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CONTENTS
1. General page 3
2. Specifications and designparameters page 4
3. Information required for designof POT bearings page 5
4. Dimensions data sheets
- POT bearing type PU page 6
- POT bearing type PL page 7
- POT bearing type PF page 8
5. Accessories page 9
6. Site installation page 10
7. POT bearings for incrementally
launched bridges page 11
8. Special POT bearings page 12
9. Recent bridge structures page 13
10. Quality control and tests page 15
2
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Structural bearings are required to connect different parts
of a structure such as bridge decks to piers and
abutments. The most widely-used structural bearings
are plain or reinforced elastomeric bearings, and POT
bearings. They are capable of transmitting forces while
absorbing the structures deformations and rotations.
The strength of reinforced elastomeric bearings is limited
by the shear properties of the elastomeric block,
especially when the three stresses, compression, shear
and bending, occur at the same time. POT bearings
maximise the shear strength of the bearings elastomer
by encasing it in a steel cylinder. They can accept working
loads in the elastomer, which, in turn, allows the
bearings dimensions to be reduced.
POT bearings are divided into three main types,
depending on restrictions to the structures
deformations: type PF (fixed), type PL (free or unguided
sliding), and type PU (guided sliding).
In all types, under vertical load, the upper plate acts on
the elastomer like a piston on a hydraulic cylinder, and
the elastomer itself, perfectly sealed, behaves like a
viscous fluid, offering minimal resistance to rotation
around any horizontal axis. No sliding movement isallowed in type PF (fixed).
Type PL (free sliding) is obtained by dividing the upper
plate into two independent elements: rectangular sliding
plate and circular piston. The sliding ability is achieved
by combining the following three materials into the
sliding system:
v ILM bridge pot bearing type
- Polished stainless steel (mirror finishing) welded
to the bottom side of the rectangular sliding plate.
- Circular dimpled PTFE disc recessed to half of its
thickness in the piston. Minimum protrusion is given
to grant full contact with stainless steel at any time.
PTFE displays excellent resistance to fatigue, impact
and ageing.
- Special lubricant grease: silicone base. This grease
fills the dimples in the PTFE disc ensuring a permanent
very low friction system coefficient and preventing
abrasion of PTFE.
The combination of these three materials gives a regular
range of friction coefficient between 1% and 3%.
Type PU (guided sliding) is obtained by assembling a
guide bar, either welded or bolted, on top of the piston.
The guide bar slides along a longitudinal recess in the
sliding plate, thus avoiding transverse movement.
Contact between guide bar and sliding plate consists of
special composite material (DU-metal) fixed to the guide
bar and stainless steel backed to the sliding plate,
ensuring a minimum friction coefficient.
v Neoprene bearing
3
1. General
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2. Specifications and design parameters
4
BASIC DESIGN PARAMETERS
UPPER PLATE
Load distribution at 60
The length of the upper plate mustgrant a proper load distribution in theconcrete in the event of max. designmovement
L5 = D6 + 2 Ex + 2T5/3+50
Where :
D6 diameter of PTFE discEx Max. design movementT5 Thickness of upper plate
P.T.F.E.
Average allowable stress at SLS undermax. vertical load D1/50>12mm
DOWELS -STUDSIn order to grant a safety factor notless than 1,5 against sliding, thefollowing condition must be verified::
/S*Vmin+n*Hd>Zh
where : = 0.5 Steel-concrete friction coefficientS = 1.5 Safety factorn Number of dowels ( or studs)Hd Shear capacity of each dowel
MATERIALS
STANDARD SPEClFlCATlONS
TOP PLATE
Quality steel St37 or
St52 according to
DIN 17.100
Stainless steel
according to AISI 304
LUBRICANT
Silicone grease type 300
P.T.F.E.
P.T.F.E. pad with dimples accordingASTM D1457-91 a Type 1
Grade 2BS 3764 Grade A
GUIDE
Quality steel St37 orSt52 according to
DIN 17.100
DU-metal
EXTERNAL SEALING
RING
Spongy neoprene
PISTON
Quality steel St37 orSt52 according to
DIN 17.100
INTERNAL SEALING
RING
Double gasket brass ring
ELASTOMER PAD
Natural rubber accordingAASHTO 50Sh+-5
POT (STEEL RING +
BASE PLATE)
Quality steel St37 or
St52 according to
DIN 17.100
ANCHOR SOCKETS
Galvanized bolts
Steel CK35 according
DIN 17.200
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It should be pointed out that the cost of the POT bearings
varies with the changes in design parameters. Forinstance the allowable bearing pressure on the concrete,
has a maj or influence. It depends on the characteristic
concrete strength, Br and the relation between the
diameters of direct circular loaded area (D2) and circular
enlarged area, with the same centre of gravity, lying totally
within the top support area (D) (see figure). The following
design rules are proposed for the allowable bearing
pressure on concrete :
5
3. Information required for the design of POT bearings
Dimensions given in the section 4 tables are indicative,
representing a presizing of the three different types of POT
bearings. They are given to make the design engineers
work easier and should be used with caution, bearing in
mind that they are calculated from the following assumed
design parameters:
Allowable concrete pressure
Pier : 20 N/mm 2 Deck : 20 N/mm2
Rotation = 0.01 rad.
