David V. Jáuregui

Photogrammetry Applications in Routine Bridge Inspection and Historic Bridge Documentation

This study explored the use of digital close-range photogrammetry for routine bridge inspection and historic bridge documentation. The major objective of the research was to evaluate the feasibility of photogrammetry for these two bridge engineering applications. Study results indicated that photogrammetry provides sufficient accuracy and is a noncontact, inexpensive, and practical measurement option. The research involved two photogrammetry projects. In the first project, photogrammetry techniques were employed in geometry measurement of a simple-span prestressed concrete bridge. The bridge was measured and evaluated according to routine bridge inspection guidelines. PhotoModeler, a consumer-grade photogrammetry software program, was used to process the images for measurements of vertical clearance, lateral clearance, deck width, and structure length. Comparison between photogrammetric and hand measurements showed minor differences, with the percentage error ranging from 0.06% to 1.43%. In the second pro...

On-Site Acoustic-Emission Monitoring for Assessment of a Prestressed Concrete Double-Tee-Beam Bridge without Plans

AbstractAcoustic emission was used in this study to assess the condition of a simple-span, prestressed concrete bridge located in southern New Mexico during a proof test. The 40-year-old bridge is county owned and no design plans were available. Acoustic emission (AE) data were collected under several loading conditions from two groups of sensors placed near the support and midspan of an interior double-tee beam. Strain measurements were also taken at midspan and used to direct the test and determine the maximum loading. AE data analysis methods were applied to evaluate the response of the structure under increasing loads and to develop crack maps. Analysis of the AE data showed signs of internal beam microcrack development near the supports (shear region) as well as in the midspan (moment region). The AE data indicated that damage in the form of crack growth was more prevalent in the region near the supports.

Higher Level Evaluation of a Reinforced Concrete Slab Bridge

In New Mexico, many reinforced concrete slab RCS bridges provide service on interstates I-10, I-25, and I-40. The load rating for this type of bridge largely depends on the live-load moment in the slab. Consequently, the objective of this study was to determine a more accurate value for the equivalent strip width using higher level evaluation techniques. A continuous RCS bridge was evaluated starting with an AASHTO load and resistance factor rating analysis. A diagnostic test was then conducted to measure live-load strains which showed that the slab stiffness fit within cracked and gross section behavior. Furthermore, slab moments from finite element analysis agreed reasonably well with experimental moments derived using the average of the cracked and gross section modulus. From refined analysis, the equivalent strip widths for positive moment were 26.1 and 22.1% greater than those calculated by the AASHTO approximate method for the exterior and interior spans, respectively. The refined widths for negative moment were greater than AASHTO by 13.1 and 11.1%. This increase in the equivalent strip width reduced the live-load effects, which proportionally increased the rating factors.

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.

Load Rating of Prestressed Concrete Girder Bridges: Comparative Analysis of Load Factor Rating and Load and Resistance Factor Rating

In light of the adoption of the load and resistance factor design (LRFD) philosophy by the AASHTO Subcommittee on Bridges and Structures, research efforts are under way to facilitate the transition from load factor rating (LFR) to load and resistance factor rating (LRFR) in New Mexico. Five prestressed concrete girder bridges, courtesy of the New Mexico bridge inventory, were rated with the BRASS-GIRDER and BRASS-GIRDER (LRFD) structural software. The objectives for this study were to evaluate and verify the BRASS (bridge rating and analysis of structural systems) software, to identify the source of dissension between LFR and LRFR rating factors, and to examine any trends in the rating factors as affected by bridge geometry. The comparison of LFR and LRFR focused on both flexure and shear for the strength limit state. The LRFR method generally yielded lower rating factors for flexure, with the longer-span bridges demonstrating a larger deviation between LFR and LRFR. The live load effects were identified as the major factor contributing to the difference in flexure ratings; the dead load effects and flexural resistance had little effect. The LRFR rating factors for shear also were generally lower than those produced by LFR. The discrepancy in the shear ratings was caused by both the live load effects and shear resistance. The dead load effects contributed little to the variation in LFR and LRFR rating factors for shear. Overall, the shear ratings controlled over those based on flexure.

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.

Case Studies Using Ultrahigh-Performance Concrete for Prestressed Girder Bridge Design

Ultrahigh-performance concrete (UHPC) develops very high compressive strengths and exhibits improved tensile strength and durability properties that make UHPC a promising material for bridge applications. Through case studies on typical prestressed concrete girder bridges (simple and continuous), the potential impact of implementing UHPC in New Mexico was investigated. Two existing bridges with high-performance concrete girders were redesigned using UHPC with a compressive strength of 155.1 MPa (22,500 psi) and a modulus of rupture of 8.0 MPa (1,160 psi). The redesign used a modified load factor design procedure for the Service III flexure limit state and a modified load and resistance factor design procedure for the ultimate shear limit state that considered the compressive strength, modulus of rupture, and modulus of elasticity of UHPC. Additionally, 15- and 18-mm-diameter (0.6- and 0.7-in.) prestressing strands were investigated. The use of UHPC and 18-mm-diameter (0.7-in.) prestressing strands reduced the required volume of girder concrete by up to 40%. Additionally, the contribution of the steel fibers in the UHPC significantly reduced the required shear reinforcement.

Load Rating a Prestressed Concrete Double T-Beam Bridge Without Plans by Field Testing

Bridges with no design plans are an issue in New Mexico because of the many that exist throughout the state. Conventional load rating techniques cannot be used because these bridges have limited or no design documentation. This lack of information has created uncertainties regarding the load-carrying capacity of these structures. Only a few states have formal procedures on how these particular bridges should be load rated. A project was conducted for the New Mexico Department of Transportation to develop a procedure for load rating bridges without plans, including prestressed concrete bridges. In accordance with the AASHTO Manual for Bridge Evaluation, a prestressed concrete double T-beam bridge was evaluated with advanced analyses and experimental methods (including load testing and nondestructive material evaluation techniques). A four-step load rating procedure was implemented that included estimating the prestressing steel by Magnel diagrams, verifying the estimate with a rebar scanner, testing the bridge at both diagnostic and proof loads based on strain measurements, and using the proof test results to rate the bridge. Rating factors and posting loads were determined for AASHTO and New Mexico legal loads. Because of the poor condition of the shear keys (some of which were broken), it is shown that the load distribution between beams was adversely affected and the bridge should be load posted.