| Better inspection techniques are needed for our deteriorating infrastructure. Recently, many reports have been published concerning the state of deterioration of public works systems which include bridges, navigation structures, pavements, etc. Statistics recently revealed that nearly half of the nation's bridges are either structurally or functionally inadequate. Another example of deteriorating infrastructure occurs in our nation's waterways. Approximately one-half of the Corps' 269 lock chambers along inland waterways will reach or exceed their 50-year design life by the turn of the century. Without on-going inspection programs to detect maintenance problems, unwanted down time will be required to solve several neglected problems. A two-week maintenance shut down has enormous effects on the whole transportation network, especially river transportation.; This thesis investigates NDE techniques applicable to civil works structures. Nondestructive testing can offer assurances, in varying degrees, of the soundness of a structure or a mechanical part. Many nondestructive techniques are used in industry and research laboratories today, but, with the current state-of-the-art, only a few of them can be applied to civil engineering.; Specifically, the use of Direct-Sequence, Spread-Spectrum, Ultrasonic Evaluation (DSSSUE) is proposed. This new method uses a continuous transmission technique that increases the detection sensitivity and "illuminates" the structural part as compared to conventional pulse-echo methods where scanning is required. The improved sensitivity can be used to overcome the signal attenuation in large structures and to detect small changes in the structures. It is anticipated that this method will have application in the field of continuous monitoring of civil works structures. |
