HONG KONG
CIVIL ENGINEERING AND PUBLIC WORKS
D
ESIGNED to relieve the east-west
traffic flow on Hong Kong Island, Government's Waterfront Road pro- ject provides for a three-lane dual carriageway from Harcourt Road in Central District to King's Road, North Point.
The project involves the construc- tion of a flyover at Tsing Fung Street to carry the town-bound right- turning traffic from North Point on King's Road, over King's Road into Tsing Fung Street, hence making a right-angle turn.
The flyover is 25 ft. wide overall, widened to 28 ft. at the bend, and has a total length of 1,500 ft. Figure I shows the alignment of the flyover superimposed on the existing street network.
Conventional composite prestressed concrete beams resting on portals are used for the access ramps, while the 90 degree curved section over King's Road is a three-span bridge of in situ prestressed concrete cellular construc- tion. The bridge has two anchored spans, each 115ft. long between sup- ports with a 31 ft. overhang to sup-
MODELS USED TO TEST FLYOVER DESIGN
by H.W. Chung and N.J. Gardner*
port the 78 ft. long central suspended span.
Each anchored span is simply supported at its remote end and is monolithic with a 6 ft. diameter cir- cular column at its inner end. The centre-line elevation is shown in figure 2.
The design of any curved bridge is complicated by the presence of large torsional effects; these are very pro- nounced when the bridge is only partially loaded. The problem is further complicated by the possibility of uplift at the supports under these partial load conditions.
No rigorous analysis exists to analyse a curved cellular bridge. Thus the design of the bridge was ef- fected by assuming that the bridge may be considered as a single curved beam with the appropriate flexural and torsional stiffnesses.
Because of the simplyfying as- sumptions used in the design the authors were requested by the Public
Works Department to undertake a model investigation of the flyover to clarify the following points:—
(1) Determine the elastic behaviour
of the bridge.
(2) Determine the torsional proper-
ties of the section.
(3) Ascertain if uplift occurs at
the supports.
(4) Determine the mode of failure
and load factor of the bridge.
Model Testing
The basic idea of model analysis is that deflection of one part of the model to any other of the model has the same relationship as that of the corresponding points on the prototype. Thus the response of the model to a load is proportional to the response of the prototype to a similar load.
* H. W. Chung, MSc, Ph D, and N. J. Gardner, B Sc, Ph D, are lecturers in civil engineering at the University of Hong Kong.
WING HING STREET
HING FAT STRRET
N
ELECTRIC ROAD
precast prestressed I beam with in-situ r.c.decking
TSING FUNG STREET,
in-sity prestressed.
81
póx girder
115-0
PERSPEX MODEL
KING'S ROAD
十
[CONC
MODEL
115.0
KING'S ROAD APPROCH RAMP
SLIP ROAD
Far East BUILDER, May 1968.
Fig. 1. Layout plan of Tsing Fung Street flyover
47