BSEC Bridge Bearings - IAStructE€¦ · BSEC Bridge Bearings TECHNICAL LECTURE SERIES ... guided or free depending on design requirements. BSEC TECHNICAL LECTURE SERIES –INDIAN

8/12/2016

1

BSEC

Bridge Bearings

TECHNICAL LECTURE SERIES

INDIAN ASSOCIATION OF STRUCTURAL ENGINEERS

ALOK BHOWMICKManaging Director,

B&S Engineering Consultants Pvt. Ltd.315‐316, VISHAL CHAMBERS, SECTOR 18, NOIDA

1

State-of-the-Art

BSEC

Outline of Presentation1. Bridge Bearing Types and Functional Properties

2. Possible arrangement of Bearing Layouts



2

g g y

3. Introduction to the New set of Limit State Codes

4. Installation Requirements for Bearings

5. Testing and Acceptance CriteriaSome of the material in this presentation is taken from :a) Presentation by Dr. Christian Braun of Maurer Shone, Germanyb) Presentation by Mr Chinmoy Ghosh of MAGEBA, (which I thankfully acknowledge) :

BSEC

Outline of Presentation



1. Bridge Bearing Types and Functional Properties


3




5. Testing and Acceptance Criteria

BSEC

TECHNICAL LECTURE SERIES – INDIAN ASSOCIATION OF STRUCTURAL ENGINEERS

Bridge Bearing Types and Functional Properties

Function of Bridge Bearings

1. Bearings are elements transferring vertical loads from Superstructure to Substructure, but allowing unrestrained rotation & displacement of superstructure thus avoiding large

4

of superstructure, thus avoiding large forces to be transferred to substructure & foundation.

2. Bearings are critical elements within overall bridge systems. They can potentially cause significant problems, if they do not function properly. Malfunction in bearing can cause distress / failure of the bridge

BSEC



Functions of Bridge Bearings .... Contd

• Allows rotation between superstructure and substructure

• Functions as per design requirements : It prevents displacements (Fixed Bearings), or allow displacements in only one direction (Guided

5

Bearings), or allow displacements in only one direction (Guided Bearings) or allows displacements in all directions (Free Bearings).

• Enables unrestrained movement of the deck, ensuring that large forces are not transferred to the substructure and foundation due to restraints in movement.

• Recent Bridge bearings are also designed to act as seismic protectors, that arrests and dissipate energy during earthquakes and other seismic activities.

BSEC

Primary Function & Operating Principles of Bridge Bearings

Sliding Rolling/Rocking Deforming

Displacements



Rotations

In addition to above application of Bearings, the modern bearing system combines the routine function of bearing with other functions (such as seismic isolators / LUD)

8/12/2016

2

BSEC

Primary Function & Operating Principles of Bridge Bearings



Continuous Bridges with Lock Up Devices

BSEC

Lead Rubber bearings

effKMT π2=



Seismic Isolators

≤ 30 % dampingCost benefit for loads ≤ 5.000kNdisplacements ≤ ±150mm period demands ≤ 2,5s Period for seismic isolation is depending on load onto the bearing

BSEC

Lead Rubber Bearings and Steel Hysteretic Dampers (SHD)Isolator resulting from the combination of a LRB and Crescent Moon Steel Hysteretic Devices



Seismic Isolators

BSEC

Curved Surface Slider (Sliding Isolation Pendulum)



Seismic IsolatorsSIP exhibits a recentering characteristics and incorporates the characteristics of a pendulum to lengthen the natural period of the isolated structure so as to avoid the strongest earthquake forces. The period of the bearing is selected by choosing the radius of curvature of the concave surface.

