Precast High Rise Buildings

Transcripción

13º ENECE, 2010:
CONFIABILIDADE E DESEMPENHO
“Precast High Rise Buildings”
David Fernández-Ordóñez
Dr. Ingeniero de Caminos, Canales y Puertos
Lecturer at the Politechnic University of Madrid, Deputy Chariman of
fib COMMISSION 6: PREFABRICATION
[email protected]
Every construction material and system has its own
characteristics which to a greater or lesser extend
influence the layout, span length, construction
depth, stability system, etc.
This is also the case for precast concrete, not only
in comparison to steel, wood and masonry
structures, but also with respect to cast in-situ
concrete. Theoretically, all joints between the
precast units could be made in such a way that the
completed precast structure has the same
monolithic concept as a cast in-situ one.
If the full advantages of precast concrete are to be
realized, the structure should be conceived
according to its specific design philosophy: long
spans, appropriate stability concept, simple details,
etc.
Designers should from the very outset of the project
consider the possibilities, restrictions and
advantages of precast concrete, its detailing,
manufacture, transport, erection and serviceability
stages before completing a design in precast
concrete.
STRUCTURAL SYSTEMS:
The skeletal structure:
consist of columns, beams and slabs for low to
medium-rise buildings and with a small number of
walls for high rise. Skeletal frames are used chiefly
for offices, schools, hospitals, car parks, etc.
The wall frame structure:
consists of solid vertical load-bearing wall and
horizontal slab units, and used extensively for
housing and apartments, hotels, schools, etc.
STRUCTURAL SYSTEMS: The skeletal structure:
Precast tower buildings are generally characterized by a
cast in-situ central core surrounded by a complete precast
structure comprising load bearing columns, prestressed
floor beams and prestressed floors. A typical
characteristic of recent realizations is the architectural layout of the floor plans, taking all kinds of non-orthogonal
shapes: elliptic, rounded, with sharp edges, etc., but
seldom rectangular. This is a clear tendency of the
market.
The skeletal structure is often built with circular columns
in high strength self-compacting concrete C80/95. The
floor beams have an L-shaped or inverted-T-shaped
cross-section with a slender booth height, the latter
varying in most projects from 80 to 120 mm. The 80 mm
booth is designed as a composite component with a steel
angle, anchored in the prestressed beam and covered by a
70 mm thick concrete layer for fire protection. Two types
of precast prestressed floors are used in the tower
buildings: hollow core slabs and ribbed floor. Both
systems have specific advantages and the choice often
depends on specific features within the projects.
Portal and skeletal structures are especially suited
for buildings, which need a high degree of
flexibility. Since the load bearing structure is
independent of the completing sub-systems like
electrical equipment, conduits, partition walls, etc.,
the buildings can be easily adapted to changes
during its lifetime, or to new functions and
technical renovations.
Skeletal structures enable to realize large spans
and henceforth greater freedom in planning and
disposition of floor areas, not being hampered by
load-bearing walls or a large number of internal
columns. The internal space can be further
subdivided with non-load bearing partition walls,
which can be taken away at any time. This is very
important in industrial buildings, shopping halls,
car parks, sporting facilities and also in large office
buildings.
STRUCTURAL SYSTEMS: The wall frame structure:
Precast walls are usually made in reinforced concrete. The
elements are usually storey height with a length of 4 to 14 m.
The thickness varies between 80 mm for non load bearing
walls to 150 to 200 mm for load bearing walls and
exceptionally even to 300 mm for special applications.
Precast walls are used for internal and external walls, lift shafts,
central cores etc. The system is mostly used in domestic
construction, both for individual housing and for apartments.
The precast walls can be load-bearing or non load bearing.
The surface of the elements is smooth on both sides and
ready for painting or wall papering. Precast walls offer the
advantage of speed of construction, smooth surface
finishing, acoustic insulation and fire resistance.
Modern systems belong to the so-called open
construction technique, which means that the
architect is free to design the project according to
the requirements of the client. The trend is to build
free open spaces between the load-bearing walls, and
to use partition walls for the internal layout. It offers
the possibility to change at a later stage the interior
layout without major costs.
- Integral wall systems: where all internal and external
walls are in precast concrete
- Envelope wall systems: where only the external or
separating walls between the apartments are in
precast concrete and the internal walls in block
masonry or in any other partition wall system.
