ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306852
12 | ASPIRE , Fall 2009 P E R S P E C T I V E Some notable concrete bridges have been constructed in the United States in recent years using criteria developed to ensure service life of 100 to 150 years. However, these examples have been limited to a relatively small number of large and exceptional projects. Limited consideration of extended service life in the United States may partially be a result of the lack of an AASHTO specification on this subject. The AASHTO LRFD Specifications 1 provides these definitions: Service Life—"The period of time that the bridge is expected to be in operation." Design Life—"Period of time on which the statistical derivation of transient loads is based: 75 years for these Specifications." Since service life involves consideration o f m a n y e n v i ro n m e n t a l , d e s i g n , materials, and construction factors, the LRFD definition of design life obviously does not represent a basis for service life. Accordingly, the AASHTO LRFD Specifications does not recommend any specific time period for service life. On an inter national basis, British Standards have required a minimum service life design of 120 years since 1988. 2 This requirement has also been implemented in other parts of the world where British Standards are used. The range of service life criteria internationally is indicated by the 300-year target service life of the Second Gateway Bridge now under construction in Brisbane, Australia, with an 850 ft-long, cast-in-place concrete, balanced cantilever main span. Special serviceability limit state specifications as well as special concrete specifications were developed for the Confederation Bridge between New Brunswick and Prince Edward Island to ensure a minimum service life of 100 years. Service life of 100 years has been used for major bridge and tunnel projects in Europe since the early 1990s. 3 The Oresund Fixed Link between Denmark and Sweden, opened to traffic on July 1, 2000, utilized concrete specifications developed to ensure a service life of 100 years. 4 In 1994, the owner and the consultants for the Oresund Fixed Link established the following as the basis for the concrete specification requirements: "The requirements will be based on well-known technology, and will secure a service life of 100 years with proper maintenance but without any major repair work." For purposes of this discussion, the service life period will be considered to be the time period to be achieved "with proper maintenance but without any major repair work." This would preclude, for example, complete removal and replacement of the bridge deck. The United Nations defined sustainable development as "meeting the needs of people today without destroying the resources that will be needed by future generations." Increasing the service life of major bridges from 75 to 120 or 150 years "without major repair work" would obviously greatly reduce the resources required for a given installation on an annual basis. From this by Cliff Freyermuth, CLF Inc. Service Life and Sustainability of Concrete Bridges The I-35W Bridge Replacement in Minneapolis uses a fixed, anti-icing spray technology (FAST) system. The bridge has been designed for a 100-year service life. Photo: FIGG. ASPIRE_fall09.indb 12 9/11/09 2:55:25 PM