ASCE 41 Seismic Rehabilitation of Existing Buildings
1.1. How to define a Rehabilitation Objective How to define a Rehabilitation Objective per ASCE 41.
per ASCE 41.
2.2. Data Collection and Testing.Data Collection and Testing.
3.3. Analysis Requirements.Analysis Requirements.
4.4. Modeling.Modeling.
5.5. Results Evaluation.Results Evaluation.
6.6. Design and Rehabilitation.Design and Rehabilitation.
Presentation Topics:
What is ASCE 41?
It is mainly a combination of two FEMA It is mainly a combination of two FEMA documents:
documents:
FEMA 356 FEMA 356 –– Technical Requirements Technical Requirements for Seismic Rehabilitation of Buildings for Seismic Rehabilitation of Buildings –– Superseded by ASCE 41.Superseded by ASCE 41.
FEMA 274 FEMA 274 –– NEHRP Commentary on NEHRP Commentary on the Guidelines for Seismic
the Guidelines for Seismic Rehabilitation of Buildings.
Rehabilitation of Buildings.
ASCE 31 ASCE 31 –– Seismic Evaluation of Seismic Evaluation of Existing Buildings (supporting
Existing Buildings (supporting document).
document).
Why use ASCE 41?
To improve the seismic performance of To improve the seismic performance of any any existingexisting structure:structure:
ASCE 41 addresses rehabilitation of ASCE 41 addresses rehabilitation of Architectural, Mechanical, Electrical Architectural, Mechanical, Electrical
and Structural systems.
and Structural systems.
ASCE 41 can be used to rehabilitate ASCE 41 can be used to rehabilitate historic structures.
historic structures.
Where performance based Where performance based rehabilitations are desired.
rehabilitations are desired.
What is required for the Rehabilitation?
1.1. A Seismic Evaluation must be performed A Seismic Evaluation must be performed to identify deficiencies to be rehabilitated.
to identify deficiencies to be rehabilitated.
ASCE 31 (Formerly FEMA 310) can be ASCE 31 (Formerly FEMA 310) can be
used for the evaluation.
used for the evaluation.
2.2. Define the Rehabilitation Objective Define the Rehabilitation Objective -- a a combination of a Target Building
combination of a Target Building
Performance Level, an Earthquake Hazard Performance Level, an Earthquake Hazard
Level, and an Objective Classification.
Level, and an Objective Classification.
Target Building Performance:
1.1. Structural Performance Level: ASCE 41 Structural Performance Level: ASCE 41 1.5.1 and Tables C1
1.5.1 and Tables C1--2,3, & 4 define six 2,3, & 4 define six levels:
levels:
•• Immediate Occupancy (Immediate Occupancy (SS--1)1)
•• Damage Control Range (SDamage Control Range (S--2)2)
•• Life Safety (SLife Safety (S--3)3)
•• Limited Safety Range (SLimited Safety Range (S--4)4)
•• Collapse Prevention (SCollapse Prevention (S--5)5)
•• Not Considered (SNot Considered (S--6)6) Tables C1
Tables C1--2 to C12 to C1--4 defines typical 4 defines typical damage that accompany these levels.
damage that accompany these levels.
Target Building Performance:
Primary component
Primary component –– Any structural element that resists loads and Any structural element that resists loads and deformations from seismic loads in addition to gravity loads.
deformations from seismic loads in addition to gravity loads. Secondary Secondary component
component –– any element that resists deformations + gravity loads.any element that resists deformations + gravity loads.
Damage increases Damage increases
Target Building Performance:
1.1. Nonstructural Performance Level: ASCE Nonstructural Performance Level: ASCE 41 1.5.2 and Tables C1
41 1.5.2 and Tables C1--5 & 6 define five 5 & 6 define five levels:
levels:
•• Operational (Operational (NN--A)A)
•• Immediate Occupancy (NImmediate Occupancy (N--B)B)
•• Life Safety (NLife Safety (N--C)C)
•• Hazards Reduced (NHazards Reduced (N--D)D)
•• Not Considered (NNot Considered (N--E)E) Tables C1
Tables C1--5 & 6 define typical damage 5 & 6 define typical damage that accompany these levels.
that accompany these levels.
Target Building Performance:
Damage increases Damage increases
Target Building Performance:
Example: N
Example: N--A + SA + S--1 yields 11 yields 1--A Target A Target Building Performance designation.
Building Performance designation.
Earthquake Hazard Level:
BSE BSE –– 2 Event: An earthquake with a 2% 2 Event: An earthquake with a 2%
probability in 50 years of being exceeded.
probability in 50 years of being exceeded.
