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Class C of prestressed concrete member (ACI318-05)

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Serviceability Requirements of Prestressed Concrete Members

 

18.4.2 of ACI318-99 (c) [?6 sq rt f?c?] and (d) [?12 sq rt f?c?] prescribes permissible tension at service loads.

18.3.3 of new ACI318-02, 05 classifies prestressed members into Class U, T and C according to f_t.

Does this mean a prestressed member classified as Class C which will have ?some cracks? definitely

 can be accepted as long as it can satisfy strength requirement?

Is engineer?s judgment required?

 

Let?s take an example.

Here is a precast prestressed double tee for the parking garage.

Its strength design shows Mu/phi Mn=1.01 (phi Mn /Mcr=1.4).

Tensile stress (service load) at the midsection is -12000 psi

 while 12 sq rt f?c is -950psi.

Camber is 0.5? downward and its overall length is 60ft.

 

Do you think this design can be acceptable?

 


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