T6 bridges tubbs jb

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  • Arches, trusses, beam, cable-supported
  • Inhabited: Operator, concessions, security buildings. LRT Systems: Signal, Communication, substation buildings
  • Types: Mined or Cut and Cover. Fire, life, and safety considerations generally for tunnels over 300 ft in length
  • Platform amenities, stairs, ramps, parking garages, platform walls. Stations most often constructed at grade or on retained fill, less frequently on bridges. Pictures of Den station on bridge?
  • Updated renderings of WRB? Other LRT crossings over water?
  • Disadvantages: Short spans, doesn’t accommodate curvature well, aesthetic limitations
  • Disadvantages: more expensive, construction duration, falsework expense and safety considerations
  • Disadvantages: Cost, higher degree of dimensional control during construction,
  • Picture of Johnson Creek
  • Disadvantages: initial and life-cycle costs, lead time,
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required.
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required. Closely follows highway loading S/D ratios – ONLY approximations
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required. Closely follows highway loading S/D ratios – ONLY approximations
  • Use updated graphic with TriMet loading and HL-93 Loading
  • Show updated covers of both, discuss LRFD as current TriMet design critieria
  • Update graphic
  • Update graphic
  • Update graphic
  • Update graphic
  • T6 bridges tubbs jb

    1. 3. OVERVIEW <ul><li>Structure Layout and Type Selection </li></ul><ul><li>LRT Loading Requirements </li></ul><ul><li>Special Considerations </li></ul><ul><li>Constructability Considerations </li></ul>
    2. 4. Basic types of structures - Bridges Structure Layout & Type Selection
    3. 5. Basic types of structures - Buildings Structure Layout & Type Selection
    4. 6. <ul><li>Basic types of structures </li></ul><ul><li>Tunnels </li></ul>Structure Layout & Type Selection
    5. 7. <ul><li>Basic types of structures </li></ul><ul><li>Stations </li></ul>Structure Layout & Type Selection
    6. 8. Basic types of structures - Walls Retaining Walls Sound Walls Structure Layout & Type Selection
    7. 9. What does a structure do? - Provides infrastructure for system - Separates facility from other features Structure Layout & Type Selection
    8. 10. What does a structure do? - Solves safety concerns Structure Layout & Type Selection
    9. 11. Crossing Types - Bridge over road Structure Layout & Type Selection
    10. 12. Crossing Types - Bridge over water Structure Layout & Type Selection
    11. 13. Crossing Types - Tunnel under road Structure Layout & Type Selection
    12. 14. Crossing Types - Tunnel under geographic feature Structure Layout & Type Selection
    13. 15. Modern Bridge Types - Pre-stressed Concrete Structure Layout & Type Selection
    14. 16. Modern Bridge Types - Pre-stressed Concrete Structure Layout & Type Selection 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
    15. 17. Modern Bridge Types - Cast-in-Place Concrete Structure Layout & Type Selection
    16. 18. 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 Structure Layout & Type Selection
    17. 19. Modern Bridge Types - Concrete ~ Segmental Structure Layout & Type Selection
    18. 20. Modern Bridge Types - Segmental Concrete Advantages - Good for longest spans - Highly aesthetic - Limited surface-level disturbance - Geometric flexibility Structure Layout & Type Selection
    19. 21. Modern Bridge Types - Steel Structure Layout & Type Selection
    20. 22. Modern Bridge Types - Steel Advantages - Longer spans - Can accommodate track geometry - Lighter foundation & seismic loads Structure Layout & Type Selection
    21. 23. Modern Bridge Types - Signature Bridges Structure Layout & Type Selection
    22. 24. Modern Bridge Types Typical 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 Structure Layout & Type Selection
    23. 25. Modern Bridge Types Typical 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 Structure Layout & Type Selection
    24. 26. Modern Bridge Types Structure Depth Don’t Forget!! Structure Layout & Type Selection Overall Structure Depth = Structure thickness + Superelevation + Track section depth
    25. 27. Retaining Walls <ul><ul><ul><li>Cut Walls </li></ul></ul></ul><ul><ul><ul><li>Fill Walls </li></ul></ul></ul>Structure Layout & Type Selection
    26. 28. Retaining Walls Common Types Structure Layout & Type Selection
    27. 29. Retaining Walls Common Types Structure Layout & Type Selection
    28. 30. Retaining Walls Common Considerations - Excavation for reinforcement/footings - Easements for subterranean elements - Increased design height on slopes - Proper consideration at wall terminations - Drainage conveyance Structure Layout & Type Selection
