Wind Resistant Design AIJ Recommendations for Wind Loads on Buildings

Transcription

1 Lecture 6 Wind Resistant Design AIJ Recommendations for Wind Loads on Buildings Tokyo Polytechnic University The 1st Century Center of Excellence Program Yukio Tamura Background Building Standard Law of Japan (BSLJ) --- Minimum building design requirements - completely revised in Performance Based Design (PBD) AIJ Recommendations for Loads on Buildings (AIJ-RLB RLB) to be revised in 004 1

2 Major Revisions Introduction of the wind directionality ity factor (8 wind directions); Explicit introduction of wind load combinations; Correction and addition of topographic effects; Substantial fulfillment of aerodynamic shape factors Wind Load Estimation in AIJ-RLB Low-rise Small Size Medium-rise Rigid Buildings and Structures igh-rise Slender Flexible Particularly Wind Sensitive Simplified Detailed Method - Crosswind Method - Along-wind - Roof - Torsion - Cladding - Quasi-steady steady- Size Reduction Effects - Quasi-static static - Resonance Effects - Vortex Resonance - Aerodynamic Instability - Wind Tunnel Tests, etc.

3 Design Wind Speed U (m/s) U = U 0 K D E k rw U 0 : Basic wind speed K D : Wind directionality factor E : Wind speed profile factor rw : Return period conversion factor k rw Basic Wind Speed Meteorological Standard Condition - 10min mean - 10m above ground - Open flat terrain year year-recurrencerecurrence Typhoon Winds : Monte-Carlo Simulation Synoptic Winds : Meteorological Data Combined probability 3

4 Basic Wind Speed U 0 (m/s) Okinawa: 50m/s Lower Limit: 30m/s Orientation of Building and Wind Direction B = 0m, D = 40m, = 40m Maximum Acceleration 63% 100% Maximum Displacement 50% 100% 4

5 Wind Directionalityity Factor Davenport (1969) olmes (1981) Cook (1983) Melbourne (1984, 1990) AS (1989) AS/NZS (00) Simiu & eckert (1998) Wind Directionalityity Factor in Major Codes ASCE Buildings: 0.85 for all directions Chimneys: 0.9 or 0.95 for all directions Except for hurricane-prone regions AS/NZS1170.(00) - Tropical-cyclone cyclone-prone regions: 0.95 or 1.0 for all directions - Non-tropical tropical-cyclone-prone regions: Wind Direction Multiplier for 8 sectors 5

6 Wind Directionalityity Factor Difficulty in tropical-cyclone cyclone-prone regions Meteorological records in Japan: - 75 years of reliable records at most - Approx. 3 landfalls/year of typhoons - Very few typhoon data in each sector divided into 8 or 16 sectors of azimuth for a given site Large sampling error Wind Distribution in Typhoon Direction of Movement 10m/s 0m/s 30m/s 40m/s 50m/s Northern emisphere Dangerous Semicircle 6

7 Wind Directionality Factor in Japan ybrid use of meteorological data during typhoon passage and Typhoon Simulation technique Reflecting effects of large-scale topography and terrain roughness - Correlations between observed wind speed and simulated friction free wind speed - Correlations between observed wind direction and simulated friction free wind direction p 1 Generation of Virtual Meteorological Data in Tropical Cyclone Prone Region p i Typhoon Path p 3 p p 4 Pressure Records at Meteorological Stations p Simulated Friction Free Wind (FFW) - Wind Speed U FF Correlations - Wind Direction D FF Meteorological Records - Wind Speed U ME - Wind Direction D ME Typhoon Simulation Virtual (FFW) Meteorological Data 5000 years 5000 years 7

8 Generation of Virtual Meteorological Data in Tropical Cyclone Prone Region Calculation of Correlations Correlations Between Evaluated FFW (U FF, D FF ) and Observed Wind Records (U( ME, D ME ) Using All Available Typhoon Records Typhoon Simulations (5,000 years) Monte-Carlo Simulation at Meteorological Stations - Wind Speed U SFF - Wind Direction D SFF (FFW) Virtual Meteorological Wind Data (5,000 years) Probabilistic Conversion of Simulated FFW W (U( SFF, D SFF ) to Virtual Meteorological Wind Data (U( vir, D vir ) Evaluation of Directional R-year Recurrence Wind Speed in Tropical Cyclone Prone Region Virtual Long-term Meteorological Data Sufficient Wind Records in Each Sector R-year Recurrence Wind Speed for Each Wind Direction 8

