Discussion of session 8 - engineering structures, bridges

Journal of Wind Engineering and Industrial Aerodynamics, 29 (1988) 429-437

429

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

DISCUSSION

OF

Chairman:

SESSION

ON

PAPER

BY MR.

We have

BY

B.W.

MR.

leading

have u n d e r t a k e n

reliable.

studies

and f l u t t e r over

wind

Only

PRENNINGER

in

the U.K.

to by

we

will

the

to

combination

make

the

for s u s p e n s i o n b r i d g e s w o u l d

at w i n d speeds b e l o w the a u t h o r s

analysis

Since

for b o t h

a wide range of b r i d g e

found

tend

on d e s i g n

the authors.

similar reliability

excitation

loading with

MATSUMOTO/P.H.W.

to the rules r e f e r r e d

vortex excitation vortex

M.

extensive

then we

Have

BRIDGES

SMITH

undertaken

guidance

For

STRUCTURES,

Prof. Dr. G. S e d l a c e k I n s t i t u t e for steel s t r u c t u r e s Aachen Technical University

DISCUSSION

QUESTION

8 - ENGINEERING

types:

of t r a f f i c

lower

modes

less

the h i g h e r m o d e s

be

the d e s i g n value. considered

the c o m b i n e d

effect with traffic

on r e l i a b i l i t y ?

AUTHOR'S

REPLY

In J a p a n if the w i n d

- MR.

all

P.H.W.

traffics

speed e x c e e d s

c o m b i n a t i o n of w i n d -

a

account

for such

present

investigation.

higher

mode

in the case

C O M M E N T BY DR.

problem. more

T.D.

of long

prefer

to

see

problem

Hence,

any

oscillations.

Consein the

span s u s p e n s i o n

bridges

these

analysis.

as a first a p p r o a c h of b r i d g e s

than

response the

s a f e t y or r e l i a b i l i t y the G a u s s i a n

m/s.

HOLMES

Reliability analysis

relation between

25

h a v e not b e e n c o n s i d e r e d

in f u r t h e r

is an e x c e l l e n t p a p e r

difficult

about

l o a d i n g m i g h t not be taken into

vortex-induced

load c o m b i n a t i o n s

e f f e c t s m i g h t be i n c l u d e d

This

level of

and t r a f f i c

quently

However,

PRENNINGER

will g e n e r a l l y be s t o p p e d on a b r i d g e

and

results

buildings wind

probability

due

speed.

expressed

i n d e x ~ g i v e n by p~

cumulative

under

to a d i f f i c u l t

w i n d are to

a much

the

complex

However,

I would

in terms of a r e l a t i v e = ~(-8) ,

function.

w h e r e ~()

is

430

AUTHOR'S

REPLY

In this 3-method) these

- MR.

P.H.W.

investigation has b e e n

failure

can

Moreover, and

fully p r o b a b i l i s t i c to

probability

be

estimate

estimates

the r e l a t e d

computed

since

D-values

information

a

applied

(without d e t e r m i n i n g values

PRENNINGER

there both

are

exists

concerning

(level Hence,

directly

However,

these

~-

the r e s p e c t i v e p f - v a l u e s .

a unique

the

approach

p~-values. obtained,

D-values).

considering

quantities

the

relation between

contain

an i d e n t i c a l

reliability

of

the

the pfamount of

structures

investigated.

DISCUSSION

ON

PAPER

BY

S.J.

ZAN,

H.

H. YAMADA,

QUESTION

BY

Do the

PROF.

A.G.

authors

AUTHOR'S

We have n o t i c e d

this

explanation

QUESTION

DR.

