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Structural Engineering Documents
Gunter Ramberger
Structural Bearings and Expansion Joints
I
for Bridges
International Association for Bridge and Structural Engineering
Association lnternationale des Ponts et Charpentes
lnternationale Vereinigung fur Bruckenbau und Hochbau
IABSE AIPC IVBH
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Copyright 0 2002 by International Association for Bridge and
Structural Engineering
All rights reserved. No part of this book may be reproduced in
any form or by any means, electronic or mechanical, including
photocopying, recording, or by any information storage and
retrieval system, without permission in writing from the
publisher.
ISBN 3-85748-105-6 Printed in Switzerland
Publisher:
ETH Honggerberg CH-8093 Zurich, Switzerland
IABSE-AIPC-IVBH
Phone: Int. + 41-1-633 2647 Fax: Int. + 41-1-633 1241 E-mail:
[email protected] Web: http://www.iabse.ethz.ch
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Dedicated to the commemoration of the late Prof. Dr. techn.
Ferdinand Tschemmernegg, University of Innsbruck.
Preface It is my hope that this treatise will serve as a
textbook for students and as information for civil engineers
involved in bridge construction. My intent was to give a short
guideline on bearings and expansion joints for bridge designers and
not to mention all the requirements for the manufacturers of such
products. These requirements are usually covered by product
guidelines, which vary between different countries.
Not all the references are related to the content of this
document. They are more or less a collection of relevant papers
sometimes dealing with special problems.
I express many thanks to Prof. Dr.-Ing. Ulrike Kuhlmann,
University of Stuttgart, chairperson of Working Commission 2 of
IABSE, who gave the impetus for this work; to her predecessor of
the IABSE Commission, Prof. Dr. David A. Nethercot, Imperial
College of Science, Technology and Medicine, London, for reviewing
the manuscript, and Prof. Dr. Manfred Hirt, Swiss Federal Institute
of Technology, Lausanne, for his contributions and comments.
I wish to thank J. S. Leendertz, Rijkswaterstaat, Zoetermeer;
Eugen Briihwiler, Swiss Federal Institute of Technology, Lausanne;
Prof. R. J. Dexter, University of Minneso- ta; G. Wolff, Reissner
& Wolff, Wels; 0. Schimetta t, Amt der 00 Landesregierung,
Linz; Prof. B. Johannsson, LuleA Tekniska Universitet, for
amendments, corrections, remarks and comments. I thank also my
assistant Dip1.-Ing. Jorgen Robra for his valuable contributions to
the paper, especially for the sketches and drawings, and my
secretaries Ulla Samm and Barbara Bastian for their expert typing
of the manuscript. Finally, I would like to thank the IABSE for the
publication of this Structural Engi- neering Document.
Vienna, April 2002 Gunter Ramberger
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Table of Contents
1. Bearings
1.1 Introduction 1.2 The role of bearings 1.3 General types of
bearings and their movements 1.4 The layout of bearings 1.5
Calculation of bearing reactions and bearing movements 1.6
Construction of bearings 1.7 Materials for bearings 1.8 Analysis
and design of bearings 1 .9 Installation of bearings
1.10 Inspection and maintenance 1. I 1 Replacement of bearings
1. I 2 Codes and standards 1.13 References
2. Expansion Joints 2.1 Introduction 2.2 The role of expansion
joints 2.3 Calculation of movements of expansion joints 2.4
Construction of expansion joints 2.5 Materials for expansion joints
2.6 Analysis and design of expansion joints 2.7 Installation of
expansion joints 2.8 Inspection and maintenance 2.9 Replacement of
expansion joints
2.10 References
7 7 7 9
16 19 29 33 37 38 39 41 42
51 51 51 58 70 72 84 86 87 88
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7
1 Bearings
1.1 Introduction
All bridges are subjected to movements due to temperature
expansion and elastic strains induced by various forces, especially
due to traffic loads. In former times our bridges were built of
stones, bricks or timber. Obviously, elongation and shortening
occurred in those bridges, but the temperature gradients were small
due to the high mass of the stone bridges. Timber bridges were
small or had natural joints, so that the full elongation values
were subdivided into the elongation of each part. On the other
hand, the elongation and shortening of timber bridges due to change
of moisture is of- ten higher than that due to thermal actions.
With the use of constructional steel and, later on, of reinforced
and prestressed concrete, bridge bearings had to be used. The first
bearings were rocker and roller bearings made of steel. Numerous
rocker and roller bearings have operated effectively for more than
a century. With the develop- ment of ageing-, ozone- and
UV-radiation-resistant elastomers and plastics, new ma- terials for
bearings became available. Various types of bearings were developed
with the advantage of an area load transmission in contrast to
steel bearings with linear or point load transmission, where
elastic analysis leads theoretically to infinite compres- sion
stresses. For the bearings the problems of motion in every
direction and of load transmission were solved, but the problem of
insufficient durability still exists. Whilst it is reasonable to
assume the life of steel bearings to be the same as that of the
bridge, the life of a bearing with elastomer or plastic parts can
be shorter.
1.2 The role of bearings
The role of bearings is to transfer the bearing reaction from
the superstructure to the substructure, fulfilling the design
requirements concerning forces, displacements and rotations. The
bearings should allow the displacements and rotations as required
by the structural analysis with very low resistance during the
whole lifetime. Thus, the bearings should withstand all external
forces, thermal actions, air moisture changes and weather
conditions of the region.
1.3
Normally, reaction forces and the corresponding movements follow
a dual principle - a non zero bearing force corresponds to a zero
movement and vice versa. An exception is given only by friction
forces which are nearly constant during the movement, and by
elastic restraint forces which are generally proportional to the
displacement. Usually, the bearing forces are divided into vertical
and horizontal components. Bearings for vertical forces normally
allow rotations in one direction, some types in all directions. If
they also transmit horizontal forces, usually vertical forces are
com- bined.
General types of bearings and their movements
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1. Bearings 8
A special type of bearing transmits only horizontal forces,
while allowing vertical displacements.
The following table (Table 1.3- 1) shows the common types of
bearings, including the possible bearing forces and displacements.
Friction and elastic restraint forces are not considered.
- Symbol Function Construction
Point rocker bearing Pot bearing; Fixed elastomeric bearing;
Spherical bearing
All translation fixed Rotation all round
Constr. point rocker sliding bearing; Constr. pot sliding
bearing; Const. elastomeric bearing; Constr. spherical sliding
bearing
Free point rocker bearing; Free pot sliding bearing; Free
elastomeric bearing; Free spherical sliding bearing; Link bearing
with universal joints (tension and compression)
Horizontal movement in one direction Rotation all around
Horizontal movement in all directions Rotation all round
Line rocker bearing Leaf bearing (tension and compression)
Roller bearing; Link bearing (tension and compression); Constant
line rocker sliding bearing
Free rocker sliding bearing; Free roller bearing; Free link
bearing
All translation fixed Rotation about one axis
Horizontal movement in one direction Rotation about one axis
Horizontal movement in all direction Rotation about one axis
All horizontal tranal. fixed Rotation all round
+ ~
HoriLontal force bearing
Horizontal movement in one direction Rotation all round
Guide bearing
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1.4 The layout of bearings 9
Tuble 1.3-1 8.2
1.4 The layout of bearings 1.4.1 General Bearings can be
arranged at abutments and piers (fig. 1.4.1-1 ; fig. 1.4.1-2) under
the webs of the main girders, under diaphragms (fig. 1.4.1-3), and
under the nodes of truss bracings. The webs and the diaphragms of
concrete bridges have to be properly reinforced against tensile
splitting; steel bridges need stiffeners in the direction of the
bearing reactions to transfer the concentrated bearing loads to the
superstructure and the substructure. Abutments and piers also have
to be properly reinforced under the bearings against tensile
splitting.
-77 Fig. I .4. I - I : Bearings at an abutment
, I - ~- ~ I
Fig. 1.4.1-2: Bearings at u pier
I7 Fig. 1.4.1-3: Bearing at a single pier
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10 1 . Bearings
The layout of the bearings should correspond to the structural
analysis of the whole structure (super- and substructure
together!). If the settlement and the deflection of the
substructure can be neglected the structural analysis of the
superstructure, including the bearings, can be separated from that
of the substructure. Sometimes the model for the analysis,
especially of the superstructure, will be simplified by assuming
the fol- lowing: bearings are situated directly on the neutral axis
of the girder (fig. 1.4.1-6), the motion of the bearings occurs
without restraint, bearings have no clearance, etc. In this case we
must consider the correct system (fig. 1.4.1-5) at least for the
design of the bearings and take into account the influence of the
simplifications on the structure.
& Fig. I .4.1-4: Reality
A Fig. I .4.1-5: Correct system
On the abutments or separating piers it is normal to use at
least two vertical bearings to avoid torsional rotations. At
intermediate piers one or more vertical bearings may be used. If
more than one bearing is used the rotational displacement at the
pier is re- strained. More than three vertical supports of the
superstructure lead to statically in- determinate bearing
conditions, but even the simplest bridge has at least four vertical
bearings. If the torsional stiffness of the superstructure is low
(e.g. open cross sec- tions) it may be neglected and the layout
with four bearings becomes isostatic. If the torsional stiffness is
not negligible (e.g. box girders) we have to take it into account
for the structural analysis, especially for skewed and curved
bridges. On a bridge with n > 3 vertical supports, n - 3 bearing
reactions can be chosen freely within a reasonable bandwidth. This
possibility can be used to prestress the superstructure and to
distri- bute the bearing reactions as desired. If the bearings are
situated (nearly) in a plane we need at least one horizontally
fixed and one horizontally moveable bearing. The moving direction
must not be orthogonal
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I .4 The layout of bearings 11
to the polar line from the fixed to the moveable bearing. If
more than two bearings in the horizontal direction are necessary,
the basic principle should be that an overall uniform extension,
caused by temperature or shrinkage, shall be possible without
restraint.
In general, there are two possibilities for the arrangement of
the bearings: a) arrangement in a horizontal position (fig.
1.4.1-7) b) arrangement in a position parallel to the road or rail
surface (fig. 1.4.1-8).
I
1 ---_---,--a
Fig. 1.4.1 -7: Horizontal arrangement of the bearings (case
a)
-(I f=-- I ,,displaced bridge (
Fig. 1.4.1-8: Inclined arrangement ofthe bearings (case b)
Case a) has the advantage that only vertical bearing reactions
and no permanent hori- zontal reactions result from vertical loads,
but it has the disadvantage that bridges with inclined gradients
require a step at the expansion joint due to movements in the
super- structure. The greater the elongation or shortening, the
greater the step required.
