Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Lateral Analysis Software for Wood Structures?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Why doesn't the code just come out with a provision: "All wood panel shearwall buildings shall have a 3-D finite element model and a response spectrum analysis" ?   I don't have a problem buying software but my answer to the new  published design guide wood building methodologies is: where are the bodies?  My college timber design Breyer's text flexible diaphragm and stiffness proportional to length method used to work so why does it not work now?   I am all for safety but come on, I don't think my local market is willing to pay for the proposed analysis time.  I think the codes should take a step back and specifically allow the old wood building simplification conventional assumptions of stiffness proportional to length, flexible diaphragms, and drift checks not required for wood buildings.  Handle drift with the "simplified method" and 2:1 aspect ratios. 
 
I think that the market is unwilling to bear the cost of an analysis of a timber frame building that requires calculating wall stiffnesses, rigid diaphragms and story drift checks, funky drag strut load combinations, etc...  I think the increased accuracy or safety is usually nebulous for most wood frame construction.  The extra design time is probably a waste because undoubtably someone is going to decide to put a huge window in the one wall holding the building up after the engineer spent 16 hours analyzing the building by hand and with spreadsheets and then will have to start from scratch. 
 
Also high period for wood buildings?  Does your house resonate violently when your dryer has a wet comforter in it or when you walk down the hall?  Although it is contrary to the popular world view, most residential wood buildings have  very short periods because they are light and stiff.   The periods are probably so short that they would land in the ramp area of a response spectrum and have less input, but the code does not allow you to do that.  Maybe the code could allow the response spectrum "ramp" to be used for wood buildings. 
 
Scott Haan.
 
-----Original Message-----
From: David Merrick [mailto:mrkgp(--nospam--at)winfirst.com]
Sent: Saturday, November 09, 2002 12:08 PM
To: SEAINT
Subject: re: Lateral Analysis Software for Wood Structures?

I have Quakemax, Wood Works and I have helped start the spreadsheet program with Dennis.

Quakemax is the best for limited configurations; I have found some errors in previous versions. I always start with it as a preliminary outline of what the shear walls will be. I can get results in about an hour.

I usually transfer the preliminary Quakmax design to Wood Works, for a final check. Editing input and output for WoodWorks is difficult. Results have sent me into the red on many projects. I am talking days.

In my last project (4 stories) I was overwhelmed with vertical shear wall reactions over beams. I decided to transferr all results to S-frame. 28 load combinations were a whiz. Modeling was about 6 hours.

I was told recently, that TrusJoist is improving its beam design for all load combinations.

My hopes are now that I can organize Sframe input for all wood design, Using Quakemax for the preliminary shear walls and the TrusJoist program for most of the basic beam designs of proprietary sections. Shell elements can represent rigid or flexible diaphragms. All output is easily transferred to Excel. Sframe and Pframe have been developed to link with TEDDS. I have more faith in the results when using Sframe I know the properties and elastic behavior that I am modeling. I make the assumptions, if any, and I am not relying on a "black box model" to tell me results.

I am not happy about the difficult wood design demands placed on the engineer. I am looking forward to a possible ruling that wood needs not to be designed for a 2,500.0 return period. Why wait for a performance code?

Why not also accept a reduction in base shear to reflect the high dynamic period in wood structures. It is already in the code!

If the loads could be just reduced enough to allow an over designed generic simplistic flexible diaphragm analysis with a few basic load combinations.

David Merrick, SE