There's a long answer to this question but I'll try and keep it brief. (At Freeform) we recommend a few methods depending on what you're trying to achieve, and how you're using the model.
What to do when there's a design change depends on how critical the change is to the construction. In simple terms, if it's significant, like an additional floor, or rail platform, or floor layout, then it's worth investing some time to update the 4D model, in the same way as you would do for the programme/schedule. If there's an impact on time, sequence, the method of construction, or the logistics requirements, then it's a good idea to run through the impact of the change and update the 4D to suit. At the other end of the spectrum, minor changes aren't usually worth the effort. For example, structural design changes to steel sections (beam dimensions), or how a facade is to be assembled (as long as there's no programme impact), or design changes to minor components. How to update the 4D model to reflect design changes depends on your method and software as they act differently.
Schedule and cost are similar, minor updates can be ignored. But if you're using full 4D software (such as Synchro) you should ideally have a process in place that 'automatically' updates the 4D model to these kind of changes. Or at least semi-automatically, like importing and synchronising updated external data and information.
Of course, good judgement is needed when deciding when a change is significant or not. If a change is not reflected in 4D that actually then causes an impact, and the 4D model is relied upon, the impact can have consequences. Same as when the programme/schedule is not updated.
I'd also add that you need to assess a 'pile up' of changes also and what impact that might have if 'minor' updates are ignored for a prolonged periods, you may well find yourself with a sizable update at some point.
This can also be better managed in the long term of a project by working with the models in agreed 'worksets' or 'subsets' allowing you to target specific areas of the model undergoing constant change, whilst 'locking in' certain parts of the design that are unlikely to change.
There's a long answer to this question but I'll try and keep it brief. (At Freeform) we recommend a few methods depending on what you're trying to achieve, and how you're using the model.
What to do when there's a design change depends on how critical the change is to the construction. In simple terms, if it's significant, like an additional floor, or rail platform, or floor layout, then it's worth investing some time to update the 4D model, in the same way as you would do for the programme/schedule. If there's an impact on time, sequence, the method of construction, or the logistics requirements, then it's a good idea to run through the impact of the change and update the 4D to suit. At the other end of the spectrum, minor changes aren't usually worth the effort. For example, structural design changes to steel sections (beam dimensions), or how a facade is to be assembled (as long as there's no programme impact), or design changes to minor components. How to update the 4D model to reflect design changes depends on your method and software as they act differently.
Schedule and cost are similar, minor updates can be ignored. But if you're using full 4D software (such as Synchro) you should ideally have a process in place that 'automatically' updates the 4D model to these kind of changes. Or at least semi-automatically, like importing and synchronising updated external data and information.
Of course, good judgement is needed when deciding when a change is significant or not. If a change is not reflected in 4D that actually then causes an impact, and the 4D model is relied upon, the impact can have consequences. Same as when the programme/schedule is not updated.
I'd also add that you need to assess a 'pile up' of changes also and what impact that might have if 'minor' updates are ignored for a prolonged periods, you may well find yourself with a sizable update at some point.
This can also be better managed in the long term of a project by working with the models in agreed 'worksets' or 'subsets' allowing you to target specific areas of the model undergoing constant change, whilst 'locking in' certain parts of the design that are unlikely to change.