> For the complete documentation index, see [llms.txt](https://docs.enercalc.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.enercalc.com/e3d-user-manual/interface/toc175916526/toc175916652/toc161393883.md).

# Load Combinations

How to define load combinations from existing load cases for analysis, steel, and concrete design in ENERCALC 3D.

Create > Load Combinations prompts you with the following dialog.

![](https://560001759-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FWNe8U6EBBBdUJHdb2X9G%2Fuploads%2Fgit-blob-ace4f9b59d33705685acb9734eb7fe1d3c32b5bb%2FFASTFR~1_img119.png?alt=media)

It allows you to define combinations of existing load cases in the model. The program solves for load combinations but not for load cases. You may assign a label with 127 maximum characters to each load combination for easy identification. Duplicate labels in load combinations are not allowed.

You may add one load combination by clicking the “Add” button. You may then define the new load combination in the following dialog.

![](https://560001759-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FWNe8U6EBBBdUJHdb2X9G%2Fuploads%2Fgit-blob-2d390ef6109c0c1761bf934090fae634f27f7fec%2FFASTFR~1_img120.png?alt=media)

The definition includes a label with 127 maximum characters, a load factor for each load case, and a P-Delta flag. A load factor of zero excludes the respective load case from participating in the load combination. You may print all load cases and their corresponding load factors in the list by clicking the “Print” button.

If you need to design concrete beams, columns and/or plates, check “Perform Concrete Design using this Load Combination” for each load combination that is appropriate for concrete design.

When concrete columns are to be designed, the program needs to calculate the infamous bd value. The easiest way to facilitate this calculation is to create a load combination specifically for the purpose of defining the *sustained loads*. (It might even be helpful to name this load combination "Sustained".)

In some models, this sustained load combination might just consist of 1.0 times the dead load case. In other situations, the sustained load combination might consist of 1.0 times the dead load case and 1.0 times a self-weight load case. In still other cases, the sustained load combination might consist of 1.0 times the dead load case and some percentage of the live load case. It depends entirely on how the load cases were set up for the given model.

Then, a sustained load factor must also be entered. This can only be a single factor, but it must be representative of the constituent load cases (like a weighted average), because this one factor will be applied to the entire sustained load combination to calculate the maximum factored sustained axial load.

Finally, this sustained load combination must be designated in Concrete Design > RC Model Design Criteria before performing concrete column design.

If you need to design steel members, check or uncheck “Perform Steel Design using this Load Combination”. If you need to use the load combination to check total or live load deflection, check or uncheck appropriate boxes.

You may modify, copy, or delete a load combination by clicking the “Modify”, “Copy”, or “Delete” button. You may also create a load combination for every load case with a unit load factor for the load case but zeros for the rest of the load cases. To do that, click the “Unit Cases” button.

You may also generate standard load combinations based on design codes such as ACI 318-02/05/08/11/14 by clicking the button “Generate Std”.

There must be at least one load combination in a model.


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