Generally when you are defining a user table general section, the software needs to know what thickness ( t ) to use for finding out the D/t or b/t ratios. This as you know is necessary for classifying the elements of the cross section during the design phase. So the onus is on the user to provide an appropriate value for TD ( thickness that may be considered as an equivalent web thickness and which is used for computing D/t ) and TB (thickness that may be considered as an equivalent flange thickness and which is used for computing b/t ). DEE may be computed as ( D – 2 x TB) for built up sections and clear distance between fillets for rolled sections. All TD,TB and DEE are user inputs.
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