Using Soft Metric Reinforcing Bars in ... - Page 6

For formed soffits, ACI 318M-95 prescribes a tolerance of minus 6 mm on concrete cover. Wire bar supports, for example, are manufactured to a height tolerance of ± 1/8 in. which is equivalent to ± 3 mm.* If 20 mm of concrete cover is specified for a formed soffit, an actual cover of 14 mm would be permitted by ACI 318M-95. A wire bar support with a nominal % in. height could have an actual height of 19 minus 3 or 16 mm. The bar support's actual height of 16 mm would be satisfactory. Similarly, if the specified concrete cover for a formed soffit is 40 mm, an actual concrete cover of 34 mm would be acceptable under ACI 318M-95. A wire bar support with a nominal 1-1/2 in. height could have an actual height of 38 minus 3 or 35 mm. The bar support's actual height of 35 mm would be satisfactory.

The minimum concrete cover of 70 mm for concrete cast against the ground is about 1/4 in. less than the minimum concrete cover required in the inch-pound ACI Building Code and ACI 301 Specifications. CRSI recommends using 75 mm of concrete cover for metric construction projects.

IMPLEMENTING THE USE OF SOFT METRIC REBARS IN CONSTRUCTION PROJECTS
The downstream effect of the rebar producing mills' initiative to manufacture soft metric bars deserves special attention in this report. Mills will be shipping soft metric bars to Rebar Fabricators. In turn, the Rebar Fabricators will be furnishing soft metric bars for construction projects. All other parties involved in the design and construction process will be impacted, viz., the Architect/Engineer, and the Reinforcing Steel Placing Subcontractor ("the Placer").** The degree or level of challenge in implementing the use of soft metric bars in a particular construction project will depend on which units were used in the structural design of the project.

* CRSI Manual of Standard Practice, 26th Ed., 1997.
** In some Western States, the Rebar Fabricator and the Placer are the same party.

Figure 2 Hook Details for ASTM Standard Metric Rebars

ALL GRADES OF STEEL
D = Finished inside bend diameter
d_b = Nominal bar diameter
Min. D = 6 db for #10 through #25
Min. D = 8 db for #29, #32 and #36
Min. D = 10 db for #43 and #57

 RECOMMENDED END HOOKS, ALL GRADES OF STEEL

NOTE: All dimensions are in millimeters (mm).

STIRRUP HOOKS (Tie Bends Similar)

*H dimension is approximate.
NOTE: All dimensions are in millimeters (mm).

SEISMIC STIRRUP / TIE

*H dimension is approximate.
NOTE: All dimensions are in millimeters (mm).