    29. 31. 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... Structure Layout & Type Selection
    30. 32. Bent location considerations: - Proximity to facilities - Right of way - Span length - Constructability - Required clearances - Environmental concerns Structure Layout & Type Selection
    31. 33. LRT Loading Requirements
    32. 34. Load effects of DL - Not much variance in stresses over time LRT Loading Requirements Load effects of LL - Transient loads produce variable stresses
    33. 35. 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 LRT Loading Requirements
    34. 36. 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 LRT Loading Requirements
    35. 37. 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 LRT Loading Requirements
    36. 38. <ul><li>Loads and Load Combinations (TriMet 2010): </li></ul><ul><li>Dead load </li></ul><ul><li>Live load </li></ul><ul><li>- LRV-specific </li></ul><ul><li>- Highway Pedestrian </li></ul><ul><li>- Seismic loads </li></ul><ul><li>- Earth loads </li></ul><ul><li>- Wind loads </li></ul><ul><li>- Thermal Loads </li></ul>LRT Loading Requirements
    37. 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
    38. 40. <ul><li>Loads and Load Combinations </li></ul><ul><li>(TriMet 2010): </li></ul><ul><li>Live Loads (LL) </li></ul><ul><li>- Highway (AASHTO) </li></ul><ul><li>- Pedestrian (AASHTO) </li></ul><ul><li>- LRV-Specific </li></ul><ul><li>~ 1 to 4 car train </li></ul><ul><li>~ Single or multiple </li></ul><ul><li> tracks loaded </li></ul>LRT Loading Requirements
    39. 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
    40. 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
    41. 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
    42. 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
    43. 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
    44. 46. Loads and Load Combinations (TriMet 2010): Other Special LRT Loads: - Thermal forces ~ Radial rail forces ~ Rail break LRT Loading Requirements
    45. 47. Special Considerations
    46. 48. Ballasted Track versus Direct Fixation (DF) Special Considerations
    47. 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
    48. 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
    49. 51. Continuously Welded Rail Rail 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
    50. 52. Continuously Welded Rail Rail 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
    51. 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
    52. 54. Continuously Welded Rail Rail-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
    53. 55. Continuously Welded Rail Rail-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
    54. 56. Mixed modes on bridge Special Considerations
    55. 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
    56. 58. Stray current protection To 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
    57. 59. Pedestrian considerations: - Restriction to trespassing - Emergency access/egress Special Considerations
    58. 60. Constructability Considerations
    59. 61. Basic bridge construction issues Constructability Considerations
    60. 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
    61. 63. Deck/Plinth Construction - Method of plinth construction can have significant impact on cost and constructability Constructability Considerations
    62. 64. CWR welding and setting track Constructability Considerations
    63. 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
    64. 66. Temporary works Shoring existing facilities Constructability Considerations Temporary work bridge
    65. 67. Temporary works Falsework Constructability Considerations
    66. 68. Foundation construction in water (cofferdam) Constructability Considerations
    67. 69. Foundation construction in water (cofferdam) Cofferdam subject to high water pressures Constructability Considerations Pile driving through template in flooded cofferdam
    68. 70. Foundation construction in water (cofferdam) Subgrade stabilization below concrete seal Subgrade excavation of footing in dry cofferdam Constructability Considerations
    69. 71. Foundation construction in water (drilled shaft) - Drilled shaft with temporary casing negates need for cost prohibitive cofferdam and reduces environmental impacts Constructability Considerations
    70. 72. Foundation construction in water (drilled shaft) Temporary Work Bridge Covered With Plastic to Keep Dredged Materials from Entering Slough Dredged Materials Removed Safely From Site Constructability Considerations
    71. 73. Girder shipping and setting - Crane placement - Girder delivery - Shipping/handling weights Constructability Considerations
    72. 74. QUESTIONS?

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