Cores:
Stability:
Stability:
Stability:
Column positioned
on grid axis
Modulation based on dimension façade units
Edge column positioned
on grid axis
STRUCTURAL SYSTEMS: North Galaxy Brussel:
Office building with
36 floors
STRUCTURAL SYSTEMS: North Galaxy Brussel:
Triangular joints cast in situ
Central cores cast in situ with climbing mould technique
STRUCTURAL SYSTEMS: Floors
Precast
Floor type
Max. span
m
Unit depth
mm
Unit width
m
Unit weight
kN/m²
20
120 - 500
600 – 1200
2.2 – 5.2
12
175 – 355
2400
1.2 – 1.8
24 (30)‫‏‬
200 – 800
2400 – 3000
2.0 – 5.0
7
100 – 200
600 – 2400
2.4 – 4.8
7
200 - 300
200 - 600
1.8 – 2.4
Overview current floor types
STRUCTURAL SYSTEMS: Columns
Horizontal
casting
Self-compacting
concrete C80/95
mortar
Projecting
bars
Fine
concrete
Steel angle
welded to
main
reinforcement
Supporting
pad
projecting bars in grout tube
bolted connection
Columns are 1 to
4 storeys high
Columns are one
storey height
column - column
Column - beam
Corbels are
needed to support
the floor beams
No corbels
needed. The floor
beams are
directly supporten
on the column
Column - foundation
Solution with corbels
Solution without corbels
STRUCTURAL SYSTEMS: Beams
Normal booth height
> 150mm
Slender booth height
Booth height 120 mm
Beam with half joint
STRUCTURAL SYSTEMS: Erection
Groove for
peripheral tie
Cast in situ topping on floor
Erection
floor
beam
STRUCTURAL SYSTEMS: Erection
Edge beam with
rounded upper flange
Ellips shaped building
STRUCTURAL SYSTEMS: Details
Cast in-situ
triangular joints
Edge beam with
rounded flange
Floor beams supported
on edge beam
Column – column
connection with
projecting bars in
grout ducts
Bolted connection
beam - column
Edge column with 3 floor beams
Edge beam
Intermediate beam
STRUCTURAL SYSTEMS: Strikjkijzer Building, NL 132m:
This pre-cast concrete residential tower that is located on a very limited
site of the Rijswijkse Plein (Rijswijk Square) in The Hague, has 42
storeys. The execution started in June 2005. The typical floor plan is Lshaped with dimensions of ca 37m x 34m.
The stability of the building is provided by the façade tube made of
pre-cast concrete elements. To reduce the shear lag and to provide
better structural integrity, the longer sides of the tube are connected by
“webs” that are formed by floor bearing pre-cast concrete walls. The
shapes of the pre-cast concrete wall and façade elements are
interlocking , to provide a dowel action for transfer of vertical shear and
to omit labour intensive connection in vertical joint between the precast concrete wall and façade elements.
42 storey building - erection speed
2 storeys/week
STRUCTURAL SYSTEMS: WATERSTADTOREN, NL: 110m
The “Waterstadtoren”, was with its 36 storeys and 110m of height, in the
time of its completion in 2004, the tallest fully pre-cast residential building
in Europe.
The typical floor of the tower with dimensions of 25 x 25m has an
irregular plan and is designed to accommodate 4 to 5 apartments. At the
south-east and south-west corners of the plan large pre-cast concrete
balconies are situated, manufactured as three-dimensional elements .
STRUCTURAL SYSTEMS: WATERSTADTOREN, NL:
STRUCTURAL SYSTEMS: WATERSTADTOREN, NL: 110m
finish
compression loaded
mortar joint
pre-cast
concrete slab
precast concrete wall
510
200
75
suspension reinforcement "a"
steel tube S275 Ø70x10x500
cast in situ
A
suspension
reinforcement "b"
tie reinforcement
pre-cast concrete wall
SUSTAINABILITY OF PRECAST SYSTEMS: Fib docs
SUSTAINABILITY OF PRECAST SYSTEMS: Fib docs
SUSTAINABILITY OF PRECAST SYSTEMS:
Concrete is an established, dependable and well-understood
building material that is used across Europe for a range of building
types. Its most common applications in buildings are:
• Floors at ground or upper floor levels.
• Structural frames (i.e. beams, columns and slabs).
• External and internal walls, including panels, blocks or
decorative
elements.
Concrete is extremely versatile in terms of its structural and
material properties, which is one of the reasons for its success. The
majority of buildings use heavyweight, or dense concrete, which is
known for its strength, fire protection, sound insulation and,
increasingly, for its thermal mass.
The benefits of thermal mass
The main energy benefit of using concrete in buildings is its high
thermal mass that leads to thermal stability. This saves energy and
produces a better indoor environment for building users.
The thermal mass of concrete in buildings:
• Optimizes the benefits of solar gain, so reducing the need for heating
fuel.
• Reduces heating energy consumption by 2 – 15% (see Section 5).
• Smoothes out fluctuations in internal temperature.
• Delays peak temperatures in offices and other commercial buildings
until the occupants have left.
The benefits of thermal mass (cont)
• Reduces peak temperatures and can make air-conditioning
unnecessary.
• Can be used with night-time ventilation to eliminate the need for
daytime cooling.
• When combined with air-conditioning, it can reduce the energy used
for cooling by up to 50%.
