a review of developments in steel: implications for long

ORIGINAL ARTICLE

A Review of Developments in Steel: Implications for Long-SpanStructures

Prem Krishna1

Received: 20 November 2020 / Accepted: 25 December 2020 / Published online: 21 January 2021

� The Indian Institute of Metals - IIM 2021

Abstract Historically, iron in different forms has been

known to exist for Architectural and Engineering applica-

tions from early periods of civilisation, but in the modern

context, it would be best to review the growth of steel,

during the last couple of centuries. This paper, first, traces

briefly the developments in steel in terms of its various

aspects, which are relevant to the design of structures. It is

perhaps needless to remind ourselves that humans perpet-

ually endeavour for a better quality of life. To meet the

challenge thus created for providing additional and

improved infrastructure, and, riding on a number of parallel

(or nearly so) developments, the frontiers for Civil and

Structural engineers and architects have moved to horizons

not easy to imagine. One exciting thrust has been towards

increased dimensions, in both height as well as span of

structures, which have touched kilometres from tens of

metres. One of the important factors responsible for the

aforesaid developments is without reservation, the

advancements in steel, and, products based upon it, for

deployment in structures, besides the related aspects of

fabrication, construction and maintenance. There are other

factors too, such as, the growth of electronics which has led

to enormously increased capabilities in computing. Also,

there are the remarkable developments in instrumentation

and robotics as tools in structural engineering. This has led

to a paradigm shift in the scenario for structural analysis,

design and drafting, construction and maintenance. In

traversing the journey above, there are different aspects and

features that have already become convention through

practice and literature, and there is extensive awareness

about them. On the other hand, there are issues and areas of

comparatively new developments about which the aware-

ness is rather limited. The emphasis in this text is largely

on the latter. Since some of these issues can provide for

extensive coverage, the attempt herein is to only bring out

the salient features.

1 Introduction

Quest for better quality of life has been a part of the human

spirit from the very beginning of civilisation, requiring the

virtually never ending need to add to existing infrastructure

as well as to seek all-round improvements in it. A great

deal of this is Civil Infrastructure such as for the habitat,

communication and transportation. Iron and then steel have

played a big part in first enabling the design of smaller

spans and for decorative purposes, and, then in medium

and long-span applications. Steel as a material began to be

used in earnest about two centuries ago, and, finally

matured to be closely entwined in the development of the

modern civil infrastructure elements, such as, long-span

roofs and bridges and tall buildings. If one looks for one

prominent reason for this popular preference for steel, it is

the high strength ratio that it possesses. Besides the

improved strengths in steel, there are the associated

developments in fabrication and construction technologies.

In addition to the growth of steel, the one factor most

responsible for enabling its effective utilisation is the

enormous development in electronics, which in turn has

given an almost unimaginable push to computing capabil-

ities, e-communications, sensor technology, robotics and

developments in the design and drafting scenario.

& Prem Krishna

[email protected]

1 Department of Civil Engineering, IIT Roorkee, Roorkee,

India

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Trans Indian Inst Met (2021) 74(5):1055–1064

https://doi.org/10.1007/s12666-020-02173-7

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https://doi.org/10.1007/s12666-020-02173-7

2 Developments in steel and associated issues [1–4]

The use of iron in structural applications, though evidenced

even earlier, could be said to have found a place in earnest

in the 1800s, replacing wood and stone to a great extent. A

cast iron bridge across the Severn near Coalbrookdale

opened in the year 1781 is generally regarded as the

world’s first cast-iron bridge. See Fig. 1. The span was

30 m, and it used 386 tons of cast iron. This did influence

bridge design, and few other important iron bridges were

built as a result. However, a flood in 1795 washed away

many bridges on the Severn, but the Iron Bridge survived.

This survival had more influence on bridge design, as did

the completion of Wearmouth Bridge the following year.

Cast iron thus established itself as a viable material for

bridges and a number of bridges followed.

Whereas cast iron has very good strength in compres-

sion, it has limitations in tension and suffers brittle failures.

