Designing with the Metric System

Abstract

Civil design discussed thus far has been based on the U.S. customary system of units. Despite numerous efforts in the private sector and in state and federal government to change to SI (System International) units (the metric system), the U.S. customary system of units continues to be the prominent system used in the United States. The American Society of Civil Engineers, for example, requires that all of their publications, such as journals and conference proceedings, be written in SI units, with conversion units allowed. Most of the state and federal departments of transportation have changed their specifications for bridge and road construction to the metric system, even though the U.S. customary unit versions are also available in some states. It is not the purpose of this book to take a position as to which system is better. The entire book is written with U.S. customary units because it is still the dominant system used in the design and construction industry in the United States. That is also the system to which the author is accustomed. Nevertheless, the author has worked on several international design projects for which the metric system was required. This chapter is written for those designers that are interested in working in SI units. In this chapter, design practices that are unique to the metric system are discussed and compared with the principles presented in this book. To illustrate the differences between the U.S. customary and metric systems, examples of drawings prepared with the metric system are shown.