9 Wind Directionality (Tokyo, 100-year Recurrence ybrid Use of Typhoon Simulation and Meteorological Records Equivalent Annual Exceedence Probability of Directional Wind Speed Corresponding to an annual exceedence probability of load effects (base shear, base moment, etc.) corresponding to 100-year recurrence Under different conditions: - load effects - building shape - orientation - geographic location - design target (structural( frames, components and cladding) 9

10 Equivalent Directional Design Wind Speed U D Annual probability of exceedence of a wind load effect = 1/ (100-year Recurrence) 1. Calculation of 100-year recurrence wind load effect (e.g. internal force, peak pressure) based on the actual wind climate at a given site Q X,100 Site, Building Shape, Orientation, Load Effect, etc. Equivalent Directional Design Wind Speed U D. Calculation of equivalent return period causing the same 100-year recurrence wind load effect in the most unfavorable case years Q X,100 10

11 Equivalent Directional Design Wind Speed U D. Calculation of equivalent return period causing the same 100-year recurrence wind load effect in the most unfavorable case 3. Calculation of average directional wind speeds U D based on the equivalent return period for various cases at each meteorological site Equivalent Directional Design Wind Speed U D Ave. ± σ (m/s) 11

12 Equivalent Directional Design Wind Speeds Chiba Wind Directionality Factor K D (8 azimuths) Equivalent Directional Design Wind Speed K D = Basic Wind Speed U 0 If you have aerodynamic shape factors for all wind directions, K D can be used directly. If you use aerodynamic shape factors C f specified in the AIJ-RLB, there is a limitation. Structural Frames : Specified method Cladding/Components : K D = 1 1

13 Wind Speed Profile Factor E E r E g E = E r E g : Exposure factor for flat terrains : Topography factor for mean wind speed E r Z G Z b Exposure Factor for Flat Terrains E r α Z 1.7 < Z b Z Z = Z G α Z b 1.7 Z Z b Z G : Gradient height : Interfacial layer height G 13

14 Z 700 m Exposure Factor for Flat Terrains E r Category V IV III II I V III I IV II E r Topography Factor E g S Escarpments θ S X S Ridges θ S X S S 14

15 Topography Factor E g A series of wind tunnel tests and numerical simulations E g C = 1 Topography Factor E g ( C 1) exp C, C and C 1 C 3 Z S C 3 Z S + 1 C + 1 : Constants depending on slope angle and distance from upper edge

16 Topography Factor E g 0 Eg 1 Proposed Formula E g X S S 1 1 Return Period Conversion Factor k rw k rw 0.6( λ 1)ln r.9λ = U U λ U = U 500 U 0 U 500 U 0 : 500-year year-recurrence recurrence wind speed for the meteorological standard conditions : Basic wind speed (100-year year-recurrence) recurrence) 16

17 500-year year-recurrence recurrence Wind Speed U 500 (m/s) Okinawa: 58m/s Lower Limit: 34m/s Turbulence Intensity I Z at eight Z I = Z I rz E gi I rz E gi = E E I g : Turbulence Intensity for flat terrains Topography factor for fluctuation wind speed σ u : Topography factor for turbulence intensity Topography factor for mean wind speed U 17

18 Turbulence Intensity for Flat Terrains I rz at eight Z Z 0.1 Z Z 0.1 Z α 0.05 G I rz = α b G Z b < Z Z Z Z b G Turbulence Scale L Z (m) at eight Z L Z = 100 Z m Z < Z Z 30m G for every terrain category 18

19 Wind Loads Specified in AIJ-RLB For Main Frames - orizontal Along-wind Load Ccrosswind Load Torsional Load - Roof Wind Load For Cladding / Components - Peak Cladding Load Along-wind Loads on Ordinary Buildings W D (N) at eight Z W q D = q C G A : Velocity pressure at reference height C D : Aerodynamic shape factor G D : Gust loading factor A : Projected area GLF based on Base Bending Moment (Zhou & Kareem, 001) D D 19

20 C φ D R D GLF for Along-wind Loads on Ordinary Buildings ' g GD = 1+ gd 1+φD RD Cg g D and g C g C : Peak factor : Fluctuating and mean coefficients for along- wind OTM : Correction factor depending on mode shape : Resonance factor Wind Loads on Roof Structures W R (N) W = q q C R G R A R R C R G : Velocity pressure at reference height C : pe C pi Aerodynamic shape factor : Gust loading factor : Subjected area for roof beam = R A R 0

