Scan of BE cover

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 Eq 1 Total vertical load

Note: this is usually expressed as a percentage

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

ConclusionA 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

http://www.icevirtuallibrary.com/content/issue/bren/166/4

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 http://www.icevirtuallibrary.com/content/issue/bren/166/4