1 lessloss sub project 7 techniques and methods for vulnerability reduction barcelona 18 th may 07...
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LESSLOSS Sub Project 7 Techniques and Methods for Vulnerability Reduction
Barcelona 18th May 07 – Lisbon 24th May 07LESSLOSS Dissemination Meeting
Nicolas Hausoul
Analysis of precast RC structures with dissipative connections
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Post-earthquake Post-earthquake surveyssurveys
Typical damage caused by earthquakeon precast reinforced concrete structure: beams fall down from their support, due to lack of resistance and energy dissipation capacity at the beam-column connections.
Example: Adana earthquake An industrial building collapses Causes : - under design of the dowel connections between beams and columns- bad implementation of the grouted mortar around these dowels.
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Reference precast Reference precast concrete portal frames concrete portal frames
structurestructure• 17 meters length beam (L x w x h: 17 m x 30 cm x 40/80 cm) • 6 meters height column (L x w x h: 17 m x 40 cm x 40 cm)
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The most used beam-to-column connections :The most used beam-to-column connections :- simple dowel connections- simple dowel connections- bolted dowel connections- bolted dowel connections
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Behaviour of frames with Behaviour of frames with beam-to-column dowel beam-to-column dowel connectionsconnections
1. Simple equivalent analytical model• Aim: determine structure conditions that cause maximum axial force in the beam (and thus transmits in the beam-column connection) → Allows to design dowel connection
→
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1. Simple equivalent analytical model• Results: the beam axial force and column fixed
end moment, in the model, are maximum when the difference of stiffness of the “column-support” system Ksyst-i between the 2 columns constituting the frame is maximum.
0
5
10
1520
25
30
35
40
0 20000 40000 60000 80000 100000
k2 [kN.m]
Nmax
[kN]
362671813390674533
k1 [kN.m]EC8 - soil D : type 1 ag = 1 m/ s²
Mmmf = 33 tons
Kcol = 504 kN/ m
0
100
200
300
400
500
0 20000 40000 60000 80000 100000
k2 [kN.m]
Mmax
[kN.m]
362671813390674533
k1 [kN.m]EC8 - soil D : type 1ag = 1 m/ s²
Mmmf = 33 tons
Kcol = 504 kN/ m
Behaviour of frames with Behaviour of frames with beam-to-column dowel beam-to-column dowel connectionsconnections
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2. Dynamic non linear analysis (time history) of the structure with dowel
connectionsAccelerogram 1
-8
-6
-4
-2
0
2
4
6
8
0 5 10 15 20 25 30
time (sec)
acce
lera
tion
(m
/s²)
• Dowel connection non-linear law modelled by springs
• Includes difference of stiffness of the column supports fixed partially fixed
Behaviour of frames with Behaviour of frames with beam-to-column dowel connectionsbeam-to-column dowel connections
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2. Dynamic non linear analysis (time history) of the structure with dowel connection
Results:
0
100
200
300
400
500
600
100 1000 10000 100000Total inertia of the 2 bars forming the dowel connection
I [mm4]
Max
imum
col
umn
fixed
end
mom
ent
Mmax
[kN
.m]
PGA = 0,1 g : Acc 1
PGA = 0,1 g : Acc 2
PGA = 0,1 g : Acc 3
PGA = 0,2 g : Acc 1
PGA = 0,2 g : Acc 2
PGA = 0,2 g : Acc 3
PGA = 0,3 g : Acc 1
PGA = 0,3 g : Acc 2
PGA = 0,3 g : Acc 3
PGA = 0,4 g : Acc 1
PGA = 0,4 g : Acc 2
PGA = 0,4 g : Acc 3
MRd column = 190 kN.m
2 bars (db = 8 mm)+ neoprene (t = 1 cm)
2 bars (db = 10 mm)+ neoprene (t = 1 cm)
2 bars (db = 12 mm)+ neoprene (t = 1 cm)
2 bars (db = 14 mm)+ neoprene (t = 1 cm)
2 bars (db = 16 mm)+ neoprene (t = 1 cm)
2 bars (db = 25 mm)+ neoprene (t= 1 cm)
2 bars (db = 28 mm)+ neoprene (t= 1 cm)
2 bars (db = 20 mm)+ neoprene (t = 1 cm) 0
0.5
1
1.5
2
100 1000 10000 100000
Total inertia of the 2 bars forming the dowel connectionI [mm4]
Max
imum
Bea
m-c
olum
n re
lative
displ
acem
ent
u [m
m]
PGA = 0,1 g : Acc 1
PGA = 0,1 g : Acc 2
PGA = 0,1 g : Acc 3
PGA = 0,2 g : Acc 1
PGA = 0,2 g : Acc 2
PGA = 0,2 g : Acc 3
PGA = 0,3 g : Acc 1
PGA = 0,3 g : Acc 2
PGA = 0,3 g : Acc 3
PGA = 0,4 g : Acc 1
PGA = 0,4 g : Acc 2
PGA = 0,4 g : Acc 3
2 bars (db = 8 mm)+ neoprene (t = 1 cm)
2 bars (db = 10 mm)+ neoprene (t = 1 cm)
2 bars (db = 28 mm)+ neoprene (t = 1 cm)
2 bars (db = 25 mm)+ neoprene (t = 1 cm)
2 bars (db = 20 mm)+ neoprene (t = 1 cm)
2 bars (db = 16 mm)+ neoprene (t = 1 cm)
2 bars (db = 14 mm)+ neoprene (t = 1 cm)
2 bars (db = 12 mm)+ neoprene (t = 1 cm)
• Relative beam-column displacement function of the second moment of area of the dowel connection
• Moment at column base function of the second moment of area of the dowel connection
Behaviour of frames with Behaviour of frames with beam-to-column dowel connectionsbeam-to-column dowel connections
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2. Dynamic non linear analysis (time history) of the structure with dowel connections
Analysis of results:• Dowel connection is not a dissipative
connection system (no reduction of moment at column base)
• Failure of the dowels before any dissipation of energy
• 2 dowels with d = 14 mm can resist to a accelogram with a PGA = 0.4 g if resistance and adherence of grouted mortar around dowels are OK
• No great relative displacement: d < 2 mm• MSd,max = MRd,column = 190 kN.m for a PGA = 0.15
g ►Yielding of columns at their bases►Failure of the structure related
to plastic rotation capacity of columns
Behaviour of frames with Behaviour of frames with beam-to-column dowel connectionsbeam-to-column dowel connections
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Bracings using INERD Pin connections Bracings using INERD Pin connections in precast concrete portal framesin precast concrete portal frames
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Pushover analysis:Pushover analysis:objectiveobjective
a) Reference structure
b) Structure with bracings using INERD Pin connection
To evaluate the effectiveness of bracings using INERD Pin Connections in precast concrete portal frames.
