3D Printing & Revit

In college, we had access to a 3D printer that could build a physical model of our drafted CAD model by spraying corn starch--or some other medium--layer upon layer.  It looks like we will be able to download a free Autodesk program to convert our revit files to useful format (.stl) for 3D printing (or Stereolithography) should we ever want to make a 3D model for a client or the CT Engineering display case.  Here are some really cool large buildings modeled: http://www.materialise.co.jp/mammoth-stereolithography

After a quick google search, it appears www.makexyz.com  has some local Seattle shops that will build a model for a price per cubic centimetres ($0.25/cm3 to $1.00/cm3).  Based on some typical assumptions, I think that would could model a 2500 sq ft house at 1/8"=1'-0" scale for about $220 (at the low end of prices).  

Simpson Price Catalog & the G:\ drive

For everyone's use, I have added the "Simpson Price Catalog P-2011" to G:\LIBRARY\Simpson Strong Tie.  This leads my post in two directions.

Foremost, I would like to know whether or not I am specifying the least expensive installed connector that meets the demand.  How do you go through the anchor/connector selection process?

Second, the G:\ library is a bit discombobulated as far as order goes (or it might just be me--the new guy--who needs some direction).  Is G:\LIBRARY\Simpson Strong Tie the proper place to put the price catalog?  Rob mentioned revamping it a few months ago.  I second that motion.

Wood Framing: Roof trusses and non-bearing walls

...The more things change, the more they stay the same....

So i got inspired to inquire about details and framing conditions relating to the use of pre-fab roof trusses that span across or parallel to "non-bearing" walls below.

The state of play, is that our STD details indicate an STC clip that allows for something like  1/4" to 1/2" of deflection.

We also have a note section the typically calls out deflections that are in excess of the code minimum for deflections for the roof trusses.
Taken together, these two elements work fairly well when one considers that the clips have about a 3/4" max delfection capacity, and the live load deflections for typical truss in the 30ft range yield about the same deflection.

The implication of the above is that the non-bearing walls should be constructed low by the deflection amount to allow the truss to deflect under loaded conditions. That is NOT the case in the field. Our experience points to the idea that ALL walls are constructed to the same height at the top-plate.

So how are we to handle this situation - where trusses are routinely being installed with "intermediate bearing points" that are not part of the truss calc, and could potentially damage the bottom chord or "overload" walls below that are not designed for these bearing conditions.

The truth appears to be that we are (almost) powerless to change the construction industry in this area without attracting significant criticism and "push-back" from contractors and owners alike - the gain would appear to be fairly minimal... trusses may deflect more freely - but then there may be other problems cropping up relating to gypboard stress/bending and other corollary cosmetic issues...

So it appears that our approach then moves to one of accommodation, where we appreciate the truss deflection issue; note an adequate solution on our plans, but then "overlook" the issue  and implementation in the field when we observe... as do others in the inspection community...

So, amazingly, if our truss conditions are in the "normal" (say up to about 30ft) range, we use our typical details as noted above, and our plans should pass muster as relates to the theory.

As mentioned, ...the changes... stay the same...

Does anyone have a comeback on this...?

 

Steel Shape Availability

For those who are interested, here a convenient site to find out whether or not it is likely a specified steel shape will be available to the contractor: http://www.aisc.org/steel/searchForm.aspx?id=2044

Modular Construction is Here... and we're missing it...?

See this article in the DJC.

Looks like a 3 story modular project went in on Capitol Hill.

DCI is the engineer... Seems like we should be the ones getting in on this ground floor situation... Do we have any "corporate knowledge" of this facet of MFR...? Would be nice to have this on our resume... Lets talk about this.

 

Concrete Specifications - ACI 318 Ch4 - Durability

The 2008 ACI had the ch4 revised for durability requirements. Anne had mentioned this a while back.

It has a potentially large impact on the specifications for concrete mixes.

We will be updating the structural notes for the concrete section to take this into account.

With some exceptions, the IBC 1904 section points us to ACI ch4, and essentially prescribes some water/cement ratios that may easily overide design considerations for the concrete mix. These prescriptions are related to:

• Freeze/thaw
• Sulphate Exposure
• Permeability requirements
• Corrosion protection of rebar

Has anyone already incorporated these code requirements into their "structural notes" yet... (and not updated the company standards?)...

Please weigh in as you feel inspired...

2012 IBC - Seismic Design - Help?!

I was reminded this morning about upcoming changes to the code for a host of different issues - not least of which is seismic. A geotech engineer was asking me how we are approaching the changes... i was not sure. Hence this note!

Has anyone started to dial into this topic yet. We will need to get up to speed fairly shortly. Also, i predict that we will see a "rash" of work trying to complete their projects under the IBC 2009 (first blush appears that 2012 will more onerous for seismic) prior to the expiration of the "grace period" which normally last 3-4 months after the adoption date. According to this post (see above) - the final date for "switch-over" happens on October 13 - a Sunday.

Nels reminded me that we had a little "introduction" to some of the changes to the 2012 IBC with a SK Ghosh webinar back in January.

In reviewing some notes we took, there are a couple of key words that could appear to some to be "alarming". These could include the words:

• Risk Target (MCEr not equal to MCE)
• Updated source model (Nehrp 2008/9 i think)
• Changes in statisical basis for design (was 2% probability of EXCEEDANCE in 50yr -> now going to a target risk of COLLAPSE of 1% in 50yr)

Can we please start a conversation on this topic.