Khalid M. Mosalam, PhD, PEAssociate Professor

Structural Engineering, Mechanics and Materials

Civil and Environmental Engineering

University of California, Berkeley

Visiting Professor

Department of Civil Engineering, METU, Turkey

Shake-Table Experiment on One-Story RC Structure With and

Without Masonry Infill

NATO International Workshop on:Advances in Earthquake Engineering for Urban Risk ReductionIstanbul-Turkey, 30 May - 1 June, 2005

Wednesday, 1 June, 2005

Outline

•The Big Picture•Objectives•Test Structure•Test Stages•Earthquake Loading•Test Results•Concluding Remarks•Further Studies

The Big Picture …

Shake-

table

tests

Pseudo-

dynamic

tests

Development

and validation

of FE model

Prototype

structure

Development of

hybrid control

algorithm with

mixed-variables

(mode switch

between force &

deformation)

Validation of

pseudo-dynamic with

sub-structuring

Infill-RC

frame

interaction

Damage sequence

& collapse

mechanism

Development of

element removal

algorithms

Improvement of

quasi-brittle

material models

Development

of new SAT

models

Development of new “progressively

collapsing” macro-elements for infilled frames

Objectives

• Develop a “benchmark” shake-table experiment for validation of “new” experimental techniques and computational models

• Develop a new experimental technique:• Multiple physical sub-structures with different properties (bare versus URM

infilled RC frames) tested simultaneously (at different locations)

• Mixed variable (force & displacement) pseudo-dynamic formulation based on

relative stiffness of sub-structures or change of stiffness of one sub-structure

• Replacing physical modeling with a simulated model of one or more sub-

structures, e.g. the connecting floor slab or upper stories

• Develop computational models for URM infill walls• Model the collapse mechanisms of infilled frames

B

C

D

E

F C

C1

C2

B1

B2

A1

A2

Shake-table test structure

Test Structure (1/4)

Prototype “hypothetical” building

A B

C D

E F

A1 A2

B1 B2

C1 C2

Test Structure (2/4)

• The prototype RC building is a 5-story structure designed following ACI318-02 & NEHRPrecommendations in seismic regions.

• URM wall (clay bricks & type N mortar) in one of

the interior frames.• Test structure is a ¾-scale of the first story with

column axial load (concentric post-tensioning) simulating upper floors gravity load.

• Uniform mass is added to the slab such that the

base-shear on the test structure matches that of the three middle frames of the prototype building model subjected to the design ground motion.

Test Structure (3/4)

• 18 accelerometers measured the base and roof accelerations at various locations and directions.

• 95 displacement transducers measured global and local displacements and rotations.

• 150 strain gages measured strains at different locations of the reinforcing bars and column post-tensioning rods.

• 17 high speed cameras monitored the experiment.

Test Structure (4/4)

N

Test Stages (1/2)

Bare structure without column post-tensioning3

Bare structure with column post-tensioning 2

Infilled structure with column post-tensioning1

DescriptionStage

Stage 1 Stages 2 and 3

Post-tensioning

Test Stages (2/2)

Test Movies

Stage 1: Wall collapse3

Stage 2: Post-tensioning acting as a self-centering system4

Stage 3: On the verge of collapse (reaching the table limits)5

Stage 1: Wall crushing2

Stage 1: Wall cracking1

DescriptionCamera

14 Movie

Earthquake Loading (1/2)

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Period [sec]

Sp

ectr

al A

ccel

erat

ion

[g

] Design Spectra

Loma Prieta

Northridge

Duzce

0 5 10 15 20 25

-1

0

1

Northridge, Tarzana

0 5 10 15 20 25

-101

Acc

eler

atio

n [

g]

Duzce

0 5 10 15 20 25

-101

time [sec]

Loma Prieta, Bran

Natural period range of the bare structure

Natural period range of the infilled structure

Earthquake Loading (2/2)

