principles of heavy weight construction - elaine toogood oct 2012
DESCRIPTION
Introduction of Precast ConstructionTRANSCRIPT
Close up Design and
Detail of Concrete
Buildings
Practical guidance for
sustainable construction
Gillingham House, Oct 2012
14:00 – 14-10 Introduction
14:10 -14:45 Principles of construction for heavyweight buildings.
Different systems, and relative benefits - Elaine Toogood
14:45– 15:15 Thermal mass for cooling in non-domestic buildings
– Tom De Saulles
15:15 – 15:30: Refreshment Break
15:30 – 17:00 Achieving visual insitu concrete - Andrew Cotter
17:00 – 17:30 Tea, Coffee and Sandwiches
17:30 – 18:40 Good practice detailing and specification for
sustainable construction – Elaine Toogood
18:40 – 18:50 Overview of Thermal Properties Calculator and Passive
Design Tool – Tom De Saulles
Further questions and close
Principles of
construction for heavy
weight buildings
• Performance issues
• Construction methodology
• Types of construction
• Factors effecting choice
How do we categorize
building methodologies-:
Light weight ?
Medium weight ?
or
Heavy weight construction?
Ideas Store, Hackney,
Adjaye Associates / Mott Macdonald
Ideas Store, Hackney,
Adjaye Associates / Mott Macdonald
The Hepworth Gallery,
Chipperfield Architects/ Ramboll
City of Westminster College,
Schmidt Hammer Lassen Architects /Buro Happold
City of Westminster College,
Schmidt Hammer Lassen Architects /Buro Happold
Why use heavyweight
construction?
Inherent performance of concrete:
• Strength
• Durability
• Fire resistance
• Acoustic Performance
• Flood resilience
• Robustness
• Security
• Airtightness
• Thermal Mass
• Visual appearance
Why use heavyweight
construction?
Other influencing factors:
• Cost
• Procurement
• Available skills
• Programme
• Quality
• Site conditions
• Health and Safety
• Flexibility / design changes
• Sustainability
• Design life
Precast hollow cored floor
Post tensioned floors
Composite floors
Contoured/coffered floors
Ribbed floors
Sprayed concrete
Tilt up construction
Fabric formwork
Some construction techniques
using concrete
Concrete blocks (masonry)
Lightweight aerated panels
Insulated concrete formwork
Beam + block floors
Cast insitu
Precast Crosswall construction
Tunnel form
Twin wall
Insitu construction ?
Or
Offsite construction ?
Or
Hybrid?
Construction techniques
•Cast Insitu reinforced concrete (frames, floors)
•Tunnel form
•Sprayed concrete
•Steel permanent formwork
•Concrete blocks
•Beam + block floors
Construction techniques
Pre-manufactured components
• Volumetric
• ‘Flat’ elements
Whole building systems
• Cross wall
Pre-cast elements
• Stairs
• external walls
• columns
• floor slabs
• cladding panels
Off Site construction
• Twin wall
• Composite floors
• Combination of precast
and cast insitu elements
Hybrid structures
Insitu or precast columns
Traditional v. Modern Methods of Construction (MMC)
Construction techniques
The Homes+Communities
Agency used to require such
approaches for affordable
homes funding
Include:
• Light weight aerated
panels
• Insulated concrete
formwork
• Cross wall
• Tunnel form
Modern methods of construction
• Twin wall
• Pre tensioned beams/slabs
• Tilt up construction
• Thin joint block work
Sprayed concrete
Darwin centre
C.F Moeller/
Ground floor:
•Insitu ground bearing slab
•Suspended slab
Screed
In-situ
reinforced
concrete
slab (150mm
dpm
Blinded fill
100mm
EPS
)
Trench fill
Ground floors
•Suspended ground floor and
upper floors
•Precast prestressed concrete
beams and standard building
blocks
•Range of beam depths (150 -
225mm) and block widths
•Generally spans up to 8m
Beam and block
• Key advantages:
• Voids can be introduced to reduce
self-weight
• Uses small repetitive components
• Easily handled and quick to place
on site.
• Immediately safe platforms
• Beam depths range from 150mm
to 225mm.