Loads and movements
1.- Free sliding type PL
1.1 Hxmax= 3 % of Vmax.
1.2 Hymax = 3% of Vmax.
1.3 Ey= +- 10mm.
1.4 Ex= * 50mm.
2.- Guided sliding type PU
2.1 Hxmax= 3 % of Vmax
2.2 Hymax = 5% of Vmax
2.3 Ey= 0 always
2.4 Ex= +- 50mm.
3.- Fixed type PF
3.1 Hxmax = 5% of Vmax
3.2 Hymax = 5% of Vmax
3.3 Ey= 0 always
3.4 Ex= 0 always
4.- For every type
4.1 Vg = 70% Vmax
4.2 Vmin = 50% Vmax
4.3 Hxg = 90% Hxmax
4.4 Hyg = 90% Hymax
4.5 Hxmin = 70% Hxmax
4.6 Hymin = 70% Hymin
Our Technical Department is at your disposal to supply any
specific information in order to assist you from the early
design stage. To assess the optimum POT bearing
dimensions for your application and to carry out a detailed
design, we need the following information:
Project: Bearing type :
Loads:
Load c as e Vmax.
Vmax: kN Hx: kN Hy: kN
Lo ad c as e Vg. ( pe rmane nt l o ad)
Vg: kN Hxg: kN Hyg: kN
Load c as e Vmin.
Vmin: kN Hx: kN Hy: kNRotation and movement :
Ex+-: mm. Ey +-: mm. Rotation: rad.
AllowablebearIng pressure on concrete :
Pier : MPa Deck : MPa
1 .- For direct distribution from the pot to the concrete:
b= Br* D < 1, 4 *Br
1, 8 D2
2.- For distribution plates through masonry plates
between pot and concrete:
b= Br * D < 1, 0*Br
2, 1 D2
3.- For distribution through sliding plates:
b= Br* D < 0, 9 *Br
2, 3 D2
Bursting reinforcement to be designed in SLS for a total
force of:
with the allowable stress in reinforcement between
18 0 MPa and 200 MPa according to the steel grade.
v Technical departement in the factory
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4. Dimensions data sheets
6
POT bearing type PU
This type of bearing :
- Allows longitudinal movements
- Constrains transversal movements
- Bears horizontal transversal loads
BEARING TYPE
PU-100PU-200
PU-300PU-400
PU-500PU-600
PU-700
PU-800PU-900
PU-1000PU-1200
PU-1400PU-1600
PU-1800PU-2000
PU-2400PU-2800
PU-3000
PU-3500PU-4000
PU-4500PU-5000
TH
8 08 1
8 58 4
9896
102
106119
115122
131198
154153
16118 0
170
192190
196216
L5
393478
538608
665719
768
8 148 57
8 98975
10451110
11711229
13371436
1515
15931705
17931885
B5
293378
438508
565719
768
8 148 57
8 98975
10451110
11711229
13371436
1515
15931705
17931885
oD2
293378
438508
565619
668
714757
7988 75
9451010
10711129
12371336
1415
14931605
1693178 5
DP
256316
360408
450501
536
568599
62868 2
732778
8 218 62
9381008
1064
11201199
12601325
DL
200200
200250
250300
300
300300
300350
350350
350350
350350
350
350350
350350
DM
40
40
4050
5060
60
6060
6070
7070
7070
7070
70
7070
7070
DIMENSIONS IN mmNOTE : The dimensions given in the tables are indicative. Design and dimensions may be modified by CTT without prior notification.
DL
TH
DL
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7
BEARING TYPE
PL-100
PL-200PL-300
PL-400PL-500
PL-600PL-700
PL-800
PL-900PL-1000
PL-1200PL-1400
PL-1600PL-1800
PL-2000PL-2400
PL-2800
PL-3000
PL-3500PU-4000PL-4500
PL-5000
TH
74
798 5
9698
96110
106
119115
122131
136154
153
16118 0
160
17218 6194
216
L5
353
457538
605665
719768
8 14
8 578 98
9751045
11101171
1229
13371436
148 2
159316931793
1885
B5
273
377458
52558 5
63968 8
734
7778 18
8 95965
10301091
1149
12571356
1402
151316161713
1805
oD2
253
357438
505565
619668
714
757798
8 75945
10101071
1129
12371336
1415
151216051693
178 5
DP
228
302360
406450
48 7521
554
58 5613
668717
7648 06
8 47
924994
1050
1118118 41246
1311
DL
150
150200
200200
250250
250
250250
250250
250250
250
250250
250
250250250
250
DM
30
3040
4040
5050
5050
50
5050
5050
5050
50
50
505050
50
DIMENSIONS IN mmNOTE : The dimensions given in the tables are indicative. Design and dimensions may be modified by CTT without prior notification.
