Todd R. Hawkinson, PE, Wire Reinforcement Institute
Use as Shear Reinforcement in Concrete Bridge Girders
Welded Wire Reinforcement (WWR) is seeing an increased use as shear reinforcement in bridge girders, such as AASHTO Type II, III, and IV-4, Bulb-Tee Girders and U-Girder Sections, due to its available increased strength and the reduction in time or labor cost to install the material in the precast beds. State departments of transportation (DOT) allow the use of welded wire shear and confinement reinforcement in girders and many have developed standards for its use.
What is Welded Wire Reinforcement?
WWR uses a cold worked/drawing process to produce differing wire sizes while increasing the tension and yield strengths of the wire. Wires are then welded together by an electrical resistance welding process to form a grid pattern. Engineers can specify the desired spacing and wire sizes.
Wire sizes range from Smooth/Plain (W) wire; W0.5 to W45 and Deformed (D) wire; D1 to D45. The number represents the area of the wire divided by 100. For example, a D31 wire has a cross-sectional area of 31/100 or 0.31 square inches. Wire is typically drawn down to the third decimal place as well. For example, the actual area of a ½” bar or wire is 0.1963495 square inches1. The wire producers will draw the wire to 0.197 square inches to meet the actual area of a ½” bar/wire. Several state DOT Bridge Departments allow the use of 0.197 square inches of welded wire reinforcement as the actual area for a ½” bar/wire.
Spacings of wires vary based on design requirements. For instance, at the end of the girder – in the confinement zone, some state DOT’s require a larger amount of steel reinforcement closely spaced to satisfy the confinement requirements. Spacing of a D31 welded wires can be as small as 2 inches; this will be limited by manufacturer .
Development of the Welded Wire Size and Spacing:
Wire Conversion Engineers convert steel reinforcing bars typically shown on state DOT standard drawings to WWR. Also, many states now have standard welded wire reinforcement drawings.
One method of conversion is to replace the shear steel reinforcement with WWR on an equal area basis to 60 ksi yield strength material that is the typical steel reinforcement yield strength used. This method does not take the higher allowable yield strength that welded wire reinforcement is produced to according to ASTM A1064. Wire size and spacing are according to the design drawings.
The other method is to determine the area of steel required by converting the 60 ksi yield strength to higher AASHTO and DOT allowed steel yield strengths of 75 ksi. Differing wire sizes and spacing are utilized to provide the required shear reinforcement.
Once converted, shop drawings such as the one shown in Figure 2 for Welded Wire Shear Reinforcement in bridge girders are prepared and once approved, the welded wire is then fabricated and provide to the precaster/prestresser in various lengths and wire sizes to satisfy design shear requirements. Also shown are holding wires to maintain the spacing and shape for placing in the precast beds. The length of the styles (sheets) is dependent upon the precast beds, the labor and equipment utilized in placing and moving the WWR styles in the plant.
The use of WWR allows for decreased production times in the precast plants. And reduced inspection times as well as reduced overhead costs.
Welded Wire Reinforcement (WWR) utilized as shear reinforcement is a viable solution to satisfying the design requirements of girder design as well as providing a potentially lower cost alternative to bridge construction.
For more information please contact Todd Hawkinson at [email protected]
1Refer to ASTM A1064, “Standard Specification for Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete” for additional information and applicable requirements.