Openings and Penetrations
You may also create a free form opening on a one way deck inside a beam loop. A free form opening is one which may take any shape inside a beam loop as shown in the following figure. Multiple openings inside a beam loop are considered an invalid configuration for calculation of opening slab edge loads. Ram Gravity gives an error for any such configuration it runs into while framing, and the beams in the beam loop associated with the opening causing an error will not have correct loads applied on them.
The calculation of opening slab edge load for each beam in the loop is not trivial due to the fact that an opening can have practically any shape. The calculation of opening slab edge load for each beam requires identifying the polygons, the loads on which are carried back to the beam. An opening slab edge load polygon for any beam is obtained by finding the nearest point on the opening from the beam nodes (beam nodes lying on the beam loop). These nearest points on the opening and the beam nodes are then used to form one or more closed polygons. More than one load polygons are formed for a beam if the opening edge or corner sits on the beam itself. If there are multiple points found on the openings which are equidistant from the beam nodes then the mid-point of the extreme points found on the opening is considered as the nearest point. This mid-point considered also lies on the opening.
Once the slab edge polygons (tributary area boundaries) are calculated for each beam in the beam loop, the loads on each polygon are carried straight back to the associated beam as if the deck was laid perpendicular to beam. Thus, the deck orientation originally assigned to the deck polygon has no influence on the load distribution; for edges the load is always distributed in a direction perpendicular to the beam. The following figure shows the opening slab edge load polygon for a few selected beams from beam loops shown in the previous figure.
For some complex openings, if there is no direct perpendicular line back to a beam, there may be some portion of the load in the opening slab edge polygon that does not get carried back to the beam, and is ignored.
It is important to recognize that when an opening of any size or placement is placed within a bay of framing supporting one-way deck, the opening edges are defining the slab edge distances for all beams framing around that opening, regardless of the distance from the beam to the opening. For that entire bay, all loads are distributed as slab edge loads, and the normal one-way distribution is not applicable. For example, the following figure shows an opening that only fills a small portion of the bay. This is improper modeling. The presence of the opening within the beam loop indicates that all loads within that loop are to be treated as slab edge loading. Therefore, the loads beneath the opening are distributed down to the bottom beam as if that was a long slab edge overhang, not left and right to the adjacent beams as would be expected with one-way distribution. To get the appropriate distribution, the opening should be framed with a beam near the bottom of the opening.
