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May 9, 2014
When structural engineers reach for concrete building code documents late this year, they may be surprised at what they find.
ACI 318, the longstanding guide for structural concrete design and construction, has been completely reorganized in a way that, its writers hope, will be easier to use by the industry.
Every three years, the American Concrete Institute’s building code committee updates ACI 318 the code to which concrete buildings and other structures are designed and built. These changes are then adopted by the International Building Code, which is the document followed by all 50 states and several other countries as the standard building code. ACI 318’s most recent changes arguably the most dramatic since 1971 is now available for review by the public.
In recent decades, changes to ACI 318 have revolved primarily around updates in materials and design technology revisions that reflect new materials, better knowledge of structural systems’ behavior, and new construction systems and analytical approaches. The changes introduced in this version, however, revolve mainly around the organization of the code requirements, shifting the focus from a “force-based” to “element-based” format.
In other words, instead of chapters dealing with forces affecting concrete structures such as “shear” and “flexure,” chapters will now be arranged by the building elements themselves, such as “slabs,” “columns,” and “beams.” Within each chapter will be all the requirements necessary to design that particular element.
This will eliminate the need to flip through several chapters to comply with all of the necessary design requirements for a particular structural member, as was necessary with the old organizational format. The code’s new design can be compared to a cookbook: all the ingredients for baking a cake such as eggs, flour, sugar, oil along with the baking instructions are in one chapter, instead of individual chapters on eggs, flour and sugar.
Changes were overdue
As the understanding of structural behavior and materials had increased over the years and design techniques had evolved and matured, existing chapters in the old code had been expanded to include the new information. The result was a complex document that had become confusing and often off-putting for its structural engineer users.
What do you think?
The revised ACI 318 building code for structural concrete is available for public review and comment through June 17. (See the ACI website for details: bit.ly/1kdlMat.) |
The ACI 318 committee will meet in August to address the comments and make any necessary revisions to the document. It will be published by ACI in November and incorporated into the 2015 edition of the International Building Code.
New chapter will help with future renovations
While most of the revisions to ACI 318 pertain to its reorganization, one new addition is a chapter on requirements for preparing construction documents. |
Previously, ACI 318 was largely silent concerning information beyond structural design itself required to be included in construction documents. It was up to each design office and the permitting authorities they worked with to determine what constituted an adequate set of drawings and specifications.
ACI 318-14, however, spells out this additional information in considerable detail.
For example, structural engineers must now include all loading assumptions, foundation design values, key assumptions concerning lateral analysis, and other related information. While many designers already include this in their drawings, others don’t, or the information they include is overly rudimentary. The latest revision to ACI 318 will change that.
Such information is useful when a building undergoes any sort of renovation, addition or upgrade. With the design criteria clearly shown on the original design documents, engineers and contractors are better able to properly assess an existing structure for modification. Since well designed and constructed buildings can remain in service for many generations, future users of the original drawings will be well served by an accurate “road map” of the design.
Depending on the structural member being designed, requirements from five or more chapters often needed to be met, requiring structural engineers to virtually memorize the location of key requirements due to the nonintuitive nature of the code’s layout. So, while the task of reorganizing a code that had grown from a small booklet years ago to a much larger and more extensive document today seemed somewhat overwhelming, the ACI 318 committee nevertheless decided six years ago to move forward. The consensus was that reorganization was long overdue and would ultimately benefit code users.
With the new ACI 318, structural engineers will be able to access all necessary information for any structural element beams, columns, footings, walls, etc. in one convenient location. The exception will be design information that applies to multiple elements. This information will be contained in “toolbox” chapters and referenced from the others to avoid redundancy. For example, requirements for rebar bends, splices and detailing will be contained in one chapter and referenced by other chapters to eliminate the need to repeat it multiple times.
Some updates shelved
The code reorganization did not come without challenges. One of the most difficult was dealing with the need to update it and reorganize it simultaneously. As it turned out, the time required for reorganization was so significant that some proposals for updating technical and other code requirements were shelved until the next issue of the code.
While the revised ACI 318 code itself can’t really be called simplified it remains at about the same page count as its previous version its reorganization should offer a code that’s easier to use and more welcoming to current and future designers of concrete buildings.
Cary Kopczynski is CEO of Bellevue-based structural engineering firm Cary Kopczynski & Co. and a long-time ACI 318 committee member. His firm has designed numerous concrete buildings throughout the United States and beyond.