Q.: We read recently that there's a new Building Code for concrete. Is this something builders and contractors have to be concerned about?
A.: You are probably referring to the American Concrete Institute (ACI), "Building Code Requirements for Reinforced Concrete (ACI 318-89)," which was approved by ACI late last year. These code provisions become binding only after they are adopted by government bodies having power to regulate building design and construction. Typically the ACI Code is adopted into model building codes that are in turn adopted by local jurisdictions. Art Mullkoff, staff engineer at ACI, tells us that ACI 318-89 has already been adopted as part of the 1990 BOCA Code. He expects it to be adopted into the Southern and UBC Codes as soon as their next editions are published. Jobs already designed under the previous code will proceed to completion under the older rules.
Code changes directly affecting the contractor are few, but there may be increased inspection on some jobs. For example, moment frames in earthquake-resistant structures now must have a specially qualified inspector continuously watching the placement of reinforcement and concrete. This inspector is to be supervised by the person responsible for the structural design.
Reinforcing bar details
There are significant changes in requirements for reinforcement splices (Chapter 12 of ACI 318). Although there are now only two classes of tension lap splices, calculation of the development lengths on which splices are based is substantially more complicated. Ideally this is not a problem for contractors and subcontractors since the new code specifically requires the designer to show "anchorage length of reinforcement and location and length of lap splices." However, since some of this in the past has been left to the rebar detailer (particularly on smaller jobs), there may be a period of some confusion as the industry and the professions begin to implement the new lap splice requirements.
New provisions for structural integrity added to Chapter 7 are intended to help a structure maintain its overall stability even when major supporting elements are damaged. You'll see designers providing for this by extending some of the joist and beam bottom bars across interior supports, either continuously or with lap splices.
Provisions of Chapter 6 covering formwork remain essentially unchanged; they are given as minimum performance requirements. In spite of requirements for inspection, the code commentary reaffirms that it is "the contractor's responsibility to design and build adequate forms and to leave them in place until it is safe to remove them."
Minimum cement content for parking structures
Reformatting of Code Chapters 4 and 5, with increased emphasis on concrete durability, has brought a new requirement for minimum cement content in Section 4.1.3. Concretes exposed to freezing and thawing in the presence of deicing chemicals must have a cement content of 520 pounds per cubic yard. Although such a requirement is limited in scope--applying primarily to parking garages--it has already attracted considerable discussion among ACI members (see Concrete International, February 1990, page 8).
New code format
ACI has issued 318-89 in a new format, with commentary paragraphs placed in a parallel column alongside the code provisions to which they relate. The commentary is for information only, giving background on many of the code requirements and suggesting other sources of information on how to comply.
To order copies of the 353-page combined ACI 318-89 and commentary, write to the American Concrete Institute, P.O. Box 19150, Detroit, Michigan 48219, or call 313-532-2600. Postpaid price of the book is $34 to ACI members and $62.75 to nonmembers.