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Re: Compressive membrane action

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Wontee,

Your suspicion about compressive membrane action affecting beam response is correct. The fundamental engineering mechanics concepts that have been developed for slabs comprised "beam strips" (see R. Park and W. L. Gamble, REINFORCED CONCRETE SLABS, 1980 - Chapter 12) apply equally well to individual beams. I am not familiar with DOT design methods so I can not comment on the reason why CMA is not applied to beams in these standards. Perhaps there are certain provisions for deep beams that account for CMA in some approximate manner for these types of members. There may be other reasons (type of loading, fatigue, boundary conditions, ... etc.) for not taking credit for CMA in design of bridge beams and girders.

Regards,

Walt Sawruk
Senior Consultant
ABS Consulting
Shillington, PA

At 08:16 AM 4/6/2005, you wrote:
Hi!
I read some papers about CMA in the slab,
 which say CMA increases flexural strength of deck slab significantly.
So, some DOTs have adopted 'isotropic bridge deck design method' and
saved deck rebars a lot.

If this action affects slab design, why doesn't it affect girder and
beam design also?
I have never heard some flexural reinforcements
 can be saved for arching action in beam design?

Can you explain my question?

-wontae

****Wontae Kim****
Unistress Corp.
Pittsfield, MA 01201
(Tel)  413-629-2031
(Fax) 413-499-0824



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