Case b) has the advantage that the slope of the expansion joint
is independent of the movement of the bridge. The inclination of
the surface of support gives the direction of the normal force.
Besides vertical reaction forces, also horizontal reaction forces
result from vertical loads. Permanent horizontal actions can lead
to a displacement by creep of the concrete and the soil and, thus,
to crooked piers.
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12 1. Bearings
1.4.2 For single span girders the layout of the bearings is
straightforward. One fixed and one moveable bearing is provided on
each abutment, all other bearings are just vertical supports,
moveable in any horizontal direction. For wide bridges the
horizontally fixed bearings are located in or near the bridge
axis.
The layout for different types of bridges
Formerly, the classical arrangement of the bearings for a bridge
with two main gird- ers consisted of one fixed and one lengthwise
moveable bearing at one abutment and one lengthwise moveable and
one free bearing at the other abutment (fig. 1.4.2- 1). This layout
has the advantage that longitudinal horizontal forces (braking and
traction forces) can be distributed into the two bearings at the
abutment, but it has the disadvantage that horizontal forces in the
cross direction (wind) and temperature dif- ferences cause
horizontal restraint forces, provided that bearings have no
clearance on the abutments.
The author prefers the statically determinate system with only
one lengthwise re- strained bearing at the abutment concerned
because the actual clearance of a bearing is not determinable in
reality (fig. 1 .4.2-2).
. - - -- _ - ++- LA- -:. ;c 11, %I, I
Fig. 1.4.2-1: Classical layout
Fig. 1.4.2-2: Horizontally statically determinate system (better
than classical layout)
. _ _ - - - -------- --- _ - -
Fig. 1.4.2-3: System with separated vertical and horizontal
bearings (statically deter- minate system)
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1.4 The layout of bearings 13
For skewed or horizontally curved single span bridges we have to
decide whether the horizontal force should be combined with the
higher or with the lower vertical reac- tion force. For all bearing
constructions it is easier to transfer horizontal forces in com-
bination with a high vertical force. In this case the resultant
force stays nearer to the centre, its angle to the vertical is
smaller and leads to smaller bending moments in sub- and
superstructure (fig. 1.4.2-4).
I I ! H I
Fig. 1.4.2-4: Inclination of the resultant force
Thus, the horizontally constrained bearings for skewed bridges
should be placed at the obtuse corners of the bridge, for curved
bridges at the outer side (fig. 1.4.2-5).
Fig. 1.4.2-5: Skewed bridge
Fig. 1.4.2-6: Layoutfor continuous girders
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14 1. Bearings
For straight continuous girders normally two bearings are used
at every abutment and pier. If the torsional stiffness is high (box
girder) the intermediate piers can be reduced to a round column
with one bearing on the axis under the diaphragm. Constrained
bearings in the cross direction are the rule at all piers. If the
horizontal bending stiff- ness is very high we can transfer the
horizontal forces only at the abutments. The same considerations
are suitable also for skewed and curved bridges (fig. 1.4.2-6).
Bearings for horizontal forces and guide bearings which transfer
only horizontal forces may be used in combination with leaf or link
bearings which cannot transmit horizontal forces.
The movement of an expansion joint must be linked by a guide
like a constraint bear- ing. The main movement of an expansion
joint should be in the axis of the traffic way. Generally, this
direction does not coincide with the direction of the polar line
from the fixed bearing to the moveable bearing at the abutment
(fig.1.4.2-7). If all other bearings have the same angle between
the polar line and the moving direction there results a layout of
the bearings with no restraints on uniform elongation or shortening
(e.g. caused by thermal actions or shrinkage), as shown below
(fig.1.4.2-8).
Fig.1.4.2-7: Layout for curved bridges
Fig. 1.4.2-8: Layout for curved continuous girders (no
constraint under overall tem- pe ra tu re)
Fig. 1.4.2-9: Geometrical situation
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I .4 The layout of bearings 15
The elongation is
A,, = k . r,
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16 I . Bearings
I A+ Fig. 1.4.3-1: Prying effect due to a eccentric loading
b) A similar situation occurs for a continuous girder with
chequer pattern loading.
~
~
Fig. 1.4.3-2: Prying effect due to chequer pattern loading
c) It is not generally known that a skewed bridge with
horizontally fixed bearings only in one line exhibits the same
effect under vertical loading, as the following figure shows:
Fig. 1.4.3-3: Prying forces for a skewed bridge with vertical
loading
Similar effects can occur for curved bridges. For the correct
analysis of the bearing reactions it is always necessary to model
the bearings at the very point where they are actually situated,
and in combination with the substructure. The deflection of the
substructure can influence the constraint bearing reactions
significantly.
1.5 Calculation of bearing reactions and bearing movements
1.5.1 Actions According to Eurocode 1 (ENV 1991) the actions can
be subdivided into:
- permanent actions, - variable actions, - extraordinary
actions.
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1.5 Calculation of bearing reactions and bearing movements
17
The bridge should take up the desired shape under all permanent
loads, at the average temperature (+lo" C in most of the European
countries) and, if time-dependant displacements occur, at the time
t = 00, at which time all moveable bearings should be in the zero
adjustment (null position). Variable actions and extraordinary
actions lead to deviation from this form.
Variable actions to consider are: - traffic loads, considering
the applicable dynamic coefficients - loads due to traffic loads,
i.e.
nosing forces centrifugal forces braking forces traction
forces
wind on construction wind on traffic loads
- wind loads
- settlements of abutments and piers - thermal actions '
uniform temperature vertical temperature gradient horizontal
temperature gradient temperature differences between individual
parts of the bridge (e.g. stay cables, pylon and stiffening
girder)
- creep and shrinkage of concrete
- earthquake actions - vehicle impact - derailment - rupture of
the conductor line others
Extraordinary actions to consider are:
1.5.2 Bearing reactions For permanent actions such as
self-weight of the construction, dead load and pre- stressing, the
bearing reactions can be calculated as one load case. For the
analysis of the bearings it is necessary to consider different
combinations of the bearing reactions: - maximum vertical force and
the adjacent horizontal force, - minimum vertical force and the
adjacent maximum horizontal force, - maximum horizontal force and
the adjacent maximum vertical force, - maximum horizontal force and
the adjacent minimum vertical force. The simplest way to obtain
these combinations is to calculate the variable actions, es-
pecially the traffic load, according to the influence line. One
should bear in mind that horizontal actions such as centrifugal
forces or braking forces are proportional to the vertical traffic
load, but other loads, such as wind or traffic or traction forces
for rail- ways, are not.
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18 1. Bearings
To obtain the extreme bearing reaction it is necessary to
consider that all bridges are three-dimensional and not merely
plane systems. The influence lines (influence surfaces) of the
bearing reactions can be found as the displacement curves
(displacement surfaces) of the system, due to unit displacements F
= 1 or cp = 1, acting at the position and in the direction of the
required force. If these analyses are performed on a three
dimensional model, the definitive influence area will result
directly (fig.1 S.2-1; fig.1 S.2-2). If plane models are used for
the analyses, special care is necessary, particularly with
continuous girders with open or box sec- tions. The following
examples demonstrate the difference:
Fig. 1.5.2-1: Influence area for the verticul bearing reaction
A, box section.
Fig. 1.5.2-2: ZnJuence area for the vertical bearing reaction A,
open section.
1.5.3 Bearing displacements As already mentioned, the zero
adjustment (null position) of every bearing has to be defined. The
displacements are measured from that position. Thus, for concrete
and composite bridges it is usual to consider displacements under
time-dependent actions such as creep and shrinkage from the time of
installation of the bearing to the time de- fined for the null
position (normally t = w), from which position the displacements
due to variable actions are measured. To obtain the maximum
displacements and rotations, again we can use influence lines. The
influence line of a displacement can be calculated as the
displacement curve due to the corresponding unit force P = I. To
take into account the imperfections due to installation, the
temperature difference for the calculation of bearing displacements
should be assumed higher than for the structural analysis of the
bridge, or some additional displacement should be consi- dered.
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I .6 Construction of bearings
1.6 Construction of bearings
Fig. 1.6-1 gives un overview for the most common bearings.
19
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20 1. Bearings
1.6.1 Elastomeric bearings Elastomeric bearings are the simplest
types of bearings. In the basic mode they con- sist merely of an
elastomeric block (usually rectangular or round). The elastomeric
works as a soft part between sub- and superstructure and allows
movements in all di- rections by elastic displacements or
rotations. Under vertical loads the elastic block bulges, leading
to vertical displacements. A solution to this problem was found by
re- inforcing the elastic block by thin horizontal steel plates,
vulcanized to the elastomer (fig. 1.6.1 - 1). The reinforcing
plates prevent the block from bulging, thus leading to very small
vertical displacements, but they do not hinder horizontal
displacements in every direction and also allow small rotations in
all directions. Every displacement and rotation leads to
restraining forces and moments which have to be taken into account
on the whole structure.
These restraining forces are possible if the friction between
bearing and sub- and su- perstructure is sufficient. The friction
forces F depend on the compressive force C and the friction
coefficient p, with F = C . p. If displacements take place under a
small compressive force, sliding between bearing and sub- or
superstructure can occur. To avoid this it is necessary to use
elastomeric bearings with resistance to sliding. This can be
achieved by applying vulcanized plates on the bottom and on the top
of the bearing, which can be connected to the sub- and
superstructure by bolts, pins or ap- propriate shapes (fig.
1.6.1-2).
Fig. 1.6.1-1: Elastomeric hearing (unanchored)
Smaller, short time, horizontal forces can be transmitted by the
restraining forces. If these forces are higher or if they are
permanent loads a restraining steel construction is required. In
these case the elastomeric bearing transmits the vertical force and
allows rotations, while horizontal forces in one or two directions
are transmitted by the steel construction (fig. 1.6.1-3 ; fig.
1.6.1-4).
Fig. 1.6.1-2: Elastomeric bearing (anchored)
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1.6 Construction of bearings 21
I
Fig. 1.6.1-3: Elastomeric bearing constraint
Combination: elastomeric bearing and steel construction fixed in
one direction.
Fig. 1.6.1-4: Fixed elastomeric bearing
Combination: elastomeric bearing and steel construction fixed in
two directions.