This is an earthquake with a 2500 year This is an earthquake with a 2500 year
reoccurrence period or the MCE as reoccurrence period or the MCE as
defined in ASCE 7 or IBC.
defined in ASCE 7 or IBC.
BSE BSE –– 1 Event: An earthquake with a 10% 1 Event: An earthquake with a 10%
probability in 50 years of being exceeded.
probability in 50 years of being exceeded.
This is an earthquake with a 500 year This is an earthquake with a 500 year
reoccurrence period or the design event reoccurrence period or the design event
defined in ASCE 7 or IBC.
defined in ASCE 7 or IBC.
BSE BSE –– Basic Service EarthquakeBasic Service Earthquake
QUIZ ???:
What document did ASCE 41 replace?
What document did ASCE 41 replace?
The History of Future Architecture.The History of Future Architecture.
Texas Architect.Texas Architect.
FEMA 356.FEMA 356.
Rehabilitation Objective Classes:
1.1. Basic Safety Objective Basic Safety Objective ––
typical for Ancillary structures typical for Ancillary structures
(Office buildings) (Office buildings)
2.2. Enhanced Rehabilitation Enhanced Rehabilitation Objective
Objective –– typical for Critical typical for Critical or Essential structures
or Essential structures
(Hospitals, Fire stations, Police (Hospitals, Fire stations, Police
stations) stations)
3.3. Limited Rehabilitation Limited Rehabilitation Objective
Objective –– (Other less critical (Other less critical structures)
structures)
You and your client define the req’d Class.
You and your client define the req’d Class.
Rehabilitation Objective:
Now that you have defined you Rehabilitation Objective what is next?:
Data CollectionData Collection
Analysis RequirementsAnalysis Requirements
ModelingModeling
Results EvaluationResults Evaluation
Design and Rehabilitation Design and Rehabilitation
Data Collection:
1.1. From existing plans From existing plans OROR
2.2. From a comprehensive testing programFrom a comprehensive testing program
Requirements depend on your Rehabilitation Requirements depend on your Rehabilitation
Objective and the information available Objective and the information available
to you from existing plans.
to you from existing plans.
Testing is needed to obtain enough information Testing is needed to obtain enough information
to build the linear or nonlinear model.
to build the linear or nonlinear model.
Material testing to support modeling can be Material testing to support modeling can be
very expensive and time consuming.
very expensive and time consuming.
Knowledge Factor
Knowledge Factor –– scale factor to reduce element scale factor to reduce element
capacity due to uncertainty in element composition.
capacity due to uncertainty in element composition.
Data Collection:
Comprehensive plan required when exist. dwgs Comprehensive plan required when exist. dwgs
don’t have enough information.
don’t have enough information.
Testing:
Wall thickness and wall to column Wall thickness and wall to column
connection check.
connection check.
Testing:
Steel coupons and clay tile wall sample for Steel coupons and clay tile wall sample for testing. Use ASCE 41 to determine number testing. Use ASCE 41 to determine number
of tests and locations.
of tests and locations.
Testing:
Core drilling of foundation to determine Core drilling of foundation to determine
concrete material properties.
concrete material properties.
Testing:
Concrete cores for compression testing.
Concrete cores for compression testing.
Testing:
InIn--situ shear test of a clay tile wall.situ shear test of a clay tile wall.
Testing:
Flexural test of clay tile to determine out Flexural test of clay tile to determine out
of plane bending capacity.
of plane bending capacity.
40” x 40”
40” x 40”
Testing:
Compression test of clay tile sample.
Compression test of clay tile sample.
Analysis Options:
1.1. Linear static Linear static -- LSP (considered the LSP (considered the least accurate)
least accurate)
Linear model subject to lateral Linear model subject to lateral loading determined by ASCE 41.
loading determined by ASCE 41.
Similar to IBC / ASCE 7 equivalent Similar to IBC / ASCE 7 equivalent
lateral force method.
lateral force method.
Allowed only for structures without Allowed only for structures without irregularities defined in ASCE 41 irregularities defined in ASCE 41
(basically the same irregularity (basically the same irregularity
types defined in ASCE 7).
types defined in ASCE 7).
Allowed only for some structures Allowed only for some structures which do not have any
which do not have any
irregularities defined for the NSP.
irregularities defined for the NSP.
Analysis Options:
2.2. Linear dynamic Linear dynamic -- LDP LDP
(considered more accurate than (considered more accurate than
the LSP) the LSP)
Linear model subjected to Linear model subjected to response spectral or time response spectral or time
history loading.
history loading.
