Wood Stud Wall Design - 5psf

Just took a brief poll in the office to talk about the 5psf horizontal loading required by the code for wood stud design on walls per [IBC 1607.13]. Interesting...

The commentray for the IBC 2003 talks about the loading being related to pressurization, or nominal impact loads. The transient nature of these loads seems to indicate the use of the Cd=1.6 factor.

The poll reveals that most of us are using a Cd = 1.6 for our combinations involving wind and seismic as applies to the Fb bending criteria. For the D+L load case, we are NOT applying the 5psf or 1.6 factor.

Steve points out that the 1997 UBC [1611.5] is actually a LOT more clear about the 5psf: It specifically mentions that the 5psf need not be applied simultaneously with the wind or seismic loads, and further gives deflection criteria...

Steve and I speculate that the 5spf may be used in lieu of actual horizontal seimic loads on wall (unless there is a heavy "special case" phenomenon) , and wind should be applied as per standard wind calcs. The question is whether to apply the 5psf as a live load to the D+L load case. When you "factor" (excuse the pun here) in the 97 UBC, it seems that we should consider the 5psf in this case as well (what Cd to use though?)

So to summarize:

1. With the Seismic combination - we are generally using 5spf in lieu of hor seismic loads, with Cd = 1.6 (for flexure and axial)
2. With wind combinations - the wind does not generally apply with the wind loads to a 2x4 wall (the main point of concern)
3. With dead and live combos - we have NOT been applying the 5psf - but should. On this note, we're floating out the idea that we may apply a Cd =1.6 for flexural component of the design only. Cd for other aspects will remain at 1.0.

This seems like a reasonable approach. Let me know what you think.

Hand Rail Design - factors?

The topic of handrail design came up yesterday, and I did a quick pole to find out what folks are up to on this front.

Interesting...

The design forces for the railing are typically indicated in the code - ASCE 7-05 [4.4.1] talks about the loads, and some exceptions for SFR.

In IBC 2006 and previous, [1607.7.1.3] used to talk about a 1/3 stress increase for members and their attachments wrt (with respect to) handrail design. In IBC 2009, this has been removed - drat! (i'm not sure that we were all taking advantage of this stress increase when we had it).

So the question came up about whether the load for handrails referred to in the code was indeed a "live" load, or more of an "impact" load? For wood design, Cd for impact is 2.0, while for live, it is 1.0. Since "common sense" would indicate that handrails loads are not likely to a sustained loading condition, it could be argued that a stress increase could be appropriate - and may be necessary - in order to come up with a reasonable solution.

Maybe we should consider getting the commentary on this section to see why they removed the section.

Any comments?

PT Design and Deflections

I've been see-ing the note on the "Ram Concept News Channel" each time the program boots up. And i've seen the heading about defelctions for the longest time now.

Today i looked at the post, and followed the link to learn more about it. I downloaded the PDF of the slides onto the server.

They talk about PT deflections like it should be something of note in our design considerations. I am not sure that we get too concerned about the absolute deflections reported by RAM Concept - we tend to look at overall deflections and compare them to other areas of the same slab, maybe trying to limit deflections to about 1/2".

The article talks about 3 methods for evaluating deflections:

1. 2D Equivalent frame
2. Spreadsheets considering cracking, creep and load history
3. 3D Finite element

In the article they review several completed buildings, and compare actual deflections with predicted.

The following results were apparent:

1. 2D Eq Frame methods significantly UNDERESTIMATE deflections
2. Spreadheets overestimated the deflection - dependant on actual cracking levels
3. 3D FE yielded reasonable predictions that generally underestimated the real world slabs.

