Kenneth R. White

Nonlinear Ultrasonic Testing with Resonant and Pulse Velocity Parameters for Early Damage in Concrete

Many types of damage or deterioration in concrete cause microcracking. Damage usually progressed from evenly distributed microcracks, to major cracks, to eventual failure of the concrete. This article reports on a study undertaken to compare the effectiveness of a nonlinear ultrasonic testing method with established ASTM testing methods in detecting early damage in concrete. In this study, geometrically identical concrete specimens were evaluated with nonlinear ultrasonic techniques. When the fundamental ultrasonic frequency interacts with a material, harmonics are generated. As damage increases, the magnitude of the nonlinear interaction increases, causing a greater portion of the fundamental frequency to be converted to higher harmonics. The authors included specimens of three distinct water-cement ratios which were compressed at regular load increments to induce damage. At each load increment, no cracking was visually observed. However, with increases in damage to the specimens, increases in harmonic ratios were measured. These increases were markedly larger as compared with changes noted with other nondestructive ASTM tests performed. The authors conclude that the nonlinear ultrasonic method shows considerable promise as a sound, nondestructive evaluation technique for detecting early damage in concrete. Sensitivity of this method generally increased with increasing water to cement (w/c) ratio.

IMPLEMENTATION OF VIRTUAL REALITY IN ROUTINE BRIDGE INSPECTION

The innovative use of QuickTime Virtual Reality (QTVR) and panoramic image–creation utilities for recording field observations and measurements during routine bridge inspections is reported. A virtual reality approach provides the ability to document a bridge’s physical condition by using different media types at a significantly higher level of detail than is possible in a written bridge inspection report. Digitally recorded data can be stored on compact disc for easy access before, during, or after an inspection. The development of a QTVR bridge record consists of four major steps: selection of the camera stations, acquisition of the digital images, creation of cylindrical or cubic panoramas, and rendering of the QTVR file. Specific details related to these steps are provided, as applied to various bridge inspection projects. The potential impact of QTVR on bridge management—in which routine inspection data are a factor in making decisions regarding the future maintenance, rehabilitation, or replacement of a bridge—is discussed.

Nonlinear Ultrasonic Evaluation of Concrete Microcracking

Microcracking is usually associated with most types of concrete deterioration. The nondestructive detection of deterioration in in‐situ concrete in its early stages is not practical using current technology. In this project nonlinear ultrasound was used to evaluate the degree of microcracking changes resulting from increasing compression stresses. Second and third harmonic amplitudes were measured and correlated to the degree of microcracking induced in the specimen. These harmonics were found to increase with increasing levels of microcracking.

STATIC MEASUREMENT OF BEAM DEFORMATIONS VIA CLOSE-RANGE PHOTOGRAMMETRY

Preliminary results from a pilot study of beam deformation measurement using digital close-range terrestrial photogrammetry (DCRTP) are reported. The study consisted of both a laboratory and a field exercise. In the laboratory exercise, photogrammetric deflection measurements of a steel beam under single-point loading were made and compared with dial gauge readings and elastic beam theory. Laboratory results showed an accuracy ranging from 0.51 to 1.3 mm (0.02 to 0.05 in.). It was shown that DCRTP provides a feasible way of evaluating the global deflected shape of a structure, which is otherwise not practical using traditional instruments. In the field exercise, the initial camber and dead-load deflection of prestressed concrete bridge girders were measured photogrammetrically and compared with level rod and total station readings. Field results fit well to the rod-measured girder camber, and an average difference of approximately 3.2 mm (0.13 in.) was achieved compared with elevation measurements made with the total station. A comparison of the photogrammetric measurements with the dead-load deflection diagram was also made. Work is in progress to improve the accuracy of photogrammetric measurements for field applications. It is anticipated that DCRTP will provide highway agencies with a cost-effective alternative to high-cost systems using metric cameras or laser technology with the potential for several types of measurements in bridge applications.

Bridge Inspection using Virtual Realty and Photogrammetry

This paper is divided into three major sections: (1) bridge inspection via virtual realty; (2) bridge monitoring via photogrammetry; and (3) potential impact and future development. The first section briefly covers the current regulations for conducting route bridge inspections. The second section gives an approach using QuickTime Virtual Realty (QTVR), which is described for recording bridge inspection data with a high level of photographic detail. The section covers the basic equipment (hardware and software) and procedures for documenting the physical condition of a bridge using virtual realty techniques. The third section provides a brief overview of photogrammetry including basic definitions, instruments, procedures, and applications. Topics discussed include aerial versus terrestrial photogrammetry; the central perspective projection; measurement by triangulation; photogrammetric camera types, characteristics, and calibration; and photogrammetric analysis fundamentals. The last section of the paper provides some concluding remarks regarding the potential impact of virtual realty and photogrammetry.

Long Range Bridge Girder Evaluation Using Lamb Waves

The detection of fatigue cracks in steel bridge girders has become a major problem for bridge engineers in the USA. Currently, most bridge inspection is carried out using visual methods. Visual methods are time consuming and often miss fatigue cracks hidden under paint or by other bridge members. Snooper trucks or platforms are often required so that the inspector can gain access to all parts of the bridge. This requirement adds to the expense and complexity of the inspection process and often requires that one or more traffic lanes be closed to accommodate the required equipment. In view of the above mentioned problems and that bridge inspection budgets are limited, there exists a critical need for global and semiglobal Nondestructive Evaluation (NDE) methods which can evaluate critical parts of the bridge structure rapidly and inexpensively.