2.28 (58)17.43 (443)0.426000BranLoma Prieta, CA, ‘89

0.75 (19)12.97 (329)0.762NLamontDuzce, Turkey, ‘99

5.13 (130)36.23 (920)1.570090TarzanaNorthridge, CA, ‘94

PGD [in

(mm)]

PGV [in/sec

(mm/sec)]

PGA

[g]Direction

Station

(Source)Ground Motion

98764321Level

2.191.951.501.000.670.440.31-Loma Prieta, CA, ‘89 (LomaPr)

2.532.001.50-----Duzce, Turkey, ‘99 (DUZ)

---0.590.390.230.170.05Northridge, CA, ‘94 (TAR)

2%10%30%50%-probability of being exceeded in 50 years

From PEER Strong Motion Database

Scale Factors for Different Levels of Input Table Motion

Design MCEHigher demands

Test Results (1/7)

0 0.5 1 1.5 2 2.5 30

20

40

60

80

100

120

140

160

180

200

Maximum Drift(%)

Max

imu

m B

ase

Sh

ear

(kip

s)

Test Results

Elastic with wall

Elastic without wall

Damaged infill wall

Damaged RC frame

Test Results (2/7)

168.0

(29.42)4.250.232

431.0 (75.48)

6.850.134After building the wall

Columns prestressed

With additional mass

167.1

(29.26)4.300.122

425.5

(74.52)5.700.055

After building the wall

Columns prestressed

No additional mass

134.0

(23.47)4.400.134

113.3 (19.84)

4.300.135Before building the wall

No additional mass

Stiffness

[kips/in

(kN/mm)]

Damping

Ratio

[%]

Natural

Period

[sec]

Stiffness

[kips/in

(kN/mm)]

Damping

Ratio [%]

Natural

Period

[sec]

Out-of-plane (East-West

direction)In-plane (North-South direction)

Conditions of the test

structure at time of the

snap-back (pull) test

Test Results (3/7)

TAR 1 TAR 2 TAR 3 TAR 4 TAR 6 DUZ 7 DUZ 8 DUZ 7-20

50

100

150

200

250

300

350

400

Test Levels

Eff

ecti

ve

Sti

ffn

ess

[kip

s/in

]

Test results

Initial stiffness with wall

Initial stifness without wall

TAR 3 TAR 4 TAR 6 DUZ 7 DUZ 8 DUZ 7-20

20

40

60

80

100

120

140

160

180

Bas

e S

hea

r [k

ips]

Test Levels

Masonry Infill

RC Frame

Variation of the effective stiffness

Distribution of base shear between the URM infill wall and the RC frames

From column shears using B.M.

obtained from strain measurements and section properties

Test Results (4/7)

-3 -2 -1 0 1 2 3

-200

-150

-100

-50

0

50

100

150

200

K = 386 kips/in

Displacement [in.]

Bas

e S

hea

r [k

ips]

Tarzana level 3

-3 -2 -1 0 1 2 3

-200

-150

-100

-50

0

50

100

150

200

K = 270 kips/in K = 359 kips/in

Displacement [in.]

Bas

e S

hea

r [k

ips]

Tarzana level 6

-3 -2 -1 0 1 2 3

-200

-150

-100

-50

0

50

100

150

200

K = 57 kips/in

K = 190 kips/in

K = 168 kips/in

K = 284 kips/in

Displacement [in.]

Bas

e S

hea

r [k

ips]

Ducze level 7

-3 -2 -1 0 1 2 3

-200

-150

-100

-50

0

50

100

150

200

K = 53 kips/in

K = 150 kips/in

K = 273 kips/in

Displacement [in.]

