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PERFORMANCE STUDY FOR REINFORCED CONCRETE BRIDGE PIERS CONSIDERING SEISMIC CAPACITY
AND DEMAND
Presented by: Sasithorn THAMMARAK (st109957)16th May 2011
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Introduction
• It is obvious that earthquake phenomenon is possible to happen in Thailand.
• Evaluation of existing buildings and bridges is needed.• Capacity spectrum method(CSM) is considered.
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BTS, Bangkok
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BTS, Bangkok
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Nimitz Freeway, San Francisco
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Capacity Spectrum Method (CSM)
Modify spectrum according to soil-structural interactive (FA, FV)
Develop structural model Select 5% damping ground motion spectrum
Modify structural model for flexible base (soil effect)
Select static load vector
Generate global force-deformation curve (push-over curve)
Convert force-deformation curve to equivalent SDOF model (ADRS format)
Determine equation for effective damping
Determine equation for effective period
Select solution procedure (A,B or C) and calculate performance point
Convert the spectrum to ADRS format
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Spectral Displacement
Spec
tral
Acc
eler
ation
(g)
ay, dy api, dpi
2.5CA
CV /T
2.5SRACA
SRVCV /T
ap, dp
Performance Point
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Assumptions
• Uniform multiple spans simply supported on uniform pier columns.
• Each bent is stand-alone model, only transverse responses are investigated.
• Effects of soil are considered in terms of demand spectra.
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APPLICATION I SINGLE COLUMN BENT
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Model of single column bentsSix columns with similar material properties but are different in cross section.
9 meters15 meters25 meters
Area = 4.5 m2
ρs = 1.7%Ties = 4x4 DB16
Solid section Hollow section
No buckling
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Material Property
- Concrete : ACI318-08Compressive strength 35 MpaEc 4700
- Reinforcement ; TIS24-2548Reinforcing steel grade SD30 SD40 SD50
Minimum tensile strength (MPa) 480 560 620Minimum yield strength (MPa) 295 390 490Elongation (%) 17 15 13
Main Rebar
Confinement
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Structural Modeling
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0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 15000
1000000
2000000
3000000
Base
She
ar (K
N)
Roof Deflection (mm)
Application I Result
9m
15m
25m
Energy (KN-m)
4.31 1337
3.91 1053
3.81 1956
3.19 1564
3.54 2867
3.00 2246
µΔ
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Sung et al. (2006) ATC-40 (1996) + Japan Road Association (2001) +Building Technology Standards (Taiwan) (1997)
PGA-displacement relationship
PGA vs. Roof Displacement
Linear relation while nonlinear analysis is applied?
Performance of a particular structure under a particular earthquake and site can be directly obtained.
Higher PGA?
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0 100 200 300 400 500 600 7000.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00Case 0.1 g
Case 0.2 g
Case 0.3 g
Case 0.4 g
Case 0.5 g
Case 0.6 g
Case 0.7 g
T1
T2
Response Spectra (ADRS format) : Soil Type B (Rock)
Spe
ctra
l Acc
eler
atio
n (g
)
Spectral Displacement (mm)
Rock site response spectrum
Original acceleration spectrum Converted demand spectra (ADRS)
CALTRANS, 2006
ATC-40, SAP2000
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For the single column bent, almost linear shape Hollow piers are stiffer = better performance
0 100 200 300 400 500 600 7000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Roof Deflection (mm)
PGA
(g)
PGA vs. Roof displacement9m 15m 25m
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Part I concluding remarks
• Hollow piers provide better ductility and absorb more energy.
• The shapes of PGA vs. roof displacement curves are almost linear, though the analysis is based on the nonlinear analysis.
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APPLICATION II DOUBLE-DECK BRIDGE PIER
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Double-deck Bridges in Bangkok
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Mwafy and Elnashai (2000)
Pushover load patterns
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Pushover load patterns
• Structures with irregular geometry, higher mode effects may be critical on some structural components than the fundamental mode.
• Other load patterns (e.g. uniform) rather than 1st mode pattern (i.e. triangle) should be employed.
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Sung et al. (2006)
PGA-displacement relationship
PGA vs. Roof Displacement
Linear relation while nonlinear analysis is applied.
Performance of a particular structure under a particular earthquake and site can be directly obtained.
Irregular structure?Does soil affect the result?
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S_1 S_21K : 4K1K : 1K
Case studies
f’c = 35 MPafy = 490 MPafyh = 390 MPaADL@each deck = 1500 tons
Uniform Stiffness Structure
Non-Uniform Stiffness Structure
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Section 3x1.25 m2
ρs = 1.27%ρh = 0.75%
Section 3x2 m2
ρs = 1.26%ρh = 0.71%
Double-deck cross sections
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Loads
Triangular load pattern Uniform load pattern
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Soil Condition
• Rock Soil
• Soft Soil
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Model of double-deck bridge pier
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Pushover curves
0 50 100 150 200 250 300 350 400 4500
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
20000000
Roof Deflection (mm)
Base
She
ar (K
N)
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PGA vs. Roof displacement
0 50 100 150 200 250 300 350 400 4500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Roof Displacement (mm)
PGA
(g)
PGA
(g)
Regular Pier
Irregular Pier
Soft soil site
Rock site
0 50 100 150 200 250 300 350 400 4500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Roof Displacement (mm)
Rock site
Soft soil site
Irregular Pier
PGA
(g)
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PGA vs. Base Shear
PGA
(g)
Regular Pier
Irregular Pier
0 5000000 10000000 15000000 20000000 250000000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Base Shear (KN)
PGA
(g)
Base Shear (KN)
PGA
(g)
Soft soil site
Regular Pier
0 5000000 10000000 15000000 20000000 250000000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Base Shear (KN)
PGA
(g)
Rock site
Soft soil site
Rock site
Irregular Pier
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Base Shear
ATC-40 procedure un-conservative
Irregular Structure
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Higher mode effect
Not considered by ATC-40
Further analysis for higher mode is important
Irregular Structure
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Vt
Vb
Mt1
Mt2
Mb1
Mb2
Fr
F1
Shear Diagram Moment DiagramApplied loads
Member forces
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Mbottom2
Mbottom1
Mtop2
Mtop1
Vbottom
Vtop
0 20000 40000 60000 80000
Triangular LoadUniform Load
-14%
3%
-13%
-16%
4%
2%
Uniform Structure
Triangular pattern governed the responses of the regular structures. Therefore ATC-40 is adequate.
KN
KN-m
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Mbottom2
Mbottom1
Mtop2
Mtop1
Vbottom
Vtop
0 20000 40000 60000 80000
Triangular LoadUniform Load
-20%
17%
-19%
-21%
18%
17%
Non-Uniform Structure
For irregular structures, the responses should be computed from the more conservative results
KN
KN-m
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Thesis Conclusion and Recommendations
• Hollow pier provides better performance in terms of stiffness and ductility.
• The ATC-40 structural evaluation method is appropriate for considering maximum displacement, but it is not adequate for estimating forces or base shear response for the irregular structural geometry.
• Higher mode effect is important for analyzing base shear.
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Thank You