Metrication
America’s metrication efforts
By Adam Neuwald
Adam Neuwald is NPCA’s
Technical Services Engineer.
In George Washington’s
first message to Congress, he pressed for uniformity
in currency, weights and measures. Some 200
years later, the United States is still struggling
with the uniformity of measures. The nation
has come a long way toward metrication over
the past 25 years, and consequently two systems
of measurement are used throughout the United
States causing confusion within many industries.
Due to the lack of any congressional mandate,
the United States joins the ranks of Liberia
and Myanmar as the only countries yet to adopt
the metric system. Both Congress and the construction
industry have been battling over this issue
for a number of years.
Whether you want to admit
it or not, metrication within the United States
is likely inevitable. It may not be in our lifetime,
but eventually the nation will go metric. Attempts
have been made in the past with considerable
success, but Congress has recently been tiptoeing
around the issue. Now the country has reached
a standstill because of the passing of new laws.
Congress is now faced with
the task of either continuing the metrication
process or reverting back to the Imperial System
(English Units). Both options have considerable
repercussions. Continued use of the Imperial
System will eventually lead to America’s
demise in the international market, while metrication
may jeopardize the livelihood of small producers
and contractors who are the backbone of the
U.S. construction industry.
Motivated by post World War
II industrialization and the former Soviet Union’s
successful launching of Sputnik in 1957, the
United States found a renewed interest in the
metric system during the 1960s. Scientific innovation,
combined with pressures from expanding foreign
markets, prompted Congress to authorize the
secretary of commerce to conduct a study determining
the advantages and disadvantages of increased
U.S. use of the metric system. The findings
of this study led to the passing of the 1975
Metric Conversion Act (P.L. 94-168), which created
the U.S. Metric Board whose role was “to
coordinate the voluntary conversion to the metric
system.”
This was easier said than
done. The American public largely ignored the
efforts of the U.S. Metric Board, and in 1981
the board reported that it lacked the clear
congressional mandate necessary for conversion.
The Board was disbanded the following year during
federal budget cutting.
Congress tried a more aggressive
approach toward metrication with the passing
of the Omnibus Trade and Competitiveness Act
in 1988 (P.L. 100-418), which amended the previous
1975 Metric Conversion Act to mandate that all
federal agencies implement the metric system
in procurement, grants and other business related
activities by the end of 1992. This legislative
mandate was further enforced by Executive Order
12770, which required agencies to develop a
conversion plan and timetable. Congress had
envisioned that this conversion of federal programs
to the metric system would act as a catalyst
for the private sector to convert.
By the end of the 20th century,
it was obvious that the United States had made
considerable progress toward metrication. A
number of industries had since switched to metric
units in order to compete in a world market.
State departments of transportation and the
Federal Highway Administration (FHWA) had been
working together to insure a smooth transition
to the metric system. By 1997, 42 state DOTs
had “substantially completed” their
conversion process, according to FHWA. Estimates
also indicated that metric units were used in
75 percent to 85 percent of state administered
highway construction projects in 1999. Metrication
was going smoothly with very few problems. So
what happened?
In 1998 Congress passed the
Transportation Equity Act for the 21st Century
(TEA-21, P.L. 105-178), which is designed to
“move Americans into the 21st century.”
But TEA-21 tended to do the exact opposite.
Section 1211(d) removed the target date for
metric conversion, thereby allowing state DOTs
the option of converting to the metric system.
It did not change any requirements placed on
federal agencies by the Omnibus Trade and Competitiveness
Act of 1988, which also defined the metric system
as the preferred measurement system to be used
in the United States. Congress believed that
if a state had already converted to metric,
then it would continue to use metric units.
Initially most state DOTs that had successfully
converted to metric said they would continue
to use the metric system, but a recent informal
study conducted by AASHTO found that only California,
New Hampshire and New York plan to continue
using the metric system exclusively. This regression
to inch-pound units was largely due to pressures
from suppliers and small contractors who are
reluctant to switch for a number of reasons.
One major reason for this
is because the U.S. construction industry has
a very large internal market, and it has yet
to see global pressure similar to what the automotive,
health care and electronic industries experienced
during the ’70s and ’80s, which
led to their conversion to metric units. Any
pressure on the construction industry to switch
has come from federally funded metric construction
projects. Producers and contractors are concerned
with an increase in cost brought on by metrication.
Another problem is that most
people just don’t have a good feel for
metric units. An engineer designing a double-tee
in metric units might not know if the design
is correct because he/she is unfamiliar with
the new system. To check the work, the engineer
may convert back to inch-pound units adding
additional work and potentially leading to an
increase in design cost.
One significant metric mishap
happened as a result of simply not having a
feel for metric units. In 1983, Air Canada flight
143 ran out of fuel in mid-flight and began
dropping at more than 600 meters per minute
(1,970 feet per minute) with no hope of reaching
its destination in Winnipeg. An incorrect conversion
factor was used in the refueling of the Boeing
767, causing the flight crew to believe the
aircraft had twice as much fuel as it actually
did. Amazingly no one was hurt during the emergency
landing at an abandoned Air Force base. Mixups
like that can be avoided with proper training
and education.
Adopting any new system takes
time – and there is a definite learning
curve that must be overcome before the benefits
of the new system can be fully appreciated.
