Wind Impact on Textile Structures

Transcription

1 Wind Impact on Textile Structures J. Wacker TensiNet Symposium, Newcastle, UK, 26 th 28 th of October 2016

2 About Wacker Ingenieure, Wind Engineering Office in Birkenfeld, Germany 3 own wind tunnels Own model fabrication shop Codes for numerical flow simulations 2

3 Typical structures to be investigated with regard to different Wind Engineering Aspects Special constructions = Not covered directly within standards 3

4 Textile Structures = Special Structures Al Bayt Stadium, Al Khor City, Qatar New Stadium in Caracas, Venezuela 4

5 Textile Structures: Wind Engineering Aspects Smoke extraction in case of fire Structural and local wind loads Wind-induced vibrations Snow loads, drift and accumulation Sand loads, drift and accumulation Wind-induced noise Wind-induced rain infiltration Natural Ventilation Wind comfort inside / outside Structural engineer Fire engineer Architect 5

6 Textile Structures: Wind Engineering Aspects Today: Structural and local wind loads Wind-induced vibrations 6

7 Wind Impact on Typical Textile Structures For structural design of textile structures: realistic wind loads are required including dynamic wind loads Examples for shapes not covered in codes Wind tunnel modelling most appropriate method to acquire wind pressure data. 7

8 Wind Tunnel Testing of Textile Structures Due to Great variability and complexity of shapes Geometrically complex eigenmodes, often across-wind vibrations Membrane structures often attached to bigger structures that complicate the wind situation and enhance turbulence and dynamic excitation no proper code approaches available, wind loads extremely case-dependent! Wind tunnel testing of textile structures necessary, realistic evaluation of dynamic responses is complicated 8

9 Wind tunnel testing - Equipment Schematic section of boundary layer wind tunnel Pitot static tube Rigid or aeroelastic building model; scale 1:100 to 1:500) Pressure taps Test building Surroundings Reference pressure (static pressure of the flow) Turn table Simulation of atmospheric boundary layer Floor roughness Approach flow Fence Spires Honeycombs Fans Differential pressure transducers Differential pressure transducer Wind pressure time series c p (t) Voltmeter Filtering + + Verstärker Amplification A D PC Simultaneous measurement of pressure time series Measurement of the reference wind speed 9

10 Wind Loads on Textile Structures: Development of Methodology Formerly: c p = p/ q W = c p,mean * q gust [kn/m 2 ] Wind pressure time series c p (t) Then: W = (c p,mean +/- k * c p,rms ) * q mean [kn/m 2 ] Today: Measurement of c p (t) simultaneously within the area of interest Extraction of critical load pattern with regard to different responses of interest Weighting with influence functions (customized load cases) Calculation of dynamic responses in time domain (several modes) Consideration of added mass and aerodynamic damping effects Typical influence function 10

11 Case study 1: Large textile umbrellas Projects in Medina and Mecca, Saudi Arabia Umbrellas up to 53 m x 53 m Full-scale tests

12 Wind tunnel simulation 12

13 Wind pressure distributions on umbrellas Simultaneous measurements of wind pressure time series cp(t) on upside and downside of umbrella membranes allow evaluation of time-varying pressure field; Time-varying pressure field reveals typical load patterns which are extracted in order to cover typical peak events (load cases) [c p,net ] Blue = upward (1) Red = downward (2) (3) 1) maximum bending moment at base 2) maximum overall suction (upward wind force) 3) maximum overall pressure (downward wind force)

14 Total vertical wind forces on umbrellas Integration of pressure field results in total (global) forces acting on umbrellas; The time-series of vertical force F z shown below exhibits strong upwards and downwards peaks despite low mean forces, there are pronounced events producing high overall suction and high overall pressure; pressure events suction events overall uplift time

15 Wind-induced dynamic response of umbrellas time-varying c p,net -distribution on umbrella and dynamic response (see bottom plot for effective base moment). Effective base moment time 15

16 Conclusion Case Study 1: Large textile umbrellas Simultaneous akquisition of time-dependent wind pressure field is important to be able to consider different load patterns which result in different load cases for one and the same wind direction Consideration of of dynamic wind effects is necessary; consideration in time domain and consideration of several modes yields higher accuracy, corresponding inertia forces cause higher effective loads 16

17 Case Study 2: Huge flat textile roof structure Horizontal flat fabric roof - Operable (retractable) - Size about 180 x 90 m - exposed to strongly turbulent wind (built-up surrounding) 17

18 Wind tunnel tests: Surface pressure distribution Quasi-static time-varying c p,net -distribution obtained from wind-pressure time series (wind tunnel tests) showing both pronounced pressure and suction events: [c p,net ] overall uplift time 18

