1. Presented by: Sasithorn THAMMARAK (st109957)
Performance study for reinforced concrete bridge piers considering seismic capacity and demand
Presented by: Sasithorn THAMMARAK (st109957)
16th May 2011

2. 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.

3. BTS, Bangkok

4. BTS, Bangkok

5. Nimitz Freeway, San Francisco

6. 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
Capacity Spectrum Method (CSM)

7. Performance Point Spectral Acceleration (g) ay, dy api, dpi
2.5CA
2.5SRACA
SRVCV /T
CV /T
ap, dp
Spectral Acceleration (g)
ay, dy
api, dpi
Spectral Displacement

8. 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.

9. APPLICATION I SINGLE COLUMN BENT

10. Model of single column bents
Six columns with similar material properties but are different in cross section.
No buckling
Solid section
Hollow section
9 meters
15 meters
25 meters
Area = m2
ρs = %
Ties = 4x4 DB16

11. Material Property
- Concrete : ACI Compressive strength 35 Mpa Ec Reinforcement ; TIS
Reinforcing steel grade
SD30
SD40
SD50
Minimum tensile strength (MPa)
480
560
620
Minimum yield strength (MPa)
295
390
490
Elongation (%) 17 15 13
Confinement
Main Rebar

12. Structural Modeling

13. Application I Result Energy (KN-m) µΔ 9m Base Shear (KN) 15m 25m
4.31
1337
3.91
1053
3.81
1956
3.19
1564
3.54
2867
3.00
2246 µΔ 9m
Base Shear (KN)
15m
25m
Roof Deflection (mm)

14. PGA vs. Roof Displacement
Sung et al. (2006) ATC-40 (1996) + Japan Road Association (2001) + Building Technology Standards (Taiwan) (1997)
Performance of a particular structure under a particular earthquake and site can be directly obtained.
Linear relation while nonlinear analysis is applied?
Higher PGA?
PGA-displacement relationship

15. Rock site response spectrum
CALTRANS, 2006
ATC-40, SAP2000
Original acceleration spectrum
Converted demand spectra (ADRS)

16. PGA vs. Roof displacement
PGA (g)
Roof Deflection (mm)
For the single column bent, almost linear shape
Hollow piers are stiffer = better performance

17. 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.

18. APPLICATION II DOUBLE-DECK BRIDGE PIER

19. Double-deck Bridges in Bangkok

20. Pushover load patterns
Mwafy and Elnashai (2000)

21. 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.

22. PGA vs. Roof Displacement
Sung et al. (2006)
Performance of a particular structure under a particular earthquake and site can be directly obtained.
Linear relation while nonlinear analysis is applied.
Irregular structure?
Does soil affect the result?
PGA-displacement relationship

23. Uniform Stiffness Structure Non-Uniform Stiffness Structure
Case studies
S_1
S_2
1K : 1K
1K : 4K
Uniform Stiffness Structure
Non-Uniform Stiffness Structure
f’c = MPa
fy = MPa
fyh = MPa
deck = tons

24. Double-deck cross sections
Section 3x1.25 m2
ρs = 1.27%
ρh = 0.75%
Section 3x2 m2
ρs = 1.26%
ρh = 0.71%

25. Loads
Triangular load pattern
Uniform load pattern

26. Soil Condition
Rock Soil
Soft Soil

27. Model of double-deck bridge pier

28. Pushover curves
Base Shear (K N)
Roof Deflection (mm)

29. PGA vs. Roof displacement Regular Pier Irregular Pier Irregular Pier
Rock site
Soft soil site
PGA (g)
Roof Displacement (mm)
Irregular Pier
Irregular Pier
Rock site
PGA (g)
PGA (g)
Soft soil site
Roof Displacement (mm)

30. PGA vs. Base Shear Regular Pier Regular Pier Irregular Pier
Rock site
PGA (g)
PGA (g)
Soft soil site
Base Shear (KN)
Irregular Pier
Irregular Pier
Rock site
PGA (g)
PGA (g)
Soft soil site
Base Shear (KN)
Base Shear (KN)

31. Irregular Structure
Base Shear
ATC-40 procedure un-conservative

32. Irregular Structure Higher mode effect Not considered by ATC-40
Further analysis for higher mode is important

33. Member forces Fr Vt Vb Mt1 Mt2 Mb1 Mb2 F1 Applied loads Shear Diagram
Moment Diagram

34. Uniform Structure
-14% 3% KN
-13%
-16% 4% 2%
KN-m
Triangular pattern governed the responses of the regular structures. Therefore ATC-40 is adequate.

35. Non-Uniform Structure
-20%
17% KN
-19%
-21%
18%
17%
KN-m
For irregular structures, the responses should be computed from the more conservative results

36. 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.

37. Thank You