• Makes best use of low-temperature heat sources such as ground
source heat pumps.
• The reductions in energy use for both heating and cooling cuts
emissions of CO2, the main greenhouse gas.
The Termodeck System.
Here mechanical ventilation passes low velocity air
through the cores of a hollow core slab in a
serpentine pattern, which ensures prolonged contact
between the air and concrete for good heat transfer.
In each slab, three of the five cores are generally
used in this way, and an air supply diffuser is located
on the underside of the slab i.e. soffit.
THE ENERGY PERFORMANCE OF BUILDINGS DIRECTIVE (EPBD)
EPBD requires that governments, designers and clients take action by:
• Providing a common framework for a methodology of calculation of the integrated
energy performance of buildings.
• Placing minimum requirements on the energy performance of buildings, including
that required for cooling.
• Requiring that measured energy use is checked in completed buildings and that they
are compliant.
• Allowing a CO2 indicator to be included in the assessment of energy performance,
which promotes the use of alternative energy sources (such as solar panels).
• Stating that passive heating and cooling concepts should be employed.
• Stating that good energy performance must not conflict with the quality of the indoor
environment.
• Imposing a system of energy certification of buildings, which increases awareness of
the issue and improves the market value of energy efficiency
A comparison of the energy consumption for precast floor and a cast
in situ floor was carried out in a study. As far as the figures for
transportation is concerned, the distance from the precast factory or
ready-mix plant to the building site is assumed to be same for both
cases. The higher energy consumption for the cast in situ slab is due
to the larger amount of concrete needed per square meter of floor.
Item
Hollow core slab (MJ/m2)
Cement
186
Steel
45
Other raw materials
15
Manufacturing process
128
Transportation
28
Total
401
Cast in situ slab (MJ/m2)
389
60
23
32
42
560
A study in the Netherlands carried out an extensive investigation comparing a
precast hollow core floor with a shuttering slab and a cast in situ floor. The results are
shown in table:
Shuttering slab
423,00
6,44
429,44
Cast in situ
423,00
6,11
429,11
0,0468
2,78
Greenhouse effect (kg CO2 eq.)55,2
Acidification (kg SO2 eq.) 0,252
Summer smog (kg C2H4 eq.) 0,0297
Human toxicity (kg)
0,318
0,0448
0,0621
5,52
58,6
0,321
0,0453
0,429
0,0410
0,0707
5,81
53,4
0,306
0,0460
0,411
Use of primary energy (MJ) 461
592
643
Solid waste (kg)
59,6
58,8
Concrete (kg)
Reinforcement (kg)
Total mass (kg)
Hollow core 1
263,72
3,22
266,94
Eutrophication (kg PO43 eq.) 0,0356
Exhaustion (x 012)
Ecotoxicity(x103m3)
36,3
The quantities are per square meter. "eq." = equivalents
Demountabilily and recirculation
One great ecological advantage for precast structures is the possibility to make
them demountable. If the structure at the outset is designed with demountability in
this can be carried out with very little difficulty. At the end of the life of a structure in
a certain location the whole structure can then be reerected at another location, or the
components can be reused. Several examples of this have been carried out lately.
A concrete structure has a very long life expectancy, and usually there are during
the years ample opportunities to use the structure for various purposes. If this is not
possible, 100% of the concrete can be recirculated. After removal of the
reinforcement the crushed concrete can be used for:
- new concrete
- embankment protection
- road subgrade
- landfills
Spanish Documents: EHE, Spanish normative on
structural concrete. Annex 13: Índice de contribución de la
estructura a la sostenibilidad:
Este Anejo define un índice de contribución de la estructura a la Sostenibilidad
(ICES), obtenido a partir del índice de sensibilidad medioambiental de la misma
(ISMA), estableciendo procedimientos para estimarlos cuando así lo decida la
Propiedad.
Los criterios a los que hace referencia este Anejo se refieren exclusivamente a
actividades relativas a la estructura de hormigón. Al ser ésta un elemento enmarcado
frecuentemente en el conjunto de una obra de mayor envergadura (edificio, carretera,
etc.), el Autor del Proyecto y la Dirección Facultativa deberán velar, en su caso, por la
coordinación de estos criterios con respecto a los que se adopten para el resto de la
obra.
Definición del Índice de sensibilidad medioambiental.
ai, bi y gi
Coeficientes
de
ponderación
de
cada
requerimiento, criterio, o indicador de acuerdo con la Tabla
A.13.4.1.a.
Vi
Coeficientes de valor obtenidos para cada criterio, de
acuerdo con las siguiente expresión en función del parámetro
representativo en cada caso.
Ki, mi, ni
y Ai Parámetros cuyos valores dependen de cada
indicador, de acuerdo con la Tabla A.13.4.1.b.
