University of Naples Federico II
Department of Structural Analysis and Design
Innovative Materials and Seismic
Retrofitting of RC Structures
PhD. Candidate
Marco Di Ludovico
Workshop - Naples, November 13
La Struttura SPEAR
C5
C1
C2
• Full Scale 3 storey structure
B1
B2
representative of existing RC building in
Southern European countries
• Designed
for gravity
loads only B7
B11
B9
following the Greek Code provisions
enforced between 1954-1995
ey
B3
C9
•Regular
in elevation,CMdoubly
non- C4
symmetric plan
C3 configuration
CR
B4
• 2 bay frames spanning
between 3-6 m
ex
X
Y
B12
• 8 square columns 25x25 cm
• Wall-type column C6 (H/B=3)
B5
• Beam (25x50) to beam connections
C8
• Smooth Steel rebars
• Poor confinement, no stirrups into joints
• ‘Weak Column – Strong Beam’
0.85
1
1.58
1.3
B10
C6
B8
B6
C7
Experimental Campaign
Bi-directional pseudo-dynamic tests
TEST
PGA
S11
0.15 g
S12
0.20 g
S16
0.20 g
S17
0.30 g
S21
0.20 g
S23
0.30 g
DESCRIPTION
‘As-Built’ Structure
FRP Retrofitted
RC Jacketed
Struttura ‘As-built’: 0.2g input
‘As-built’ Structure: Experimental Test results
Limited damages during the test at PGA= 0.15g
Significant damages (during the test at PGA =
0.20g) on column ends:
¾Structure designed to sustain gravity loads only – No
attention to the strength hierarchy problem
¾Columns geometrical dimensions and longitudinal
reinforcement inadequate to satisfy the biaxial bending and
axial load demand
¾Older construction practice
¾Weak column-strong beam condition led to the formation of
the plastic hinges in the columns
 The lack of stirrups on joints, the poor local
detailing and the insufficient columns
confinement have increased the risk of brittle and
local failure mechanisms
Non linear Static Analysis: CSA Verification
(c)
FRP Retrofit Design (a)
Strength
 OBJECTIVES :
(b)
¾ To increase the global ductility of
the structure by enhancing its
energy dissipation capacity (design
target increase: 48%)
(a) Seismic
Existing
Structure
demand
Ductility
There are 2 main strategies to pursue such objective (CNR-DT 200/2004):
1) Increasing the ductility of potential plastic hinge without modifying
their position (COLUMN CONFINEMENT).
2) Relocalizing the potential plastic hinge by restabilishing a correct
hierarchy of strength.
¾ To prevent brittle mechanism failure modes in order
to fully exploit the increased deformation capacity
 Shear Strengthening of wall-Type column C6
 Shear Strengthening of corner joints
FRP retrofit Design (a)
Direction X
Direction Y
Taglio alla base - Spostamento al tetto
lungo la direzione X
750
750
500
Tagliante alla base [
Tagliante alla base [K
500
0.20g
Taglio alla base - Spostamento al tetto
lungo la direzione Y
250
0
-250
‘As Built’
-500
-750
-250
-200
-150
-100
-50
250
0
-250
-500
‘As-Built’
S12_X
0
50
100
150
200
-750
-250
250
-200
-150
-100
-50
0
S12_Y
50
100
150
Spostamento al tetto [mm]
Spostamento al tetto [mm]
Taglio alla base - Spostamento al tetto
lungo la direzione X
Taglio alla base - Spostamento al tetto
lungo la direzione Y
200
250
750
500
500
Tagliante alla base [K
Tagliante alla base [K
0.30g
750
250
0
COLUMNS
CONFINEMENT
-250
-500
2 PLIES
UNIAXIAL
FRP
-750 LAMINATES
GFRP
-250
-200
-150
-100
EXTERNAL JOINT SHEAR
STRENGTHENING
2 PLIES QUADRI-AXIAL
S17_X
GFRP LAMNATES
-50
0
50
100
Spostamento al tetto [mm]
150
200
250
250
0
-250
-500
-750
-250
WALL TYPE COLUMN C6 SHEAR
STRENGTHENING
2 PLIES QUADRI-AXIAL GFRP
S17_Y
FRP
LAMNATES
-200
-150
-100
-50
0
50
100
Spostamento al tetto [mm]
150
200
250
(c)
RC Jacketing (b)
Strength
OBJECTIVES
(b)
¾ Torsional Effect reduction
¾ Both strength and ductility increase
1°storey
(a) Seismic
Existing
Structure
demand
Ductility
RC Jacketing of columns C1 and C4
CM centre of mass
CR centre of stiffness
CP centreof strength
RC Jacketing (b)
Longitudinal reinforcement passing trough holes drilled into the slab
and beams to guarantee the reinforcement continuity
- “L” and “C” shaped stirrups in corrispondence of the joints
-
‘As-Built’
RC Jacketed
CONCLUSIONS: Rehabilitation Strategies
400
RC Jacketing at LSDL
RC Jacketing at LSSD
350
RC Jacketing
ductility increase
Base Shear [kN]
300
RC Jacketing
strength increase
250
FRP Ductility Increase
200
150
RC Jacketing
stiffness increase
'As-Built' and FRP at
LSDL
'As-Built' at LSSD
FRP at LSSD
"NX_AS-BUILT"
100
"NX_FRP"
"NX_JACKETED"
50
"LSSD"
"LSDL"
0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Top Displacement [m]
Experimental validation on a FULL SCALE RC structure of seismic code
provisions and modelling assumption. Opportunity to select the most appropriate
rehabilitation technique by using either composites or traditional techniques