APA Portal Frame with Holdowns: Design Aid

IBC 2308 "Conventional Light-Frame Construction" provides a prescriptive specification for using wood framed portal frames with holdowns.  However, in their Techinical bulletin TT-100E, APA did some testing and provided some engineering values that we may use for our engineered light-frame wood projects (e.g.- Polygon Homes).  The bulletin  allows various parameters and values to be interpolated.  For your interest and use, I've customized APA's table with common scenarios we see in our projects (heights, Hem Fir, actual width).  Their is a PDF or you made copy the Excel file and further tweek it for you project.

You can find it in the folder: G:\LIBRARY\AF&PA\APA

ENERCALC: RESOLVING THE SLOWNESS

I've see many of you walking around with red foreheads--much like me from been banging my head on the desk as I wait for Enercalc to regenerate while between tabs and modules.  Alas, this solution may work for you too with just a few clicks.  Here is what I found online:

Use memory mapped Project Files during program operation:  This option is particularly oriented toward users who store Project Files on network drives, USB memory sticks, or other storage locations that are not on the local hard drive.  When storing files in this way, some users experience slow performance within the Structural Engineering Library.  This is not an issue with the Structural Engineering Library, but rather with the file handling system of the network or attached storage device.  If this applies to you, try selecting the option to "Use memory mapped Project Files".  When this option is selected, the program reads an entire Project File into RAM (Random Access Memory) on your computer, and it can greatly improve the performance of your computer when running the Structural Engineering Library.  When this option is deselected, Structural Engineering Library Project Files continued to be saved only to the source drive and location.

Here is what I did and you can try out: 

1. Select "Settings" tab>"General"
2. Under the "General Settings & File Locations" tab, click the box "Use Memory Project Files during program operation"

Estimating Material Costs

There was a conversation a month or so ago regarding collecting final cost data from contractors in order to generate rough cost comparisons between design approaches (e.g.-PT slabs, structural steel).  Such a list would be handy when talking with clients at the outset of a project.  Here is a folder on the server to drop that information in as we gather it:

G:\LIBRARY\Cost Estimating

Similarly, Plywood Supply in Kenmore sent me a cut sheet of this week's lumber prices for relative comparison that I have added to this folder.  It was suggested that I get it updated every 6 months.

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