Journal of Performance of Constructed Facilities

This paper summarizes the results of field tests on the decommissioned Montreal Dickson Bridge, undertaken over a grid of 0.25 by $0.25m$ on four randomly selected 5 by $6m$ deck patches, and the associated laboratory tests as part of a detailed research program aimed at determining why the bridge deteriorated so rapidly. The basic cause of deterioration was determined to be the lack of quality control (concrete mix composition, placing, compaction, and curing) and the resulting higher permeability of the concrete cover and the associated chloride ion ingress. As a consequence, the resistivity of the concrete was low and reflected in a high steel bar mass loss due to corrosion at several locations on the bridge after a period of only 35 years.

A nondestructive strength evaluation of the I-40 Bridge over the Rio Grande River in Albuquerque, N.M. was completed for the New Mexico Department of Transportation (NMDOT). The I-40 Bridge is a precast, prestressed concrete girder bridge located within $3\mathrm{mi}\text{.}$ of the “Big I” interchange carrying Interstates I-40 and I-25. Because of its location, the I-40 Bridge is subjected to large amounts of heavy truck traffic. The primary objective of the study reported herein was to determine a more accurate capacity rating for the I-40 Bridge and thus, reduce the number of overweight vehicle permit denials. To achieve this objective, a conventional rating analysis is first performed based on American Association of State Highway and Transportation Officials (AASHTO) guidelines. A diagnostic load test and a finite-element analysis are then completed. Details of the AASHTO rating analysis as well as the approach by which measured girder strains from the load test and finite-element results were considered in the capacity rating of the I-40 Bridge are discussed. Findings from the study confirmed that the capacity ratings of the I-40 Bridge could be safely increased by a factor of 1.7.

This paper presents the procedure and results of a strain gauge study completed on the eastbound 6th Avenue Viaduct in Denver. The 6th Avenue Viaduct was modified in a 1997–1998 rehabilitation, making the entire superstructure continuous. New sliding bearing pads failed to properly accommodate expansion and contraction of the bridge superstructure due to temperature changes. Visible damage due to contraction of the superstructure in the winter of 1999–2000 prompted a study of substructure elements to determine the short-term safety and long-term viability of the bridge. Substructure elements were instrumented with a total of 62 strain gauges and two concrete crack gauges. Data were taken for a period of 3 months. Analysis of the data suggests that the bridge is safe for short-term use, but that the long-term viability of the structure has been compromised. Repair or replacement of substructure elements is recommended, along with frequent monitoring during the interim period.

This paper describes the developments and application of a laser-based instrument used to experimentally load test bridges. The instrument is used to quickly and unobtrusively measure bridge girder deflections under static loading. The system can be set up in the median or shoulder of the roadway under the bridge without altering traffic. Data can be collected on multiple girders from one measurement location without requiring access to the girders, and no special targets are required on the girders. As a result, this type of a system can greatly speedup the process of load testing a bridge. In fact, the system can allow bridges to be load tested that would be difficult or impossible under other circumstances. To help understand the way the instrument is used, a description of the basic system operation is given followed by a detailed explanation of the main instrument features. Details of the procedure used to measure vertical deflection of bridge girders are discussed. Finally, an overview of the experimental local tests performed with the NDEVC laser system is presented.

Impact-echo tests were performed on a precast, reinforced concrete bridge slab that was removed from a maintenance bridge built in 1953 in South Carolina. Impact-echo tests were first performed to nondestructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. It was found that the velocity varied by as much as $900m/s$ throughout the slab. After the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slab that were not visible from the surface. Areas with preexisting damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.