Monday, February 25, 2013

Level of Detail and the Risk vs R.O.I: How much should we model in support of the construction effort?

It's one of the hardest thing to quantify in the industry: at what point does the A/E team's responsibility to design a workable solution end, and the TC's logistical design of construction means and methods begin?  Additionally, what risk is left in the gap where that split occurred?

Often, the gap is made up in sketches by the A/E team.  Sketches are about as useful as the napkin they're drawn on: okay to clean up a bloody mess, but not really efficient at preventing the initial nail through the foot.

Most T.C.s we've encountered are hesitant to model from the conceptual phase in parallel with the designers, as they see the means and methods, design, and logistics as an extension of the direction of the A/E team, rather than an iterative process that they can shape to both their fiscal benefit and the overall quality of the project process.

This gap of modeling responsibility leads to an issue in scheduling on IPD projects with compressed time-fames, especially when a design consultant refuses to model schedule-sensitive elements in 3D.

Ultimately, the responsibility falls on the CM to ensure the proper coordination of elements installed to the design-intent of the A/E team.  Because of this, CMs cannot stand by and plead ignorance of designed elements when there are potential spatial, sequencing or schedule risks.  Buildings have become so complicated, and owners so tight-fisted with the state of the economy, that processes not utilizing a complete, integrated VDC effort will suffer fee-erosion due to factors outside their control.

For example:

On a life-sciences building in New England, Gilbane is faced with a site that requires extremely accurate placement of underground plumbing elements.  Because we know the placement and sequencing of sub-surface precast structures is of the utmost importance to keep our tight schedule, we actually modeled the zone-of-influence below the structural footings (based on a typical structural criteria) to avoid subsurface undermining.

Now, I have no business designing footings. We have a wonderful structural design team sitting in colocation with us who does that.  What is my business is the successful execution of the coordination effort of all ME&P in the building.  Because of that, I needed to be able to tell my plumbing designer how close to the footings he could place his precast structures before we were in the "danger zone."

This type of modeling could be considered by some to be 'risky', in that we are providing (a sort of) dimensional data to a subcontractor who is contractually obligated to a set of 2D drawings and a spec.  But what ended up happening was that our structural engineer saw the value of the coordination effort, and she incorporated the zone-of-influence family into her design model, which then goes on to produce later documentation.

So, in the TLDR version, Gilbane was able to coordinate a tight underslab ME&P situation to an accuracy of under an inch using total-station layout and drive a model-based process in a situation where the sub-surface engineer refused to model in 3D.