1.6.2 Steel bearings Steel bearings are the oldest type of
bearings. They have been used for more than 100 years. The
principle is simple: a flat plate rolls on another steel plate with
a curved sur- face. If this surface is part of a sphere,
theoretically we obtain a point tangency. If this surface is part
of a cylinder, theoretically we obtain a linear tangency. In the
first case we speak of point rocker bearings, in the second case of
line rocker bearings. These bearings allow rotations in all or in
one direction, but they do not allow displacements
Under minimal vertical reactions in combination with horizontal
loads point rocker bearings and line rocker bearings can exhibit
damage of their connections, because of tension. In combination
with sliding elements these bearings are very sensitive to this
phenomenon, and it causes partial uplift and excessive wear as a
result. Linear tangencies can be found also in roller bearings
consisting of a roll and a lower and an upper plate (fig. 1.6.2-5).
These bearings allow rotations in one direction and displacements
in one direction. The problem with these bearings is a point or
linear concentration of the bearing force, which theoretically
leads to infinite stresses. In 188 1, the physicist Heinrich Hertz
found the solution of this problem: caused by the elastic
deformation the theo- retical point of tangency yields to a circle,
the theoretical line of tangency yields to a rectangle. The
infinite stresses decrease to high but finite stresses, the so
called Hertz compression stresses over a very small contact zone.
If the radius of the sphere or of the cylinder decreases the Hertz
stresses increase. From the local stress concentration the stresses
have to be distributed to the contact zones between bearing and
sub- and superstructure. Therefore, steel bearings normally need
thicker plates for the stress distribution than other types of
bearings which transfer the bearing reactions over an area.
(fig. 1.6.2-1 ; fig.1.6.2-4).
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22 1. Bearings
Point rocker bearings are used for bearing reactions in the
range 500 and 2500 kN, line rocker bearings and roller bearings for
loads in the range 200 and 20 000 kN.
Fig.1.6.2-I: Fixed point rocker bearing
Fig. 1.6.2-2: Point rocker bearing constraint in one
direction
Fig. 1.6.2-3: Free point rocker bearing
Fig. 1.6.2-4: Line rocker bearing
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I .6 Construction of bearings 23
i Fig. 1.6.2-5: Roller bearing (left side without guide rail;
right side with guide rail)
The contact zones of steel bearings cannot be protected against
corrosion. Therefore corrosion-resistant layers of high alloyed
steel should be used for the contact areas. This can be done by
building up a surface by forging or by welding. Between the mild
steel and the hardened high alloyed steel of the surface there
should be a welded or forged tough buffer zone. The thickness (in
mm) of the hardened layer both on the roller (radius R in mm) and
of the plate should be t 2 0,14 . R - 2.
1.6.3 Pot bearings These bearings were invented in the 1950s.
They combine the two desirable proper- ties: rotation capacity with
a very small resistance and transmission of the bearing reaction
over a defined area.
The pot bearing consists of a steel pot, filled with an
elastomeric disc and a lid or a piston to the top (fig. 1.6.3- 1).
When subjected to high compression forces, the unrein- forced
elastomeric disc behaves similarly to a liquid. Rotations can occur
due to the nearly constant volume of the elastomer (v = 0,5). Of
great importance is the sealing between the elastomeric pad and the
lid: if this sealing has a defect the elastomeric pad escapes like
a viscous liquid.
The standard type of pot bearing allows only rotation (fig.
1.6.3-2). Vertical forces are transmitted to the pad, horizontal
forces from the lid to the pot. To release one sliding direction,
an additional construction becomes necessary (fig. 1.6.3-3 and fig.
1.6.3-5). This sliding construction consists of three components: a
polytetrafluorethylene (PTFE) disc, a surface of polished stainless
steel connected to a sliding plate of struc- tural steel and
lubrication grease. PTFE is a plastic with high mechanical and
chemi- cal resistance, great toughness and very small friction when
combined with polished stainless steel. The PTFE disc is 5 to 6 mm
thick, where half a thickness is enclosed by the lid. This disc has
small round pockets on the surface for the lubrication grease
(normally silicon grease) to reduce friction and wearing.
To constrain the movement in one direction an additional guide
is used for the lid. This guiding device allows movements in only
one direction (fig. 1.6.3-3). Pot bearings are used for vertical
bearing forces from 1000 kN up to 100000 kN. Depending on the
standard applied the allowable compression between lid and
elas-
-
1. Bearings 24
tomeric pad should not exceed 4.0 kN/cm2. The allowable
compression for the PTFE is 3 kN/cm2 for permanent loads and 4.5
kN/cm2 for short term loads (traffic, wind etc.). Pot bearings have
the advantage of a very high vertical stiffness (nearly incompres-
sible elastomeric part). It is comparatively independent of the
size of bearing and the applied load. This characteristic is
important for the bearing of high velocity railway bridges.
Bearings with low vertical stiffness can lead to damage of the
rails.
Fig.1.6.3-1: Function of a pot bearing
astomere disc
Lid Sealing
Pot - wall
Pot - bottom
Fig. 1.6.3-2: Fixed pot bearing
Fig. 1.6.3-3: Pot bearing constraint in one direction
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1.6 Construction of bearings 25
Fig.1.6.3-4: Members of a pot bearing
Anchoring plate Sliding plate Polished stainless steel PTFE
(Polytetrafluorethylen) Lid Pot -wall Sealing Elastomere disc Pot -
bottom
Fig.1.6.3-5: Free pot bearing
1.6.4 Spherical bearings The basic type of spherical bearing
consists of three main parts: the pan, the part of a sphere and the
upper plate made of constructional steel (fig.1.6.4-1). To allow
dis- placements between the parts, sliding surfaces are necessary.
The pan has a PTFE plate on the upper surface, the part of the
sphere has a chrome-plated polished surface on the underface and a
PTFE plate also on the upper surface, and the upper plate has a
polished stainless steel plate on the underface. The PTFE plates
are chambered over half the thickness and have lubrication pockets
with silicon grease, like the sliding plates for pot bearings. The
friction resistance of the sliding parts causes reaction moments
due to rotations. They must be taken into account to consider
additional design stresses of the bearing material.
The vertical bearing reaction is transferred over the compressed
areas of the PTFE. The basic model is a moveable bearing (fig.
1.6.4-4). To constrain horizontal displace- ments an additional
construction to connect the upper plate with the pan becomes
necessary (fig.1.6.4-2; fig.1.6.4-3). British and Italian bearings
have one sliding plane only and a deeper concave part to take over
horizontal forces (fig. 1.6.4-5). The construction must be checked
for uplift and exceeding the stresses in the contact area. In the
bearings with two sliding planes the centre of rotation is between
the contact areas of the sliding surfaces, whereas in Italian and
British bearings it is somewhere in the bridge structure or in the
pier or the abutment.
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26 1. Bearings
Like pot bearings, spherical bearings are used for vertical
forces in the range of 1000 to 100 000 kN.
Polished Sliding plate
hb Part of sphere PTFE Chrome plated
polished surface
Fig.1.6.4-1: Members of a spherical bearing
I Fig. 1.6.4-2: Fix spherical bearing
I I I
Fig. 1.6.4-3: Spherical hearing constraint in one direction
I 1
I I
I Fig. 1.6.4-4: Free spherical bearing
-
1.6 Construction of bearings 27
Fig. 1.6.4-5: Italian and British spherical bearing (one sliding
su face )
1.6.5 Leaf and link bearings All the above mentioned bearings
are able to transfer compression forces. If tensile forces as well
as compressive forces must be transferred, leaf and link bearings
are used. These bearings can only transmit forces in the direction
of the leaf. To transfer forces in the crosswise direction,
separate bearings must be used.
A leaf bearing consists of a foot plate, one or two lower leafs
with pin holes and two or one upper leaf with foot plate and pin
holes, connected by a pin. Leaf bearings al- low free rotation in
one direction. Pin and pin holes must have a fit less than 0.3 mm,
as in cases of greater slackness and changing forces the pin will
punch the hole. Pin plate and pin should be of different types of
steel to avoid seizure. Pin plates are made of structural steel,
pins often of tempered steel.
For link bearings a pendulum is linked to the foot leaf and to
the upper leaf by pins. Link bearings allow rotation and
displacement in one direction. For pin holes and pins the same
rules apply as given for leaf bearings.
Link bearings with universal (Cardan) joints are used only in
special cases. They allow rotation and displacement in all
directions.
Displacements 6 of link bearings are always combined with a
small displacement 6, , with R equal to the distance between the in
the perpendicular direction. 6, = __
2 R axes of the pins. Therefore this distance should not be too
small.
62
1.6.6 Disc bearings Disc bearings were introduced in the late
1960s. The vertical loads are transferred by an elastomeric disc
made of polyether-urethane polymer. In contrast to a pot bearing a
transverse extension of the elastomeric disc is possible. Bearing
capacity and func- tioning is comparable with an elastomeric
bearing. Rotations around the horizontal axis are transferred by
differential deflection of the disc. The rotations cause a shift of
the axis of the load from the centre of bearing, which must be
considered in the design. Horizontal forces are transferred by a
shear-restriction device which allows vertical deformation and
rotation. The basic type is a fixed bearing. Free bearings are con-
structed by additional sliding elements and (if necessary) guiding
systems.
-
28 1. Bearings
!
Fig. I . 6.6- I : Fixed bearing
I
Fig. 1.6.6-2: Uni-directional guided
-top plate
bearing assembly
base plate
Fig. I . 6.6-3: Multi-directional non-guided
Next Page
-
1.7 Materials for bearings 29
1.7 Materials for bearings
1.7.1 Steel Structural steel Structural steel is used for all
parts of bearings which are not under extraordinary local stress or
do not require special properties against corrosion. Structural
steel for bearings can be: - Non-alloy structural steels according
to EN 10025 - Fine-grained structural steels according to EN 101 13
- Quenched and tempered steels according to EN I0082
Eurocode 3 may be used for the design of all bearing components
made from struc- tural steel according to EN 10025 and EN 101 13
and for all connections (bolts, welds etc.). Quenched and tempered
steels are used mostly for non-welded parts under high pressure
(parts with Hertz compression, bolts of leaf and link bearings). In
contact areas with Hertz compression layers of corrosion-resistant
hard steel can be applied by forging or by welding. In the case of
hard-surface welding a tough intermediate (puffer) layer must be
welded between the steel and the hard-surface.
Stainless steel Stainless steel according to EURONORM 88-2 or I
S 0 683 can also be used for bear- ings. For design one should use
EC 3 , part 1-4. Concerning stainless steel for sliding plates see
1.7.3.
