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127 C h a p t e r 4 The main objective of SHRP 2 Project R19A, Bridges for Ser- vice Life Beyond 100 Years: Innovative Systems, Subsystems and Components, was to develop the methodology and means to design bridges for service life. The term â100 yearsâ in the original project title represents a vision in which enhanced service life of bridges is achieved. In the early stages of the research, it was not clear what form the ultimate product or result of the project would be. To gather information regard- ing the state of knowledge for service life, the research team searched both published and unpublished data in the United States and abroad. This extensive search indicated that cur- rently there is no comprehensive document that can be used to design bridges for service life in a manner similar to design for strength, which is provided by the LRFD Specifications. During this search one point became evident. In some cases, designers, or even specifications, were referring to design of concrete for durability and service life as design of bridges for service life. It is very important to recognize that a bridge as a system contains many parts that are not concrete, and although design of concrete portions for service life is important, it is not by itself equivalent to design of overall bridges for service life. Review of the state of knowledge also indicated that a gen- eral framework or systematic approach that could be used as a basis for designing bridges for service life is lacking. Consequently, the following important questions were raised: 1. What are the service life issues? 2. What are the knowledge gaps with respect to service life? 3. What framework should be used to design bridges for service life? 4. How should the design for service life be communicated to end users? An extensive amount of work was carried out to identify and comprehend the issues that have historically resulted in reduced service life for bridges. A summary of this work is provided in Chapters 2 and 3. In evaluating the knowledge gaps, the study identified a sig- nificant number of issues that needed additional research to develop practical solutions. Considering the project limita- tions, the original request for proposal asked for only proof of concept testing to evaluate possibilities. In this case, proof of concept refers to a process in which a solution to a given prob- lem is identified; limited testing is conducted to examine the feasibility of the concept; and if appropriate, further research is recommended for others to complete the development of the concept. Following this approach, the project prioritized a number of needed research topics into three categories. Topics in Categories 1 and 2 were addressed within this project; no work was carried out on Category 3 topics. Chapter 3 pro- vides a summary of Category 1 and 2 topics, and Appendix A describes Category 3 topics. One of the major study observations was that although eliminating movable or expansion joints was recognized by many to be the most effective approach to enhance bridge service life, there was no corresponding scientific approach to design jointless bridges. At this point in the project, the research team was faced with two important questions (Questions 3 and 4 listed above): How should design for service life be approached? and How should the information about service life design be communi- cated to the end users? The team ultimately concluded that development of the Design Guide for Bridges for Service Life was the answer. The Guide is now available through TRB (http:// www.trb.org/Design/Blurbs/168760.aspx). The main objective of the Guide is to provide information about, and define procedures for, systematically designing both new and existing bridges for service life and durability. The Guideâs initial approach to designing for service life is to provide a body of knowledge relating to bridge durability under different exposure conditions and constraints and to establish an array of options capable of enhancing service life Summary, Conclusion, and Recommendations
128 relative to those conditions. However, the philosophy used in the Guide could also be used to establish a plan for designing a specific bridge for service life by customizing certain steps within the framework. In general application, the Guide is not intended to dictate a unique solution for any specific service life problem or identify the âbest and onlyâ solution, unless it is used to establish a plan for the service life design of a specific bridge. The Guide does not include discussions on the application of the framework for the service life design of specific bridges. Further work is needed to elaborate on the steps for customizing the Guide for specific bridges, especially for signature and long-span bridges. The Guide recognizes that not all bridges can or need to have 100 years of service life. Therefore, maintenance, reha- bilitation, and replacement are part of the service life design process. Included in the Guide are 11 chapters, each devoted to par- ticular bridge elements, components, subsystems, or systems. Collectively, these chapters provide a basis for approaching service life design in a logical and systematic manner. The vision to develop the Guide was born from the need to have a single reference for integrating the many related activi- ties that are necessary to keep a bridge in service for a speci- fied period of time. Closer examination of the Guide reveals this vision of an integrated approach, in which the design of a bridge is viewed in a holistic manner. The current concept of design, for the most part, refers to checking supply and demand with respect to strength on an individual element basis. In contrast, design of a bridge should be viewed as a process in which a structure, on a total-system basis, is cre- ated to last a specified period of time. For a bridge to last and provide its intended function for a specified period of time, it is necessary to consider more than just strength parameters. There is a need for future development of the Guide. How- ever, further development should be undertaken only after having a comprehensive blueprint for its final state, as the evo- lution of the Guide will be incremental. Each incremental development should be a step in turning the Guide into a document that can provide comprehensive procedures to design, construct, and keep bridges in service for specified periods of time. Further development of the Guide should not be approached as simply updating chapters and incorporat- ing missing data. Instead, integrating the various activities necessary to keep a bridge functional for a specified period of time should be the objective. Future development of the Guide should focus on seamlessly connecting the activities of design, fabrication, construction, inspection, maintenance, and retrofit. Currently, several independent documents govern design, fabrication, construction, and management of bridges, and each of these steps has its own governing speci- fications. The roadmap for future development of the Guide should be constructed such that the divisions and boundaries between each of these stages are eliminated, and the entire process of keeping a bridge in service for a specified period of time is seamlessly connected and transparent to the owner. The Guide also contains significant amounts of informa- tion that may not be needed or relevant for certain agencies. For instance, in rural areas or smaller municipalities where there are many short-span bridges, customized and reduced versions of the Guide may better serve the local bridge com- munity. For longer-span or more complex bridges, higher expectations with respect to service life and more correspond- ing information will be required. The main elements missing from the first edition of the Guide are detailed examples and tools capable of demonstrat- ing how to apply and navigate through the massive amount of information provided. The development of these tools and examples should not take place in a vacuum and should be done in cooperation with the bridge community. This final report and the Guide also include several innova- tive ideas, details, and design procedures. These new ideas are mainly placed in the appendices, signifying that these ideas have not yet been used in practice and that their use should be approached with caution.
