Editor provides a way to create or modify wall footing definitions in a graphical way. This editor automatically updates any information input into the Wall Footing Definitions spreadsheet.

Note:

General/Geometry tab for Retaining Walls

 

General/Geometry tab for Strip Footings

 

Soil tab not applicable for Strip Footings

 

Details tab applicable for Concrete Retaining Walls

and Strip Footings

Details tab applicable for Masonry Retaining Walls

and Strip Footings

Accessing the Wall Footing Editor

To access this editor you can click the red arrow on any tab in the Wall Footing Definitions spreadsheet (click in the Label column to make the red arrow appear).

This dialog can also be accessed from the Draw Wall Footings dialog as well by clicking either of these buttons.