• Field Notes 10.11.2010

    A couple of blogs ago, I mentioned that building information modeling (BIM) has a chance to be what CAD was to the drafting and engineering world back in the late 80s and early 90s. In reality, it has the potential to be much more because of the depth of information it can contain. But as a glazier, why should you care? BIM clearly benefits architects, but what’s in it for you? And what should they include in BIM to make your job easier?

    Most of the BIM models are going to be developed by the architects and specialty consulting firms (structural engineering for example, doing the building frame). They aren’t always thinking down the line to the glazing sub, but there’s some key information they can build into the models that would be useful to glaziers.

    From the architect’s view, and based on what I was seeing from the consulting side of the table, at project inception – from schematics through issuing construction documents – there is not a lot of value to an architect modeling a specific product within their BIM model prior to bid.

    There are too many variables that may – or, more likely, may not – result in a specific window system, for example, being used on the project. The selected glazing subcontractor may not have used that system as the basis of their bid, using a competitor’s or one of their own. If that were the case, everything in the BIM model would be of little worth. Only if a project were to be awarded based on a negotiated bid would it make any sense to utilize a fully developed model with the specific glazing system selected.

    However, taking as an example a curtain wall or window wall, what the architect can do in developing a BIM model that would really be of benefit to the eventual glazing subcontractor is fourfold:

    1. Model in 3D the curtain wall or window wall centerline-to-centerline grid dimensions. Call this a building envelope grid, but put it on its own layer.  This way the building enclosure grid, from which most, if not all, wall component geometry is basically dependent on is set, and can be used by the glazing sub in their development later.

    2. Model only the outline of the wall system framing members, the glass and any special features, like sunshades and louvers, doors or operable vents.

    • Show the aesthetics: system width, depth, special profiles, etc. – not the guts of the system. It doesn’t make sense to model a specific wall product if the winning subcontractor ends up using a different wall system when they perform the work.  If the architect selected Company A’s unitized wall and modeled it in BIM, the curtain wall portion of the BIM model is almost a complete waste if Company B uses a different wall and wins the contract.  The work to change out one for the other would have to be addressed.
    • This information can be used for preliminary budget exercises, determining the number of glass lites, the linear footage of frame members, etc, and special conditions that have to be developed through the course of the project.  It gives an overall intent of what the architect is looking for in the exterior envelope package.

    3. Indicate anchor points and connection to the structure.  The single biggest factor affecting subcontracting field labor is the types and quantities of anchoring conditions.  Seeing how many anchors go into steel or concrete, and whether the wall will be anchored to parapets or face of slab, top of concrete curbs, etc., will be of significant worth to the glazing sub in estimating their field labor rates.  Obviously, if anchor points are not in the immediate vicinity, the span of the frame member may suggest larger profile sizes, or additional / secondary steel to be furnished by either the general contractor or curtain wall sub.

    4. Next, link the specifications and other drawing packages to the model geometry, which is where BIM (at least at this stage) starts to become more of a weapon.  For example, attach the related specifications to the generic model components:  Section 088800 Glass and Glazing to the glass model, Section 084413 Curtain Wall to the curtain wall framing. And if not modeling the sealant or thermal insulation, link the spec sections to the components you know they belong to.  So that when the user selects a line of the mullion in the model, not only would the curtain wall spec come up, all the related specs would be available to select, as well, including sealants, insulation, doors, glass, etc.  Also add links to drawing packages.  If the concrete or steel structure were modeled, then it could be selected, and the drawing of the beam / edge-of-slab detail could be linked, along with all of their related specification documents or contract documents.

    There’s still some basic legwork to doing all of this that can’t be skipped by those preparing the models, be they architects, structural engineers, or HVAC systems designers (the primary users of BIM at present).  For example, the architect can’t model an 8” deep system when a 6” depth would have sufficed, or a 12” system was required for the wind load and / or span conditions.  Glass lites that are too big or too small for the glass manufacturer’s standard sizes create bidding and budgeting anomalies that have to be addressed sooner or later.  The upfront design development that now goes on still has to be completed.

    Also, this is still a GIGO world. Remember that expression – it’s true of anything computer related – the information to be gotten out of a computer is only as good as the information put in. If you don’t believe me, try adjusting your checking account register in your favor, and see how long it takes the bank to send you nasty notices.  Accuracy in checkbooks is just as critical in CAD drawings, and so it is in BIM models, too.

    This accuracy thing is why the GC’s are jumping in to BIM with both feet. If the BIM model is accurate, there are no holes in the architects’ models and controlling costs on the project gets easier. And the architects have the added responsibility of ensuring the models are complete and accurate. BIM closes a loophole in the construction process since the GC’s can now show where a building plan is based on incomplete information, not due in any part to their shortcomings (the opinions expressed herein are those of the author – and I’m sure the GC’s of the world would rise up and take issue as to their motivation for BIM, but this is just one of them – in my opinion).

    And this is now where the glazing sub or supplier can take the BIM model and do their thing:  estimating, value engineering, material takeoffs, shop drawings and structural engineering. I’ll cover that more in detail in the next blog, but first wanted to lay the foundation of what would be ideal to get out of a good, accurate and complete BIM model before the models come through the project pipeline.

    In the meantime, please shoot me a note on your BIM experience – the good, the bad and the ugly. What can and should architects and suppliers be doing differently with BIM from your perspective?

    Posted by Blogger @ 9:18 am

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