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ASCE 41-13 and the NEHRP Provisions
Bob Pekelnicky
ASCE/SEI Seismic Rehabilitation Standards Committee
NEHRP PUC Meeting
May 9, 2012
Starting Point
≠
Inconsistencies
ASCE 31 vs. ASCE 41
• ASCE 41 evaluation reveals more
deficiencies and leads to greater
upgrades
• 0.75 factor is hidden with the
ASCE 31 m-factors
• Sometimes there is no logical
transition from ASCE 31 to ASCE
41 m-factors
• Simplified Procedure ASCE 41
can be used in fewer instances
than ASCE 31 Deficiency-only
Tier 2
Combine ASCE 31 & 41
• Eliminate any “steps” between the two
documents
• Eliminate inconsistencies between ASCE
31 Tier 2 and ASCE 41
• Make user explicitly select to give
existing buildings a break
• Allow greater use of “deficiency-based”
procedures for evaluation AND upgrade
• Create a chapter for system specific
procedures, such as URM
Next Issue
≠
Make ASCE 41 & NERHP Provisions consistent
Inconsistencies between
ASCE 41-06 & 2009 NEHRP
> Seismic hazards do not use the same USGS
maps (NGA, Max Direction, etc.)
> Determination of response spectra & time
history record scaling different
> No risk targeting
> Levels of seismicity different from SDC’s
> Nonstructural provisions out of sync for SDC’s
> Wall out-of-plane forces
> ASCE 41 has more soil-foundation-structure
interaction martial
Revised Seismic Hazards
• Consistent seismic hazard science between
ASCE 7-10 and ASCE 41-13
• NGA relationships and new USGS maps used
• All hazards are maximum direction
• Scaling of site specific hazards matches ASCE
7 provisions for response spectra & time
histories
• Scaling of response histories now can be
done by using spectral matching or other
approved methods
Levels of Seismicity
ASCE 7-10
Seismic
Design
Category
ASCE 41-13
Level of
Seismicty
A
Very Low
B
Low
C
Moderate
D, E, & F
High
General Provisions
• Consistent regardless of whether you’re
evaluating or upgrading
• Basic Performance Objective for Existing Buildings
• Preserves giving existing buildings a break, but use
different seismic hazards instead of 0.75 factor
• Eliminates confusion about what to do with RC III and IV
buildings
• Basic Performance Objective for New Building Equiv.
• Provides similar performance as it intended for
a new building
• Uses ASCE 7-10 MCER seismic hazards
New Seismic Hazards
New Design Equivalent Hazards
• BSE-2N is the ASCE 7-10 MCER
• BSE-1N is 2/3*ASCE 7-10 MCER
Existing Building Hazards
• BSE-2E is the 5% in 50-year (975-year)
• BSE-1E is the 20% in 50-year (225-year)
BSE-2E and BSE-1E cannot be greater than the
BSE-2N and BSE-1N
• In SF, San Jose, parts of LA and Oakland this
means no reduction for existing buildings.
