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The deflections for the counteracting load combination .6D + W were not being calculated correctly. This affects beams with critical wind uplift loading, and columns where moments due to eccentric axial dead loads are counteracted by lateral wind load from the opposite direction.
The problem is apparent in the load diagrams when the .6D + W combination is selected, and in the design check output if that combination happens to be critical.
Live Deflections
The line (non-dead) deflection, which is in this case from wind load, was derived by subtracting the deflections from the dead load D from the deflections from .6D + W, creating “live” deflections that were W - .4D. Since this load case is critical when wind is acting as an uplift force, the .4D added to the magnitude of the wind load deflections, and the error was thus conservative.
Total Deflections
Total deflections were then calculated as W -.4D + D*KCT, , where KCT is the user-input time dependent factor. This is correct in the case that KCT = 1. For the default value of 1.5, this creates a load combination of W + 1.1D. This is a greater dead load counteracting force than if the D was multiplied by 1.5 and .6 ( W + .9D), so the effect is non-conservative for our original interpretation of the long term factor, and even more so for our new interpretation, that the long term factor should not be applied to this load combination ( see 3.c) above).
The error for the default value of 1.5 does not cause this combination to become critical for non-uplift when it shouldn't, as it is be W + 1.1D, v.s. W + 1.5D for the usual downwards load combination. Similarly, for the wet service KSD value of 2.0, the load combination becomes W + 1.6D vs. W + 2.0D.