New Nautilus: the voided

biaxial

slab

former

rev. 2012 1.1

Lightweight

reinforced

concrete slab:

The necessity of decreasing the weight of RC slabs has various reasons:

ARCHITECTURE* Obtain large spans, with fewer columns or walls; * Avoidance of drop‐beams.

ENGINEERING* Self‐weight reduction of the slab in order to:

‐

reduce its deformation

‐

reduce the weight (loads)  transmitted to the foundation

‐

reduce the oscillating mass, thus the movements during an earthquake

The solution :to hollow out the slab

Voided

slabs

in reinforced

concrete

The use

of

precast

elements

has

certain

constraints:

LOGISTICS

A 

flatbed

truck 

must

be

used

even

for

small

quantities

or 

single 

parts. 

This

may

cause difficult

access

to

jobsites

in 

city centres

and with

heavy

trafic

Precast

slabs

occupy

a 

lot

of

space

on 

site. 

A 

crane

is

mandatory

for

placing. 

In case of

polystyrene

void

formers

the 

precast

parts

must

be

protected

from

rain.

USE The 

precast

parts

are 

handled

with

some difficulty

above

the fourth

floor.Drop‐beams

are often

required.

TRANSPORT

Precast

concrete elements

The

new

The advantages

of

the new

Nautilus void

former

are numerous:

TWO‐WAY 

STRUCTURE: 

a 

two‐way

slab

will

distribute

loads

on 

4 

sides

(instead

of

2 

for

one‐way

slabs), 

reducing

the 

maximum

loads

on 

beams

or 

mushroom

posts.

LIGHT: 

the 

concrete 

not

essential

for

the 

structure

is

eliminated. 

The 

self‐weight

of

the 

slab

is

limited, 

reducing

the 

loads

transferred

to

the 

foundation; 

deformation

of

the structure

is

reduced. 

FLEXIBLE: 

it

will

allow

to

eliminate 

drop‐beams

and 

create 

flat‐soffit

slabs

without

interruptions

of

large

surface. 

Advantages

QUAKE 

RESISTANT: 

the 

voids

reduce 

the 

self‐weight

of

the slab, reducing

the seismic

mass. 

LARGE 

SPANS:    larger

spans

between

columns

are 

possible. 

The 

number

of

columns

is

reduced, 

the 

result

are archutecturally

more manageable

volumes.

COST‐EFFECTIVE: 

a 

slab

with

new

Nautilus 

with

the 

same

static

and 

seismic

characteristics

consume

a 

smaller

amount

of

concrete 

and 

steel than

the full‐concrete equivalent

slab:

‐

up to

35% slab

weight

reduction

‐

up to

50% fewer

columns

‐

combined

saving

effect: 5 to

10% cost

reduction

potential

The advantages

of

the new

Nautilus void

former

are numerous:

Advantages

The 

new

Nautilus 

void

formers

are 

available

in 

various

heights, 

all

measure

520x520 

mm 

in 

plane. The “feet”, are spacers

which

determin

the thickness

of

the lower

slab, and are available

in height

between

o and 100 mm.

Geoplast Nuovo Nautilus h20

Geoplast Nuovo Nautilus h16

Geoplast Nuovo Nautilus h24

H16

H20

H24

Geoplast Nuovo Nautilus

new

Nautilus single

The new

Nautilus “single”

void

formers

can be

combined

in a “double”

configuration

to

allow

larger

void‐formers.

Geoplast Nuovo Nautilus h16

Geoplast Nuovo Nautilus h16 Geoplast Nuovo Nautilus h20

Geoplast Nuovo Nautilus h24Geoplast Nuovo Nautilus h20

H32 H36 H40 H44 H48

new

Nautilus double

Installation

of

the new

Nautilus void

formers

is

very

simple

and fast:

1.

The 

new

Nautilus 

void

formers

don’t 

have

an

orientation. 

Installation

is

fast 

and does

not

require

any

special

care or attention. 

2. 

The 

spacer

strip 

makes

spacing

control

between

void

formers

simple

and 

accurate.

3. It

is

possible

to

tread

on 

the 

new

Nautilus 

void

formers. 

This

keeps

the 

laying

of

the upper slab

armature really

simple.

Installation

The new

Nautilus caissons

resist

up to

1500 N 

pressure

on an

80x80 mm footprint

for

safe

job‐

site application.

INSTALLATION

1.  Prepare

a slab

formwork; lay

the welded

mesh

on spacers.

2.

Install

the new

NAUTILUS void

formers, spacing

between

caissons

as

per drawing. Use

the spacer

strip to

check

correct

distance.

Steps

1-2

3.    Install

all

required

extra 

reinforcement

(shear‐

and 

moment‐reinforcement); 

lay

the 

upper 

slab

welded

mesh.

4.  First pouring

phase: pour concrete to

fill

the lower

slab, starting

from

the ribbing, up to

the lower

side of

the new

Nautilus void

formers. Vibrate the concrete immediately. 

INSTALLATION

Steps

3-4

5. 

Second

pour 

phase: 

after

completion

of

the 

first 

pour 

phase, 

when

concrete 

has

achieve

some strenght, fill

the ribbings

and complete the top slab

as

required

by

the project.

INSTALLATION

Step 5

Cross‐section

of

actual

pour:concrete type: S3 poured

in two

lifts

as

per 

instructions, vibrated

with

eccentric

poker.

