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Precast concrete structures
History of prefarication
• early 20.century – 1904 – concrete precast panels system in Liverpool (house.12
flats)
– 1907 – hollow wall and slab panels for low-storey family houses
– 1926 – W. Gropius – family houses in Dessau – tranversal wall system
– 1930 – Le Corbusier – panel house in Geneva
• great development – after World War II– to replace houses bombed during WWII
– Europe 60ties/70ties
– France, Sweden, Danmark
– at the end of 70ties the flat shortage in European countries was fixed and prefabricated construction was reduced
Design Culture in Liverpool,
the Liverpool School ...
Od autorů: Christopher Crouch
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Philosophy of industrialisation in the building industry
• economic view
• manufacture
– better conditions – better material (const. temperature, higher concrete class, better surface)
– lower cost (reuse of mould, decrease of the cross-section dimension, holes)
– shorter time of producing (vertical and horizontal at the same time, manufacturing at low temperature - frost)
Pozitives of precast structure
• manufacturing of element– mechanization
– automatization of production
– better quality control (HPC, HSC)
• more economic dimensions– reuse of mould
– decrease of weight
• decrease of labour consumption– speeding of building process
– savings in formwork erection and demoulding
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shape, self weight
Surface quality
appearance, durability
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image is printed on the membrane with a surface retarder of concrete setting
Graphic Concrete
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Negatives od prefabrication
• abandon of monolitic – shape
• not for complicated plans
• no rigid joints
• transport of element form plant to the site
– special road permits for oversized elements
– shape of the piece may affect the ease of
transportation (beams x complicated shapes)
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Structural design
Standards and Codes
• EN 1992: Design of concrete structures
Section 10 Precast concrete elements and structures
old ČSN 73 1201 Clauses on connections and lifting anchors
ČSN 73 1211 for panel buildings
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Specifics of the design of precast
structures
Design
• the entire structure, system
• precast element
• connections
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Design of the structural system
• dividing of the load-bearing structure – precast elements, layout of connections
• modular coordination
• simplicity of assembling
• optimal shape and possible weight decrease of the element
• large-scale production
→ careful elaboration of the design
→ potential of savings
Choice of a suitable load-bearing system with respect to manufacturing and assembling
Layout of connections
• where small inner forces are transmitted or
where compression forces act
• end sections of straight elements
• reduced number of connections
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Layout of connections
• where small inner forces are transmitted or
where compression forces act
–big quantity of connections
–complicated shape of connections
–differences in elements´ dimensions
Layout of connections
• end sections of straight elements
+ simple shape of precast elements
+ their equal weight
–connections of elements have usually
complicated loading and design
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Layout of connections
• reduced number of connections
– lead to large precast elements with
complicated shapes
+ smaller numer of precast elements is benefitial
– big weight of precast elements – more
demanding lifting devices
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Design
• USL
• SLS
• specialities
– load states, load situations (manufacturing,
transport, assembling, final acting)
– lifting anchor systems
– connections
Structural model of precast
structures
• consider simplicity of assembling
• divide structures into particular elements
(position of connections)
• shapes and weight-decrease of elements
• modular coordination
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Design of the structure
• dividing of the structure to elements
• design of the precast element
Design of the precast element
ULS, SLS + special problems
• consider situations (change of structural system):
– manufacturing
– manipulation
– transport
– storage
– assembling
– final
• design of lifting anchors for transport and assembling
• modular and manufacturing dimensions
• design of connections
• uvažovat statické působení v průběhu výstavby –spojování prefabrikátů
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Dimensions and shape of precast element
• Modular x manufacturing dimension
• optimal decrease of the self-weight –choice of structurally efficient sections
–quality concretes utilisation
–prestressing
• consider possibilities of transport (dimension limited by possibilities of means of transportˇ)
Dimension and shape
• weight decrease
• efficient section
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• dimensions of elements, tolerances (for
manufacturing, for assembling)
work size x coordinate system
Load situations
• manufacturing (lifting from mould)
• manipulation
• storage (position, supporting)
• assembling – erection (temporary
supporting before connection and grouting)
• transport (stiffness, spalling of parts
sticking out from element)
• final acting
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Load cases, transient situations
• manufacturing (lifting from mould)
• transport
• assembling
• final acting
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qd (užitné)
Change of structural model
Lifting Anchors
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Lifting anchors
• shapes
– bent bar
– notch
– special devices (screw)
Design for (load)
• separation from mould
• subsequent manipulation
• type of lifting device
Lifting anchors design
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• lifting from mould
Nd = 1,3 . (Fk + Fn,adh)
• manipulation
Nd = 1,8 . (Fk)gG
n.cos a
gman.gG
n.cos a
Nd … manipulation force(ČSN 731201)
1
2 kN/m2 * area
3!
Spreader lifting beams
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lifting spreader beam rigging - 4 ropes (chains)
n
swing
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Bent bars
steel 11 373
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• strain: tensile, shear
Reusable anchors for lifting
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Lifting
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Lifting Eye Bolt
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system BS
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Possible failures
• breaking, rupture of the anchor
• pulling out of the anchor
• pull out of the whole anchor area
• due to concentrated load
• rupture due to tensile stresses ┴ load
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Assembly
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Connections
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Classification of connections
• according to way of fabrication:– wet, dry, combined
• according to structural acting– hinged, fixed
– don't transmit forces
• according to connection– close contact (with concrete)
– dry (plane surface)
– filled connections (by concrete) – thickness of gap min. 2x gravel diameter, max 2x smaller depth of the element
– glued
Connections
According to way of fabrication:
• wet
filling of the connection by concrete or glue
+ simple
– attached after hardening
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Connections
According to way of fabrication:
• dry
welding, screwing together → filling by cement mortar to protect steel
+ attached immediately after welding (screwing)
– more complicated
– more demanding (accuracy, control) –tolerance
Connections
design
– analytic
– experimental
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Connection slab – slab
grouted connections welded or screwed reinforced concrete topping
shearing
Connection slab – slab
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Connection slab – slab
shear key
Dutinové panely – ČSN EN 1168
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connection wall – wall
anchor plate welded bar hook shear tie
shear hook
connectors
Welding
Dowel connection
Shear connection
Concrete topping
Connection beam – slab
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Connection beam – slab
connection beam – slab
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connection beam – slab
connection beam – slab
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connection beam – slab
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connection beam – beam
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Connection beam to column
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Connection column – beam
• continuous column
– without corbels (splicing of beam
reinforcement)
– with corbels
• continuous beam
• connection block
Connection beam – continuous column
soustředěný tlak
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Connection beam – continuous column
connection beam – continuous column
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plate („knife“)
Connection beam – continuous column
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connection beam – continuous column
steel plate („knife“)
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connection column – column
• výztužné pruty vyčnívající z prefabrikátu + ocelové příložky
• ocelové patky + přivařit ocelové příložky
• ocelové patky + spojení šroubovanými spoji
- náročné na přesnost, demontovatelné
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connection column – basement
monol precast prefa-monol
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Halfen-Deha Pfeifer
Bolt connectors (Halfen-Deha)
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System Crazy Brush (SICON)
