Reduction in
critical design section for moment due to opening, can be overcome providing
more closely on each side of the opening to maintain the necessary As. This is
possible only when opening is possible to locate where moment is well below the
compression capacity of the slab, thereby leaving the arrangement of
reinforcement as the only problem. Of course, shear strength must be
maintained, but this is rarely a problem except near the columns in flat slab
type, as noted previously.
The arrangement of bars around any but minor opening can
constitute a real problem. Bars running perpendicular to the face of an opening
are not fully effective when simply cut0off at the opening.
This is acceptable if there is a beam at the opening to
act as reaction for the slab. If there is no beam it is better to fan the bars
out or splay them to go around the opening. If fanning or splaying leaves too
wide an area without steel, extra bars can be placed parallel to the side of
the opening, as indicated.
Code Requirement
13.5.2.1 In case of opening in intersecting middle strips, total amount of reinforcement required for the panel without opening is maintained.
13.5.2.2 In case of opening in intersecting column strips, an amount of reinforcement equivalent to that interrupted by an opening shall be added on the sides of the opening.
13.5.2.3 In case of opening common to one column strip and one middle strip not more than ¼ the reinforcement in either strip shall be interrupted by openings. An amount of reinforcement equivalent to that interrupted by an opening shall be added on the sides of the opening.