BSEC

gRT π2=

Curved Surface Slider (Sliding Isolation Pendulum)



Seismic Isolators

≤ 45 % dampingLarge elongation of period not depending on load High load and rotation capacityExtended working lifeGood recentring capacityFriction is load dependent

BSEC

Isolation and Energy DissipationCombined effect of period shift and damping

a[m/s2]

period shift



damping

[ ]

ag

8/12/2016

3

BSEC



1. Until the middle of this 20th century, the bridge bearings used consist of following types only :• Pin• Roller & Rocker

Brief History of Bridge Bearings

• Roller & Rocker• Metal sliding bearings

2. Increased demands and improvements in engineering materials, particularly plastics & elastomers have led to innovative designs and led to use of following types :• Elastomeric Bearings

• High Load Multi Rotational Bearings (Pot, Spherical, Disc)

. . . . Flexible Bearing

. . . .Rigid Bearing

BSEC

Types of Modern Bridge Bearings



GENERAL CATEGORY BEARING TYPE

Elastomeric Bearings Plain Elastomeric Pads

Laminated Elastomeric Bearings

Sliding Bearing Mechanism PTFE Sliding MaterialSliding Bearing Mechanism PTFE Sliding Material

Alternative Sliding Materials (ULTRA HIGH MOLECULAR WEIGHT

POLY ETHYLENE) …. Patented materials like MSM, ROBO Slide.

High Load Multi‐Rotational Bearings

Pot Bearings

Disc Bearings

Spherical Bearings

Fabricated Steel Mechanical Bearings

Rocker Bearings

Rocker cum Roller Bearings

BSEC

Types of Modern Bridge Bearings



1. The most widely used structural bearings are reinforced elastomeric bearings and pot bearings (90%).

2. Spherical bearings are the best solution for large rotations.

3. Elastomeric, pot and spherical bearings can be fixed, guided or free depending on design requirements.

BSEC



Some very important general principles in bearing design :

1. Bearings are to be designed such that their components can be inspected, maintained and replaced if necessary. Lifti f th t t f i t /Lifting of the superstructure for maintenance / replacement of Bearings shall be foreseen in design.

2. Bearings shall be designed to permit the specific movements & rotations with the minimum possible reacting force & couple.

BSEC



Some very important general principles in bearing design :

3. ‘Pre‐setting’ shall be avoided as far as possible. This principle reflects negative past experience caused by wrong pre setting or installation that cancelled the verywrong pre‐setting or installation that cancelled the very small economical saving that could be achieved by reducing the movement capacity of the bearings.

4. For dynamically stressed structures like railway bridges or structures subject to the earthquake, the horizontal forces cannot be transferred by friction.

BSEC

Reinforced Elastomeric Bearings



8/12/2016

4

BSEC

• Long life span•High loading capacity•Free of wear•Small reaction forces




Small reaction forces• Inspectable during service•Vertical stiffness•Horizontal play•Horizontal load transfer

passed in generalfailed for some applications like high speed railway bridges

BSECReinforced Elastomeric Bearings

MERITS DEMERITS

1. Reinforcing Steels are enclosed in Elastomer, therefore protected against corrosion

1. Defects arising from poor product quality such as corroded steel, inadequate vulcanization, lack of bond between laminate and elastomer poor rubber



corrosion bond between laminate and elastomer, poor rubber quality, …etc, leading to splitting, slippage, bulgingand cracking of the rubber.

2. Long Life Span with little need for maintenance

3. Suitable for short to medium spans (for load upto 12 MN at ULS)

4. Good performance under low to moderate seismic activity

2. Errors in dimensioning, that leads to laminates being too short and of insufficient area.

5.Low Cost 3. Problem from incorrect installation, such as ingradient

BSEC




The trend in USA is to avoid using an alternative bearing system where a conventional reinforced elastomeric pad can

id h i d h i i h h hprovide the required characteristics through shear deformation.

Only when the practical limits of elastomeric bearing pads are exceeded, designers should consider using Pot, Spherical, Disc or other types of Bearings.