BY

the

buffeting

AUTHOR'S

reasons

REPLY

We w e r e

exceeded

the

attributed

value,

like

in our

aeroelastic

to c o m m e n t on how well

with

S.

work,

but have

the

model

sections

experimental since

were

there

results with buffeting

we

had

static

deflections.

by q u a s i - s t e a d y

of 60%

results were brought

and

results

the a e r o d y n a m i c d a m p i n g

than p r e d i c t e d

of a e r o d y n a m i c d a m p i n g

force

The e x p e r i m e n t a l

15 to 204 for v e r t i c a l

to the fact that

the a n a l y t i c a l

and

disagreements?

for these sections.

is less

data

the t u r b u l e n c e

ZAN

t h e o r y by about

these s e c t i o n s Using a value

trend

compare

two

This was

increa-

than unity?

for this p h e n o m e n o n .

for any p a r t i c u l a r

to

coefficients

the r e s p o n s e

IRWIN

- MR.

able

t h e o r y for o n l y moment

P.A.

authors

theory agreed

particular

any e x p l a n a t i o n why

S. Z A N

no d e f i n i t e

Would

WARDLAW

i n t e n s i t y w i t h a power h i g h e r

- MR.

REPLY

R.L.

DAVENPORT

have

ses w i t h t u r b u l e n c e

TANAKA,

for

theory.

of the q u a s i - s t e a d y in line w i t h

the

431

experimental

result.

experimentally, range

This v a l u e of d a m p i n g has not b e e n v e r i f i e d

but in our w o r k we have seen a e r o d y n a m i c d a m p i n g

from 30 to i00% of the q u a s i - s t e a d y value.

Another

source

analytical

results

little

of

discrepancy between

D I S C U S S I O N ON P A P E R BY R.H.

C O M M E N T BY PROF. Prof. survive

and

of w h i c h

a

in our work.

SCANLAN

M. N O V A K

Scanlan

critical

makes

temporary velocity.

an i m p o r t a n t increase

It

s u p p o r t e d by a few

may

more

dynamic derivatives,

in

be

factors:

increase

AUTHOR'S These

PROF.

-

are c e r t a i n l y

particular bridge derivative most stability

Of

In

There

in the p a p e r as to w h a t

DR.

By way

the

could be

of the aero-

for

low c r i t i c a l

the

that d e p e n d u p o n case

as

of

the f l u t t e r

it can h a p p e n

in the

the

instance

that

of the

is also in fact some p o s s i b l e is a g u s t

and what

upon which gusts

is a rise

are s u p e r p o s e d .

IRWIN

P.A.

of c l a r i f i c a t i o n ,

l a t i o n of the g u s t correlation

beyond

s h o u l d not be applied.

observations

is l e s s e n e d w i t h a m p l i t u d e

Q U E S T I O N BY

course,

for i n s t a b i l i t y ,

in the level of the m e a n wind,

did the

a l o n g the

span

authors or

was

assume the

correlack of

included?

W i n d tunnel be a cause of due

nonlinear parts

arguments

circumstances.

twist.

velocity

SCANLAN

correct

responsible

squat H - s e c t i o n under confusion

R.H.

wind

that b r i d g e s m a y

in s t r u c t u r a l d a m p i n g w i t h s t r a i n

all such m i t i g a t i n g

REPLY

conclusion

that this o b s e r v a t i o n

and n o n s t a t i o n a r i t y of the gust. velocities,

2.

admittance,

is k n o w n for b r i d g e decks.

We u s e d the Irwin e x p r e s s i o n

i.

the e x p e r i m e n t a l

c o u l d be the a e r o d y n a m i c

tests

s h o w gusts

an e a r l i e r

(turbulence)

flutter

do not s e e m to

instability premubably

to the u n c o r r e l a t e d n a t u r of the gusts.

How r e a l i s t i c

432

do

the

authors

uniform

AUTHOR'S To

their

calculation

are

based

on

a

gust?

REPLY

the

think

PROF.

-

first

R.H.

question:

SCANLAN

We

assumed

that

the

gust

was

correla-

ted. To

the

involved

a)

second in

the

The

sectional

"average" lence

b)

question:

thinking

The

gust

tives

response

at

The

wind

and

the

the is

theory,

under

as

of

the

process

follows:

are

determined

a given

velocity

level

of

as

turbu-

predict

level

new

to b r i n g

is in

period

B.W.