Beam and block
Janet Street Porter House
CZWG/
• Continuous voids to reduce
self weight and provide an
efficient structural section
• Panel depths typically from
110mm to 400mm
• Panel widths typically
1200mm wide but others
are available
• Length of panel dependent
upon the project
(4m – 16m)
Pre-cast hollow core floors
• Designed to have efficient
shear key joints between
slabs
• When grouted, the
individual slabs become a
system that behaves
similarly to a monolithic
slab
• Often pre-stressed to
improve span
• Min 200mm for shared
bearings before ties are
required
Pre-cast hollow core floors
Continuous wet mortar
to take up camber
Min 140mm bearing with
grouted reinforcement ties
Key advantages:
• Range of spans and loadings
• Precasting reduces time on site
• Immediate safe working
platform
• The soffit can be exposed or
simply treated
• No propping or formwork on
site
• Thermal mass potential
Pre-cast hollow core floors
National trust HQ, Swindon
Fielden Clegg Bradley Studio /
• Insitu flat slab
• ‘traditional’ steel reinforcement
(spans 4 - 12m)
• Post-Tensioned Slabs
(spans 6 -14m)
Cast insitu floors
Key advantages
• Speed of construction
• Simple and fast formwork
• Flexible plan for partitions
and services
• Can aid daylight
• Simple services installation
• Pre-stressing can improve
spans and material efficiency
further
Flat slabs (aka solid slabs)
Environmental benefits:
– Less concrete
– Reduced use of raw
materials
– Reduced lorry movements
Rapid construction:
– Larger pour area for same
volume of concrete
– Less traditional steel
reinforcement
Post-tensioned Concrete Floors
Minimum floor thickness
– Minimises the self-weight and
foundations
– Up to 300mm less than steel frame
– Cladding area is minimised –
reducing cost.
– Reduces solar gain
Long spans
– Less columns and foundations
– Increased flexibility for space
planning
– Maximises net lettable area
Potential for an extra storey in
a ten-storey building.
Post-Tensioned Concrete Floors
Flat slab with column heads:
• Supports higher loads and reduces
thickness of rest of slab
• Cost effective 5m – 10m spans
One-way flat slab with beams
• Beams in direction of longest span
• Upstand beams typical around
perimeter to maintain daylight
Flat slab options
One-way flat slab band beams:
• Can be economical for columns
size for structures with light loads
• Thinner slabs
2 way flat slab with beams:
• Common for high loads and
limited services (eg warehouses)
• spans 4-12m
Flat slab options
Ribbed slab with beams:
• Reduces self weight with
increased surface area
• 6 – 14m spans, and slightly deeper
Trough slab
• Similar to ribbed, but included
integral band beams
• spans 4-12m
Other insitu floors
Waffle slab
• Uses less concrete with deeper
slabs
• Distinctive profiled soffit with
increased surface area
• 7 – 14m spans
• Higher formwork costs and longer
construction times
Other insitu floors
Steel Deck Composite Floors
• Decking acts as permanent formwork
to the concrete, and provides
sufficient shear bond with the
concrete, so that the two materials
act compositely together.
• Principally for use with steel frames,
but can also be supported on brick,
masonry or concrete components.
• Reinforcement can be traditional
mesh or steel fibres
Hybrid Construciton
• Precast concrete as permanent
formwork to insitu topping
• Eg: Twin wall; lattice girder
floors; omnia deck
• Composite floors using lattice
girder normally consists of a
temporarily propped pre-cast
plank which is not pre-stressed.
Twin Wall construction
• This contains most of the
bottom reinforcement in
addition to the lattice
girder.
• Plank depths typically
range from 50mm – 100mm
• Finished overall depth
between 115 – 250mm
• Plank widths are usually
either 1200mm or 2400mm
• Depending on loadings and
overall slab depth, spans of
over 11.0m can be
achieved.
