An advertisement in the December 2005 issue of Concrete Construction depicts a masked wrestler diving to grapple with a roll of welded wire reinforcement. The pictured roll of welded wire reinforcement appears to have been deliberately sabotaged—cut and bent to support the advertiser's claims. Rolls of WWR do not look like that unless they have been the subject of vandalism or intentional staging.
As a professional engineer and experienced consultant familiar with the uses and applications of synthetic fibers, steel fibers, and welded wire reinforcement in concrete construction, I submit that the advertisement embellishes the attributes of fibers while misrepresenting welded wire reinforcement.
Concrete floors and precast/pre-stressed components containing fibers do not have structural values comparable to those that have been reinforced with welded wire. Fibers are not an effective or efficient replacement for welded wire reinforcement in terms of resisting tensile stresses and reducing or eliminating diagonal shear cracks in concrete girders. Fibers also have not been shown to be an effective alternative to welded wire reinforcement in reinforcing supported structures.
I question whether “fiber only” slabs can be designed for cut-and-fill situations, slabs bearing on expansive clays, and precast and cast-in-place supported structures. In the case of cut-and-fill projects, the engineer and contractor will be dealing with subsidence or differential settlement. The substrate soils must be compacted to the proper density and sufficiently designed steel reinforced concrete slabs should be specified. When there are expansive clays, the slabs may be subjected to significant vertical forces, which require special design considerations to provide adequate stiffness and moment-resisting capacity to deal with external forces. Precast and cast-in-place supported structures also must be designed with adequate shear and moment-resisting capacity.
Experience in this area leads me to the conclusion that people who understand superior quality construction know that fibers can be a supplement in concrete structures but are not a substitute for steel reinforcing.
Roy H. Reiterman
Technical Consultant to the Welded Wire Reinforcement Institute