REINFORCING STEEL SUPPORTS

GENERAL

Supports for reinforcing steel in Section 2404.03, E, 2 come in various sizes and types. These types have specific names such as slab bolsters, high chairs or continuous high chairs. The supports are used to hold reinforcing steel in place while concrete is being placed. They are typically made of small diameter steel rods, steel wire, or various shapes of molded plastic.

Table 1 identifies the various configurations of steel wire supports available. Table 2 lists the minimum sizes of steel wire required for the supports. Approval is based on meeting the minimum wire diameter sizes listed in Table 2.

Also, this IM provides an approved list of plastic supports.

Steel wire supports requiring a coating of PVC shall meet the requirements of ASTM A-933. Steel wire supports requiring a coating of Epoxy shall meet the requirements of ASTM A-884

APPROVAL PROCESS

A manufacturer of plastic supports, wishing to obtain approval shall submit the following to the Iowa Department of Transportation, Office of Materials, 800 Lincoln Way, Ames, IA 50010:

1.                     Technical Product Information

2.                     Samples:

      For individual chairs - 5 pieces

      For continuous support - 10 lineal feet (3 m)

TESTING PROCEDURE

The testing procedure involves determining a point load limit for all supports and also a linear load limit for continuous devices.

The point load limit is determined by placing a #4 (#10 M) reinforcing bar on the support. The support is then placed on a 3/4 in. (19 mm) piece of fir plywood. A load is applied to the bar at a rate of 0.5 in. (13 mm) deflection per minute until the support fails. Point loads are determined at the weakest point on continuous supports.

The linear load limit is determined by placing a 1 ft. (300 mm) long plate on top of the continuous support. The support is again placed on a 3/4 in. (19 mm) piece of fir plywood and loaded at 0.5 in. (13 mm) deflection per minute until the support fails.

The supports fail in one of three principle ways:

1.   Breaking

2.   Excessive bending or deformation - more than 1/2 in. (13 mm)

3.   Excessive gouging into the plywood - more than 0.1 in. (2.5 mm)

ACCEPTANCE

Steel supports will be accepted based on meeting the minimum wire diameter based on the type and size as listed in Tables 1 and 2. There is not an approved suppliers list for steel supports.

Plastic supports will be accepted based on approved brands as noted in Appendix A.

MONITOR SAMPLING & TESTING

Samples may be secured from the project and tested to verify compliance.

TABLE 1 METRIC - TYPICAL TYPE & SIZES OF WIRE BAR SUPPORTS

TABLE 2 METRIC – MINIMUM WIRE SIZES

Gauge Decimal Equivalent (mm)

                                             0                                           7.78

                                             1                                           7.19

                                             2                                           6.67

                                             3                                           6.19

                                             4                                           5.72

                                             5                                           5.26

                                             6                                           4.88

                                             7                                           4.49

                                             8                                           4.11

                                             9                                           3.77

TABLE 1 ENGLISH – TYPICAL TYPE & SIZES OF WIRE BAR SUPPORTS

TABLE 2 ENGLISH - MINIMUM WIRE SIZES

Gauge Decimal Equivalent (Inches)

                                                  0                                  .3065

                                                  1                                  .2830

                                                  2                                  .2625

                                                  3                                  .2437

                                                  4                                  .2253

                                                  5                                  .2070

                                                  6                                  .1920

                                                  7                                  .1770

                                                  8                                  .1620

                                                  9                                  .1483