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

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Failures of Formwork 187
Force Produced by Concrete Falling on a Deck
Deck forms that support fresh concrete are designed to withstand the
weight of the concrete plus an additional load, frequently referred to
as a live load, resulting from workers, concrete buggies, and materials
that may be stored on the concrete slab before it attains full strength.
Where concrete is placed with a bucket or by pumping from a concrete
pump truck, consideration should be given to the additional
pressure or force resulting from the sudden reduction in velocity as the
concrete strikes the deck.
Figure 7-1 represents a condition where concrete flows from a
bucket suspended above a deck and strikes either the deck or the top
surface of fresh concrete already on the deck. Assume that the velocity
of the concrete is V 2
at point 2 and the velocity V 3
is zero at point 3, a
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short distance below point 2.
For this condition, the following symbols will apply:
W = original weight of concrete in bucket, lb
h = height of fall from point 1 to point 2, ft
y = distance between points 2 and 3, ft
T = time required to empty bucket at uniform rate of flow, sec
w = weight of falling concrete, lb per sec, = W/T
m = w/g = w/32.2 = W/32.2T
a = acceleration or deceleration of concrete between points 2 and
3, ft per sec 2
t = time required for a given particle of concrete to travel from point
2 to point 3, sec
FIGURE 7-1 Force produced by dropping concrete on decking.
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