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For structures close to hills, ridges, and escarpments, the program calculates the topographic factor Ct using NBC 2015 4.1.7.4, applies it to the wind pressure equation in 4.1.7.3.(3) and displays it in the Wind Load Generation Details output. The terrain characteristics needed are entered in the Site Information dialog.
For NBC 2010. the provisions for speed-up effect due to hills and escarpments are given in NBC Structural Commentary I-13 to I-16, Table I-1 and Figure I-6. The program modifies the Ce factor with the equation
Ce*(z) = Ce(z) (1 + Smax ( 1 – x / kL ) e - z L/2 )
where the parameters are described in the Commentary. This procedure is mathematically equivalent to the NBC 2015 4.1.7.4 procedure.
There is some ambiguity in the Commentary as to whether the Ce factor for the detailed procedure, ordinarily for dynamic analysis, should be used with the topographic effect to create C*e. We concluded that the Ce used for the simplified would be used and modified to become Ce* as described in the text. This has been borne out by the reorganization to NBC 2015.