Form: Define Load Combinations, Load Combination Data
Program design is based on a set of loading combinations. In SAP2000, load combinations, or combos, are generated automatically by SAP2000 or user defined. If the automatically generated load combinations are acceptable (note that these combos are created/recreated after each design run), no definition of additional load combinations is required.
Use the Design menu > {Steel, Concrete, Aluminum, Cold Formed Steel} > Select Design Combos command to work with automatic load combinations.
Use the Define menu > Load Combinations command to specify your own user combinations. The user-defined combinations can be created manually or based on a selected code, as described in this topic. This command can be used to convert automatic load combinations to user-defined combinations that can then be modified to meet specific needs.
Note: The Design menu command must be used to select the user-defined combinations to be used in design, regardless of whether the combos were created manually or if the combination(s) is based on code using the Define menu. The program automatically selects the automatic code-generated combos (generated after each design run).
Automatic and user-defined combination may be used simultaneously for design. Note that each time a design is run, the automatic combos are regenerated, thereby replacing any previous automatic combos. User-defined combinations (manual or based on code) are not changed during design. The Define menu > Load Combinations command can be used to convert automatic code-generated combos to user-defined combos.
Note: Notional loads are not included in code-generated or automatic combinations. Thus, to consider the combination of notional and lateral loads, appropriate User Load Combinations should be generated.
Manually Create User-Defined Load Combination
Click the Define menu > Load Combinations command to access the Define Load Combinations form.
Use the following buttons on that form to complete the appropriate action.
Add New Combo button. Click this button to display the Load Combination Data form and manually create a user-defined load combination for the model.
Use the default or type another name in the Load Combination Name edit box. Note that each load combination and load case must have a unique name. Also, the word Mode is reserved and can not be used for either a load case name or a load combination name.
Select the Load Combination Type:
Linear Add. All load case results are multiplied by their scale factor and added together. This Combo Type can be used for static loads.
Envelope. A max/min Envelope of the defined load cases is evaluated for each frame output segment and object joint. The load cases that give the maximum and minimum components are used for this combo. Therefore the load Combo holds two values for each output segment and joint. The Combo Type can be used for moving loads and any load case where the load producing the maximum or minimum force/stress is required.
Absolute Add. The absolute of the individual load case results are summed and positive and negative values are automatically produced for each output segment and joint. Use this Combo Type for lateral loads.
SRSS. The Square Root Sum of the Squares calculation is performed on the load cases and positive and negative values are automatically produced for each output segment and joint. Use this Combo Type for lateral loads.
Range Add. The combined maximum is the sum of the positive maximum values from each of the contributing cases (a case with a negative maximum does not contribute), and the combined minimum is the sum of the negative minimum values from each of the contributing cases (a case with a positive minimum does not contribute). This Combo Type is useful for pattern or skip-type loading where all permutations of the contributing load case must be considered.
Select the appropriate action:
Add button. Add a load combination.
Select a load case name from the Load Case Name drop-down list and type in the multiplier in the Scale Factor edit box. The Load Case Type display box shows the load case type for the specified load case.
Click the Add button to add the load case and multiplier to the Load Case Name/Scale Factor display areas.
Repeat as necessary.
Modify button. Modify a load combination.
Select the load case/multiplier to be modified in the Load Case Name/Scale Factor display areas.
Type the revisions into the Load Case Name/Scale Factor edit boxes.
Click the Modify button.
Delete button. Delete a load combination.
Select the load case/multiplier to be deleted in the Load Case Name/Scale Factor display areas.
Click the Delete button.
Convert to User Load Combo button. Use this button to convert a Code-Generated Automatic Load Combination to a User Load Combination that can then be modified using the options described herein.
Select a Code-Generated Automatic Load Combination. Note that, as explained previously, this type of load combination is generated automatically by the program during the design process. Therefore, this button will not be available until at least one iteration of analysis and design has been completed.
Click this button to convert the selected load combination to a user-defined load combination. This action occurs immediately; no form displays.
Create Nonlinear Load Case from Load Combo button. Use this button to create/add a new nonlinear load combination from a linear static load case(s).
Select a user defined load combination that has a Load Combination Type of Linear Add and has at least one linear static load case in the combination.
Click this button to combine all linear static load cases in the combination into a new nonlinear static load case. This action occurs immediately; no form displays.
Modify/Show Combo button. Use this button to modify an existing combo without adding a new combination.
Select the load combination to be modified in the Load Combinations display area.
Click the Modify/Show Combo button to access the Define Response Combinations form.
Make the necessary adjustments using the options on the form (see above).
Click the OK button to return to the Define Load Combinations form. Then click the OK button on that form to close it.
Delete Combo button. Use this button to delete a combo.
Select the load combination to be deleted in the Load Combinations display area.
Click the Delete Combo button.
User-Defined Load Combinations Based on Code
Click the Define menu > Load Combinations command to access the Define Load Combinations form.
Click the Add Default Design Combos button to access the Add Code-Generated User Load Combinations form.
Select the design type (e.g., steel frame, concrete frame, aluminum frame, cold-formed steel frame).
If necessary, click the Set Load Combination Data button to access the Code-Generated User Load Combinations for {Code} form and refine the definition of the code-generated combination.
Converting Automatic Code-Generated Combos to User-Defined Combos
Click the Design menu > {Steel, Concrete, Aluminum, Cold Formed Steel} > Select Design Combos command to access the Define Load Combinations Selection form.
Check the Automatically Generate Code-Based Design Load Combinations check box.
Run an analysis and design.
Click the Define menu > Load Combinations command to access the Define Load Combinations form.
Highlight the automatic load combination to be converted into a user-defined load combination.
Click the Modify/Show Combo button to display the Load Combination Data form.
Click the Convert Combos to User Load Combo button.
A query will be displayed asking that the conversion be verified and advising that the conversion can not be undone.
Click the Yes button and SAP2000 will convert the automatic code-generated load combinations into a user-defined load combination. Click the No button and the conversion will not take place.
As indicated above, each time a design is run, the automatic code-generated combos are regenerated, thereby replacing any previous automatic code-generated combos. However, any automatic code-generated combo that has been converted to a user-defined combinations will not be changed during design.
Example: Definition of combinations is demonstrated in Problem A, Problem B, Problem I and Problem U.
See Also
Aluminum Frame Design - Select Design Combos
Cold-Formed Steel Frame Design - Select Design Combos