3D® Construction System - American Concrete Homes

Transcription

3D® Construction System
Strength of
3D Construction System
Copyright ©
, 2001
STRENGTH OF EVG 3D CONSTRUCTION SYSTEM
2
EVG 3D CONSTRUCTION SYSTEM
A major part of inhabited areas all over the world pass for “earthquake areas”. Especially
within the last few years it could be seen that apparently safe areas or areas with low or
medium risk had to sustain unexpected heavy earthquakes. Due to the longevity of modern
buildings there is a high probability that these buildings will be subject to earthquakes one
day. Therefore, it seems to be indispensable to build structures with a certain resistance
against earthquake forces.
Buildings, which pass for ”earthquake resistant” have to fulfil a few basic prerequisites:
•
To reduce acting forces to a minimum the structure has to be built as light as possible.
•
The basic structure of a building has to ensure that all acting forces can be transferred
to the foundation.
•
Deformations and cracks appearing under heaviest loads must not lead to an
immediate collapse of the entire building.
•
Non-bearing parts have to have a certain strength, as well. Otherwise secondary parts
may be dangerous for inhabitants even if the basic structure stays intact.
Structures made from 3D panels fulfil these requirements in an ideal way. The EPS-core and
the two thin concrete shells form a structure which shows both, i.e. high strength and a low
weight. The reinforcing mesh with small mesh size on both sides of the wall makes a 3D
structure more or less insensitive to cracks. Additionally, in contrast to brick walls non loadbearing walls made of 3D-elements are no danger to the inhabitants.
3D CROSS SECTION
COVER MESH
SHOTCRETE
DIAGONAL
EPS CORE
3D CONSTRUCTION SYSTEM
STRENGTH OF 3D STRUCTURES
3
3D STRUCTURES
3D components are thin-walled reinforced concrete sandwich elements which can mainly
transfer compression- and shear forces in the plane of wall. Therefore buildings erected as 3D
structures are composed in a “box-like” way where 3D elements are interconnected. That
means the joints between slab and wall or wall and wall in general transfer minor bending
moments only.
Forces acting horizontally on 3D buildings, such as earth quake forces, are transferred most
effectively by 3D shear walls. The respective “box-like” infilling with 3D panel walls in Xand Y-direction of 3D buildings has to be provided. For dimensioning, 3D slabs and 3D walls
can be considered independently of each other. A frame-like design of 3D buildings with
heavy reinforcement in the joints is not necessary.
BOX-LIKE STRUCTURE
held by the slab
immovable slab
(diaphragm effect)
LATERAL LOADS
cross wall
(shear wall)
anchored in the foundation
possibly boundary elements
tension force
compression force
shear forces in the
foundation anchors
In areas with a high earthquake risk it is recommended to use strengthened boundary elements
at the edge of a shear wall. These boundary elements are easy to carry out and they only
contain a small amount of reinforcement. They serve as tension ties and form a structure with
a very high resistance against earthquake forces. Unlike frame structures boundary elements
are flush with the walls and therefore, they will not affect the architectural design. Especially
in case of residential buildings a box-like 3D-structure is the best solution to receive high
strength and meet architectural requirements at the same time.
4
LOADBEARING CAPACITY
To proof the strength of the
EVG 3D Construction
System numerous tests at
several test institutes all
over the world have been
performed. All of these tests
showed clearly that EVG 3D
Panels can serve as wall
panels for multi-storey
buildings and as slab panels
for residential buildings,
office buildings and
industrial buildings.
The photo on the right side
shows a test carried out by
the company Insteel Construction Systems Inc. of
Brunswick, Ga., USA.
Please note the extra load of
more than 4000 kg applied by the means of cement bags. Total load including dead weight of
the slab amounts to more than 1400 kg/m², which is at least twice the load in usual residential
buildings.
The photo on the left shows one building out of a
group of 4-storey buildings erected in Venezuela.
The walls of these buildings not only have to
resist the loads of 4 stories, but they are subject
to major earthquake forces as well. The coastal
area where they are built is considered as area
with “highest earthquake risk”. Despite of all of
these severe requirements the EVG 3D Construction System offers a rigid and strong structure
that withstands all vertical and lateral loads. As
can be seen on the photo no other structural
elements like columns are used in combination
with 3D panels.
Under average conditions loadbearing capacity of
walls made of 3D panels can be assumed to be
sufficient for 5 to 8 stories. Even under most unfavourable circumstances a few extra reinforcement bars can extend the limits for 3D structures.
A 4-storey building in an area with a high earthquake risk is still far below the limits of EVG 3D
construction system.