21 GLF for Wind Loads on Roof Structures G C R = 1± G R 1.3r Re ( 1+ R ) 1 r Re c + 0.3r c ( 1+ R ) 0. 3 = ± r Re Re + C pi 0.4, C 0 = R C pi 0.4, C = 0 = R R ( ) G + r R = 1± 1.3rRe 1+ RRe 0. 3rc R Re, Re, and r c C pi = 0 : Parameters depending on roof beam direction, dynamic characteristics of roof structure, and wind characteristics Along-wind Loads on Lattice Towers W D (N) at eight Z W = q q Z C D G D A D Z C D G D A F : Velocity pressure at height Z : Aerodynamic shape factor : Gust loading factor : Projected area 1

22 g D C φ D R D GLF for Along-wind Loads on Lattice Towers C G = 1+ φ 1+ D and g C g g g D D RD Cg : Peak factor : Fluctuating and mean coefficients for along- wind OTM : Correction factor depending on mode shape : Resonance factor Crosswind Loads and Torsional Loads Slender and flexible buildings to satisfy following condition: BD 3 U D B

23 W Crosswind Loads on Buildings W L (N) at eight Z g L L Z = 3q C L A g L 1 + φl R 3 ( D B) 0.071( D B) + 0. ( D B) C L = φ L R L : Peak factor : Correction factor for mode shape : Resonance factor L Torsional Wind Loads on Buildings W T (Nm) at eight Z W = 1.8q C AB Z g 1+ φ R T T T T T C T = g T φ T R T { 0.015( D / B) } 0.78 : Peak factor : Correction factor for mode shape : Resonance factor 3

24 Correction Factors Depending on Mode Shape φ Ordinary buildings 1 0.4ln β M φd = + β M ( ) M B + D φt = I T M Z φl = 3M L β 1 Lattice Towers φ D = M M D B 0.5 B 5 D 0 Z β 1 ( 1 0.4ln β ) Along-wind loads (1 0.4 ln β ) Crosswind loads Torsional wind loads 0.3 ( β ) ( 1 0.4ln β ) Along-wind loads β Z µ = Mode shape Vortex Resonance and Aerodynamic Instabilities Particularly wind-sensitive buildings to satisfy following conditions: Non 4 BD and f, L f T U Non-dimensional onset velocity D B U * U * 0.83U Lcr or 0.83U Tcr f L BD ft BD : Fundamental natural frequencies of crosswind vibration and torsional vibration 4

25 Non-dimensional Onset Velocity (Crosswind) Terrain Category I & II III, IV & V Side Ratio D/B D/B <D/B <D/B.5 D/B >.5 D/B <D/B 1. D/B>1. Mass-Damping Parameter δ L δ L 0.7 δ L > 0.7 All δ L 0. 0.<δ L 0.8 δ L > 0.8 δ L 0.4 δ L > 0.4 All Onset Velocity U* Lcr 16δ L 11 1.δ L δ L 3.7 Not occur 4.5δ L δ L D B Non-dimensional Onset Velocity (Torsional) Side Ratio D/B D/B <D/B.5.5 <D/B 5 Mass-Damping Parameter δ T δ T <δ T 0.1 δ T > 0.1 δ T <δ T 0.15 δ T > 0.15 δ T 0.05 δ T > 0.05 Onset Velocity U* Tcr 11 Not occur 4 + 8δ T δ T δ T D B 5

26 Vortex Resonance of Circular Cylinders Buildings with a circular plan to satisfy following conditions: D m U 7 and f D L m 4. U D m f L : Fundamental natural frequency of crosswind vibration W Wind Loads on Circular Cylinders W r (N) for Vortex Resonance at eight Z U = 5 f r C r r f L = 0.8ρU D r C r Z A U : Resonance wind speed L m (m/s) : Equivalent aerodynamic shape factor for vortex resonance - tabulated in AIJ-RLB : Fundamental natural frequency of crosswind vibration Z D m 6

27 Phase-plane Expressions of Column Tip Displacements and Base Bending Moments Displacement Bending Moment Peak Normal Stresses in Column C1 Load Conditions ALL : F D F L F T M D M L M T Along-wind F D only Crosswind F L only Torsional Moment M T only ALL Along-wind F D only (Low-rise Sq. Model, α =1/4) Tensile Compressive Stress kn/cm Stress kn/cm Peak Value (P.F.) Peak Value (P.F.) 5.4 (4.56) 4. (4.4) 1.7 (3.95) 0.9 (4.) 130% Ensemble averaged values of 1 samples The worst case was a 75% increase in tensile stress. 4.7 ( 4.50) 4.1 ( 4.4) 1.8 ( 3.95) 0.9 ( 4.) 115% 7

