Extreme Wind and Snow loads for structural design

Transcription

1 COST Action C26 Urban habitat constructions under catastrophic events Extreme Wind and Snow loads for structural design D. Lungu C. Arion

2 Technical University of Civil Engineering Bucharest

3 Wind action in Romania 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.

4 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 V U = with mean 0.23 and standard deviation Romanian Code for Wind Loads, 2004 was prepared by UTCB.

5 Romania Meteorological database of wind record (example) PARAMETRII DE VANT Viteza caracteristica (m/s) NR STATIA Viteza Viteza medie Nr.ani Coef.var. Coef.asim. max (m/s) (m/s) T=25ani T=50ani T=100ani 1 Adamclisi Adjud Alexandria Apa Neagra Avrameni Bacau Relative frequency Maximum annual wind speed Cov 0.26 Mean Coefficient of variation

6 Romania Maximum recorded wind velocity

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

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10 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, Skewness coefficient, min V T = 50 yr = = 25.7 m/s = V ref 1min mean wind velocity at 10meters above the ground in Tg. Jiu Mean recurrence interval 10 yr 50 yr 100 yr Wind velocity in Gumbel largest extreme distribution 28 m/s 31m/s 34 m/s the mean, standard deviation and coefficient of variation of maximum wind velocity in N years in Gumbel distribution The statistic indicators for maximum annual wind velocity averaged on 10 min in Tg. Jiu are: m N = m 1 + ln N σ 1 m 1 = m/s = 14.5 m/s σ 1 = 4.35 m/s (since V 1 = 0.3). V σ N = σ 1 N σ = m N N = m 1 σ 1 ln N + σ = V1 ln N 1 + V

11 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.

12 Power spectra of the along-wind gust velocity Solari in Eurocode 1 von Karman in JCSS and CIB codes ng (n) 6.868x = σ ( x ) u 2 5 u 3 ng (n) = σ u 2 u 4x ( x ) x=l uc n / V(z), where: L uc =300(z/300) lnz0 x=l u n / V(z) where L u is either L uc =300(z/300) lnz0 L old_esdu u =25z 0.35 z or ng u (n)/σ u2 is the normalized spectrum (i.e. unit area) n the frequency in Hz V(z) the mean velocity at height z

13 L u is the integral length scale (after Couniham or ESDU) 300 Couniham and ESDU integral length scales Integral length scale C ouniham Old_ESDU z [m ]

14 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). vref=30m/s, z0=0.05m, z=10m vref=30m/s, z0=0.05m, z=100 Normalized spectrum 0.1 Normalized spectrum 0.2 van Gelder & Lungu, 1998 Normalized spectrum Frequency [Hz] vref=30m/s, z0=0.3m, z=10m Normalized spectrum Frequency [Hz] vref=30m/s, z0=0.3m, z= Frequency [Hz] Frequency [Hz] For every combination of input values (V ref =30m/s, z 0 = m, and z= m), the same ordering in spectra is found (from high to low): KE, SC, KC.

15 Comparison between various spectral densities over the whole frequency range at z=100m, v ref =30m/s and z 0 =0.05m vref=30m/s; z0=0.05m; z=100m van Gelder & Lungu, 1998 Normalized spectrum Frequency [Hz] 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).

16 Snow action in Romania 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.

17 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 V U = 0.57 and maximum value close to 1. Romanian Code for Snow Loads, 2005 was prepared by UTCB.

18 Relative frequency Maximum annual ground snow 119 meteo stations Cov 0.25 Mean Coefficient of variation

19 Romania - Characteristic snow load s 0,k, kn/m 2

20 s N + s 0,k 2 ( C 2.054) ln( 1 V = e ) Ratio of characteristic values defined by various recurrence intervals (lognormal distribution) 1.2 Mean recurrence interval, MRI=N years C s N/s0,k V=0,1 V=0,3 V=0,5 V=0, Interval mediu de recurenta IMR, ani