Theatre Design & Technology - Fall 2009 - 60

Your visual experience is equally pristine.
You look toward the stage and have a sight line
that is perfectly clear, even if every seat were
occupied. Above you, seemingly floating in mid
air, is the first of a number of balconies. Walk
forward until you are just beyond the leading
edge of the first balcony, turn and look up at
the other two balcony levels above the first. You
ponder, how do they float, what is supporting
these balconies? You continue to look further
up along the walls and to the ceiling. At first it
appears solid, but as you squint, the surface is
actually an open mesh, and beyond is a maze of
catwalks and equipment painted black.
You turn and make your way toward the
stage and notice the orchestra pit is replaced
by floor and seats. Up on the stage you go, and
from the middle of the proscenium you turn and
call out, "hello." Your voice reverberates as if
you were wearing head phones with no delay
and no echo. From the stage, you can see every
seat in the house.
As you move further toward the back of the
stage, you see various levels of access walkways,
and high above is a grid of steel with cables and
ropes that penetrate it in purposely located slots.
The ropes and cables support backdrops to be
used in an upcoming production. The stage space
is voluminous and houses numerous props. You
pass stage right, where a grand piano is waiting to
be moved on to the stage. Around the corner, you
step over a floor covering that obviously hides a
gap in the floor. down the hall, you enter a room
and notice a humming noise, and you can feel the
machines as they work to produce chilled water
to cool the air that is gently pushed into the massive metal ducts.
Feeling adventureous, you take a set of
stairs down into a space below the auditorium.
large, evenly distributed metal ducts emanate
from the wall in the area of the mechanical
room. The ceiling of the space has holes that
penetrate up through the concrete and are
capped with grills, apparently one hole under
virtually every seat above. Curious as to what
happened to the humming of the massive machines, you turn to the nearest set of stairs and
make your way up to the black catwalks. You
can see speaker clusters, pipes loaded with
lights, curtains, and scenery suspended below
the grid. Above you is a large opening that appears to be the roof, but upon further examination it is another room that has another series
of very large steel ducts that lead to the side and

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disappear. (The air that was cooled and entered
the hall from below the seating has warmed, has
risen up to this level and is being routed back
down to the machine room to be re-circulated
with some new fresh air.)
You make your way back down to the lobby
where we, the authors, meet you and offer to answer any questions you might have about the structural engineers' role in the design of this facility.

Questions Answered
As you know, it takes a whole team of professional consultants to create a performance arts
center such as this. The team includes the lead
architect, the design architect, theatrical consultants, acoustical consultants, mechanical
engineers, structural engineers, and others,
depending on the type of venue. The structural
engineer's purpose, as part of the team, is to
design the structure of the facility including
the foundations, columns, walls, floors, etc.
We account for structural loads such as the occupants, the equipment, and lateral loads such
as wind, snow, and seismic movement. Our
structure serves the acoustical and theatrical
functions, the architectural design, and the
building HvAC services. In your tour, you experienced how the structure served these purposes and the challenges that were overcome.
The authors' firm, Walter P Moore, has
designed over twenty major performing arts
facilities. Two of those are presented here as
case studies-the Cobb Energy Performing
Arts Centre and a theatre repurposed from a
museum and exhibit hall at the venetian Resort
Hotel and Casino in las vegas to be the home
of their production of Phantom of the Opera.
but first, let's go through some questions
you may have had in your imaginary facility
tour. First, as you entered the hall and the door
closed, there was total silence. This is because
we created a theater box inside of the outer
building box. An acoustical gap between the
inner and outer boxes kept the noise out. For
the foundation of the building, we isolated the
clanking wheels of the subway by supporting
the structure of the inner box on a special
bearing system that was sized for the weight
of the building and the frequency and type of
noise from the subway. The inner walls of the
hall are typically solid concrete from the foundation to the roof. The shape of the walls and
relationship to the stage were dictated by the

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acoustical and theatrical consultants. Mass is
important in acoustical design, and we provide
that mass with thicker-than-normal concrete
floor slabs and walls. Remember that gap at
the hallway just off stage that was covered by a
plate? That was another acoustical gap to keep
vibration noise from being transmitted from
the mechanical room into the hall.
You next experienced the full width of the
stage, free of any columns or hint of support.
This is because we designed roof trusses to
span the entire width of the hall. Supported by
the concrete walls along the sides and ends,
these trusses were designed to support everything above your heads, except the balconies.
The balconies are supported internally by stiff,
specially tapered concrete beams and slabs
that cantilever out from the back and side
walls. They are tapered so the leading edge is
very thin. With today's technology, structural
engineers are able to create computer models
of the proposed beams and slabs of the balcony in order to optimize them for strength
and for dynamic characteristics. We run the
computer models to simulate various types of
vibratory loads to make sure that whoever is
on the balcony will not feel the motion of the
person behind them running up the steps. The
number of balconies depends on the size of
the venue and number of seats required. All of
the sight lines are designed to be unobstructed
to the stage.
The orchestra pit that you didn't see today was in place for a performance last night.
This morning, the pit area was filled with seats
that were brought up from a special storage
area below. The floor of the pit is a lift that can
be positioned to align with the stage, seating,
or orchestra pit level, or it can drop all the
way down to the lower level where the chair
wagons are stored. Construction tolerances
are important so that the edges of the openings
align well with the edges of the pit.
And the room below the main level of
seating is where the cool air is delivered to
filter up into the hall. All of those holes in the
floor slab were cored through the concrete
slab at precise locations relative to the seating.
We made sure that the slab reinforcing could
be cut without compromising the strength of
the floor.
As in many new theatres, the fly space
above the stage is quite impressive. As specified by the theatre consultants, about eighty

Table of Contents for the Digital Edition of Theatre Design & Technology - Fall 2009