Bas

e S

hea

r [k

ips]

Ducze level 8

Stage 1

of

testing

Test Results (5/7)

Change in spectral demand due to the change in natural period of the test structure

0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5 ← Begining of the test

← TAR 6

← Removal of the wall

← Before removal of prestressing

← After removal of prestressing

← End of the test

Sp

ectr

al A

cce

lera

tio

n [

g]

Period [sec]

LomaPrieta

Duzce

Northridge

Design Spectra

B

C

D

E

F C

C1

C2

B1

B2

A1

A2

Test Results (6/7)

0 0.01 0.02 0.03 0.04 0.05 0.060

500

1000

1500

2000

2500

DUZ 7

DUZ 8

AWR-DUZ 7

LomaPr 7LomaPr 9

LomaPr 9-2LomaPr 7-2

Maximum Base Rotation [rad]

Max

imu

m B

ase

Mo

men

t [k

ip-i

n]

Stage 1

Stage 2

Stage 3

0 0.01 0.02 0.03 0.04 0.05 0.060

500

1000

1500

2000

2500

DUZ 7

DUZ 8

LomaPr 7 LomaPr 9 LomaPr 9-4

LomaPr 7-2

Maximum Base Rotation [rad]

Max

imu

m B

ase

Mo

men

t [k

ip-i

n]

Stage 1

Stage 2

Stage 3

0 0.01 0.02 0.03 0.04 0.05 0.060

500

1000

1500

2000

2500

DUZ 7

DUZ 8

AWR-DUZ 8LomaPr 9

LomaPr 9-6

LomaPr 4-2

LomaPr 6-2

LomaPr 8-2

LomaPr 9-2-4

Maximum Top Rotation [rad]

Max

imu

m T

op

Mo

men

t [k

ip-i

n]

Stage 1

Stage 2

Stage 3

0 0.01 0.02 0.03 0.04 0.05 0.060

500

1000

1500

2000

2500

TAR 4

DUZ 7

DUZ 8

AWR-TAR 4

LomaPr 7

LomaPr 9 LomaPr 9-6

LomaPr 4-2

LomaPr 9-2-4

Maximum Top Rotation [rad]

Max

imu

m T

op

Mo

men

t [k

ip-i

n]

Stage 1

Stage 2

Stage 3

Column A2, column-foundation joint Column B1, column-foundation joint

Column A2, beam-column joint Column B1, beam-column joint

Test Results (7/7)

0 1 2 3 4 5 6 7 80

20

40

60

80

100

120

140

160

180

200

TAR 3

TAR 4

TAR 6

DUZ 7 DUZ 8

DUZ 7-2

AWR-DUZ 7

AWR-DUZ 8

LomaPr 7

LomaPr 9

LomaPr 9-6

LomaPr 2-2

LomaPr 3-2

LomaPr 4-2

LomaPr 6-2

LomaPr 8-2

LomaPr 9-2-1

LomaPr 9-2-4

Maximum Drift [%]

Max

imum

Bas

e S

hea

r [k

ips]

LomaPr 7-2

Stage 1

Stage 2

Stage 3

Global Results

Concluding Remarks (1/2)

• Test structure at design level showed 17% reduction of stiffness, but the overall behavior is almost linear.•At MCE, first significant damage occurred with 25%shift of stiffness from beginning to end of motion with cracking along column-wall interface and small vertical cracks in mortar joints at the corners.•Most significant change in behavior occurred at DUZ 7 (1.5 original) with significant wall cracks (large cracks at 60o with hrz. connected with a hrz. crack & 45o crack into opposite bottom corners.) • For small drifts (< 0.2%), cracks opened and closed without engaging the wall. Once the cracks closed, the wall picked up load causing stiffness increase and further wall damage.

Concluding Remarks (2/2)

•At small forces, static friction between cracked surfaces existed and the wall acted as a whole increasing the stiffness. Afterwards, the stiffness reduced approaching to that of the bare RC frames. •Damage in the URM infill increased the natural period from 0.13 sec to 0.36 sec (167% increase).•Removal of post-tension rods increased the natural period from 0.44 sec to 0.61 sec (39% increase). •URM infill wall significantly changed the demands and the key global and local response parameters, e.g. drift ratio, base shear and joint rotations. • The experimental findings represent benchmark dynamic test data to validate newly developed on-line testing with hybrid control and sub-structuring.

