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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.