18-12, Nishiochiai 2-chome,
Shinjuku-ku, Tokyo 161-8575, Japan
Phone: +81-3-5906-0211
FAX: +81-3-5906-0112

Water Resource Development

BACKGROUND & PURPOSE OF PROJECT

This overbridge was planned as part of the reconstruction project of Monou Toyoma Road within National Route 45 Sanriku Jukan Expressway and passes over a newly constructed major prefectural road. The middle-sized bridge will measure approx. 30 m in length to meet the required width as an overbridge. However, the construction site used to be a paddy field and the ground underneath has been classified as Type II Ground (a bearing strata of 16.0 m), which is relatively soft. Considering these conditions, we drew up designs to reduce construction costs of the Toyama IC bridge on the basis of the "Design Policy Considering the Cost Reduction in the Construction of a Bridge on Soft Ground.

CHARACTERISTICS, CONCEPT, STANCE & SKILLS OF PROJECT

We reduced costs significantly by adopting a "rigid-frame composite bridge (integral bridge)" design that consists of a steel superstructure and a concrete substructure to be connected together rigidly as the most ideal solution for a bridge to be constructed on soft ground.
(1) Economic efficiency: The adopted structure reduces reaction forces on the pile head by balancing lateral earth pressure on both abutments and relying on the passive resistivity of the soil even during an earthquake. By using steel girders, vertical reaction forces are also reduced. This led to a significant reduction in foundation construction work. Construction costs were also reduced because bearing supports, an expansion joint and a bridge restrainer were no longer needed.
(2) Maintenance: As maintenance of bearing supports and the expansion joint, normally points on a bridge that require the most maintenance, is no longer needed, factors adding to the damage and degradation to the bridge are significantly less than with traditional structures. LCC will be reduced as a result of this. Furthermore, the degree of stress imparted on the superstructure will be reduced because of an elimination of impact damage from girders caused by wheel loads.
(3) Traveling performance: Vibration and noise are reduced due to the joint-less structure.
(4) Earthquake resistance: As it is a rigid-frame composite bridge integrating both the superstructure and the substructure into its structure, there is an increase in the degree of its static indeterminacy and an improvement in the structure's earthquake resistance.

EFFECT OF PROJECT

(1) Construction costs for the substructure and the foundation were reduced by adapting an integral bridge structure.
The integral bridge design also made it possible to adopt the single line pile arrangement rather than 3 lines for A1, 4 lines for A2, as is often seen in traditional design. The single line pile arrangement also eliminates the need for the bottom slab in the substructure.
(2) Validation boring eliminated the necessity for liquefaction countermeasures.
The initial plan called for the use of an EPS embankment, a lightweight embankment, because it was judged that the construction site was in danger of liquefaction. In this project, as preload embankments were already being installed, we proposed the application of validation boring to confirm the increase in strength of the preload embankments and as a result found that liquefaction countermeasures were unnecessary.
(3) Costs were reduced further by constructing the main beam of the superstructure as a H beam.
We proposed to construct the main beam of the superstructure as a H beam with improved workability and economic efficiency in mind. We verified that the structure with a H-1000 large-section steel beam was feasible, and this helped reduce the cost of build-up materials by approx. 30% while also improving workability.