My take-away:

• For our typical Mixed-Use type projects with the 16/24/16 spans that we prefer, these deflection issues do not seem to come up much at all.
• On some of the larger or unusual spans, we may pay closer attention to the deflection - or when you have unusual; loading (like Pete did on his Athletic club - had large Dead load Relative to live load). In these cases it may be wise to use larger deflection multipliers for creep and shrinkage than normal, or consider "tightening up" the deflection range
• In talking with steve and others, it seems that 1/2" long term deflection is a common number to aim at for long term deflections on most span conditions.
• Be aware that creep and long term delfections may be a factor in unusual or long-span conditions.

CT Engineering List of Revit/BIM projects

Just in case you've been wondering if we've ever used Revit, and on what projects, we actually do have quite a few projects of various shapes and sizes under our belt. If you are interested, you could "forage" through this list... Since this is an update to a previous posting, I'm including some further information about how many Revit models we have actually received, and had the opportunity for a team collaborative experience:

• 13239 Widgeon Condo - (Guditz)
• 13138 Thrifty Supply - Pasco - Gene Morris Revit model
• 13076 Arena Sports TI - Misc modeling with CAD backgrounds
• 11247  Ash Way - Bldg E - whole bldg
• Bldg B lobby framing
• Bldg D Lobby framing
• Elevator Framing
• 11123  Nickerson Street Storage
• 11073   High Point Center - seismic upgrade
• 11061   Early World Bridge over Kelsey Creek
• 11002   Hilcrest -storage foundation - and - hilcrest structure
• 10232   McDade Houseboat remodel
• 10090   ADDS Center (drug re-hab center with Miller Hull)
• 10174   Stoneway Concrete - building enclosure - schematic design - model built from photos!
• 10064   Schnitzer #1 - Downstream structure - #2 - Schematic for screener building
• 10030  Open Window School - Truss Repair of existing
• 09177  Ericksen Avenue Office (Anisoglu)
• 09069  Metropolitan Place (GGLO)
• 09156  Wall Aprtments - Green house addition
• 09132   Nunez - misc modeling
• 08175   Little Duncan - 4 story of PT - project went on hold at 40%
• 08129   Newell-Macke - Townhomes - wood framing - piled foundation
• 08156   Jacobsen Residence
• 08070   Magnolia Deck
• 07198   Sprinker Ice Skating Rink Upgrade/remodel - on hold at 40%
• 07258   Warrenton Retail
• 07042   Sortino Office

27 projects/applications so far in Revit, and counting. Some of these projects are small and used the Revit platform to do basic drafting to keep in practice with doing Revit. Most of the newer ones are full blown projects in which we produced final construction docs in Revit.

If you have questions about this, or other want to "engage" with Revit, fire away...!

Going Green... Things continue to develop

I don't keep track of the "green thing" very much, but i am amazed by how much information/literature there is out there... If i didn't know better, i'd think people were actually paying attention to this and (gasp) trying to apply it in real life!

So today i was innocently going over some TJI/iLevel stuff on there website, and going over the ESR reports came across a "new" animal. The report that iLevel has "piggy-backed" onto a  number of their ESR reports is "VAR" report. The full reference is the "ICC-ES SAVE: Verification of Attributes Report". Never heard of this before... obviously i don't get out much!

So iLevel has a VAR-1008 out that talks about its products in light of green standards, LEED etc. I don't know much about this, but iLevel apparently thinks its important to designate its products in terms of these various requirements.

Have you heard of the following:

1. National green Building Standard (ICC700-2008)
2. USGBC (US Green Building Council) LEED for homes 2008
3. USGBC LEED 2009 for New construction and Major Renovations
4. USGBC LEED 2009 for Schools - new construciton and major renovations
5. USGBC LEED 2009 for Core and Shell Development
6. USGBC LEED 2009 for Commercial Interiors
7. USGBC LEED for existing buildings 2008
8. 2010 california Green Building Standards
9. ANSI/GBI 01-2010 - Green Building Assesment protocol for commercial buildings
10. ASHRAE Standard 189.1 - 2009.

I can't say that i'm "boned up" and au fait with any one of these standards or publications. However, iLevel thinks well enough of these standards to publish tables of how their products conform or contribute to these standards... amazing...!

