Bridge Evaluations Using Nondestructive Techniques

Abstract

In the fall of 2002, I had the privilege of moderating a half-day seminar on nondestructive evaluation (NDE) techniques at ASCE’s 150th Anniversary Conference, in Washington, D.C. Eight speakers addressed a wide range of established and developing technologies that allow us to learn how a building is put together, without taking it apart. At that seminar, Ken Carper, editor of this Journal, suggested devoting one or more special topic issues to NDE techniques and technologies. This is the first of what we hope will be a recurring series of journal issues focused on NDE. The six papers presented here all address the critical issue of bridge evaluation, with particular attention given to the implementation and standardization of NDE techniques. There are more than a half-million bridges in the United States. Many are well-known and receive the special care and attention commensurate with their celebrity status. My esteemed New York neighbor, the Brooklyn Bridge, frequently carries my feet to and from my home across the East River, and is no less inspiring or serviceable than the day it opened more than 120 years ago. The vast majority of our bridges, however, labor in relative obscurity, but have equal importance. On a highway drive of any length we may unknowingly entrust our safety to dozens of utilitarian bridges. Despite their lowly status, these structures perform in an environment far more challenging than most buildings ever experience. In addition to lateral forces (wind and seismic), foundation settlement, and materials deterioration, bridges are subjected to constant dynamic loading and associated fatigue, aggressive erosive forces from flowing water, the corrosive impact of road salts, and cyclic freezing. Sadly, from time to time we have been reminded of the reality of the forces that affect bridge performance. The wind-driven failure of the Tacoma Narrows bridge, an image that often graces the cover of this journal, is the most widely known, but numerous other failures have imparted equally tough lessons to the profession. For example, the 1987 failure of the Schoharie Creek Bridge was one of several caused by scour, but in a broader sense it represented a failure of the inspection and evaluation program. Numerous observations of the bridge before the fatal collapse failed to detect critical weaknesses. Because of the importance of our bridges and the aggressive environments in which they serve, mandatory periodic bridgeinspection programs exist throughout the United States, and indeed throughout much of the world. These programs and the professionals who execute them serve a continuing vital role in protecting the safety and welfare of the public. The work of bridge inspectors has undoubtedly averted countless potential failures. Nevertheless, even an occasional failure is one too many, and we continue to strive to improve the accuracy, consistency, and