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Dr. David RhodesMay 2017
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The old way: “Rigid” bridge structure with short spans;“Flexible” track structure with jointed rails, wooden sleepers and ballast.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The new way: “Flexible” bridge structure with long spans;“Rigid” track structure with continuous rails, on concrete slabs.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge decks are different: They are longer on hot days thanthey are on cold days.
Continuous welded rail does not expand or contract –Whatever the temperature it stays the same length.
Dr. David RhodesMay 2017
In cold weather the bridge deck contracts –the longer the bridge, the more the free end of the deck moves.
Bri
dg
e d
eck
dis
pla
cem
ent
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
“Ad
dit
ion
al”
rail
stre
ss
In cold weather the bridge deck contracts –the longer the bridge, the more the free end of the deck moves.
If there is enough “give” between the track and bridge, the track is not affected.
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
Note: Here (and for the rest of the presentation!):
“Additional” rail stress means rail stress which is added to the stress which would be present of the same track form were to be used in the same conditions but without the bridge being there.
We’ll also talk about “additional” track forces, displacements, etc., etc.
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
In real life, there is never enough “give” and so the bridge deck drags the rail with it,
Rai
ld
isp
lace
men
t
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
In real life, there is never enough “give” and so the bridge deck drags the rail with it,generating a stress in the rail which is proportional to the slope of the displacement.
Rai
l str
ess
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
For a single span bridge net forces in the rail are reacted at the abutments, whichare usually very stiff in compression, but for multi-span bridges it is also necessaryto think about the stiffness of piers and the forces at the bearings on each pier:
TRACK-BRIDGE INTERACTION
?
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements
Dr. David RhodesMay 2017
Similar effects to those of temperature, but this time the (train drags the) rail drags the bridge deck.
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge deck end rotation.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge deck end rotation.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge deck end rotation.Longitudinal movement plus rotation / uplift
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge deck end rotation (DB DS804 App 29.)
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The key factors determining the significance of Track-Bridge Interaction effects are ….
a. Expansion length of bridge deck(s)
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The key factors determining the significance of Track-Bridge Interaction effects are ….
a. Expansion length of bridge deck(s)
b. Resistance to shear forces between the rails and the bridge deck
FO
RC
EDISPLACEMENT OF RAIL RELATIVE TO BRIDGE DECK
TRACK-BRIDGE INTERACTION
FO
RC
E
DISPLACEMENT OF RAIL RELATIVE TO BRIDGE DECK
Useful approximations:
u0
k
u0 is the maximum elastic displacement:For some cases (e.g. long bridges withlongitudinally stiff track) you can make a further simplification by putting u0 = 0.
k is the force per unit length of track i.e. itis the force in two rails. The units are kN/m but this k is NOT a stiffness!!
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The key factors determining the significance of Track-Bridge Interaction effects are ….
a. Expansion length of bridge deck(s)
b. Resistance to shear forces between the rails and the bridge deck
c. Stiffness of piers
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
The key factors determining the significance of Track-Bridge Interaction effects are ….
a. Expansion length of bridge deck(s)
b. Resistance to shear forces between the rails and the bridge deck
c. Stiffness of piers
d. Detail design of bridge deck ends
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
For example:
• Additional rail stress due to temperature with no train present: 54 MPa
• Additional rail stress due to braking forces at neutral temperature with “zero axle load”: 25 MPa
• Additional rail stress due to deck end rotation at neutral temperature with no traction or braking: 16 MPa
• Therefore total additional rail stress due to Track-Bridge Interaction effects: 95 MPa
This simple approach is accepted by most codes and standards – but it gives the wrong answer!
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Think about rail force vs.displacement:
FORCE
DISPLACEMENT
F temp
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Think about rail force vs.displacement:
FORCE
DISPLACEMENT
F brake
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Think about rail force vs.displacement:
FORCE
DISPLACEMENT
F deck end
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Think about rail force vs.displacement: (Simple linear superposition)
DISPLACEMENT
FORCE
F temp
Ftemp + F brake
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Think about rail force vs.displacement: (Realistic superposition?)
FORCE
DISPLACEMENT
F temp + F brake + F deck end
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Simple linear superposition of load cases generally leads to over-estimates of additional rail stress …….
…. but it also tends to under estimate forces on piers .
