Reinforced Concrete

There is more to design than calculating the forces in the structural members and proportioning the sections.  The American Concrete Institute’s Building Code Requirements for Structural Concrete (ACI 318-08) Section 7.13  and PCA Notes on ACI 318-11 Building Code, EB712, set forth provisions for structural integrity reinforcement intended to enhance continuity, improve the redundancy and ductility of structures. This is achieved by providing, as a minimum, some continuity reinforcement or tie between horizontal framing members. The code provides provisions for reinforcement detailing to prevent excessive crack width under service conditions. 

Good structural analysis and design must be complemented with appropriate reinforcement detailing to insure that the structure as a whole behaves as it is modeled by the designer. On the other hand, a poorly detailed structure may suffer from unsightly cracks, excessive deflection, or even collapse. Good details and bar arrangements should be practical, buildable, cost-effective, and suitable for their intended use. 

Reinforcement is provided mainly to resist internal tensile forces calculated from analysis. Also, reinforcement is provided in compression zones to increase the compression capacity, enhance ductility, reduce long term deflections or increase the flexural capacity for beams.

In addition, reinforcement is required to prevent excessive cracking resulting from shrinkage or temperature changes in restrained structural elements. Lateral reinforcement (stirrups, ties and hoops) are used to provide resistance to principal tensile stresses resulting from shear. Lateral reinforcement in highly stressed areas of compression zones of columns beams and joint provides confinement. This is important especially in structures located in high seismic risk zones.

It is important to provide the adequate area of reinforcement required to resist internal tensile or compression forces required to attain the design section strength. The provided area of reinforcement is not fully effective unless it is fully developed. The fundamental requirement for development of reinforcing bars is that a reinforcing bar must be embedded in concrete a sufficient distance on each side of the critical section to develop the peak tension or compression force in the bar at the section. The reinforcement may be developed by embedment length, hooks, mechanical anchorage devices, headed deformed reinforcement, or a combination of these methods.

In addition to providing the sufficient areas of reinforcement and the required development lengths, good detailing should be done considering the overall structural integrity. The overall ability of a reinforced concrete structure to withstand abnormal loads resulting from unforeseen events, which cannot be considered in design, can be enhanced substantially by providing relatively minor changes in the detailing of the reinforcement.

Publications

PCA Notes on ACI 318-11 Building Code, EB712
The emphasis is placed on “how-to-use” the code incorporating discussions behind the code provisions and fully worked design solutions to real world problems. The manual has been found to be also an invaluable aid to educators, contractors, materials and product manufacturers, building code authorities, inspectors, and others involved in the design, construction, and regulation of concrete structures. The over 900 page publication adds to the understanding of the art and science of structural engineering through presentation of the latest research and design procedures. By incorporating discussions of the history and philosophy of concrete design, the document strives to inform the reader of both the ‘letter of the law’ and, more importantly, the ‘spirit’ behind the code provisions.

Simplified Design of Reinforced Concrete Buildings, EB204
This new, fourth edition presents practicing engineers with timesaving analysis, design, and detailing methods of primary framing members of a reinforced concrete building. Revised and updated to ACI 318-11, it incorporates seismic and wind load provisions to comply with the International Building Code (2009 IBC). All equations, design aids, graphs, and code requirements have been updated to the current codes. Expanded illustrations of the theory and fundamentals and new timesaving design aids were added to include a wider range of concrete strengths. Also contains a new chapter on sustainable design.

PCA 100-2012, Prescriptive Design of Exterior Concrete Walls for One- and Two-Family Dwellings, EB562
This publication provides a simplified approach to the design of concrete footings, foundation walls, and above-grade walls, both load bearing and non-load bearing, intended primarily for use in detached one- and two-family dwellings. This second edition of the standard is revised to coordinate with the criteria of the 2010 edition of the American Society of Civil Engineers (ASCE) Minimum Design Loads for Buildings and Other Structures in the 2011 edition of the American Concrete Institute Building Requirements for structural concrete. A $70 value. Available as PDF with password.

Seismic Detailing of Concrete Buildings, SP382 
This publication contains a comprehensive summary of the seismic detailing requirements contained in Building Code Requirements for Structural Concrete (318-05) and Commentary (318R-05), which is adopted by reference in the 2006 International Building Code. A supplemental CD is included with reinforcement details for beams, columns, two-way slabs, walls and foundations. 2007, 80 pages. Available as Print

PCA Notes on ACI 318-08 Building Code Requirements for Structural Concrete with Design Applications

Industry Resources

The Concrete Reinforcing Steel Institute (CRSI) offers many resources for engineers, architects, contractors—almost anyone who works with reinforced concrete. The CRSI Manual of Standard Practice offers standards for estimates, detailing, fabrication and placement of reinforcing steel, and their Design Handbook (based on ACI 318-98 Building Code Requirements for Structural Concrete) is a valuable reference. The Precast/Prestressed Concrete Institute (PCI) and the Post-Tensioning Institute (PTI) both also offer resources for work with reinforced concrete.