Bridge Bearing Inspection

Chris Whitehead MA MBA CEng FICE

April 2016

Agenda

• Function

• Types

• Common defects

• Preparatory work

Function

• To transfer vertical and/or horizontal loads from the superstructure to the substructure

• To allow longitudinal/transverse movement of the superstructure

• To allow rotation of beam slab ends due to dead and live loading

Common types

• Elastomeric

• Pot

• Spherical

• Plate

• Rocker

• Guide

• Anticlastic

• Compound

Symbols (table 1, BS EN 1337-1)

Symbol in plan

Type of bearing

Relative movements

X direction

Y direction

Z direction

About X axis

About Y axis

About Z axis

Elastomeric bearing

deforming deforming small deforming deforming deforming

Elastomeric bearing with restraints for one axis

deforming none small deforming deforming deforming

Pot bearing none none very small deforming deforming deforming

Pot bearing with unidirectional sliding

sliding none very small deforming deforming deforming

Pot bearing with multidirectional sliding

sliding sliding very small deforming deforming sliding

2-span continuous bridge

Elastomeric bearing (1)

Unconstrained elastomeric bearing

Elastomeric bearing (M40)

Elastomeric pot bearing (1)

Elastomeric pot bearing

Elastomeric pot bearing (HS1)

Spherical (1)

• Expensive

• Used on major structures to accommodate high rotations

Spherical (2)

Guided spherical bearing

Plate bearings

Fixed plate bearing

Free plate bearing

Rocker (1)

• Often used when impact loading is high, such as on railway bridges

Rocker (2)

Fixed pedestal bearing Free rocker bearing

Fixed rocker bearing

Free rocker bearing

Fixed rocker

Rocker bearing deployment

Guide bearings (1)

• Ensure structure maintains location/alignment

• Take no vertical load

Guide bearing (HS1)

Anticlastic bearings

Compound bearings

?

Dampers

Common defects

• Refer to B-11 et seq Inspector’s Handbook

• Corrosion leading to seizure (and movement being accommodated between bearing and seating)

• Bearing beyond designed extent of travel

• Splitting and deformation (of elastomeric bearing)

• Delamination of bearing shelf

Preparatory work

• Does the client have any specific requirements regarding bearing inspection?

• What does the previous inspection report have to say?

• Is there a bearing schedule in the as-built drawings?

• What is the function of the different types of bearing on the bridge? – what loads are they transferring and what movements are they designed to accommodate?

• Note that the Inspection Manual for Highways Structures requires that the position of bearings be recorded at each Principal Inspection

Summary

• Bearing failure is one of the most common root causes of bridge failure

• Understand how the bearings are supposed to perform

• Know the most common types of bearing failure

• Be aware of any special client requirements for bearing inspection

• Record the longitudinal and lateral position of each bearing for a Principal Inspection (relative to neutral position)