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")
• 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

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.

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. Wind and seismic categories accept 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. 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 distinct Snow ULS (Su) and Snow SLS (Ss) cases. For Eurocode 0, the wizard uses EN 1990 recommended psi values; confirm the governing National Annex and imposed-load category.

For ASCE 7-22 seismic combinations, map a separate vertical seismic action case, Ev, in addition to the horizontal cases. The wizard applies horizontal sign mirroring without reversing Ev. For NBCC 2020, increase live-load companion factors where Table 4.1.3.2-A requires the storage, equipment-area or service-room adjustment. The generator includes independent NBCC earthquake-axis rows and additional 100% + 30% rows for non-orthogonal SC3/SC4 systems under Article 4.1.8.8.

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. When both are mapped, the generator includes100% + 30% direction-combination variants: 100% of the earthquake force in one direction combined with 30% in the perpendicular direction, and vice versa. Retain these variants where required by the governing standard and structural configuration.

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. Enable ± Mirror on both earthquake categories to generate both positive and negative direction combinations.

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 multiple load combinations are defined, you may want to find the maximum or minimum values across all combinations. The Summary Results Dialog and Member Analysis dialog already display governing values across combinations. Visual envelope overlays on the 3D viewport are a planned enhancement.

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 and seismic, remember to include both positive and negative directions
• Use presets to maintain consistent combinations across projects