SMITH

flutter

deriva-

degradation

the

then

RMS

raised

overall

values

about

time

such

spanwise

of g u s t

gust

response

beyond

critical

velocity.

change

corresponding assumed

to

wind

expected

involving

for

is u s e d

a given

a given

view

is

derivatives hold

allowance

correlation,

c)

that

a truer paper

10%).

and

level

the

flutter

values

(say

Perhaps

behind

of

a rise

inferred

damping,

the in

from

inferred

flutter total

from

derivatives,

response

meteorological

within consi-

derations.

QUESTION In

BY

the

allowed "mean"

MR.

british

for

the

speed

our

specifying

the

design

1.3.

I

REPLY in

-

of

cause

120

used allow

PROF.

fact,

for

this

yr

if

flutter hourly Dr.

in

for

This speed

mean)

by

the

we

higher

resulted should

in

exceed

a factor

believes

bearing this

stability

and

Scanlan

confidence,

a reduction

R.H.

speed

instability.

return

with

aerodynamic

flutter

calculated

interested

be to

rules

up

the

(the be

could

It was,

can

that

speed

uncertainties,

AUTHOR'S

build

that

would

procedure

design

in m i n d

of

that

his

all

the

factor.

SCANLAN

reflection

on

the

rationale

for

the

factor

433

1.3

that

paper. paper

led

to

However, to

exploration

of cases,

be g e n e r a l l y

raised

the p a p e r

is that

specific

mechanism

of flutter

if flutter

DISCUSSION

QUESTION

i)

ON

BY

PAPER

PROF.DR.

Could

H.

R.

problem whole

build-up.

may

I believe

that

a fair

one p a r t i c u l a r

It may be

B.

worth

BIENKIEWICZ,

of

vibrations

with

occur

together

bridge

of the

the factor

case-

further

are available.

vibrations

span b r i d g e s

vibrations

the a p p l i c a t i o n

J.E.

CERMAK

CIESIELSKI

torsional

At long

or lowered.

KOBAYASHI,

vertical-torsional

2)

in the

it e m p h a s i z e s

derivatives

BY

outlined

so I do not know w h e t h e r

view of

research,

of the case

I have not yet r e s e a r c h e d

a range

1.3 w o u l d

the

-

with

the

deck

and

(vortex-excited)

very so

small

that

aerodynamical

may be i m p o r t a n t

occur?

damping

a

coupled

horizontal

spatial

vibration

instability

for p r a c t i c a l

of the

cases.

I ask for comments.

AUTHOR'S

1)

REPLY

- MR.

The p r e s e n t e d wind-tunnel bridge.

practical

Mechanism

The

would

response

indicated

bridge

in h o r i z o n t a l

was

of t u r b u l e n c e are

taken

deck

were

relatively

was

tested

spatial

account

of

however,

at low wind

of freedom

a

flutter

speed range

exhibited,

presented

with

cable-stayed

torsional wind

investigated

deck was

and

into

conjunction

the

response

degree

model

in

proposed

in the

The b r i d g e

of the i n v e s t i g a t i o n

section

a that

not occur

of this r e s p o n s e

The b r i d g e effects

of

vortex-induced

investigated

response

conducted

investigation

interest.

significant

2)

BIENKIEWICZ

study was

The results

instability

results

B.

speed.

and the m a i n in the paper.

stiff

and its

was not modeled.

in smooth

aspects

flow.

The

of the bridge

in an a n a l y t i c a l

analysis

434 employing tunnel

DISCUSSION

QUESTION With

PAPER

PROF.

very

important

long

role

been

considered?

been

taken

AUTHOR'S We span

aerodynamic

into

REPLY

bridges.

MIYATA,

I.

OKAUCHI,

N.

NARITA,

N.

NAHARA

A.G.

