Prestressed Floors

Standard depths available: 120mm, 150mm, 170mm, 200mm and 250mm
Standard widths: 1 200mm
Non-standard widths: In 100mm increments
Min. concrete strength at detensioning: 35mPa for 120mm, 150mm, 170mm and 200mm deep slabs,
40mPa for 250mm deep slabs
Min. concrete strength at 28 days: 50mPa
Suggested max. span/depth ratio: L/50
Prestressing wire type: 5mm dia. triple indented low relaxation wire
Prestressing strand type: 9,53mm dia. stabilized strand
12,5mm dia. stabilized strand
Suggested bearings: On brickwork – 100mm
On steel – 75mm
On concrete – 75mm
Fire rating: 1 hour standard. Higher ratings are possible.

SELF WEIGHT AND FINISHES – Weight – Kg/m2

Depth of Slab

120mm

150mm

170mm

200mm

250mm

Slab only

222

253

275

306

358

Slab and Joint

237

270

292

328

383

Slab, Joint & 40mm levelling screed

337

370

392

428

483

The above self weights of the various slab depths are 30% lighter than an in-situ slab of a similar depth.
Prestressed slabs achieve longer spans than in-situ concrete of a similar depth. This achievement is attributed to high strength concrete and prestressed wire and strand.

No propping is required. Only a 40mm leveling screed is required over the slab.
Echo Prestress may be specified with cantilevers by incorporating reinforcing into the hollow cores which are grouted in the factory during the casting process.

Where Echo Prestress is used as roof slabs or balconies, a minimum Ref. 100 mesh is required in the insulating screed over the panels, as well as a slip joint on the walls. On indoor areas where tiles are specified a minimum Ref. 100 mesh is required in the screed. Expansion joints are required in tiled areas. All unfinished areas also require the same mesh. Refer to the detailed screeding specifications.

typical-slab-layout-echoprestress

SECTIONAL INFORMATION

Cross section area

102,365 10e3mm2 Conc. 28 day strength 50N/mm2

Moment of inertia

154.393 10e6mm4 Conc. strength at transfer 35N/mm2

Section modulus top

2,549 10e6mm3 Mod. of elasticity of conc. 34kNm/m2

Section modulus bottom

2,598 10e6mm3 Stressing of strand/wire

70%

Total breadth of webs

468mm Check: stresses at transfer O.K.

Centroidal axis from bottom

32,5mm Cover to steel 30,0mm
Core cover 25,0mm

STRUCTURAL INFORMATION

Moment & Shear Capacities

Wiring Pattern

B

C

D

E

Service moment

20,66kNm/m

24,83kNm/m

27,44kNm/m

31.10kNm/m

Ultimate moment

28,14kNm/m

37,73kNm/m

43,25kNm/m

50.38kNm/m

Ultimate shear resistance

99,56kN

104,75kN

107,06kN

109.39kN


STANDARD WIRING PATTERNS

B = 12 x 5mm wires C = 9 x 5mm wires + 3 x 9.53mm strand
D = 7 x 5mm wires + 5 x 9.53mm strand E = 4 x 5mm wires + 8 x 9.53mm strand

LOAD CAPACITY TABLE

Note: Span=Clear span +100mm

Live Load
kN/m2

Wiring Pattern / Span

B

C

D

E

Span

Span

Span

Span

0,75

5,5

6,2

6,5

6,8

1,5

5,1

5,7

6,0

6,4

2,5

4,6

5,2

5,5

5,9

4,0

4,1

4,7

4,9

5,2

5,0

3,8

4,4

4,6

4,9

7,5

3,3

3,9

4,1

4,3

10,0

3,0

3,5

3,7

3,9

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m2.