Check our the VAR at: G:\LIBRARY\DETAILS\MFR\iLevel

This looks like something we can no longer continue to ignore... any comments thoughts about this...

BIM - Risa and Wood Framed Design

You may have heard talk about Woodworks teaming up with Risa with a view to providing software in exchange for essentially a "glowing report" and feedback etc about the process. I have spent several days on this issue since we decided to model our smallest building on the Ash Way project in Revit. We thought this to be a good chance to further our Revit experience AND to enter the fray of modelling anaylis. These are my findings:

1. Building the model: The idea of building a model once, and using it to perform your analysis and then doing "double duty" and using it in drafting duty is indeed enticing. It is the definition of Nirvana in the BIM circles...
   Unfortunately, Nirvana has not yet arrived! The marraige between Revit and Risa leaves a LOT to be desired. Having used Revit previously, we can build the model well enough - although there are some new nuances with respect to (wrt) ensuring that the "analytic model" (where the centerlines and workpoints of entities are that an analysis software would use for crunching numbers) is well thought out, and that the nodes connect EXACTLY!
   Revit is able to export its model to RISA through a link. This does effectively transfer info about geometry to RISA, however there is MUCH legwork to do after that.
   It should be mentioned that using RISA - actually using TWO pieces of software - RISA floor and RISA 3D. To try to create "Nirvana" it si necessary to know BOTH these softwares well!
2. Some of my pet peaves with the RISA match up are:

• Material properties are not imported from Revit - you need to set up every wall with correct parameters - once set the parameters do not make it back "into the model in Revit"
• Doorways and Windows are not imported into the RISA model... wth!? you may well ask - i did! The answer is to be found in the small print - you have to model each opening as an "opening in a face" - a Revit term that requires a different process than a window or a door insertion! (did i mention legwork...?)
• Import of DXF files: There is not import of a DWG background. additionally import is very querky into RISA. I finally got a dxf to import - but you ahve to "doctor" the file to import walls - walls need to drawn on a layer with a polyline - where the "gage specified" is the wall thickness - only then will it import walls! - Who knew!
• RISA itself does NOT model flexible diaphragms: The whole point of doing wood framing....! Insted you are left to apply an "area load" which apparently applies loads to walls based on a "pseudo-area" assignment. It was not immediately obvious to me exactly how this was assigned on a complex wall arrangement.
• Re-work of walls: Even though the models were imported form Revit, and did stack, RISA had problems with many of the node points... Leading to re-create nodes in the RISA software... can you say "time consuming...?"
• 2-stage analysis - redefined: RISA wants you to use Risa Floor in order to provide some "pre-processor" capability as a prelude to the RISA 3D work over... The problem with this initial setup is the software wants you to do a "complete" framing plan, and model all aspects of the wood framing BEFORE it will transfer you to RISA 3D - where the heavy lifting is done - the lateral analysis!
3. RISA Output: In theory RISA can provide a good calc and some decent output - see printouts below. However the overhead required seems onerous. It seems that in "our world" where we have 3 or 4 span conditions to design floor joists for - its unreasonable to create a whole model to determine something that we can do by hand in 15 min. Also the wall design fro gravity - again the same comment applies - we have a couple of wall types... it takes 30min to design the studs... do we really have to model every single wall in the project in order to proceed onto the "the juicy bits" ie lateral design. (of course Risa will tell you all you need to do is input dummy elements and sdummy loads etc... all that still takes time, and now you're starting to wonder if these short cuts are going to affect the veracity of the output... ie what is it using in its calcs...? )

SDWC Strong-Drive® Structural Wood Screw for Truss and Rafter Connections

I saw this new screw connection in Simpson's "arsenal" ... does it have a place in the Polygon/Quadrant world, and maybe more...?

SDWC Strong-Drive® Structural Wood Screw for Truss and Rafter Connections