If you've been following our monthly updates, you know ACI's Tolerances committee has three projects under way and all recently have been in the “ongoing hard work” phase. The process of updating the A117 “Standard Specifications for Tolerances for Concrete Construction and Materials and Commentary” continues as committee members work to resolve the many comments and issues raised since the document was last approved in August 2006 (see the June 2007 Tolerances column for more background information). This, of course, is simply the standards development process playing out as it does in each revision cycle.
The committee reached a milestone in August 2008 when it put its draft compatibility document out for ballot. The “Guide for Tolerance Compatibility in Concrete Construction” is notable, says committee chair Eldon Tipping, because it is the first formal attempt within the tolerances area to deal with issues related to materials other than concrete and how they interface. The plan for this project was described in our September 2007 issue.
The draft document brings together in one place tolerances that are used by various manufacturers and trades throughout the construction industry. Under project leader David Ballast, the committee gleaned these tolerances from numerous specifications, guidelines, and other publications.
As expected, this document makes it much easier to see that some of the tolerances established by different organizations are in direct conflict. In other cases, it is apparent that various organizations have adopted tolerances addressing the same building element with different concerns in mind. This document also identifies the areas in which no standard industry tolerances exist.
What is being made clear by this initial compilation is that builders and manufacturers need to work together far more closely to provide designers and owners with coordinated guidelines to facilitate project constructability and minimize rework requirements. Although the balloting period closed Sept. 11, the draft will remain available to committee members on the ACI Web site.
As a point of information, any ACI member with an interest in tolerances should consider joining the 117 committee as an associate member. The online application process is simple—in essence, it's a registration of your interest—and involves no added cost or obligation. It does put you on the distribution list for committee correspondence and gives access to draft documents as they are made available for comment. To join this or any other ACI committee, log on to www.concrete.org, go to the Committee pull-down menu, and select Join.
The committee's third ongoing project is development of its “Standard Measuring Protocol for Evaluation of Concrete Elements for Conformance to Specified Tolerances.” Colin Milberg is coordinating this project, which has several elements including development of data collection methods and procedures, data collection from jobsites, and data processing and statistical analysis. Developments in this project have been described in these pages for the last two years. Visit the CONCRETE CONSTRUCTION Web site for an index of the Tolerances columns. Much of that coverage has focused on the use of laser scanning technology to help in understanding just how well the concrete industry is doing with key tolerance issues such as the orientation, alignment, and location of concrete elements.
Milberg reports that although data collection is ongoing, the effort needs more input. If you can provide data, contact Milberg by sending an e-mail to email@example.com. To visit the project's data collection Web site, go to www.itmcc.sdsu.edu/homepage.php. Meanwhile, the analysis of data from earlier field scans has been completed and now is being prepared for presentation.
The tolerance compatibility document is one interesting intersection point of the committee's other projects. In the commentary, the committee spells out the challenge in describing the geometric properties of a feature and their variations, using two anchor bolts cast in concrete as an example. The section also includes a discussion of possible ways to eliminate tolerance incompatibilities.
The committee is seeking more specific examples from the field to include in the report's third section, which addresses methods of accommodating tolerances. As always, the invitation is open for those with experience and insights to join the committee and contribute to this effort.