It thus began to be replaced by wrought iron, which has a

more fibrous character as against the granular one for cast

iron. The use of iron in structures dominated the nineteenth

century in Britain, France, Russia and America. However,

by the end of the century, the use of cast or wrought iron as

a structural material appeared to have been stretched to its

limits and, steel began to be preferred.

In India, the story of use of iron is similar, with some

fascinating examples like the iron pillar in Mehrauli, pur-

ported to have existed from around the fifth century AD.

Likewise, there are also examples of use of cast iron and

wrought iron in small structures. The first landmark

structure using steel was the 655 m long Rabindra setu

(The Howrah bridge). When commissioned in 1943, this

was the third—longest cantilever bridge in the world, and

is currently the sixth longest. See Fig. 2.

The mainstay amongst structural materials for the

industrialised world has been steel, from almost the middle

of the nineteenth century. An alloy with about 0.2 per cent

carbon and the balance mainly iron (with very small

quantities of Manganese and Silicon depending upon the

grade and allowing for some percentage of Sulphur and

Phosphorous), the initiation of the manufacture of steel is

due to Sir Henry Bessemer of England in 1857. The

introduction of the blast furnace changes the earlier process

of producing steel from wrought iron to its manufacture

from a combination of pig iron and carbon, with the pro-

portion of carbon being reduced to the required percentage.

Following this, the processes such as the open-hearth

process and the electric arc furnace were adapted to

steelmaking.

Whereas the leadership in steel development and pro-

duction was with the British in the late nineteenth century,

it passed on to the USA by the end of it. Later during the

century, many other countries such as France, Russia,

Fig. 1 The world’s first iron Bridge opened in 1781 at Coalbrookdale, UK

Fig. 2 The Howrah Bridge, a Balanhed cantilever Bridge over the

Hooghly River in West Bengal, India, commissioned in 1943

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1056 Trans Indian Inst Met (2021) 74(5):1055–1064

Japan and Germany played a big role. In the current cen-

tury, China is the biggest producer of steel, with nearly

1,000 MT in 2019.

In India, the Bengal Iron Works was founded at Kulti in

Bengal in the year1870 followed by The Tata Iron and

Steel Company (TISCO) which was established by Dorabji

Tata in the year 1907. Later, after its independence from

the British, a government owned company, Hindustan Steel

Limited (HSL), was established in the year 1954 and set up

three steel plants in the 1950s. The Indian steel industry

began expanding into Europe in the twenty-first century,

with Tata Steel buying European steel maker Corus Group,

and with the setting up of ArcelorMittal (based in Lux-

embourg City) having an Indian management. With about

110 MT in 2018, India became the second largest producer

of crude steel.

2.1 Conventional products

The various types of steel products deployed in structural

engineering applications are rolled or drawn sections,

reinforcing bars, prestressing wire, ropes and strands. Till

the 1950s, the commonly available steel structures were

plates and sections with rounded fillets and edges rolled

from mild steel (with strength of 250 MPa). Common

shapes being flats, angles, channels, Is, Ts, etc. While,

further developments have now expanded the range to

parallel flange sections and rectangular tubes, with the

strengths now available in India being of the order of

450 MPa. Japanese had developed 800 MPa steels by the

1960s and used this steel in many bridges, including the

510 m span truss for the Minato Ohashi bridge in the year

1974. The challenge in developing steels for structural

application has not only been the higher strengths but also

improved weldability, toughness, ductility. Other devel-

opments worth mentioning are those of, high performance

steels, steel with high HAZ toughness (which provides

proper fracture toughness in welding), super-high-tension

bolts (SHTB), developed in Japan in 2001.

Furthermore, corrosion has been a concern in the

deployment of steel. The global cost of corrosion in 2013

was considered as US$2.5 trillion, which is equivalent to

3.4% of the global GDP. Therefore, quite naturally there

have been efforts to mitigate the problem with various

types of coatings, and the use of special steels, such as

stainless steel, and weathering steel (COR-TEN steel)

became feasible. Though the use of special steels or pro-

tective measures may be costlier in terms of the initial

estimates, it will be pertinent to look at life cycle costs in

this context.

