Cable stay bridges, summary of a lecture delivered as part of MSc course at University of Surrey UK. Outlines key issues for sizing major bridges. The work draws on Manual of bridge Enginnering, the authors book Steel Concrete composite bridges - which has a chapter on cable stay bridges, and recent research on cable stay and extradosed bridges.

1. Cable-Stayed Bridges; Introduction
and Analysis.
Making the complex simple.
Summary Presentation of a lecture by
David Collings BSc CEng FICE
at University of Surrey, UK; March 2014.

2. Introduction
Start by looking at bridges others have
designed and built. See books such as
Collings, Steel Concrete Composite
Bridges and ICE Manual of Bridge
Engineering, as well as papers in
Proceedings of ICE, Bridge Engineering.

4. Chapter 10
Cable stay bridges
“..have a system of forces that are
resolved within the deck-stay-tower
system..”

6. From MOBE by ICE publishing

7. Left, Stonecutters
bridge during
construction, picture
from VSL. Below,
cantilevering of
Rusky Bridge, picture
from NCE.

8. Scan of BE cover

10. Ahkai Sha Bridge a stiff decked
cable-stayed form
Ah Kai Sha bridge; a cable-stay form with a stiff double deck, the deck
stiffness of such bridges is often larger than that of an extradosed
bridge, for some layouts of stay there may be some overlap in
behaviour (see figure 6).
Image from RBA archives

11. Analysis
The basic stay system is basically a series of
superimposed triangular trusses. A good
approximation of the behaviour can be
obtained relatively simply, however, in detail
the bending, shear and axial load interaction
together with non linear behaviour of the
stays make detailed analysis relatively
complex.

12. Analysis
Consider an isolated deck-stay-tower system shown in
the figure. Element 1 of the main span has a weight
W1 and is located a distance L1 from the tower, it is
attached to a tower of height h1. A tension T1 in the
stay and compression C1 in the deck is required for
stability.

13. C1 = W1 L1 /h C2 = W2 L2 / h
T1 = (W12
+ C12
)½
T2 = (W22
+ C22
)½
To
avoid out of balance forces at the tower top and in the
deck, C1 = C2, and W2 = W1 L1/ L2. Which
also gives equilibrium about point o.

15. The natural frequency (fn) of a structure is a
function of its mass (m) and stiffness (K):
fn = 1 (K / m )½
2π
The frequency of various bridge structures
are shown in figure (see full presentation).
Dynamics

16. Analysis of Second
Severn Bridge,
see Collings, Steel-
concrete composite
bridges.

17. From MOBE by ICE publishing

18. Loads
Key loads to consider:
• Construction;
• Traffic, Rail, People;
• Wind;
• Ship Impact.

19. Loads
Viana Bridge, see Proceedings of ICE,
Bridge Engineering, Dec 2013

20. Wind, vortex shedding and flutter. Picture is an extract from
Collings, Steel-Concrete Composite Bridges.

21. The susceptibility of a bridge to dynamic wind
effects can be determined by a factor P
P = (ρ b2
/m) (44 vmo
2
/ b L fb
2
)
Where ρ is the density of air, b is the bridge width, L is the span, m
is the mass per unit length of the bridge and fb the first bending
frequency of the structure. For P < 0.04 the structure is unlikely to
be susceptible to aerodynamic excitation. For P < 1 the structure
should be checked against some simplified criteria to check for any
aerodynamic instability. If P > 1 the structure is likely to be
susceptible to aerodynamic excitation and some changes to the
mass, stiffness or structure layout may be required, wind tunnel
testing will be required to verify the structures behaviour.

22. Ship Impact

24. Design stays to limit stress at
working loads to 0.4Pu, or limit live
load variation to 200 Mpa.

25. Deck- Stay Connection
From SCCD by D COLLINGS,ICE publishing

26. Towers
The main visual element,
they can use many
differing shapes.

29. Example 1
Taney Bridge, Ireland, see ICE
Proceedings paper by Collings
and Brown.

33. Summary

34. Cable-Stayed Bridges; Introduction
and Analysis.
Making the complex simple.
Summary Presentation of a lecture by
David Collings BSc CEng FICE
at University of Surrey, UK; March 2014.

35. Presentation by CRD and Wolf
productions.