1.7.2 Elastomeric parts Elastomeric parts of bearings consist
normally of natural or artificial (chloropren) rub- ber (NR or CR,
respectively). Artificial rubber has the same good properties as
natu- ral rubber, and in addition it has a higher resistance
against ozone, ultraviolet radiation and ageing and is more rigid.
The characteristic mechanical property is the shear modu- lus G
between 0.7 and 1.15 N/mm2 at room temperature, decreasing with
increasing temperature. When undergoing stress changes the volume
of rubber is nearly constant. So we have a Poissons ratio v = 0.5
and a Youngs modulus of elasticity E = 2 . ( 1 +v) . G -- 3 . G.
The fracture strain of rubber lies between 250 % and 500 %. Rub-
ber creeps under stress by up to 50 % of the elastic strain, but
creeping ends within some days or weeks. Rubber does not break
under compression, it can only break under tensile or shear
stresses. Compressing a rubber pad changes its shape. The changing
of the shape depends on the possibility of displacement at the
compressed areas. If the compressed areas are fixed to a rigid
surface, the displacement remains small. Thus we obtain the
inequality A, > A , > A3 (fig.1.7.2-1).
Fig. 1.7.2- I : Vertical displacements depending on the lateral
expansion
Previous Page
-
30 1. Bearings
Fig. 1.7.2-2: Stress distribution
If the surface of the rubber is fixed to a rigid body shear
stresses develop between the two surfaces under compression (fig.
1.7.2-2). Under compression we obtain a virtual modulus of
elasticity E, Lllmpr which depends not only on the shear modulus G
but also on the thickness of the part between two plates. For
rectangular parts a good approxi- mation for E, co,npr is given
by
'1 conipr = G (: ) . (1 - 0,6 g) for b 2 a The maximum stresses
under compression between two rigid bodies are
F ab
with o = -, F: compression force.
For bending, the effective modulus of elasticity E, bcndlng is
lower than E, i
-
1.7 Materials for bearings 31
the maximum (3 is not in the middle of one half but nearer the
outer side; thus we finally obtain: a + < - , El compr. This is
described very well by the following approximate formula:
1 - - a 2 El
-
for b 2 a
Under the rotation a we obtain a curvature p = ~ = a 'b
with I = _____ 12
a Mi? and a restraining moment bending ' I
d
Fig. 1.7.2-3: Rotution - restraining moment
Fig. 1.7.2-4: Displacement - restruining~forces
1.7.3 Sliding elements For sliding elements in constructional
bearings it is normal to use PTFE, also known by the registered
trade names Teflon and Hostaflon. PTFE is a so called thermoplast.
For bearings it is used in the original (virgin) condition, i. e.
not sintered and without fillers. As a counterpart to this rather
soft material polished stainless steel plates are normally used,
and sometimes acetal resin plates or hardened chromium-plated steel
plates. Chromium-plated steel plates are not resistant to fluorine
ions and are rather prone to corrosion than stainless steel plates.
They are allowed for convex elements only. The combination of a
soft and a hard part has the advantage that there is no danger of
cold welding which can occur on polished metal or plastic surfaces
under high pres- sure. To minimise the friction silicon grease
should be used to provide lubrication. To keep this grease between
the two surfaces the PTFE has lubricant pockets on its sur- face,
so that a permanent lubrication takes place over several years. The
PTFE plates for bearings are normally 5 to 6 mm thick, the depth of
lubricant pockets is 2 mm. Un-
-
32 1 . Bearings
der pressure the PTFE yields. To keep the PTFE in the desired
shape it is necessary to keep about half the thickness in a with
sharp edges. Over the sharp edges we obtain a small bulge. It is
also possible to glue PTFE to a steel surface. In this case the
PTFE is about 2.5 mm thick. The friction coefficient increases with
decreasing temperature and with decreasing compression. The static
friction coefficient (first movement) is higher than the dy- namic
coefficient. After movement has taken place the dynamic friction
coefficient re- mains at this value and returns to the static value
after a few hours. This might depend on the orientation of the
large polymer molecules; during movement they are orientat- ed into
the direction of motion within a very thin surface layer. When the
motion is stopped, the orientation is lost within a few hours. Fig.
1.7.3-1 shows the design val- ues of the friction coefficient pLd
between PTFE and stainless steel, depending on the compression
force (EN 1337-2).
I
I I I I I I I I I
0.00
Fig. 1.7.3- I : Friction coejficient depending on the
compression force
I I I I I I - 0.0 0.5 1 .o 1.5 2.0 2.5 3.0 p [kNicm']
The design value of the ultimate compression load is
f , = 6,5 (1 - 0,02. [ 6 - 30'C)) kN/cm2 for 6 2 30'C , 6 :
maximum temperature of the bearing.
The wearing of the PTFE depends on a) the product of compression
and velocity of the displacement b) the total amount of sliding
during the life-time c) the lubrication of the surface (a loss of
lubrication leads to extremely high wearing) d) the roughness and
the hardness of the stainless steel surface e) the contact pressure
near the edge of PTFE (ironing effect)
-
I .8 Analysis and design of bearings 33
For slow movements caused by thermal actions we obtain long
sliding movements but at a low velocity. Quick movements caused by
traffic loads have short sliding move- ments but they occur at high
velocity. Wearing is mostly caused by the second case.
For the stainless steel plate, austenitic steel X6CrNiMo17122
according to EU- RONORM 88-2, surface n (IIIc), should be used. The
stainless steel plate must cover the PTFE plate completely in all
situations. The thickness of the plate should be at least of 1 .5
mm. The connection to the carrying plate of mild steel can be
welded or glued. For 2.5 mm thick plates the connection can be
riveted or bolted.
1.8 Analysis and design of bearings
1.8.1 Hertz compression For the design of bearings the following
problems should be addressed: compression between two spherical
bodies, compression between a spherical and a flat body, com-
pression between two cylindrical bodies, compression between a
cylindrical and a flat body along a generator line. As already
mentioned, Heinrich Hertz obtained the solu- tion under the
following assumptions (1881): 1. The two bodies consist of
isotropic, homogeneous and infinitely elastic materials. 2. Only
normal stresses (no shear stresses) occur at the contact areas. 3.
The radius (width) of the contact areas is small compared with the
radii of the
Hertz found the following maximum compression stresses max (T
and widths b on the contact areas:
involved bodies.
Spherical body on spherical body
= 1,109 1 1 -f- 7
3 F ( I - v 2 ) . 1
3 E -*- b = 1 7 2E 1 Cylindrical body on cylindrical body
-
34 1 . Bearings
with
1 1 + ~-~ rl r2
Fig. I .8. I - I b: Arrangement of the radii
F bearing reaction 1 length of the cylinder r,, r2 radii of the
bodies in contact E Young's modulus Fig. 1.8.1-2: Stress
distribution V max (3 b
Poisson's ratio (v = 0.3 for steel) maximum normal stress at the
contact area half the width of the contact zone
For the usual rocker or roller bearings the max (3 beneath the
vertical bearing reaction greatly exceeds the material yield
strength (fig. 1.8.1-2). However, at the contact zone we have not
only vertical but also horizontal compression stresses. According
to the von Mises criterion the comparison stress
Ov = d0i2 + O2 + Oj3 - (3~(32 - reaches the material yield
strength f,. In the present three-dimensional compression regime,
(3" will be less than (3, and yielding will not begin until o1 =
f,. On the other hand, the maximum strain does not occur at the
surface in the middle of the compression zone, so that the hardness
of the surface is not the only criterion for the assessment of
Hertz compression.
I 2 - O3Oi and yielding begins when
EN 1337-4 - roller bearings - gives for the design line load pd
of a roller bearing
(cylindrical body on flat surface): pd 5 18. R . f 2
E d with
f, R radius of the cylinder Ed design value of the modulus of
elasticity
tensile strength of the material
-
1.8 Analysis and design of bearings
a c h c ,
35
a
Compared to Hertz's formula with
maxo, =0.418. R
we find
maxo, 1 0 . 4 1 8 . f i . f " = 1,77.fu =oRd .
EN 1337-6 - rocker bearings - gives for the design load Fz,d of
a point rocker bearing
(sphere against plane surface) Fz,d 5 170. R2 . f" . Ed
Compared to Hertz's formula with
we find m a x o , 10.388..1/170.f, = 2,15f, =oRd.
For cylindrical rocker bearings the same formulae as for roller
bearings are used.
1.8.2 A special problem of all leaf and link bearings concerns
the design of the pin and the pin plate. Eurocode 3, part 1 - 1,
gives simple but satisfactory design rules. The design values of
the shear force and the bending moment for the pin can be found
using the simple model of distributing the force of each pin plate
uniformly over the pin.
Pin and pin plate for leaf and link bearings
In the case of fig. 1.8.2-1 we obtain the shear force and the
bending moment according to fig. 1 3.2-2 and fig. 1.8.2-3.
-
36 1. Bearings
cw Fig. 1.8.2-2: Shear force
Fig. 1.8.2-3: Bending moment
For normal bridge bearings we have: c = 0, a = ~ .
The design values for the resistances are
b 2
d 2 n 4
Shear: F,,, = 0.6. A . fup / Y M p = 0.6. ~ . fup / Y M p = 0.47
1. df,, / Y M p
The combination of shear and bending has to fulfil the
inequality
In this inequality, the central pin plate is controlling.
The bearing resistance of plate (thickness t and yield strength
f,) and pin is: F,,,, = 1.5.t . d . f y /YM,
f,, field strength of the pin fUp tensile strength of the pin
yMp = 1.25 according to EC 3- 1 - 1 The bearing capacity of the pin
plate at the hole is achieved under one of the following conditions
(EC 3- 1 - 1 gives two possibilities):
-
1.9 Installation of bearings
a) Depending on the pin plate thickness t:
t = min (2a, b),
e >-- FSd ' Y M p + d 7 - - 2t ' f y 3
FSd ' Y M p + e, 2 2t . f, 3
b) Depending on the geometry of the pin plate:
37
d = e 2 +-
3
1.9 Installation of bearings
Concerning the installation of bearings, the need for a later
simple replacement must be taken into account. So it should be
common practice to put every bearing between a lower and an upper
steel cover plate. These cover plates are anchored or connected
both with the substructure and the superstructure. These cover
plates are connected to the bearings during the installation but
remain fixed to the structure while the bearings are replaced (fig.