In reinforcing steels used in reinforced concrete, a sig-

nificant development is that of TMT bars. In India, range of

strengths up to 550 MPa is available. Prestressing wires

and wire ropes and strands, are well known to have higher

strengths of 1,500 MPa or above.

2.2 Wire ropes and strands [4, 5]

Wire ropes and strands are generally part of long-span

roofs and bridges, though also used in guyed towers and

ropeways. Since such long-span structures are still few and

far between, particularly in India, there is comparatively

lesser awareness about ropes and strands too. These are

therefore briefly described in this section.

It is significant that wire ropes and strands for various

applications are of strengths ranging up to 1,800 MPa.

Wire of 1,100 MPa was used in the Brooklyn bridge, which

was the first American suspension bridge to use galvanised

wire, in the year 1883, and, 1,600 MPa in several bridges

from the years 1970 to 1990. Already a mature steel pro-

duct, there have been no dramatic developments recently in

this, except for wire drawing processes. The wires used in

Akashi Kaikyo bridge, Japan were having a strength of

1,800 MPa, and, now steel wires having a strength of

2000 MPa have been developed in Japan [6].

Twisted wire ropes and strands are typically assembled

from thin high strength steel galvanised wires, say, of the

order of 5 mm. Figure 3 shows the cross section through

various types of ropes/strands. Flexibility and extensional

stiffness of a cable are dependent upon the size and number

of wires used and the method of forming it.

Wire ropes have been traditionally used as suspension

bridge hangars, in guyed masts and in suspended roofs.

These are formed by assembling together a required

number of strands and twisting the assembly. Whereas

ropes offer the advantage of flexibility, the size has

essentially to be kept limited. A rope has a more open form

of construction and has a low extensional modulus. Much

of the design technology pertaining to spiral strands is also

common to locked coil ropes since they share the same

form of construction (in concentric helical layers). How-

ever, the use of shaped (interlocking) wires instead of

round wires enables substantially higher fill factors to be

achieved with a proportional increase in mass for a given

cable diameter. These have a greater corrosion resistance,

but are comparatively costlier. Diameter of ropes varies

typically between 10 mm and 50 mm.

As opposed to this, there are parallel wire products,

employed mostly as straight elements such as those in

cable stayed bridges. Thus, one can have a parallel wire

bundle (PWB) in which a number of small size galvanised

wires are assembled straight. The advantage is a higher

breaking strength and extensional modulus. A further

possibility is to produce parallel strand cables (PSC) which

have been used in several cable stayed bridges.

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Trans Indian Inst Met (2021) 74(5):1055–1064 1057

Suspension bridge cables are usually much larger in

diameter than strands or ropes. These are made up by

‘spinning’ thin zinc-coated wire. The process of ‘spinning’

cables for a bridge may take up to a year or more. In order

to take advantage of factory production, however, it is

possible to put together wire bundles (which can be

transported on reels from the factory). This would be

quicker. The diameters for these cables could be as large as

a meter.

A crucial feature of any type of cable is the means of

attachment to the structure or anchorage. Most factory-

made stays are supplied cut to length and with the end

fittings already attached. The stay manufacturer therefore

designs, fits and warrants the cable end attachments. To be

effective, the end fitting must withstand the breaking force

of the cable without significant yielding and endure

dynamic cycling without risk of fatigue failure and without

inducing fatigue failure of the cable.

The issue of corrosion protection is generally of concern

as mentioned earlier. Steel cables are no exception. In

deciding the protection measures, it is important to keep in

view the extent to which the environment is aggressive—is

it only the ingress of moisture, or industrial gases or coastal

conditions, or a combination thereof! This will determine

the extent and levels of protection required. There are

several types of protection possible. The first kind is gal-

vanic protection for the wire, which involves different

thicknesses of zinc coating. The next is the painting of a

strand or a rope. The third is sheathing. The other is

grouting an outer protective sleeve.