Allowed only for some Allowed only for some
structures which do not have structures which do not have any irregularities defined for any irregularities defined for
the NSP.
the NSP.
V = 0.85 VV = 0.85 VLSPLSP
Analysis Options:
3.3. Nonlinear static Nonlinear static –– NSP NSP
(considered accurate enough (considered accurate enough
for most structures) for most structures)
Structural model with Structural model with
nonlinear material behavior nonlinear material behavior
assigned to structural elements assigned to structural elements pushed to a static displacement pushed to a static displacement
defined by ASCE 41. This is defined by ASCE 41. This is
called the Target called the Target
Displacement.
Displacement.
Can be required by your clientCan be required by your client..
V = 0.7 VV = 0.7 VLSP
Analysis Options:
Buildings with nonBuildings with non--orthogonal orthogonal lateral system.
lateral system.
Building with a vertical stiffness Building with a vertical stiffness irregularity.
irregularity.
Building which has a torsional Building which has a torsional stiffness irregularity in any story.
stiffness irregularity in any story.
When the first mode period is more When the first mode period is more than 3.5Ts with Ts = S1 / Ss p. 26.
than 3.5Ts with Ts = S1 / Ss p. 26.
Any structure where the horizontal Any structure where the horizontal dimension of any story exceeds that dimension of any story exceeds that
of an adjacent story by 1.4.
of an adjacent story by 1.4.
Required if any of the following are true:Required if any of the following are true:
Analysis Options:
4.4. Nonlinear time history Nonlinear time history -- NDP NDP (considered the most accurate) (considered the most accurate)
Structural model with nonlinear Structural model with nonlinear material behavior assigned to material behavior assigned to
structural elements subjected to an structural elements subjected to an
earthquake time history loading.
earthquake time history loading.
Required for certain structures Required for certain structures including those when R> R
including those when R> Rmaxmax. R is . R is a parameter related to the
a parameter related to the
structures’ capacity / the seismic structures’ capacity / the seismic
demand.
demand.
Permitted for all structures and a Permitted for all structures and a third party review may be required third party review may be required
for this analysis method.
for this analysis method.
QUIZ ???:
What should you do if the existing plans do What should you do if the existing plans do
not have information on the existing not have information on the existing
materials in the building?
materials in the building?
A.A. Ask the Architect for more fee?Ask the Architect for more fee?
B.B. Initiate a comprehensive testing program?Initiate a comprehensive testing program?
C.C. Analyze the structure using the Nonlinear Analyze the structure using the Nonlinear Dynamic Procedure?
Dynamic Procedure?
Nonlinear Modeling for NSP:
A model that considers material nonlinearity in A model that considers material nonlinearity in
all elements which comprise it including:
all elements which comprise it including:
1.1. Likely plastic hinge regions modeled with Likely plastic hinge regions modeled with FEMA 356 nonlinear hinges.
FEMA 356 nonlinear hinges.
2.2. Material stress strain relationships Material stress strain relationships assigned to concrete, steel, masonry, assigned to concrete, steel, masonry,
Fiber Reinforced Polymer (FRP) and clay Fiber Reinforced Polymer (FRP) and clay
tile structural elements (etc).
tile structural elements (etc).
Material Stress-Strain Relations as defined by ASCE 41:
Curve 1 Curve 1 –– Ductile material with a post yield Ductile material with a post yield residual strength (deformation controlled).
residual strength (deformation controlled).
Curve 2 Curve 2 –– Ductile material without post yield Ductile material without post yield residual strength (deformation controlled).
residual strength (deformation controlled).
Curve 3 –Curve 3 – Brittle material (force controlled).Brittle material (force controlled).
HCT in compress.HCT in compress.
HCTHCT in shear.in shear.
Steel Steel
Force
Force--Deformation Relations for Concrete Deformation Relations for Concrete (Chapter 6 ASCE 41):
(Chapter 6 ASCE 41):
Q Q –– applied load. Qapplied load. Qyy –– yield force.yield force.
a, b, c, and d defined by ASCE 41.
a, b, c, and d defined by ASCE 41.
The Engineer must use these relationships The Engineer must use these relationships
along with definitions for points a, b, c, and d along with definitions for points a, b, c, and d
to define material nonlinearity.
to define material nonlinearity.
Nonlinear Modeling for NSP:
Acceptance Criteria
Acceptance Criteria –– Concrete Hinges:Concrete Hinges:
C C –– conforming transverse steel (ties). conforming transverse steel (ties).
NC NC –– Nonconforming transverse steel.Nonconforming transverse steel.
