RAM Foundation Tutorial

This section illustrates the analysis and design of the spread footings and continuous foundations in an integrated model. This section can only be completed if you have licensed and installed the RAM Foundation module. You may begin with the model that you generated in the previous portions of this tutorial, or you may open the model called RAMTutorial_v14_US.rss from the RAM Manager.

RAM Foundation Basics

To invoke RAM Foundation from the RAM Manager:

• Select Design – RAM Foundation or click the last square button on the left.

Because RAM Foundation is integrated into the RAM Structural System, it uses the same model and database as RAM Frame and RAM Steel when designing foundations. In order for the program to design the foundations, the loads must be determined by running the gravity column design and/or lateral analysis in RAM Frame. If this has not been done, do so now, then proceed with this Tutorial. While most of the information needed for foundation design is taken from the database, some data does need to be entered in the Foundation program itself.

Before foundations can be designed, the following must be defined:

• Soil Capacity.
• Base plate size for lateral steel columns.
• Width for Continuous foundations.
• At least one load combination for Concrete.
• At least one load combination for Soil.
• Pile capacity information and layout.

Once this is complete, a design can be performed, but we recommend that you review the design and optimization criteria closely first.

To establish the source for the design loads:

• Select Criteria – Forces.

Leave the Forces on Gravity Members criteria set to use the third option: RAM Steel for steel members and RAM Concrete for concrete members.

Since this model has 2 way decks RAM Steel cannot account for the loads on members underneath those decks. This is why the first option is grayed out.

To set the design criteria:

• Select Criteria – Design.
• Choose ACI 318-08 (BS8110-97) as the desired code on the Code Tab
• Click the Design tab.

These parameters have a significant effect on the way the foundations are designed. For a complete description of the option see the RAM Foundation manual. For this example:

Under Design Method:

• For Spread Footings,

Select Design footings based on applied forces (rather than soil capacity)

sub-option = Selectoptimum footing design for each column.

• For Pile Cap Footings select Design pile caps based on pile load.

Under Design Method:

• Check all three footings for Include Moments Due to Shear in Column for:
• Check: Include Spread Footing Self-Weight When Checking Soil Stress.
• Check: Keep Spread Footing Square During Optimization.
• Uncheck to Increase Spread Footing Size to Prevent Uplift in Concrete Load Combinations.
• Check to Design Continuous Footing as Beam when Footing’s Full Width to Depth Ratio is less than.
• Enter 2 for the ratio.
• Click on the Reinforcement tab

• Set the Clear Bar Spacing, Clear Bar Cover and Reinforcement Ratios to Code (as shown above)
• For Bars Sizes to Consider for Design, select
  • Shear:  #3 and #4 bars (F08 and F10)
  • Flexure: #4 through #14 (F10-F20).
• Click [OK].

Optimization Criteria

There are additional criteria that affect the design of the foundations. To set those options now:

• Select Criteria – Optimize.
  
• Set the Minimum distances from the base plate to 12 (250).
• Set the minimum from the column center to 18 (500).
• Set the Plan dimension increment to 6 (125).
• Set the minimum Thickness to 18 (500).
• Set the Thickness Increment to 6 (250).
• Set the Uplift Safety Factor to 1.
• Click on the Pile/Pile Cap tab.
  
• Set the spacing variables to 0.5, 18 and 6 (0.5, 450 and 150).
• Set the Center to Center of Piles options to 2, 32, and 24 (2, 800, 600).
• Set the Thickness options to 24, 6 (600, 150).
• Click [OK].

Assign Soil Capacity

To assign soil capacity to this model

• Select Assign – Soil.

Initially, only the Allowable Bearing Capacity option for entering the soil capacity is available. This option allows the engineer to idealize the soil capacity by using just one value to represent the soil capacity regardless of dimensions of the foundation or depth of the soil.

You can also create a soil table by using the wizard. This feature allows you to assign the modulus of subgrade reaction that affects the springs that will be used in the analysis of the footing.

To assign an Allowable Bearing Capacity:

• Enter 4 (200) in the Allowable Bearing Capacity edit box.
• Click [All].

