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[SEAOC] Concrete Dilema
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- Subject: [SEAOC] Concrete Dilema
- From: "Eric J. Scott" <sac39899(--nospam--at)saclink1.csus.edu>
- Date: Fri, 12 Apr 1996 18:50:26 -800
- Comments: Authenticated sender is <sac39899(--nospam--at)saclink.csus.edu>
- Priority: normal
I am studying to take the PE exam on the 19th, and I have run into a snag on determining where the neutral axis is in a RC beam. The method that I have used in the past is to simply use the expression: a=As*fy/.85*f'c*b and a=B1*c However, in flipping through my concrete book and Lindburg's PE review manual I found another method which uses a factor multiplied with the depth, or: c=k*d where k=sqrt(2*p*n+(p*n)^2)-p*n p= the steel ratio (since rho is not part of my keyboard) n= the modular ratio of E (steel)/ E (conc.) I know that one expression is based on Ultimate Strength and the other is based on Working Stress, but since they both assume a cracked section shouldn't they give similar values? The example that I used was a concrete beam with the following properties: b=18" d=37" f'c=3000 psi fy=60,000 psi As=6.0 in^2 Ec=3,122,000 psi Es=29,000,000 psi n=9.29 k=0.333 The location I get for the neutral axis using the Ultimate Strength method is 9.23". The value I get using the Working Stress Method is 12.34". I have less than a week till the exam and I would really appreciate it if anyone can let me know which method is the correct one. Thanks, ============================== Eric J. Scott escott(--nospam--at)csus.edu ASCE-YMF Membership Chair, Sacramento Cline, Agee, and Swedin Engineers and Architects ============================== ...
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