1.9- 1). Thus, the connection between bearing and cover plates
should be constructed in order to allow a simple release. Bolted
connections are often used but after many years often the bolts can
hardly be unscrewed. According to the author's experience,
fastening the bearings with small fillet welds that can be ground
off and remade during the replacement process is simpler.
Fig. 1.9-1: Fixing of a bearing
Generally, bearings should not be built directly on the
construction beneath. To guar- antee that the area below a bearing
is fully sealed a layer of mortar or of a similar prod- uct is
used. So the height of the bridge at the abutments or piers can be
adapted easily and very exactly. It is useful to fix the bearing to
the bridge so that there is no clear- ance at the upper plate and
to adjust the bridge by hydraulic jacks. In this situation the
-
38 1. Bearings
bearings should be adjusted exactly. Thus, the lower plate will
get exactly the desired inclination (horizontal or parallel to the
gradient, see fig. 1.9- 1) and all moveable bear- ings will have
the desired pre-adjustment, which depends on the temperature of the
bridge and the expected shrinkage and creep. The installation of
the bearings should be done early in the morning when the bridge
has a (nearly) constant temperature. The designer has to provide a
table with the pre-adjustment of every bearing depending on the
measured bridge temperature. For good functioning, careful handling
of the bearings during installation is very im- portant. The
bearings must be kept free of dirt, mortar, water and dust,
especially from all moving parts. Many bearings, such as pot
bearings and spherical bearings, are pro- tected against dust by
rubber bulges, but others are not protected at all. These have to
be cleaned to remove mortar and sand after the installation. The
gap between the lower plate of the bearing and the substructure is
normally 3 to 5 cm thick and must be completely filled with a
mortar bedding. This can be done in dif- ferent ways: - by a fresh
mortar bedding, chambered in the centre where the bearing is set.
The
excess of mortar will come out on all sides and must be removed.
- by a special joint filling mortar which must be mixed in a pan
type concrete mixer
with a precise quantity of water. This mortar is liquid at first
and should be poured in a formwork around the bearing only from one
side, so that the air can escape on the other side. The special
mortar fills the gap without air bubbles, it sets and hard- ens
very quickly so that after one day the mortar bedding can be fully
loaded and the formwork removed. If the gap is less than 1 cm a
two-component epoxy resin should be used instead of mortar.
Initially this resin is a lighter fluid than mortar, thus
completely filling even very small gaps.
- by boxing up earth-damp mortar in the gap with a wooden stick
also from one side to avoid air bubbles. This method will be
difficult for the lower plates with a short side larger than half a
metre.
All mortars should be non-shrinking.
1.10 Inspection and maintenance
Visual tests of all bearings should be done by qualified
personnel at regular intervals. The following properties of the
bearings have to be checked: a) sufficient ability to allow
movement, taking into account the temperature of the su-
b) correct positioning of the bearings themselves and of parts
of the bearing relative to
c) uncontrolled movement of the bearing d) fracture, cracks and
deformations of parts of the bearings e) cracks in the bedding or
in adjacent parts of sub- and superstructure f) condition of the
anchorage g) condition of sliding or rolling surfaces h) condition
of the anticorrosive protection, against dust, and of the sealings.
For the different types of bearings the following checks are of
importance:
perstructure
each other
-
1.1 1 Replacement of bearings 39
Elastomeric bearings: Displacements and rotations, cracks in the
elastomer. Roller and rocker bearings: Displacements and rotations,
adjustment of the guiding device, no gap in the contact line. Pot
bearings: Sufficient mesh of the lid in the pot, tight sealing of
the elastomer in the pot (if the sealing has a defect, the
elastomer comes out like a pancake!) Sliding devices - PTFE and
stainless steel: Thickness of the PTFE, clean surface of the
stainless steel.
The result of an inspection should be recorded in a report. EN
1337- 10 gives an ex- ample for such a report. For maintenance the
bearings should be cleaned, lubricated (if necessary and pos-
sible) and coated with paint. Small defects should be repaired as
far as possible.
1.11 Replacement of bearings
The replacement of bearings is a normal maintenance operation
for bridges. Thus, a bridge designer has to provide measures so
that a replacement can be carried out easily. The owner of a bridge
has to define in the tender if the replacement of the bear- ings
must be carried out under full traffic, restricted traffic or
without traffic, depend- ing on the importance of the bridge and
the possibility of a traffic ban or a traflk diversion. In case of
a replacement under traffic the jacking equipment should allow the
same movements as the bearing. To allow rotations the jacks around
one bearing should be connected to a single hydraulic circle. That
means that the security devices must have a sufficient clearance.
Translations are possible by means of additional sliding con-
structions.
- -
I i
\ / - _m_
reinforcement against splitting tension
Fig. 1. I I - I : Stiffened areas f o r hydraulic jacks
To replace a bearing, the bridge has to be lifted by one or more
hydraulic jacks. For hy- draulic jacks, adequately stiffened areas
to transmit the hydraulic jack forces to the sub- and
superstructure are required. Concrete parts must be reinforced
against split- ting tension, steel parts need stiffeners (fig.
1.11-2). Thus, the construction drawings must show in which areas
or at which points hydraulic jacks can be set, what are the maximum
lifting forces and up to which level the bridge may safely be
lifted. This
-
40 1. Bearings
kN 500 1000 2000 SO00
data is of particular importance if the bridge is supported in a
statically indeterminate way at one abutment or pier, in which case
the lifting force depends on the height of lift. High stresses can
be induced in the cross girder or diaphragm by the lifting device.
In such cases it may be necessary to lift the whole cross section
uniformly with two or more hydraulic jacks even for exchanging only
one bearing. If more than one jack is used the forces can be
controlled by hydraulic connection of some or of all jacks: all
connected jacks have the same pressure. Hydraulic jacks need some
clearance for the installation. For lifting by a few millimetres up
to two centimetres flat piston jacks can be used. The following
table gives a guide for the required clearances:
Normal hydraulic jack Flat piston jack mm mm 300 150 3 60 180
450 200 600 250
I Force I Required clearance I Required clearance
Table 1.11-1: Required clearance for hydraulic jacks
There are flat jacks with a height of 80 mm and a lifting force
up to SO00 kN. But their stroke is only 20 mm and there is no
security device. This kind of jack should be ap- plied for special
cases only. New bridges should be constructed for normal hydraulic
jacks. In all situations, during the replacement of a bearing the
hydraulic jack should be se- cured by a mechanical device such as
an adjusting nut for the piston or lining plates to avoid dropping
in case of pipe rupture or rupture of the piston sealing which
some- times can occur (fig.l.11-3 and tig.l.11-2).
I !! I
pipe or
I t-------- I L - - - - _ _ _ _ c =
Fig. 1.1 1-2: Hydraulic jack with lining plates
-
1.12 Codes and standards 41
Fig. 1. I 1-3: Hydraulic jack with thread and nu1
If the replacement of a bearing takes a long time so that
displacements of moveable bearings will occur, the hydraulic jacks
have to be equipped with a sliding device, normally PTFE plus a
sliding plate of stainless steel.
Particular care is required when replacing bearings which
transmit horizontal forces: if the friction between the jack and
the surface of sub- and superstructure is not suffi- cient it is
necessary to restrain the movement of the bridge by appropriate
devices. If the replacement is done under traffic, in most cases,
and especially for railway bridges, these devices have to transmit
all horizontal forces due to a possible loss of friction.
1.12 Codes and standards
The first attempts to standardize bearings in national codes
were made decades ago. In Europe several codes and national
standards are available. The best known national standards in
Europe on this topic are Germany: DIN 4141 Lager im Bauwesen
(structural bearings),
United Kingdom: BS 5400 Teil 1 bis 14. Steel, Concrete and
Composite Bridges.
Section 9.1 Code of Practice for design of bridge bearings
Section 9.2 Specification of materials, manufacturing and
installa-
tion of bridge bearings
New European Standards about bearings are the following EN 1337
Structural bearings with the parts EN 1337- 1 General design rules
EN 1337-2 Sliding elements EN 1337-3 Elastomeric bearings EN 1337-4
Roller bearings
-
42 1. Bearings
EN 1337-5 Pot bearings EN 1337-6 Rocker bearings EN 1337-7 EN
1337-8 EN 1337-9 Protection EN 1337- 10 Inspection and maintenance
EN 1337- 1 1 Transport, storage and installation
Spherical and cylindrical PTFE bearings Guided bearings and
Restrained bearings
A recommendable American Standards about bearings is the
following: AASHO-LRFD: American Association of State Highway
Officials ( I 994).
1.13 References
Books and special chapters about bearings for bridges: Eggert
H., J. Grote, W. Kauschke: Lager im Bauwesen. Verlag von Wilhelm
Ernst & Sohn, Berlin, Munchen, Dusseldorf 1974. Lee D.J.:
Bridge Bearings and Expansion Joints. Second edition by E & FN
Spon, London, Glasgow, New York, Tokyo, Melbourne, Madras 1994.
Eggert H., W. Kauschke: Lager im Bauwesen. 2. Auflage, Ernst &
Sohn, Berlin 1995. Rahlwes K., R. Maurer: Lagerung und Lager von
Bauwerken in: Beton-Kalender 1995, Teil2, Ernst & Sohn,
Berlin.
Papers: Albrecht, R.: Zur Anwendung und Berechnung von
Gummilagern. Der Deut- sche Baumeister 1969, Heft 4, Seite 326, und
Heft 6, Seite 563. Andra, Beyer, Wintergerst: Versuche und
Erfahrungen mit neuen Kipp- und Gleitlagern. Der Bauingenieur 5 (1
962). Andra, W. und Leonhardt, F.: Neue Entwicklungen fur Lager von
Bauwerken, Gummi- und Gummitopflager. Die Bautechnik 39 (1 969),
Heft 2, Seite 37 bis 50. Bayer, K.: Auflager und Fahrbahnubergange
fur Hoch- und Bruckenbauten aus Kunststoff. Verein Deutscher
Ingenieure VDI im Bildungswerk BV 1956 (Vor-
tragsveroffentlichung). Beyer, E. und Wintergerst, L.: Neue
Briickenlager, neue Pfeilerform. Der Bau- ingenieur 35 (1960), Heft
6, Seite 227 bis 230. Eggert, H.: Briickenlager. Die Bautechnik 50
(1973), S. 143/144. Bub, H.: Das neue Institut fur Bautechnik.
