> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/openbrimfea/result-combinations-fea/combination-items-fea.md).

# Combination Items \[FEA]

A Combination Item is a single **case-and-factor pair** belonging to a combination, expressed as its own row. It is the alternative to the fixed slots on the Combinations & Envelopes sheet, and it is the better one for anything non-trivial: there is no 20-case limit, each pair is visible on its own line, and the list can be sorted, filtered and reviewed like any other table.

Combination Items are **result-time post-processing**. They re-analyse nothing.

## Data

**Combination:** The combination this item belongs to.

*Engineering influence.* This is the **connectivity** parameter. An item with no combination assigned belongs to nothing and contributes nowhere — it sits in the model looking like a defined contribution while affecting no result. Because items are rows in a flat list rather than nested under their parent, an unassigned item is easy to overlook.

**Case:** The analysis case contributing to the combination.

*Engineering influence.* Selects what is being combined. A case that is **inactive**, or that failed to solve, contributes nothing — again silently, so a combination can be short a contribution without any indication. Referencing a **nonlinear** case here is possible and generally invalid, since nonlinear results do not superpose.

**Factor:** The multiplier applied to that case's results.

*Engineering influence.* This is where the code's load factors live. The combined result scales linearly with it, so it directly sets the design demand.

The default is **0**, which means an item created but not given a factor contributes **nothing**. This is the characteristic failure of this object: the row exists, names a case, and adds zero to the combination without any warning. Check every row has a deliberate factor.

**Negative factors are legitimate and important.** A load that can act in either direction — wind, temperature, settlement — often governs in its reversing sense, and uplift checks depend on applying dead load at its minimum factor while an opposing action acts at its maximum. Codes specify these minimum/maximum pairs precisely because the unfavourable case is not always the largest.

For an **enveloped** combination the factors still apply to each alternative before the envelope is taken, so a factor error affects which alternative governs as well as its magnitude.

## Verification

* Hand-check the combination: multiply each case's result at a known location by its factor, sum them, and compare against the combined value. This validates the whole item list at once.
* Confirm every item has a non-zero factor and an assigned combination.
* List the items per combination and compare against the code's load combination table, factor by factor — this is the only way to be confident a combination is complete.
* Confirm that reversing actions appear with both their maximum and minimum factors where the code requires it.
* Check that no referenced case is inactive.
* Confirm no nonlinear case is included.

## Common mistakes

* **A factor left at the default of 0**, so the item contributes nothing while appearing complete.
* **No combination assigned**, leaving the item orphaned.
* **Missing the minimum-factor variant** of a load in an uplift or stability check, where the unfavourable case is the one with less dead load rather than more.
* **Omitting a case entirely** from a combination — invisible unless the item list is checked against the code table.
* **Referencing an inactive case**, which contributes nothing without warning.
* **Including nonlinear cases**, whose results cannot legitimately be superposed.
* **Mixing the fixed slots on the Combinations sheet with items here** for the same combination, making the true content of the combination hard to establish.


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