Title:
Design of Reinforced Concrete Flexural Sections by Unified Design Approach
Author(s):
Javeed A. Munshi
Publication:
Structural Journal
Volume:
95
Issue:
5
Appears on pages(s):
648-625
Keywords:
design aids; design examples; design of flexural sections; design
procedure; reinforced concrete design; unified design;
DOI:
10.14359/576
Date:
9/1/1998
Abstract:
This paper presents a general procedure for the design of flexural sections by the Unified Design Approach (Appendix B of ACI 318-95). Rectangular and flanged sections with single or multiple layer tension reinforcement and sections having both tension and compression reinforcement are included. Step wise procedure is given for design of each type of the section using familiar equations used in the conventional design. Simple design aids are given for the design of rectangular sections with multi-layer tension steel at the tension control limit. The design by the Unified Design Approach involves a transition region between the tension control and compression control behavior regions for which the strength reduction factor f is varied linearly from 0.9 to 0.7 (0.75 for spiral transverse reinforcement). This presents a problem for the designers who, due to architectural or other reasons, may not be able to provide the depth required for tension control design and may end up being in this transition region. The design in the transition region would involve an iterative procedure since increase in the tension reinforcement to satisfy the factored moment would decrease the strain in the extreme tension steel and reduce the f factor and the design strength. This paper presents design aids for sections which fall in this transitional behavior region. Several examples that illustrate the design procedure and the use of the design aids are available as an Appendix to this paper. The new provisions do not specify any upper limit on the steel reinforcement ratio for flexural members. This may encourage use of higher reinforcement ratios to attain the required strength and promote compression control behavior of flexural sections, which may not be the intent of the code.