Technical notes from both the Brick Institute of America and the National Concrete Masonry Association state that whenever a concentrated load occurs over an opening, the lintel must be designed taking this concentrated load into account. In the calculations, the concentrated load is assumed to act as an uniform load applied over the region defined by extending lines down from the bearing point at 60-degree angles from horizontal. If the concentrated load occurs over the jamb of the opening, say within 8 inches of the opening, should this load be taken into account by spreading it over a portion of the lintel?
If the concentrated load near the jambs is not above the opening, it need not be included because there is an uninterrupted vertical load path. Do check the stress at the jamb, however, including the concentrated load. If the load occurs over the opening, either the masonry must arch to carry the loads around the opening or the lintel must transfer loads to either side of the opening in bending. In this case, the concentrated load must be included in the lintel calculations.