Sizing Concrete for Balanced Section Proporties

[ELIofVA]

I have learned the method of calculating concrete beams and slabs from the 9th addition of "Simplified Engineering for Architects and Builders". They describe a method of sizeing beams for balanced section properties. Locally the steel rebars are 60ksi. This book states that 40ksi and 60ksi are commonly available sizes. Yet their process for calculating rectangular cross sections relies on table for Balanced Section Properties for Rectangular Sections w/Tension Reinforcement Only. This table gives values for n, k, j, p, and R for different combinations for fs (steel tension)and fc (concrete compression). Unfortunately, the tables in the book only include fs values of 20ksi and 24ksi with Fc values of 2, 3, 4, and 5 ksi. I work the problems and come up with the answers in the samples. However, I need a table for fs of 60ksi at various Fc. Can someone advise me on sources on table for Balanced Section Properties for Rectangular Sections w/Tension Reinforcement Only for Fc of 40 and 60 ksi? I will appreciate your experienced comments.

 

[Taro]

"fs" refers to the allowable stress in the reinforcing for the Working Stress Design method. 20 ksi is used Grades 40 & 50 rebar, 24 ksi is used for Grade 60 rebar. For more information, see ACI 318 Appendix A (1999 or earlier edition) or a 40-year old reinforced concrete text book.

I would also recommend spending $200 to hire a structural engineer to review your design for a couple hours to keep you out of trouble.