60 TheStructuralEngineerSeptember 2012

OpinionBook review

Arup's Naeem Hussain comments on a recently published bookfrom one of the industry's most eminent bridge designers

Author: Professor Holqer Svensson

ln the global bridge fraternity, HolgerSvensson ìs well known for his contributionto the design and development of cable-stayed bridges. He has designed bridgesthat have been built on virtually everycontinent, so it was with great eagernessthat I read this book. There are severalexcellent publications on cable-stay andcable supported bridges written by eminentacademics and practicing engìneers, butthis book is different. The title belies thecontents of the book, which is not just

about the bridges that Holger has beeninvolved with, but is a compendium brìngingtogether in one book the history, theory anddevelopment of cable-stay bridges on aworldwide scale.

The book is lavishly illustrated withphotos of bridges, extracts of engineeringdiagrams and drawings from the earliestdevelopment of cable-stay bridges to thepresent (including the record-breakingRusski Bridge in Vladivostok with a span of1104m). This makes understanding the texteasier as engineers by nature are able tograsp the language of diagrams. To bringthis knowledge together in one book is

a major undertaking and achievement ofhistorical research. Students, academicsand practicing engineers will find the bookhelpful, particularly graduate engineers whowill obtain essential and informative insightinto the behavior of cable-stay bridges fromreading the chapters'Deslgn Fundamentals'and'Precursors of Cable-Stayed Bridges'.For the practicing engineer, the wealth ofpractical details captured from the diverse

range of bridge types illustrated ìn thebook, are a valuable source of knowledge ìn

addressing design issues that theymight encounter.

Holger quite rightly advocates thatsimplicity and refinement to the purestructural shape is most important. This isparticularly relevant at the present time, aswith the use of powerful computational aidsalmost any shape can be realised. The desirefor unconventional bridge shapes is in manyinstances led by architects who in Holger'swords "do not appreciate the logic of a purestructure and create bridges in which theflow of forces is wrong". Holger suggeststhat the jury for design competitions shouldalways contain a majority of engineers in

order to avoid the winning design not beingrealised for technical or economic problems.

The book has separate chapters on steel,composite and concrete cable-stay bridgesand sets out how engineers in different partsof the world have addressed the designissues to reflect the particular period, typeof bridge and environmental conditions.Within each type, several variations in theconfiguratìon of the deck, pylons and stayarrangements are shown, underlining themany possibilities that exist in the design fora cable-stay bridge.

The progression in the span lengths

of cable-stayed bridges is going to beinfluenced by the type of stays and howthe dynamic behavior of the stays canbe controlled. A review of currently usedstay cable systems is given, along withexplanation of the dynamic behavior ofcables due to actions such as parametricstructural excitation and rainlwind oscillationand how they can be suppressed by veryrecent developments in damper design byvarious manuf acturers.

The issues of bridge dynamics, influenceof wind and ship impact are addressed.Wind in particular for long span cable-stay bridges has a major influence on thedesign especially in cyclonic areas of theworld. Each of these topics is dealt within an exhaustive manner, firstly explainingthe phenomenon/problem and then settlngout how the problem was addressed andresolved for various bridges.

A welcome addition to the book is achapter on construction engineering.A bridge is most vulnerable duringconstruction and the configuration ofthe bridge in its permanent state canbe governed by the construction stage.Representative construction techniquesdeployed on a number of bridges includingvery recently completed bridges such as

Stonecutters Bridge and the Millau Viaductare given. This is a useful reference sourcefor the design of both temporary andpermanent works.

Lastly, and perhaps of great use tograduates and engineers starting in the bridgeprofession, are the samples of prellmÌnary

calculations. ln the present day culture of

totally relying on the computer, it is essential

that engineers are aware of and understand

the principles of engineering and are able to

carry out preliminary and approximate analysis

by hand, in order to carry out a health check

on the computer analYsis.

Publisher: Wilev-Blackwell, Hard cover, 458 paqes

Price: f105ISBN: 978-3-433-02992-3

Naeem Hussain MSc DIC gSc(Eng)CEng FlStructE FICE

Recognised by the industry for his significant contribution to bridge design, Naeem Hussain ioined

Arup in 1969 and has 49 years of civil engineering experience. He was awarded the Prince Phillip

Medal (the Royal Society of Engineering's highest individu al awardl in 2012.

CABLE,STAYED

BRIDGES