seismic design of bridges nysdot policy and scobs... retrofit of existing bridges existing bridges,

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  • April 20, 2015


    Mathew Royce, P.E.

    Assistant Bureau Director

    Structures Design Bureau

    Office of Structures

    * Seismic Design of Bridges NYSDOT Policy and Practices

  • Design of new or replacement bridges

    Seismic retrofit of existing bridges

    Downstate seismic zone

  • Typical NYSDOT Bridge

  • Seismic Design Policy

    Seismic design shall be in accordance with the provisions NYSDOT

    LRFD Specifications

    Seismic design in accordance with the provisions given in the

    AASHTO Guide Specifications for LRFD Seismic Bridge Design can

    be used with the approval of Deputy Chief Engineer (Structures)

  • Bridge Classification Critical



    Hazard Levels Upper level 2500 Yr (2% in 50 yr probability of

    exceedance) for safety evaluation/design level

    Lower level 1000 yr (7% in 50 yr probability of

    exceedance) for essentially elastic performance

  • Minimal Damage

    Essentially elastic behavior

    Narrow flexural cracking in concrete/masonry elements.

    No permanent deformations to structural members

    May have permanent deformations to non-structural members

  • Repairable Damage Inelastic response acceptable

    Restoration without replacement of structural members

    Concrete cracking

     Minor cover spalling

    Reinforcement yielding

    Localized yielding of structural steel members

    Damage to secondary and non-structural components

    Repair feasible without the closure of the bridge

  • Significant Damage

    No collapse, but permanent offsets may occur.

    Extensive cracking, major spalling of concrete and

    reinforcement yielding, cracking of deck slab at the shear


    May force closure for repair

    Excessive differential settlements

    Partial or complete replacement

  • Critical Bridges

    Lower level event

     Immediate access

    Upper level event

     Limited access

     Function as a part of the lifeline

     Fully open to civil defense, police, fire within 48 hours after the event

  • Critical Bridge Design

    Lower level evaluation for minimal Damage

    Upper level evaluation for repairable Damage

    Site-specific soil effects

    Soil-Structure Interaction

    Spatial variation long bridges

  • Essential Bridges

    Lower level event

    Limited access

    Function as a part of the lifeline

    Fully open to civil defense, police, fire

    within 72 hours after the event

    Other Bridges

    Lower level event

    No collapse, Significant damage acceptable

  • Essential Bridge Design Lower level evaluation repairable damage

    Generic response spectra for Soil Class C, D, or E

    Site specific response spectra Soil Class F

    Designer may use Site specific response spectra

    for Soil Class C, D, or E

    Other Bridge Design Lower level evaluation no collapse

    Generic response spectra Soil Class C, D, or E

    Site specific response spectra Soil Class F

  • Retrofit of Existing Bridges

     Existing bridges, programmed for rehabilitation shall be

    evaluated for seismic vulnerability.

     For the evaluation and upgrading conventional bridges, FHWA’s

    “Seismic Retrofitting Manual for Highway Structures: Part 1 –

    Bridges” (January 2006, Publication No. FHWA-HRT-06-032) is

  • Conventional Bridges

    Beam, box girder, truss superstructures on single or multiple-

    column piers, wall-type piers, or pile-bent substructures

    Conventional bridges are founded on shallow or piled footings

    or shafts

    Nonconventional bridges include suspension bridges and bridges

    with truss towers or hollow piers for substructures and arch


  • Strengthening of Existing Bridges

    The strengthening to the same resistance of new bridges is not

    always practical or cost effective

    Elements to be retrofitted to “new bridge” seismic criteria where


  • Seismic Criteria Downstate Zone Downstate Zone: The counties of Bronx, Kings, New York,

    Queens, Richmond, Nassau, Rockland and Westchester as

    shown in Figure below

  • Seismic Criteria Downstate Zone

  • Very Hard Rock Spectra  Very hard rock spectra quantified in the form of 5%

    damped horizontal Uniform Hazard Spectra (UHS) for four earthquake return periods, 500, 1000, 1500 and 2500 years

     The motions are for Very Hard Rock (VHR) in NYC, typical of the eastern United States (US), with a shear wave velocity of at least 2.83 km/sec (approximately 9,000 ft/sec)

     This 2.83 km/sec shear wave velocity is an average of eastern US continental crust

  • Rock Spectra

  • Rock Spectra

  • Soil Spectra: Soil on top of Rock A/VHR

  • Soil Spectra: Soil on top of Rock A/VHR

  • Vertical Response Analysis Response spectrum analysis is not recommended for

    calculating response quantities in vertical direction

    Response spectrum analysis only in two horizontal


    Vertical response quantities shall be calculated using

    time-history analysis method

  • Time History Records  Three sets of very Hard Rock ground motion time-history records

    in 3 directions for 500-yr, 1000-yr, 1500-yr and 2500-yr

    earthquake return periods

     Time histories incorporate the effects of spatial variation along

    21 hypothetical piers on Very Hard Rock spaced at 100 m (328 ft),

    and extended over a straight line with a total length of 2 km

     These Very Hard Rock response spectra and time-history records

    are to be used either for the structural dynamic analysis of the

    bridge (design of the bridge) in the case of a bridge at a rock

    site, or as rock input to the soil in dynamic site response analyses

  • Site Liquefaction  Soil liquefaction assessment when potentially liquefiable

    saturated soils are present

     State of the art guidance on liquefaction assessment provided

    NYSDOT blue pages

    Non-Critical Bridges: Evaluation of liquefaction potential for the 1000-year earthquake using the generic PGA values and

    earthquake magnitude, M = 6.0. Optionally the owner may

    require an evaluation of liquefaction potential for the 1500-

    year and earthquake magnitude, M = 6.0

    Critical Bridges: Evaluation of liquefaction potential for the 2500-year earthquake and earthquake magnitude, M = 6.25

  • Site Specific Study  Site specific study for 1000 Yr and 2500 Yr for critical bridges

     Site specific study for 1000 or 1500 Yr for essential or other

    bridges (optional)

    Peer Review  For Critical Bridges, a peer review shall be performed

     Peer review can be waived if the site specific spectra comply

    with two third rule

     Peer review optional for non-critical bridges

  • Concluding Comments

    All new and replacement bridges are designed and

    built meeting current LRFD specifications

    Retrofitting of existing bridges are undertaken

    during major rehabilitation

    Efforts are underway for retrofitting existing critical


  • Questions


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