8/13/2019 Concrete Roof Shells

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 A radical innovation in modernmotel building, featuring a roof 

of site precast hyperbolic para b o-loid concrete shells, has won na-tional recognition for the arc h i t e c t

 who made this novel use of con-c rete in a $175,000 hostelry n ow n e a ring completion at Wa rm Mi n-e ral Sp ri n g s, Fl o rida. This exc i t i n g use of concre t e, although not alto-gether unique in the annals of  A m e rican arc h i t e c t u re, does in-vo l ve an entirely new method of e m ploying concrete roof shells, ac-cording to the nationally-renownedarchitect.

 Wa rm Sp rings is about 40 milesnorth of Fort Myers on the heavily-

t ra veled Tamiami Trail leading toMiami. Since this area abounds inhe al th - s ee ke rs, and because WarmSprings has an abundance of miner-al water, the new concrete structure was designed to attract tourists onthe prowl for Fl o ri d a’s legendary “Fountain of Youth,” and this direct-ly influenced the concrete construc-tion of the inn.

The stru c t u ral system consists of a series of square concrete hyper-bolic paraboloids in two heights andmeasuring 14 feet 5 inches on a side. All precasting was done at the job

s i t e. Since the supporting pre c a s t ,p re s t ressed columns occur in thes o u n d p roof partitions betwe e nunits, different ceiling levels res ult ,defining use are a s, with lower sur-faces over sleeping and dining areas,higher planes above the living space.

 As may be seen in the picture s, aside view of this motel bears someresemblance to cocktail glasseslined up by the hundre d s. The“s t e m s” are pre s t ressed columns

that separate the units.Each roof slab is cast in the form

of an inve rted peak, re s e m b l i n g f rom the top a square cake whichhas fallen in the middle. To form theroof, these 5-ton slabs we re cra n e -hoisted and welded atop the con-c rete columns in t heir peak-dow nposition. Rain drains down to thecenter of the slabs and runs through

The roof of a Florida motel made t his strange appearance while under construct ion. The site precast hyperbolic paraboloidconcrete shells, each weighing approximately 5 t ons, were hoisted by crane and welded to t he top of reinforced concretecolumns. The open areas between t he overlapping slabs were filled with t ranslucent plastic sk ylights.

Florida motel makes unique use of...

Concr ete Roof Shel ls

Here a welder is shown fastening oneof the shells to its center supportingcolumn. Since the shells aredepressed at t he center, t he pipeserves to catch rain water andbecomes part of a drainage systemwhich embraces all of t he shells.

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a hole in the center of the support-ing column to a central dra i n a g es ystem.

The upright columns are built ontwo leve l s, with every other one ei-ther seve ral inches lower or higherthan the adjacent column. Thismeans the roof slabs overlap slight-l y, and t he space between is filled

 with translucent plastic skylights.Eighty roof slabs were poured on

the job to cover the 20-unit motel,and each unit measures 14 by 28feet. Center columns are also weld-

ed at their bases to a steel plate setbelow the concrete floor slab. Sinceeach of the shells has a steel collar atthe top, these we re welded to thesteel in the supporting column aftereach shell was stabilized atop itscolumn. Plexiglass fills the spacesa b ove door height between thehigher and lower shell leve l s. Eachshell is 2 inches thick and measures2 feet from its apex to its perimeter.

Since the shells had to be liftedvery soon after casting, they were re-m oved from their molds within 48

to 72 hours and stored for thre e weeks to cure. There are four differ-ent heights in each motel unit andeach building has a 7-foot front anda 7-foot back in the ove rhang. Anunusually rich mix was employed toattain the desired strength for early lifting from the molds. Since the soilis a mixture of sand and marl, thefoundation footing slab was made10 inches thick and 21 ⁄ 2 feet square

for each column base. Each shelltook about 11 ⁄ 2 cubic yards of read y mixed concrete.

Here on of the precast inverted-umbrella-type roof shells is shown being lifted from a cast ing form. Old tire carcasses notonly were helpful in the lift ing process but also served t o guard t he corners from damage during the handling operati ons.

All t he slabs were precast on the job-site, using assembly-line t echniques.Two of t he casting beds are shown inthe foreground, while at the right maybe seen the portable covering thatwas built to facil i tat e curing.

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