5
OPEN STRUCTURES WITHOUT
INTERMEDIATE SUPPORT
Due to the loadbearing capacity in plane of panel a lot of wide open structures can be built.
structures which are not possible or not feasible with conventional materials.
The roof shown
on the left is part
of a building in
Malaysia. There
is no intermediate support for
the roof slab. The
length of span is
variable. At the
centre of the
building the
width of the roof
structure is in the
range of 8 to
10 m. Beside the
external walls
only a few
partition walls
running in parallel to the roof panels have been arranged. Due to the special loadbearing
behaviour of the EVG 3D Construction System no other loadbearing walls are required.
Another special construction is the roof shown at the bottom. The clear internal length is some
11 m. The only walls required are the external walls. The residential building is built in St.
Croix, US Virgin Islands. During designing the structure special attention has been given to
the safety against hurricanes. The house has to withstand 250 mph wind speed (approx.
400 km/h).
In both cases the box-like structure provides for sufficient strength to build the roofs with a
span of 8 to 11 m without intermediate support.
6
3D - A SYNONYM FOR STRENGTH
In October 1996 a dam near the
Country Club and Golf Course
of Cabo San Lucas, Mexico
broke during a heavy thunderstorm. The force of the water
washed out the ground below
some foundations in this area.
The below article was published in Cabo Life, a local newspaper:
The dam holding back the lake near
the 15th hole broke and the rest is
history as the mass of water flowed
and continued to flow toward the
ocean. Without the breaking dam,
little damage would have occurred.
Across the paved roadway, 3-D Panel
was putting the final touches on a twostory home. The flooding waters
decided to course under the fairway
view of that structure.
The building, left high and (not so) dry,
with no support from below, lost non of its
tinsel integrity as may be seen in the
photographs. Pete and Ed of 3-D Panel
Construction need only to pour concrete
footings under the existing columns,
backfill with dirt, and the owners of the
structure can rest assured that their home
will stand safely throughout whatever
nature may have planned for the future.
3D Panel homes, which some refer to as monolithic construction, prove once again that they
will withstand not only winds in excess of 250 kilometers per hour, but, as is apparent,
torrential flooding, as well. In this case, the 3-D Panel construction was stronger even than
hurricane Fausto.
Throughout the storm, the 3-D Panel building sustained no cracks or fissures interiorly or
exteriorly - quite remarkable since the second floor patio is a 4.3-meter-overhang. It appears
that the monolithic construction is so strong that the roof of the structure supported the
foundation.
7
IN THE EYE OF THE STORM
Especially in the southern parts of the United States year by year a lot of houses are getting
lost due to hurricanes. One of the worst hurricanes in the 20th century has been Hurricane
Andrew. Also a group of houses made of 3D panels was exposed to this thunderstorm.
The below article was published in the Washington Post. The first photo shows parts of a
destroyed wooden structure in front of a 3D house.
In the aftermath of Hurricane
The Washington Post, September 10, 1992
Andrew, the debate is intensifying
why so many houses were lost in
South Florida, despite Dade
County's strict building code requiring structures to endure
winds of 190 kilometers per hour.
Preliminary analysis indicates
that many older cinderblock
houses erected during the building boom of the 1980s suffered
because of shoddy workmanship
or shortcuts.
One group of new houses that
came through the storm virtually
unscathed was built in 1991 by
Habitat for Humanity, the international volunteer organization
whose best-known house builder
isformer president Jimmy Carter.
The habitat dwellings were all
constructed using a new process
involving prefabricated polystyrene and wire panels sprayed
with concrete. All 14 houses built
in Liberty City in North Miami
were structurally intact. And so
was the house of Irma Cordero of
Homestead, the site of the worst destruction.
Cordero's one-story house (see the picture above) was fashioned from welded wire sandwich
panels instead of wood frame construction. These panels are made by Insteel Construction
Systems Inc. of Brunswick, Ga., which says it uses a
technique developed in Austria a few years ago. The
lightweight panels, which require minimal labor to install,
consist of two parallel sheets of wire mesh connected by
diagonal truss wires that pierce an insulating core of
polystyrene 40 to 100 mm thick. The panels are attached to a
concrete foundation and connected to one another with a
special fastening tool.
8
HURRICANE PROOF STRUCTURES
Beside Florida the Caribbean
Islands have to suffer frequent
damage as a result of hurricanes.
Especially in the last decades
losses due to hurricanes have
increased tremendously.
The two photos on the right show
buildings on St. Thomas, US Virgin Islands, short time after the
hurricane Marilyn has passed in
September, 1995.
The first building is a concrete
block structure with a wooden
roof. The roof structure has been
removed completely by the hurricane. Some of the external walls
have been removed, as well. The
entire upper floor had to be
renewed.