19 Dynamic Response: Implementation of 12DOF-model Membrane oscillation caused by short-time vertical force pulse in its center shows need of considering more than 1 eigenmode; (animation below based on 12 modes; multimodal representation) Eigenmodes f e,1 =0.32 Hz f e,2 =0.42 Hz f e,3 =0.47 Hz f e,3 =0.49 Hz 19

20 Dynamic Response: Consideration of added mass and aerodynamic damping Movement of membrane up and down caused by wind very light roof with 1st eigemode like horizontal beam Air masses above and beneath moving membrane will be moved, too, and consequently, damping and eigenfrequencies will be changed. 2D-FSI-simulation of middle section was performed for oscillating roof after initial displacement in order to check effective damping and added mass effects. Afterwards the original structural parameters, i.e. structural damping and eigenfrequencies, were adapted carefully. 20

21 Dynamic response caused by wind Wind-induced oscillations (top) and quasistatic and effective vertical force F z (bottom) effective vertical force F z blue = qstat green = effective time 21

22 Final effective load distributions Elaboration of representative load cases for respective target variables c p,net -distribution for load case pressure without dynamic effects (quasi-static wind load): Without dynamics c p,net -distribution for load case pressure including inertial contributions from the moving membrane mass): With dynamics [c p,net ] 22

23 Final effective load distributions Elaboration of representative load cases for respective target variables c p,net -distribution for load case pressure without dynamic effects (quasi-static wind load): Without dynamics c p,net -distribution for load case pressure including inertial contributions from the moving membrane mass): With dynamics [c p,net ] Higher wind loads in central roof part due to pronounced oscillation amplitude in this area (see 1st mode amplitude to the right) 23

24 Conclusion Case Study 2: Huge flat textile roof Consideration of dynamic wind effects is necessary Consideration of higher vibration modes may be important for widely spanned membrane structures Consideration of added mass effects and aerodynamic damping effects may be important for light-weight membrane structures 24

25 Case Study 3: TK Test Tower for high-speed elevators Site: Rottweil, Germany Height: H = 245 m Structure: reinforced concrete cylinder Skin: permeable membrane facade Airspace between structure and skin 25

26 Skin: Curtain-type permeable nord - sued grid membrane ost - west Crosssection porosity Öffnungsanteil 50% porosity Öffnungsanteil 40% porosity Öffnungsanteil 30% porosity Öffnungsanteil 20% porosity Öffnungsanteil 0% EB ,8 25,

27 Wind tunnel tests: Aeroelastic models of tower well-known: Slender cylindrical structure prone to across-wind vibrations caused by wind (vortex shedding) Question (beside wind loads): Is there an impact of curtain-type grid membrane facade on suspectibility to wind vibrations? Measurements of dynamic response in wind tunnel using aero-elastic model of tower Without membrane facade With (nearby) closed membrane facade With permeable membrane facade 27

28 Impact of membrane facade on across-wind vibrations of total structure caused by wind 100% 90% 80% 28

29 Conclusion Case Study 3: TK Test Tower Advantages of curtain-type permeable membrane facade: More interesting appearance of tower Reduction of asymmetric solar heating of concrete Reduction of across-wind vibrations caused by wind due to helix shape and permeability (including air space) of membrane facade 29

30 Outlook: Numerical Fluid-Structure-Interaction (FSI) Computation In theory, FSI could be fully accounted for using two techniques: 1. Full aeroelastic model in wind tunnel only possible for relatively simple modal shapes, but in general not feasible, especially if membrane itself shows significant vibration modes 2. Full numerical FSI computation still extremely high computational effort, sometimes possible for selected configurations and over short simulation times*** In general, exactly accounting for FSI in either way is still prohibitively expensive and would only be profitable in very few, very special cases. *** Example: FSI for umbrella project Calculation time on high performance computing cluster (HPC) 768 cores Calculation time: 4 weeks for 600 seconds in full-scale Equivalent wind tunnel time: <10 seconds 30

31 Conclusion Wind effects often are decisive for textile structures design Wind tunnel testing is still the most exact and affordable tool to gather raw data (simultaneously measured wind pressure time series) Subsequent dynamic and statistical computations are essential in order to obtain optimized and safe load distributions for the structural engineer The more the wind engineer is involved in the structural planning from an early stage, the more optimization is possible Canopy Roof, Rotterdam, Netherlands Gulf Shade, Canopy in Riad, Saudi Arabia Canopy, Aarau, Switzerland 31

32 THANKS FOR YOUR ATTENTION 32