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01 February 2013
1
Design principles for precast concrete
Technical workshop : South Africa
Prof.dr.ir. Joost Walraven
01 February 2013 2
Recent projects
Precast façade elementsBearing inner wallsPrestressed hollow core slabs
Floor plan triangularAtrium triangularFaçade elements: derived from triangular shape
City office, The Hague, The
Netherlands
01 February 2013 3
Recent projects
Crystal Court Dwellings, Amsterdam
-36 multistory apartments (all different)- precast walls- thin precast floors
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01 February 2013 4
Recent projects
Shopping Centre Velperbroek
The Netherlands
Ground level: shopping centre
1th floor: parking garage
2-9th floor: 106 apartments
Advantantages:
- long spans
- short construction time
- low nuisance for environment
- precast floor with integrated
ducts.
01 February 2013 5
Recent Projects
City harbour hotel
Amsterdam, The Netherlands
20 stories 61x18 m2
01 February 2013 6
Recent Projects
City harbour hotel
Amsterdam, The Netherlands
Hotelrooms 5th-19th storey supported by two prestressed precast concrete trusses, h = 4.2m, b=2,5m and l = 61m. Cantilevering at both sides 7.6m and supported any 15.2m
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Recent projects Parking Garage de Cope
Utrecht, The Netherlands
Helical access ramps consisting of
precast concrete elements: no
complex formwork at building site
needed.
01 February 2013 8
Title
Parkinghouse Kelfkensbos
Nijmegen, The Netherlands
4 parking levels 90 x 48 m2
prestressed inverse T-beams for
roof structure
01 February 2013 9
Recent projects
Parking garage Amsterdam
Inverted T-beams
Hollow core slabs
Composed to composite
floor system
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01 February 2013 10
Advantages of precast concrete
High concrete strength:
under controlled factory conditions high concrete strength can easily be achieved.
For the precast concrete industry this is a “must” anyhow: high production requires a
high early strength, which corresponds to a high 28-days strength: fcyl ≥ 50 Mpa
Low cost prestressing
Prestressing with wires and strands: anchorage by bond: no expensive prestressing
anchors required.
01 February 2013 11
Office building to be created over access road to city
of The Hague in The Netherlands
Advantages of precast concrete
Precast prestressed high strength concrete beams (fck = 100 Mpa) to support the building
placed in
one night
01 February 2013 12
High strength concrete in combination with prestressing can be used to produce large span slender beams and slabs: that means freedom in arranging the interior ground plan and flexibility to change this in future
Advantages of precast concrete
Car park with 9.60x16m gridOffice with free span 18m
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- Small construction site needed. No storage of structural elements required. Mounting even large elements directly from transport vehicle. Important in urban areas.
Advantages of precast concrete
Mounting a TT- element for a car park directly
from transport car.
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- Reduced construction time:no delay by hardening of concrete at construction site. Elementsare already approved in factory. In general simple assembly ifrational connections are used. Lower noise level, less waste, less dust.
Advantages of precast concrete
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High quality detailing in factory possible
Advantages of precast concrete
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Design philosophy
1. Design the structure from the beginning as a precast structure and not
as assembled parts of an in-situ
In-situ structure: frame with monolytic nodes
Precast alternative:
columns fixed at
bottom and beams
supported by corbels
01 February 2013 17
Design philosophy
2. As little as possible different element types
Structure built with bearing facade
elements and prestressed hollow
core slabs
01 February 2013 18
Design philosophy
3. Shape of precast elements as simple as possible
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Design philosophy
Solution too complex
Simple system with simple
connections
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Design philosophy
Examples of standard solutions for connection of column to foundation
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Design philosophy
4. Precast elements as large as reasonable (transport limitation)
The larger the elements, the
lower the number of
connections and the lower the
number of operations
Prestressed precast beams for a car park.
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Design philosophy
5. Precast elements should be designed in such a way that they can easily be transported.
01 February 2013 23
Design philosophy
6. As little as possible in-situ concreting
- Joints between hollow core decks to be cast in-situ.
- Moreover, in-situ concrete for small areas in irregular floor systems may be more appropriate than precasting
one single fitting element
- In situ concrete leads often to delay
- It is more complicated to cast small volumes of in-situ concrete than large volumes.
01 February 2013 24
Design philosophy
7. Design preferably in such a way that the structure is stable in all stages.
Statical system inappropriate for
precasting:-Columns have to stabilized in
construction stage- moment resistant connections column-
beam require cast in situ concrete in small volumes
Statical system suitable for precasting:
-Columns are stable in construction stage
- hinged connection is easily achievedsimple support
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Design philosophy
8. Use as much as possible modular systems
Example of modular system for precast structure
The basic module is mostly 3M
(M = 100 mm), and 6M and
12M are widely used measures
Internal columns are positioned
centrically on the modular axis
grid.
Modulation in connection with
industrial production is not
imperative, but has an influence on the cost of the elements
01 February 2013 26
Design philosophy
Example of modular system
(top view)
front view side view
01 February 2013 27
Design philosophy Example of modular system, with limited deviation of modular grid
(Kern = Core)
Corner solution
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Design philosophy
9. Take due account of dimensional tolerances
01 February 2013 29
Design philosophy
Tolerances
Avoid combinations of
camber in two directions
Connections able to cope with
dimensional deviations
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Design philosophy
10. Use as much as possible standardized elements and connections
Standard products are cast in existing moulds. The designer can select the length, dimensions and
load bearing capacity within certain limits. This information can be found in catalogues from the precast element producers.
Standardization constitutes an important economic factor in prefabrication, because of the lower costs for moulds, industrialization of the production process with high productivity, large
experience in execution, etc. Repeated handling at the construction site means also avoiding errors and bad experiences.
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