Pile cap design workflow
Pile cap design workflow
The small concrete building model shown below will be used to demonstrate the pile cap design process.
The model has already been designed prior to placing the pile caps.
Apply pile caps under supported columns
Before a pile cap can be placed the Pile Type Catalogue must contain at least one pile type.
Pile caps can only be placed under and be loaded by supported columns.
If a ground beam is attached to the same support, loading from the beam will also be considered in the pile cap design.
At this stage, as you are not aware of the individual pile cap size and depth requirements; you can simply choose to place pile caps where required, accepting the default size/depth offered.
Auto-size pile caps individually for loads carried
To obtain an idea of the range of potential sizes, pile caps should initially be designed individually for their respective loads
Note that when piles are auto-designed the outcome will depend on the auto-design method selected; the pile cap size will either be based on the minimum number of piles required, or on the minimum pile capacity.
To individually size the pile caps:
- In the Design Settings dialog box got to Concrete> Foundations> Isolated Foundations > Piles to choose the pile auto-design method required: (minimize pile capacity, or minimize number of piles).
- Access Design Groups page of the Design Settings dialog box to ensure that group design is turned off for Isolated Foundations.
Select the pile caps to be auto-sized and then in the Properties Window choose to auto-design both the piles and depth; In this way the program will establish suitable pile cap dimensions for you.
Similarly, the reinforcement can be set to be auto-designed in the same manner.
- From the Foundations tab, click Design Pile Caps and all the pile caps set in auto-design mode will be sized accordingly. (Those not in auto-design mode will simply be checked). Similarly the piles beneath the pile caps will either be designed (if pile auto-design mode is enabled) or checked.
At any point you can switch to a user defined arrangement, modify the pile cap configuration and have the design re-checked.
One example where you might choose a user defined arrangement is where the site boundary imposes restrictions on the positioning of the pile cap relative to the column/wall it supports. Switching to a user defined arrangement allows you to specify an eccentricity and create an offset pile cap.
In the current release lateral stability of piled foundation systems is not considered in software design checks.
Apply grouping to rationalize pile cap sizes
Once pile caps have been sized individually, the designs can be rationalized by activating grouping, in order to obtain one design per group sufficient for all pile caps within the group.
This is done as follows:
- Select a pile cap that you want to be in a particular group.
- In the Properties Window, ensure it is set to auto-design.
- Right-click the same pile cap and from the context menu choose Create Property Set...
Select all the other pile caps that you want to be in the same group.Note:
When applied moments are significant, be cautious when grouping pile caps where auto-design has initially determined different principal directions.
In the Properties Window, click Apply... to apply the property set you have just created to the selected pile caps.Note:
Ensure you click Apply... from the Properties Window and not from the right-click menu, otherwise the properties will only be applied to the last pile cap selected.
- From the Groups page of the Project Workspace, right-click Pile Caps (under the Design branch) and choose Regroup Members - this will put those pile caps that share similar properties into the same group.
- Open the Design Settings dialog box, and from the Design Groups page select the option to design isolated foundations using groups.
Click Design Pile Caps - the results obtained will reflect the grouping that has been applied.
Review/optimize pile cap design
In the Review View you can graphically examine the pile cap design status & efficiency by switching between Foundations Status and Foundations Ratio. Note that the tool tip also indicates the base size and status as you hover over any base.
Similarly you can graphically examine the pile design status & efficiency by switching between Piles Status and Piles Ratio.
If the selections are unacceptable you may need to review the settings in Design Options> Concrete> Foundations.
Design results can be examined in more detail by selecting Tabular Data and setting the View Type to Design Summary. By selecting the Pile Caps or Piles as the Characteristic (and the appropriate material) the full results for each pile cap or pile can be examined.
Create drawings and quantity estimations
Drawings that convey the structural intent are easy to create. It should be borne in mind that these are NOT the final detail drawings, their purpose is to eliminate the need for manual mark-up drawings as a means of communication between the engineer and the detailer.
Create a model report that includes the concrete pile cap design calculations that have been performed. (The default Building Design report includes these along with design calculations for other member types in the model).