Low Initial Cost
Bridge owners and designers are often surprised to learn that precast prestressed concrete bridges are usually lower in first cost than other types of bridges. Coupled with savings in maintenance, precast bridges offer maximum economy.
The overall economy of a structure is measured in terms of life-cycle costs. These include the initial cost of the structure plus the total expected maintenance costs. The lifetime cost of repainting steel bridges can amount to 10 to 20% of the original cost of the original cost of the bridge.
Precast prestressed concrete bridges built in accordance with provincial government requirements should require very little if any maintenance. They are constructed using high quality materials to exacting manufacturing tolerances. Fatigue problems are minimal because traffic loads induce only minor stresses.
Fast Easy Construction
Precast prestressed bridge girders require minimal lead times because they are locally manufactured in standard shapes and sizes. The precast components are easy to erect in any weather. Simple connections join the deck girders to the substructure.
Formwork for the superstructure can be eliminated when the tops of girders are placed together to form the entire deck slab. Ties between adjacent units often consist of a grouted keyway and welded or transverse post-tensioned connections. For logging or low volume secondary roads, traffic can run directly on the girder deck.
Carefully planned details will speed the construction process and save money.
Minimum Traffic Interruption
Maintaining traffic and eliminating detours are difficult problems for bridge owners. Precast prestressed concrete integral deck bridges can minimize traffic interruption because of the availability of long span, plant-produced sections and the speed of erecting a bridge. In emergencies, precast girders can be rush ordered and a bridge reopened in a matter of days or weeks using standard components.
Replacement of` substandard bridges can be easily accomplished with precast prestressed sections. In some cases, existing abutments can be reused. In others, precast concrete piles, footings, abutments, wingwalls and piers can be precast and installed along with the deck girders.
Simple span precast bridge deck girders can be pinned to the abutments to resist horizontal earth pressures or be designed as integral abutments to eliminate troublesome expansion joints. Multi-span bridges can be made continuous for a smoother ride and to reduce the number of expansion joints.
Minimum Span/Depth Ratio
A common requirement of many bridges is to keep the superstructure as shallow as possible in order to provide maximum clearance and minimum approach grades. Using prestressing and continuity, a designer can obtain a depth/span ratio as low or lower than 1:32. While deeper sections will require less prestressing steel, the overall economy of a project may dictate the use of the lowest possible depth/span ratio.
Assured Plant Quality
Precast prestressed concrete products are inspected and quality controlled at the plant. Each operation in the manufacturing process provides an opportunity for inspection and control. During fabrication, portions of prestressed beams are proof tested as they are subjected to some of the highest stresses they will ever encounter in service. CPCI member plants manufacture certified products per the CSA Program for Architectural and Structural Precast Concrete in accordance with CSA Standard A23.4 "Precast Concrete - Materials and Construction".
Bridges are subjected to hostile environments as well as repeated impact loading. These structures must withstand not only freezing and thawing but artificial cycles of weathering and chemical attack through the use of deicer chemicals. High strength air-entrained precast prestressed concrete has excellent resistance to freeze-thaw and chloride attack. Also, precast prestressed concrete bridges are non-combustible and resistant to damage by fire.
Precast prestressed concrete bridges can be designed to elegantly blend harmoniously with their surroundings and offer an attractive view from above, beside and below. Strong, tough, durable yet graceful bridges can be constructed using the low depth/span ratios possible using high strength precast prestressed concrete and the simple clean shapes of locally available sections. Contact your local CPCI members to discuss your next project.