2003 2003

DESIGN OF PRECAST CONCRETE

BUILDING STRUCTURES

PRECAST FLOORS

2003 2003

Types precast floorsFloor type Span Height Width kN/m

9 m 100 - 300 mm 300 - 1200 mm 2.0 - 4.0

20 120 - 550 1200 2.0 - 4.8

24 (30) 200 - 800 2400 2.0 - 5.0

9 150 - 300 600 1.5 - 3.5

6 100 - 250 300 - 600 0.7 - 3.0

7 100 - 200 600 - 2400 2.4 - 4.8

7 200 - 300 - 1.8 - 2.4

2003 2003

Totally precast floors

Hollow core floorsExtrusion or slipform

production processes

Smooth soffit

Low self-weight

2003 2003

Totally precast floors

Ribbed floors

Prestressed concrete

High load bearing capacity

2003 2003

Totally precast floors Roof elements

Large spans

Light weight due to

slender cross-sections

Different types of elements

2003 2003

Partially precast floors

Floor- plate floors

Semi-prefabricated floor system

Plain or ribbed floor-plates

Propping normally needed

during construction

2003 2003

Partially precast floors

Beam and bloc floors

Blocs are placed between

prefabricated joists, and filled

wit a cast in-situ topping

Blocs are available in

different mateials

2003 2003

Precast stairs Straight stairs

Round or helicoidal stairs

Individual flights and landings, or

combined flights and landings.

Surface finishing in smooth concrete

or polished terrazzo.

2003 2003

Modulation Basic module normally 300 mm

Common widths: 600, 1200,2400 mm

Large flexibility in floor layout

Floor span not necessarily

in the same direction

Changes in floor level or thickness

Match plate allow to Wide floor beam enables plain ended

accommodate floor width floor units and free modulation

2003 2003

Design precast floor elements

Hollow core slabsShear capacity

ctdcp

wc f + f

S

b I = V

2ctdRd,

d b ] 0,15 + )f (100k [0,12 = V w3/1

ckRd, cpc

2003 2003

Design precast floor elements

Hollow core slabs

Punching resistance

is function of slab

cross-section and

presence of topping

Allowable punching resistance for extruded HC slabs type Variax without

topping

Slab type 50mm 100 mm 200mm

150/200 20 kN 30 kN

270 40 kN 60 kN

320/400 45 kN 65 kN

500 60 kN 80 kN

2003 2003

Design precast floor elements Beam-bloc floors

Semi-bearing beams and non-

resisting polystyrene blocs

Floor ready for topping casting

Semi-bearing beams and

semi-resisting blocs

Semi bearing beams and Types of joists resisting blocs

Transverse

reinforcement

2003 2003

Design of the whole floor

The essential objectives are:

Structural integrity

Distribution of horizontal forces

Transverse distribution of concentrated loading

2003 2003

Structural integrity Tying system

Minimum proportioning of ties

(L1 + L2) / 2 x 20 kN/m 70 kN 70 kN L1 / 2 x 20 kN/m 70 kN

20 kN / m

l1

l2

l3

2003 2003

Diaphragm action Tensile reinforcement from in-plane bending taken up by

peripheral ties

Shear forces along the joints max. 0.10 N/mm for smooth surfaces and 1.5 N/mmfor rough surfaces

2003 2003

Concentrated loading

Transverse load distribution

Longitudinal joints take up vertical shear forces

No lateral displacement of joints

Structural topping is alternative solution

Joint profiles hollow core slabs TT-slabs with structural topping

Anchorage bar welded

to steel plate

TT-slab Welded jointStructural

topping

2003 2003

Determination load distribution Test hollow core slab floor

Deflections of the 6 slabs of a 6.00 m span floor,

with concentrated loading at the centre of the floor

Loading

Mid span deflections at

successive loading steps

Measuring devices

HC slabs

2003 2003

Determination load distribution Test hollow core slab floor

Deflections of the 6 slabs of a 6.00 m span floor,

with concentrated loading in the middle the edge slab

Loading

HC slabs

Mid span deflections at

successive loading steps

Measuring devices

2003 2003

Determination load distribution

Example load distribution factors for 1.20 m wide hollow core floor units

for points loads in the center area of 5 floor elements

2003 2003

Determination load distribution

Beam - bloc floors

Load distribution factors for composite beam -bloc floors

2003 2003

Cantilevers

Cantilevering hollow core slabs

Only small direct cantilevering possible

Maximum

2.00 m

Structural topping

with cantilever

reinforcement

Topping anchored in

casted open sleeve

2003 2003

Balconies

Balcony fixing without cold bridges

Balcony along longitudinal

edge of hollow core floor

Balcony in prolongation of

hollow core slabs

Steel strut to take

compressive forces

across joint

Cantilever

reinforcement

2003 2003

Connections

Support length

Nominal values support length for initial stage of projects

Supporting Hollow core Ribbed units Floor plate Beam - bloc

structure 120 - 400 mm low - heavy floors floors

loading

Reinforced concrete 70 - 130 75 - 150 70 100

or steel girders

Brick masonry 100 - 150 - 100 125

2003 2003

Connections Hollow Core floors Tie arrangements at support

Anchorage of connecting tie-bars

in hollow core floors

Tie bar also possible

though hole in beam

Connecting bars in cast

cores, but also possible

in longitudinal joints

2003 2003

Connections Hollow Core floors

Lateral joints

Reinforcement in recesses

at the edge of hollow core units

Openings in top of

hollow core units

Connecting

reinforcement

projectingnt

from wall

2003 2003

Connections Hollow Core floors

Steel girders

Examples of hollow core floors supported on steel beams

2003 2003

Connections TT-floors

Support connectionsHalf jointsenable to reduce

construction height.

Welded connection only at top

face to avoid restrainment

Neoprene pad

2003 2003

Connections TT-floors

Lateral jointsIt is advisable to allow for slight

deflection of TT-unit under

variable loading

Threaded reinforcement bar

connected to socket in wall

Welded connection between

TT-unit and faade element

welded steel

plate

embedded steel

plates

Cast-in socket

Structural topping

2003 2003

Openings and cut-outs

Hollow core slabs

Small openings are formed

during production of the units

Large voids are trimmed using

transverse supports such as steel

angles or trimmer concrete beams

Example of possible dimensions

2003 2003

Openings and cut-outs

Ribbed elements

Holes are formed in the top flange

in-between or outside the webs.

Horizontal holes are also possible

through the webs, above the

prestressing tendons.

Example of possible openings in TT-units