Civil Engineering Reference
In-Depth Information
Figure 10.12
Concrete geometry and striking of shutters
tendons, precast end blocks that incorporate the tendon anchors are frequently used.
Alternatively, the fi rst tendons to be stressed may be provided with oversize anchor
plates.
Beams of this shape have also been cast in-situ. However, it is diffi cult to achieve
the degree of control that is typical of a precasting yard, and the formwork must allow
inspection of the heel to confi rm its integrity before signifi cant prestress is applied.
There are two basic methods of placing the beams. The launcher may remain on
one line, and once the beams have been launched they must be rolled sideways on the
crosshead into their fi nal position. Alternatively, the launcher itself may be capable of
sliding sideways across the deck, placing the beams in their fi nal position. Lateral sliding
of a launcher using long-stroke hydraulic jacks is a very quick operation, taking no
more than a few minutes if the falsework has been well designed, and this is likely to be
the quickest form of erection for large decks that justify the expense of mechanisation.
In countries where precast beams are used regularly, dedicated launchers of various
load and span capabilities are often available for hire.
10.3.7 Bridge across the Sungai Kelantan at Pasir Mas, Kelantan Province,
Malaysia
This bridge consisted of 14 spans of 45 m, Figures 10.13 and 10.14. It was originally
designed with 9 AASHTO type beams in the cross section, and was redesigned by
Benaim with four customised T beams, Figure 8.3, requiring a total of 56 precast
beams. The consulting engineers responsible for the overall project were HSS Consult
Consulting Engineers and it was built by the Kedeco-Kelcon Joint Venture with the
help of Pilecon.
Each beam had a height of 2.7 m, a length of 45 m and weighed 130 tons,
Figure 10.15. They were spaced at 3.367 m, had a 1.5 m wide top slab incorporated
with the beam and 220 mm thick webs. The webs were reinforced with 10, 12 and
16 mm links, with 30 mm side cover and the 10 mm lacers were placed inside the links.
Each beam was prestressed with two cables of 12 No 12.9 mm strands in ducts with
