View
1.140
Download
0
Category
Tags:
Preview:
DESCRIPTION
Citation preview
Light Rail Transit Facilities
Design Course
Bridges & Structures05.11.2010
Joel Tubbs, P.E., S.E.
2
Light Rail Transit Facilities
Design Course
Bridges & Structures 3
OVERVIEW
1. Structure Layout and Type Selection2. LRT Loading Requirements3. Special Considerations4. Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures 4
Structure Layout & Type Selection
Basic types of structures- Bridges
Light Rail Transit Facilities
Design Course
Bridges & Structures 5
Structure Layout & Type Selection
Basic types of structures- Buildings
Light Rail Transit Facilities
Design Course
Bridges & Structures 6
Structure Layout & Type Selection
Basic types of structures• Tunnels
Light Rail Transit Facilities
Design Course
Bridges & Structures 7
Structure Layout & Type Selection
Basic types of structures• Stations
Light Rail Transit Facilities
Design Course
Bridges & Structures 8
Retaining Walls Sound Walls
Structure Layout & Type Selection
Basic types of structures- Walls
Light Rail Transit Facilities
Design Course
Bridges & Structures 9
Structure Layout & Type Selection
What does a structure do?- Provides infrastructure for system- Separates facility from other features
Light Rail Transit Facilities
Design Course
Bridges & Structures 10
Structure Layout & Type Selection
What does a structure do?- Solves safety concerns
Light Rail Transit Facilities
Design Course
Bridges & Structures 11
Structure Layout & Type Selection
Crossing Types- Bridge over road
Light Rail Transit Facilities
Design Course
Bridges & Structures 12
Structure Layout & Type Selection
Crossing Types- Bridge over water
Light Rail Transit Facilities
Design Course
Bridges & Structures 13
Structure Layout & Type Selection
Crossing Types- Tunnel under road
Light Rail Transit Facilities
Design Course
Bridges & Structures 14
Structure Layout & Type Selection
Crossing Types- Tunnel under geographic feature
Light Rail Transit Facilities
Design Course
Bridges & Structures 15
Structure Layout & Type Selection
Modern Bridge Types- Pre-stressed Concrete
Light Rail Transit Facilities
Design Course
Bridges & Structures 16
Structure Layout & Type SelectionModern Bridge Types
- Pre-stressed Concrete
Advantages- Lowest cost bridge alternative- Good for shorter crossings- No falsework required in roadway or
stream- Fast, simple installation, saving
construction time- Shallow depth providing greater
clearance to stream or roadway surfaces below
Light Rail Transit Facilities
Design Course
Bridges & Structures 17
Structure Layout & Type Selection
Modern Bridge Types- Cast-in-Place Concrete
Light Rail Transit Facilities
Design Course
Bridges & Structures 18
Structure Layout & Type Selection
Modern Bridge Types- Cast-in-Place concrete
Advantages - Good for longer spans - Resistance to seismic forces - Accommodating horizontal
curves, gradelines, or superelevations
- More aesthetically pleasing
Light Rail Transit Facilities
Design Course
Bridges & Structures 19
Structure Layout & Type Selection
Modern Bridge Types- Concrete
~ Segmental
Light Rail Transit Facilities
Design Course
Bridges & Structures 20
Structure Layout & Type Selection
Modern Bridge Types- Segmental Concrete
Advantages- Good for longest spans- Highly aesthetic- Limited surface-level disturbance- Geometric flexibility
Light Rail Transit Facilities
Design Course
Bridges & Structures 21
Structure Layout & Type Selection
Modern Bridge Types- Steel
Light Rail Transit Facilities
Design Course
Bridges & Structures 22
Structure Layout & Type Selection
Modern Bridge Types- Steel
Advantages- Longer spans- Can accommodate track
geometry- Lighter foundation & seismic
loads
Light Rail Transit Facilities
Design Course
Bridges & Structures 23
Structure Layout & Type Selection
Modern Bridge Types- Signature Bridges
Light Rail Transit Facilities
Design Course
Bridges & Structures 24
Structure Layout & Type Selection
Modern Bridge TypesTypical span ranges (order by superstructure
cost)- Precast concrete slabs up to 80
feet- Precast concrete box beams up to 120
feet- Precast concrete girder up to 180
feet- CIP post-tensioned box girder 100-600 feet- Steel plate girder 60-300 feet- Steel box girder 60-500
feet- Segmental concrete
~ Span-by-span 80-150 feet
~ Balanced Cantilever up to 800 feet
Light Rail Transit Facilities
Design Course
Bridges & Structures 25
Structure Layout & Type Selection
Modern Bridge TypesTypical Span-to-Depth ratios (structure thickness
only)- Precast concrete slabs/boxes
Span/33- Precast concrete girder
Span/23- CIP post-tensioned box girder
~ simple span Span/26~ continuous, uniform depth
Span/29~ continuous, variable depth
Span/35 - Steel plate girder
~ simple span Span/25~ continuous
Span/31
Light Rail Transit Facilities
Design Course
Bridges & Structures 26
Structure Layout & Type Selection
Modern Bridge TypesStructure Depth
Don’t Forget!!
