Seismic Performance of Reinforced Concrete C-bent Columns

Seismic Performance of
Reinforced Concrete C-bent C
Columns
Jun 11, 2005
Department of Civil Engineering
Tokyo Institute of Technology
Seiji Nagata

C-bent Columns
In urban area, there exist a large number of RC columns
with the lateral beam being longer in one side than the other.
Eccentric
Dead Load
Eccentric
Dead Load
Eccentricity
Column
Center
RC Pier
Steel Pier
C-bent columns have a poor seismic performance!

Current Researches on C-bent C
Columns
• Cyclic loading and shake table tests in transverse
direction, Kawashima and Unjoh, 1994.
• Cyclic loading tests in longitudinal direction, Tuchiya
and Maekawa et al, 1999.
• Cyclic loading tests in bilateral direction, Kawasima
et al, 2002
Longitudinal
Eccentric
Dead Load
Transverse
Lateral Force
Tension Side
Residual Drift
Compression
Side

Objectives
• To clarify seismic response of RC C-bent columns
under bilateral excitation, a series of hybrid loading
test were conducted.
• To reproduce the experimental response of RC C-bent
columns, a fiber element analysis was conducted

Test Specimens
RC Columns were designed based on the current Seismic
design codes.
e: Eccentricity
D: Width of Columns
e=0
1350 mm
e=0.5D
e=D
• 1350mm
Effective Height
• 400mm x 400mm
Square Section
400 mm
400 mm
Axial Reinforcements 1.27 %
1.35 %
1.9 %
Tie Reinforcements 0.79 %
0.99 %
1.19 %

Hybrid Loading Test on C-bent C
Columns
Input Ground Motion: JMA Kobe Record
Acceleration
(m/s 2 )
10
0
-10
0
Unilateral Excitation
Longitudinal
NS
Time (s) 30 0
Time (s)
Bilateral Excitation
EW
30
EW
Transverse
NS
NS

e=0
Damage after the Unilateral Excitation
Damage of columns at the eccentric completion side
e=D
e=0.5D
NS
NS
NS
Separation of the
covering concrete
The damage increases as the eccentricity increases.

Displacement (mm)
e= = 0.5D
50
0
NS
Seismic Response under
the Unilateral Excitation
Residual
Drift
e= D
NS
-2
-50
0 30
Time (sec)
Drift (%)
The residual drift increases as the eccentricity increases.
2
0
Prescribed
Displacement (mm)
Drift (%)
0 1 2
40
20
0
-20
1.2% Drift
2.6% Drift
-1
-2
-40
0 10 20 30 40
Residual Drift in the eccentric
compression side (mm)
2
1
0
Drift (%)

Hybrid Loading Test under
the Bilateral Excitation
Residual Drift
After Loading
Before Loading
NS
EW

Effect of Bilateral Excitation
Unilateral Excitation
Bilateral Excitation
e=D
NS
Separation of the
covering concrete
NS
EW
Bilateral excitation results in more extensive damage

Unilateral
NS
Bilateral
NS
Effect of Bilateral Excitation
EW
Dislacement (mm)
Dislacement (mm)
60
40
20
0
-20
-2
-40
0 5 10 15 20
Time (sec)
25 30
20
0
0
-20
-40
3.9 % Drift
2.9 % Drift
Unilateral Excitation
-60
-80
0 5 10 15 20 25 30
Time (sec)
e=D
Bilateral Excitation results in larger residual drift.
Effect of bilateral excitation is important in evaluation of a residual drift
4
2
0
-2
-4
Drift (%)
Drift (%)

Fiber Model of the RC C-Bent C
Columns
Torsinal Stiffness
T=GJφ
Plastic
Hinge
Rotational
Spring
Fiber Element
Concrete
Stress (MPa)
Hoshikuma et al. Model
Covering Concrete
Core Concrete
Strain
Sakai Model
T : Torsional Moment
φ : Curvature
G: Shear modulus
J : Torsional moment of
inertia
Stress
Reinforcements
E s2
E s
Menegotto and Pint Model
Strain

Fiber Element Analysis
e=0
Analysis
Experiment
Displacement (mm)
Longitudinal
70
0
-20
0 10 20
Time (Sec)
Drift (%)
Displacement (mm)
4
2
0
40
0
Transverse
-50
0 10 20
Time (Sec)
2
Drift (%)
0
-2

Fiber Element Analysis
e=0.5D
Analysis
Experiment
Displacement (mm)
Longitudinal
70
0
-30
-2
0 10 20
Time (Sec)
Drift (%)
Displacement (mm)
4
2
0
30
0
Transverse
-4
-60
0 10 20
Time (Sec)
2
0
-2
Drift (%)

Fiber Element Analysis e=D
Analysis
Experiment
Displacement (mm)
60
Longitudinal
0
-40
-2
0 10 20
Time (Sec)
4
2
Drift (%)
0
Displacement (mm)
20
0
Transverse
-4
-70
0 10 20
Time (Sec)
The analysis correlates the accumulation of residual drift
in the eccentric compression side.
0
Drift (%)
-2

Conclusions
• Extensive failure occurs at the eccentric compression
side under both the unilateral and the bilateral
excitations. This results in a large residual displacement
in the eccentric compression side.
• The failure and the residual displacement under the
bilateral excitation are more extensive than those under
the unilateral excitation.
• A fiber analysis correlates the accumulation of residual
drift in the eccentric compression side. However, the
analysis underestimates the residual drift.

Thank you for your attention