2.3 Fabrication

A major factor in enabling the utilisation of developments

in steel has been the simultaneous growth in fabrication

and construction techniques and equipment. Thus, for

example, there is the automation in cutting and welding of

structural elements and jointing. Similarly, the availability

and large scale use of High Strength Friction Grip bolts

(HSFG) to replace riveting has brought about a sea change

in the construction of large steel structures in terms of

greater convenience and speed. Likewise, it has increas-

ingly become possible to lift/transport larger/heavier fab-

ricated modules. The advent of robotics offers a potential

for in-shop fabrication as well for tackling fabrication

problems in terrains where access is difficult.

3 Design and construction

There are many aspects of steel as a construction material,

which lead to its application in modern steel structures,

often of large dimensions. These are mentioned below.

However, these large span, lighter weight and flexible

structures have certain features and challenges for the

designer. These issues are also addressed briefly in this

section.

3.1 Benefits of using steel

Steel as a construction material offers greater adaptability,

easier modifications, repairs, retrofitting, economy—cer-

tainly on life cycle basis, speedier construction, well

defined mechanical properties, and higher strength–weight

ratio. If amongst the other factors, one sees benefits of

higher strength–weight ratio alone, these are reduced dead

weight, saving in usable space, lighter load on foundations.

As a structure gets taller or longer in span, the live load to

dead load stress ratio becomes smaller. This implies that

the structural material begins to be utilised increasingly by

its own dead weight. It is therefore imperative to use

materials with high strength weight ratios to keep the dead

weight to a minimum. In the context of a tall building, the

column cross sections will become un-manageable with

materials of low strength, and useful floor space will be

wasted besides increasing the load on the foundations.

With the use of steels, this problem is overcome effectively

and is even more so if higher strength steels are used. In the

case of large covered spaces using arches or space frames,

the same logic is applicable. The deployment of suspended/

tension systems further enhances this advantage. However,

one needs to be cautioned that unduly reduced mass of the

structural elements, or increased slenderness, can give rise

to the structure becoming prone to unacceptable instability

problems—aerodynamic or otherwise. Some typical rela-

tive strength–weight ratios are given below:

Fig. 3 Cross section through

various types of ropes/strands

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Mild steel 30

Higher strength structural steel (800 Mpa) 100

High strength wire steel (1800 Mpa) 225

Aluminium alloys 90

Medium strength concrete (M30) 12

3.2 Structural form

The choice of structural form is of great consequence in

determining the efficacy with which the material is utilised.

It is known that an axially loaded tension member, a tie,

made in steel carries load most efficiently. Likewise, a

strut, which carries compression, is also efficient, but not as

much as a tie. This is because, in a compression member,

the permissible stresses may have to be limited for ensuring

that instability (buckling) does not occur. In comparison, a

member in flexure has a lower utilisation ratio. Thus, for

carrying loads, a latticed truss (members in axial tension or

compression), an arch (axial compression plus flexure) or a

suspended cable (only tension) will utilise the material

used more effectively compared to a girder in flexure.

Figure 4 is indicative of the comparison between a girder,

arch and a cable. Proceeding on this simple dictum, the

upper limit of span achieved in bridges become higher as

one moves from girders to latticed trusses to arches to cable

stayed structures to suspension systems. Similar is the

scenario for wide span roofs, where beam and slab systems

yield space to trusses, arches, space grids, cable nets

(mostly in steel), as one moves for higher span ranges.

Given below are the notional upper limits (see also Fig. 5)

for bridges of various forms:

Girders, Trusses, Cantilever 500 m

Arches 500 m

Cable stayed 1100 m

Suspension 2000 m (on the anvil 3300 m)

In buildings, the spans/heights achieved are,

Roofs 150 m Spans

Building Towers 1000 m height

A few large modern structures, chosen randomly, are

worth a mention here as examples. Figures 6, 7 and 8 show

some striking ones. Figure 9 shows an impression for an

iconic steel arch bridge over the Chenab river in Jammu &

Kashmir, now under construction in a difficult hilly terrain,

to carry the new railway line there. One of the longest arch

bridges in the world with a span of 486 m, it is claimed to

be the highest with the track at 359 m above the high flood

level for the river. Figure 10 has the photograph of another

iconic bridge, the Akashi Kaikyo, located at Kobe in Japan,

being the longest in the world, and completed in the year

1998. The bridge has a main span of 1991.6 m and has two

side spans of 960 m each. The two towers are founded on

80 m diameter steel caissons filled with concrete. The two

suspension cables are 1.1 m diameter each. The bridge uses

2,63,100 tons of steel. This is a high point of a fascinating

bridging journey which started with the 30 m iron bridge in

the year 1781 (Fig. 1) and has landmark bridges such as the

Brooklyn (year 1883), Washington (year 1931), Sydney

Fig. 4 Utilisation of material in

Flexture compared with that in

an Arch and a cable

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Harbour (year 1932), Golden Gate (year 1937), Severn

(year 1966).