Further Studies

Pseudo-Dynamic Experimentation

3-frame5-story

building

Physical substructures

Computational substructure

Infilled frame

Bare frame

Setup in nees@berkeley facility for pseudo-dynamic testing

Comparisons

0 0.5 1 1.5 2 2.5 30

20

40

60

80

100

120

140

160

180

200

TAR 1

Maximum Drift [%]

Maxim

um

Bas

e S

hear

[k

ips]

TAR 1

TAR 2

TAR 3

TAR 4

TAR 6

DUZ 7

DUZ 8DUZ 7-2

DUZ 8DUZ 9

Shake-table test

Pseudo-dynamic test

-3 -2 -1 0 1 2 3-200

-150

-100

-50

0

50

100

150

200

Displacement [inch]

Bas

e S

hea

r [k

ips]

Pseudo-dynamic results

Duzce Level 7

Duzce Level 8

-3 -2 -1 0 1 2 3-200

-150

-100

-50

0

50

100

150

200

Displacement [inch]

Bas

e S

hea

r [k

ips]

Shake-table results

Duzce Level 7

Duzce Level 8

TAR 3 TAR 4 TAR 6 DUZ 7 DUZ 8 DUZ 9-20

20

40

60

80

100

120

140

160

180

Bas

e S

hea

r [k

ips]

Test Levels

Masonry Infill

RC Frame

TAR 3 TAR 4 TAR 6 DUZ 7 DUZ 8 DUZ 7-20

20

40

60

80

100

120

140

160

180

Bas

e S

hea

r [k

ips]

Test Levels

Masonry Infill

RC Frame

Shake-table test Pseudo-dynamic test

Errors (1/3)Fw: Infill resisting force

FI: Inertia force

FD: Damping force

FF: Concrete frame resisting force

: error term

14.7 14.8 14.9 15 15.1 15.2 15.3 15.4-150

-100

-50

0

50

100

Time [sec]

FW

[k

ip]

with modelwithout model

8 8.2 8.4 8.6 8.8

-100

-50

0

50

100

Time [sec]

FW

[k

ip]

with modelwithout model

∑∑∑===

−+−−+−−=cba n

k

ok

n

j

j

n

i

i ktcjtUbitat111

)(.)1(.)(.)( εεε

εε −−−−=−−−−= F

t

FDIW FuCumFFFF ɺɺɺ ..ˆ

εεεε ⇒+−=+−=+= uCFFF DFIɺ.1⇒= 0WF

ε=+++ DWFI FFFF

Model for as error in a similar run after removal of the wall

Estimate of FW considering the error terms

5 10 15 20 25 30-150

-100

-50

0

50

100

150

Time [sec]

FW

[k

ip]

with modelwithout model

Better estimation of infill resisting force (FW) using

ARMA model

Inputs (U): FF , ground displacement

ε

ε

Errors (2/3)

0 500 1000 1500 2000 2500 3000 3500-5

0

5comandfeedback

0 500 1000 1500 2000 2500 3000 3500-0.04

-0.02

0

0.02

0.04

1209.5 1210 1210.5 1211 1211.5 1212 1212.5 1213 1213.5-0.9

-0.8

-0.7

-0.6

-0.5comandfeedback

Time Step

Dis

pla

cem

ent

[in

ch]

(zoo

med

in)

Err

or

[inch

]D

ispla

cem

ent

[in

ch]

0 500 1000 1500 2000 2500 3000 3500-5

0

5comandfeedback

0 500 1000 1500 2000 2500 3000 3500-0.04

-0.02

0

0.02

0.04

1209.5 1210 1210.5 1211 1211.5 1212 1212.5 1213 1213.5-0.9

-0.8

-0.7

-0.6

-0.5comandfeedback

Time Step

Dis

pla

cem

ent

[in

ch]

(zoo

med

in)

Err

or

[inch

]D

ispla

cem

ent

[in

ch]

Error in implementing target displacement command is unavoidable in PID control

Errors (3/3)

