Precast concrete structures -...

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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)