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Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-1
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 1
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy, M.Eng., P.Eng.Manager, Bridge Engineering
Associated Engineering
The Canadian Society for Civil Engineering, Vancouver Section
THE RESPONSE SPECTRUM
A Technical Seminar on the Development and Application of the Response Spectrum Method for Seismic Design of Structures
1-2 June 2007 Vancouver, BC
Filename, 2 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
2
Don Kennedy
Outline
Four Case Studies:1. Application of RSA to bridge seismic design2. Mission Bridge – Comparison of demands from RSA
and time history analyses3. Lake City Overpass: RSA demands and
combinations4. Knight Street Bridge retrofit – RSA and modeling
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-2
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 3 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
3
Don Kennedy
Outline
Four Case Studies:1. Application of RSA to bridge seismic
design2. Mission Bridge – Comparison of demands from RSA
and time history analyses3. Lake City Overpass: RSA demands and
combinations4. Knight Street Bridge retrofit – RSA and modeling
Filename, 4 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
4
Don Kennedy
Implications of design forces on columns
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-3
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 5 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
5
Don Kennedy
Implications of design forces on columns
Filename, 6 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
6
Don Kennedy
Implications of design forces on columns
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-4
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 7 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
7
Don Kennedy
Implications of design forces on columns(Too much strength?)
Filename, 8 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
8
Don Kennedy
Implications of design forces on columns(Too little strength, little ductility (old codes))
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-5
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 9 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
9
Don Kennedy
Implications of design forces on columns
Filename, 10 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
10
Don Kennedy
Implications of design forces on columns
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-6
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 11 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
11
Don Kennedy
Column proportions and curvature ductility demands
AVAILABLE DISPLACEMENT DUCTILITYvs Clear Height / Diameter
FOR COLUMN IN DOUBLE CURVATURE
with µφ capacity of 14
0
2
4
6
8
10
12
0.0 10.0 20.0 30.0
COLUMN CLEAR HEIGHT / COLUMN DIAMETER
Filename, 12
Application to Design: Displacement – based Design Issues
Foundation flexibility effect on deformation demands – Scenario 1∆ u from analysis∆ f ∆ f less as pier
yielded earlier∆ p ∆ p
∆ u from analysis
∆ p
greater than assumed from linear scaling
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-7
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 13
Foundation flexibility - Scenario 2 : Design Criteria requires 1.5 x Danalysis
∆ u need 1.5 times that from retrofit analysis
∆ f∆ p
Criteria may require capacity of 150% of the ultimate displacement – not merely of the pier’s mechanism displacement from pushover analysis.
If retrofit is designed to achieve a target mechanism displacement, prior to (say) a column shear failure, the criteria may not have been met.
This criteria may be very difficult to achieve if foundation flexibility contributes significantly to drifts. Consider alternative retrofit (e.g. pile hinging)
Filename, 14
Foundation flexibility - Scenario 2 : Design Criteria requires 1.5 x Danalysis
If consider also shape of displacement spectrum & period shift from flexibility, may find little benefit to drift demands
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-8
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 15 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
15
Don Kennedy
Outline
Four Case Studies:1. Application of RSA to bridge seismic design2. Mission Bridge – Comparison of
demands from RSA and time history analyses
3. Lake City Overpass: RSA demands and combinations
4. Knight Street Bridge retrofit – RSA and modeling
Filename, 16
Acceleration Response Spectra
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-9
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 17
Site variation
Filename, 18
Acceleration Response Spectra
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-10
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 19 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
19
Don Kennedy
Idealization of the real structure
• The continuum…
is replaced by discrete joints and elements
Modeling
Filename, 20
• 4 SADSAP Pivot Elements per Pier
Pier modeling
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-11
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 21
Structural Analysis – Pier Nonlinearities
Filename, 22
Structural Analysis – Pier Nonlinearities
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-12
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 23 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
23
Don Kennedy
MISSION BRIDGE SEISMIC ASSESSMENT - FIGURE 7.13Longitudinal Displacement Demands
-200
0
200
400
600
800
N5 N4 N3 N2 N1 S1 S2 S3 S4 S5
NORTH RSAExpansion Joints FreeExpansion Joints Fixed
SOUTH RSAExpansion Joints FreeExpansion Joints Fixed
Mission Abbotsford
CENTRE RSAExpansion Joints FreeExpansion Joints Fixed
DISPLACEMENT DIRECTION
Soft Springs - Original Spectra
Filename, 24
Structural Analysis – Model Calibration
• Cracked Pier Stiffness Properties• SAP 2000: Ie/Ig = 35%• SADSAP: Ie/Ig = 25%
• Directional Effects• SAP2000: SRSS combination• SADSAP: simultaneous inputs in orthogonal directions
Mission Bridge Seismic Retrofit and Rehabilitation
SMSB VI – July 30, 2002
Response Spectrum Analyses Case Studies, Applications to Bridges
Don Kennedy
Response Spectrum Seminar Lecture 11A P11A-13
University of British ColumbiaVancouver, June 1st & 2nd
Filename, 25 Mission Bridge Seismic Retrofit and RehabilitationSMSB VI – July 30, 2002
Filename, 26 1-2 June 2007The Response Spectrum - CSCE Vancouver Section
26
Don Kennedy
Pushover Analysis
MISSION BRIDGE SEISMIC ASSESSMENT - FIGURE 8.1Pier N1 & S1 Transverse Pushover Response
Cap BeamShear Failure
1st Flexural Hinge
2nd Flexural Hinge3rd & 4th Flexural Hinges
5th Flexural Hinge
Ultimate CurvatureCapacity (Hinge 4)
Tension ColumnJoint Shear Failure
Compression Column
Joint Shear Failure
Tension ColumnShear Failure
(Hinge 1)
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350
Bearing Displacement Relative to Top of Caisson (mm)
Shea
r (kN
)
No P - ∆Allowance
P - ∆Included
12%
Joint ShearFailure
Shear Failure
12%
38% 38%
32
14
5
Joint ShearFailure
Top of Caisson
N1 Transverse Displacement Demands
Order of FlexuralHinge Formation
(Typ.)
S1 Transverse Displacement DemandsExpansion Joints Free
Expansion Joints FixedLPNSMOD Based
Time History
