Page:America's Highways 1776–1976.djvu/338

 One of the circular test tracks built in Arlington, Va., for measuring the impact forces of various wheel loads on pavements.

In the early 1950’s, the use of prestressed concrete structural members in this country was hastened by the many research studies dedicated to the solution of problems arising in connection with the adoption of this new structural concept. As a result, the use of prestressed concrete bridges advanced rapidly in the United States, achieving predominance as a construction material in many sections of the country. Similarly, an intensive program of structural research led to the widespread acceptance of the use of high-strength bolting of steel structural connections, an improvement over the previous exclusive dependence on riveting.

A profilometer is used to measure wear and displacement of pavement caused by traffic on the Arlington, Va., test track.

Public Roads studied a number of full-scale bridge loadings in cooperation with the various State highway departments beginning with the Yadkin River Bridge Test in 1928. And in 1950, Public Roads instrumentation and assistance were made available to any State highway department requesting assistance. As a result of these studies and the road tests, which included bridges, a significant contribution was made over the years to the improved fatigue design of steel structures. Out of these studies came a better-understanding of such theoretical concepts as the effects of structural fatigue on load distribution between members and the effect of incorporating new materials, such as high-strength reinforcing steel or 332