АLGASLAB SOLUTIONS FOR POST-TENSIONED SLABS

ANTISEISMIC DEVICES | BEARINGS | EXPANSION JOINTS | POST TENSIONING SYSTEMS | STRUCTURAL REPAIR AND MAINTENANCE

Re-development of Michelin complex ex-area, Trento - Client: Trento Futura S.c.a.r.l.

Alga solutions for post-tensioned slabs Technical evolution in the construction of post-tensioned slabs has been successfully developed over the recent years by incorporating post-tensioned tendons increasing design performance of the structures. The use of post-tensioned cables in slabs has many direct and indirect advantages:

Direct - Increased span relatively with slab loading - Increased loading relatively with slabs span - Reduction of slabs thickness - Reduction of slabs reinforcement - Reduction of slabs deformability

EXPANSION JOINT

SAVING AREA

HEIGHT REDUCTION

SAVING OF EXCAVATION

WITHOUT EXPANSION JOINTS 60m 60m TYPICAL STRUCTURE WITH REINFORCEMENT STRUCTURE WITH POST-TENSIONED CABLES

Indirect - Reduction /elimination of the expansion joints - Reduction /elimination of concrete cracks due to reactions of tensioning, increasing durability of structures - Reduction of columns number - Reduction of the vertical loads and foundation size - Reduction of the seismic mass - Quick removal of formwork - Increased effectiveness of sealing (cracks restraint) The cables can be used for any type of construction such as small buildings, office facilities having large span slabs, parking areas at malls, even small or large industrial facilities. The post-tensioning system can be adopted to meet the demands of high performance slab design. Two possible solutions can be adopted: bonded strand cables or un-bonded cables (also called sliding cables). 1. The solution of bonded cables provides the placement of cables inside steel corrugated sheaths installed in the slab before casting. After the completion of tensioning process, the sheaths are grouted using cement grout made of cement, water and suitable additive as per approved design mix grout. 2. The solution of un-bonded cables is utilizing greased and polyethylene (PE) coated strands by means of a polyethylene sheath surrounding the strand having thickness of about 1.5 mm. The filling of voids with grease between strand and sheath, ensures an adequate protection against atmospheric conditions. The PE cables are placed directly in the slab before casting. The selection of the type of strand cables (bonded or un-bonded) depends on the demands of the design approach.

Post-tensioning of slabs: Centered post-tension: the cables are placed in the mid of the section obtaining a uniformly compression. This type of solution is used in order to restrain the effects of concrete shrinkage, the cracks due to thermal variations (i.e. large industrial slabs with under floor heating) or even to reduce the joints of industrial pavements and increase the resistance to bending. Post-tension with elevation geometry profile variations: commonly adopted solution for post-tensioned beams, where the elevation of the cable varies and guarantees a moment of resistance absorbing the effects of bending loads. The dimensioning of post-tensioned slabs may provide different design approach according to customer’s requirements. One side or both sides tensioning can be utilized. The permanent or accidental loads can be compensated totally or partially only. The solutions are very flexible and can meet any technical requirement. Alga provides post-tension cables for cast-in-situ slabs. The anchorages proposed by Alga ranges from single-strand (monostrand) anchorages to multi-strands anchorages. Alga slab tendons are proposed in both versions with bonded or un-bonded strands. All anchoring systems are tested in accordance with the current and valid norms and approved as per European legislation ETAG013. Alga’s anchorages are applicable for the use of strands diameter ranging from 0.5’’ to 0.6’’S as per below tables.

BARE STRAND (BONDED) 

Diameter

Norm

Nominaldiameter

[mm]

Nominal Area

[mm2]

fptk [N/mm2]

fp(1)k [N/mm2]

Weight [kg/m]

Breaking load [KN]

T13 EN 10138 12,5 93 1670 1860 0,73 173

T13S EN 10138 12,9 100 1670 1860 0,785 486

T15 EN 10138 15,2 140 1670 1860 1,09 269

T15S EN 10138 15,7 150 1670 1860 1,172 279

T15C EN 10139 15,2 165 1670 1860 1,29 307

UN‐BONDED STRAND WITH PE DUCT & GREASE 

Diameter

Norm

Nominal diameter

[mm]

Nominal diameter with sheath thickness

1,5mm

Nominal- Area [mm2]

fptk [N/mm2]

fp(1)k [N/mm2]

Weight[kg/m]

Breaking load [KN]

