A more practicable bearing plate is illustrated in Fig. 14 (_b_). Here,
instead of providing dowels, or a lip, to set into the girder, the top
of the plate is cast with teeth, as indicated at _c_. While these teeth
tend to destroy fibers at the bottom of the beam, they nevertheless
sink into the timber, creating great friction, and thus accomplish a
tie to the wall fully as efficient as a dowel-pin, or lip, let into the
timber would be.
Probably the most common form of bearing plate is that illustrated
in Fig. 14 (_c_), which is known as the Goetz-Mitchell bearing box.
This is usually built flared, as indicated in the illustration, so
that when built into the brickwork it will have a hold in it, and the
timber acts as a tie by being notched over the lip, as at _d_ in this
figure. These Goetz-Mitchell boxes are generally provided with a plate
that sets on top of them, on which the brickwork may be built, and not
infrequently the sides of the boxes are grooved so that the ends of the
girders are ventilated.
[Illustration: FIG. 15]
=33. Window Heads.=—In Fig. 12 was shown a form of window head that
is the best for strength, but possesses the disadvantage of lowering
the top of the window, thus cutting off light to the room, which is a
serious objection where the room is wide, or where it depends on the
windows in one side for lighting the entire floor area. In order to
keep the window head up near the under side of the floor construction,
an =I= beam, lintel, or some similar form of support for the brickwork
over the head that takes up little room, must be employed. A
construction using shallow =I= beams is illustrated in Fig. 15. Here
the window head is directly beneath the rough flooring; and while
the outside face of the window is formed with an arch, the brickwork
above the window head is supported on shallow =I= beams. This figure
illustrates a section through the wall extending parallel with the main
girders, a bearing being obtained for the floor planking by bolting to
the =I= beams a bearing strap _a_.
This construction would not be permitted in some of the larger cities,
as the building laws require that all steel beams supporting brickwork
must be fireproofed. Consequently, a steel lintel of this construction
would have to be surrounded with concrete, and the window head dropped
somewhat to allow a bearing for the floor planking, or some other form
of construction adopted.