3.3 Analysis

The routine aspects of the analysis and design of steel

structures are generally well understood. Although too well

known to be pointed out, ensuring stability of compression

elements is a prime design issue. However, as spans,

heights or complexities of structures become greater, there

are several challenges related to analysis and design. A

brief discussion on these follows.

Fig. 5 National upper limits for different forms of Bridges

Fig. 6 L&T Steel Melting Shop, Hazira, Gujarat, 2011 (Area

covered: 70,000 m2. Plan Dimension: 86m–116m 9 750 m. Steel

used: 20,000 t. Cost of steelwork: Rs. 220 Crores) [Courtesy: Institute

for steel Development and Growth]

Fig. 7 GMS Grande Palladium, Kalina, Mumbai, 2010 (Built area:

18,000 m2. Cost: Rs. 60 Crores) [6] [Courtesy: Institute for Steel

Development andGrowth]

Fig. 8 TCS Technopark Project: Phase-I, Chennai 2009 (Architec-

ture: Butterfly/Dragon Engineering Buildings: 21 m 9 85m (3 Nos.).

Central spine: 345 m long, 45 m high. Steel used: 28000 t. Cost of

steelwork: Rs. 172 Crores. Number of steel member elements running

into lacs) [Courtesy: Institute for SteelDevelopment and Growth]

Fig. 9 A view for the Railway Bridge under construction over the

River Chenab in J&K (personal communication from Konkan

Railway Corporation Limited)

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3.3.1 Indeterminacy

Steel structures of the kind in focus in this paper are all by

and large indeterminate, and, usually the degree of inde-

terminacy is large too. The examples are those of multi-

storeyed multi-bay frame works for buildings, space frames

and grids, cable roof networks, cable stayed and suspension

bridges. The response of these structural systems to loading

is also often nonlinear (see next). However, the develop-

ments in digital computing capabilities since the 1950s,

which have continued to grow beyond imagination during

the last few decades (a palm held calculator being more

powerful than one housed in a big room amongst the early

versions), have meant that it is now an amenable exercise

to analyse a structure of 1000 (plus) degrees of indeter-

minacy for static or dynamic effects, even taking account

of nonlinearity, if, applicable. Thus, an entire range of

software packages, dealing with analysis to drafting and

automation in fabrication, have provided a rich repertoire

for the engineer and the architect.

This is not to say that such challenging steel structures

were not constructed before the computer era. In fact, some

of the most fascinating large span suspension bridges were

constructed in the period between 1880 and 1940, besides

the Empire State building, Rabindra setu, the Eiffel tower

and so on. However, all this was based on hand calcula-

tions with approximate theories.

3.3.2 Nonlinearity

In most structures, whether in steel or another material, the

relationship between applied load and the response of the

structure thereto can be represented by a straight line.

However, for tall or wide span structures, particularly using

steel, the relationship quoted above can be nonlinear. As

indicated in Fig. 11 and described as under, there are

several reasons for this.

1. These large structures can be flexible and undergo

large deformations, thus violating the assumption that

analysis can be based on the initial geometry of the

structure. The nonlinearity thus caused is termed as

’geometric’. This is common in cable supported roof or

bridge structures.

2. Another factor leading to a nonlinear response is what

is commonly called the ‘P-delta’ effect in members

where axial compressive force interacts with flexure of

the member. This is a distinct possibility in such cases

as self-supporting towers, bridge pylons, girders in a

cable stayed bridge, curvilinear supporting elements of

a cable or a membrane roof structure.

