I write regarding a recent Verulam letter 'Comparison of BS 6399/EC1 wind pressures' by Colin Mitchell, which appeared in the June 2014 issue. Colin does not refer to the principal difference between the two code systems, which is the difference in the load factors. Generally γ_Q , for BS codes (timber excepted) is 1.4 and for EC codes it is 1.5. I have not seen it stated, but it would not surprise me that this difference has been taken into account in the preparation of the codes. That does not account for all the difference noted by Colin, but does indicate the general philosophy that code systems should not be mixed. Each wind code is designed to work with a specific system of codes and comparison should only occur with the final design, not an interim step.
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