Wind Tunnel Applications for Buildings

Transcription

1 Wind Tunnel Applications for Buildings Presented by: Jim Swanson, Halvorson and Partners Donald Scott, PCS Structural Solutions Jon Galsworthy, RWDI Add Company Logo Here Outline 1. Introduction 2. ASCE7 Wind tunnel code requirements 3. Types of wind tunnel testing 4. Input requirements for tests 5. Climate study 1

2 Outline (cont d) 6. Model construction 7. Understanding the Report 8. Occupancy comfort thresholds 9. Improving building performance Introduction Advantages to use of Wind Tunnel Studies: Wind loads cannot be accurately determined by code prescribed methods for all building geometries. Building cost and safety depend on good knowledge of the wind loading and its associated response. Building profiles can be formed to reduce wind loads with the aid of wind tunnel tests. Evaluation of motion 2

3 Introduction Buildings Benefitting From Wind Tunnel Studies: Tall or slender structures. Buildings with irregular geometries. Long span, light weight roof structures. Introduction Slender Buildings and Motion Perception: 3

4 Introduction Irregular Geometries: Introduction Building Appendages: 4

5 Introduction Accuracy of Cladding Pressures: Damage following Hurricane Wilma ASCE7 10 Section Limitations (MWFRS Directional) The provisions of this chapter take into consideration the load magnification effect caused by gusts in resonance with along wind vibrations of flexible buildings. Buildings not meeting the requirements of Section , or having unusual shapes or response characteristics shall be designed using recognized literature documenting such wind load effects or shall use the wind tunnel procedure specified in Chapter 31. 5

6 ASCE7 10 Section 31.1 Scope User Note: Chapter 31 may always be used for determining wind pressures for the MWFRS and/or for C&C of any building or structure. This method is considered to produce the most accurate wind pressures of any method specified in this Standard. ASCE Mean Recurrence Intervals of Load Effects The load effect required for Strength Design shall be determined for the same mean recurrence interval as for the Analytical Method, by using a rational analysis method, defined in the recognized literature, for combining the directional wind tunnel data with the directional meteorological data or probabilistic models based thereon. 6

7 ASCE Mean Recurrence Intervals of Load Effects The load effect required for Allowable Stress Design shall be equal to the load effect for Strength Design divided by 1.6. ASCE7 10 Section Limitations on Loads Loads for the main wind force resisting system determined by wind tunnel testing shall be limited such that the overall principal loads in the x and y directions are not less than 80 percent of those that would be obtained from Part 1 of Chapter 27 or Part 1 of Chapter 28. 7

8 ASCE7 10 Section Limitations on Loads Pressures for components and cladding determined by wind tunnel testing shall be limited to not less than 80 percent of those calculated for Zone 4 for walls and Zone 1 for roofs using the procedure of Chapter 30. ASCE7 10 Section Limitations on Loads The limiting values of 80 percent may be reduced to 50 percent for the main wind force resisting system and 65 percent for components and cladding if either of the following conditions applies: 8

9 ASCE7 10 Section Limitations on Loads (cont) There were no specific influential buildings or objects within the detailed proximity model Loads and pressures from supplemental tests for all significant wind directions in which specific influential buildings or objects are replaced by the roughness representative of the adjacent roughness conditions, but not rougher than exposure B, are included in the test results. Wind Tunnel Testing 9

10 Wind Tunnel Testing Common Testing Options: Structural loads and motion. Exterior wall/roofing pressures. Wind induced vibrations. Pedestrian comfort. Snow loading. Ventilation. Wind Tunnel Testing Structural Load Models: 1. High Frequency Force Balance Model 2. Pressure Integration Model 3. Aeroelastic Model 10

11 Wind Tunnel Testing Structural Load Model: Wind Tunnel Testing Cladding Model: 11

12 Wind Tunnel Testing Pedestrian Model: Wind Tunnel Testing Pedestrian Model: 12

13 Wind Tunnel Testing Surface Velocity Vector Test Model Snow Drift: Input Requirements MWFRS and C&C Testing: A 3D CAD model of the development. Current architectural drawing files. Sections detailing the external characteristics of the structure. All available information regarding the surroundings within a 1800 ft radius of the site. 13

14 Input Requirements Additional for MWFRS Testing: Mass properties for each floor/story. Mode shapes and corresponding natural frequencies. Typically the first two translational modes and the first torsional mode are required. A drawing showing the origin of the structural model co ordinate system with respect to an architectural floor plan. Input Requirements Structural Load Input Data in Excel: 14

