CS454 Load Assessment Combinations

Intro

A CS 454 assessment combination is quick to state and slow to build. Table A.1 gives a separate partial factor for every action in each of the four combinations, at ultimate and serviceability, and a different value again depending on whether that action is adverse or relieving.

The live-load models have to be kept apart so that a normal-traffic case never appears beside the abnormal vehicle it is meant to replace; every permanent action has to be run both favourably and unfavourably; and the whole set has to be rebuilt whenever a load case is added or a factor is revised — before any of it is typed into the Load Combinations table by hand.

The CS 454 Load Assessment Combinations plugin turns that into one definition. It reads the load cases from the connected model, maps each to a Table A.1 action, applies the factors you confirm, and writes the complete set of combinations, with their envelopes, into CIVIL NX in a single confirmed step.

Developed with

Benefits of this plugin

• Straight from Table A.1 — every combination is built from CS 454 version 1.1.0, Appendix A, Table A.1, with the adverse and relieving γ_fL for each action, a separate factor set for cast iron structures, and γ_f3 either folded into the combination factors or left to the resistance check.
• Mapped from the model, not retyped — static, construction-stage, settlement and moving load cases are read from the connected model, and each is assigned a CS 454 action and, for moving loads, a load model: ALL Model 1 and 2, SV, SOV, STGO, SO, HB, associated normal traffic and footway. An unmapped case blocks generation rather than defaulting silently, and prestress is rejected outright as CS 455 work.
• Live-load exclusivity handled properly — each category can act together, independently or exclusively, so a normal-traffic case never lands in the same combination as the abnormal vehicle that replaces it, with cross-category excludes and requires for the cases that the category rules alone cannot express.
• Both permanent directions, automatically — any permanent group set to both is generated adverse and relieving, and the full set of permutations is produced without building any of them by hand.
• Fewer combinations where the code allows it — mutually exclusive groups can be collapsed into one Envelope sub-combination that the generated combinations then reference at the Table A.1 factor, which cuts the number of rows committed to the model.
• Names that read as English — a combination is written ULS2-ALL1s-W2-Adv rather than as a packed code, so the limit state, the combination number, the live-load model, the wind sub-case and the permanent variant are all legible in the MIDAS table, and the description spells the same thing out in words.
• Checked before it is written — the preview lists every combination with its components, its equation and a full ledger of which clause and factor produced each term, and nothing reaches the model until the commit is confirmed.

How to use this plugin?

1. Open the assessment model in CIVIL NX and start the plugin
   The connection details are supplied automatically. Use Connection if the status badge does not read CIVIL NX connected.
    
2. Read Model Validation
   The structure type and the model's load cases are reported before anything is generated. Cast iron switches to its own factor column and disables the serviceability scope, because cast iron is assessed on a permissible-stress basis under Section 8. Masonry arches are out of scope in this version.
    
3. Map the load cases
   On Load Cases & Mapping, give every enabled case its CS 454 Table A.1 action, and every moving load case its CS 454 load model and assessment level. Where Auto Live Load Combination is set in MIDAS, the ULS-only or SLS-only restriction is picked up from the model and reported, so a serviceability vehicle is never factored into an ultimate combination.
    
    
4. Choose the scope
   On Combinations Scope, tick the combinations, 1 to 4, and the limit states the assessment requires. Only what is ticked is generated.
    
5. Confirm the factors
   Table A.1 is shown in full, with the adverse and relieving γ_fL for every action. Edit any value the assessment calls for, and set whether γ_f3 is folded into the combination factors or left to the resistance check.
    
6. Group and relate
   On Groups & Relations, build the groups within each category, or apply a template, then set how the category behaves: together, independently or exclusively, whether it may be absent altogether, and whether its exclusive groups should be collapsed into a single Envelope sub-combination. Add cross-category excludes and requires, and set each permanent group to unfavourable, favourable or both.
    
    
7. Review the Preview
   Every generated combination is listed with its name, family, live-load model, component count and warnings. Select one to read its equation and the full ledger of which Table A.1 row and factor produced each term.
    
8. Commit
   Choose the target table, decide how any existing Load Combinations are handled, add a prefix if names would collide with the model's existing ones, and tick envelopes to have a per-family envelope written on top. The summary reports exactly what will be written before anything is sent.

Conclusion

The CS 454 Load Assessment Combinations plugin removes the slow, error-prone part of a DMRB assessment: reading Table A.1 across four combinations and two limit states, keeping the live-load models exclusive, running every permanent action both ways, and typing the result in by hand.

Define the mapping once, check it in the preview, and rebuild the whole set in seconds whenever a load case, a factor or the scope changes — leaving the engineer's time for the assessment rather than the bookkeeping.