In time, using the metric system in the United
States may lead to increased productivity and
quality brought about by the use of a decimal-based
measurement. No longer would designers and contractors
have to work in three separate length units
(feet, inches and inch-fractions). Instead,
they could reap the benefits of one simple length
unit (millimeter) that is decimally based. Using
the metric system would also eliminate the confusion
between mass, force and weight with the use
of the kilogram for mass and the Newton for
force.
Granted, conversion will not
be an easy task – it will be filled with
many obstacles. But case studies have shown
that metric projects have experienced little
if any cost increases and minor scheduling problems.
In 1998 the Construction Metrication Council
conducted 23 case studies on metric projects
submitted by 15 state DOTs ranging in size from
a $270,000 bridge replacement in Kansas to a
$1.3 billion dollar reconstruction of Interstate
15 through Salt Lake City. It was found that
none of the projects experienced cost or scheduling
problems. A Missouri contractor even made the
comment, “I’m anti-metric and too
old to change, but there were no real problems
on the job.”
Conversion to the metric system
would be mostly a paper change, although production
equipment manufacturers may beg to differ. The
model codes and most construction standards
contain metric units, as do all federal and
state highway standards, criteria and specifications.
For drawings, feet and inches would change to
millimeters, not centimeters, in accordance
with ASTM E621, “Standard Practice for
the Use of Metric (SI) Units in Building Design
and Construction.” Meters would be used
for sight plans and civil drawings. By using
millimeters on drawings, unit notations are
no longer needed. If there is no decimal point,
the number is considered to be in millimeters,
and if there is a decimal carried to one, two
or three places, it is considered meters. One
rule of thumb is to never use dual units on
a drawing; it increases drawing time and cost,
as well as adding confusion to the drawing increasing
the chance for errors.
Construction products are
dimensioned so they can be multiplied or divided
by a simple whole number making for easy design
and construction. The United States currently
uses the 4-inch building module. The metric
system would change the inch-pound module of
4 inches to the world standard of 100 millimeters
(3.94 inches) creating a change in a few modular
products, such as concrete block, prefabricated
wall sections, drywall, plywood, suspended ceilings
and raised floors. All these products’
dimensions would be converted to “hard”
dimensions. A “hard” metric dimension
is attained by strictly designing and producing
a product in metric dimensions, while a “soft”
metric dimension is found by converting the
dimensions of an already manufactured inch-pound
product to an approximate equivalent metric
dimension as would be the case with rebar, which
would simply be renamed in metric dimensions.
Since most clay masonry bricks
are within a millimeter or two of metric modular
sizes, a slight variation in mortar widths can
accommodate the 100 mm building module, but
it is not as easy for concrete masonry unit
products that are too big to fit within a 100
mm module. Block manufacturers would be forced
to purchase all-new manufacturing equipment
and maintain dual inventories leading to a potential
increase in product costs.
This added cost is the main
reason why the industry as a whole is reluctant
to switch to the metric system. However, simple
economics tells us that if there is a demand
for a product, metric-block manufacturers will
compete to supply it. Larger companies are able
to internally absorb the metric production costs
and offer metric block at competitive prices,
in turn threatening the future of smaller block
manufactures. For now this problem has been
solved by the Cox Bill (P.L. 104-289), which
prohibits federal contract documents from solely
specifying concrete masonry units in modular
metric sizes.
Most precast concrete products
such as box culverts, septic tanks, manholes,
utility vaults and concrete pipe can all be
“soft” converted to metric units.
Just like wooden 2-by-4s, which are not actually
2 inches by 4 inches, pipe is identified by
“nominal” values or “trade”
names that are close to their actual dimensions.
Therefore pipe and manholes would remain the
same size they have always been, and only their
names will be “soft” converted to
a rounded metric equivalent designation.
In terms of concrete production,
mix proportions would be converted from standard
inch-pound units to metric units. A simple one-step
conversion factor of 0.5933 can be used to successfully
convert pounds of cement per cubic yard to kilograms
of cement per cubic meter. (Example: 550 lbs/yd3
* 0.5933 = 326.315 kg/m3) All admixtures would
be added in milliliters (ml) instead of fluid
ounces, and only the name of rebar will change
in accordance with ASTM A615M-01b, “Standard
Specification for Deformed and Plain Billet-Steel
Bars for Concrete Reinforcement,” and
ASTM A706M-01, “Standard Specification
for Low-Alloy Steel Deformed and Plain Bars
for Concrete Reinforcement.”
Compressive strength would
also be converted from “psi” to
“megapascals” per ACI 318M. However,
this conversion could lead to design problems
because ACI 318M presents a few rounding discrepancies.
For example, ACI 318M says that 4,000-psi concrete
can be considered to be 30-MPa concrete. However,
a 30-MPa concrete is actually 4,350-psi concrete,
which is an 8.75-percent difference. A design
value of 28 MPa is closer to the 4,000-psi value
and is probably a better choice. Nonetheless,
when it comes to the placing of concrete, nothing
changes because concrete will easily conform
to the size and shape of any form.
If your company does decide
to convert to metric units or at least produce
metric products, there are a few simple things
that can be done to ensure a quick and easy
conversion.
Train people to “think
metric.” By associating metric measurements
with common items, employees will have a feel
and better understanding of metric units.
Examples:
