- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report
I have recently carried out a basic validation exercise to compare the wind loads generated using wind simulation in Robot 2017 against those calculated manually from the Eurocode. I thought it worth sharing on this forum for the benefit of other users.
I undertook this exercise for a simple, steel-framed rectangular box building, 10m x 10m x 3m high with full cladding surround. I’m only really interested in the global structural design (ULS and SLS for beams and columns), not the more localised forces which should be considered for cladding design.
For simplicity, I only compared the loads in the windward/leeward direction and the vertical wind uplift.
The rough process for deriving wind loads to Eurocode 1 (+ UK National Annex) is as follows:
- Calculate the basic wind velocity (vb) using the wind map, and incorporating coefficients for direction, season, probability, and altitude.
- Calculate the basic velocity pressure (qb) by multiplying the basic wind velocity by 0.613 (0.5 x air density)
- Calculate the peak velocity pressure (qp(z)) by multiplying the basic velocity pressure to incorporate exposure, orography etc.
- Calculate the external and internal pressures on each face of the building by multiplying the peak velocity pressure (qp(z)) by external and internal pressure coefficients cpe and cpi for that face. I generally derive two sets of loads, one for positive internal pressure (cpi) and one for negative internal pressure (cpi)
For this building, my approximate loads calculated from Eurocode were as follows:
Total horizontal (windward + leeward): 10.2kN – 12kN
Total vertical (roof): 23.2kN (uplift) or 7.5kN (downward)
In Robot wind simulation there are two options for inputting the wind parameters: wind velocity (m/s) or wind pressure (kPa).
At first I ran the simulation with the basic wind velocity (vb) in m/s that I had calculated from Eurocode. The wind pressure maps were as expected but the resulting reactions underestimated the wind loads by a factor of approximately 2:
Total horizontal (windward + leeward): 7.6kN
Total vertical (roof): 11.6kN (uplift)
I suspect this underestimation is because, when the peak velocity pressure qp(z) is derived in the Eurocode, the pressure is multiplied by an exposure factor ce(z) which is always greater than 1.5 and typically around 1.8. Robot will not include this factor when simulating from the basic wind velocity vb.
I repeated the wind simulation by instead inputting the peak velocity pressure qp(z) in kN/m2 that I had calculated from Eurocode. These reactions were much closer to what I expected:
Total horizontal (windward + leeward): 11.2kN
Total vertical (roof): 19.3kN (uplift)
From this I have concluded that the Robot wind simulation seems reasonable for mimicking the Eurocode wind surface loads by inputting the peak velocity pressure qp(z), derived using hand calculations. This appears to be suitable for global member design, although I haven’t undertaken detailed checks for localised forces.
Some follow-up thoughts:
- Has anyone carried out a similar exercise. If so, did you find similar results?
- Are there any pitfalls to be aware of where the wind simulation may underestimate loads?
- For cladding panels, the wind simulation generates area loads (kN/m2) and line loads on the edges of the cladding (kN/m). If the steel members are included within the selection, the wind simulation generates line loads on the beams/columns, resulting in slightly higher overall reactions. Why is this? Is the simulation considering the geometry of those members e.g. flanges sticking out? Is it best practice to include members within the simulation, or just the panels?
Solved! Go to Solution.
