It is possible to create multiple load combination sets and associate these sets to various footing design parameters. This topic describes how load combination sets may be used for foundation design.
Note: Creating multiple load combination sets is a Premium Edition feature and is not available in Basic or Professional Editions of Foundation3D and Mat3D. The buttons to create multiple load combination sets are only visible in the Premium Edition.
In Foundation3D and Mat3D, when a new workspace is created, the Load Combinations input page displays 3 tabs - Summary, Allowable, Ultimate.
The Summary page displays a section called Selection containing association of footing design parameters such as Bearing Capacity, Stability, Sliding, Uplift, Pile Capacity, Concrete Design to the load combination set such as Allowable or Ultimate. When a new workspace is created, default load combination sets "Allowable" and "Ultimate" are created by default and the default association between the footing design parameters and load combination set is established as follows:
Bearing Capacity, Stability, Sliding, Uplift, Pile Capacity --> Associated with Allowable load combination set
Concrete Design --> Associated with Ultimate load combination set
Each footing design parameter listed above can be associated with one and only one load combination set. For eg if Bearing Capacity is associated with Allowable load combination set, it cannot then be associated with Ultimate load combination set. If a footing design parameters is associated with a second load combination set, its association with the original load combination set is automatically broken. If a footing design parameter is associated with more than one load combination set, when Calculation button is clicked, a validation message displays stating that the footing design parameter is associated with more than one load combination set. The calculation will not proceed further until this multiple association is broken.
The load combination sets are displayed as items in the drop-down list which lists all the available load combination sets to select from.
The Summary page also provides a description on how additional load combination sets may be created and associated with the footing design parameters.
Click the default "Allowable" load combination set to display additional items such as "Name" and "Use For" properties. The "Name" refers to the name of the load combination set which by default is called "Allowable" for the Allowable load combination set. However it is possible to change the name of this load combination set to a different name.
"Use For" property displays 5 tabs - Bearing Capacity, Stability, Sliding, Uplift, Concrete Design for a soil supported foundation. For default Allowable load combination set, Bearing Capacity, Stability, Sliding, Uplift are highlighted or selected indicating that Allowable load combination set is associated with these 4 footing design parameters. Similarly clicking on the default Ultimate load combination set displays that it is associated with "Concrete Design".
For a pile supported foundation, 2 tabs will display against "Use For" property - Pile Capacity, Concrete Design. Pile Capacity is associated with Allowable and Concrete Design with Ultimate load combination set by default.
Note: In many cases, different set of calculations are performed when the "Use For" case is for Soil bearing or Pile Capacity as compared to Concrete Design. Therefore it is imperative that different load combination sets are used for these Use For cases. FOr eg the Use for case for soil bearing, stability, sliding, uplift must be on a different load combination set than that used for the Use For case of Concrete Design. Similarly the Use For case for Pile Capacity must be on a different load combination set than the one used for the Use For case of Concrete Design or else the results will not be as expected. If the same set of load combinations are to be used for say calculating Pile Capacity and Concrete Design, ensure that the load combination set for "Pile Capacity" Use For case and the one for "Concrete Design" is different even though both load combination sets contain the exact same load combinations.
Selecting the same load combination set say Allowable for both Bearing Capacity and Concrete Design Use For cases will display a message that this selection will not work. Similarly if say Allowable load combination set is used for both Pile Capacity and Concrete Design, a message will display that this selection will not work. Even if the load combinations are identical for soil bearing and concrete design, different load combination sets must be created for bearing and concrete design. Similarly different load combination sets must be created for pile capacity and concrete design use for cases.
On Load Combinations input page, a set of 4 buttons under a heading called "Combination Sets" display to the right of Workspace Commands buttons at the top of the page. The buttons allow adding, deleting, cloning a load combination set and copy the Use For case to all the footings from a source footing.
