Holdowns/Shrinkage Take-up Devices - Deflection Limitations

I'm curious about some developments with STD's (not what you think... Shrinkage Take-up Devices)...


My recent 3-story project has shop dwgs from Cummins, and there are take-up devices located at each level. This seems like a lot of devices... my first thought is that the supplier is flagrantly selling his products at the expense of our project and client - since we could probably easily manage the holdowns with only 2 STDs.


Looking through the calc pack that accompanied the shops however, I notice a reference to a 0.2" deflection limitation, that I had vaguely  heard about in our office before, but have no direct knowledge of.


Looking through the IBC and  NDS - there are no clues about limitations that potentially could affect the design of the building structure.


Looking through the ESR-1344 report, we find this nugget:





It talks about a 0.2" limit, but gives no clear rationale for why this is so - merely pointing to IBC 1604.4 which generically talks about analysis and a rational approach etc...


It is only when we look into the acceptance criteria (AC316), that we start getting some illumination. First thing we notice is the cover letter by G Nichols - indicating in item 3 that the .. errr ... "limit"... may be exceeded.... WTH!!@?!



Indeed, reading further we note in section 6 that:





So apparently the 0.2" limitation may be exceeded...  you "just" have to demonstrate deformation compatibility requirements... huh?


I thought that the codes we use direct our design actions and approaches? Now we have to look at acceptance criteria for individual construction elements... for design direction...? Am I missing something...? I suppose we could motivate for the exceedance of the 0.2", but who would pay for our services for same, and do we really have enough time for yet another "meaningless" calc.


This would not be the first time we have come across something like this: recall that the stud-rail issue was also "governed by the wrong branch of government"... dictated by the acceptance criteria for stud-rails, and not code or other publications.


Seems to me like every "official" document source is vying for pole position in order to have "first crack" at directing our design... Its just becoming increasingly difficult to keep up with all the competing interests and sources...


As a personal curiosity, I'm increasingly more curious about who directs for the adoption of these " limiting " or "additional" criteria, and how it comes to influence our design world without having been through the rigors of code review and committees?


Does anyone have any light to shed on this subject?

Temporary Sloping & Benching with OSHA/WISHA Soil Types A, B & C

If you have a soil's report that classifies the soil as type A, B or C per OSHA/WISHA for purposes of temporary cuts, this document might be a helpful aid:

"Sloping and Benching - OSHA WISHA 1926 Subpart P App B" found in G:\LIBRARY\Shoring

It provides some great clarifying pictures that may have been (partially) verbally translated into the soil's report.  A picture is worth a thousand words.

Advance Framing

We've received a few calls recently asking about advance framing, and there seemed to be some confusion within the office as to what that means for us.

I've downloaded the APA guide and placed it on the server.  You can find it on the server at
G:\Codes and Publications\APA\Advanced Framing Construction Guide M400.PDF

From a review of advance framing techniques online, it appears that the term refers to a group of techniques that, when taken together, result in using less lumber for a home, reducing energy inefficiencies and building costs at the same time.

There are quite a few parts of the Advance Framing System that are relevant to us.  Please note that individual contractors and clients may want to use some, all or none of these options.

1. Stud Spacing:  Wall stud spacing is increased to 24" o.c. typical.  For a single family dwelling, this is rarely a serious concern for typical 8' plate heights; even HF studs can support sufficient load to carry two stories of load with typical spans.
2. Wall Corners:  Wall corners are built with fewer studs; two studs with either drywall clips or blocking to support the edge of the drywall at the side without a full stud.  The largest concern I see here is that it makes locating tiedowns slightly more difficult (taller tiedowns must compete with the blocking, or be moved to one side) and that it leaves the corners weaker for vertical load.  Additional care must be taken when providing beam support at corners; we can't assume that either direction will be braced unless we detail the connection.  This also reduces the usefulness of shared holdown corners.
3. Blocking:  One of the goals is to reduce thermal bridging; blocking should be specified as vertical, with one face aligned with either the drywall or the exterior sheathing.
4. Top Plate:  Per 2012 IRC R602.3.2, single top plates may be used when rafters or joists are centered over the stud with a tolerance of 1" or less.  Combined with item #1, that means that all framing on every floor must be lined up at 24" o.c..  In addition, the top plate must be spliced to serve as a proper chord for the shear walls.  
5. Wood Structural Box Panels:  Window and door headers may be designed as box headers instead of solid wood.  Refer to 2012 IRC Section 602.7.2, Table 602.7.2 and Figure 602.7.2 for specifications, sketches and span tables for conventional construction.
6. Jack Stud Reduction:  This one isn't entirely in our field.  Depending on where the smaller (4'-0") openings in the walls are placed, the jack studs may be eliminated if a header clip or similar mechanical connection is used (re: Table 3.23D of the 2012 WFCM).  In addition, fewer studs should be specified at openings in general; again, refer to Table 3.23D.
7. Truss Heel:  Expect to see more buildings with larger truss heels.
8. Diaphragm to Diaphragm connection:  Metal strapping and connectors for floor to floor load transfer are discouraged.  I don't see an alternative for uplift at shear wall corners, but the APA has a reference (SR-101, also in G:\Codes and Publications\APA\) that recommends placing the sheathing such that it splices over the rim joist (or, in the case of trusses, at the raised heel) or at blocking at mid-height.  Since one of the goals is to eliminate lumber used, I think that using 10' sheets and splicing at the rim joist is the better solution.  If 8' sheets are used, either option will add blocking to the wall.

The only one of these items I see a significant issue with is item #4, the single top plate.  I see too many issues in the field to be happy with the idea of requiring that contractors provide 1" tolerance for framing members.  In addition, I see quite a few concerns when it comes to top plate slices.  I recommend that we discuss that one in depth as a group.  The others are either (un)common sense or less problematic.

Holdown Reinforcement

Just checked into the March 2014 edition of Structure.

Saw that they had an article on pg52 - Structural Testing - Testing tension-only steel anchor rods embedded reinforced concrete slabs...

Quite interesting - basically demonstrating exactly how "conservative" Appendix D requirements are/have been.

Attached clips shows rebar being used in field tests at Simpson Facitities in CA.

Seems similar to what some of us are doing / trying to do with holdowns...

This appears to be the same crowd that got us the "break" ...sorrow pun... for anchor bolts with wood sills - governed by wood strength - not Concrete break-out....

Anyway ... interesting...

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.