BSEC

• Long life span•High loading capacity•Free of wear•Small reaction forces• Inspectable during service

Steel Roller and Rocker Bearings



These types of bearings are used only• Inspectable during service•Vertical stiffness•Horizontal play•Horizontal load transfer


These types of bearings are used only very seldom in new constructions due to the rotation capacity around one axis only and to the fact that roller bearings can provide the movement only in thedirection perpendicular to the rotation axis. However they still exist in a large number of old bridges

BSEC

Steel Roller-cum-Rocker and Rocker Bearings



Cut‐Rollers

BSEC

Brittle Fracture

Steel Roller Bearings



8/12/2016

5

BSEC

Pot Bearings



1. pot bearings represent the largest portion of the bearings market in the world.

2. First used in Germany in 1958 Suitable for design

Pot Bearings can be of Fixed, Guided and Free Type

1958. Suitable for design load between 1MN to 50MN and more

3. Elastomer inside a steel pot is confined & functions like a viscous fluid.

4. Flat brass sealing rings are used to contain the elastomer inside the pot.

BSEC


(PTFE Sliding) Pot Bearings



•Small reaction forces• Inspectable during service•Vertical stiffness•Horizontal play•Horizontal load transfer


BSECComposition of a Pot bearing



The most important detail of the pot bearings is the seal, preventing the leakage of the elastomer through the gap between pot and piston and governing the durability under repeated rotations.

BSEC

SLIDING SURFACE OF BEARINGS :



Pure PTFE has a low compressive strength and a high coefficient of thermal expansion. To make it suitable for use in bridge bearings, PTFE must be combined with suitable fillers. These fillers are typically glass fiber and bronze.

BSECPure, virgin PTFE Polished Stainless Steel Sheets



Special silicon grease

SLIDING MATERIAL IN BEARINGS

BSEC



Fixed Free Sliding Guided Sliding

8/12/2016

6

BSECPot BearingsInternal seal failure = elastomeric disc extrusion : Special attention shall be paid to very flexible structures and to large sized bearings

BSEC

Spherical Bearings



1. This is a very robust bearing system that is traditionally considered to be the most reliable HLMR type.

2. It can be designed to accommodate large loads (1 MN to 100 MN) and rotations.

3. It requires high degree of manufacturing quality control.

BSEC

• Long life span•High loading capacity

F f

PTFE Spherical Bearings

•Free of wear•Small reaction forces• Inspectable during service•Vertical stiffness•Horizontal play•Horizontal load transfer


BSEC

Spherical Bearings



The latest invention & developments in the field of Bridgesupport & protection system "Spherical Bearing" havelonger durability, enhanced service & performance life whenlonger durability, enhanced service & performance life whencompared with conventional Steel, Elastomeric & even PotBearings.

In Signature Bridge, Wazirabad, Delhi. Spherical Bearingshas been used with a ULS load capacity of 23,000 MT, thesebridge bearings will be one of the biggest ever manufactured& used in a bridge structure.

BSEC

Spherical Bearings



MANUFACTURING OF BEARING FOR SIGNATURE BRIDGE

Spherical bearing @ P19

BSEC

Spherical Bearings :

Advantages :• Multirotational Bearings. Can accommodate higher rotations• Relatively high vertical load capacity

L h i ht



• Low height• Negligible vertical deflection under load.

Disadvantages :• Require high degree of quality control and careful attention when installing

– especially to ensure no dis‐assembly. • Requires periodic maintenance.

8/12/2016

7

BSEC

Spherical BearingsVARIOUS FORMS OF SPHERICAL BEARINGS



1. For the curved surfaces, aluminium or chromium plated mating surfaces are allowedmating surfaces are allowed.

2. For the guides of sliding guided bearings the use of un‐dimpled PTFE or composite materials based on PTFE are allowed.

