Responding to "Concern over fiber reinforcement"
In reaction to the comments from Roy H. Reiterman, P.E., FACI in his letter printed in the March issue of Structural Engineer, we want to be clear that the fibers accepted by ANSI/SDI C1.0 Standard for Composite Steel Floor Deck are either macro synthetic "course fibers" (per ASTM Subcommittee C09.42) or cold-drawn steel fibers meeting ASTM A820. Briefly, there are two categories of fibers "micro" (small size, low volume dosage) meant to control plastic shrinkage cracks and macro fibers (much larger fiber, higher volume dosage) designed to replace temperature and shrinkage steel in slabs-on-ground and composite steel floor deck. According to the Steel Deck Institute’s (SDI) C1.0, section 2.4, paragraph B.6.a, "Fibers shall be permitted as a suitable alternative to welded wire fabric specified for temperature and shrinkage reinforcement." In the Commentary for the same paragraph, SDI states, "If a welded wire fabric is used with a steel area given by the above formula, it will not be sufficient as the total negative reinforcement. If minimum quantity of steel fibers, or macro synthetic fibers are used for shrinkage and temperature reinforcement, they will not be sufficient as a total negative reinforcement."
There is also no comment found in the newest standard that welded wire fabric provides any added loading capability to a composite deck slab when used at the minimum values stated above. We agree that in areas with unusual concentrated loads that rebar or heavier wire reinforcement would be required and we would not intend to replace this type of reinforcement. The SDI has reviewed all the tests performed on fiber reinforced composite steel floor decks (at Virginia Institute of Technology for concentrated and flexural loading) and made the determination that macro synthetic and steel fibers are a suitable replacement, as defined in SDI C1.0.

Reiterman’s remark about contractors commenting that over time the wire reinforcement will hold cracks better than fibers will be true in particular if "micro" type fibers were used and the wire was properly positioned. However, according to an FMI study, 35 major contractors all agreed that "more than 50 percent of the time WWF is not properly placed". Most contractors and structural engineers understand this common field issue with wire, hence the acceptance of "macro" type fibers by structural engineers as temperature and shrinkage reinforcement as the macro fibers are uniformly dispersed throughout the slab and will hold cracks tight.

Macro fibers, both steel and synthetic, have been used around the world successfully and are being more widely accepted. There are many established standards, test methods, and references for macro fibers. Listing below outlines some standards and tests that validate the use of macro fibers in many concrete applications.

• ACI 360R-06, Design of Slabs-on-Ground

• ASTM 1609-05, Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam with Third-Point Loading)

• Japan Concrete Institute Standard Test Method for Flexural Strength and Toughness of Fiber Reinforced Concrete (Standard SF-4)

• The Concrete Society Technical Report 34 Concrete industrial ground floors—a guide to their design and construction

• ANSI/SDI C1.0 Standard for Composite Steel Floor Decks.

Reiterman raises two other points concerning percentage of waste/overlap and amount of concrete over reinforcement. The most common requirement for WWF overlap in field is at minimum 1 square (6"x6") and up to 2 squares (6"x12") around the whole sheet of WWF which is higher than 10 percent waste as most contractors we have interview normally use 15—20 percent waste and overlap when bidding a project

As far as his comments on concrete cover we are not clear about the validity. It is our understanding that SDI recommends following ACI 318, which requires a 3/4-inch minimum cover for slabs not exposed to weather.
Macro type fibers (steel and polyolefin) are among the leading products used around the world in major distribution centers, auto manufacturing, institutions, offices, retail, and many others establishments. Structural engineers who understand the technology and standards approve the use of "macro" fibers on these large projects and are specifying them on a regular basis in lieu of WWF. It is a technology that provides a more productive, safer, and economical system for the contractor and owner while providing full depth reinforcement.

Joseph Balik, P.E, and Robert Madore
Grace Construction Products