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
TECHNICAL SOLUTIONS:
1. Bridge design
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Bridge design – basic principles
1. Accept policy on use of rail expansion devices and acceptable rail stresses
2. Short, stiff, simply supported spans are good for Track-Bridge Interactions!
3. Control expansion lengths by positioning thermal fixed points
4. Control bridge deck end effects by attention to detail design
5. Integral / semi-integral bridges need integrated structural design (i.e. analyse the bridge and track together as a total structure)
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:
1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
TECHNICAL SOLUTIONS:
1. Bridge design 2. Track design
Dr. David RhodesMay 2017
Track design – basic principles
1. Retain standard track configuration and component selection as far as possible
2. Decide policy on use of rail expansion devices and acceptable rail stresses
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Rail expansion joints in ballasted track
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Rail expansion joints in ballastless track
Dr. David RhodesMay 2017
Rail fastenings for “Reduced Longitudinal Restraint”
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Rail fastenings for “Zero Longitudinal Restraint”
Dr. David RhodesMay 2017
Use of ZLR fastenings to optimise positioning of REJ
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Ballast retention at structural movement joint
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
TECHNICAL SOLUTIONS:1. Bridge design 2. Track design
ORGANISATIONAL ISSUES
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
ORGANISATIONAL ISSUES:
BRIDGE DESIGN TEAM
TRACK DESIGN TEAM
Initial design concepts
Select optimum configuration
Detail design calculations
Track-Bridge Interaction assessment
Re-evaluate configuration??
?
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
ORGANISATIONAL ISSUES:
BRIDGE DESIGN TEAM TRACK DESIGN TEAM
Initial design concepts
Select optimum configurationDetail design calculations
Track-Bridge Interaction assessment
Final bridge design
Agree Track-Bridge Interaction principles
Final track design
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
ORGANISATIONAL ISSUES:
BRIDGE DESIGN TEAM
TRACK DESIGN TEAM
Initial design concepts
Select optimum configuration
Detail design calculations
Track-Bridge Interaction assessment
Final bridge design
Set Track-Bridge Interaction limits
Consultation
Consultation
Final track design
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
ORGANISATIONAL ISSUES:
Key considerations:
1. Some track design parameters must be established from the outset.
2. Track-Bridge Interaction effects must be assessed before the final bridge configuration is fixed.
3. Any assumptions made by bridge designer about track configuration must be agreed with track engineers.
4. Any assumptions made by bridge designers about track configuration must be recorded.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
TECHNICAL SOLUTIONS:1. Bridge design 2. Track design
ORGANISATIONAL ISSUES
“CULTURAL” ISSUES
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
“CULTURAL” ISSUES: Bridge Department
TrackDepartment
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
“CULTURAL” ISSUES: Bridge Department
TrackDepartment
Each project designed from a “clean sheet of paper”
Maximum use of standard components and track designs
Calculate from first principles for Ultimate and Service load states
Empirical data underlie strength and durability requirements
Explicit safety and dynamic factors applied to theoretical load cases
Safety and dynamic factors implicit in design and test requirements
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
TECHNICAL ISSUES:1. Effect of temperature on axial forces and displacements2. Effect of traction and braking on axial forces and displacements3. Effect of vertical loads on axial forces and displacements4. Characteristics of structures5. Combinations of load cases
TECHNICAL SOLUTIONS:1. Bridge design 2. Track design
ORGANISATIONAL ISSUES
“CULTURAL” ISSUES
CODES and STANDARDS
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
CODES and STANDARDS:
Begin by understanding the technical issues –then see how codes and standards should be applied!
(Later this year (or early in 2018?) CEN will publish a Technical Report to explain the technical issues)
Dr. David RhodesMay 2017
CODES and STANDARDS:
TRACK-BRIDGE INTERACTION
In Europe,
for bridge engineers, the key document is in the Eurocode EN1991-2:2003 section 6.5.4
for track engineers, the key document is UIC 774-3R
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
CODES and STANDARDS:
Standards set limiting values on additional axial rail stress and displacements at structure movement joints.
Limiting values on additional axial rail stress are only valid for a ‘standard’ trackform:Standard gauge ballasted trackStraight track (or large radius curve)60E1 (“UIC60”) or 60E2 railConcrete sleepers >250kg massRail steel grade R260 or better
For other track configurations, the track engineer must confirm that the same limits are acceptable, or set alternative requirements.
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017
TRACK-BRIDGE INTERACTION
Dr. David RhodesMay 2017