Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Failures of Formwork 191
F = Ma
= Wa/g (7-2)
where F = average horizontal force, lb
M = mass of loaded buggy, W/g
g = acceleration of gravity, 32.2 ft per sec 2
a = average acceleration or deceleration of buggy, ft per sec 2
a = (14.7 ft per sec)/(5 sec)
= 2.94 ft per sec 2
F = Wa/g
= [(3,000 lb)(2.94 ft per sec 2 ]/(32.2 ft per sec 2 )
= 274 lb
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If this buggy is stopped in 3 sec, the horizontal force will be 457 lb.
The forces produced by various speeds and stopping times are tabulated
in Table 7-1.
The horizontal forces listed in Table 7-1 are for one buggy. If more
than one buggy will be stopped at the same time, the force listed
should be multiplied by the number of buggies in order to obtain the
probable total force on the formwork.
If motor-driven concrete buggies are to be used in placing the
concrete for slabs, the formwork, especially the vertical shoring system,
must be constructed to resist the horizontal forces that will act
on the forms. It will be necessary to install two-way horizontal braces
to reduce the unsupported lengths of the shores. In addition, twoway
diagonal braces should be installed, extending from the tops to
the bottoms of shores to resist the horizontal forces resulting from the
operation of the buggies. Also, the tops of the shores should be
securely fastened to the stringers which they support.
Impact Produced by Motor-Driven Concrete Buggies
Although it is difficult or impossible to calculate accurately the effect
of the impact on formwork caused by motor-driven concrete buggies,
it is known that the effect may be substantial, especially when the
buggies are traveling at relatively high speeds. It is possible that the
combined weight and impact of a buggy on a given span may lift a
stringer in an adjacent span off a shore, thereby permitting the shore
to shift its position from under the stringer unless the two members
are securely connected together.
If the shores consist of two tiers, it is possible that the bottoms of
the top tier of shores may have moved with respect to the lower system
of supporting shores, thereby producing unstable supports for
the top shores. If the forces resulting from the movement of equipment,
such as motor-driven concrete buggies, or the forces resulting
from any other kind of load or impact are likely to produce an uplift
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