More stringent reqs More stringent reqs
Nonlinear Modeling for NSP:
FEMA 356 Hinges
FEMA 356 Hinges -- Concrete:Concrete:
Nonlinear Modeling for NSP:
Steel (Type 1 Curve):
Steel (Type 1 Curve):
Ductile Range Ductile Range
Nonlinear Modeling for NSP:
Concrete (Type 3 Curve):
Concrete (Type 3 Curve):
Brittle Brittle
Nonlinear Modeling for NSP:
Clay Tile
Clay Tile –– Shear Only (From Judgment and Shear Only (From Judgment and published research. Allowed by
published research. Allowed by ASCE 41 C1.2ASCE 41 C1.2))
Shear yield Shear yield
Shear failure Shear failure
Zero tension Zero tension
CompComp
Clay Tile
Clay Tile –– Compression (Type 3 Curve):Compression (Type 3 Curve):
Nonlinear Modeling for NSP:
Brittle Brittle
EE11 EE22
EE22 = 0.1 E= 0.1 E11
Programs:
SAP 2000 AdvancedSAP 2000 Advanced
STAAD Pro NonlinearSTAAD Pro Nonlinear
PERFORMPERFORM
ANSYSANSYS
These programs are expensive per license These programs are expensive per license
and require a “strong” computer to run the and require a “strong” computer to run the
models. Example 12 NL load combos models. Example 12 NL load combos
takes 20 hours to solve.
takes 20 hours to solve.
QUIZ ???:
The following represents what kind of material The following represents what kind of material
behavior?
behavior?
A.A. Brittle.Brittle.
B.B. ElasticElastic--Perfect Plastic.Perfect Plastic.
C.C. Ductile.Ductile.
Nonlinear Modeling Process:
For a Nonlinear Static Model you are For a Nonlinear Static Model you are basically in need of establishing the basically in need of establishing the pushover curve for the structure and pushover curve for the structure and
verifying that R < R
verifying that R < Rmaxmax. This is done by:. This is done by:
1.1. Defining the Target Displacement for the Defining the Target Displacement for the structure at the
structure at the control nodecontrol node::
CCoo –– factor to equate a SDOF system to actual bldg.factor to equate a SDOF system to actual bldg.
CC11 –– inelastic scale factor. Tinelastic scale factor. Tee –– effective first mode period.effective first mode period.
CC22 –– factor for pinched hystersis + cyclic strength degradation.factor for pinched hystersis + cyclic strength degradation.
Nonlinear Modeling Process:
2.2. Push the model, using inertial forces Push the model, using inertial forces
applied to the model in proportion to the applied to the model in proportion to the
first mode shape, to the target first mode shape, to the target
displacement and define the
displacement and define the Static Static Pushover Curve
Pushover Curve for the building. The for the building. The target displacement will vary for each target displacement will vary for each
major direction of the structure. This major direction of the structure. This
process is iterative and time consuming.
process is iterative and time consuming.
Nonlinear Modeling Process:
3.3. Define R based on the results of the push Define R based on the results of the push over analysis. R is a measure of system over analysis. R is a measure of system
stability. R
stability. Rmaxmax is a measure of system is a measure of system ductility.
ductility.
CCmm –– mass effective in the first mode and Vmass effective in the first mode and Vyy is the structure is the structure first yield force.
first yield force. yy –– yield displacement. yield displacement. dd –– target disp.target disp.
RRmaxmax –– roughly the same as R from ASCE 7.roughly the same as R from ASCE 7.
VVyy –– structure first yield, W str weight, Sstructure first yield, W str weight, Saa –– response spectra response spectra acceleration at T
acceleration at Tee..
Nonlinear Modeling Process:
4.4. The target displacement is dependent on the The target displacement is dependent on the level of seismic activity expected at your
level of seismic activity expected at your site, the soil properties of your site, mass site, the soil properties of your site, mass effective in the first mode, and amount of effective in the first mode, and amount of
viscous damping capacity of your structure.
viscous damping capacity of your structure.
Static Pushover Curve:
VVdd –– maximum capacitymaximum capacity
Actual Struct performance Actual Struct performance
Static Pushover Curve:
Structure Structure
capacity curve capacity curve
ASCE Bilinear ASCE Bilinear pushover curve pushover curve
inches inches
kipskips
Example – Simple Nonlinear Model:
Description: 2
Description: 2 –– story reinforced concrete story reinforced concrete structure with r/c second floor and roof.
structure with r/c second floor and roof.