Spray on Plaster Finish
Pre-cast Plate
• Panels craned into
position from the
delivery truck
• Panel weight
determined by
dimensions and number
of door/window openings
• 5 m long by 2.7 m high
panel will weigh approx
3.7 tonnes
Construction
• At corners the outside skin
of the double wall panels
project beyond the inside to
provide a fully “shuttered”
junction
• All vertical joints are sealed
with foam filler or wood
Twin wall
• Steel projecting from the
wall acts as a starter bar for
the next wall lift
• The timber kicker shutter
seals the 30 mm horizontal
gap at the base of the wall
• In filling the wall void the
concrete is driven out under
the wall plates to fill the
nominal 30 mm gap and
ensure full contact bearing
for the structural wall
Construction
• Erection sockets are cast
into the face of the wall
panel for a rapid
connection of the push pull
props
• Note where the outside
face of the panel extends
on up to act as a shutter
for the edge of the floor
slab
Construction
Self finished walls to
receive spray on thin
coat plaster
Structure Ready for Finishes
• Precast permanent shuttering
• Hollow spheres (recycled high
density polyethylene) trapped
in reinforcement cages above
concrete biscuit
• Reduction in concrete usage by
approximately one third
• Opportunity for exposed soffits
• Precast reinforced panels upto
~ 2.4 x 9m
Permanent void formers
• Prefabricated, lightweight formwork system for cast insitu concrete
• Different systems available:
– Block
– Plank
– Panel (Twin wall)
• Variety of fixing methods and systems
Insulated Concrete Formwork
(ICF)
• Polystyrene insulation is used as
permanent formwork for the
concrete
• Provides monolithic structure
• Pour heights limited – usually
require additional falsework
• Very simple assembly
• Cold weather working
Insulating Concrete Formwork (ICF)
Masonry (blockwork)
‘Traditional’ construction
• External walls
• cavity construction
• partial/full fill
• brick or block outer leaf
• Internal partitions
• Basement walls
• Separating walls
Walls
• Modern method of
construction
•Special dimensionally
accurate aerated blocks
• Specific thin-joint mortar
• 2-3mm joints
• No pointing necessary
•Independent of brickwork
provides programming
benefits
Walls: thin joint masonry
Prefabricated cavity wall system
• Rapid on-site build
• Consistent quality in controlled factory conditions
• No on-site wastage
• All weather construction
• Any combination of brick and blocks and any brickwork bond
• Higher resistance to rain penetration
• Immediate finished envelope and façade
Quickbuild™
• Structural or as cladding
• Rainscreen or waterproofing finish
• Insulated sandwich panel options
• Range of finishes possible
Walls: Precast
Athletes Village
Crosswall construction
• Pre cast cellular building
system
• Particularly appropriate for
residential sectors including
hotels, student residences
• Comprises factory
engineered concrete
components including:
• Loadbearing walls
• Floors & Ceilings
• Lift Shafts and stair
• Elevation panels
Crosswall Construction
• Prestressed flat
slabs spanning from
cross wall to cross
wall
External walls
with window
openings
Internal
dividing walls • Floor slabs are
stitched together
and act as a
diaghram providing
lateral stability
Ties in
every unit • Walls are stitched
together to form
load bearing joints
Buildability
Construction and Design benefits:
• Less infill wall panels
• High quality finishes minimises
follow-on trades
• Flush walls and ceilings – no
downstands or columns
• Tight tolerances
Construction
• Precast concrete panels are
delivered directly to site in
line with the construction
programme
• Units are lifted directly from
the delivery vehicles into
place
Insitu-stitching carried out on site using reinforced
bar and a high strength non-shrink grout
Fixing Detail
Fixing and Inspection Detail
• Repeated elements will be
erected off foundations or a
transfer slab
• Scaffolding not always
necessary
• A movable safety netting
system is secured to the
concrete frame which moves
with the construction of each
floor
For optimum solution try to
minimise number of
panels. This depends on:
• Crane capacity at precast
yard
• Crane capacity on site
• Site access
• Maximising number of
units on lorry
• Transportation limits
University of East London, Fraser Brown MacKenna architects
Five seven-storey and four three-storey structures
3,526 precast panels
Constructed in 33 weeks
•Time on site v time to design
•Co-ordination of trades
•Phasing of works
Programme and Resources
Cost model studies
www.concretecentre.com/publications
Flexibility/Design changes
•Time available to fix brief and design prior to start on site
•Future adaptability: on site and post occupancy
New Square, London
Bennetts Associates
Cost
• Materials
• Labour
• Transport
• Programme
• Compare like for like
ie Include all additional finishes
Independent study
•Architecture plb
•Arup
•Davis langdon
•Costain
• 6 structural
options considered
•Published 2008
Secondary School – 1400 Pupils
16,000m² of gross external Area
Mix of 2 & 3 storey spaces
Ground Floor Plan
Cost model study - school
Less than 2% cost variation
Cost model study - office
Procurement
•Design responsibility and quality control
•Specialist items
•Specialism of different contractors
Site Conditions
•Location
•Access for delivery
•Possible crane size and location
•Size of site (for storage)
•Local labour force
•Weather conditions / exposure
Quality
•Design brief
•Fair faced finish
•Control and responsibility
•Workmanship
Buildability
•Appropriate designs
•Sequence of works
•Skills/labour to match requirements
•Space for working
•Falls from height
•Edge protection
•Safe access
•Heavy lifting
•Repetitive lifting
Health and Safety
Sustainability issues
•Use of thermal mass
•Waste
•Use of recycled material in specification
•Use of local and responsibly sourced materials
•Design for future re-use or recycling
•Long term performance