Study of 2 structures:
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Pushover analysis:Pushover analysis:AssumptionsAssumptions
Rd,column
Rd,connection
MM 152 kN.m
1,25
d m22
0
50
100
150
200
250
0 0.01 0.02 0.03 0.04
Rotation [rad]
Mom
ent M
[kN
.m]
Low ductility(FEMA-273)
Average ductility(FEMA-273)
High ductility(FEMA-273)
Low ductility (used in the model)
Average ductility(used in the model)
High ductility (used in the model)
Plastic hinges at column bases• 3 plastic rotation capacity of columns at their bases in the 2 considered structures a) and b)Design of INERD Pin Connection• One INERD Pin connections law in structure b)
With the dimensions indicated on the figure:
Pu.d = MRd, connection Rd connectionu
MP kN
d, 2.152
2152
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Pushover analysis:Pushover analysis:AssumptionsAssumptions
-250-200-150-100-50
050
100150200250
-80 -60 -40 -20 0 20 40 60 80
[mm]
P [kN
]P [kN]
-200
-150
-100
-50
0
50
100
150
200
-0.15 -0.05 0.05 0.15
d [rad]
M =
P.d
[kN
.m]
M [kN.m]
Design method of INERD Pin Connection exist (contribution of Callado – IST Lisbon)
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Pushover analysis:Pushover analysis:Load – Displacement Load – Displacement
curvescurves
Pushover analysis
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.1 0.2 0.3 0.4 0.5
Displacement at the top of column dr [m]
Spec
tral
e ac
cele
ration
/g [m
/s²]
Pushover with Inerd Pin Connection : low ductilityPushover with Inerd Pin Connection : average ductilityPushover with Inerd Pin Connection : high ductility
ag = 0,8 g ag = 1 gag = 0,4 g
ag = 0,3 gag = 0,2 g
ag = 0,1 g ag = 0,6 g
Pushover analysis
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.1 0.2 0.3 0.4 0.5Displacement at the top of column dr [m]
Spec
tral
e ac
cele
ratio
n/g
[m/s
²]
Pushover reference structure : low ductilityPushover reference structure : average ductility
Pushover reference structure : high ductility
ag = 0,8 g ag = 1 gag = 0,4 g
ag = 0,3 gag = 0,2 g
ag = 0,1 g ag = 0,6 g
• Reference structure
• Structure with bracings using INERD Pin connection
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Pushover analysis: Pushover analysis: Analysis of resultsAnalysis of results
• Under PGA ag ≤ 0.2 g low seismic area => no failure, even in low ductility structures. Bracings with INERD Pin connections
- only bring rigidity to the structure - reduce rotation and displacement (SLS state). - For ULS , bracings with INERD Pin connections
are not needed in precast concrete structures.
• For PGA ag > 0.2 g high seismic area Bracings with INERD Pin connections - effective, especially for low plastic rotation capacity at column base.- ensure stability (ULS)- reduce deformations of the structure (SLS).
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Pushover analysis: Pushover analysis: Analysis of resultsAnalysis of results
• Comparison of pushover curves for structure with and without INERD Pin Connections at same level of ductility :
=> Deformation capacity and rigidity are increased
=> Yielding of column base occur for greater horizontal force
=> Bracings with INERD Pin connection also reduce damage of the structure
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Pushover analysis: Pushover analysis: Analysis of resultsAnalysis of results
• The first part of the curve represents the formation of plastic hinges at the base of columns.
• The second part of pushover curves represents the behaviour of the INERD Pin Connection.
• By modifying INERD Pin Connection characteristics, the behaviour of the structure, rigidity, ductility, rotation capacity and strength can be modified.
• Results are confirmed by dynamic non linear analysis.
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General ConclusionsGeneral Conclusions
• Globally, the study has demonstrated the possibility to reduce the vulnerability of existing precast concrete portal frames by means of added bracings.
• These bracings must be dissipative.• Using INERD Pin Connections is one
practical solution which has the advantage of putting the designer in real control of plastic capacity.
• The system is applicable to new design as well as to retrofit of existing structures.