Overall Structure Depth = Structure thickness + Superelevation +
Track section depth
Light Rail Transit Facilities
Design Course
Bridges & Structures 27
Cut WallsFill Walls
Structure Layout & Type Selection
Retaining Walls
Light Rail Transit Facilities
Design Course
Bridges & Structures 28
Structure Layout & Type Selection
Retaining WallsCommon Types
Light Rail Transit Facilities
Design Course
Bridges & Structures 29
Structure Layout & Type Selection
Retaining WallsCommon Types
Light Rail Transit Facilities
Design Course
Bridges & Structures 30
Structure Layout & Type Selection
Retaining WallsCommon Considerations
- Excavation for reinforcement/footings- Easements for subterranean elements- Increased design height on slopes- Proper consideration at wall terminations- Drainage conveyance
Light Rail Transit Facilities
Design Course
Bridges & Structures 31
Structure Layout & Type Selection
Common bridge layout considerations:- Site conditions- Bent locations and required span lengths- Cost- Material availability- Aesthetics- Vertical clearance- Horizontal alignment- Schedule- Seismic resistance- Maintenance, future widening, and more...
Light Rail Transit Facilities
Design Course
Bridges & Structures 32
Structure Layout & Type Selection
Bent location considerations:- Proximity to facilities- Right of way- Span length- Constructability- Required clearances- Environmental concerns
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
33
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
34
LRT Loading Requirements
Load effects of DL- Not much variance
in stresses over time
Load effects of LL - Transient loads
produce variable stresses
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
35
Vehicle Bending Moments on Simple Spans
HL93
LRT
Cooper E80
0
1000020000
30000
40000
5000060000
70000
80000
0 50 100 150 200 250
Span Length (ft)
Mid
span
Mom
ent (
k-ft)
LRT Loading Requirements
General Design Criteria:- Agencies allow both AASHTO & AREMA- Most light rail loads are greater than the HL93 used
by AASHTO LRFD, but much less than AREMA’s Cooper E80
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
36
LRT Loading Requirements
General Design Criteria:AREMA
- Restrictive for light rail transit structures due to the great differences in loading
- Wheel spacings don’t correspond to those found on LRV’s
- Impact criterion is not consistent with the suspension and drive systems used
on LRV’s- Types of loading not consistent with LRV’s
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
37
LRT Loading Requirements
General Design Criteria:AASHTO
- Ratio of LL to DL more closely approximates that of highway loadings than heavy rail loadings
- Axle loads and car weights are similar to LRV’s
- Results in conservative design that is not overly restrictive or uneconomical
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
38
LRT Loading Requirements
Loads and Load Combinations (TriMet 2010):• Dead load• Live load
- LRV-specific- Highway Pedestrian- Seismic loads- Earth loads- Wind loads- Thermal Loads
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
39
Loads and Load Combinations (TriMet 2010):Dead loads (DC)
- Superstructure weight- Superimposed loads- Cross Beam weight- Column weight- Footing weight- OCS poles- Ductbanks- Plinths/Ballast- Rail
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
40
Loads and Load Combinations(TriMet 2010):• Live Loads (LL)
- Highway (AASHTO)- Pedestrian (AASHTO)- LRV-Specific
~ 1 to 4 car train~ Single or multiple tracks loaded
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
41
Loads and Load Combinations (TriMet 2010):Other LRV-specific live loads:
- Vertical impact (Iv or IMv)~ Max between AASHTO and AREMA but
generally not exceeding 30%
- Horizontal impact (Ih or IMh)~ 10% of each axle load applied transversely
at 4 ft above TOR- Impact applies generally only to structural
elements above ground for trains that are not stationary
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
42
Loads and Load Combinations (TriMet 2010): Other LRV-specific live loads:
- Longitudinal forces (BR):~ Acceleration = 16% of LRV load~ Deceleration = 21% of LRV load~ Combine as necessary to obtain max force
effect(e.g., one track accelerating while other
track decelerating)
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
43
Loads and Load Combinations (TriMet 2010): Other LRV-specific live loads:
- Centrifugal forces (CE):~ 10% of axle load for track CL radius <=
2450 ft~ Axle load*0.0875*(V^2)/R for larger
radius~ Applied transversely at 4 ft above TOR
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
44
Loads and Load Combinations (TriMet 2010): Special LRV-specific live loads:
- Emergency Braking (EB)~ 46% of LRV on one track~ Combine with BR loads on other tracks as necessary to obtain max force effect~ Considered only for Strength II limit state,
and is not combined with derailment loads
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
45
Loads and Load Combinations (TriMet 2010): Special LRV-specific live loads:
- Derailment Loads (DR)~ Vertical – 100% impact applied for any
truck~ Horizontal – 10-30% of single LRV
vehicle applied at 2 ft above TOR over 10 ft
distance~ Only one track assumed to derail, other
tracks unloaded or loaded with stationary train
~ Considered only for Strength II limit state, and is not combined with EB loads
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:LRT Loading Requirements
46
Loads and Load Combinations(TriMet 2010):
Other Special LRT Loads:- Thermal forces
~ Radial rail forces~ Rail break
LRT Loading Requirements
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
47
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
48
Ballasted Track versus Direct Fixation (DF)
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
49
Ballasted track versus direct fixation on structures
Ballasted track- Greater DL requires larger structural
members- Flexible track structure support- Most prevalent track type used at grade- Must contend with electrical isolation & acoustic attenuation- Results in deeper bridge structure
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
50
Ballasted track versus direct fixation on structures
Direct Fixation- High initial cost- Rail interacts with structure- Standard method of construction on aerial
structure- Much stiffer vertically than ballasted track- Lower maintenance costs
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
51
Continuously Welded RailRail Break Gap
- Occurs when a thermally induced tensile force
exceeds the ultimate tensile strength of the rail.
