foot for reinforced concrete square box girders is slightly lower than those for other types of reinforced concrete, prestressed concrete or steel bridges.
The average span length between each support is 70 ft. Of the ten piers, seven together with the two end abutments are supported by 18 in. sq.. 80 ft. long, precast reinforced concrete piles, spaced at a minimum distance of 4 ft. centres.
One of the other piers is supported by 18 in. sq., 53 ft. long piles equip- ped with rock shoes and driven to the invert of the dry dock, while the remaining two piers are supported by spread footings resting on top of the dock walls. It was considered pre- ferable to use the precast piles, due to the large amount of ground water to be encountered.
the
Two separate designs for the super- structures were prepared. The initial one assumed a continuous bridge of three spans in each unit. This was finally considered unsuitable since
of any differential settlement different types of pier foundations would have a detrimental effect on a statically indeterminate structure. The final design was of simply supported box girders with expansion joints at alternate piers.
The top slab of the box girder is 9 in. thick, with due allowance for subsequent wearing by traffic. The use of a bitumen wearing surface was not considered suitable in this case since its maintenance would always be a problem. The bottom slab is only 6 in. thick, while the stem of the girder is 10 in. wide, spaced at a dis- tance of 6 ft. centre to centre. Haun- ches of 9 in. x 6 in. are provided at cach junction of the stem with the slabs.
The total depth of box girder is 4 ft. 6 in.. representing a depth to span ratio of 0.064. The computed dead load deflection at the centre of span is half an inch, which is considerably
smaller than the allowable value of 2 inches.
Intermediate diaphragms. 15 in. deep and 9 in. wide, are placed near the top slab at the centre of each span for stiffening the stems in the com- pression zone. The end diaphragms. 9 in. deep and 15 in. wide, are placed near the top and bottom slabs, leav- ing a central gap of 18 in. for access to the cells. Drain holes of 11⁄2 in. diameter are provided at the lower end of each cell for draining off any water that may happen to collect within the box girder.
By keeping the depth of flyover constant and providing recesses at the top of each pier, a uniform cross fall of 1 in 60 is maintained throughout the flyover.
The uphill gradient of the flyover is 1 in 14 while the downhill one is 1 in 12. The middle portion of the flyover is given a gradient of 1 in 200 to facilitate drainage of surface water. Vertical curves of 80 ft. length are provided at the intersection of every two different grades. These are made possible by shaping the box girders to the required profile while maintain- ing the depth of the girders constant.
The lin. expansion joints spaced at a maximum distance of 140 ft. apart. These are sealed off on top by means of 9 in. rubber water-stop and 2 in. deep pliastic compound. For reasons of economy the expansion de- vices used are 1⁄2 in. thick mild steel plates planed in the direction of slid- to the concrete by ing and keyed means of 4 in. diameter mild steel bars.
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Handrail lanterns are used to il- luminate the carriageway in lieu of the conventional lighting standards. The lanterns are encased in the top precast concrete channels supported by concrete posts spaced at a distance of 8 ft. apart. The bottom precast
concrete channels serve as barriers to the flow of traffic.
CONSTRUCTION
Tenders were called for in June 1964 for the construction of the foun- dations, piers. superstructure, ramps and abutments as well as other ancil- lary works involving the widening of Harcourt Road and forming the first part of Kapok Drive, which is a new road eventually linking with Garden Road near its junction with Kennedy Road.
Tenders were lodged in July 1964 and that of Fook Lee and Co. was accepted later in the same month in the sum of $1,875.057.20.
The contractor was instructed to commence the work on August 26. 1964 and after allowing for the 16 months contract period the comple- tion date became December
28 1965. However the work was delayed by constructional difficulties and in the event was not completed until April, 1966.
The flyover is built on the line of the existing westbound carriageway of Harcourt Road which
was in full daily use and arrangements had to be made for this traffic to be diverted before construction could commence. Fortunately much of the traffic diver- sion work was
facilitated by the presence of a service road to the south of the westbound carriageway and it was decided to make use of this by extending and resurfacing it an alternative route during the construction period.
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Piling
The contractor decided to cast the 160 No. 18 in. x 18 in. x 80 ft. long piles required. on the site; to lift them from the mould beds with a mobile crane and to transport them the short distance to piling frames by under- slinging from two four wheel steerable bogies towed by a motor lorry. The four point slinging method was used for all handling, transporting and pitching of the piles.
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† IN 150
DOWELS @ 12 %
TT
+ IN O
28-0
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MAM BARS
1
T
+ Va*COVIE
LA COVER
14* COVER
FRO MAN BARS
4:0
_14 SPACES @ 446 148
„A-UK'
TYPICAL DECK SECTION
'WIDE GLOSVE FILLED
WITH PLEASTIC
S'RUBBER, WATER STOP
WATERPROOF BLOG PAPIR
PACKINGS
-CALPBOARD SELEVE
FILLED WITH BITOMEN
-1'ê dowels 2'0"Love @ 11*%
7 [COATS OF BIT, PLANT 154 PRAIN NOLE AT LOWER END OF EACH CELL
HINGE JOINT DETAIL
Far East Architect & Builder June, 1966
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1'DEEP PLASTIC SEALER 9"LEBBER WATER STOP
L
59'4 LOURD BARS @ 12'SE
FILLET WELDED TO PLATES
-KÄIMICE SITE, PLATES SEPARATED I" APART
Spears
HL LOUND BAAS. @ !?"1⁄2
FALET WELDED TO BASE PLATE
K THICK SPELL BASE MATE
HOLE AT LOWER END OF LACH CELL
LONE
EXPANSION JOINT DETAIL
59