World's longest girder span with corrugated steel plate webs: Aigawa Bridge
The Aigawa Bridge is a continuous multi-span rigid frame bridge on the Shin-Meishin Expressway in the northern part of Ibaraki City, Osaka Prefecture. Its longest spans, which cross both the Aigawa River and a prefectural road, are 179 m in the eastbound direction and 170 m to the west.
In order to produce a lightweight superstructure, corrugated steel plate webs were used. Approximately 200 bridges have previously been built in Japan using corrugated steel webs, but the Aigawa Bridge is the world's longest girder span in which these webs have been used.
Tendons consisting of high-strength prestressing steel
The main girder was constructed using the cantilever erection method. Since long span lengths require many prestressing tendons for cantilever erection, tendons consisting of high-strength prestressing steel were used. Regular strength prestressing steel would have required the use of 52 tendons, and this amount would have prevented to distribute over the cross-section. By using high-strength prestressing steel strands, the required number of tendons was reduced to 46. Moreover, 50 MPa high strength concrete was used for the main girders to allow early tensioning of the tendons for cantilever erection and to further reduce the weight of the main girders.
New cantilever construction method
To shorten construction time of the cantilever section at the westbound pier P2, which was critical for construction progress, a new cantilever construction method was used. The corrugated steel webs were first installed and then used as erection members. The form traveller was placed on the installed, corrugated steel webs; during concrete placement, the weight of the upper and lower slabs was directly suspended from the traveller. This way, the form traveller was simplified and its capacity increased, thereby allowing for longer construction segment lengths. The segment lengths of 6.4 m reduced the number of segments from 16 to 12, which shortened the overall construction period. Standard segments are 4.8 m long.
The longitudinal post-tensioning is provided by a combination of both internal and external tendons. Type 12S15.2 MA strand tendons and high strength strand tendons were installed as internal tendons. The external tendons were strand tendons with epoxy coated and filled strands. Pre-grouted monostrand tendons were used as transversal tendons in the bridge deck.