Theatre Design & Technology - Spring 1988 - 15

750

E
C 550

o
....J

U

OJ
;:; J50
OJ

Platform 8

o

I-

OJ
--J

150

I-'_"_'~""\

C

u

I

* , *. - ...... __ .

-----------

......

-. '-.

.' ".

.--

- sgiO:'O~~0":!.0~2~n::On:.0!'4~n:0:".0"6~~O:2"'.:r.08:=,cn:r0.'T0::rrr~0;'·:'2 ,-----n"::0~·~"~n:0:-'.
Elapsed Time (sec)

-

Figure 4: Comparison of Dynamic Response of Various Platforms to
Dropped-Weight Impact. (Initial Impact Energy = 90 ft.-lb.).

c
0

....J

U

75

tlJ

~
~

tlJ

0

Platform A

25

OJ
OJ)

'U -25

W

-75-tn~~.,--n~~.,--n-~~.,--n-~.,__n_,__rr~~~~~~~~

0.00

0.02

0.04

0.06

0.08

O. ; 0

0.12

O.. "

Elapsed Time (sec.)
Figure 5: Dynamic Edge Deflections of Platforms Subjected to an Initial
Impact Energy of 90 ft.-lb.

Impact Energy (F) = Weight (W) x Height (HI
All of the deformation-time histOries of Figure 4 are for the
same impact energy of 90 ft.-lb. achieved by the falling
weight just before contact with the platfonn deck.
The duration of the impact event can be defined by the
length of time it takes for the displacements of defom1ations to reach their maximum values. In Figure 4 the
impact duration time can be seen to be about 0.020 seconds for all platfom1s tested.
After a weight strikes the deck of the platfom1, it radiates displacement 'waves' in a manner analogous tc the
way water ripples from a stOne dropped into a still pond.
Transducers positioned away from the center of impact
will record these waves a they pass the point being
monitOred. Figure .5 illustrates the vibration of the edge of
the platfom1s as these displacement waves pass the transducer at that location. With an array of transducers, such
as shown in Figure 1, there exists the ability to define the
complete nature of the deformation wave as it propagates
through the platfoI111. Figure 6 is'a composite illustration
of the wave propagation across transducer locations T9,
T8, T3, T7, and T6 during the impact event. Such a wave is

significant because it portrays the vibration and bounce
that a performer might experience on a platform of a
particular construction.
The significance of a displacement-time histOry such as
presented in Figure .5 is that it can characterize the vibrations and vibration dampening abilities of particular platform materials and constmction techniques. It is apparent
that Platform C (ply/2 x 4) sustains a high magnitude of
edge displacement for this panicular impact event while
Platfom1 D (OSBI2 x 41 does not. Because the constmction
of these tWO platfom1s are very similar, one could conclude
that the OSB (Oriented Strand Flakeboardl employed in
Platform D has superior energy and vibration dampening
characteristics.
Also of interest is the response of PlatfoI111 A (ply/l x 2
steel tube). The edge displacement-time histOry of this
platfonn can be characterized by a reasonably well-defined, smooth wave fom1 with dissipating amplitude. The
peaks and valleys of this wave have a distance period of
time between each. This vibrational pattem is indicative
of rigid "elastic" stmctures made from a material such as
steel. It is apparent that the response of Platfonn A is
dominated by the platform framing while the response of
Platforms C and D is influenced significantly by the decking materials.
The response of modular staging platfom1s to live loads
is dependent not only upon the structure and material of
the platfom1 but also on the nature of the impacting object.
To illustrate this fact the data presented in Figure 7 defines
the dynamic center deflection of Platfom1 C to two drops,
each with the same initial impact energy of 60 ft.-lb. The
primary difference between the two data plots is that the
higher deformations are generated by the impact of the
rather rigid, 30. lb., leather-bagged weight (dropped from a
height of 2'). The lower data plot was produced by the
impact of the flexible, 20 lb., cloth-bagged weight (dropped
from a height of 3 'I. This figure illustrates that the material of the 20 lb. weight can absorb some of the energy of
impact by the friction of the lead spheres as they move over
each other as the cloth bag defom1s upon impact. Some
energy will also be absorbed as the soft and pliable lead
pellets actually deform permanently with the impact.
These processes do not occur in the 30 lb. weight because
the leather bag is far more confining and does not deform
significantl y upon impact wi th the decking. The steel
pellets have a lower frictional factOr that lessens energy
dissipation. Finally, the steel has a much higher strength
than lead and thus will not dissipate energy by permanently defomling upon impact.

Table III: Equivalent Static loads for Dynamic Impact

Center Oispl.
(ins,)

[Quiu. Static Load
(Ibs.)

Weight
(Ibs.)

Height
(ins.)

A

30

24

0.628

2125

8

3D
20

24
36

0.610
0.304

1892
936

C

30
20

24
36

0.534
0.326

1867
1140

0

30

24

0.508

2604

Platform

TD&T

*

SPRING 1988

13



Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1988

Contents
Theatre Design & Technology - Spring 1988 - 1
Theatre Design & Technology - Spring 1988 - 2
Theatre Design & Technology - Spring 1988 - 3
Theatre Design & Technology - Spring 1988 - Contents
Theatre Design & Technology - Spring 1988 - 5
Theatre Design & Technology - Spring 1988 - 6
Theatre Design & Technology - Spring 1988 - 7
Theatre Design & Technology - Spring 1988 - 8
Theatre Design & Technology - Spring 1988 - 9
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Theatre Design & Technology - Spring 1988 - 12
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Theatre Design & Technology - Spring 1988 - 18
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Theatre Design & Technology - Spring 1988 - 68
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https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1971Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1971May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1971Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1970Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966May
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Feb
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Dec
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Oct
https://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965May
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