Page 25 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Fig 2 Construction stages

The six-span river crossing is a continuous DESIGN
prestressed concrete box girder with end spans Use was made in the design of the secondary
of 190 ft (57.91 m) and four interior spans of moments which can be developed in indeterminate
219 ft (66.75 in) each. To minimise friction losses prestressed concrete structures through post-
associated with cable post-tensioning, the tensioning. When wheel loads are adjacent to the
kerb, Fig 4, the cantilever moments developed create
construction was carried out in stages. Fig 3 shows
large moments in the relatively heavy vertical web.
construction up to stage 3. Splice points between
To counteract these moments it was found useful
stages were located at 0.2 of the span so that some to place the transverse prestressing tendon of the
negative support moment was generated during deck above the centroid of the section between
construction. the webs. In this way compensating secondary
moments were developed at the junction of the
The roadway consists of two 13-ft (3.96-m) wide cantilever and the web and this reduced transverse
web moments.
lanes with 5-ft (1.52 m) wide sidewalks. The deck
slab is transversely post-tensioned and is slightly
superelevated to suit the horizontal curvature.

The cross-section, Fig 4, is constant throughout
the length of the river crossing. Flanking spans
are 36 in (91.4 cm) deep continuous slabs which
are lightened by large formed voids. Longitudinal
and transverse prestressing is used. The deck
is topped with 2 in (50 mm) of asphalt, while the
faces of the kerbs are inset with a continuous strip
of granite. This is done to reduce deterioration of
the kerb concrete through contact with salts which
Fig 3 The construction up to stage 3
are used extensively for melting snow during
winter. Aluminium guard rails and posts, as well The use of stage construction, Fig 2, also provided

as aluminium lamp standards, have been used a means of changing the distribution of dead load
moments in the structure. As successive spans are
throughout.

26 The Indian Concrete Journal | November 2018