Strasse und Autobahn, Band 20 (1 969), Seite 189. Burkhardt, E.:
Gepanzerte Betonwalzgelenke, Pendel- und Rollenlager. Die
Bautechnik 17 (1939), Seite 230. Cardillo, R. und Kruse, D.: Paper
(61/WA-335) ASME (1961). Cichocki, F.: Bremsableitung bei Briicken.
Der Bauingenieur 36 (1961), Seite 304 bis 305.
-
1.13 References 43
Clark, E. und Moutrop, K.: Load Deformation Characteristics of
Elastomer Bridge Bearing Pads. University of Rhode Island, May
1962. Desmonsablon, Philippe: Le calcul des piles ddformables avec
appuis en caoutchouc. Annales des Ponts et Chaussdes, Paris 4/1960.
Eggert, H.: Bauwerksicherheit bei Verwendung von Rollen- und
Gleitlagern. Strasse Brucke Tunnel 1971, Heft 3, Seite 71. Eggert,
H.: Die baurechtliche Situation bei Lagern fur Briicken und
Hochbau- ten. Der Stahlbau 39 (1970), Heft 6, Seite 189. Einsfeld,
U.: Erlauterungen zu den Richtlinien von unbewehrten Elastomer-
lagern. Mitteilungen Institut fur Bautechnik 6/1972. Franz:
Gummilager fur Brucken. VDI-Zeitschrift, Bd. 101/1959, Nr. 12,
Seite 47 1 bis 478. Gent, A.: Rubber Bearings for Bridges. Rubber
Journal and International Plas- tics 1959. Grote, J.: Neoprenelager
- einige grundsatzliche Erwagungen. Kunststoffe im Bau 7/1968.
Grote, J.: Unbewehrte Elastomerlager. Der Bauingenieur 44 (l969),
Seite 121. Grote, J.: Vermeidung von Rissen und Dehnungsschaden
durch gummielasti- sche Lagerungen. Kunststoffe im Bau 11/1968.
Hakenjos, V.: Untersuchungen uber die Rollreibung bei Stahl im
elastisch-plas- tischen Zustand. Technisch-wissenschaftliche
Berichte der Staatlichen Materi- alpriifungsanstalt an der
Technischen Hochschule Stuttgart 1967, Heft 67/05. Heesen:
Gepanzerte Betonwalzgelenke, Pendel- und Rollenlager. Die Bau-
technik, Jahrgang 25 (1 948), Seite 26 1. Hutten, P.: Beitrag zur
Berechnung der Lagerverschiebungen gekrummter, durchlaufender
Spannbeton-Balkenbriicken. Dissertation TH Aachen 1970. Jorn, R.:
Gummi im Bauwesen. Elastische Lagerung einer Pumpenstation. Der
Bauingenieur 36 (1961), Heft 4, Seite 1371138. Keen: Creep of
Neoprene in Shear Under Static Conditions, Ten Years, Trans-
actions of the ASME, Juli 1953. Leonhardt und Andra:
Stutzungsprobleme der Hochstrassenbriicken. Beton- und
Stahlbetonbau 55 (1960), Heft 6. Leonhardt, F. und Reimann, H.:
Betongelenke, Versuchsbericht, Vorschlage zur Bemessung und
konstruktiven Ausbildung. DAfStb, Heft 175. Berlin: Verlag Ernst
& Sohn 1966, und Leonhardt, F. und Reimann, H.: Betongelenke.
Der Bauingenieur 41 (1966), Seite 49. Leonhardt, F. und
Wintergerst, L.: Uber die Brauchbarkeit von Bleigelenken. Beton-
und Stahlbetonbau 1961, Heft 5, Seite 123 bis 131. Maguire, C. und
Assoc.: Elastomeric Bridge Bearings Pads 1959. Massonnet: Zuschrift
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(1964), Seite 428. Monnig, E. und Netzel, D.: Zur Bemessung von
Betongelenken. Der Bauinge- nieur 44 (1969), Seite 433 bis 439.
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-
44 1. Bearings
[351
[361 [371
[431
[441
[491
[531
Nordlin, E., Stoker, S. and Trinble, R.: Laboratory and Field
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Bauingenieur 46 (1971), Seite 334. Rieckmann, H.-P.: Einfluss der
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Grote, J.: Einige Versuche an Neoprenelagern. Der Bauingenieur 38
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Conference (1964). Thul, H.: Bruckenlager. Der Stahlbau 38 (1969),
Seite 353. Topaloff, B.: Gummilager fur Briicken - Berechnung und
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Heft 9. Uetz, H. und Breckel, H.: Reibungs- und Verschleissversuche
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Reibungsuntersuchungen mit Polytetrafluorathylen bei hin- und
hergehender Bewegung. Die Bautechnik 44 (1967), Heft 5, Seite 159
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Gleitverschleissversuche an Kunststoffen. Kunststoffe, 59. Jahrgang
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Briicken. Elsners Taschenbuch fur den Bau- technischen
Eisenbahndienst, 1967, Seite 23 1 bis 277, Abschnitt E Brucken- und
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994). Dupont de Nemours Co.: Design of Neoprene Bridge Bearing
Pads, Wilming- ton ( 1959). CNR-UNI 1001 8-68 (Italian Standards
for rubber bearings).
-
1.13 References 45
Ministry of Transport: Provisional Rules for the Use of Rubber
Bearings in Highway Bridges, Memo. 802, London (1962).
Mitteilungen, Institut fur Bautechnik, 1970, Heft 2 und 4, und
1971, Heft 4 und 6. Ohne Verfasser. Auflager aus Teflon. Ausziige
aus dem Journal of Teflon 1964, 1965 und 1966, Druckschrift der Du
Pont de Nemours International S.A. Geneva, Switzerland. Ohne
Verfasser. Bruckenlager. Beratungsstelle fur Stahlverwendung,
Dussel- dorf, Merkblatt 339,2. Auflage 1968. ORE Office de
Recherches et dEssais: Verwendung von Gummi fur Brucken- lager,
Frage D 60, Utrecht (1 962, 1964, 1965). Wiedemann, L.: Zusatzliche
Richtlinien fur Lager im Brucken- und Hochbau. Mitteilungen
Institut fur Bautechnik 3/1973, S. 73. Verlag Ernst & Sohn.
Eggert: Vorlesungen uber Lager im Bauwesen. Wilhelm Ernst &
Sohn 1980/1981. Kauschke, W.: Entwicklungsstand der
Gleitlagertechnik fur Briickenbauwerke in der Bundesrepublik
Deutschland. Bauingenieur 64 (1989), Seite 109 bis 120.
BattermandKohler: Elastomere Federung, Elastische Lagerungen. W.
Ernst & Sohn, Berlin, Munchen 1982. Gerb:
Schwingungsisolierungen. Berlin, 9. Auflage 1992, Eigenverlag
(gegen Schutzgebuhr erhaltlich). Grote, J. und Kreuzinger, H.:
Pendelstutzen mit Elastomerlagern. Der Bau- ingenieur 53 (1978),
Seite 63/64. Kanning, W.: Elastomer-Lager fur Pendelstutzen -
Einfluss der Lager auf die Beanspruchung der Stutzen. Der
Bauingenieur 55 ( 1 980), Seite 455. MauredRahlwes: Lagerung und
Lager von Bauwerken. Betonkalender 1995, Ernst & Sohn, Teil 11.
Weihermuller, H. und Knoppler, K.: Lagerreibung beim
Stabilitatsnachweis von Bruckenpfeilern. Bauingenieur 55 (1980),
Seite 285 bis 288. Andra, W.: Der heutige Entwicklungsstand des
Topflagers und seine Weiter- entwicklung zum Hublager. Bautechnik
(1984), Seite 222 bis 230. Eggert, H.: 7 Grundsatze bei der
Lagerung von Brucken. 9. IVBH-Kongress Amsterdam 1972,
Schlussbericht. Internationale Vereinigung fur Briickenbau und
Hochbau, Zurich, Schweiz. Deinhard, J.M., Kordina, K., Mozahn, R.,
Storkebaum, K.-H.: Der Schadens- fall an der Mainbrucke bei
Hochheim. Beton - Stahlbetonbau, 72 (1977), Seite 1 bis 7. Eggert,
H. und Wiedemann, L.: Nutzungsgerechte Lagerung von Stahl- und
Verbundbrucken und unterhaltungsgerechte Konstruktion von
Bruckenlagern. IVBH Symposium Dresden 1975. Vorbericht. Eggert, H.:
Lager fur Brucken und Hochbauten. Bauingenieur 53 (1 978), Seite
161 bis 168, und Zuschrift 54 (1979), Seite 200. Konig, G. et. al.:
Spannbeton: Bewahrung im Bruckenbau. Analyse von Bau- werksdaten,
Schaden und Erhaltungskosten. Springer-Verlag Berlin, Heidel- berg,
New York, London, Paris, Tokio 1986.
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46 1 . Bearings
Pfohl, H.: Reaktionskraft am Festpunkt von Briicken aus
Bremslast und Bewe- gungswiderstanden der Lager. Bauingenieur 58
(1983), Seite 453 bis 457. Eggert, H. und Hakenjos, V.: Die
Wirkungsweise von Kalottenlagern. Der Bau- ingenieur 49 (1974),
Heft 3 , Seite 93/94. Lehmann, Dieter: Beitrage zur Berechnung der
Elastomerlager. Die Bautech- nik I (1978), Seite 19 bis 22, I1
(1978), Seite 99 bis 102, I11 (1978), Seite 190 bis 198, IV (l979),
Seite 163 bis 169. Kordina, K. und Nolting, D.: Zur Auflagerung von
Stahlbetonteilen mittels unbewehrter Elastomerlager. Der
Bauingenieur 56 (1981), Seite 41 bis 44. Kordina, K. und Osterath,
H.-H.: Zur Auflagerung von Stahlbetonteilen mittels unbewehrter und
bewehrter Elastomerlager. Der Bauingenieur 59 (1 984), Seite 461
bis 466. Kessler, E. und Schwerm, D.: Unebenheiten und
Schiefwinkligkeiten der Auf- lagerflachen fur Elastomerlager bei
Stahlbetonfertigteilen. Fertigteilbau- forum 13/83, Seite 1 bis 5
(Betonwerk + Fertigteil-Technik). Kessler, E.: Die Anwendung
unbewehrter Elastomerlager. Betonwerk + Fertig- teil-Technik, Heft
6 (1987), Seite 419 bis 429. Bundesminister fur Verkehr: Schlden an
Brucken und anderen Ingenieurbau- werken. Dokumentation 1982.
