How Low do you go?

When is model detail required, the decision making process and how you can manage it.

Its is a common refrain “The design model does not take into account the individual concrete pours during construction”.. you may even have uttered these words yourself if you have dipped your toes into the world of 4D.

It is a basic fact that design models don’t and arguably shouldn’t need to distinguish such things, however this does affect those downstream recipients (if they are lucky enough to be allowed access to or if a 3D model even exists) whose needs are specific if they are to benefit from the value of a models creation.

So should designers go that extra yard? or should 3D models be created exclusively for downstream construction use? or perhaps should that design model be repurposed to account for the inevitable needs of Contractors, their Planners and Estimators?.

A few choices that are worth exploring..

Going the extra yard

There are inherent issues that immediately arise; designers are not contractors and with a world of ever more atomic and specialist professional divisions it is becoming ever more less likely that convergence will provide us with the “yes” answer to this question. So the question is dead?. Well “No” actually; it is conceivable that through early collaboration between designers and suited contractors that such requirements might be determined and reflected in output 3D models; not withstanding the value add in not having to pay for exclusive 3D models or their repurposing, there are other natural benefits that would accrue such as feedback on constructability.

Exclusive construction models

A straightforward option which can be assessed on a cost/benefit basis; if no designer generated 3D model exists then there is the opportunity to use the model for a series of other purposes such as “clash detection”, “environmental analysis”, “estimation”, “visualisation”, “4D visualisation” and if you are fortunate enough to have the option then full “construction simulation” [plug for SUperPlan].

Repurposing that design model

The last of the 3 options; “repurposing” can be a bit of an indefinable beast. The format of 3D models that may have been originated by different organisations, using different software, applying different standards to the quality of the data they create. Combining such models is becoming less of a ‘black art’ with the advent of BIM (IFc’s) and cooperation agreements between the likes of Autodesk and Bentley in recent years. Pitfalls do still exist but it is now a plausible undertaking.

Pursuing the positive slant, 3D models can be combined and so repurposing can be achieved.. well umm yes.. hesitation raises its ugly head because the knowledge required to drive many of the commonly used CAD offerings falls squarely outside the professional remit and skill base of the one person who will actually determine those required subdivisions of concrete slabs and the like.. OK so you hire a CAD professional and tell them what you need and hey presto! or you use the most straightforward of CAD tools such as Google’s Sketchup which requires you to simply draw line across object faces to chop them in two!

To pick up on the original question – How Low do you go?

You now have 3D models by one means or another so its time to set those model detail requirements.. You want and need a model that reflects your construction sequence expectations; your schedule is probably already waiting for you to associate objects to your tasks for that pretty 4D visualisation that you expect to see after all your efforts.

The good news is that many objects are naturally atomic, they are hopefully modelled as components, many of which are ‘instanced’ in the model; think steel columns/beams, doors and windows. So we are concerned primarily with objects that by virtue of being of the same ‘class’ are amalgamated into homogenous representations; think concrete, brick/block work, cladding, roofing and the like.

So what options do we have to subdivide these homogenous representations? Popular planning work breakdown structures (WBS) are probably the key influencer, commonly WBS’s describe groupings by ‘construction phases’, by ‘building levels’, by ‘grid lines’ or by ‘locations’ and more often than not a mixture of these. So these are what one should use to dictate the subdivisions of those homogenous representations? Answer is that ‘Yes’ they can be, however there are other overriding factors that should additionally influence our requirements.

• Ability to create uniform task buckets – if subdivisions of 2 different classes of object are not equal (location/level etc) then the flow of work (likely represented in a ‘Gantt’ or ‘line of balance’ (LOB) chart) will create bottlenecks for trades moving through and occupying spaces with inevitable consequences. A 4D visualisation will look ‘wrong’ and further revisions to a construction 3D model will likely be required.
• Flexibility (micro -> macro works but not macro -> micro) – The greater the starting granularity of objects the better. All 4D software tool’s principal function is to group data (association of objects to tasks). There is no way back from a non granular starting point apart from going back to the model for a further revision. Imagine that the “construct walls in North West quadrant” is delayed (for any one of hundred reasons – you can undoubtedly come up with or have experienced yourselves) suddenly the visualisation shows your task either in continuation, complete or not started none of which are a reflection of the actual progress. Not a great thing to communicate!
• Progress reporting – Achieved differently by 4D visualisation tools, but whatever the methodology/functionality there is nothing better than discriminating between the objects that are complete, partially complete or not yet started. A lack of granularity is again going to cause you problems.

In all cases a universal truism exists; the greater the level of complexity of a design and therefore the construction of such a design, the greater the need for 3D as a means of shining a light on the potential issues in project coordination and delivery.

Lastly, it should be brought to your attention that the decisions above are predicated on the basis that a ‘4D visualisation’ is the required output. The whole discussion does change somewhat when ambitions turn to the realm of ‘4D Simulation’; simulation vs. visualisation is discussed in a separate article (read more..) however in summary, simulation is a ‘construction calculator’, it is intelligent and overcomes many of the pitfalls described previously

• Data quality – automated object recognition overcomes missing or poor classification of objects.
• Pre and post requirements are established and visualised
• Schedule sequences are derived from rules (gravity/directionality)
• Relationships (task links) are automatically established
• Bill of quantities and Bills of materials are generated alongside weekly/monthly budgets.
• 4D visualisation is a calculated and predictable outcome.

For more information on 4D/5D Simulation we invite you to take a look at SUperPlan offered to you by Delivery Simulation Ltd.