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American Concrete Institute’s ACI 318-14: A modern, accessible code platform

The contemporary use of structural concrete is a complex endeavor, requiring the skills, training, insights and experience of a broad range of professionals. These include designers, engineers, construction specifiers, insurers and code officials, as well as the general contractors, subcontractors and construction personnel.

The goal is to build the safest possible structures that incorporate and reflect state-of-the-art knowledge and experience in the use of structural concrete. At the same time, on any assignment, all involved in the process strive to enhance the user experience, community “look and feel,” and overall value for investors and asset and property managers.

A integral guide in achieving these ends is the American Concrete Institute’s (ACI) “Building Code Requirements for Structural Concrete and Commentary,” a Code that more than 22 nations incorporate in whole or in part into their Building Code requirements.

ACI 318-14

In 2014, ACI published ACI 318-14, the first significant reorganization of the Code since the 1970s. Over the ensuing four decades, the Code has more than tripled in its provisions as knowledge and experience with structural concrete advanced, especially in areas such as torsional strength, seismic design and detailing, integrity reinforcement, concrete exposure classes, strain-based strength reduction factors and anchoring to concrete.

After years of thorough research, including study groups and queries of industry professionals, it was determined a new Code would be easier to reference when designing the use of structural concrete. The reorganized ACI 318-14 needed to follow, as much as possible, the real-world design process, and better delineate the responsibilities of entities tasked with structural concrete design, specification and construction. To support this latter goal, ACI 318-14 includes a new chapter on Construction Documents and Inspection (Chapter 26), which will assist in the process of design to construction. Here, we review ACI 318-14’s principles of organization, along with its implementation and expected benefits

PRINCIPLES OF ORGANIZATION

At its core, ACI 318-11, the previous Code, is built around the design and detailing of cast-in-place beams and columns. Most of these requirements are in chapters 7 through 12. 

In the reorganized ACI 318-14, the committee made the decision that ACI 318’s content and requirements in use are the responsibility of the licensed design professional (LDP). Moreover, this more intuitive version of 318 provides the designer with confidence that all provisions relevant to a particular design have been addressed. In 318-11, there was no internal road map to assure the user of having addressed all relevant provisions. When considering a common construction detail, the user had to refer to multiple chapters governing issues like nominal flexure, axial length, nominal shear strength, strength reduction, tie spacing and bend details, or lap splices. As a result, the existing organization relied heavily on familiarity with the code, requiring visits to multiple chapters to design and detail members and make judgments on which provisions apply.

In contrast, with its member-based organization, ACI 318-14 keeps the user within a given design chapter as much as possible. This means all design and detailing rules for each building member are provided within one chapter. Whether the member is cast-in-place or precast, or mildly reinforced or prestressed, all requirements for a particular member type are contained within the member chapter. When needed, specialty reference is made to a universal set of Toolboxes that support the individual member chapters.

IMPROVED ORGANIZATION

The 27 chapters of ACI 318-14 can be grouped into six core sections: General; Systems; Members; Joints and Connections; The Toolbox; and, Construction.

The General chapters include information on the scope, application and interpretation of the Code, notation and terminology, referenced standards, concrete design properties, and steel designed properties.
The System chapters cover minimum requirements for structural systems. This includes a new chapter that clarifies the overall design and detailing requirements of reinforced concrete building structures; loads and load combinations; and, structural analysis, with a new section on requirements for a finite element analysis. A seismic chapter that addresses earthquake resistant structures, an area of increasing interest and importance, has been added as well.

The Member chapters, the heart of the reorganized ACI 318-14, include One-Way Slabs; Two-Way Slabs; Beams; Columns; Walls; Diaphragms (new); Foundations; and, Plain Concrete Members, as appropriate. Each member chapter references all design and detailing provisions that apply to that member by way of uniform headings.

The Joints and Connections chapters address beam-column and slab-column joints, connections between members, and anchoring to concrete.

The Toolbox chapters are an essential feature of ACI 318-14, comprising Strength Reduction Factors, Sectional Strength, Strut-and-Tie, Serviceability and Reinforcement Details. Many requirements are common to several members, and to reduce duplication of information, these common, supporting requirements are gathered into toolbox chapters.

The Construction chapter now consolidates construction and inspection requirements for the designing engineer. The requirements are designated either as “design information” or “compliance requirements.” In particular, this section is designed to help the engineer fulfill his or her responsibility to communicate field requirements to construction and inspection teams.

Dissemination and adoption 

ACI 318-14 has been published, and will be available in various electronic formats plus the traditional printed copy in both U.S. Customary and S.I units. It will appear in English, Spanish, Chinese and other languages. The 2015 International Building Code (IBC) includes reference to ACI 318-14. 

It has been, and continues to be, a top priority for ACI to ensure a smooth transition to the new Code. These efforts include publishing transition keys that map provisions in ACI 318-11 to their location in ACI 318-14, as well as updating the Reinforced Concrete Design Manual to reflect the new Code.

Moreover, in addition to the Institute website, www.concrete.org, ACI is scheduling approximately 50 seminars for 2015 in various locations to provide additional information about the reorganized 318-14.
Organized from an engineer’s perspective, ACI 318-14 provides many benefits to the concrete and construction community, including:

  • More user-friendly Code, with eliminated gaps and redundancies, reduced cross-references and increased use of graphs and tables;
  • Easier to understand which code requirements apply to a particular design, increasing confidence on whether a design fully meets the Code;
  • Chapters and sections paralleling the design process and following the flow of forces from slab to foundation;
  • Fosters more complete contract documents, resulting in better construction management and less potential for performance liabilities; and,
  • Easier for students and new engineers to learn and apply the Code, and to introduce topics in the future.

ACI wishes to thank the engineering and construction community for their input and recommendations in formulating and subsequent publishing of the reorganized ACI 318-14. It is anticipated to accommodate new topics, incorporate knowledge and construction standards for many decades to come.

Randall Poston is Former Chair, ACI Committee 318: Structural Concrete Building Code. For further information and updates please visit: www.concrete.org/ACI318, as well as www.facebook.com/AmericanConcreteInstitute.