Material nonlinearity assigned to the Material nonlinearity assigned to the
concrete and reinforcing steel. Plastic hinge concrete and reinforcing steel. Plastic hinge
zones modeled with FEMA 356 hinges.
zones modeled with FEMA 356 hinges.
Modeling and analysis completed in SAP Modeling and analysis completed in SAP
2000 Advanced for a BSE
2000 Advanced for a BSE--2 event in 2 event in Albuquerque, NM.
Albuquerque, NM.
24’ x 30’ bays with 2
24’ x 30’ bays with 2 –– 12’ tall stories, 18” x 12’ tall stories, 18” x 18” columns, and 6” thick diaphragms at the 18” columns, and 6” thick diaphragms at the
roof and second floor.
roof and second floor.
Nonlinear Results Evaluation:
1.1. R < RR < Rmaxmax
2.2. Individual component behavior is within the Individual component behavior is within the acceptance criteria limitations for that
acceptance criteria limitations for that
component. This is dependent on the load component. This is dependent on the load--
deformation limits prescriptive to the deformation limits prescriptive to the
Rehabilitation Objective. (i.e. IO, LS, CP) Rehabilitation Objective. (i.e. IO, LS, CP)
3.3. Individual component behavior is within the Individual component behavior is within the limits defined by the governing code using limits defined by the governing code using
load combinations and
load combinations and factors defined by factors defined by ASCE 41. (i.e.
ASCE 41. (i.e. = 1.0) = 1.0)
Rehabilitation Options:
Addition of new concrete shear wallsAddition of new concrete shear walls
Use of Fiber Reinforced Polymer laminates Use of Fiber Reinforced Polymer laminates to strengthen masonry, unreinforced clay to strengthen masonry, unreinforced clay
tile, or concrete members.
tile, or concrete members.
Add steel bracingAdd steel bracing
Improve connection capacitiesImprove connection capacities
Reduce structure massReduce structure mass
Global stiffeningGlobal stiffening
Rehabilitation Options:
Fiber Reinforced Polymers
PrePre--cured system => BASF. Is a the process cured system => BASF. Is a the process of installing FRP “belts” or strips to the
of installing FRP “belts” or strips to the
substrate. Strips are fully cured prior to being substrate. Strips are fully cured prior to being
laminated to the substrate with epoxy.
laminated to the substrate with epoxy.
Wet layup system => Fyfe. Is the process of Wet layup system => Fyfe. Is the process of installing FRP fabric to the substrate following installing FRP fabric to the substrate following
saturation of the fabric with epoxy. This saturation of the fabric with epoxy. This
process is “like paper
process is “like paper machemache”. ”.
Rehabilitation Options:
Fiber Reinforced Polymers
FRP can add an additional 25% to 30% to FRP can add an additional 25% to 30% to
column capacities.
column capacities.
FRP Pull Test
ASTM D4541ASTM D4541Rehabilitation Options:
Fiber Reinforced Polymers
FRP can add an additional 50% to beam FRP can add an additional 50% to beam
strength.
strength.
Rehabilitation Options:
Fiber Reinforced Polymers
MBrace system from BASF MBrace system from BASF
Rehabilitation Options:
Fiber Reinforced Polymers
MBrace system from BASF MBrace system from BASF
Rehabilitation Options: Fiber Reinforced Polymers
Rehabilitation Options:
Fiber Reinforced Polymers
MBrace system from BASF MBrace system from BASF
Rehabilitation Options:
Fiber Reinforced Polymers
MBrace system from BASF MBrace system from BASF
Fiber direction
Fiber direction –– FRP is typically a FRP is typically a uniaxial material
uniaxial material
Rehabilitation Options: Fiber Reinforced Polymers
Rehabilitation Options:
Fiber Reinforced Polymers
Nueces Courthouse
Nueces Courthouse –– Corpus Christi, TXCorpus Christi, TX
Rehabilitation Options: Fiber Reinforced Polymers
Rehabilitation Options:
Fiber Reinforced Polymers
FRP pre
FRP pre--cured laminates can give you cured laminates can give you about 10 klf (5 klf for wet lay ups) per about 10 klf (5 klf for wet lay ups) per
side of additional shear capacity.
side of additional shear capacity.
Rehabilitation Options:
Fiber Reinforced Polymers
Fiber direction
Fiber direction –– FRP is typically a uniaxial materialFRP is typically a uniaxial material
Rehabilitation Options: FRP Details
Rehabilitation Options: FRP Details
Rehabilitation Options: FRP Details
FRP Suppliers and Codes:
BASFBASF
FYFEFYFE
SIKASIKA
ACI 440.7ACI 440.7