The second photo on the right
shows a 3D structure close to the
building on the first photo. A few
days after hurricane Marilyn all
cleaning work had been done and
the only visible sign of the hurricane is the lack of foliage on
trees (see left side of photo).
Finally, the condominiums shown on the photo at bottom have been built in 1992 using 3D
panels only. They suffered no damage from hurricane Luis in September, 1995.
9
GRANITE MOUNTAIN RESERVE
In January of 1992, the Insteel 3-D Panel System was
selected for use in the construction of all exterior load
bearing walls in four buildings to be erected in the Mojave Desert at Granite
Mountain Reserve, California.
The unique complex was to
house the University of California arid-zone research facility and was designed using
3-D panels to meet exacting
thermo-insulating specifications to achieve 96% energy
independence. The project
was funded jointly by the
National Science Foundation,
Southern California Edison,
Inc., and the University of
California.
On June 28, 1992, this area
of California was struck
twice by earthquakes measuring 6.5 and 6.9 on the
Richter Scale (the second
quake was the worst recorded
in over forty years). The epicenter of these
quakes was located only 80-110 kilometers from the research facility site. According to Dr. Phillippe Cohen who resides at the site, the facility was subject to
continuous shaking at one point for over
one full minute.
Incredibly, the four buildings in the
facility, some with walls over 7.3 meters
in height, showed no signs of any damage
despite the existence of large areas of
glass. A full structural analysis of the
building was ordered and the findings, testimony to the remarkable strength and integrity of
Insteel 3-D Panels, are summarized in the letter at right. Of particular significance is the sentence which reads, “There was no sign of any crack or damage of any kind to the superstructures and foundations.”
10
A 6-STOREY MODEL
To ensure earthquake resistance, some
tests in renowned research centers have
been carried out. One of these tests was a
model of a 3D building built on a scale of
1:6 at the Tongji University in Shanghai,
China.
The model consists of panels with a size
of 400×200×30mm. The cover mesh has a
yield strength of 210 N/mm². Cube strength
of micro concrete was measured to be
10 N/mm².
The model was subject to El-Centroearthquakes of different intensity starting
with a 7-degree earthquake. According to
the test report the model lost structural
integrity when it came to a 9-degree
earthquake After this earthquake the model
was unable to bear the lateral loads.
Nevertheless the building did not collapse.
In a real building the inhabitants will not
get injured by collapsing walls or slabs.
• During the frequently occurred
7-degree
earthquakes no fissures appeared on the
tructure. The structure worked elastically.
• During the 8-degree earthquakes
cracks on
top of the ring beam of the first storey
propagated little. During the other
earthquakes , the crack propagated
gradually, though growth was not very
intensive.
• During the 9-degree earthquakes
the model
lost its capability of standing the lateral
loads. However, the structure did not
collapse.
11
EARTHQUAKE FORCES
Movements during an earthquake lead to forces in horizontal and vertical direction. Mostly
the walls or columns are able to transfer forces in vertical direction to the foundation in a safe
way. On the other hand the structure of many buildings is insufficient to sustain major lateral
loads.
The total horizontal force acting on the building results from the weight of the building and
the maximum horizontal acceleration during the earthquake. As a consequence, lateral forces
are acting mainly at the level of the floor slabs of a building. Due to the kind of vibrations the
lateral load will not be distributed uniformly to the individual floor slabs. The lateral load in
the upper stories is significantly higher than the load acting on the first storey. The exact
distribution depends on the height and kind of the structure. In addition, the total force in
horizontal direction depends on the kind of structure, too. Within elastic constructions like
frames the deformation of the structure leads to a significant absorption of lateral forces. In
contrast to frames, stiff constructions with shear walls show small deformations only.
Therefore, the full amount of lateral loads have to be applied to this kind of buildings.
The biggest internal forces generated by lateral loads are acting in the first stories of a
building. In the upper stories the internal forces are significantly smaller. Therefore, additional
stiffening is mainly required in the first stories of a building.
MULTI-STOREY BUILDING WITH LATERAL LOADS
LATERAL LOADS
SHEAR FORCE
BENDING MOMENT
H5
th
5 storey
H4
th
4 storey
H3
rd
3 storey
H2
nd
2 storey
H1
st
1 storey
foundation
12
FAILING OF FRAME STRUCTURES
This kind of structure very often can be found in the first storey of multi-storey buildings.
They are used mainly as car parks or for shops and offices. To resist an earthquake the
connections between columns and frames or columns and the slab has to have sufficient
strength. Additionally, these connections have to be carried out with ductile steel. Otherwise
the movement during an earthquake will lead to a brittle failure.
