Saturday, July 14, 2012

Reinforced Concrete Design

What makes Unique of RC...?

It is a COMPOSITE MATERIAL...
  • It requires APPLICATION of more involved Principles of Mechanics...
  • Structural Design is iterative requiring both ANALYSIS and DESIGN DECISIONS aided by judgment and EXPERIENCE.
  • ACI 318 -the model code in the United States of America for guiding the design of RC members, look at Chapter 8.
  • NSCP Code -the code in the Philippines..conforms to the provisions of ACI 318 Code!!!
Important Material Properties...

Concrete Strength and Steel Strength...
  • 28-day Compressive Strength, f'c: ACI 318 Code 2011 edition, Chapter 5.
  • Modulus of Elasticity of Concrete, Ec: ACI 318 Code 2011 edition, Chapter 8.5
  • Strength property or yield strength, fy..
  • Modulus of Elasticity of Steel, Es: 29,000,000 psi --ACI 318 Code 2011 edition.

1. --Procedures on how to Design Reinforced Concrete Beams!!!

Concrete Beam Sizing..!



Determination of Beam Size (b x h)---USE Spreadsheet or Hand Calculation!!!

Concrete Beam Size (b x h) or (b x d), FORMULA:

Formula for Beam Sizing
Beam Section, Strain and Force Diagram

Equilibrium Equation or Neutral Axis Distance, c -- Quadratic for c

Rebars Determination..

Area of Steel (As) determination!!!

Strength Formula and Area of Steel (As)
Area Steel (As) Formula
rho formula

The ACI Code 10.3.3 to 10.3.5 limits on the Steel Ratio (rho):

rho maximum
rho balance
1.1 Minimum Beam Size for which Deflections are NOT LIKELY to be a Problem.
1.1.1 Set Neutral Axis distance, c =< 0.375cb....

FORMULA for Beams Size NOT LIKELY to HAVE DEFLECTION PROBLEMS


1.2 Arrangement of Rebars, Splicing points and splice length, development length, hooks requirement, and required Stirrups.

Design of Stirrups and Spacing
Stirrups Spacing Requirements per ACI Code

Structural Integrity Requirements for Perimeter Beam

Structural Integrity requirements for Interior Beams

ACI Standard Bar Details

2. --Procedures on how to Design Reinforced Concrete Columns!!!

Lateral Tie Design

ACI Standard Bar Detailing for Columns
ACI Columns Rebars splicing details

ACI Standard Bar Bending Diagram

Minimum Column Steel and Ties requirements
2.A.--Structural design for Column using Interaction Diagram.

Column Interaction Diagram
2.B.--Example of ACI Interaction Diagram.
Interaction Diagram-Rectangular Section-Courtesy of ACI
Interaction Diagram-Spiral/Circular Section-Courtesy of ACI
2.C.--Summary of Column detail Requirements.

Column Design Requirement

2.1 Strength Reduction Factor, phi =0.70 -applicable up through ACI 318-1999; they have been changed to phi =0.65, for compression members (columns and beams under compression controls) beginning with ACI 318-2002 Code, and continuing with the ACI 318-05 and 2008 up to present.

3.--Example: Design of Column using MS Spreadsheet.

Design of Column MS Spreadsheet page #1

Design of Column MS Spreadsheet page #2

Rectangular Beam Design Example:

Data:
  1. Load and Span
  2. Material Properties -f'c, fy
material strength
Simple Beam with uniform load and point load
Calculation #1
Calculation #2
Calculation #3
Calculation #4

Hence, in more than 20 years of my practice, reinforced concrete design needs an in depth STUDY, and RESEARCH; therefore, for the information of the DRAFTSMAN drawing and/or drafting ("pag GUHIT" in local dialect) a proposed project and then observing a design drawings are not enough to say that you will know every aspects of concrete design. Concrete Design and Analysis are more on CALCULATIONS and application of more PRINCIPLES of MECHANICS.

References:
  1. Reinforced Concrete Design by Chu-Kia Wang and C. G. Salmon, 6th edition-1998;
  2. Building Code Requirements for Structural Concrete, ACI 318-2011, American Concrete Institute;
  3. Building Code Requirements for Structural Concrete, ACI 318-1963, 1971, 1977, 1995, 2002; 2005, 2008, 2011 editions;
  4. NSCP Code, volume 1-Buildings and volume 2-Bridges, 5th edition-2001, 6th edition-2010, Association of Structural Engineers of the Philippines;
  5. ACI Design Handbook -ACI 318-2004;
  6. ACI Detailing Manual 2004;
  7. ACI Manual for Concrete Practice 2005 and 2008;
  8. CRSI DESIGN HANDBOOK, 10th edition, 2008;
  9. Design of Concrete Structures by Arthur H. Nilson, 12th edition -1997, 13th edition, 14th edition-2008;
  10. Design of Reinforced Concrete by Jack C. McCormac, 3rd edition,-1993, 5th edition 2005; 7th edition;
  11. Reinforced Concrete, Mechanics and Design, by Wight and Macgregor, 6th edition-2012,
  12. Reinforced Concrete Fundamentals by Phil M. Ferguson, John E. Breen, James O. Jirsa, 5th edition -1988;
  13. Building Design and Construction Handbook, by Frederick S. Merritt, Jonathan T. Ricketts, 6th edition -2002, McGraw-Hill International Edition.

Reference Books #1
RC Books#2
RC Books #3