As the bridge stock in many countries is ageing, the topic of bridge assessment is gaining more importance. Bridge load testing is one of the tools that can be used to assess existing bridges. Over the past decade, assessment, and by extent, bridge load testing, have been applied, studied, and improved in various countries. This paper provides an international overview of bridge assessment practices, load testing practices, and recent research insights. Moreover, synergies in the research activities, collaboration efforts via technical committees, and recently published codes and guidelines are highlighted. The major topics of importance identified are linking load testing to global and element structural behaviour, improved on-site sensing techniques, incorporating load testing with structural monitoring, non-destructive evaluation, numerical modelling, probabilistic analysis, and leveraging the use of digital tools for embedding detailed load testing insights into modern bridge management systems. It can be concluded that bridge load testing is a dynamic field of application and research, for which international collaboration and comparing best practices is essential.

Bridge load testing can answer a variety of questions about bridge behavior that cannot be answered otherwise. The current governing codes and guidelines for bridge load testing in the United States are the 1998 NCHRP Manual for Bridge Rating through Load Testing and Chapter 8 of the AASHTO Manual for Bridge Evaluation. Over the last two decades, the practice of load testing has evolved, and its intersections with other fields have expanded. The outcomes of load tests have been used to keep bridges open cost-effectively without unnecessarily restricting legal loads, when theoretical analyses cannot yield insights representative of in-service performance. Load testing data can be further used to develop field-verified finite-element models of tested bridges to understand these structures better. In addition, structural reliability concepts can be used to estimate the probability of failure based on the results of load tests, and noncontact measurement techniques capturing large surfaces of bridges allow for better monitoring of structural responses. Given these developments, a new Transportation Research Board (TRB) Circular, Primer on Bridge Load Testing, has been developed. This document contains new proposals for interpreting the results of diagnostic load tests, loading protocols, and the determination of bridge load ratings based on the results of proof load tests. In addition, included provisions provide an estimation of the resulting reliability index and the remaining service life of a bridge based on load testing results. The benefit of load testing is illustrated based on a cost-benefit analysis. The current state-of-The-practice has demonstrated that load testing is an effective means for answering many important questions regarding bridge behavior that are critical to decisions on bridge maintenance or replacement. Load testing has evolved over its history, and the newly developed TRB Circular reflects this evolution in a practical way.

The TRB Testing and Evaluation of Transportation Structures committee consists of members from infrastructure owners, practicing engineers, nondestructive testing providers, and researchers. This committee is concerned with condition assessment and evaluation of the performance of transportation structures. The committee addresses the use of testing, monitoring, and nondestructive evaluation methods to assess the load-carrying capacity of structures, detect and quantify defects, and assess condition. The primary focus of the committee has been the transfer of knowledge to promote practical application of research for evaluation of structures for effective asset management. To encourage rapid adoption of the latest technologies and methods, the committee has been pursuing products that demonstrate the successful application of technologies and methods for the condition assessment and performance evaluation of transportation structures. This ECircular is a product of these efforts. Load testing has been one of the recognized methods to evaluate and load rate bridge structures. While advanced calculation methods are available to determine the ultimate capacity of existing structures, timely and accurate in-service data needed for model input and service life prediction is not always forthcoming. Load testing provides a useful alternative for such cases where current calculation methods, for one reason or another, cannot provide satisfactory answers to performance questions on existing bridges. AASHTO’s Manual for Bridge Evaluation and the 1998 Manual for Bridge Rating Through Load Testing have been generally used as a guidance to load testing. This E-Circular provides significant updates to the existing documents to reflect the current state of the practice on bridge load testing, and will cover the preparation, execution, and analysis of load tests, including diagnostic and proof tests. If effectively used, these methods can extend the useful life of existing bridges in a cost-effective fashion.