Existing Building BPO-E
Risk Category
I & II
III
IV
Tier 1
BSE-1E
Tier 2
BSE-1E
Tier 3
BSE-1E
Life Safety
Structural
Performance
Life Safety
Structural
Performance
Life Safety
Structural
Performance
Life Safety
Nonstructural
Performance
Life Safety
Nonstructural
Performance
Life Safety
Nonstructural
Performance
(3-C)
(3-C)
(3-C)
Position
Retention
Nonstructural
Performance
Position
Retention
Nonstructural
Performance
Position
Retention
Nonstructural
Performance
(2-B)
Immediate
Occupancy
Structural
Performance
(2-B)
Immediate
Occupancy
Structural
Performance
(2-B)
Immediate
Occupancy
Structural
Performance
Position
Retention
Nonstructural
Performance
Position
Retention
Nonstructural
Performance
Position
Retention
Nonstructural
Performance
(1-B)
(1-B)
(1-B)
BSE-2E
Collapse
Prevention
Structural
Performance
Nonstructural
Performance Not
Considered
(5-D)
Damage Control Damage Control Damage Control Limited Safety
Structural
Structural
Structural
Structural
Performance
Performance
Performance
Performance
Nonstructural
Performance Not
Considered
(4-D)
Life Safety
Structural
Performance
Nonstructural
Performance Not
Considered
(3-D)
New Code Equivalent BPO-N
Risk Category
I & II
BSE-1N
Tier 3
Life Safety
Structural
Performance
Position
Retention
Nonstructural
Performance
III
Collapse
Prevention
Structural
Performance
Nonstructural
Performance Not
Considered
(3-C)
(5-D)
Damage Control Limited Safety
Structural
Structural
Performance
Performance
Position
Retention
Nonstructural
Performance
IV
BSE-2N
(2-B)
Immediate
Occupancy
Structural
Performance
Operational
Nonstructural
Performance
(1-A)
Nonstructural
Performance Not
Considered
(4-D)
Life Safety
Structural
Performance
Nonstructural
Performance Not
Considered
(3-D)
Performance Levels
No Major Changes to the Structural Performance
Levels
Nonstructural Performance Levels
• Life Safety – It can seriously injure or kill…
greatly reduced from ASCE 31-03 & 41-06
• Position Retention – Matches ASCE 7 IP = 1.0
• Operational – Matches ASCE 7 IP = 1.5
Analysis Provision Updates
• Significantly more guidance on nonlinear
response history (NDP)
• Wall out-of-plane forces revised to
correlate with ASCE 7
• Force-controlled elements permitted to be
modeled and fail in nonlinear analysis
• Simplified NSP deleted
• Simplified table for C1C2 in the linear
procedures added
Material Testing Updates
• Kappa can be taken as 0.9 when you are
evaluating to the BSO-E, have good drawings,
but don’t do testing
• Rebar testing provisions updated
• Concrete testing provisions updated
Geotechnical Provision
Updates
• Site hazards evaluated at same hazard the
building is being evaluated to
• Liquefaction Analysis Procedure
• Analyze the structure with no Liquefaction
• Analyze the structure with a liquefaction adjusted spectra and
•
foundation properties
Analyze the structure for the lateral spreads and differential
setttlements
• New provisions for foundation rocking
• Updated soil-foundation-structure interaction
provisions
Steel Provision Updates
• Addition of BRBF Provisions
• Updated CBF Provisions
• Updated default material properties
Concrete Provision Updates
• Supplement 1 changes completely
included in the published document
• Updated bi-axial column provisions
• Updated anchors in concrete provisions
Light-Frame Provision Updates
• Separate sections for wood and coldformed steel light frame – CFS no longer
references wood acceptance criteria
• Updated wood and CFS reference
standards
• Updated provisions for shear walls and
horizontally sheathed walls
Masonry Provision Updates
• Re-introduction of bed-joint sliding as a
deformation controlled action
• Updated pier/wall rocking provisions and
re-introduction of toe-crushing limit state
• Updated provisions for masonry infill
• Provision for anchors into masonry
• Updates to the Special Provision for URM
Seismic Isolation /
Supplemental Damping
Provision Updates
• Design can proceed with upper and lower
bound properties instead of waiting for
isolator testing
• Accidental torsion reduced
• Vertical force distribution equation
updated
• Damper testing revised to be more
stringent
• Peer review requirements reduced to one
independent reviewer
Recommended Part 1
Changes from ASCE 41
> Bring in ASCE 41 additional SFSI material –
Base Slab Averaging and Embedment
Reductions (based on FEMA 440 & ATC-83)
into Chapter 19
> Bring forth changes to Chapters 17 and
Chapter 18 based on the Seismic Isolation &
Energy Dissipation revisions
Future Coordination Items
> Coordinate ASCE 41 collapse prevention
acceptance criteria with NEHRP Provisions 10%
conditional probability in the MCE
> Update ASCE 41 analysis procedures with IT-4
work
> Revise levels of seismicity and performance
objectives based on IT-2 work
> Coordinate ASCE 41 liquefaction procedures with
IT-8 work
End goal to get to a place
where the documents can
provide similar results
ASCE 41-13 and the NEHRP Provisions
Thank you…any questions?
NEHRP PUC Meeting
May 9, 2012