lungu arion

Extreme Wind and Snow loads for structural design

WG 4 Meeting in Delft, 17-18 November 2006

D. LunguC. Arion

COST Action C26Urban habitat constructions under catastrophic events

Technical University of

Civil Engineering

Bucharest



The meteorological database comprises the maximum annual wind velocity (at 10 m, averaged on 1 min) at more than

140 National Institute of Meteorology and Hydrology locations in Romania, at which wind speed measurements were made.

The period of records for these locations is between 20 to 60 years, up through the 2005.

Wind action in Romania


The extreme value distribution used for the estimation of the characteristic wind velocity is the Gumbel distribution for maxima.

The coefficient of variation of the maximum annual wind velocity is in the range VU = 0.15÷0.3 with mean 0.23 and standard deviation 0.06.

Romanian Code for Wind Loads, 2004 was prepared by UTCB.


Romania – Meteorological database of wind record (example)

T=25ani T=50ani T=100ani1 Adamclisi 27 24 17 0.21 0.37 25 27 29

2 Adjud 27 40 22 0.21 2.58 31 34 36

3 Alexandria 27 40 26 0.29 0.81 41 45 49

4 Apa Neagra 27 17 11 0.28 0.39 18 20 21

5 Avrameni 27 40 25 0.19 1.22 35 37 40

6 Bacau 27 40 18 0.35 1.73 32 35 39

Viteza caracteristica (m/s)

Coef.asim.NR STATIA

Nr.ani Viteza max (m/s)

Viteza medie (m/s)

Coef.var.

PARAMETRII DE VANT

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.1 0.2 0.3 0.4 0.5

Coefficient of variation

Rel

ativ

e fre

quen

cy Maximum annual wind speed

Mean 0.23

Cov 0.26


Romania – Maximum recorded wind velocity


Romania - Characteristic wind velocity averaged on 1 min having 2% annual probability to be exceeded


Test site – Tg. Jiu (Romania)The statistical indicators for the maximum annual wind velocity averaged on 1 min in Tg. Jiu are as follows:

- Maximum observed wind velocity, 35 m/s- Mean of the annual maxima, 17 m/s- Standard deviation, 5.1 m/s- Coefficient of variation, 0.30 - Skewness coefficient, 1.65.

34 m/s100 yr

31m/s50 yr

28 m/s10 yr

Wind velocity in Gumbel largest extreme distribution

Mean recurrence interval

1min mean wind velocity at 10meters abovethe ground in Tg. Jiu

= 0.83⋅ 31 = 25.7 m/s = Vref

min1050 yrTV =

The statistic indicators for maximum annual wind velocity averaged on 10 min in Tg. Jiu are:

m1 = 0.83⋅17m/s = 14.5 m/sσ1 = 4.35 m/s (since V1 = 0.3).

11N 282.1Nln

mm σ⋅+=

1

1

11

1

N

NN

V282.1Nln1

V

282.1Nlnmm

V⋅+

=⋅+

==σ

σσ

σN = σ1

the mean, standard deviation and coefficient of variation of maximum wind velocity in N years in Gumbel distribution


Wind turbulence

POWER SPECTRAL DENSITIES FOR ALONG-WIND GUSTINESS

Karman (1948), Panovski (1964), Davenport (1967), Harris (1968), Flicht (1970), Kaimal (1972), Simiu (1974,1975), ESDU (1976, 1985), Naito (1978, 1983), Kareem (1985), Solari (1987,1993).

Solari and von Karman spectral densities are compared.


x=Lu n / V(z)where Lu is eitherLu

C=300(z/300)0.46+0.074lnz0 orLu

old_ESDU =25z0.35z0-0.063

x=LuC n / V(z),

where:Lu

C=300(z/300)0.46+0.074lnz0

von Karman inJCSS and CIB codes

Solari inEurocode 1

Power spectra of the along-wind gust velocity

nGu(n)/σu2 is the normalized spectrum (i.e. unit area)

n the frequency in HzV(z) the mean velocity at height z

u

u2 5

3

nG (n)=

6.868x

(1+10.32x )σu

u2

256

nG (n)=

4x

(1+ 70.8 x )σ


Lu is the integral length scale (after Couniham or ESDU)

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 00

5 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

z [m ]

Inte

gral

leng

th s

cale

C o un iha m a nd E S D U in te g ra l le ng th s c a le s

C o un iha m

O ld _ E S D U


10-1

100

101

102

0

0.1

Frequency [Hz]

Nor

mal

ized

spe

ctru

m

vref=30m/s, z0=0.05m, z=10m

10-2

100

0

0.2

Frequency [Hz]

Nor

mal

ized

spe

ctru

m

vref=30m/s, z0=0.05m, z=100

10-1

100

101

102

0

0.1

0.2

Frequency [Hz]

Nor

mal

ized

spe

ctru

m

vref=30m/s, z0=0.3m, z=10m

10-2

100

0

0.2

Frequency [Hz]

Nor

mal

ized

spe

ctru

m

vref=30m/s, z0=0.3m, z=100

Solari spectrum with Couniham integral length scale (SC), the Von Karman spectrum with Couniham integral length scale (KC),the von Karman spectrum with old ESDU integral length scale (KE).

For every combination of input values (Vref=30m/s, z0=0.05..0.3m, and z=10..100m), the same ordering in spectra

is found (from high to low): KE, SC, KC.

van Gelder & Lungu, 1998


Comparison between various spectral densities over the whole frequency range at z=100m, vref=30m/s and z0=0.05m.

1 0-4

1 0-2

1 00

0

0 .0 5

0 .1

0 .1 5

0 .2

0 .2 5

0 .3

F r e q u e n c y [H z ]

Nor

mal

ized

spe

ctru

m

v r e f= 3 0 m /s ; z 0 = 0 .0 5 m ; z = 1 0 0 m

Solari spectrum with Couniham integral length scale (SC), the Von Karman spectrum with Couniham integral length scale (KC),the von Karman spectrum with old ESDU integral length scale (KE).

van Gelder & Lungu, 1998


The meteorological database comprises the maximum annual snow height and water equivalence at more than

110 National Institute of Meteorology and Hydrology locations in Romania, at which the measurements were made.

The period of records for these locations is between 20 to 60 years, up through the 2005.

Snow action in Romania


The distribution used for the estimation of the characteristic snow load is the lognormal distribution for maxima.

The coefficient of variation of the maximum annual snow weight has the mean value VU = 0.57 and maximum value close to 1.

Romanian Code for Snow Loads, 2005 was prepared by UTCB.


0

0.05

0.1

0.15

0.2

0.25

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Coefficient of variation

Rel

ativ

e fre

quen

cy

Maximum annual ground snow119 meteo stations

Mean 0.57Cov 0.25


Romania - Characteristic snow load s0,k , kN/m2


( ) ( )2V1ln054.2C

k,0

N ess +⋅−=

0.6

0.7

0.8

0.9

1.0

1.1

1.2

10 20 30 40 50 60 70 80 90 100

Interval mediu de recurenta IMR , ani

s N/s

0,k

V=0,1V=0,3V=0,5V=0,7

2.326100

2.05450

1.75125

1.28210

CMean recurrence interval, MRI=N years

Ratio of characteristic values defined by variousrecurrence intervals (lognormal distribution)

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