28 Combinations of Wind Load Components Low- and medium-rise buildings - Y. Tamura,. Kikuchi and K. ibi (00) -. Kikuchi, Y. Tamura and K. ibi (00) Peak normal stresses in columns igh-rise buildings - Asami (000, 00) Combination methods considering correlations of along-wind, crosswind and torsional responses Wind Load Combination for Low- and Medium-rise Buildings W D W LC = γ W D Combination Factor 8

29 Combination Factor γ for Low- and Medium-rise Buildings Combination Factor γ = Column Normal Stress by All Wind Force Components Column Normal Stress by Along-wind Force only 1 Combination Factor γ for Low- and Medium-rise Buildings (Kikuchi, Tamura & ibi,, 00) Combination Factor γ Building eight Only Quasi-static static Component With Resonant Component 9

30 Combination Factor γ Combination Factor γ for Low- and Medium-rise Buildings Combination Factor γ Side Ratio D/B (Kikuchi, Tamura & ibi,, 00) B W L = γ W D D W D ( = 40m) Combination Factor γ for Low- and Medium-rise Buildings Combination Factor γ B W L = γ W D D W D γ = 0.35 (D/B( D/B) Side Ratio D/B (Kikuchi, Tamura & ibi,, 00) With Resonant Component Quasi-static static Component only ( = 80m) 30

31 Wind Load Combinations s for igh-rise Buildings m my,max 1 + ρ 1 ρ 0 ( M x, M y ) 1 1 ρ y Design Points for M x,max = M + m m x x,max x m x,max Wind Load Combinations s for igh-rise Buildings Combination Along-wind Load Crosswind Load Torsional Load 1 W D 0.4 W L 0.4 W T G D G D W D W D W L ( ρ 1) + LT W L ( ρ 1) + LT W T W T 31

32 Correlation Coefficient ρ LT between Crosswind Response and Torsional Response - tabulated in AIJ-RLB - depends upon D/B f θ / f L f 1 B/U The smaller of f θ and f L Combinations of orizontal Wind LoadL and Roof wind Load It t is recommended to simply superimpose the horizontal wind load and roof wind load. - Y. Tamura,. Kikuchi and K. ibi (003) The vertical component of the wind force acting on medium-rise buildings tended to become largest when one of the horizontal wind force components reached its maximum value. 3

33 Wind Loads for Components and Cladding W R (N) Cˆ W C Ĉ pe * C pi A C = Cˆ pe = C q * pi Cˆ C A C : Peak external pressure coefficient : Coefficient accounting for the effect of the internal pressure fluctuation : Tributary area Equivalent internal pressure coefficient Aerodynamic Shape Factors External wind pressure coefficients for structural frames: - Buildings with rectangular sections (>45m)( - Buildings with rectangular sections with flat, shed, or gable roofs ( 45m) - Circular arc roofs ( 45m)( - Dome roofs Internal wind pressure coefficients C pi Internal wind pressure coefficients for structural frames - Buildings without dominant openings C pe 33

34 Aerodynamic Shape Factors External wind force coefficients for structural frames:, C D X - Buildings with circular sections - Pitched free roofs with a rectangular plan - Lattice structures - Fences - Members with various sections - Nettings C, C Y Aerodynamic Shape Factors External peak pressure coefficients for cladding and components: - Buildings with rectangular sections (>45m)( - Buildings with rectangular sections with flat, shed, or gable roofs ( 45m) - Buildings with circular sections - Circular arc roofs ( 45m)( - Dome roofs Coefficients accounting for the effect of the internal pressure fluctuation for * C cladding and components pi - Buildings without dominant openings Ĉ pe 34

35 Aerodynamic Shape Factors External peak wind force coefficients for cladding and components: Ĉ - Pitched free roofs with a rectangular plan C 1-year-recurrence recurrence Wind Speed U 1 (m/s) AIJ Guidelines for the Evaluation of abitability to Building Vibration (1991) (Its revised version will be published in 004) - 1-year-recurrence recurrence peak acceleration has been applied for the evaluation 35

36 1-year-recurrence recurrence Wind Speed U 1 (m/s) 0 10min mean Flat open category 10m above the ground Miscellaneous Evaluation formulae for along-wind, crosswind and torsional acceleration responses Interference effects of neighboring buildings Uncertainty and dispersion of parameters included in AIJ-RLB RLB to achieve reliability based design