Extradosed Bridges: Exploring the Boundaries

Extradosed and cable-stayed
bridges; exploring the
boundaries1
Summary presentation of a paper published in ICE
Proceedings; Bridge Engineering; December 2013.
The full paper can be read at
http://www.icevirtuallibrary.com/content/issue/bren/166/4

Authors
David Collings BSc
CEng FICE

A S Gonzalez BEng
ITOP MSc

Introduction
The extradosed bridge can be thought of
as an intermediate between the girder
and cantilever bridge forms.
The paper 1 explores the boundaries of
this form of bridge to define them more
clearly.

Figure 1 Development of form, from girder and cable-stayed to
extradosed (modified from Shirono et al 4.)

The Ganter Bridge
by Menn and a
slightly less
elegantly engineered
fin wall bridge.
These are related to
extradosed bridges
and have developed
from cantilever
girder bridges.

The study
The paper 1 summarises previous work
on extradosed bridges and then outlines
the author’s findings from their own
parametric study of a bridge at the
boundary between cable stayed and
extradosed.

Figure 3. The reference structure for the parametric study,
Karnaphulli Bridge (see Austin et al 3)

Parameters
The key parameters of extradosed
bridges are outlined and compared with
those for girder and cable-stayed
bridges.

Note: this figure is taken from Collings 4 which outlines the behaviour of cable stay and
extradosed bridges in the context of steel-concrete composite construction.

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

Parameters (continued)
The load distribution ratio (β) is defined as:
β = Vertical load carried by stays
Total vertical load
Note: this is usually expressed as a percentage

Eq 1

Figure 6. Variation in load distribution ratio with
span for cable stayed and extradosed bridges,
extradosed bridges have lower Bv.

Summary
A clearer definition of an extradosed
bridge is offered based on this work.

Definition
“ … The extradosed bridge is a form of
cable-stayed bridge… ”

Sunnisberg Bridge; again by Menn, is actually a shallow cable
stayed form with a flexible deck, but it is often confused with
the true extradosed form.
Image by Ikiwaner

Definition (continued)
“ … it has a short tower and a relatively
stiff girder; the arrangement of girder,
tower and stays will have been chosen to
ensure the girder stiffness is significant
compared with that of the cables, such that
the girder carries the majority the live load
(βp + βv ≤ 125).”

The classic extradosed form of the Tokunoyamahattoku
Bridge in Japan.
Image from HighestBridges.com

Conclusion
 A clearer definition of an extradosed bridge
is offered by the paper 1.
 The extradosed bridge is a form of
cable-stayed bridge.
 The form is best defined using the load
distribution ratio.
 The full paper can be read at

References
1. Collings D, Santiago A S, Extradosed and cable
stayed Bridges: Exploring the boundaries, Proc ICE BE
166, Dec 2013, pp 231-239.
2. Collings D, (2005), Steel-concrete composite bridges,
Thomas Telford, London.
3. Astin D, Xie H, Gillarduzzi A (2010), Design and
construction of Third Karnaphuli Bridge, Bangladesh,
Proc ICE, BE163, Dec 2010, pp 161-171.
4. Shirono Y, Takuwa I, Kasuga A, Okamoto H (1993),
The design of an extradosed prestressed concrete
bridge – The Odawara Port Bridge, FIP Symposium 93,
Kyoto, Japan, Oct. 17-20, 1993, pp 959– 966

Presentation by CRD and Wolf
productions.
The full paper can be read at

Extradosed Bridges: Exploring the Boundaries

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Extradosed Bridges: Exploring the Boundaries