Required Horizontal Extents of Boundary
Once the neutral axis depth for a load combination has been calculated as described in Section 7.7.1, the required boundary length is found from ACI Section 21.9.6.4(a). Here it is stated that the boundary shall extend horizontally from the extreme compression fiber a distance not less than the larger of:
where lw and c are defined in Section 7.7.1.
Figure below illustrates the View/Update, Boundary Elements page for an "L"-shaped Section Cut. The black dot in the cross-section sketch identifies the point of extreme compression in the Section Cut. The dimension extending from the point of extreme compression is the required boundary length for the currently selected load combination. Note that this dimension extends from the point of extreme compression at the angle β corresponding to the selected load combination.
