CRSI |
ENGINEERING
DATA REPORT NUMBER 42 |
USING SOFT METRIC REINFORCING BARS IN NON-METRIC CONSTRUCTION PROJECTS |
 A
SERVICE OF THE CONCRETE REINFORCING STEEL INSTITUTE
933 N. Plum Grove Rd., Schaumburg, Illinois 60173-4758 |
SYNOPSIS
Metrication in the reinforcing steel industry is becoming a reality.
Several mills have started to make soft metric reinforcing bars. The purpose of this
report is to present guidelines for using soft metric bars in non-metric construction
projects in the private sector. Non-metric projects, which were designed initially in
inch-pound units and which will be built in inch-pound dimensions with inch-pound
materials, represent the major challenge to the acceptance of soft metric reinforcing
bars. The information presented in this report is intended to assist design professionals,
contractors, and the reinforcing steel industry outside the mills, in making a smooth
transition to using soft metric bars in non-metric projects.
INTRODUCTION
A number of manufacturers of reinforcing bars, the "mills",
announced during the first quarter of 1997 that they were beginning to phase in the
production of soft metric bars. Generally, the mills intend to shift their production
entirely to soft metric bars. During the transition period of phasing in and moving toward
the production of only metric bars, the mills will reduce and may even eliminate their
output of inch-pound bars. When the shift to exclusive production of soft metric
reinforcing bars is achieved, it is expected that the mills will discontinue making
inch-pound bars. Several mills will be in a fully metric production mode by mid-1997.
Additional mills are expected to initiate production of soft metric bars later this year.
Various factors will influence the timetable for an individual mill
to complete the changeover to the exclusive production of soft metric bars and the phasing
out of making inch-pound bars. These factors include the mill's current inventory level,
general business condition in the mill's market area, the rolling schedule for reinforcing
bar sizes, the status of completed roll inventory, and the availability of the necessary
new tooling. Uncertainty about the acceptance of metric bars in the private business
sector, and an overall learning curve about the metric system and the metric versions of
the rebar specifications have had some effect on movement toward the change to metric.
TERMINOLOGY
Use of the terms "soft metric" and "hard metric" is
necessary in any discussion of metrication. Invariably, the terms "inch-pound"
and "inch-pound units" will also enter into such a discussion. The meaning of
these terms, as applied to reinforcing bars and in the context of this report, are:
Soft metric conversion
- describing the dimensions of inch-pound reinforcing bars in terms of Sl metric units,
but not physically changing the bar sizes.
Hard metric conversion
- establishing the sizes of reinforcing bars entirely on Sl sizes. Hard metric conversion
would involve re-engineering of the sizes and physically changing the bars.
Inch-pound units -
units based upon the inch and the pound commonly used in the USA and defined by NIST.*
Inch-pound units are often inappropriately called "Imperial" or
"English". Until a few years ago, inch-pound units were also called "USA
Customary Units". The label "USA Customary" has become outdated due to the
use of metric units.
SI units - are defined
as units of the International System of Units (SO and other units specifically approved in
ASTM E380 for use in SI.
WHY METRIC REBARS
The announcement by the mills to fully metricate leads to the question:
Why is the reinforcing steel industry changing to the
production of only soft metric reinforcing, bars?
Federally-funded construction projects are now required to be
designed in metric units and built with metric materials. Construction projects in the
private sector are not mandated to be in metric units. The reinforcing steel industry is
committed to support metrication. By producing only soft metric bars, it should be
feasible economically for the industry, to furnish metric reinforcing steel to metric
projects. And at the same time, the industry will be able to supply non-metric projects
with reinforcing steel meeting (inch-pound) design and construction requirements. Prior to
the adoption of soft metric bar sizes in the ASTM Specifications for Reinforcing Bars, the
Achilles' heel to implementing metrication in the reinforcing steel industry was the
challenge of maintaining a dual inventory to serve two markets - furnishing metric
reinforcing bars for federally-funded metric projects and supplying inch-pound bars for
non-metric projects.
The dual inventory issue was the impetus that provoked the
reinforcing steel industry to press for adoption of soft metric bar sizes in the ASTM
Rebar Specifications. It was estimated that the additional cost incurred by the industry
to supply the two markets would be $200 million to $400 million annually. However, because
the soft metric bar sizes adopted in the ASTM Rebar Specifications in 1996 are completely
interchangeable with corresponding inch-pound bar sizes, the onerous challenge and
significant extra costs associated with a dual inventory can be mitigated.
* NIST stands for National Institute of Standards and
Technology, formerly called National Bureau of Standards (NBS).
© Copyright 1997 by the Concrete Reinforcing Steel Institute
