presentation on pot bearinngs
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Upgrading of Falaj Al Qabail R/A POT BEARINGS
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Project Location
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Project Particulars
Client: Ministry of Transport & Communications
Consultant: Renardet S.A & Partners L.L.C.
Contractor: Consolidated Contractors Co. Oman L.L.C.
Contract No.: 51/2012
Commencement Date: 30.12.2013
Completion date: 29.06.2015
Original Contract Value R.O. 17,884,403
Main Works: Flyover Bridge of 240 m length
4.073 Km of 6 lanes (Batinah Highway)
0.5 km of 4 lanes (Buraimi Road)
3.0 km of 2 lane Service roads
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Details of Flyover Bridge
02 Bridges of 03 Lanes; Length 240m and width 16.78m.
Total 06 spans of 40m in each Bridge.
Superstructure with 03 spans continuous Box Girders.
Piers with Flared type columns
Foundations with 09 Piles of 1000mm diameter and 25m depth in Piers and 05 no. in Abutments.
Superstructure rests on 03 no. POT BEARINGS above each Piers and Abutments (except 06 no. in Pier no. 3)
Expansion Joints at spacing of 120m on each abutment and Pier No. 3 (mid point of Bridge)
The Bridges are in Curve of radius 1230m
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Details of Pot Bearings
Consists of a metal piston supported by a disc of unreinforced elastomer confined within a metal cylinder
Rotations are accommodated by deformation of elastomer
Movements are accommodated by sliding of polished stainless steel on PTFE
Types: movable, guided, unguided, or fixed
Fixed bearing prevents differential translation of abutting structural elements. May or may not provide differential rotation.
Movable bearing facilitates differential horizontal translation of abutting structural elements in a longitudinal and/ or lateral direction. May or may not provide rotation. Translation may be constrained to a specified direction by guide bars.
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Details of Pot Bearings
Corrosion protection shall not be less than 15 years to first maintenance
Sliding bearing accommodates movement by translation of one surface relative to another. Translation may be constrained to specified direction by guide bars.
Bearings shall not be dismantled at site.
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Situations to use Pot Bearings
For high vertical loads combined with large angle of rotations, rubber bearings are undesirable when compared with pot bearing.
Elastomeric bearings require large bearing surfaces so that compression can be maintained between the contact surfaces of bearings and piers.
Moreover, it also leads to uneven distribution of stress on the piers and some of these highly induced stresses may damage the piers.
Consequently, pot bearings are better alternatives than elastomeric bearings in such a scenario as suggested by David J. Lee.
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Advantages of Pot Bearings
Pot Bearings have:
beneficial properties of elastomer in fixed bearings & design of large expansion bearings
Rotational movement permitted by shear deformation of an elastomeric pad
Translational movement restraint by completely encasing the elastomeric pad in a POT
No compressive deflection of elastomer as it is encased
Sliding component can be added at top
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Reference Standards
Highway Design Standards Volume 3: Standard Specifications for Road & Bridge Construction 2010
AASHTO 2008: AASHTO LRFD Bridge Construction Specifications, 2nd Edition
AASHTO 2008: AASHTO LRFD Bridge Design Specifications, 3rd Edition
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Project Design Drawing
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Types - Fixed Bearing FX
Quantity = 04 no.
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Shop Drawing FX Type
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Types Free Sliding Bearing - GXY
Quantity = 24 no.
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Shop Drawing GXY Type
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Type Guided Sliding - GX
Quantity = 12 no.
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Shop Drawing GX Type
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Type Guided Sliding - GY
Quantity = 08 no.
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Shop Drawing GY Type
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Storage of Bearings
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Installation of Bearings
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Installation of Bearings
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Applicable Specifications
Shall be designed as per AASHTO LRFD Bridge Design Specifications, section 14.7
Shall be constructed as per AASHTO LRFD Bridge Construction Specifications, section 18
Alternatively may be designed and constructed as per BSEN 1337-5 Structural Bearings Part 5: Pot Bearings
Sampling lot is not more than 25 bearings of same type either fixed or sliding
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Materials - PTFE It is a
Linear chain polymer of high molecular strength
Chemically inert
Low coefficient of friction
Not oxidized easily
Remains stable at extreme atmospheric temperatures
Resistant to all common solvents
Conforms to AASHTO LRFD Bridge Construction Specifications Article 18.8.1 or BS EN 1337-2
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Materials Steel conform to Section 6 of Standard Specifications for Road
& Bridge Construction
Stainless steel conform to requirements of 11.2.1.1 item (5)
Neoprene and natural rubber conform to AASHTO M251 (ASTM D4014) and Shore A durometer hardness 5010 points
Elastomer shall be lubricated between steel pot and top steel bearing plate with a silicon grease which does not react chemically with elastomer
Sealing rings between steel piston and elastomeric rotational element is made of Brass
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Submittals Working Drawings including any modifications of abutting structural
elements and fixings to superstructure and substructure
Details of Protective Coatings with Data Sheets
Method Statements
Manufacturer experience details (min 10 years)
Design Calculations
Program of manufacture, testing and delivery
Certificates/ test reports of all materials used in manufacturing (not older than 12 months)
Replacement procedures
Inspections and maintenance Plan
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Tests to be Conducted
Dimension check: As per AASHTO LRFD Bridge Construction Specifications Article 18.1.5.2.4
Clearance Test: As per Article 18.1.5.2.5
Bearing Friction Test: As per Article 18.1.5.2.6 in addition to compression of 100% of the full service dead load + live load, shall be checked for 50% and 80% of full service dead load + live load.
Bearing Horizontal Force Capacity: As per Article 18.1.5.2.8. Failure or excessive deflection of any of components is cause for rejection.
If one bearing fails, all bearings of the lot are rejected unless the manufacturer elects to test each bearing at his expense.
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Tests to be Conducted (Continued) Vertical Load Test: Tested for vertical load of 1.5 times full
service dead load + live load. Test load applied in 5 equal increments and held for one hour or until deformation ceases whichever is greater. Then Load removed in equal decrements as increments.
A second cycle of load increment and decrement applied with max. test load held for 30 minutes.
Load deformation graph plotted for both load cycles and set determined.
If set is excessive all bearings to be pre-loaded before installation.
After vertical load test, bearing to be dismantled and surfaces checked for visible excessive wear, cracks, or splits which lead to rejection.
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Certificates
certificates for physical and chemical properties of all materials used in manufacturing
Test Reports for all tests conducted on the samples
Delivery Notes along with Certification of Origin and details of Bearings
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