State of The Practice and Art for Structural Health Monitoring of Bridge Substructures

CHAPTER 1. INTRODUCTION

In order to develop safe, cost-effective, and reliable structures in the future, it is imperative for designers to cross-check assumptions made during the design phase with the conditions that the structure will actually experience. Ideally, the designer’s understanding of those conditions is reflected in the design, and the structure’s response to such loads should show close agreement. However, in many cases, the worst-case scenarios controlling the design do not actually occur; therefore, the true structural design is never fully verified. This does not suggest that the design is unreasonable; rather, it indicates that the response to extreme loads remains somewhat hypothetical. In the instances where extreme events occur, there are rarely quantifiable measures of how the structure performed due to the absence of permanently installed or embedded instrumentation along with a continuously sampling acquisition methodology. More common and less critical loading states can and have been used to provide insight into the response that can be either extrapolated or used to provide a lesser degree of verification. However, this type of post-construction verification is not commonplace.

Civil engineering applications are typically the last to adopt and/or receive the inroads into newer technological breakthroughs that are used in other arenas of science. Similar to the personal computer industry, advances in wireless microwave and satellite communications occur daily. Even some past technologies have not been fully implemented or explored with the exception of atypical high profile structures (i.e., in high-risk seismic regions). The upshot is that many past technologies are now relatively inexpensive and can be reasonably applied to civil-type structures more routinely.

As a civil engineering application, remote monitoring has only begun to make a breakthrough into the field, having historically been used as a research and development tool. Its benefits are finally coming to realization. There is a push for the United States to become wireless; therefore, it has increasingly become a necessity for civil engineering to lead the way, specifically in the area of remote structural health monitoring (SHM).

Remote monitoring, at its most basic, provides users with a way to collect data from an event, such as a foundation capacity test or ongoing thermal recording, and then transmit the collected data to another location, such as a database or spreadsheet file on a computer. This concept can be taken one step further by introducing limits on the data collector for alerting users or programming triggers on the data collector to initiate retroactive data collection and transmitting.

Remote monitoring can be used for many different civil engineering applications, from quality assurance in construction to ongoing health verification. It can provide assurance to engineers and society as a whole that infrastructure withstands into the next generation. Furthermore, as new technology is upgraded, the cost and effectiveness benefits of remote monitoring continue to increase. As with all new approaches, they are not fully embraced by the construction and engineering society alike until there are recognizable savings. However, with catastrophic failures like the St. Anthony Falls Bridge (also referred to as the I-35W bridge) collapse over the Mississippi River, additional pressure to investigate the use and/or require the implementation of new technological advances plays into acceptance.

PROBLEM STATEMENT

As a civil engineering tool, remote monitoring is a priceless benefit for the health monitoring of structural members. Currently, the most common monitoring technique for inspecting bridges is visual inspection. Based on standards set by the Florida Department of Transportation and the Federal Highway Administration (FHWA), every bridge is required to undergo a visual inspection once every 2 years. While this method is satisfactory for structurally sufficient noncritical structures, it does not provide a reliable way to determine the actual health of a structure. Providing a remote monitoring system will allow researchers to monitor a bridge in real time at a remote location. This method will help reduce man hours and provide accurate results and up-to-date data to assess the structural integrity of a structure and not just its visual appearance. Foundations, however, are not readily amenable to retrofitted instrumentation regardless of whether or not remote monitoring is employed. Therefore, a concerted effort to incorporate these more peripheral options must be considered at the design phase for proper inclusion during construction.

SCOPE AND SIGNIFICANCE

This study provides a brief overview of previous foundation health monitoring schemes. It also proposes the use of wireless communication and Internet systems technologies as a means of providing remote monitoring capabilities for structural members or systems for agencies such as State transportation departments and FHWA. However, the use of these technologies as described is not limited to the use by these agencies. The original intent of the research was not to determine the best technology to carry out the project but rather to provide examples of monitoring procedures and data from a variety of tests that were monitored using this concept.

Another focus of this study is to provide several different monitoring techniques that can be applied to a structural member to enable it to be monitored throughout its life. These techniques include sensors and devices that would provide data related to temperature, load, strain, and video recording. All of these parameters are vital for the determination of the structural health of a member or system.

REPORT ORGANIZATION

This report consists of five chapters. Chapter 1 introduces the topic of the report. Chapter 2 summarizes the state of SHM in general with an emphasis on substructure health monitoring (SSHM) and the ability to convert current wired systems into wireless. Chapter 3 provides an in-depth look at a case study that was carried out on an innovative type of drilled shaft. It is used to highlight the convenience and, in some instances, limitations and considerations that should be addressed when planning a prototypical remote monitoring program. Therein, it summarizes the successes and learning experiences gained from this project. Chapter 4 discusses the culmination of all the work performed on this project and reviews the short- and long-term monitoring procedures implemented on the I-35W bridge. It also explains the construction, setup, instrumentation, monitoring procedure, and results for a full-scale remote SHM system. Chapter 5 summarizes the main discoveries made throughout the study and presents conclusions and recommendations for future work.