3. Slender members under axial compressive forces are

liable to undergo buckling and behave nonlinearly in

the post buckling range. Furthermore, the buckling of

an element, which is a sudden phenomenon, can render

a determinate structure deficient, whereas an indeter-

minate structure will experience a sudden change in its

stiffness.

4. A feature specific to cable stays can be termed as the

‘sag’ effect, whereby the extensional stiffness of the

stay varies nonlinearly with its sag (or tension). This is

similar to the ‘P-delta’ effect except that the force is

tensile rather than compressive.

5. If the material constituting one or more elements in a

structure has a nonlinear stress–strain relationship,

partly or wholly through the stress range, the structure

response will become nonlinear to applied loading. For

steel structures, this is not an issue, except if a part or

whole of the structure enters into the post-elastic

range. Twisted wire ropes do exhibit a degree of

nonlinearity in the initial stress range, because of the

way these are constructed.

3.3.3 Wind effects

Steel structures are lighter than the stone, masonry or the

concrete ones. For these, generally the wind loading may

be expected to govern rather than the seismic load, from

amongst the two occasional loads. For the larger span or

taller buildings, roofs and bridges, which fall under the

category of ‘wind-sensitive’ structures, this is certainly

true.

The last 100 years, or so, have seen the use of these

structures increasingly, and, thus also an increase in wind

engineering related development. The features of wind

loading and related design issues are briefly addressed

below.

Wind is a randomly varying dynamic natural phe-

nomenon. This, when obstructed by a structure, causes

pressures upon its surface, which are essentially dynamic,

Fig. 10 The Akashi Kaikyo suspension Bridge-longest in the world

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because of the inherent nature of wind. For comparatively

rigid or stocky structures, these dynamic effects can be

treated as being quasi-static for simplification in the design

of the structure. However, for the larger and more flexible

ones, particularly in focus in this paper, aerodynamic

effects have to be taken into account. This aspect is one of

the more important challenges in the design of modern

steel structure design. The related features are brought out

for flexible, roofs, buildings and bridges.

3.3.4 Tall Buildings and Towers

Tall structures, particularly those made primarily in steel,

are essentially wind-sensitive and evoke an aerodynamic

response. In this category, one can place, buildings, bridge

pylons, towers-latticed or otherwise. There are specifically

two ways in which these structures are affected due to wind

loading. The first is the wind-induced fluctuating vibration,

called buffeting, which effects the structure along the

direction of the wind. The other is the across-wind oscil-

lation due to shedding of vortices, which create an across-

wind

Pulsating force: Whereas the along-wind effect is

monotonic, the across-wind effect is akin to a pendulum

vibrating across the vertical axis of the tower. This often is

the more important problem for the designer. While the

basic requirement is to ensure safety and limit the dis-

placements, control of accelerations is another objective

for the comfort of occupants in buildings.

3.3.5 Wide-Span Roofs

There are several reasons due to which, loads and effects of

wind have an important place in as far as steel or cable

roofs are concerned. These roofs have a unique geometrical

shape (see for example Figs. 7 and 8), and the wind load

coefficients are not easily available. It may often become

necessary to make a wind tunnel model study to obtain this

information. It is pertinent to point out in this context that,

particularly in fabric roofs, the deformations of the mem-

brane would modify the pressures, and there is as yet

hardly any work done to test models taking into account the

roof membrane flexibility, in the wind tunnel. Another

aspect that needs to be highlighted is that, wind causes non-

uniform pressures on cable roof surfaces [7] (see Figs. 12

and 13) and this may lead to large displacement in such

flexible roofs.

Aerodynamic oscillations are a distinct possibility for

these flexible roofing systems, though there does not appear

on record any indications of serious distress on this

Fig. 11 Different sources of

nonlinear response of structures

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account. Amongst the Tension structures under discussion,

cable bridges are far more of an issue from the wind

engineering standpoint and are addressed below.