NOTE: All of the Assign commands in RAM Foundation give the option of Single, Fence or All for making assignments. [Single] will change the cursor to the target and allow for assignments on a foundation - by - foundation basis. [Fence] will change the cursor to a rubber band. Assignments are made to foundations completely enclosed within the rubber band. [All] assigns the value to all foundations within the model. If a new foundation is added to the model it must also have a soil assignment made.

Assign Base Plate Sizes to Lateral Columns

The Assign – Base Plate Size command allows the engineer to assign different base plate sizes to different columns on a continuous foundation.

In our example the columns are mostly concrete columns with a specified size. For the gravity steel columns, base plates are already provided by the RAM Steel Column design. These sizes can be overridden with the Assign – Base Plate Size command. This size will only be used in RAM Foundation. It will NOT be exported back to RAM Steel Column Design. Additionally, once an override is made in the foundation module, this size will continue to be used by RAM Foundation even if the size is changed in RAM Steel Column Design. To update a base plate so that that the optimum base plate size is again obtained from the RAM Steel Column Design module, the “Clear User Defined Base Plate Size” option must be selected and assigned.  Upon re-running the RAM Steel Column Design, the new optimized base plate size will automatically be assigned.

Assign Geometry

The footing module allows you to assign any of the footing dimensions that you do not wish to have optimized. For spread footings, all of the dimensions may be optimized. Continuous footing design requires you to assign at least the width.

To assign the geometry of the spread foundations:

• Select Assign – Geometry – Spread.
  
• In the Assign – Spread Footing Geometry dialog box that opens, Check the Assign boxes for all three dimensions.
• Check the Optimize box for all variables.
• Click [All].

NOTE: The footing need not be centered under the column. Any of the length dimensions may be set or limited and the eccentricity will be considered in the design.

To assign the geometry of the continuous foundations:

• Select Assign – Geometry – Continuous.
  
• Check the Optimize box for lengths and thickness.
• Type 3 (1) for both width dimensions.
• Type 4 for the Number of Shear Reinforcement Legs.
• Click [All].

Assign Surcharge

Since the footing is typically underground, you can assign a surcharge load to be considered in the design. The surcharge will affect the soil check and the possibility of uplift, but does not enter into the design calculations for the foundation itself. The self weight of the foundation is automatically accounted for by the program.

To assign a surcharge:

• Select Assign – Surcharge.
  
• Type 120 (6) for the Dead Load Surcharge.
• Click [All].

Assign Pile Geometry

In order for the program to check the pile design, you must provide the unfactored capacity of the piles and the layout which should be used.

• Select Assign – Edit Piles.
  
• For the Label type 14in.
• Set the Diam to 14 (300)
• Compression capacity to 120 (500)
• Tension Capacity to 20 (100)
• Shear capacity to 5 (25)
• Click [Add].
• Click [OK].

To assign the pile cap geometry:

• Select Assign – Geometry – Pile Cap.
  
• Select the 14in pile on the left and the 3 Pile Group on the right
• Leave the other options in the default position and click [All].

Load Combinations

Before any foundations can be defined, you must specify the load combinations to consider. These may be created manually as User Defined Load Combinations or Code Generated Combinations can be utilized..

• Select Combinations – Generate for Concrete.
  
• Select IBC 2006 (BS 8110 1997) from the Code Combo list box.
• Type 0.5 for Live Load Factor
• Type 1.113 for Sds.
• Set Rho to Use Calculated.
• Choose reduced snow factor…
• Click [Generate].

The Load Combinations box should be filled with load combinations and each should be checked to Use.

• Click [OK].
• Select Combinations – Generate for Concrete.
• Select IBC 2006/ASCE7-05 (BS 8110 1997) from the Code Combo list box.
• Type 1.113 for Sds.
• Used Reduced factor for snow…
• Set Rho to Use Calculated.
• Click [Generate] and click [OK].

Design All and View/Update

The foundations should now appear yellow indicating that the foundations are all ready to be designed (with the exception of the mat foundation which can only be designed using RAM Concept). To design the foundations:

• Select Process – Design – All Footings.

The program will calculate the optimum sizes for all of the footings. When finished, each should be drawn in green and sized appropriately. Any foundations that appear in red could not be successfully designed.