CROSS SECTIONAL DIMENSIONS

prestressed-concrete-design-120mm

SECTIONAL INFORMATION

Cross section area

117.248 10e3mm 2 Conc. 28 day strength 50N/mm2

Moment of inertia

286.517 10e6mm4 Conc. strength at transfer 35N/mm2

Section modulus top

3.790 10e6mm3 Mod. of elasticity or conc. 34kNm/m2

Section modulus bottom

3.851 10e6mm3 Stressing of strand/wire 70%

Total breadth of webs

468mm Check: stresses at transfer O.K.

Centroidal axis from bottom

32,5mm Cover to steelCore Cover 30,0mm25,0mm

STRUCTURAL INFORMATION

Moment & Shear Capacities

Wiring Pattern

B

C

D

E

F+2

Service moment

29,94kNm/m

36,03kNm/m

39.83kNm/m

45.15kNm/m

51.51kNm/m

Ultimate moment

38.50kNm/m

52.60kNm/m

61,64kNm/m

73,53kNm/m

86.03kNm/m

Ultimate shear resistance

121.83kN

128.35kN

131.28kN

134.27kN

141.47kN


STANDARD WIRING PATTERNS

B = 12 x 5mm wires C = 9 x 5mm wires + 3 x 9.53mm strand
D = 7 x 5mm wires + 5 x 9.53mm strand E = 4 x 5mm wires + 8 x 9.53mm strand
F +2 = 12 x 9.53mm + 2x5mm wire (top)

LOAD CAPACITY TABLE

Wiring Pattern

Live Load
kN/m2

B
Span

C
Span

D
Span

E
Span

F+2
Span

0,75

6,2

7,2

7,6

7,8

8,6

1,5

5,7

6,7

7.0

7,5

8.0

2,5

5,2

6.1

6,5

6,9

7.4

4,0

4,7

5,5

5,8

6.2

6,6

5,0

4,4

5,1

5,5

5,8

6.2

7,5

3,8

4,5

4,8

5.2

5,5

10,0

3,5

4,0

4,4

4,7

4,9

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m 2 .
Span=clear spam +100mm

CROSS SECTIONAL DIMENSIONS

prestressed-concrete-design-150mm

SECTIONAL INFORMATION

Cross section area

126.715 10e3mm2 Conc. 28 day strength 50N/mm²

Moment of inertia

403.072 10e6mm4 Conc. strength at transfer 35N/mm²

Section modulus top

4.715 10e6mm3 Mod. of elasticity of conc. 34kNm/m²

Section modulus bottom

4.770 10e6mm3 Stressing of strand/wire 70%

Total breadth of webs

468 Check: stresses at transfer O.K.

Centroidal axis from bottom

32,5mm Cover to steel
Core Cover
30,0mm
25,0mm

STRUCTURAL INFORMATION

Moment & Shear Capacities

Wiring Pattern

B

C

D

E

F+2

Service moment

36.40kNm/m

44.06kNm/m

48.68kNm/m

55.16kNm/m

62.91kNm/m

Ultimate moment

45.53kNm/m

62.35kNm/m

73.27kNm/m

88.72kNm/m

105.60kNm/m

Ultimate shear resistance

136.4kN

143.34kN

146.73kN

150.21kN

158.407kN


STANDARD WIRING PATTERNS

B = 12 x 5mm wires C = 9 x 5mm wires + 3 x 9.53mm strand
D = 7 x 5mm wires + 5 x 9.53mm strand E = 4 x 5mm wires + 8 x 9.53mm strand
F+2 = 12 x 9.53mm strand + 2 x 5mm wires (top)

LOAD CAPACITY TABLE

Note: Span=Clear span + 100mm

Wiring Pattern

Live Load
kN/m2

B
Span

C
Span

D
Span

E
Span

F+2
Span

0,75

6,7

7,8

8,2

8,7

9,3

1,5

6.1

7,2

7.6

8,1

8,7

2,5

5,6

6.5

7,0

7,5

8,0

4,0

5.0

5,9

6.3

6,8

7,2

5,0

4,7

5,5

6,0

6,4

6,8

7,5

4,2

4,8

5,3

5,6

6,0

10,0

3,7

4,4

4,7

5,1

5,5


Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m ² .