3. These materials allow a considerably higher pressure but have also a much higher friction.

BSEC


Disc Bearings



• Inspectable during service•Vertical stiffness•Horizontal play•Horizontal load transfer


Disc Bearings, introduced in 1970, offers lower profiles over other multi‐rotational bearings such as Pot Bearings. This is due to the use of an elastomeric unconfined polyurethane disc to accommodate rotation instead of a confined elastomer, a pot and a piston in case of Pot Bearing

BSEC



39FIXED DISC BEARINGGUIDED SLIDING DISC BEARING

BSEC



Typical Disc

40

Bearings with Pintle Pin, having Vmax = 2000T

BSEC

DISC BEARINGS : REASONS FOR IT’S LIMITED USE IN BRIDGES

1. They have not been extensively used because of proprietary status until recent years.



2. Service life experience and fatigue testing experience is limited.

3. There is concern that rotational stiffness can cause high stresses on sliding surfaces.

BSEC



SELECTION OF APPROPRIATE BEARING TYPE FOR A GIVEN SITUATION5. The choice of bearing depends on a

wide variety of factors, including :

Type of Structure (Rail /

17000

Pot Bearings & Disc BearingsHighway, Span length)Vertical load (max. and min.)Max. rotation, Horizontal displacement, Environment (Climate, Seismicity, Wind), Economics Structural arrangements.

8000

500

8/12/2016

8

BSEC






43





BSEC


Possible arrangement of Bearing Layouts

FOR SIMPLY SUPORTED SPANS:

BEARING LAYOUT WITH ELASTOMERIC BEARINGS

BSEC

PIN BEARING METALLIC GUIDED BEARING




BEARING LAYOUT WITH ELASTOMERIC BEARINGS WITH PTFE SLIDING SURFACE TO TAKE VERTICAL LOADS & A SEPARATE MECHANISM TO TAKE

LATERAL LOADS

BSEC




V i l S i

BEARING LAYOUT WITH ELASTOMERIC BEARINGS WITH PTFE SLIDING SURFACE TO TAKE VERTICAL LOADS & A SEPARATE ELASTIC RESTRAINTS

TO TAKE LATERAL LOADS

Vertical Stopper Bearings to take lateral loads

BSEC



FOR SIMPLY SUPPORTED SPANS ‐ HLMR BEARINGS :

Structural bearings are fixed, guided or moveable in all directions

Plan View of Span

BSEC

Braking and acceleration

FOR HLMR BEARINGS :



Fixity in longitudinal direction

Braking and acceleration

Plan View of Span

8/12/2016

9

BSEC

FOR HLMR BEARINGS :



Fixity in transverse direction

Wind or other impacts

Plan View of Span

BSEC

FOR HLMR BEARINGS :



Structural bearings allow movements – several layout patterns are possible.

Plan View of Span

BSEC



FOR SIMPLY SUPPORTED SPANS ‐

Structural bearings are fixed, guided or moveable in all directions

BSEC



FOR CONTINUOUS SPANS(WITH HLMR BEARINGS) :

BSEC



Guided in direction of Expansion (line joining ZMP with the guide)

Guided in constant direction ‘α’ from direction of Expansion

BSEC


Possible arrangement of Bearing LayoutsGuided in direction tangential to curve

8/12/2016

10

BSEC



FOR CURVED & SKEWED, CONTINUOUS SPANS(WITH HLMR BEARINGS) :

α

α

α

FREE BEARING

FIXED BEARING

GUIDED BEARING

PIN BEARING

FREE BEARING

FIXED BEARING

GUIDED BEARING

PIN BEARING

BSEC






56





BSECEN 1337 : “Structural Bearings” consists of following 11 parts : IRC:83 : Code for Bearings :

Part 0 – General Design Rules

Part 1 – Metallic Bearings


Introduction to the new set of Limit State Codes

g

Part 2 – Elastomeric Bearings

Part 3 – Pot cum PTFE Bearings

Part 4 – Spherical & Cylindrical Bearings

57

BSEC

1. This codes on Elastomeric Bearings & Rocker / Roller bearings have been revised. The new design code is based on ‘Limit State’ concept with particular reference to Ultimate Limit State and this is the fundamental change from earlier code.