This may take a few minutes to complete. Keep in mind that the program is running an individual finite element analysis of each continuous foundation considering compression-only springs representing the soil below. The progress is indicated in the status bar in the lower left hand corner of the screen. For a complete explanation of how foundations are designed by the program refer to the RAM Foundation manual.

To investigate the design of individual spread footing:

• Select Process – View/Update.

With the target cursor, select the spread footing at Grid B - 2.

The dialog box will open to the Results Tab provided a successful design was accomplished. From here you can see the size of the footing and the reinforcement required. The signal light indicating the status of the design is shown. From here you can change the sizes or the reinforcement, redesign the footing and update the model if desired.

NOTE: The orientation of the foundation in the view/update dialog box is adjusted to so that the footing length points to the right. This may not match the orientation on the plan.

• Uncheck the box marked Optimize Reinforcement. New text boxes will appear allowing you to specify the reinforcement to use.
• Select #6 for Major and Minor Axis Bar Size. Notice that the provided steel area is immediately updated and it appears red since the quantity of bars is no longer adequate.
• Type 8 for Major and Minor Axis Bar Quantity.
• Click [Redesign].
• Take a moment to become familiar with the contents of the other two Tabs: Design and Material Properties. The Design tab summarizes the current design. When there is a problem with the foundation design this page will indicate why the footing could not be designed. There is no need to change any of the Material Properties at this time.
• Click [View Results].
• The Spread Footing Design Report should appear. Read through the results.
• Close the report and return to View/Update.
• Click [Update Database].
• Click [Close].

The foundation will now appear blue since it is user assigned. Note that the arrow should still appear green. This indicates that the design is still satisfactory. If something should change later causing the foundation to fail, the arrow will change to red.

To investigate the design of individual continuous foundations:

• Select Process – View/Update.
• With the target cursor, select the continuous footing along Grid A.
  

The dialog box will open to the Results Tab provided a successful design was accomplished. From here you can see the size of the footing and the reinforcement required. The signal light indicated the status of the design as shown. In this case you have optimized for the length of the footing beyond the last column as well as the thickness. Furthermore, the top and bottom reinforcement has been selected. The reinforcement box shows what reinforcing bars have been selected. It defaults to the Longitudinal Top bars.

To change the selection:

• Select Longitudinal Reinf – Bottom from the drop down list. The data in the box should be updated for bottom bars. You can also view the transverse and shear reinforcement in this way.
• If you wish to change the bar selection – uncheck the Optimize Reinforcement box. Then you can change the numbers in the table directly.
• When finished Click [Redesign] to have the foundation checked.

Take a moment to become familiar with the contents of the other two Tabs: Design and Material Properties.

• Click [View Results] to see a complete design report for the foundation.
• Close the report when finished and click [Close] to exit the View/Update dialog box without making any changes.

To investigate the design of individual continuous foundations:

• Select Process – View/Update.
• With the target cursor, select one of the pile cap foundations.

As with the other foundations, the pile cap thickness or rebar may be altered through the view/update command.

• To see the design results, select [View Results].
• To see the maximum individual pile forces click [View Pile Forces].
• Click [Close] when finished.

Reports

Many different reports can be generated from the Foundation Module. The printed output is mostly generated using the Reports menu.

To print the service loads for a foundation design:

• Select Reports – Screen.
• Select Reports – Foundation Loads – Single.

Click the same continuous footing along Grid A. The Foundations Load report should appear. Notice that the various elements that are supported by the foundation are listed separately. For an explanation of sign convention see the Foundation manual.

• Click  to exit the report.

To print a summary of the spread footing designs:

• Select Reports – Spread Footing Design Summary.
• Click  to exit the report.

For a continuous foundation design report:

• Select Reports – Continuous Footing – Single.
• Select one of the continuous foundations.
• Click  to exit the report.

The foundation envelope report is also available from the reports menu. This report lists the maximum design forces and soil stresses along the length of the foundation. This is the same report that you see when you select [View Envelope] from the View/Update dialog box.

Take time now to review the various reports available in the Reports menu.

Thank you for taking time to complete this RAM Structural System Tutorial. Refer to the various program manuals for additional information on any aspect of the program that you do not fully understand.

• Go back to RAM Concrete Shear Wall Tutorial
• Up to the RAM Structural System Tutorial