occur. Likewise, you require a second application over
Various types of foundations are used in the
construction industry today. Because of space
limitations, lets consider only two of the main
typesmat foundations and spread footings.
The mat (raft or floating) foundation is a continuous
footing that supports a reinforced concrete slab covering
a minimum of 75 percent of the total area within the
exterior walls. It is normally used when the subsoil is
not considered good enough for spread footings. Mat
foundations may take the form of a hollow concrete box
with intermediate walls or columns to permit taking
advantage of the weight of the earth removed in the
excavation to offset, in part, the load imposed on the mat
foundations. When inspecting, you must make sure that
the subgrade is carefully leveled to the specified
elevation so that the concrete will be of full thickness
and that special sand or gravel is spread and compacted
if called for. Be alert to detect any wide variations in
the quality of the subgrade.
The spread footing (fig. 6-8) is the lowest
foundation support and is wider at the base than at the
rest of the foundation. For example, a common 8-inch
Figure 6-8.Spread footing with a keyway joint.
concrete retaining wall is placed on a 16-inch footing.
Spread footings are designed for a definite load per
square foot, based on prior investigations of the site, or
on general knowledge of the characteristics of the soil
in the area. Usually, the drawings indicate both the sizes
of the various footings and the load on which they are
based, normally twice the size of the foundation wall.
Your primary function is simply to make sure the
footings are the correct size, with satisfactory concrete
reinforcement, or other parts, as shown or specified.
However, be alert to detect any significant variations in
the quality of the substrata from that indicated by boring
records or assumed designed loads.
It is essential that anchor bolts be set with the utmost
accuracy relative to both position and level. Errors
discovered after the concrete has set are extremely
expensive to correct. This is particularly vital when
sleeves are not specified or permitted to allow for lateral
play. Anchor bolts are usually set to a template, which
is carefully aligned with the building lines and leveled
to a definite elevation. You must check the setting and
verify beyond question that the template is accurate
within permissible tolerances before permitting
concreting to proceed. Check the templates
periodically during the course of the work to make sure
they have not been disturbed. Pay particular attention
to the bolt settings to make certain that there is sufficient
thread exposed above the top of the steel base plate to
permit full engagement of the nuts without excessive
projection of the threaded bolt. You must also make
sure that the anchor bolts are provided with hooks,
L-bends, swaging, or other anchorage devices, as shown
or specified. When sleeves are specified, you should
make sure that the bolts are centrally located in the
sleeves to provide leeway in adjustment in all directions.
Ensure that the sleeves are NOT installed in such a
manner as to decrease the holding power of the bolts.
Later, take care to make sure that the sleeves are
properly filled with grout, lead, or sulfur, as the
specifications may require, after the steel has been
erected and aligned.
Concrete floors may be built on the ground at grade
or on well-reinforced overheads. Structural concrete
floors may be of flat slab, beam and slab, beam and
girder, or steel decking.
On floor construction, you must be sure that forms
and supports are designed and installed so that they are
readily adjusted to exact grade. Also, ensure that slab
forms and beam and girder side forms can be removed