# 9. Combinations

This section defines load combinations for design checks and load rating per AASHTO LRFD specifications.

{% hint style="info" %}
Load combinations combine individual load cases with appropriate factors for different limit states (Strength, Service, Fatigue, etc.).
{% endhint %}

## Combination Definitions

| Definition                                                                                                                                                                                   | Description                                              |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------- |
| [Result Extraction (From Stages)](https://docs.openbrim.org/examples/steel-bridge-examples/example-steel-i-girder-bridge-ex1-sig/combinations-ex1-sig/result-extraction-from-stages-ex1-sig) | Extract results from construction stages for combination |
| [Design Load Combinations](https://docs.openbrim.org/examples/steel-bridge-examples/example-steel-i-girder-bridge-ex1-sig/combinations-ex1-sig/design-load-combinations-ex1-sig)             | Limit states, load combination tables, and rating tables |

## Load Cases Combined

* **Non-composite Dead Load**: Girder self-weight during erection
* **Composite Dead Load**: Deck, barriers, and wearing surface
* **Live Load**: HL-93 with dynamic allowance
* **Wind Load**: Structure and live load wind effects
* **Temperature**: Uniform temperature change effects

## Limit States

| Limit State  | Purpose                             |
| ------------ | ----------------------------------- |
| Strength I   | Basic load combination without wind |
| Strength III | Load combination with wind          |
| Service I    | Normal operational loads            |
| Service II   | Steel yield control                 |
| Fatigue      | Repetitive live load cycles         |


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