Verkehrsblatt-Verlag, Dortmund. Bundesminister fur Verkehr: Bericht
uber Schaden an Bauwerken der Bundes- verkehrswege. Januar 1984.
Eigenverlag BMV. Beyer, E. und Eisermann, G.: Nachstellbare
Bruckenlager. Erfahrungen beim Bauvorhaben Dusseldorf-Hauptbahnhof.
Beton 5/1983. Dickerhoff, K.J.: Bemessung von Bruckenlagern unter
Gebrauchslast. Disser- tation Universitat Karlsruhe 1985. Petersen,
Chr.: Zur Beanspruchung moderner Briickenlager. Festschrift J.
Scheer, Marz 1987. Hehn, K.-H.: Priifeinrichtung zur Untersuchung
von Lagern. VDI-Z 118 (1976), Seite 1 14 bis 118. N.N., Sanierung
der Kolnbreinsperre, Projektierung und Ausfuhrung. 1. Auf- lage Mai
199 1. Herausgeber: Osterreichische Donaukraftwerke AG. Hakenjos,
V. und Richter, K.: Dauergleitreibungsverhalten der Gleitpaarung
PTFE weiss/Austenitischer Stahl fur Lager im Briickenbau. Strasse,
Briicke, Tunnel 1 1 (1979, Seite 294 bis 297. Imbimbo M. und Kelly
J.M.: Influence of Material Stiffening on Stability of Elastomeric
Bearings at Large Displacements. Journal of Engineering Me-
chanics. Sept. 1998. Zederbaum, J. (1966): The frame action of a
bridge deck supported on elastic bearings. Civil Engineering and
Public Works Review 61(7 14), 67-72. Leonhardt, F. und Andra, W. (1
960): Stutzprobleme der Hochstrassenbrucken. Beton- und
Stahlbetonbau, 55(6), 121-32. Tanaka, R., Natsukawa, K. and Ohira,
T. (1984): Thermal behaviour of multi- span viaduct in frame. In
International Association of Bridge and Structural Engineering,
12th Congress, Vancouver, Canada, 3-7 September. Building Research
Establishment (1 979) Estimation of thermal and moisture movements
and stresses; Part 2, Digest 228, Watford.
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1.13 References 47
[96] Emerson M. (1977): Temperature differences in bridges:
basis of design re- quirements. TRRL Laboratory Report 765.
Transport and Road Research Lab- oratory, Crowthorne. Emerson M.
(1968): Bridge temperatures and movements in the British Isles. RRL
Report LR 228, pp.38. Road Research Laboratory, Crowthorne. Emerson
M. (1973): The calculation of the distribution of temperature in
bridges. TRRL Report LR 561. Transport and Road Research
Laboratory, Crowthorne. Emerson M. (1976): Bridge temperatures
estimated from the shade tempera- ture. TRRL Report LR 696.
Transport and Road Research Laboratory, Crow- thorne.
[ 1001 Stephenson, D.A. (1961): Effects of differential
temperature on tall slender co- lumns. Concrete and Constructional
Engineering, 56(5), 175-8: 56( 1 l), 401-3.
[ 1011 Garrett, R.J. (1985): The distribution of temperature in
bridges. The Journal of the Hong Kong Institution of Engineers,
May, 35-8.
[ 1021 ComitC Euro-International du BCton (1984). Design manual
on structural effects of time-dependent behaviour of concrete
(Bulletin No. 142). George Publishing Company.
[ 1031 ComitC Euro-International du BCton (1985). Manual of
Cracking and Defor- mations. Bulletin 158E, Lausanne.
[ 1041 Neville, A.M., Dilger, W.H. and Brooks, J.J. (1983):
Creep of Plain and Struc- tural Concrete. Construction Press,
London and New York.
[ 1051 Mattock A.H. (1961): Precast-prestressed concrete bridge
5.Creep and shrink- age studies. Journal of the Portland Cement
Association Research and Devel- opment Laboratories, May.
[ I061 Institution of Geological Sciences: National
Environmental Research Council (1 976), Atlas of Seismic Activity
1909-1968. Seismological Bulletin No.5.
[ 1071 Dollar, A.T.J., Abedi, S.M.H., Lilwall, R.C. und
Willmore, R.L. (1975): Earth- quake risk in the UK. Proceedings of
the Institution of Civil Engineers, 58, 123-4.
[ 1081 ICE and SECED (1 985): Earthquake engineering in Britain.
Proceedings of Conference of the Institution of Civil Engineers and
the Society of Earthquake and Civil Engineering Dynamics,
University of East Anglia, April.
[ 1091 Lee, D.J. (1 97 1): The Theory and Practice of Bearings
and Expanison Joints for Bridges, Cement and Concrete
Association.
[ 1 101 Buchler, W. (1987): Design of Pot Bearings, American
Concrete Institute Publication, SP-94, V01.2, pp. 882-915.
[ 1 1 11 Black, W. (1971): Notes on bridge bearings, RRL Report
LR 382, Transport and Road Research Laboratory, Crowthorne.
[ I 121 Kauschke, W. and Baignet, M. (1987) Improvements in the
Long Term Dura- bility of Bearings in Bridges, American Concrete
Institute Publication SP-94,
[ 1 131 Taylor, M.E. (1970): PTFE in highway bridges. TRRL
Report LR 491, Trans-
[ 1141 Eggert, H., Kauschke, W.: Lager im Bauwesen, Ernst &
Sohn, Berlin 1996.
[97]
[98]
[99]
V01.2,577-612.
port and Road Research Laboratory, Crowthorne.
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48 1. Bearings
[ 1 151 Hakenjos, V.: Lager im Bauwesen mit Komponenten aus
Kunststoff verdran- gen hochbeanspruchbare stahlerne Rollenlager.
13th H.F. Mark-Symposium on 19- 10-94 in Vienna.
[ 1 161 Marioni, A.: Apparecchi di appoggio per ponti e
strutture. ITEC, Milano 1983 [ 1 171 Campbell, T. I. and Kong, W.
L.: TFE Sliding Surfaces In Bridge Bearings. Re-
port ME-87-06, Ontario Ministry of Transportation and
Communications, Downsview, Ontario, 1987.
[ I 181 Crozier, W. F., Stoker, J. R., Martin, V. C. and
Nordlin, E. F.: A Laboratory Evaluation of Full-Size Elastomeric
Bridge Bearing Pads. Research Report CA DOT, TL-6574- 1-74-26,
Highway Research Report, June 1979.
[ 1 191 Gent, A. N.: Elastic Stability of Rubber Compression
Springs. ASME, Journal of Mech. Engr. Science, Vol. 6, No. 4,
1964.
[I201 Jacobsen, F. K. and Taylor R. K.: TFE Expansion Bearings
for Highway Bridges. Report No. RDR-3 1, Illinois DOT, June 197
1.
[ 1211 McEwen, E. E. and Spencer, G. D.: Finite Element Analysis
and Experimental Results Concerning Distribution of Stress Under
Pot Bearings. Proceedings of 1 st World Congress on Bearings and
Sealants, ACI Publication SP-70, Niagara Falls, 1 98 1 .
[ 1221 Nordlin, E. F., Boss, J. F. and Trimble, R. R.:
Tetrafluorethylene (TFE) as a Bridge Bearing Material. Research
Report, M & R 64642-2, California DOT, Sacramento, CA, June
1970.
11231 Roark. R. J. and Young, W. C.: Formulas for Stress and
Strain. 5th Ed., McGraw Hill, New York, 1976.
11241 Roeder, C. W., Stanton, J. F. and Taylor, A. W.:
Performance of Elastomeric Bearings. NCHRP Report 298, TRB,
National Research Council, Washington, D. C., October 1987.
[ 1251 Roeder, C. W. and Stanton, J. F.: State of the Art
Elastomeric Bridge Bearing Design. ACI Journal, 199 1.
[ 1261 Roeder, C. W., Stanton, J. F. and Feller, T.: Low
Temperature Performance of Elastomers. ASCE, Journal of Cold
Regions, Vol. 4, No. 3, September 1990,
[ 1271 Roeder, C. W. and Stanton, J. F.: Failure Modes of
Elastomeric Bearings and lnfluence of Manufacturing Methods.
Proceedings of 2nd World Congress on Bearings and Sealants, ACl
Publication SP-94, Vol. 1, San Antonio, Texas, 1986.
11281 Roeder, C. W., Stanton, J. F. and Taylor, A. W.: Fatigue
of Steel-Reinforced Elastomeric Bearings. ASCE, Journal of
Structural Division, Vol. 116, No. 2, February 1990.
[ 1291 Roeder, C. W., and Stanton, J. F.: Elastomeric Bearings:
A State of the Art. ASCE, Journal of the Structural Division, No.
12, Vol. 109, December 1983.
[ 1301 Saxena, A. and McEwen, E. E.: Behaviour of Masonry
Bearing Plates in High- way Bridges. Proceedings of 2nd World
Congress on Bearings and Sealants, ACI Publication SP-94, San
Antonio, 1986.
[ 13 11 Stanton, J. F. and Roeder, C. W.: Elastomeric Bearings
Design, Construction, and Materials. NCHRP Report 248, TRB,
National Research Council, Wash- ington, D. C., August 1982.
pp 113-132.
-
1.13 References 49
[132] Stanton, J. F., Scroggins, G., Taylor, A. W. and Roeder,
C. W.: Stability of Laminated Elastomeric Bearings. ASCE, Journal
of Engineering Mechanics, Vol. 116, No. 6, June 1990, pp
1351-1371.
[ 1331 Structural Bearing Specification. FHWA Region 3
Structural Committee for Economical Fabrication, Subcommittee for
High Load Multi-Rotational Bear- ings (HLMRB), October 1991.
-
51
2 Expansion Joints
2.1 Introduction
As mentioned in chapter 1.1, movements in old stone and timber
bridges were small and no additional devices were necessary to
close the gaps between bridges and abut- ments due to bridge
movements. The first expansion joints were built for steel railway
bridges because their movements were not negligible. With the
increase of road traf- fic and of its speed, closing the gaps
became necessary for safety reasons, especially at the moveable
bearings. Initially, cover plates were used for expansion joints.