2. Code of Spherical & Cylinderical Bearing also introduced based on Limit State concept.

3. Conversion from ‘Working Stress’ to ‘Limit State’ method of design is a part of the Harmonization process being undertaken by IRC to convert all the codes from WS to LS

58

BSEC

SUBSTANTIVE CHANGES IN THE CODE FOR ELASTOMERIC BEARINGS:

a. Scope & Applicability of Code broadened



b. Size and Shape Parameters of ‘EB’ modified

c. New Criteria introduced for Transfer of Seismic forces through EB

d. Choice in Material Properties for the designer

e. Maximum and Minimum permissible stresses & strains in Bearings amended

59

BSECCHANGES IN THE CODE :

a. Scope & Applicability :

o Previous Code restricted to Rectangular Laminated EB only.o Present Code covers EB with or without complimentary

b i d i I i li bl L i d EB Pl i P d

Laminated Elastomeric Bearings

Plain Elastomeric Bearings



bearing devices. It is applicable to Laminated EB, Plain Pad Bearings, Sliding Bearings…etc. New Code permits Rectangular, square as well as Circular shaped Bearings.

o New Code permits hole inside the bearing to reduce the loaded area without changing plan dimensions.

o Many other possibilities of combining sliding and fixing device with elastomer exists, which was never tried before.

Circular Elastomeric Bearings

60

8/12/2016

11

BSECConventional Rectangular Laminated Bearings with Steel Plates of same thickness, completely buried in Elastomer (TYPE‐B)

TYPE‐C : Same as TYPE‐B, with end laminate thicker, which ensures better load distribution, ensures better rotation and avoids possible lifting of bearing corners under shear..



Rectangular Laminated Bearings with thick External Bands of Steel Plates (TYPE‐D)

Circular Laminated Bearings with Steel Plates completely buried in Elastomer. Useful when rotation in both axis are of similar magnitude. Bearing with central hole for running specific materials through (cross bar anchor), for fitting damping material or reducing vertical stiffness61

BSEC

Bearings fitted with corrugated outer plates directly vulcanised with the bearing to guarantee frictional resistance with thin connection.

Bearings fitted with outer plates on one side / both sides, directly vulcanised with the bearing, to facilitate connection with steel superstructure (TYPE‐E)



Bearings with sliding Interface using PTFE Sheets (TYPE‐H)

Bearings with restraint against translation to simulate support condition (TYPE‐I)

Anchored Elastomeric Bearings fitted with Outer Plates, Anchor Plates and Connection Devices or Shear Discs

62

BSEC

CHANGES IN THE CODE ….Contd….:

b. Size :

Previous Code



63

BSEC


b. Size :

PresentCodal

• Between 8mm & 20mm• Can be 25mm under special situation



Provisions

• 2.5mm for Top & Bottom

• 4mm for Sides Clause 5.2.2 of the New Code

Maximum Size : 1200mm x 1200mm

• To be decided as per Design

64

BSECCHANGES IN THE CODE ….Contd….:

c. Transfer of Seismic Forces through EB’s :New Code : Elastomeric Bearings, in its conventional form shall generally be used to transmit vertical loads, rotations and horizontal forces other than the forces due to Seismic.



As a consequence of this requirement, conventional non anchored elastomeric bearings can rarely be used for taking Seismic Forces.

In case they are used for taking Seismic forces, the bearings shall be :

1. Suitably Anchored to Substructure & Superstructure2. Suitable devices for dislodgement of Superstructure need to be

incorporated and 3. Bearings shall be tested for cyclic loadings, for which specialist literature

shall be referred. 65

BSEC


d. Wider Choice in Material Properties :

Code permits Structural Designer to specify the design material properties as per the requirement.



q

This is a positive development as it opens a dialogue between structural designer and rubber technologist, which was hitherto absent.

66

8/12/2016

12

BSEC


e. Maximum and Minimum axial compressive stress in Bearing

Previous code : Restricted the average compressive stress in bearing,



10 Mpa > σm > 2 Mpa

In the New Code : There is no limitation for the maximum pressure on the bearings. Minimum pressure under ULS, for permanent load is restricted to 3 Mpa.

