NAEEM HUSSAIN ON BRIDGES
As Arup Global Bridge Leader
Naeem Hussain
Introduction
Mankind has always been fascinated by bridges and it is
probably the oldest form of civil engineering object
used by all communities and cultures in the world
ranging from age old rope bridges, wooden bridges,
masonry bridges, iron bridges to modern concrete and
steel bridges.
Invariably form and function of bridges went together,
but as societies got more sophisticated, bridges were
adorned to give them a visual and architectural
elegance. Bridge design developed in stages with long
periods between radical changes in design.
The advent of iron and steel saw a major leap in bridge
design development with longer spans being realised
principally as cable supported suspension bridges. After
World War 2, the greatest advance in bridge design was
cable-stayed bridges and the introduction of computers
has had by far the greatest influence on bridge design.
Computers have given bridge designers the tools to
create designs that would not have been possible to do
with hand calculations. This freedom however has
meant that almost any configuration and geometrical
shape can now be realised which can ignore the ethos
of form and function and is akin to geometrical and
structural gymnastics. This is further influenced by a
societies´ culture and in many cases the desire to have a
unique bridge like no other.
The desire to have a visually unique bridge has led to
design competitions with the winning design sometimes
being chosen by a politician or local leader with little or
no knowledge of structural engineering. The design is
chosen purely on visualisations done by architects with
no engineering input, resulting in designs which do not
respect engineering principles, and/or are difficult to
construct and maintain.
Good design respects the client’s budget, respects the
local environment and culture, respects form and
function and is easy to inspect and maintain. Good
bridge designers, whether they are engineers or
architects, are aware of this and can create designs that
are visually pleasing to the general public and yet are
economical and functional.
On a personal level I was and have been fortunate to
work at Arup. The Arup approach to bridge design,
which in many cases has been done in collaboration with
architects has always been to strive for form and
function and yet be aesthetically pleasing.
There are basically five structural forms for bridges:
girder, truss, arch, suspension or cable-stayed. The art of
bridge design is to identify the form most suited to a
particular location and use it in a visually pleasing
arrangement and proportion.
The concern about unrealisable and/or structurally
unsound designs and to achieve a sound outcome from
design competitions led the International Association for
Bridge and Structural Engineering (IABSE) to publish the
“Guidelines for Design Competitions for Bridges” (You
can read them here). I was the chair of the Working
Group for compiling the Guidelines and I would
commend it to owners and other interested parties
contemplating acquiring a bridge via a design
competition to use it to compile the brief and conditions
for the design competition.
In this article I have attempted to set out the basis of the
design of some of the bridges I have worked on, which
tried to follow the principles of form and function, easy
inspection and maintenance and affordability.
A visually pleasing bridge need not cost more than an
ordinary looking bridge but it does require more thought
and effort to realise it.
1/2018