POT bearing type PL
This type of bearing :
- Allows longitudinal and transversal movements
- Does not resist any horizontal load (except friction)
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8
POT bearing type PF
This type of bearing :
- Constrains longitudinal and transversal movements
- Bears longitudinal and transversal horizontal loads
BEARING TYPEPU-100
PU-200
PU-300
PU-400PU-500PU-600
PU-700PU-800
PU-900PU-1000
PU-1200
PU-1400PU-1600
PU-1800PU-2000
PU-2400
PU-2800PU-3000
PU-3500PU-4000
PU-4500PU-5000
TH
8 0
8 1
8 5
8 49896
102106
119115
122
131198
154153
161
18 0170
192190
196216
L5
393
478
538
608665719
7688 14
8 578 98
975
10451110
11711229
1337
14361515
15931705
17931885
B5
293
378
438
508565719
7688 14
8 578 98
975
10451110
11711229
1337
14361515
15931705
17931885
oD2
293
378
438
508565619
668714
757798
8 75
9451010
10711129
1237
13361415
14931605
1693178 5
DP
256
316
360
408450501
536568
599628
68 2
732778
8 218 62
938
10081064
11201199
12601325
DL
200
200
200
250250300
300300
300300
350
350350
350350
350
350350
350350
350350
DM
40
4040
505060
6060
6060
70
7070
7070
70
707070
70
7070
DIMENSIONS IN mmNOTE : The dimensions given in the tables are indicative. Design and dimensions may be modified by CTT without prior notification.
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5. Accessories
ANTIDUST SKIRTS
These devices are installed in order to avoid the dust on the sliding parts of the bearing,
that could affect the friction coeficient.
They are recommended either for both free sliding and guided sliding types. They aremanufactured from neoprene strips bolted to the upper plate of the bearing through a
metallic ruler.
v Antidust skirts
RULER MEASURING MOVEMENTS
This device is designed to measure then movements of the bearing, and consequently,
the movements of the deck visually.A metallic or aluminium ruler is connected to the upper plate and a rod is welded, by
means of a support, to the masonry plate or to the pot.
The proj ection of the rod on the ruler indicates the movement of the deck.
Measurement rulerv
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6. Site Installation
10
2. LEVELLING OFTHE BEARING
Place the pot bearing in its position levelling it with
timber wedges. It is important to ensure that the Xaxis of the bearing is aligned in the longitudinal
direction of the bridge and that the X and Ydirections are accurately horizontal. For bearings
allowing horizontal displacements it should bechecked that the arrow painted on the slide plate
is pointing in the correct direction.
1. PREPARATION OF THE PIERS
Build the piers leaving on them the required
recesses according to the dimensions indicatedon the drawings.
w
v
v
v
3. GROUTlNG
Install the form for grouting the space betweenpier and pot bearing. Grout the space between
pier and pot bearing. Fill in the recesses checkingthat the level is the correct.
5. REMOVAL OF FIXING PLATES
Once the formwork has been removed, thebearing is definitively installed. Remove the lateralfixing plates of the bearing in order to allow its
free movement.
4. FORMING OF DECK
The formwork of the deck is placed embeddingthe upper dowels of the bearing.
w
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7. POT bearings for incrementally launched bridges
POT bearings for incrementally launched bridges have a
dual function. First, they provide low friction sliding surfacesover piers as the deck is launched during construction.
Thereafter, they become permanent bearings for the
completed bridge. A POT bearing serving both functions is
shown in the picture above.
During construction, a fixing device avoids relativemovement between sliding plate and pot cylinder.
v POT bearing for ILM bridge
The sliding plate is supplied with a second stainless
steel sheet on top. Inserting neoprene-teflon padsbetween deck and bearings allows the launching
operation to be carried out. Pads, second stainless steelsheet and fixing device are removed after launching. To
achieve this, the deck is lifted by means of hydraulic j acks
placed on top of the piers.
Once this operation is achieved, the deck is lowered toits final position, the j acks are removed and the sliding
plate is connected to a previously embedded steel platein the deck.
Finally, the fixing devices used for transportation are
released, thus the bearing is in its final service position.
For the correct design of these bearings, it is very
important to know the loads during launching, because,they have maj or influence in the actual length and
thickness of the sliding plates.
Although the cost of this type of bearing is higher than
the standard ones, their use represents a saving for thej ob because :
- Temporary launching bearings are not required
- Demolition and replacement of the temporary bearingsby permanent ones, are costly and time consuming
are avoided.