Especially in case of a basement floor built as a frame structure with additional stories made
from walls the problems are substantial. Due to the wall structure the upper stories are heavy
and, additionally, they are too stiff to allow a significant damping of lateral loads. Even if the
building has been constructed carefully the earthquake strength is limited.
REINFORCED CONCRETE FRAME
moments in the beam
connection between beam and column
lateral load
moments in
the columns
connection to the foundation
moments in
the columns
During an earthquake the frame structure has to resist additional moments and shear forces.
The biggest moments are acting in the connections between column and foundation and
column and beam. Therefore, insufficient connections will effect strength significantly.
13
FAILING OF WALL STRUCTURES
The strength of walls has to be sufficient to be considered as shear walls. Walls made from
bricks are hardly able to resist the acting lateral loads. Due to the kind of brick walls damage
through an earthquake is to be expected. Even smaller aftershocks following the main
earthquake may destroy an already damaged brick wall. In contrast to brick walls a wall made
of reinforced concrete is capable to bear horizontal shear forces. Even if the concrete wall was
subject to a certain damage it can resist the forces during aftershocks. Prerequisite to do so is a
continuous reinforcement with wires in a small distance. Otherwise the width of cracks can be
dangerous.
Anchoring of walls in the foundation has to be ensured, as well. In general, brick walls have
no connection to the foundation. Due to reasons of cost reduction walls made of precast
reinforced concrete elements also very often do not contain sufficient connection
reinforcement to the foundation. The connection to load bearing walls in the next storey often
is too small, as well.
SHEAR WALLS
connection to the slab or the next storey
boundary elements
shear forces
diagonal compression
forces
shear forces
connection to the foundation
In general, shear walls need boundary elements with additional reinforcement. This
reinforcement is subject to tension forces and has to be properly anchored in the foundation
and slab or in the shear wall in the next storey.
14
3D-WALLS AND SLABS
The strength of 3D-structures mainly depends on interaction between 3D-shear walls and
boundary elements. Therefore, the amount of reinforcement in the boundary elements is
decisive for the overall strength of the structure.
3D WALL WITH BOUNDARY ELEMENTS
SIMPLE DESIGN
STRENGTHENED DESIGN
20
30
5
20
4ø12
8ø12 30
10
ø8/20
5
45
splice mesh
ø8/20
73
83
73
83
14
14
ø8/20
ø8/20
25
16
16
16
ø8/20
ø8/20 25
16
25
25
Such an additional reinforcement is required for just some walls and increases the total
amount of reinforcement only insignificantly. At the same time, strength of the entire structure
is increased considerably.
ring beam in the slab
compression in the 3D wall
scheme of a wall
reinforcement in a multistorey building
lateral forces
boundary elements in the wall
15
STRENGTHENING WITH 3D PANELS
3D panels can be used both for the construction of new buildings and for the strengthening
of already existing structures. For both cases, the basic requirements are the same. Loadbearing parts of new buildings and additional stiffening in existing buildings have to fulfil the
following prerequisites:
•
The weight of the total building may be increased by a small amount only.
On the one hand the vertical load on the existing foundation is restricted. On the other
hand, in case of earthquakes, heavy walls will generate additional lateral loads.
•
The flexural rigidity of the additional structure has to be the same or higher than the
rigidity of the existing building.
Using a frame structure to stiffen a building with walls can not be recommended. The
frame needs substantial deformation to bear lateral loads. Therefore, the wall structure
will be destroyed before the frame has an effect on the earthquake resistance of the
building.
•
The connection to the existing structure has to be ensured by means of drilled anchors.
To do so it is recommended to use epoxy resin.
•
Shear walls mainly have to bear diagonal compression forces.
To reduce danger of buckling the wall must not be too slender. In case of a thick
concrete wall the weight of wall has to be taken into consideration, as well. Of course,
the wall needs continuous reinforcement and the distance between the wires has to be
as small as possible. Otherwise wide cracks may appear or parts of the wall can break
off.
Finally, shear walls have to be arranged in a way, that they create a structure with the same
stiffness in all directions. Mostly, this results in a certain number of shear walls in the two
main directions of a building. Possibly some non-bearing light walls have to be replaced by
3D-walls.
concrete
3D ELEMENTS
EPS
concrete
Due to the low weight and the high
compression strength 3D panels are
the ideal material to create shear
walls.
In existing buildings, where it is
difficult to work with form work, 3D
panels are easy to erect and to spray
with shotcrete.
Anchors can be drilled in existing
structures and placed with epoxy
resin to increase the strength of the
connection.

3D® Construction System - American Concrete Homes

Transcription

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