Pi Valor que toma la función representativa para cada indicador, de
acuerdo con lo señalado en el apartado 4.3 de este Anejo.
Hormigón, donde:
p
es el porcentaje de utilización en la obra
de cada uno de los tipos de hormigón considerados (preparado, en
1i
central de obra o prefabricado) y li es la suma de los valores que
sean aplicables según las condiciones medioambientales de las
instalaciones, para la
correspondiente columna de la Tabla A.13.4.3.1.
1,00
3,00
0,80
Vind = 1,02 * 1 - e
-0,50 *
Xind
50
Valor
0,60
0,40
0,20
0,00
0,00
10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00 90,00 100,00
Puntuación
donde p2i es el porcentaje que representa cada una de
las posibles procedencias de las armaduras que se colocan en la obra
(instalación de ferralla ajena a la obra, instalación de obra o
instalación de prefabricación) y "2i es la suma de los valores que
sean aplicables según las condiciones medioambientales de las
instalaciones, para la correspondiente columna de la Tabla
A.13.4.3.2.
Ferralla,
Optimización de armado, l3i
obtenidos de la tabla A.13.4.3.3.
representa los valores
Sistemática del control de ejecución, p4i
es el
porcentaje de utilización en la obra de cada uno de los casos que se
definen en la tabla A.13.4.3.4 y l4i es el coeficiente reflejado en la
misma para cada caso.
Reciclado de Áridos, p51
y p52 son los porcentajes de
utilización en la obra de elementos de hormigón ejecutado in situ y
de elementos de hormigón prefabricado, respectivamente, y donde
los coeficientes l51 y l52 son los porcentajes de árido reciclado
correspondiente a cada uno de los mencionados tipos de elementos.
Cada uno de estos porcentajes (l5i) está limitado al valor 20.
Optimización de Cemento,
donde:
- H: Porcentaje de hormigón con distintivo de calidad oficialmente reconocido, con
adición de cenizas volantes o humo de sílice
- p6i: Porcentaje de utilización en la obra de cada tipo de cemento identificado
según la tabla A.13.4.3.6
l6i: Coeficiente obtenido de la tabla A.13.4.3.6
- n: Representa el número de tipos diferentes de cemento suministrados a la obra,
identificados según la tabla .13.4.3.6
Optimización de Hormigón,
donde:
- H Porcentaje de hormigón con distintivo de calidad oficialmente reconocido, con
adición de cenizas volantes o humo de sílice
- p7i Porcentaje respecto a la cantidad total de hormigón con adición en central,
que corresponde a los hormigones fabricados con cada tipo y proporción de
adición según la tabla A.13.4.3.7
l7i Coeficiente obtenido en la tabla A.13.4.3.7
- n Representa el número de tipos diferentes de adición empleados, identificados
según en la tabla A.13.4.3.7
Control de Impactos,
de la tabla A.13.4.3.8.
donde: p8i y l8i son los parámetros obtenidos
Gestión de Residuos,
A.13.4.3.9.
donde: l9i son los valores obtenidos de la tabla
Gestión del Agua,
A.13.4.3.10.
donde:
l10i son los valores obtenidos de la tabla
Índice de contribución de la estructura a la Sostenibilidad
siendo:
k=1,50 para obras de ingeniería civil.
k=2,00 para obras de edificación.
donde:
a Coeficiente de contribución social, obtenido como suma de los
coeficientes indicados en la Tabla A.13.5, según los subcriterios
que sean aplicables.
b: Coeficiente de contribución por extensión de la vida útil,
donde:
- tg: Vida útil realmente contemplada en el proyecto para la
estructura, dentro de los rangos contemplados en el artículo 5 y
- tg,min: Valor de la vida útil establecido en el apartado 5.1 de esta
Instrucción para el correspondiente tipo de estructura
Índice de contribución de la estructura a la Sostenibilidad
A partir del ICES, puede clasificarse la contribución de la
estructura a la sostenibilidad, de acuerdo con los siguientes niveles:
Nivel A: 0,81 ICES 1,00
Nivel B: 0,61 ICES 0,80
Nivel C: 0,41 ICES 0,60
Nivel D: 0,21 ICES 0,40
Nivel E: 0,00 ICES 0,20
donde A es el extremo máximo de la escala (máxima contribución a
la sostenibilidad) y E es el extremo mínimo de la misma (mínima
contribución a la sostenibilidad)
AKNOWLEDGEMENTS:
- Arnold Van Acker, Former President of Fib
Commission 6 Prefabrication. Expert and Lecturer
of Prefabrication.
- Jan Vamberski, member of Fib Commission 6
Prefabrication, Lecturer at TU Delft and Expert
designer on prefabrication.
- Antonio Aguado, Professor at the Polytechnic
University of Barcelona, responsible for Spanish
Normative on Sustainability
Thank you for your attention

Precast High Rise Buildings

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