Load Testing of Bridges

Current Practice and Diagnostic Load Testing

Eva Lantsoght

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9780429560446
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

Load Testing of Bridges, featuring contributions from almost fifty authors from around the world across two interrelated volumes, deals with the practical aspects, the scientific developments, and the international views on the topic of load testing of bridges.

Volume 12, Load Testing of Bridges: Current practice and Diagnostic Load Testing, starts with a background to bridge load testing, including the historical perspectives and evolutions, and the current codes and guidelines that are governing in countries around the world. The second part of the book deals with preparation, execution, and post-processing of load tests on bridges. The third part focuses on diagnostic load testing of bridges.

This work will be of interest to researchers and academics in the field of civil/structural engineering, practicing engineers and road authorities worldwide.

Part IBackground to Bridge Load Testing

Chapter 1Introduction

Eva O. L. Lantsoght

Abstract

This chapter introduces the general topic of load testing of structures. In this chapter, the reader can find a short background to the topic of load testing of structures, the scope of this book, the aim of this book, and a short discussion of the structure and outline of this book.

1.1 Background

Load testing of bridges can be considered a very specialized topic as well as a very broad topic. On the one hand, it is a very specialized topic since it is one type of testing that is part of the bridge engineering profession. On the other hand, the amount of information and different views and practices in this book demonstrate that load testing is a broad topic and that load testing can be used to serve a large number of purposes.

Both new and existing bridges can be subjected to a load test. Two types of load tests can be distinguished: diagnostic load tests and proof load tests. This book separates these two topics in separate parts with best practices and examples of application. Diagnostic load tests are used to obtain direct information from a bridge in the field, to verify behavior, or to update analytical models. Proof load tests are used to demonstrate directly that a bridge fulfills the code requirements.

For new bridges, diagnostic load tests are the most common type of load tests. In some countries, diagnostic load tests are required prior to opening of some or all new bridges to demonstrate that the bridge behaves in the way it was designed and to confirm the assumptions made in the analytical models used for the design. In the past, proof load tests on new bridges were used prior to opening to demonstrate to the traveling public that the bridge is “safe” for use. Safety in this context was defined as the bridge being able to carry a large number of heavily loaded trucks.

For existing bridges, diagnostic load tests can be used to update the analytical models developed for the assessment of the bridge. A diagnostic load test can be used to determine the transverse distribution of the actual structure, the actual stiffness of the structure, the amount of restraint at the supports, the effect of unintended composite action in non-composite sections, and so forth. This information can then be used to have a better understanding of the bridge behavior. Proof load tests on existing structures can be used to demonstrate that a given bridge fulfills the code requirements by applying a load that is representative of the factored load combination. Proof load tests can be interesting when there are large uncertainties on the structure and its behavior; these may be caused by the effect of material degradation and deterioration on the capacity, the case of planless bridges, or uncertainties on the structural behavior at larger load levels, for example. Since they involve larger loads, proof load tests are more expensive and require a more extensive preparation than diagnostic load tests.

With an increasing need to assess existing structures, methods of field testing including load testing, monitoring of structures, and nondestructive testing have increased in importance over the past decades. The elements of the method of load testing that are discussed in this book are the general procedures regarding deciding on load testing, preparing load tests, executing load tests, and evaluating the results of a load test after the test. These elements are described in general terms, as well as separately for diagnostic and proof load tests, for which different considerations are important. This book contains a number of case studies, showing for specific bridges how these considerations are applied in practice and providing guidance and advice for practicing engineers who are preparing load tests. Besides the tried and tested methods for load testing, this book also discusses novel measurement techniques that can improve the practice of load testing in the future. Additionally, this book shows how load testing can move from a singular test to a method to evaluate the safety of a given bridge by linking the principles of load testing to concepts of structural reliability.

The field of load testing is moving from deterministic approaches based on rules of thumb to practices in which the proven safety after a load test can be quantified. Many researchers have worked on making this step over the past years, often in close collaboration with practicing engineers, bridge owners, and road authorities. With an increasing need to consider structures within their life cycle and as part of a network, there is an incentive to place load testing within the framework of a decision-making process at the network level and to carry out load tests at the optimal time during the life cycle of a structure. These principles are not present yet in the existing codes and guidelines for load testing, but they are topics of research that are discussed in this book.

1.2 Scope of application

As the title indicates, this book discusses load testing of bridges. However, the same procedures can be applied to other structures. For this purpose, a chapter on load testing of buildings has been included. In the introductory chapters on the history of load testing and the current codes and guidelines, both bridges and buildings are discussed. The general principles for load testing of bridges and buildings are the same, but closing a building for a load test has a lower impact than closing a bridge, which results in driver delays and secondary costs. As such, in the past, loading protocols that last more than a day were common for buildings. Another element of particular interest for buildings is that a building may contain a large number of floor spans with similar dimensions. An open question here is how many spans should be tested to have a statistically relevant number of tests for the evaluation of all floor spans in the building. This topic is addressed in Chapter 4 of Volume 13 about load testing of buildings.

This book encompasses all bridge types, and both new and existing bridges. The presented case studies show cases of new bridges that were load tested upon opening because they are built with a novel material, and/or to verify the structural behavior of the new bridge. Other case studies show how load testing can be used for the assessment of existing bridges. The presented case studies of proof load tests all deal with existing structures with large uncertainties, where a proof load test is used to directly demonstrate adequate performance.

The scope includes all building materials. Most of the presented case studies are based on reinforced concrete road bridges, but some applications of steel bridges and prestressed concrete bridges are included as well. The case studies do not include timber, masonry, or plastic composite bridges, but the same principles can be applied to these building materials. In the chapters that deal with general considerations and methodology of load testing, topics of interest related to these building ma...

Table of contents

• Cover
• Half Title
• Series Page
• Title
• Copyright
• Table of Contents
• Editorial
• About the Book Series Editor
• Preface
• About the Editor
• Author Data
• Contributors List
• List of Tables
• List of Figures
• Part I Background to Bridge Load Testing
• Part II Preparation, Execution, and Post-Processing of Load Tests on Bridges
• Part III Diagnostic Load Testing of Bridges
• Author Index
• Subject Index
• Structures and Infrastructures Series