- Likely to occur at or near~ Bridge expansion joints~ At a bad weld~ A rail flaw~ Weak spot in rail
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
52
Continuously Welded RailRail Break Gap
- Established limits on gap size~ Usually based on LRV’s wheel diameter~ Decreasing the fastener’s longitudinal
stiffness results in increased gap size
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
53
Continuously Welded Rail- Rail-Structure Interaction
~ Thermal deformations of bridge induce stress on rails
~ Restraint of CWR and DF fasteners induce stresses on rails and structure
~ Rail break forces transferred through DF fasteners to structure and to remaining unbroken rails according to relative stiffnesses
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
54
Continuously Welded RailRail-Structure Interaction
DF Fasteners:~ Proprietary devices that allow differential
movement between structure and rail
~ Full lateral restraint~ Provide varied levels of longitudinal
restraint
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
55
Continuously Welded RailRail-Structure Interaction
DF Fasteners:- Lower restraint fasteners often used at
locations of highest structure thermal deformation (i.e., near expansion joints)
- Higher restraint fasteners used near middle of frame
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
56
Mixed modes on bridge
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
57
Stray current protection- Stray currents are leaking current from the rails that
return to the ground grid of the substation- Corrosion is the most common result of stray
currents
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
58
Stray current protectionTo minimize stray currents:
- Insulate rails from their fastenings and encase rails in embedded track with extruded boot
- Continuously weld reinforcement in underlying slab
- In ballasted track areas the ballast should be clean, well-drained and not in contact with the rail
- Conduct corrosion surveys and perform regular monitoring and maintenance
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Special Considerations
59
Pedestrian considerations:- Restriction to trespassing- Emergency access/egress
Special Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
60Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
60
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
61Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
61
Basic bridge construction issues
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
62Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
62
Basic bridge construction issues- Maintenance of traffic- Adequate easements for construction equipment
and laydown areas- Detailing with construction tolerances in mind- Staged construction- Concrete pour sequences- Work site access
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
63Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
63
Deck/Plinth Construction- Method of plinth construction can have significant impact on cost and constructability
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
64Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
64
CWR welding and setting track
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
65Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
65
Downdrag on foundations & long term settlement:
- Downdrag~ Occurs as layers of soil consolidate~ Causes: Additional fill, liquefaction,
secondary compression~ Can introduce substantial vertical load on
piles~ Can create settlements in shallow foundation
systems- Mitigation
~ Coat piles to create slip-plane~ Design for additional loads~ Surcharge prior to construction to pre-
consolidate soils
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
66Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
66
Shoring existing facilities
Temporary works
Constructability Considerations
Temporary work bridge
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
67Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
67
Temporary worksFalsework
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
68Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
68
Foundation construction in water (cofferdam)
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
69Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
69
Cofferdam subject to high water
pressures
Foundation construction in water (cofferdam)
Constructability Considerations
Pile driving through template in flooded
cofferdam
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
70Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
70
Subgrade stabilization below concrete seal
Subgrade excavation of footing in dry
cofferdam
Foundation construction in water (cofferdam)
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
71Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
71
Foundation construction in water (drilled shaft)- Drilled shaft with temporary casing negates need
for cost prohibitive cofferdam and reduces environmental impacts
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
72Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
72
Temporary Work Bridge Covered With Plastic to Keep Dredged Materials from Entering Slough
Dredged Materials Removed Safely From Site
Foundation construction in water (drilled shaft)
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures:Structure Layout & Type Selection
73Light Rail Transit Facilities
Design Course
Bridges & Structures:Constructability Considerations
73
Girder shipping and setting- Crane placement- Girder delivery- Shipping/handling weights
Constructability Considerations
Light Rail Transit Facilities
Design Course
Bridges & Structures 74
QUESTIONS?
Recommended