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8. Special POT bearings
12
DOUBLE POT BEARINGS
Bearings with double pot and single upper plate.They are designed for an ILM bridge. The aim was
to center the loads during launching under the websof the concrete deck.
These bearings were installed in the High speed
railway Madrid-Sevilla at Ademuz (Cordoba).
BEARINGS WITH "SPRINGS"
These bearings incorporate external springs that
control the relative movements between slidingplate and pot.
These bearings were installed in the Cartuj aviaduct in Seville (approaches to Alamillo bridge).
w
v
ELIPTIC POT BEARINGS
The pot has an elliptical shape. These bearings werespecially designed for the Aruca-Las Palmas j unctionin the Canary islands.
w
CTT manufactures special tailor-made POT bearings
designed to fit the technical specifications and requirements
of individual proj ects.CTT offers a wide range of technical solutions for the design
of special POT bearings; our technical department has thecapability to develop alternatives to the standard product,
thus adapting our design to the proj ect requirement.
The pictures below show several special bearingsdesigned for specific j obs.
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9. Recent bridge structures
4TH BRIDGE OVER GUADIANA RIVER
IN BADAJOZ. SPAIN
OWNER:
J unta de Extremadura.
CONTRACTOR:
UTE Puente de Badaj oz
DYCSA-FCC
CONSULTANTS:
FCC Construccion. Servicio Tecnico.
D. J os Ignacio Gonzalez Esteban,
D J os Luis Alvarez Poyatos
BEARING TYPE:
PL-1000, PL-500, PU-1000, PU-500
VIADUCT OVER GOR RIVER INGRANADA. SPAIN
OWNER
Direccion general de carreteras
J unta de Andalucia
CONTRACTOR:Entrecanales y Tavora
CONSULTANTS:
Direccion general de carreteras
BEARING TYPE:
PL-350, PUE-1150, PLE-1100
BRIDGE OVER VAROSA RIVER
LANCO REGUA-RECONCOSPORTUGAL
OWNER
J AE
CONTRACTOR:
ENGIL - Soares da Cosat
CONSULTANTS:
Ing. Armando Rito
BEARING TYPE:
PL-380, PU-1550,S PU-1450
v
w
v
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ACCESS TO ALAMILLO BRIDGE IN
SEVILLE. SPAIN
OWNER:
J unta de Andalucia
CONTRACTOR:
U.T.E. Alamillo
DYCSA-FCC
CONSULTANTS:
FCC
BEARING TYPE:
PL-380, PU-1550, PU-1450
v
w
MADRID-SEVILLE HIGH SPEED
TRAININ ADEMUZ (CORDOBA).SPAIN
OWNER:
M.T.T.C.
CONTRACTOR:
DYCSAEntrecanales y Tavora, s.a.
COMSA
CONSULTANTS:
EPTISA
BEARING TYPE:
PL-400, PPUE-1650, PPLE-1650
w
LAHORE-ISLAMABAD MTY.
PAKISTAN
OWNER:
National Hghway Authority Pakistan
CONTRACTOR:
DAEWOO Corporation (Korea)
MTY CONSULTANTS:
SMEC (Australia)
ILM BRIDGES CONSULTANTS:
CTT-Stronghold (Spain)Mr. Wolfgang Buchler (Switzerland)
BEARING TYPE:
PL-1000, PUE-1600, PLE-1000
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10. Quality control and tests
TESTING
The quality and behaviour of CTT POT bearings is
regularly checked by several tests :
- vertical load tests- vertical and horizontal load tests
- friction tests
- rotation test
These tests are generally carried out in an officiallaboratory next to our factory :
- Laboratori General dAssaigs i lnvestigacions LGAI
in Barcelona.
v Testing POT bearings in laboratory
CORROSION PROTECTION
All steel areas in contact with the atmosphere areprotected with the following standard corrosion protection:
- surface conditioning by sand blasting according to
SIS-055900, grade Sa 2 1/2,
- two layers of epoxy primer (cathodic protection),- one finishing layer of acrylic resin and chloride
plasticizer paint.
The minimum total thickness of the three-layer protection
is between 100 n and 120 n.
POT bearings are supplied with different corrosionprotection following specific requirements such as
metalisation or use of special self-protected steels.
High precision techniques are used in the manufacturingand finishing of POT bearings. Given the loads to be
transmitted and the deformations to be absorbed, thequality of the materials and workmanship are ensured
by Quality Control Plans regularly revised to meet anyparticular specification.
Since early 1997, we have established a quality manualand a manual of procedures in order to be certified ISO-
9002-94.
CTT, acting as a member of the European StandarisationCommitee CEN collaborates in the European Standard
for POT bearings.
v Testing platform general view
v Quality control document
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