For longer bridges these cover plates were not sufficient, so that
finger joints and sliding plate joints were used. All these types
of expansion joints were not watertight and so the water ran down
to the bearings and to the abutments. The first watertight expan-
sion joints were built using steel rails between rubber tubes to
absorb the movements. This principle led to a lot of different
multisealed expansion joints which differed in the means of
supporting the steel rails, in the rubber profiles and in
controlling the gap widths. Another type of watertight expansion
joint is the cushion joint, consisting of a rubber cushion with
vulcanised steel plates which transfer the traffic loads. In spite
of continuous amendments of all constructions for expansion joints,
these still remain wearing parts, especially in bridges with high
traffic density and high traffic loads. The following chapters give
a short survey of expansion joints for different move- ments used
in the construction of bridges.
2.2 The role of expansion joints The role of expansion joints is
to carry loads and to provide safety to the traffic over the gap
between bridge and abutment or between two bridges in a way that
all bridge displacements can take place with very low resistance or
with no resistance at all. A further requirement is a low noise
level especially in an urban environment. The expansion joints
should provide a smooth transition from the bridge to the adjacent
areas. The replacement of an expansion joint is always combined
with a traffic inter- ruption - at least of the affected lane.
Therefore expansion joints should be robust and suitable for all
loads and local actions under all weather conditions, moisture and
de- icing agents. The replacement of all wearing parts should be
possible in a simple way.
2.3 Calculation of movements of expansion joints Movements of
expansion joints depend on the size of the bridge and the
arrangement of the bearings. Normally the form of construction
depends on the horizontal transla- tion orthogonal to the joint.
But it is necessary to consider all translations and rotations to
ensure that the displacements will not reach the limits of the
joint construction. To describe the movements of an expansion joint
in detail we have to consider three translations and three
rotations (fig. 2.3- 1).
-
52 2. Expansion Joints
/
/
Fig.2.3-1: Possible movements
These movements result from temperature, displacements due to
external loads, and creep and shrinkage in concrete and composite
bridges. We may obtain the move- ments (displacements and
rotations) from the structural analysis of the system. Move- ments
due to loads depend on the location of the loads. The controlling
deformations can be determined with influence lines (fig. 2.3-2 and
fig. 2.3-3). The influence line of a deflection is the bending line
due to a unit load acting in the direction of the con- sidered
movement.
1
. -
Fig.2.3-2: Influence line for a translation
I"
Fig.2.3-3: Influence line for a rotation
To obtain the displacement caused by a rotation it is also
possible to calculate the rotations; the displacements can be
determined from the known rotations.
2.3.1 A change of the environment temperature, creep under
normal force and shrinkage lead to a uniform extension or
shortening of the bridge (fig. 2.3.1 -1). The thermal expansion
coefficients of steel and concrete have approximately the same
value ( a , = 1,0 ... 1,2. / K ). A uniform change of temperature
about the cross section causes only a horizontal translation of the
joint. This applies to composite bridges, too.
Horizontal translation in the direction of the bridge axis
u,
-
2.3 Calculation of movements of expansion joints 53
Fig.2.3.1 - I : Uniformly extension or shortening
n
Temperature: UXt. = UT C l i ATi
Creep and shrinkage of concrete bridges i=l
N,, Permanent normal force (compression > 0)
n
Shrinkage: u,,., = -EcbW li E,,, Shrinkage coefficient i=l
A possible problem is the change of the location of the fixing
point or the unknown lo- cation of the fixing point. On arch
bridges the superstructure is usually fixed at the crown of the
arch. The fixing point is moved by the deformation of the arch due
to the asymmetrical load. Buried expansion joints are often used
for short bridges (Chapter 2.4). If the fixing point is situated on
longer piers, it acts as a horizontal spring bearing. Due to a
movement in the joint a plastic deformation of the asphalt layer
occurs and the construction has a certain rigidity. A different
rigidity of the expansion joints on the right and left abut- ment
and a possible longitudinal deformation can lead to the cracking of
the asphalt layer at one abutment. As the rigidity of this joint is
higher than the rigidity of the piers the new fixing point is
situated near the undamaged expansion joint (fig. 2.3.1-2).
Cracking of the asphalt layer of the buried expansion joint
Fixing point after cracking
I
Fig.2.3.1-2: Change of the fixing point
-
54 2. Expansion Joints
In the case of an elastic fixing point there are additional
movements at expansion joints due to acceleration and braking
forces. The actual rigidity of piers can differ from the planned
rigidity. Moreover, if the bridge is fixed on more than one pier,
the position of the fixing point can differ from the planned
position.
Creep and shrinkage in composite bridges (acting in the concrete
parts of cross- section only) mainly lead to deflections which
result in rotations above the y-axis (fig. 2.3.1-4). Creep can be
considered using a reduced section area and a reduced moment of
inertia, shrinkage by a substitute tensile force Nsh acting on the
free shrinking con- crete. N\,, is a compression force acting on
the composite cross-section.
-1 -I- - E,,, Shrinkage coefficient A, Area of concrete
E, Reduced modulus of elasticity of concrete to consider
creep
Fig.2.3.1-3: Equivalent shrinking force
Fig.2.3.1-4: Deflection under load
Horizontal movements of expansion joints can also be caused by
vertical movements of the abutments. They are caused by foundation
settlements or by replacement of bearings (fig. 2.3.1-5).
Statically indeterminate steel and composite bridges can be
prestressed by intentional lifting and/or lowering at the
bearings.
yr+ -+ positive definition: cp u x
-
2.3 Calculation of movements of expansion joints 55
'xd 1
(bn Tn
e _ r C 1
F Y I ~
Fig.2.3.1-5: Displacement of bearings
U X d 1 = 44 ' (e" +e,> U x d n = $1 ' e, + @" . e ,
If a fixing point is located on a high pier the additional
movements due to pier defor- mation must be considered in the
structural analysis. The movements can result from acceleration,
braking forces, uniform and non-uniform temperature actions.
2.3.2 A horizontal translation in the crosswise direction
results if the angle between the joint and the moving direction of
the bearing is not 90 O (e. g. in skew bridges). The magnitude of
the movement depends on the magnitude of the movement in the direc-
tion of the bridge axis and on this angle (fig. 2.3.2-1 and fig.
2.3.2-2).
Horizontal translation in direction of the cross-section u,
u, = sincp. ueff
u y = C 0 S c p ~ U e f f
Fig.2.3.2-1: Skewed bridge
-
56 2. Expansion Joints
Fig.2.3.2-2: Skewed bearing conditions
2.3.3 Vertical translation u, Vertical translations u, can be
caused by the replacement of bearings (fig. 2.3.3-3) and the
geometrical conditions on the abutment (fig. 2.3.3-1 and fig.
2.3.3-2).
u, = u x .tan)
Fig.2.3.3-1: Sloping bridge with horizontal bearings
h Fig.2.3.3-2: Bridge with short cantilever on the abutmen2
-
2.3 Calculation of movements of expansion joints 57
SN+ I / ...............
I ............. -7 Hydraulic jack Fig.2.3.3-3: Vertical
displacement of bearings (due to bearing replacement)
2.3.4 In the case of a replacement of one single bearing at one
side a rotation cpx occurs (fig. 2.3.4-1). However, it is possible
to avoid this movement by uniform lifting over the
cross-section.
Rotation around the bridge axis cpx
T r - ........ . . . . . . . . -
Hydraulic jack Fig.2.3.4-1: Lijting on one side
2.3.5 This deformation is caused by vertical loading and
non-uniform temperature. The controlling load positions of the
traffic loads can be determined with influence lines.
Rotation around the y-axis cpr
Fig.2.3.5-1: Rotation due to deflections
2.3.6 The deformation cpz is caused by non-uniform temperature
action in the horizontal direction, and by wind loads (fig.
2.3.6-1).
Rotation around the z-axis cpz
-
58 2 . Expansion Joints
....~~..........~.... ' P Z
Fig.2.3.6-I: Non-uniform temperature action
2.4 Construction of expansion joints
2.4.1 General The construction of expansion joints has to fulfil
the following requirements: - movement capacity - bearing capacity
for static and dynamic loading, - watertightness to save bearings,
substructure and possible linkage of expansion
- low noise emission, - traffic safety. To fulfil the last two
requirements a limitation of gap widths is essential. Additional-
ly, it is recommended to avoid slopes exceeding about 3 % and
vertical steps between joined surfaces exceeding 8 mm (fig. 2.4.1 -
1).
joints from deterioration,
Fig.2.4.I-I: Recommended safety requirements
Expansion joints are exposed to pollution. The sealing should
not be damaged by inclusions of bigger external bodies. If the gap
width is reduced due to a movement of the superstructure the joint
must be able to expel grit and silt to the carriageway surface.
-
2.4 Construction of expansion joints 59
In particular, all elastomeric components must be readily
accessible and easily re- placeable.
2.4.2 For movements up to 15 mm it is possible to construct a
continuous asphaltic car- riageway pavement with a supporting
element covering the gap of the superstructure. This kind of joint
is also called a buried expansion joint (fig. 2.4.2-1). Up to 10 mm
a flat metal plate is sufficient; for movements above 10 mm an
elastomeric pad is nec- essary to avoid pavement cracks at the
edges of the supporting plate. An additional re- inforcement of the
pavement is advisable to provide a uniform strain distribution. The
thickness of the pavement should be at least 80 mm and should be
equal to the thick- ness of the corresponding parts of the
superstructure and the abutment. To fulfil this requirement the
cover of the gap is usually extended into a niche. The asphaltic
pavement does not provide sufficient watertightness. An additional
seal- ing is recommended to protect bearings and substructure from
deterioration.
Small movements (up to 25 mm)
Flexible filler .
Fig.2.4.2-I: Buried expansion joint
There are covering elements fulfilling the requirements of
support, strain distribution and watertightness without additional
sealing, e.g. the following kind of joint con- struction (fig.
2.4.2-2 and fig. 2.4.2-3).
Flexible filler
Fig.2.4.2-2: Buried expansion joint sealed by a rubber
profile
-
60
Flexible filler / / Reinforcement
2. Expansion Joints
Fig.2.4.2-3: Buried expansion joint with continuous sealing and
additional rubber projile
For movements between 15 and 25 mm the asphaltic material above
the joint can be replaced by a specially modified asphaltic
material. Constructions of this kind are called asphaltic plug
joints (fig. 2.4.2-4 and fig. 2.4.2-5). The thickness should be at
least 80 mm, while the length should not exceed 700 mm. Though
movements exceeding 25 mm could be managed in laboratory tests the
influ- ence of temperature and of deformation velocity is not
kno