67

BSEC


f. Maximum Strains

Previous code : Limits of permissible total design strain was 5.0 and maximum



shear strain was 0.7 under serviceability limit state (SLS).

New Code : The limits of total strain and shear strain is taken as 7.0 and 1.0 respectively under ultimate limit state (ULS). The partial safety factor on action is taken as 1.4.

68

BSEC






69





BSEC


Installation Requirements for Bearings

1. Inappropriate handling, storage and installation will have an adverse effect on the bearing life.

2. The best bearing in the world will not perform

70

satisfactorily, if it is damaged during transport and handling or if it is not correctly installed.

3. There are several examples of bridge failure / distress due to improper installation of Bearings.

BSEC



Specification, workmanship and installation of the grout or mortar are extremely important to control shrinkage / expansion and compressibility, to ensure that voids do not remain between the bearing and the structure, and to ensure sufficient strength.

DISTRESS IN DELHI METRO LINE‐AIRPORT LINK

71

1. ELASTOMERIC BEARINGS OF SIZE – 300MM X300 MM X50 ON RCC PEDESTALS OF 500 MM X 500 MM SIZE PROVIDED

2. VIBRATIONS OF RAILWAY TRACK CAUSED FURTHER DETERIORATION.

3. BEARINGS FOUND LOOSENED AND DAMAGED.4. ADJOINING CONCRETE FOUND DISINTEGRATED.5. SPEED REDUCTION AND SHIMMING UNDER RAILS DID NOT

HELP.6. RAIL TRAFFIC SUSPENDED JULY 2012.7. IN ALL 216.0 BEARINGS RECTIFIED.

BSEC



72

Collapsed UltadangaFlyover, Kolkata : March 2013

8/12/2016

13

BSEC



Bearing Layout as per Approved Drawing

73

Bearing Layout as built at site

Orientation of Guide Bearing Changed

GAUNDALIM BRIDGE AT GOA

80m Bow String Girder Bridge

BSEC



DERA BASSI FLYOVER, PUNJAB

HANGING BEARING SLEEVES !!

74

BSEC



75

BSEC



BEARING INSTALLATION FOR CAST‐IN‐SITU DECKS BEARING INSTALLATION FOR PRECAST GIRDERS

76

BSEC






77





BSEC

The conformity evaluation of the bearings is verified through:

1. Tests on Materials

2. type tests, to be performed before starting the production


Testing & Acceptance Criteria for Bearings

78

2. type tests, to be performed before starting the production or any time significant modification to the design of the bearings are introduced,

3. routine test, to be performed during the manufacture of the bearings. Routine tests mainly refer to row materials and components

8/12/2016

14

BSECTesting of Elastomeric Bearings

1. Short‐term behaviour tests :‐ Shear Modulus test for G‐ Shear strength tests for shear bond‐ Compression test for stiffness

2. Long‐term behaviour tests‐ Compression Set test (Creep test)

3. Environmental Influence Tests‐ Accelerated Ageing test‐ Ozone resistance test

79

BSECTesting of HLMR Bearings

1. Tests on Raw Materials : o On Cast Steel, Mild Steel, Forged Steel, Mating

Surface, Stainless Steel, Elastomer, PTFE, Bolts and Nuts.

2. Inspection of Finished Bearings‐ Visual Inspection for all Bearings‐ Testing of One pair of Bearings (Vertical Load Test,

Friction Test and Rotation Test)

2. Process Inspection‐ Tests on Welding‐ Surface Hardness‐ Corrosion Protection

80

BSEC

For any query, contact bsec.ab@gmail

81

BSEC Bridge Bearings - IAStructE€¦ · BSEC Bridge Bearings TECHNICAL LECTURE SERIES ... guided or free depending on design requirements. BSEC TECHNICAL LECTURE SERIES –INDIAN

Documents