CROSS SECTIONAL DIMENSIONS

170mm1

SECTIONAL INFORMATION

Cross section area

141.325 10e3mm2 Conc. 28 day strength 50N/mm²

Moment of inertia

626.385 10e6mm4 Conc. strength at transfer 35N/mm²

Section modulus top

6.240 10e6mm3 Mod. of elasticity of conc. 34kNm/m²

Section modulus bottom

6.287 10e6mm3 Stressing of strand/wire 70%

Total breadth of webs

468mm Check: stresses at transfer O.K.

Centroidal axis from bottom

32,5mm Cover to steel
Core Cover
30,0mm
25,0mm

STRUCTURAL INFORMATION

Moment & Shear Capacities

Wiring Pattern

B

C

D

E

F+2

Service moment

46.48kNm/m

55.79kNm/m

61.61kNm/m

69.76kNm/m

80.64kNm/m

Ultimate moment

55.47kNm/m

76.98kNm/m

90.73kNm/m

110.80kNm/m

137.75kNm/m

Ultimate shear resistance

157.61kN

166.63kN

170.77kN

175.07kN

184.22kN


LOAD CAPACITY TABLE

Note: Span=Clear span + 100mm

Live Load
kN/m2


kNm/m2

B
Span

C
Span

D
Span

E
Span

F+2
Span

0,75

7,2

8,4

9,0

9,6

10,3

1,5

6,6

7,8

8,4

8,9

9,6

2,5

6,1

7,1

7,8

8,3

8,9

4,0

5,5

6,4

7,0

7,5

8,0

5,0

5,1

6,0

6,6

7,1

7,6

7,5

4,5

5,3

5,8

6,3

6,7

10,0

4,1

4,8

5,2

5,7

6,1

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m².

CROSS SECTIONAL DIMENSIONS

200mm

SECTIONAL INFORMATION

Cross section area

165.675 10e3mm2 Conc. 28 day strength 50N/mm2

Moment of inertia

1143.163 10e6mm4 Conc. strength at transfer 35N/mm2

Section modulus top

9.137 10e6mm3 Mod. of elasticity of conc. 34kNm/m2

Section modulus bottom

9.154 10e6mm3 Stressing of strand/wire 70%

Total breadth of webs

468mm Check: stresses at transfer O.K.

Centroidal axis from bottom

34,5mm Cover to steelCore Cover 30,0mm25,0mm

STRUCTURAL INFORMATION

Moment & Shear Capacities

Wiring Pattern

C

D

E

G+2

H+2

J+4

Service moment

77.07 kNm/m

85.03 kNm/m

96.27 kNm/m

118.87 kNm/m

127.18 kNm/m

141.96 kNm/m

Ultimate moment

101.17 kNm/m

119.86 kNm/m

147.01 kNm/m

205.42 kNm/m

227.22 kNm/m

263.67 kNm/m

Ultimate shear resistance

204.44 kN

211.64kN

217.16 kN

235.08 kN

238.96 kN

252.03 kN

STANDARD WIRING PATTERNS

C = 9 x 5mm wire + 3 x 9.53mm strand D = 7x 5mm wire + 5 x 9.53mm strand
E = 4 x 5mm wires + 8 x 9.53mm strand G+2 = 10 x 9.53mm strand + 2 x 12mm strand + 2 x 5mm wires (top)
H+2 = 8 x 9.53mm strand + 4 x 12.5mm strand + 2 x 5mm wires (top) J+4 = 4 x 9.53mm strand + 8 x 12.5mm strand + 4 x 5mm wires (top)

LOAD CAPACITY TABLE

Span = clear span + 100mm

Wiring Pattern

Live Load
kN/m2

C
Span

D
Span

E
Span

G+2
Span

H+2
Span

J+4
Span

0,75

9,2

10,0

10,8

12,0

12,4

13,0

1,5

8,6

9,4

10,1

11,2

11,6

12,2

2,5

7,9

8,6

9,4

10,4

10,8

11,4

4,0

7,2

7,8

8,5

9,5

9,8

10,4

5,0

6,8

7,4

8,1

9,0

9,3

9,8

7,5

6,0

6,5

7,2

8,0

8,3

8,8

10,0

5,5

5,9

6,6

7,3

7,6

8,0

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m 2 .