15 Input Requirements Mode Graphics: T 1 = 5.91 sec Input Requirements Locate Model Origin 78-9 ORIGIN

16 Input Requirements Additional for Pedestrian Wind Studies: Preliminary Landscaping plans. Location of pedestrian use areas of the site. Wind Climate Study Wind Climate Modeling: Wind loads are dependent on wind climate at the project site. Wind climate for each site originates from historical data. Hurricane regions may be simulated. Wind climate expressed in form of probability of wind speed being exceeded for each direction. 16

17 Wind Climate Study Wind Climate Modeling: Probabilistic methods used to predict potential wind speeds in each direction. Values are scaled such that wind velocities for a specified return period correspond with ASCE 7 maps. Wind Climate Study Directional Distribution of Winds: 17

18 This image cannot currently be displayed. Wind Climate Study Probability Winds Will Be Exceeded: Model Construction 1:400 Scale Model on Rotating Table: 18

19 Model Construction Wind Simulation Spire and Roughness: Model Construction Varying Exposure Conditions: 19

20 This image cannot currently be displayed. This image cannot currently be displayed. Model Construction Structural Model Force Balance Model: Model Construction Cladding Pressure Model: 20

21 Report Output Essential Structural Report Data: Floor by floor wind loads to be entered in structural analysis model. Directional wind load combinations. Once combined, wind loads are to be factored per ASCE Basic Load Combinations. Building accelerations, evaluated at the top occupied floor of the structure. Report Output Floor by Floor Wind Loads: Floor Height (m) Above Base Fx (N) Fy (N) Mz (N m) Base

22 This image cannot currently be displayed. Report Output Base Loads by Wind Direction: Figures indicate base forces for the design wind speed (50-yr or 100-yr) from each direction. Alternative forms include are wind load coefficients by wind direction. Report Output Directional Wind Load Combinations: Load Case X Forces (Fx) Y Forces (Fy) Torsion (Mz) 1 +85% +30% +40% 2 +85% +30% 30% 3 +85% 55% +40% 4 +85% 55% 30% 5 100% +65% +50% 6 100% +65% 30% 7 100% 35% +50% 8 100% 35% 30% 9 +30% +100% +65% % +100% 35% % 90% +50% % 90% 50% 13 60% +100% +65% 14 60% +100% 35% 15 45% 90% +50% 16 45% 90% 50% % +70% +100% % +50% 90% % 35% +100% % 60% 90% 21 60% +70% +100% 22 55% +50% 90% 23 60% 30% +100% 24 55% 60% 90% The 24 load combinations represent all the permutations with each load component maximized and minimized. Each combination is derived from the directional wind response data. 22

23 This image cannot currently be displayed. This image cannot currently be displayed. Report Output Load Combination: Example: Load Combination #5-100%, +65%, +50%; and Load Combination #13-60%, +100%, -35%. The two combinations are each derived from the responses at 120 Report Output Accelerations: 23

24 This image cannot currently be displayed. This image cannot currently be displayed. This image cannot currently be displayed. Report Output Essential C&C Report Data: Design pressures for all wall and roof surfaces. Separate diagrams required for positive and negative wall pressures. Report Output Cladding Pressure Diagrams: 24

25 This image cannot currently be displayed. Report Output Snow Load Diagrams: Building Motion 25

26 This image cannot currently be displayed. Comfort Thresholds CTBUH 1 Guidelines 1 Year and 10 Year: 1. Isyumov, N.I., Criteria for Wind-Induced Accelerations of Tall Buildings, Presented at Rio de Janeiro CTBUH Conference, Comfort Thresholds ISO 2 Motion Criteria 1 Year: Office Residential 2. ISO Standard

27 Comfort Thresholds Comparison of Predicted to Threshold Limits: Pedestrian Comfort Thresholds 27

28 Comfort Thresholds Pedestrian Threshold Limits: No universally recognized standard for pedestrian comfort levels. Some cities have implemented standards as part of approval and permitting process Recommendations vary from firm to firm, yet should yield comparable outcomes. Comfort Thresholds Pedestrian Threshold Limits Example 1: 28

29 Comfort Thresholds Pedestrian Threshold Limits Example 2: Improvements Adjustments to Improve Accelerations: 29

30 Improvements Adjustments to Improve Accelerations: Improvements Shaping Strategies: 30

31 Improvements Corner Softening Taipei 101: Improvements Tapering, Changes in Cross Section Burj Khalifa: 31

32 Improvements Tapering, Twisting Spoilers Chicago Spire: Improvements Vertical Ribs Break Up Vortex Shedding: 32

33 Questions? Jon Galsworthy Jim Swanson 33