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Class C of prestressed concrete member (ACI318-05)[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Class C of prestressed concrete member (ACI318-05)
- From: "Wontae Kim" <kimwontae(--nospam--at)email.com>
- Date: Mon, 10 Sep 2007 12:00:52 -0500
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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