CROSS SECTIONAL DIMENSIONS

250mm

Applications of the concrete slabs in conjunction with structural steel.

typical-sections-8-picslr

Service holes of up to 90mm may be made in the panels on site. Any service holes larger than 90mm should be referred to the design engineer. It is very easy to make holes up to 90mm diameter by hand in the hollow core of the slab as the concrete thickness is a maximum 30mm. The holes can be made in the slab after they have been erected in position.

  • Larger cut-outs can be formed in the factory. These holes require more specific strengthening, but can be catered for at the design stage.
  • Skylight and stair openings are formed by specifically fabricated steel hangers which are supplied and erected by Echo Prestress. Alternatively a steel, brick or concrete beam can be used as support around the opening.
  • The tops of the hollow cores can be opened to take steel when the units are used in composite action with steel or concrete beams.
  • Skew ends can be cut in the factory with a diamond tipped saw blade specifically manufactured to accurately cut any angle.

34

open2-300x201open-300x201open1-300x201

Fitting of downlights is as simple as coring holes through the hollow core of the slab or using a hammer and chisel (recommended chiseling from the underside) to form the required diameter hole to accommodate the downlight.

For suspended or other light fittings, simply drill a hole through the slab and into the slab’s hollow core to fit the electrical wiring through.
Any excessive edge chipping is easily repaired with ‘Rhinolite’ or similar material.

Costs of such electrical light points also become more economical as electrical wires and single light transformers can be placed into the horizontal hollow cores of the slabs the day after installation, instead of the traditional light boxes and conduits.

cross-section-of-downlight-hr

downlights-300x164downlights1-300x164

Clear, level and sound access up to and around the building on which the slabs are to be erected. In order to obtain a flush ceiling on brickwork the load bearing walls must be level. Avoid internal walls being higher. If brickwork is not level a mortar bed will be required on top of the brickwork.

As the panels are designed and manufactured specifically for your project, site dimensions need to be accurate to avoid delays. Site dimensions are checked by Echo prior to manufacture. Sand and cement for grouting between the Echo panels are to be supplied by the customer. The actual grouting is done by Echo.

Window and door openings in load bearing walls up to 2,0 meters wide can be covered by lintols side by side with five courses of brickwork with brick force in every course for slab spans up to 7 meters. Openings wider than 2 meters must be referred to the engineer for detailing of additional structural steel supports.

site-requirementsite-requirement1

Electrical conduits should be run over the top of the Echo slab with a 40mm river sand and cement leveling screed placed over the top.

finishes

Electrical conduits should be run over the top of the Echo slab with a 40mm river sand and cement leveling screed placed over the top.

  • The underside or soffit of the slab is smooth and does not require plastering.
  • To finish, rake the underside of the joint clean soon after grouting.
  • Trowel a small quantity of Rhinolite or similar into the underside of the joints.
  • Finish to a smooth rounded shape by running a piece of plastic conduit along the joint.
  • N.B. It is not recommended that the joints are plastered closed. (Should you wish to do so, ask Echo for a recommended specification).
  • Apply a bonding liquid to the soffit before applying a textured paint.

finishes1

On contracts where Echo Prestress slabs are used indoors a simple 40mm levelling screed is all that is necessary. In buildings with a larger area, adequate movement joints should be specified by the Consulting Engineer.