If the default Allowable and Ultimate load combination sets are adequate for foundation design, additional load combination sets need not be created. However if additional load combination sets are desired to associate a different footing design parameter with each load combination set, there are many ways to create these load combination sets as described below:
If the new load combination set that must be created to associate with a footing design parameter contains combinations very similar to the combinations in an existing load combination set with minor differences, follow the steps below:
Click on the existing load combination set so that it is the active or selected load combination set. For eg if the new load combination set must use load combinations from the Allowable set, click on the Allowable tab
Click "Clone the selected load combination set" button under the button group "Combination Sets"
A new load combination set called "User" will be created and is placed as a tab after the "Ultimate" tab or the last combination set
All the load combinations from the "Allowable" set are copied to the "User" set
Rename the "User" set to a different meaningful name. For eg if this new set is meant to be associated with Bearing Capacity, it may be named "Bearing"
Click on the appropriate "Use For" tab to associate the design parameter with this set. For eg click on "Bearing Capacity" use for tab to associate Bearing Capacity with the Bearing set
Change the load combination factors as desired to change the load combinations on this set
If a few load combinations from an existing load combination set need to be used to create a new load combination set, follow the steps below:
Click on the existing load combination set so that it is the active or selected load combination set. For eg if the new load combination set must use selected load combinations from the Allowable set, click on the Allowable tab
Using the "Ctrl" and "Shift" keys on the keyboard, select the load combinations that need to be used to create the new load combination set
Click the button "Clone the selected Load Combinations to a new Load Combination Set" under the button group "Load Combinations"
A new load combination set called "User" will be created and is placed as a tab after the "Ultimate" tab or the last combination set containing the selected load combinations
Rename the "User" set to a different meaningful name. For eg if this new set is meant to be associated with Bearing Capacity, it may be named "Bearing"
Click on the appropriate "Use For" tab to associate the design parameter with this set. For eg click on "Bearing Capacity" use for tab to associate Bearing Capacity with the Bearing set
Change the load combination factors as desired to change the load combinations on this set
If the new load combination set that must be created will contain load combinations that are vastly different from the load combinations in the existing load combination sets, follow the steps below:
Click the button "Add a new load combination set" under the button group "Combination Sets"
A new load combination set called "User" will be created and is placed as a tab after the "Ultimate" tab or the last combination set
Rename the "User" set to a different meaningful name. For eg if this new set is meant to be associated with Bearing Capacity, it may be named "Bearing"
Click on the appropriate "Use For" tab to associate the design parameter with this set. For eg click on "Bearing Capacity" use for tab to associate Bearing Capacity with the Bearing set
Click the button "Add a new Load Combination" under the button group "Load Combinations" to create a new load combination in the pane below
Change the load combination factors as desired to change the load combination
Add additional load combinations in a similar manner to complete creating a new load combination set
Similarly, create additional load combination sets to associate various footing design parameters. It is also possible to import load combinations into any of these load combination sets. However this import applies to the entire workspace and therefore each footing in a footing group workspace will be populated with identical load combination sets. The load combination import format is as described in the topic "Importing Load Combinations" but can include additional load combination sets in addition to the default "Allowable" and "Ultimate" sets. The set names can also be user-specified. After import, each load combination set may have multiple "Use For" tabs selected. It is necessary to select one and only one of the "Use For" tab (footing design parameter) on the load combination sets as described above.
D. Copy currently selected "Use For" case(s) for all load combination sets for all footings
This button allows changing the "Use For" case on all the load combination sets of the source footing to all the load combination sets of the remaining footings in the workspace.
For eg in a footing group workspace if there are 4 footings say F1, F2, F3 & F4 and let's say F1 is the source footing. On the Load Combinations page, select F1. Let's say there are 3 load combination sets on F1 - Allowable, Ultimate and User with Use For set to Bearing Capacity, Sliding, Uplift for Allowable set, Use For set to Concrete Design for Ultimate set and Use For set to Stability for User set. Also let's say that footings F2 to F4 only have Allowable and Ultimate load combination sets but not the User set and the Use For for Allowable set on these footings is set to Bearing Capacity, Stability, Sliding, Uplift and the Ultimate set has the Use For set to Concrete Design. Clicking this button will create the "User" load combination set on footings F2 to F4 and also set the same Use For for all 3 sets to those of the source footing F1. The "User" load combination set created for footings F2 to F4 will be empty since this button will not copy the same load combinations to the User set as those of the source footing. To copy the load combinations from footing F1 User set, select F1 and then click "Copy the selected load combinations" under the "Load Combinations" group buttons.
If all footings of a footing group workspace have identical load combination sets, but different Use For selected on each footing, clicking this button will align the Use For to all other footings based on the selected source footing.
Navigating back to the Summary page shows that the "Use For" selections made in each of the load combination sets are appropriately reflected on this page. The association of the design parameters to the load combination sets can also be made on this page by selecting the desired load combination set from the available drop-down list. When the association change is made on this page, the "Use For" case selection of the footing design parameter with which the change is associated results in the unselection of that parameter on the previous load combination set. For eg. if "Bearing Capacity" design parameter was orignally associated with say the load combination set "Allowable" and a change was made on the Summary page to associate "Bearing Capacity" to say "User" load combination set, "Bearing Capacity" tab against "Use For" property on the "Allowable set will be unselected and the "User" load combination set will display "Bearing Capacity" against "Use For" property highlighted.
Note: To provide maximum flexibility in creating and associating load combination sets, a footing group workspace can have different load combination sets on different footings of the same group. It is the user's responsibility to ensure that each footing is correctly associated with the desired footing design parameter for each of the footings in the footing group.
When none of the "Use For" tabs are assigned to a load combination set, that load combination set is not used for any calculations nor is that load combination set displayed in the reports.
Use the button "Delete the selected Load Combination Set" to delete the active or selected load combination set.
With this added capability of creating, deleting and cloning load combination sets, not only can design be completed for the correct set of load combinations to be used for various footing design parameters, but also can test many what-if scenarios.
Strap Footings:
To create identical load combination sets on the two footings in addition to Allowable and Ultimate, ensure that the two footings are not connected by a strap beam at first. Create the load combination set and then strap the two footings together.