September_1971 — Page 45

Мнемо

Far East BUILDER, September 1971

THE tunnel relief flyovers have been constructed to separate inward and outward bound City Centre traffic from traffic entering and leaving the Mersey Road Tunnel. The conflict be- tween these two traffic movements had for some years given rise to con- siderable delays at the approaches to the Tunnel and in the surrounding City streets.

Within the immediate environs of the project are several buildings of architectural interest and it was neces- sary to pay special attention to the appearance of the structures. The provision of a footbridge near or under the Northern Flyover and the severe curvature of the Southern Flyover were two important additional factors which influenced the choice of struc-

ture.

It was decided to construct the fly- overs using in-situ concrete box girders of constant cross section tilted as necessary to provide the required super-elevation. The soffits of the fly- over structures were to be curved en- abling a 'scaled-down' version to be employed for the footbridge.

Both flyovers have an overall width of 10 m (32 ft 10 in). The width between parapet faces is 8.8 m (29 ft) which comprises a carriageway of con- stant width of 7.3 m (24 ft) flanked on both sides by a 0.8 m (2 ft 6 in) emergency footway. The soffit of the flyovers is 'saucer' shaped set out from an arc of 7.1 m (23 ft 3 in) radius at the centre of the section join

ed at its ends by straights which slope upwards to the edge of the structure. A fascia panel finished with white glass mosaic and a coping of white concrete were bolted on to the parapet upstand, above which was fixed a steel rail.

The overall length between abut- ment faces of the Northern Flyover is 240 m (786 ft) and of the Southern Flyover is 284 m (932 ft). The col umns are of reinforced concrete, 1.53 m (5 ft) in diameter, and have a light grit blasted finish. The decks were de- signed as continuous concrete box gir- ders prestressed longitudinally, span at a time.

The footbridge is entirely of rein- forced concrete construction, ter- minating at each end in a spiral vamp.

Judges' comment: The elegant and ef ficient profile of the structure is im- pressive. The smooth telescopic box section combines an attractive main- tenance-free appearance with essential high torsional stability. The latter fea- ture is required in this case to deal efficiently with the comparatively sharp radii of the approach sections.

The traffic solution is simplified by the adoption of separated parallel lanes at the approach to the junction.

The shallow deck appears to float on top of the circular columns and the whole concept blends in well with the important buildings adjacent to the site which presented considerable dif- ficulties in harmonising traffic with the surroundings.

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