TEST RESULTS

Typical

cross‐section:NEW NAUTILUSDouble

H32, lower

slab

thickness

60 mm

NEW NAUTILUSSingle H16, lower

slab

thickness

50 mm

No concrete ingress

;lower

slab

completely

filled

The new

NAUTILUS caissons

create voids

in a RC slab

poured

in situ.The condition

in shich

the new

Nautilus void

former

gives

the most

advantage

is

in a two‐way

slab

configuration. 

In 

order

to

have

a 

two‐way

behaviour

the 

ratio

between

the 

sides

of

the 

slab

must

be

between

1.7 

and 

1: 

beyond

this

ratio

the 

behaviour

will

become

one‐way, 

and 

other

methods

to

reduce slab weight may be more advantageous.

SLAB THICKNESSThe 

first 

step 

in 

the 

study

of

a 

full 

concrete 

slab

is

to

formulate 

an

hypothesis

of

the 

indicative thickness. This

thickness

depends

from

the 

type

of

structure

being

studied:

Slab

on columns

d = L / 25

Slab

on beams

d = L / 30

Waffle

slab

on columns

d = L / 20

STUDY

Calculation

Once the hypothesis

of

the minimum slab

thickness

has

been

formulated, the voided

slab

with

equivalent

charactesistics

of

resistance

and deformation

must

be

identified.

A full concrete and a voided

slab

are compared

based

on their

inertia. 

The inertia

of

the full concrete slab

must

be

calculated, and compared

with

the voided

slab

solution.

2full H100

121

I ⋅⋅=52B

II fullall +=

The inertia

of

the voided

section

is

calculated

according

to

the span

of

the void

formers.Based

on the inertia

values

of

the voided

section

is

is

possible

to

calculate

the thickness

of

the slab, and 

consequently

choose

the size

of

dimensions

S1, S2 and h.

STUDY

Inertia

Here

below

the comparison

between

a full concrete slab

and an

equivalent

voided

slab.

The 

thickness

of

a 

voided

slab

is

slightly

greater

that

the 

one

of

the 

equivalent

full 

concrete 

slab.

STUDY

I=225000cm^4/m I=153626cm^4/iI=225920cm^4/m

I=422108cm^4/m I=304140cm^4/iI=422417cm^4/m

Full vs voided

slab

Once the thickness

of

the voided

slab

has

been

established

it

is

possible

to

calculate

the steel 

reinforcement.Loads

will

be

divided

in two

directions: this

can be

calculated

with

the Grashof

formulae.

This

calculation

considers

also

the 

conditions

at the limits.

4y

4x

4y

x llk

lqq

+⋅⋅

= 4x

4y

4x

y llklq

q+⋅⋅

=

STUDY

Slab

support

Geoplast Nautilus h24 Geoplast Nautilus h24 Geoplast Nautilus h24Geoplast Nautilus h24Geoplast Nautilus h24

The reinforcement

of

a voided

slab

with

new

Nautils

is

typically

composed

by:

‐ a welded mesh in the lower

slab, with

spacers

to

assure

the required

concrete cover; 

‐ additional

reinforcement

(bars

or grids);

‐

a welded

mesh

in the upper slab, laid

directly

on the void

formers

(which

include ribbing

on 

their

upper surface

that

serve as

spacers).

STUDY

Reinforcement

Example

of

additional

reinforcement

between

the two

welded

meshes.

In the case of

a slab

and beam

system there

are typically

rather

high values

of

shear

stress and 

negative moment.To

manage

these

stresses

is

possible

to

use

void

formers

of

lower

height

close

to

the supports

in order

to

increas

the resistant

section.

STUDY

Slab

profile

close

to

support

-

beams

In the case of

a voided

slab

without

beams

it

will

be

necessary

to

create 

a 

full concrete 

zone 

around

the top of

the columns

(“mushrooms”).

The 

armature 

must

be

properly

calculated

in 

order

to

manage

shear‐stress

and 

negative 

moment.

STUDY

Geoplast Nautilus h20

Slab

profile

close

to

support

-

columns

New Nautilus projects realised or in development

New Nautilus projects realised or in development

PROJECT: SHOPPING CENTRESITE: VITROVICA, CROATIAPRODUCT: new NAUTILUS®SURFACE: 30.000 m2

NOTE: with post-tension

PROJECT: DIGITEO LABSITE: SACLAY, FRANCEPRODUCT: new NAUTILUS®SURFACE: 38.590 m2

new Nautilus to decrease the self-weight of the slab

and allow a wide span.

Modulo used to fill the gap between the slab and the

beam.

Typical project with new Nautilus + Modulo

PROJECT: DIGITEO LABSITE: SACLAY, FRANCEPRODUCT: new NAUTILUS®SURFACE: 38.590 m2

PROJECT: new hospitalSITE: PISTOIA, ITALYPRODUCT: new NAUTILUS®SURFACE: 39.000 m2

PROJECT: ERICSSON LABSSITE: GENOVA, ITALYPRODUCT: new NAUTILUS®SURFACE: 20.000 m2

BID

IREZ

ION

ALE

PROJECT: PADOVA UNIVERSITYSITE: PADOVA, ITALYPRODUCT: new NAUTILUSSURFACE: 20.000 m2

Thank you for your attentionwww.geoplast.it