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.005

0.01

0.015

0.02

0.025

0.03

0.035

RecordedModeled

Absolute Value of Velocity [inch/sec]

Ab

solu

te V

alue

of

Err

or

[in

ch]

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.005

0.01

0.015

0.02

0.025

0.03

0.035

RecordedModeled

Absolute Value of Velocity [inch/sec]

Ab

solu

te V

alue

of

Err

or

[in

ch]

( )1-v 0.780.03e=Er(t)

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3 Disp100*Error

0 1 2 3 4 5 6 7 8 9 100

500

1000Disp/Error

0 1 2 3 4 5 6 7 8 9 100

500

1000f*Disp/Error

Frequency, Hz

FF

TF

FT

FF

T

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3 Disp100*Error

0 1 2 3 4 5 6 7 8 9 100

500

1000Disp/Error

0 1 2 3 4 5 6 7 8 9 100

500

1000f*Disp/Error

Frequency, Hz

FF

TF

FT

FF

T

Developing Computational Models (1/2)

• Assessment of existing algorithms for manual and semi-automatic element removal and potential for use in progressive collapse analysis

• Case study: Masonry-infilled one-story structure:– Masonry modeled by three

diagonal struts in compression– Dynamic analysis: center strut

brittle failure during Northridge Tarzana record

Case study specimen and OpenSees model rendition

• Displacement envelope doubled

• Residual displ. reversed• Demand on other elements rose

→more likely to fail

• Needs reliable automation– Internal force release– Element loads– ”Dangling” nodes

Developing Computational Models (2/2)

Roof displacement and strut force time history for ductile and brittle failure of one center strut

0 2 4 6 8 10 12 14 16 18 20

-0.2

-0.1

0

0.1

0.2

0.3

Roo

f Dis

plac

emen

t (in

.)

0 2 4 6 8 10 12 14 16 18 20

-60

-50

-40

-30

-20

-10

0

For

ce in

Opp

osite

Cen

ter

Str

ut (

kip)

Time (sec.)

Center Strut Removed

No Element Removal (Ductile Center Strut)Brittle Center Strut

Ductile Center StrutBrittle Center Strut

Opposite Center Strut should fail. Procedure isdoable but tiresome and not guaranteed

Original Strut force history shownin dotted light black for reference (for the ductile softening case).Strut force capacity is 50 kips and should be removed afterwards

Strut Force Capacity

Time (sec.)

Developing Computational Models

Steel Shoe

Steel Shoe

xy

z

t

t

1

2

mortarforbrickfori

dVV

dVV

Viixx

Viixx

2&1

)(1

)(1

=

=

=

∑∫

∑∫

εε

σσ

21 tt

tp i

i+

= 1=∑ ip

• In-plane SAT models

10

8

4

2

6

5

4

912

6

15

12

17

1421

20

1310

8

1422

19

16

11

18

13

11

5

7

9

7

3

1

3

2

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

10

20

30

40

50

60

70

80

Horizontal Displacement(in.)

Hor

izon

tal F

orce

(kip

s)

PushOver Analysis

PN/PD = 0

PN/PD = 0.01

PN/P

D = 0.05

PN/P

D = 0.10

PN/PD = 0.15

PN/PD = 0.20

PN/PD = ∞-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-80

-60

-40

-20

0

20

40

60

80

Horizontal Displacement(in.)

Hor

izon

tal F

orce

(kip

s)

PushOver Analysis

• Combination of In-plane and

Out-of-plane SAT models

• Material properties for various elements of the SAT model

• Considering the effects of out-of-plane and cyclic loading in in-plane degradation of the infill.

Development of new SAT Models for infilled frames

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

x 10-3

0

0.2

0.4

0.6

0.8

1

1.2

StrainS

tres

s(ks

i)

Compression struts

-15 -10 -5 0 5 10 15-1

0

1

2

3

4

5

6

Axial Displacement(in)

Axi

al F

orce

(kip

s)

Link element