WS-Snake
(by WS-SNAKE)

WS-Snake consists of several components written in Python to calculate different factors which finally determine the amount of wind pressure on building façade according to its position and orientation. The wind calculation method is obtained from the National Building Code of Canada 2015 (NBCC 2015), hence in order to get further information about the factors and equations, please check out NBCC 2015.

WS-Snake works based on the main direction of the wind and determines compression/suction on each building side according to its normal vector. It takes into account different types of exposure to the wind (open terrain, urban context, etc.) and generates unique values for any given part of the building façade according to its height and the building side which that part is located on.

Similar models have been checked with this plug-in and a separate CFD analysis, a process by the end of which the output results were found very close. Since WS-Snake provides numerical values for wind pressure, it is strongly recommended to use it alongside Karamba plug-in which is a tremendously strong tool in Grasshopper for parametric structural design and analysis. Pressure values generated by WS-Snake can be use as inputs for the Mesh-Load component in Karamba where a mesh list of façade parts is given as input mesh. This component automatically multiplies the pressure to the mesh area and generates the load values subjected on different parts of the façade.

One of the applications of this plug-in is the design of glass and dry facades, which calculate the wind load accurately on the shell elements.

Any building is subject to the two main categories of loads: vertical and lateral loads. Vertical loads constitute dead and live loads. Most important lateral loads consist of wind and seismic loads. For tall buildings, the lateral loads play the dominant factor in determining the height of the building.1 As the building grows taller and more slender wind loads gain a more significant role than seismic loads.2-3

Compared to seismic loading, wind load is the governing load in tall building design in most instances for lateral stability system design. This is due to the longer natural period of the tall building, which results in a smaller earthquake response compared to low rise buildings. For low-rise buildings, such as building below eight stories, oscillation due to wind loading is rarely a problem. For the building with 8 and 20 stories, the dynamic effect of wind loading becomes more important with height.4

For a tall building of certain height and slenderness, wind forces resulted motions in the upper levels become dominant actors in the structural design. This is primarily for the sake of the occupants' comfort. It is important to ensure first the buildings to meet strength and safety requirements under wind action for ultimate state design. Secondly, serviceability limit state design of a tall building during wind-induced motion is another critical design issue, as the occupant's comfort needs to be assessed, in addition, the excessive deflection of the structure may cause the fracture of the facade or glazing.

Engineers need to take all aforementioned design issues into consideration to deliver a high standard design for clients and future occupants. In most of the cases, the service limit design for occupants' comfort is a major control of the structural system and structural member sizes in tall building design.

In real design practice, tall buildings such as Taipei 101 and Burj Khalifa, an extensive program of wind tunnel tests and other studies were normally undertaken by the wind tunnel consultant, to evaluate the effects of wind on building loading, behavior, and occupant comfort.4

Please feel free to share your opinions and feedback with us on:

ws.snake2019@gmail.com

1. Khan F R. Future of High-Rise Structures. Progressive Architecture 1974; 10: 78-91.
2. Sutjiadi H Y. The Suitability of Double-Layer Space Structures for Super-Tall Buildings: A Study from Structural and Building Systems Integration Perspectives. Ph.D. Thesis, Victoria University of Wellington, New Zealand, 2011.
3. Miyamoto K and Gilani A. High-rise Buildings and Wind Effects. Construction Specific 2007; 60: 134.
4. Fu F. Design and Analysis of Tall and Complex Structures. Elsevier 2018

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