DAVENPORT

span

bridges

in

the

Has

the

account

PROF.

-

understand

the

This

effect

T.

really

associated

cerned,

the

reduction

great

span

necessarily

the

deck

leads

to

shallow of

The

effect account

open, As

ments deck

open

but

for

in

the

hilly

effects

turbulent

proposals.

decrease

in

terrain

a bit

the

wind-

of

low

of

over

Has

a more

this

frequency scale

factor

turbulence

topography?

in

are

the

of

of

of

for

a

torsional

in

has

page

been

site both

full

of 267

taken for

is

an

rather

anchorages.

model

couple

is

fact

in c a s e

responses

at

the

deck

This

the

construction

weight

to s u s p e n d

seen

turbulence

con-

carry

road

description

shore

is

length.

typically

in

torsional

the

pitch

span

long-

design

the

to

weight

hanger

aeroelastic

scheduled

as

stability

buffeting The

very

bridge

far

increase

any

span

with

inertia)

the the

along-wind

inside

by

of

frequency

turbulence,

the As

is

limit

condition. only

cables

contribution

which

(ref.

flow

SHIRASHI,

take

flutter

comparison,

deck,

very

the

caused

so m u c h

of

of

moment

invariable

decks

low

large

with

because

road

very to

governs

increased

box-like paper).

ordinal,

In

cables

aspects.

is

polar

relative

of

the

into

their

not

the

stiffness

dynamic

length.

not

is

during

MIYATA

factor as

N.

aerodynamics.

of

importance

frequency

(and

the and

- perhaps

natural

greater

well

mass

as

cables

obtained

BY T.

static

of

data

studies.

ON

BY

the

of

experiselected

435 DISCUSSION

ON

QUESTION

B Y DR.

Your amount

wind

Y.

BY

N.

SHIRASHI

TUJINO experiment

seems

(rain)

needed

supply

possible

is

(or p r o b a b l e )

in a h o r i z o n t a l

direction

AUTHOR'S

to i n d i c a t e to

have

that

small

a rain-wind

that

such

a vibration

or s l i g h t l y - i n c l i n e d

cable

can

for

occur

a certain

of w i n d ?

REPLY

is

MR.

-

Y.

possible.

the u p p e r change

HIKAMI,

vibration.

Is it

It

Y.

tunnel

of w a t e r

induced

even

PAPER

revulet

the

cable

HIKAMI

For

horizontal

or s l i g h t l y - i n c l i n e d

c a n be

formed,

and

the r e v u l e t

cross

section

to

an a e r o d y n a m i c a l l y

cable,

formation

might

unstable

section.

QUESTION I.

B Y MR.

Use

B.W.

of p a r a l l e l

covered

in

vibration

formed.

wire

the

these

D o the

I have

severe

cable.

Are

Have

AUTHOR'S

i.

-

We a g r e e

with

the g r o u t

any

Y.

surface,

in the

case

cables?

We have

strand

the u s e has

the

would

would

have

not

have

of

not

this

form

of

due

to

damage

to

cracked

corrosion?

signs

of

Can you

conducted

conducter

we have

spiral

and

for

fatigue inspect

these?

HIKAMI

you.

vibration"

although

consequent the

grout

agree?

to p r e m a t u r e

of

by

reason

as r i v u l e t s

leading

on a o v e r - h e a d "rain

spiral

convinced

been

MR.

of

prime

about

sockets

REPLY

use

surrounded

the

reservations

you

there

the e n d

was

vibrations

authors

the v i b r a t i o n s ,

3.

in b u n d l e s ,

polythene and

eliminated

2.

SMITH

(diameter

reported observed

ref.

the u p p e r

vibrations

of a s p i r a l

in

the w i n d 23mm)

did not

3.

In

revulet occur.

configuration,

tunnel

test

to i n v e s t i g a t e the

test,

formation

It seems,

the u p p e r

on

that

revulet

436

formation

does

not

aerodynamically rain

2.

