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Metrics: Hard to Swallow

Why metrics proved impractical for U.S. construction.

By Sue McCraven, NPCA

You can lead a horse to water, but you can’t make him drink.” This adage is apropos of the unsuccessful adoption of metrics in U.S. construction. Our federal government has vacillated on mandating metrics as the primary system of measurement for decades. After almost 50 years of failed efforts, this article explains why the building industry has abandoned metrication.1

Metrics make sense
Metric units make more sense, right? In the first place, metric units are based on a rational, interrelated base unit system with prefixes in powers of 10. Secondly, the whole world has already converted to metrics. Even the U.S. pharmaceutical, electronics, education, beverage and auto industries use metrics. So why hasn’t the building industry gone metric? To help clarify the answer, some historical background is in order.

Metric trivia for conversation starters
• 1866: U.S. Congress legalizes the use of the metric system. While American scientists and engineers embrace and advance metrics, the general public clings to the familiar inch-pound or Imperial System of measurement.

1975: The Metric Conversion Act of 1975 establishes the U.S. Metric Board to coordinate and plan increased use and voluntary conversion to the metric system; no target dates are set.

1982: President Ronald Reagan disbands the U.S. Metric Board because of its ineffectiveness at bringing about national conversion.

1988: Congress encourages metrification in the Omnibus Trade and Competitiveness Act by designating metrics as the preferred system of weights and measures for U.S. industry, trade and commerce. Most federal agencies are required to use metrics. There is no mandate for the private sector or for highway and construction industries to convert.

1991: President George H. W. Bush signs Executive Order 12770, “Metric Usage in Federal Government Programs,” directing all executive departments and federal agencies to implement the use of the metric system. Consequently, the Federal Highway Administration (FHWA) mandates metrification and state DOTs administer the policy. The Concrete Reinforcing Steel Institute (CRSI)2 encourages reinforcing steel manufacturers to use soft metric markings for rebar size and grade (a No. 8 bar still retains its 1.00-in.-diameter measure, but includes the 25 mm [25 M] “soft” metric conversion marking).

1991 to 2011: Use of metric markings on reinforcing bars continues to generate confusion on job sites with respect to specifications. Non-governmental firms and private organizations do not adopt metric units.

2008: Because all FHWA partners have effectively abandoned metrics, the mandate is deemed to no longer make sense, and state DOTs abandon metrics.

2011: ACI’s Technical Activities Committee3 encourages CRSI members to mark steel bars with traditional designations. CRSI passes a resolution for members to revert to inch-pound markings on steel reinforcing bars.

Why metric mandates don’t work for construction
Bob Risser, P.E.
NPCA asked Bob Risser, P.E., president and CEO of CRSI, for his perspective on why the U.S. construction industry has abandoned metric conversion:

Do any U.S. construction projects use metric units?
Risser: No. There are no plans or specifications for construction produced anywhere in the U.S. that currently use metric units. By the late 2000s, the remaining DOTs using metric specifications had converted to inch-pound units. The U.S. GSA (General Services Administration) and the U.S. Army Corps of Engineers no longer use metrics. In fact, no one in the engineering community, federal government, state government or private business anywhere in the country uses metrics for construction projects.

Why is CRSI reverting back to the traditional inch-pound system?
Risser: It makes logical sense for the industry to begin the process to move away from soft metric markings, because none of our private or government customers are using metric plans or specifications any longer. CRSI’s recent resolution phase-in period (until January 2014) will allow industry members (who produce more than 90% of domestic steel) to make the changeover at minimal additional expense. CRSI is now in the process of making the appropriate changes to our manuals and literature.

With the rest of the world using the metric system, why doesn’t construction make this seemingly logical conversion?
Risser: Because there is no incentive, no motivation, no market force pushing U.S. construction to use the metric system. It is important to understand that construction is not an “exportable” product. The U.S. liquor and pharmaceutical industries, for example, use dual units (both inch-pound and metric), because these businesses trade in the international marketplace where buyers use metrics as the primary system of measurement. There is a necessary mandate for metrics for industries that sell products globally. There is no market incentive or profit motive for the domestic building industry to use metrics.

If metrics never made sense for the building industry, why was there ever an effort to transition to metric units?
Risser: Money. In the ’90s, the federal government mandate forced state DOTs to go metric if they wanted to be eligible for federal infrastructure dollars. The private construction sector (about 80% of all domestic construction) was never affected by the federal mandate and remained with inch-pounds, so private architects and engineers designing structures stayed with inch-pounds. This meant that contractors were forced to go from project to project, switching from metric to inch-pound units on the job site depending on the funding source. DOTs spent millions of dollars converting from inch-pound units to metric units. Money, not international pressure, was the only reason for federal-money agencies to convert to metric.

Even though there was a federal agenda for metrics, there was general public backlash to the metric system. Our speed limit signs remain in miles/hour, not kilometers/hour. We purchase gas in dollars/gallon, not dollars/liter, and so on. Does the typical person think of housing cost by sq ft or m2? How does a construction worker visualize concrete compressive strength – in psi or MPa?

Why did many consider converting to metric a fiasco?
Risser: Millions of dollars were wasted because the FHWA, representing less than 20% of the total construction market, wanted to go metric. But because private industry and designers never budged, the entire metric conversion agenda was dead in the water. We haven’t calculated the cost to the steel reinforcing industry to retool the stamps to show soft metric conversions.

steel reinforcingOne of the reasons it was unworkable can be explained with a practical example. We have 12-ft traffic lanes in the U.S., and Europe has 3.8-m lanes (or 11 ft 10 in.). Well, when we started talking hard metric (actual narrower lanes: 11 ft 10 in. instead of 12-ft widths for vehicular traffic), the lawyers got involved. There was the possibility of lawsuits involving safety if lane widths were decreased in a metric conversion. Also, all the American paving equipment manufacturers were producing 12-ft or 24-ft equipment according to the inch-pound system of measurement. These paving equipment manufacturers would have to completely retool, at a cost of millions of dollars, to go to hard metric machinery. Eventually, by the early 2000s, about 40 state DOTs had abandoned metric units entirely.

U.S. construction industry stands alone
Outside the United States, this discussion of reverting to inch-pound units might take a different turn. From a more international vantage point, the U.S. construction industry’s failure to convert to the metric system of measurement is apt to be viewed as a step backward. In the late 1960s, for example, England mandated the use of SI units of measurement for all construction, and private designers and engineers followed suit. The U.S. construction industry stands alone in the world in retaining inch-pound units.

One thing is clear after more than 40 years of pushing metrics on the U.S. construction industry: International market forces, not the government, are more effective at mandating wholesale conversion in measurement systems. Apparently you can give Americans the metric system, but you can’t make them swallow it.

1 Metrication is the conversion to the International System of Units (SI), a metric system of measurement, from a region’s customary units of measurement, such as inch-pound.

2 See “Steel & Concrete: Love at First Sight,” Nov-Dec 2011 issue of Precast Inc. magazine, for an overview of CRSI.

3 ACI is The American Concrete Institute. In 2003, ACI’s Technical Activities Committee decided to maintain the inch-pound system of measurement in all its documents. For more information on the American Concrete Institute (ACI), see the May-June 2011 issue of Precast Inc. magazine for “ACI Strength through Consensus.”

Sue McCraven, NPCA technical consultant and Precast Solutions magazine editor, is a civil and environmental engineer.


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