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/306897
by Mary Lou Ralls Accelerated Bridge ConstruCtion 16 | ASPIRE , Spring 2007 P E R S P E C T I V E Accelerated bridge construction includes both the replacement of existing bridges and the construction of new bridges. Innovative design and construction m e t h o d s a n d h i g h p e r f o r m a n c e materials are used to reduce the typical bridge construction timeline without sacrificing bridge quality. The goal of accelerated bridge construction is to open a cost-effective, long-lasting bridge to traffic with increased safety and reduced traffic disruption in a shortened construction period. Delivering projects quickly to improve safety and reduce congestion is now the priority on many of today's bridge construction projects across the country. This trend is increasing. Improved safety is needed to avoid injury to construction crews in the work zone and to motorists as they move through the growing number of work zones. Reduced congestion is needed to provide reliable travel times for motorists and emergency response teams and to avoid negative economic impact to surrounding businesses. Rapid delivery of both emergency and planned bridge construction projects ensures that people and goods continue to be efficiently and effectively moved across cities, counties, regions, states, and bordering countries. In addition to delivering bridge projects more quickly, the need exists to deliver bridges that last longer. Almost a quarter of the nation's 595,000 publicly owned vehicular bridges are currently structurally deficient or functionally obsolete 1 at a time when the average age of the bridge inventory is approaching its design life. This state of the nation's bridges requires bridge professionals to pursue design and construction materials and methods that extend the service life of bridges to 100 years and that reduce maintenance requirements during this extended life. 2 To obtain longer life with improved performance, bridge owners increasingly specify the use of high performance m a t e r i a l s , i n c l u d i n g c o n v e n t i o n a l strength and high strength, high performance concrete, as the standard for accelerated bridge construction projects. Accelerated bridge construction encom- passes the entire process from planning through construction. Planning and preconstruction activities may include: • early meetings between the owner, contractors not bidding on the project, and suppliers to discuss possible innovations; • right-of-way acquisition and utility relocations before advertisement of the project; • early environmental clearance and permitting; • innovative contracting strategies such as A+B bidding, lane rental, and incentive/disincentive clauses in the contract documents; • electronic shop drawing submittal and approval process; • procurement of prefabricated products, such as prestressed concrete girders before advertisement of the project; • stockpiling of standardized compo- nents. D e s i g n a c t i v i t i e s m a y i n c l u d e prefabrication of bridge components or the entire bridge. In addition, geotechnical engineering enhancements, such as mechanically stabilized earth walls instead of conventional cantilever retaining walls, may be included. Reinforced or lightweight backfills may also be used. Construction activities may include allowing contractors to adopt innovative ideas, use innovative equipment, and perform concurrent on-site engineering operations. Innovative equipment i n c l u d e s s e l f - p r o p e l l e d m o d u l a r transporters (SPMTs) to move the entire bridge into place. Concurrent operations can include building abutments and intermediate supports simultaneously. Bridge prefabrication is an accelerated bridge construction method in which the bridge components or the entire bridge are built in an off-site or nearby controlled environment. This helps achieve quality construction. The components or entire bridge are then moved to the final bridge location for rapid installation. A decision- making framework to assist owners in determining whether prefabricated bridges will provide benefits for their specific project is available on the Federal Highway Administration (FHWA) website. 3 Because of the success of accelerated bridge construction projects to date, the FHWA has increased its support efforts and resources to further advance the development of these systems into more conventional practice nationwide. Aspects of accelerated construction may be included in any concrete 3. 2. 1. ASPIRE_spring_2007.indb 16 3/7/07 12:31:38 PM