Upgrading of Falaj Al Qabail R/A POT BEARINGS

Project Location

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

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

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.

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.

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.

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

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

Project Design Drawing

Types - Fixed Bearing FX

Quantity = 04 no.

Shop Drawing FX Type

Types Free Sliding Bearing - GXY

Quantity = 24 no.

Shop Drawing GXY Type

Type Guided Sliding - GX

Quantity = 12 no.

Shop Drawing GX Type

Type Guided Sliding - GY

Quantity = 08 no.

Shop Drawing GY Type

Storage of Bearings

Installation of Bearings

Installation of Bearings

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

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

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

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

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.

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.

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