CS454 Moving Load Generator

Intro

A CS 454 live load assessment is a long typing job before it is an engineering one. Appendix B, Table B.1 sets out twenty-two vehicle models spread across five assessment live loading levels, each with its own axle weights and axle spacings; clause 5.12.1 requires every level up to the one being assessed, not just the level itself; a convoy doubles the count again; ALL model 2, the fire engine groups and a special vehicle add more still.

Every one of those vehicles has to be created in the Vehicular Load dialog with its factors set, and then named, lane-assigned and given a limit state in a Moving Load Case of its own — and the whole set has to be rebuilt whenever a level, a lane or a factor changes.

The CS 454 Moving Load Generator plugin turns that into one definition. Define the traffic lanes in MIDAS, pick the models and levels here, and the plugin creates the vehicles and the moving load cases in the connected model in a single confirmed step.

Developed with

Benefits of this plugin

• Straight from Appendix B — all twenty-two Table B.1 vehicle models are built in, with the published axle weights and spacings and the gross vehicle weight of each, written as the matching MIDAS ALL MODEL 1 sub-type. The Table B.2 fire engine groups are included as user-defined vehicles, because MIDAS has no built-in sub-type for them.
• Level stacking done to clause 5.12.1 — ticking an assessment level pulls in every level below it, because the clause requires all of the vehicle models up to the level being assessed, and its note records that some 26T vehicles are more onerous than heavier ones. The vehicle list can then be narrowed to the axle arrangements that govern.
• Both live load models in one run — ALL model 1 as discrete vehicles from Appendix B, and ALL model 2 as the combined uniform and knife-edge load of clauses 5.17 to 5.19, whose UDL and KEL MIDAS derives from the loaded length. Single vehicle, convoy, or both, with the 1.0 m minimum longitudinal spacing of clause 5.14.
• Lanes assigned once, not per case — traffic lanes, straddling lane pairs and the clause 5.16 remaining-area lane are set once and carried onto every generated case. A special vehicle rides in the same traffic lanes, with the 25 m fore and aft clear distance of Appendix C.
• Every factor in one place — the Factors tab carries everything the Vehicular Load and Moving Load Case dialogs would ask for: surface category and traffic flow category for the Table 5.19c K-factors, dynamic amplification, critical and other axle impact factors, overload, unit number, vehicle speed, limit state and load combination. Neither MIDAS dialog needs opening.
• Ultimate and serviceability together — tick both and every vehicle gets two cases, one per limit state, suffixed -ULS and -SLS. Names and descriptions are kept inside the MIDAS field limits automatically, and the preview reports anything it had to shorten.
• Written by copying a verified entry — new entries are cloned from an entry that already exists in the model, so the exact field nesting and enum spellings MIDAS uses are preserved and only the name, sub-type, vehicle and lane fields are rewritten. Where the model has nothing to copy, a built-in CS 454 template reproduces a verified MIDAS entry field for field.
• Checked before it is written — the preview lists every vehicle and every load case with its axle data, lanes and status, alongside the CS 454 code notes that govern them, and nothing reaches the model until Generate 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. The Validation Check reports PyScript, the base URI and the MAPI key before anything else runs.
    
2. Read the model
   On the Model tab, press Read model. The traffic lanes, vehicles and moving load cases already in the model are reported, and the vehicle and load case used as the payload template are chosen here. Define the traffic lanes in MIDAS first; this plugin assigns lanes, it does not create them.
    
3. Choose what to generate
   On Loading, pick normal or abnormal traffic, tick ALL model 1 and ALL model 2 as required, tick the assessment load levels, and leave level stacking on unless you are deliberately assessing a single level. Untick any vehicle model you do not want, and choose single vehicle, convoy or both.
    
4. Assign the lanes
   On Lanes, tick the traffic lanes every generated case applies its vehicle to, set the remaining-area lane where clause 5.16 calls for it, and add any straddling lane pairs. For abnormal traffic, set the special vehicle type and the name it is created under.
    
5. Set the naming
   Also on Lanes, the vehicle and load case name patterns take tokens for the sub-type, the Table B.1 reference letter, the level, the special vehicle and the sequence number. Choose how a name that already exists in the model is handled: add alongside and number it, overwrite it, or skip it.
    
6. Confirm the factors
   On Factors, set the surface and traffic flow categories, the dynamic amplification and axle impact factors, the overload, unit number and vehicle speed, and the design combination: the limit state or states, and Combination 1, Combination 2 or Combination 3.
    
7. Review the Preview
   Every vehicle to be created is listed with its reference, level, gross weight, axle weights and spacings, and every moving load case with its vehicle, special vehicle, lanes and status. The code notes record the CS 454 clauses behind what is being generated, and any errors block generation until they are resolved.
    
8. Generate
   On the Generate tab, Preview payload builds the exact JSON that would be sent without writing anything; Write to model commits it. The log reports what was written, what was skipped or renamed, and what the model holds afterwards. If anything is not picked up, the Diagnostics tab shows exactly what each MAPI endpoint returned.

Conclusion

The CS 454 Moving Load Generator removes the slow, mechanical part of a DMRB live load assessment: transcribing Appendix B axle data into the Vehicular Load dialog, remembering which levels clause 5.12.1 pulls in with the one being assessed, and building a Moving Load Case for every vehicle, every convoy and every limit state by hand.

Define the lanes once, check the preview, and rebuild the whole set in seconds whenever a level, a lane, a factor or the scope changes — leaving the engineer's time for the assessment rather than the data entry.