We

have

no

was

vibration

3.

We

think

of

large

idea

QUESTION The

BY

where

authors

the

Could type

of

AUTHOR'S In o u r the is

a

hear

max.

REPLY

this

The

problem

if

QUESTION

BY

no

cracked we

nor

think

is m o r e

the

because that

severe

fatigue

damage,

experienced

is

hours

I0

damage

J.

any

at

since

XIE,

Z.

since

most.

there

the

than

a

was

the

hour

before We

the

did

not

no n e e d .

KIN

are

was any

and

list

a

of

vortex-induced

few

cross-sections

observed. provisions

applicable

(acceptable~not

Japan

to

this

acceptable,

etc.)?

H.

XIANG

full-bridge

aeronautical is

too

response any

appearances

al.

oscillation

M.

that

strand.

a cable

motion

China

tunnel

PROF.

load

geometry

believe

which

et.

there

MR.

of

has

However,

live

mention

amplitude

-

we

a spiral

grout

it.

XIANG,

Miyata

in

on

section

TANAKA

aeroelastic

low-speed of

H.

not

T.

a

the

vortex-induced we

vortex-induced

I.

do

the

was

taken

BY

H.

vortex-induced

speed

there

was

and

motion

allowable

to

inspected

PAPER

Therefor, occur

check

vibration

PROF.

oscillations

to

cross

a crack.

that

directly

ON

not

whether

due for

prevention

DISCUSSION

does

no w a y

deformation

the

unstable.

vibration

there

make

of

model

because wind

high, the

test, the

tunnel, which

we

did

wind the

not

tunnel min.

is b e y o n d

observe we

used

stable

wind

the

range

of

model.

provisions

we

have

not

yet

investigated.

ITO

What

values

of

wind

tunnel

model

structural tests?

damping

were

assumed

in y o u r

437 2.

Concerning Table the t u r b u l e n t fact that, grows

3, h o w was

the c r i t i c a l w i n d speed u n d e r

flow d e f i n e d ?

under

continuously with

combined with

This q u e s t i o n

t u r b u l e n t wind,

arises

from the

the t u r b u l e n c e

response

increasing wind speed

aerodynamic

instability

and may be

at v e r y high w i n d

range.

AUTHOR'S

REPLY

i.

MR.

-

H. X I A N G

We h a v e m e a s u r e d aeroelastic critical

2.

the

structural

full-bridge

to d e f i n e

the

flow

turbulent

BY

MR.

S.

this

bridge, low

is

ratio about

of our

2-2.5% of

as

critical wind We

just

speed u n d e r estimate

the

from the v - A curve.

ZAN

identified

very

the

accurately.

flutter point very roughly

You have

It

for the first mode.

It is d i f f i c u l t

QUESTION

damping

model.

the e r e c t i o n

the

critical

balanced

velocities

state as a

cantilever for

the

critical

technique onset

of

one

results

for in

a torsinal

instability. It has b e e n our e x p e r i e n c e technique moderate

results

is if

the v e r t i c a l m o d e s response

AUTHOR'S

as well,

that this e r e c t i o n

deflections

aeroelastic

REPLY

MR. H. X I A N G

we

-

have

considered

In our

(1-3m)

at

have n o t i c e d

to i n v e s t i g a t e

to s t i f f e n this

large

ties on

the e f f e c t of i n i t i a l

the d y n a m i c

s t a b i l i t y of the e r e c t i o n

we c o n s i d e r e d

facility.

tie downs

investigation?

test the b a l a n c e d - t w i n

because

considered

and if you

in y o u r

as the a e r o d y n a m i c

tunnel

vertical

you have

t e n s i o n in the t e m p o r a r y

out,

of late at NRC

large

velocities.

My q u e s t i o n

Yes,

in

cantilever

that it

behaviour

as w e l l

state. case has not c a r r i e d

is d a n g e r o u s

for the w i n d