April 20, 2015

NEW YORK STATE DEPARTMENT OF TRANSPORTATION

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

Essential

Other

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

studs

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

bridges

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

feasible

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

directions

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

bridges

Questions