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

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.

BTS, Bangkok

BTS, Bangkok

Nimitz Freeway, San Francisco

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)

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

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.

APPLICATION I SINGLE COLUMN BENT

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 = 4.5 m2 ρs = 1.7% Ties = 4x4 DB16

Material Property - Concrete : ACI318-08 Compressive strength 35 Mpa Ec 4700 - Reinforcement ; TIS24-2548 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

Structural Modeling

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)

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

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

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

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.

APPLICATION II DOUBLE-DECK BRIDGE PIER

Double-deck Bridges in Bangkok

Pushover load patterns Mwafy and Elnashai (2000)

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.

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

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 = 35 MPa fy = 490 MPa fyh = 390 MPa ADL@each deck = 1500 tons

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

Loads Triangular load pattern Uniform load pattern

Soil Condition Rock Soil Soft Soil

Model of double-deck bridge pier

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

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)

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)

Irregular Structure Base Shear ATC-40 procedure un-conservative

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

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

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.

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

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.

Thank You