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RE: structures & ethics

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Load, Shear, Moment, Rotation, Deflection. 
Shear = f(l)
Moment = f(l^2)
Rotation = f(l^3)
Deflection = f(l^4)
-----Original Message-----
From: Hans E Boge [mailto:Hanseb(--nospam--at)]
Sent: Wednesday, November 24, 2004 12:52 PM
To: seaint(--nospam--at)
Subject: RE: structures & ethics

I’m rusty on singularity functions.  Is it:  load, shear, moment, deflection.  Deflection is derivative of moment.  Or Moment is integral of deflection.  Is this correctin.


Hans E. Boge, P. Eng.
Boge Boge (1980) Ltd.
268 Ellen Street
Winnipeg MB, Canada, R3A 1A7
p:(204) 942-7276 ext 223
f:(204) 942-7288

-----Original Message-----
From: ASQENGG2(--nospam--at) [mailto:ASQENGG2(--nospam--at)]
: Wednesday, November 24, 2004 11:43 AM
To: seaint(--nospam--at)
Subject: Re: structures & ethics


In a message dated 11/23/2004 6:29:25 PM Pacific Standard Time, dennis.wish(--nospam--at) writes:

I must, with all respect, disagree with you. Deflection is much more than an
indicator - it is a function of bending stress and while you should consider
service loading as a means to calculate if creep is the cause of deflection
(or some other issue such as installing crown side down), it does tell me
that there is a bending problem or that deflection due to bending exceeds or
comes close to exceeding the code allowable limits for deflection of wood
products. If I recall my calculus (and please - it's been over twenty years
- deflection is a derivative of moment or bending, which is a derivative of
shear. Therefore the relationship of bending to deflection is a real issue.
Furthermore, in a flat roof or low slope roof, deflection can lead to
Ponding problems that can exceed allowable bending due to increased short
term live load

Deflection is not necessarily an indication that bending stress stress has been exceeded and it is not a function of the bending stress.  Eventhough you have excessive deflection as long as the bending stress and shearing stress are within the allowable then the structure is still safe.  Deflection is only a serviceability issue.  It is not a life treathening issue.  Deflection are being controlled to minimize creeking sounds and bouncy floors on wood members,  unsightful appearance, ponding as you have mentioned, and etc.