T13 EN 10138 12,5 16 93 1670 1860 0,83 173

T13S EN 10138 12,9 16,4 100 1670 1860 0,89 486

T15 EN 10138 15,2 18,7 140 1670 1860 1,21 269

T15S EN 10138 15,7 19,2 150 1670 1860 1,305 279

T15C EN 10139 15,2 18,7 165 1670 1860 1,41 307 SINGLE-STRAND TENDONS (MONOSTRAND) The single strand tendon (monostrand) consist of a cast-iron element (anchorage) having an internal conical shape for nesting the strand locking wedge and a proper shape to transfer the tension loads into concrete. The anchoring unit is equipped with accessories for the proper connection between sheath and anchorage by ensuring also strand’s protection.

Two holes for fixing purposes of casting units to the formwork are foreseen ensuring recess proper casting and allowing tensioning operations. The fixed anchoring is usually achieved by locking the wedge inside the conical shape of casting unit and sealing the strand using a screwed protective cap.

Single strand fixing detail in formwork Preassembled cables having a fixed head 

Cables prior of casting Single strand cables prior of tensioning

g asso

97

35,5

70

A

G1

G

2

B

G

SINGLE-STRAND (MONOSTRAND) ANCHORAGE (type 1F13 / 1F15)

LIVE ANCHORAGE DEAD ANCHORAGE water-tight connection

filling mortar

protective cap

connecting tube

coupler

locking wedge

spring

grease 144

22

47 64

cup for recess

130 STRESSING ANCHORAGE (type F)

injection tube

cast-iron unit 50

70 in aggressive environment

MULTISTRAND CABLES PREFABRICATED WITH FIXED PRE-ASSEMBLED ANCHORAGE  Multi-strands cables consist of a cast-iron element (anchorage) having internal conical shapes for nesting the strand locking wedges and a proper shape to transfer the tension loads into concrete. The anchoring unit is equipped with accessories for the proper connection between sheath and anchorage by ensuring also strand’s protection. Two holes for fixing purposes of casting units to the formwork are foreseen ensuring recess proper casting and allowing tensioning operations. All the anchorages are available in types for use with bonded strands.

 

cup for recess

coupler

C H

flat duct

A 3F

A 4F

A 5F

DIMENSIONS A B

C

G

H G1 X G2

A 3F 13 85 180

163

95

190 58 X 21

A 4F 13 85 230

163

95

240 58 X 21

A 5F 13 85 270

163

95

280 75 X 21

A 3F 15 85 190

163

95

200 58 X 21

A 4F 15 90 230

163

100

240 75 X 21

A 5F 15 95 270

163

105

280 91 X 21

                         grease 

AN

CH

OR

AG

E

A

NC

HO

RA

GE

DIMENSIONS

A

B

C G H

A 3F 13

85

180

163 95 190

A 4F 13

85

230

163 95 240

A 5F 13

85

270

163 95 280

A 3F 15

85

190

163 95 200

A 4F 13

90

230

163 100 240

A 5F 13

95

270

163 105 280

L1

T13

: 15

0 / 2

00 /

250

B

100

T

15:

225

/ 300

/ 3

75

A

G

ANCHORAGES FIXED (type NE) ANCHORAGES FIXED (type G)

injection pipe injection pipe

strand’s grip

connection

sealant

flat duct

bulb

connection

sealant

flat duct

300 / 300 / 400 W

950 W

Steel plate

80 80

55 55 55 55 55 55 55 55

260

260

Values of L1 & W are only for anchorages of 3, 4 & 5 strands respectively

MULTI-STRAND ANCHORAGES (type F)

filling mortar

A 3F

A 4F

70 in aggressive environment

fixing plate

H

A 5F

slab formwork recess

filled with grease

sealant

grease

Multi-strand tendons

Anchorages fixed in the formwork properly forming recess   

Tendons arrangement inside formwork prior of casting

Cables over-length required for tensioning

Tensioning of strand cables using a monostrand jack 

 

Head Office Alga S.p.A. +39 02 485691 www.alga.it - alga@alga.it tel. +39 02.48569.1 fax. +39 02.48569.245 Via dei Missaglia 97/A2 20142 MILANO Italy

Workshop Alga S.p.A. +39 0383 892931 | montebello@alga.it Via per Lungavilla, 43 27054 MONTEBELLO DELLA BATTAGLIA (PV) Italy Printed 5.2011