Load Combinations

Load combinations apply factors to load case results and sum them together, as required by structural design codes. This allows you to determine the worst-case design forces under various loading scenarios.

What are Load Combinations?

A load combination multiplies the results from each load case by a specified factor and sums them:

Combination Result = f₁ × LC₁ + f₂ × LC₂ + f₃ × LC₃ + ...

For example, the ASCE 7 combination 1.2D + 1.6L means:

• Multiply Dead Load results by 1.2
• Multiply Live Load results by 1.6
• Add them together

The factored results represent the design forces that structural members must resist.

Opening the Load Combinations Dialog

Click the Load Combos button in the ribbon toolbar to open the Load Combinations dialog.

Creating Load Combinations

The dialog displays a spreadsheet with:

• ID - A unique identifier for the combination
• Title - A descriptive name (e.g., "1.4D", "1.2D + 1.6L")
• Limit State - ULS for strength checks, SLS for serviceability checks, or Unclassified
• Factor columns - One column for each defined load case, where you enter the multiplier

Adding a Combination

1. Type an ID and Title in an empty row
2. Enter factors for each load case you want to include
3. Leave factor cells empty or set to 0 for load cases not included
4. Click Apply & Close to save your changes

The combination wizard assigns ULS or SLS automatically. For manual and older combinations, the table can infer a selection from whole-word title labels such as ULS, SLS, ultimate, strength, serviceability, LRFD, or ASD. Confirm inferred values before design. An explicit dropdown selection takes precedence over the title.

The field is optional for compatibility with older projects. During member design, ULS combinations run strength and stability checks, while SLS combinations run serviceability checks. Timber member design requires an explicit ULS or SLS classification. Unclassified timber combinations and raw load cases publish an incomplete result and do not run either check group.

Example Combinations

Common Load Combinations (ASCE 7-22 Strength Design)

The following are strength-design combinations from ASCE/SEI 7-22:

Common Load Combinations (AS/NZS 1170)

For Australian/New Zealand standards (ULS, Section 4.2):

Auto-Generate Combinations

Generate standard combination templates for the action categories you map. Click Auto-Generate in the toolbar to open the wizard. The design-code dropdown starts on ASCE 7-22 when the project unit system is imperial, and on AS/NZS 1170 when it is metric. You can still switch codes after the wizard opens.

How it Works

1. Select a design code (e.g., ASCE 7 or AS/NZS 1170)
2. Map every applicable load action to a standard category. Each non-directional category accepts one load case; wind and seismic categories retain multiple separately authored directional cases.
3. Use +/- Mirror only for seismic sign reversal. Wind must use separate direction load cases because roof uplift and pressure patterns do not reverse by multiplying the full case by -1.
4. Choose ULS, SLS, or both
5. Click Generate - the wizard creates the relevant template permutations for mapped actions.

The wizard auto-detects category mappings from load case names. If several cases match a single-select category, it leaves that category unmapped and asks you to select one manually. Unmapped action categories are omitted from generation; before using the combinations for design, confirm that every action applicable to the model is mapped.

For AS/NZS 1170, map all applicable Snow ULS (Su), Snow SLS (Ss), and Earthquake SLS (Es) cases, and choose the imposed-action psi preset that matches the live load use. Eurocode 0 uses EN recommended Category A/B imposed-action and H <= 1000 m snow psi values; edit generated rows for other uses, regions, or National Annexes. The combination generator factors snow cases you have already created. It does not generate roof-snow arrangements, derive pg, Ss/Sr, or sg, or apply unmapped snow provisions.

For ASCE 7-22, the optional SLS set follows the suggested, nonmandatory combinations in Appendix CC: short-term D + L and D + Sser, long-term D + 0.5L, and wind drift D + 0.5L + Wa. Map Sser and Wa as separately determined service actions; the generator does not derive them from strength snow or wind.

For ASCE 7-22 seismic combinations, map a separate vertical seismic action case, Ev, when applicable. If horizontal earthquake is mapped and Ev is not mapped, generated seismic titles record Ev = 0 assumed. Horizontal sign mirroring does not reverse Ev. NBCC factors assume ordinary areas; storage, equipment and service-room adjustments require manual review. The generator creates combination rows from mapped earthquake cases; it does not create earthquake loads.

Directional & Mirroring Support

The wizard is designed to handle complex multi-directional loading in a single step:

• Multi-Directional Selection: If you have Wind X and Wind Z, select both in the Wind category dropdown. The generator will loop through both, creating a full set of combinations for each direction.
• Seismic Mirror Pattern: Enabling +/- Mirror for an earthquake category generates positive and negative sign variations. Wind categories intentionally have no mirror option; map explicit opposing wind-direction cases instead.

Seismic Load Combinations

Earthquake loads are split into separate Earthquake X and Earthquake Z categories to support direction-combination rules. ASCE 7 generates both independent-axis and100% + 30% orthogonal variants so users can retain the procedure applicable to the project. NBCC generates independent-axis rows by default; its 100% + 30% rows remain opt-in for applicable non-orthogonal SC3/SC4 systems.

If you used the Seismic Load Wizard (ESA) to generate load cases, the 6 cases (EQX, EQX+e, EQX-e, EQZ, EQZ+e, EQZ-e) are automatically detected and mapped to the correct X and Z categories. The wizard defaults +/- Mirror on for those earthquake categories so both positive and negative direction combinations are generated.

Supported Design Codes

Generated combinations can be appended to your existing entries or replace them entirely.

Dialog Actions

The toolbar provides:

• Auto-Generate - Generate combinations from a design code
• Download CSV - Export combinations to spreadsheet
• Copy - Copy to clipboard
• Save Preset - Save the load cases and combinations together for reuse, including load-case colours
• Load Preset - Replace both tables with the saved, validated preset

Viewing Combination Results

After running analysis, you can view factored combination results:

1. Enable a result view (Moment, Shear, etc.) in the left sidebar
2. In the top ribbon, open the load selector dropdown and pick a load combination (or use PgUp / PgDn to step through them)
3. The displayed diagram shows the factored, combined results

You can switch between individual load case results and combined results at any time using the same ribbon selector.

Envelope Results

When a static General or P-Delta analysis has at least two solved load cases or combinations, choose Envelope (all cases) in the top ribbon to display the maximum and minimum solved-result envelope in the 3D viewport. The Summary Results Dialog reports governing member, reaction, displacement, and plate summary values, while Member Analysis shows member-specific governing values.

This is an envelope of response results, not an envelope of factored applied-load glyphs. Load glyphs remain specific to the selected load case or combination; an all-case load-glyph envelope is not generated.

For member design envelopes, the Limit State selection controls which design-check group is eligible for each combination. It does not change the FEA solution or the load factors.

Best Practices

• Name combinations clearly using the factor notation (e.g., "1.2D + 1.6L")
• Include all combinations required by your governing design code
• Consider both strength (ultimate) and serviceability combinations
• For wind, include explicit opposing direction cases; for seismic, confirm the mirror-generated positive and negative directions are present
• Use presets to maintain consistent combinations across projects