APPLICATION OF SCREED

All loose material is to be removed from the tops of the slabs. The slabs should be thoroughly wetted and screed applied immediately. The levelling screed should comprise a 1:4 mix by volume of cement and clean river sand. Water should be added to the mixture to an extent that the mixture is relatively dry but remains easy to float finish. The screed should be laid to an approximate thickness of 40mm. Note that in some areas additional screed may be necessary to level out the camber in the units. After laying the screed it should be steel floated and then wetted for 48 hours to prevent shrinkage cracks.

In certain areas, namely balconies, roofs, walkways, tiled areas, car parks and areas where the screed is to be left unfinished, the screed specifications change slightly. On balconies, roofs, walkways etc., i.e. all areas where Echo Prestress slabs are exposed to the elements – a Ref. 100 mesh* must be placed in the leveling screed to counteract the transverse forces created by large temperature differences.

Where tiles are to be used on the slab, a Ref. 100 mesh* must be placed in the levelling screed as for balconies, roofs and walkways. Expansion joints should be allowed in the tiles every 3 metres and particularly where the section alters shape such as doorways. It is recommended that a flexible tile adhesive be used. TAL (Pty) Ltd. have produced a technical specification for tiling on Echo slabs which is available on request from Echo Prestress.

On car parks a Ref. 193 mesh** must be placed in a structural topping of not less than 50mm thickness to help spread the load from one panel to the next. The screed can be left rough to suit the clients requirements.

In areas with exposed screed a Ref. 100* mesh is required to control shrinkage/drying stresses. These areas would also require adequate movement joints.

Where the screed thickness is 50mm or less the mesh should be laid flat on top of the slab and the screed placed on top. Where the screed depth exceeds 50mm the mesh should be placed 20mm from the top surface of the screed.

Providing the above procedures are followed, the screed will adhere extremely well to the prepared surface of the slab. Experience has shown that it is impossible to remove the leveling screed from the top surface of the slab after a few days.

* A ref. 100 mesh is a 4,0mm wire in a square pattern at 200mm centres.
** A ref. 193 mesh is a 5,6mm wire in a square pattern at 200mm centres.

Specifications for the following are available from Echo prestress on request:

  • The tiling of Echo Prestressed slabs
  • Grouting between joints (generally undertaken by Echo Prestress)
  • Structural toppings to enhance the slab capacity
  • Methods of finishing Echo Prestress slabs

The Cement and Concrete Institute (Tel. 011 315 0300) have produced a standard specification for sand/cement screeds and concrete toppings for all types of floors. Request a copy from Echo Prestress.

composite

The term ‘composite’ refers to structures where Echo Prestress slabs and in-situ concrete work together to form an integral structural component.

The Echo Prestress slab can be made composite with the supporting beams to increase the overall structural depth of the supporting beams. Echo Prestress has pioneered the use of Prestressed concrete panels utilizing composite action between the support beams and the slab construction. Echo Prestress have a versatile approach in that various schemes may be proposed using Prestressed Hollow Core slabs in conjunction with the following:

  • Reinforced precast beams supplied by Echo
  • Cast in-situ reinforced, prestressed or post tensioned beams.
  • Structural steel framework with shear connectors welded to the beam to provide composite action.
  • Mixed Use – Load bearing masonry perimeter walls with internal in-situ columns and precast beams in composite action with Echo Prestress slabs.

DESIGN SYNOPSIS

As in any composite structure, the design principal is to bond separate elements together to form one element which by virtue of shear interaction, is considerably stiffer than the two elements acting independently.

In the case of Prestressed Hollow Core concrete panels and concrete support beams this shear interaction is provided by steel stirrups projecting above the surface of the beam and transverse shear steel, which facilitates the transfer of the forces between the slab and the beam.

Structural steel beams are provided with shear connectors on the top flange in the form of channels or welded studs to provide the shear interaction.

The support framework is generally designed to support the loads imposed by the Prestressed Hollow Core floor panels and a nominal construction loading with or without the use of props, depending on the budget. Provision is made for continuity steel in the slab across the support beams to accommodate the increased mass imposed by finishes, partitions and super- imposed loading.

precast