seismic design of bridges nysdot policy and practicessp.bridges.transportation.org/documents/2015...
TRANSCRIPT
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