Load Combinations

Load combinations apply factors to the loads in one or more load cases, as required by structural design codes. Each selected case or combination is then solved and stored as its own result set, allowing you to determine the governing design forces under different loading scenarios.

What are Load Combinations?

A load combination multiplies the applied loads in each load case by a specified factor:

Combination Loads = f₁ × Loads(LC₁) + f₂ × Loads(LC₂) + f₃ × Loads(LC₃) + ...

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

• Apply the Dead Load case with a factor of 1.2
• Apply the Live Load case with a factor of 1.6
• Solve the structure for those factored loads as one combination

For linear elastic analysis, this produces the same response as linear superposition of the individual case results. P-Delta and tension/compression-only behaviour are evaluated while solving the factored combination and must not be treated as a post-processing result sum.

Opening the Load Combinations Dialog

Open the Applied Loads dialog and click Manage Load Combinations.

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 Sections 2.3.1 and 2.3.6:

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. When the project contains seismic cases generated by the seismic load wizard, the design-code dropdown starts on the standard that combines the latest seismic run (ASCE 7-22 → ASCE 7-22; AS 1170.4 or NZS 1170.5 → AS/NZS 1170; EN 1998-1 → Eurocode 0; NBCC 2020 → NBCC 2020). Otherwise it 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; selecting a standard that does not combine the generated seismic cases shows a warning.

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. Dead accepts several cases that act together, such as Dead and SDL: each takes the dead load factor in every combination. Wind, snow and horizontal seismic categories accept multiple separately authored cases as alternatives (wind and seismic directions, or alternative snow arrangements). Every other category accepts one load case.
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 Serviceability (Es) cases, and choose the imposed-action psi preset that matches the live load use. Eurocode 0 uses EN recommended psi values (EN 1990 Table A1.1): snow for sites at H <= 1000 m, and imposed load per the Imposed Load Category selected once a Live case is mapped: A/B (default; psi0 0.7, psi1 0.5, psi2 0.3), C/D and F (0.7, 0.7, 0.6), E (1.0, 0.9, 0.8), G (0.7, 0.5, 0.3) or H roofs (0, 0, 0). The category sets psi0 on accompanying imposed load (1.5 psi0 at ULS), psi1 in frequent and psi2 in quasi-permanent and seismic combinations, and applies to every case mapped as Live; generate separately for parts of the building in other categories. With psi = 0 (Category H) the imposed load is left out of rows where it would only accompany, as with AS/NZS psi = 0 presets. Edit generated rows for other 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 NBCC 2020, map the separately calculated specified snow values to Snow ULS (S) and Snow SLS (S). The SLS row is the Article 4.1.6.2 value using Is = 0.9; it is not an alternative pattern in the ULS snow envelope. NBCC has a single Wind (W) category: SLS rows apply the mapped wind case unchanged, so it carries the ULS importance factor Iw. Scale or edit the SLS wind rows where the serviceability value (Iw = 0.75) is required. Tick Storage, equipment or service areas (shown once a Live case is mapped) for those areas: the companion factor on L is increased by 0.5 at ULS (Sentence 4.1.3.2.(7): 1.0L to 1.5L with principal snow, 0.5L to 1.0L with principal wind or earthquake) and the SLS companion 0.35L becomes 0.5L (Table 4.1.3.4, Note 2). Principal-load factors are unchanged.

Stability rows (AS/NZS 1170 and Eurocode 0, off by default) add static-equilibrium combinations in which the dead case is taken as wholly stabilizing. AS/NZS 1170.0 Clause 4.2.1 rows are titled ULS stability: 0.9G with 1.5Q, Wu + psi_c Q, Eu + psi_E Q (100% + 30%, mirrored like the strength rows) and Su + psi_c Q, each also without Q; 0.9G + Wu is already the strength row 4.2.2(e) and is not repeated. Eurocode 0 EQU rows (EN 1990 Table A1.2(A)) are titled ULS EQU: 0.9G + 1.5 x the leading variable action + 1.5 psi0 x each accompanying action, with and without each accompanying action. Where the dead load destabilizes, the strength rows already govern (1.35G for EN 1990, 1.2G/1.35G for AS/NZS). Split stabilizing and destabilizing permanent loads into separate cases and edit the factors where a check needs both.

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, the ASCE 7-22 Seismic Load Effect inputs appear once a horizontal earthquake case is mapped:

• Redundancy (rho): 1.0 or 1.3 (Section 12.3.4). Horizontal earthquake cases are factored as Eh = rho QE.
• SDS (g): when no vertical seismic case (Ev) is mapped, Ev = 0.2 SDS D (Eq 12.4-4a) is folded into the dead-load factor: strength (1.2 + 0.2SDS)D and (0.9 − 0.2SDS)D; ASD (1.0 + 0.14SDS)D, (1.0 + 0.105SDS)D and (0.6 − 0.14SDS)D. These rows are titled [Ev in D]. A mapped Ev case always takes precedence and disables SDS. With neither, generated seismic titles record [Ev=0 assumed] and a warning is shown.
• Overstrength rows: optional (off by default). When ticked, enter Omega0 (1.0 or more) to add combinations with Emh = Omega0 QE (Section 12.4.3), titled ULS Ω0 / ASD Ω0.

When the seismic cases were generated by the seismic load wizard, SDS is prefilled from the latest ASCE 7 run, together with rho and Omega0 where that run recorded them (the larger of the X and Z values, since one value applies to both directions). Confirm each value for the project. Horizontal sign mirroring does not reverse Ev.

Eurocode 0 seismic combinations (EN 1990 Eq 6.12b) use psi2 of the selected imposed-load category on Q (0.3 for Category A/B).

If seismic cases generated by more than one seismic code exist, only one code's cases are mapped (the latest run among codes the selected standard combines) and the wizard lists the cases it left out; Model Health also warns. Where a direction has both +e and −e accidental-eccentricity cases mapped, any matching base case without torsion is not combined, because in a linear analysis the two eccentric cases bound it. 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 and 100% + 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. AS/NZS 1170 and Eurocode 0 generate 100% + 30% rows; when only one direction is mapped, the rows contain that direction alone.

If you used the Seismic Load Wizard (ESA) to generate load cases, its cases (EQX+e, EQX-e, EQZ+e, EQZ-e with accidental eccentricity, or EQX and EQZ without it) 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