Speaking

Case studies will be presented focusing on post-tensioned (PT) bridge evaluation projects involving varying structure types and bridges for multiple DOT’s. DOT’s recognize that beneath the surface of otherwise visibly sound PT bridges lies potentially significant corrosion and deterioration that, if left untreated, can lead to shortened service life and reduced load carrying capacity of bridges. Tendon corrosion is more common in bridges built prior to 2003 due to the grouting materials and construction procedures that were used at the time. If identified early, measures can be taken to arrest corrosion and protect tendons from further deterioration at relatively low costs.

The first project involves 10 PT bridges which first required extensive review of the construction documents of all the bridges. From this review, all 10 bridges received a field assessment, including arms-length visual surveys. A nondestructive testing (NDT) program was then developed for the PT tendons using a risk-based protocol. The NDT techniques consisted of in-situ testing procedures to assess the condition of the tendons taking care to not damage the strands. Assessment methods included visual inspection utilizing a borescope, corrosion rate testing of strands, as well as sampling and testing of the grout. Significant deficiencies were identified in four of the bridges and repair plans were prepared for these structures. Repairs included remedial grouting, removal and replacement of anchorage pourbacks, and installation of a corrosion-resistant impregnation system. Construction observation was also performed to assist DOT personnel during the final phase of repairs. 

The second project involves two, three-span PT bridges. A Phase 1 risk-based protocol NDT program was developed to utilize borescope testing, corrosion rate testing of the steel strands, as well as sampling and testing of the grout. 120 tendon locations were borescope tested, and five locations were selected for corrosion rate testing and grout sampling. Of the 120 borescope tested locations, 21 locations had large voids with corrosion of the steel strands that varied from light to heavy deterioration. This project is at its initial stages of development and is currently ongoing.

Overviews of both projects will be presented along with descriptions of the specialized techniques utilized to thoroughly, yet cost effectively, assess the PT systems of the bridges. Important lessons learned will also be discussed.

Three steel bridges located on a remote stretch of Interstate 15 in northern Arizona are currently the subject of an intensive study involving inspection, load testing, long-term instrumentation and remote structural health monitoring. This project is being funded by the Arizona Department of Transportation (ADOT) through a Federal Highway Administration (FHWA) Accelerated Innovation Deployment Grant. These bridges demonstrate widespread fatigue and distortion-induced cracking in primary steel members which has been monitored by conventional methods during past visual inspections. 

The purpose of the project is to utilize state-of-the-art structural health monitoring (SHM) systems to provide actionable information that will ensure the safety of the traveling public and provide real, practical data to assist ADOT in short-and-long-term decision making about these significant and remote bridges. The systems include strain gauges, crack growth detection sensors, temperature sensors, acoustic emissions, traffic detection, and cameras with a remote data logging system transmitting data to a website. The website allows elements of the bridge to be monitored remotely by ADOT in real time, and the functionality of the website will also be demonstrated live. The three primary goals of this project will be discussed: gain an understanding of the true behavior of the bridge superstructures; monitor critical areas of concern remotely without requiring significant on-site field inspection; and provide the department with an additional tool in making strategic bridge preservation decisions.

The presentation will provide an overview of the project, which began in 2016 and is ongoing through 2020, and will include a history of these unique bridges, load testing and instrumentation, analytical modeling, cutting edge technology and instrumentation selection, fatigue analysis, challenges overcome, and long-term monitoring strategies. The presentation will also include insights from and the perspectives of ADOT, the bridge owner and the specialized project team.