3.3.6 Bridges

Usually, wind loading takes on important proportions for

medium span bridges, such as those over 200 m, but

becomes a serious design concern for 400 m or over. While

this space is taken up by a few arches, it is mostly the cable

stayed and suspension bridges. The dynamic behaviour of

the bridge under the action of wind loads is dependent upon

the flow; particularly in terms of the turbulence charac-

teristics, angle of attack, and the structural as well as

aerodynamic characteristics—the mass, stiffness, fre-

quency, geometrical shape and damping. It is noteworthy

that the site peculiarities can often manifest themselves into

a dramatic influence on the aerodynamic effect on such

bridges. For cable bridges, while pylons have issues such as

those mentioned earlier, the aerodynamics of decks is of

primary concern, and there are some aspects of cable stays

need to be addressed.

Deck: Various forms of aerodynamic response for the

deck can be described as buffeting, vortex induced oscil-

lations, and self-excited oscillations such as in vertical

bending, torsional bending, galloping in towers, or, flutter.

Initially, cable bridges used stiffening girders of trusses

along with a concrete or a steel deck. Collapse of the

Tacoma Narrows suspension bridge led to the idea of using

box girder decks to minimise wind loading, as well as to

meet the requirements of adequate torsional stiffness. It is

noteworthy that split boxes were found to be superior to

single boxes for aerodynamic stability, which also led to

the idea of using multiple boxes connected through cross

girders. Figure 14 shows one such concept for a long-span

suspension bridge [8]. One of the major design concerns in

this respect has been to choose a deck and stiffening system

to raise the critical wind speed for the initiation of flutter

above the design wind speed, by introducing adequate

stiffness. It is also possible to use fairings on the edges of

the deck along parts of its length, in order to reduce its

oscillatory motion. It is being investigated too whether the

use of passive controls such as the use of control surfaces

or ‘wings’, or, pendulums can be of advantage in sup-

pressing deck oscillations.

Cables: Cables are employed in suspension bridges as

‘main’ cable and hangers and in cable stayed bridges as

‘stays’. For suspension bridges, cables are quite massive,

and do not generally have an aerodynamic problem. These

being tied up with the deck and the pylon tops, participate

in overall bridge vibrations. The hangers often experience

‘singing’ which is an across-wind vibration of the hanger.

The same kind of vibration is possible in cable stays. As

stays become longer, the problem of rain–wind-induced

vibrations also becomes a possibility. Furthermore, hangers

and stays may often be provided in pairs, or may even

consist of 4 small size ropes or strands. In such cases,

‘wake’-induced across-wind oscillations may occur. To

overcome these problems, provision of auxiliary cables for

long stays, use of damping devices to control ‘singing’ and

use of surface features to take care of ‘rain–wind’ and other

oscillation problems are resorted to.

4 Conclusions

Developments in Steel as a construction material, and, the

allied issues of fabrication, construction and maintenance

in the past 200 years, have been largely responsible for its

deployment in modern structures with large dimensions—

both height as well as spans—such as roofs, building

towers and bridges. Thus, a great fillip has been made in

meeting the challenge of adding good quality infrastruc-

ture. Another factor most responsible in the effective util-

isation of the latest steel products is the enormous growth

Fig. 12 The Shell shaped Yoyogi National Gymnasium for the

Swimming pool, Tokyo Olypics, 1964, designed by Kenzo Tange

Fig. 13 Wind pressure distribution over the roof in Fig. 12 [7]

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in electronics and its applications in computing, sensors,

communication and robotics. India is catching up with the

rest of the world surely though slowly.

Acknowledgements The author thanks Er. Amitabha Ghoshal and

Er. Alok Bhowmick, two eminent structural engineers, for their time

in reading through the script and for their valuable inputs. Likewise,

thanks are due to Professors Toshio Miyata and Yukio Tamura for

information about the Akashi Kaikyo suspension bridge. Permission

by Institute for Steel Development and Growth for use of technical

material from their archives is thankfully acknowledged. The author

is thankful to Mrs. Pratigya Laur helping with the script and

illustrations.

References

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Publisher’s Note Springer Nature remains neutral with regard to

jurisdictional claims in published maps and institutional affiliations.

Fig. 14 Cross section of a

proposed Deck for the Messina

Straits suspension Bridge [G.

Diana et al. Ref. 7]

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