
Concrete Cutting Sawing Berkley MA Mass Massachusetts
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The
practical applications of the principles of reinforced concrete which have
already been discussed, have been almost exclusively those required for
sustaining vertical loads but a structure consisting simply of beams, girders, concrete
slabs, and concrete columns may fall down, like a house of cards, unless it is
provided with lateral bracing to withstand wind pressure hor. bars f and any
lateral forces tending to turn it over. The necessary provision for such
stresses is usually made by placing brackets in the angles between posts and
girders, as has been illustrated in Fig. 102. These brackets are reinforced
with bars J which will resist any tensile stress on the brackets. The
compressive strength of concrete maybe relied on to resist a tendency to crush
the brackets by compression usually such brackets will occur in pairs at each
end of a beam supported on two concrete columns. If we consider that any given
moment is to be divided equally between two brackets, then, if we are to have a
working tension of 15,000 pounds per square inch in the steel, and a working
compression of 500 pounds per square inch in the concrete, the area of the
concrete must be 30 times the area of the steel. But since the outer face of
the concrete will have practically twice the compression of the concrete at the
angle of the beam and concrete column, and since the maximum of 500 pounds per
square inch must not be exceeded, we must have twice that area of concrete; or,
in other words, the area of the concrete from the point of the angle down to
the face must be 60 times the area of the steel.
Although these brackets are
frequently put in without any definite design, it is possible to make some sort
of computation, especially when a building is directly exposed to wind
pressure, by computing the moment of the wind pressure. For example, if a
building is 100 feet long and 50 feet high, and is subjected to a wind pressure
of 30 pounds per square foot, the total wind pressure will be 50 X 100 X 30 =
150,000 pounds. Considering the center of pressure as applied at half the
height, this would give a moment about the base of the building, of 150,000
>< 25 3,750,000 footpounds = 45,000,000 inchpounds. If this 100foot
building had eight lines of concrete columns with a pair of brackets on each
line, and was four stories high, there would be 64 such brackets to resist wind
pressure. Each bracket would therefore be required to resist 61T of 45,000,000
inchpounds, or about 700,000 inchpounds. We shall assume that the bracket
will have a depth of 25 inches, from the intersection of the center lines of
the concrete column and the beam to the steel near the face of the bracket.
Then, since each bracket must withstand a moment of 700,000 inch pounds, the
stress in the steel will be 700,000 25 28,000 pounds. If the actual stress in
the steel is 15,000 pounds per square inch, this would require 1.87 square
inches of steel, which would be more than supplied by four inch square bars.
If
these brackets were 12 inches wide and 25 inches deep, the area of concrete is
300 square inches, which is 160 times the area of the steel. There is,
therefore, an ample amount of concrete to withstand compression, on the part of
those brackets which are subject to compression rather than tension. It is
probable that the above calculation is excessive on the side of safety, since
it is quite improbable that such a broad area would ever be subject to a
pressure of 30 pounds per square foot over the whole area. The method of
calculation also ignores the fact that the monolithic character of a
reinforcedconcrete structure furnishes a very considerable resistance at the
junction of concrete columns and girders, and that they should not by any means
be considered as if they were pinconnected structures, which would require
that the whole of the lateral stiffening should be supplied by these brackets.
Are You in Berkley
Massachusetts? Do You Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 7815192456
We Service Berkley MA
and all surrounding Cities & Towns

