Precast Options for Bridge Superstructure Design

Precast construction offers many options for bridge owners and designers: Traditional solutions are I-girders, slab girders and box girders with traditional I-girders being replaced by a new family of more efficient bulb T girders with depths ranging from 1200 to over 2400 mm. Box and trapezoidal girders provide lower span/depth ratios and are more aesthetically pleasing. Each province has their own limitations on the size and weight of bridge members that can be transported by road. Multi-axle and steerable trailers are available to maximize girder component size. Spliced girder construction can be used when these limits are exceeded; here girder elements are erected on temporary scaffolding, connected together and post-tensioned to achieve spans of 60 to 80 m. Longitudinal post-tensioning through girders for live loading may reducing the number of girder lines. Custom solutions can be explored for large projects where the tooling-up costs can be spread over a large number of similar precast concrete components. The same thing can apply with new solutions for types of bridges that can be repeated on a variety of sites over a number of years. The fast erection of precast bridge components can speed up bridge construction. Installation in urban areas can occur in off-peak and at night to minimize traffic interruptions. Multiple cranes, barges, temporary bridges, launching trusses can be implemented on difficult sites to help protect the environment. Safe efficient precast concrete construction with built-in durability will ensure the lowest total cost of ownership for the traveling public.