IN-PLANE SEISMIC BEHAVIOR OF A STRONG MASONRY INFILL … · IN-PLANE SEISMIC BEHAVIOR OF A STRONG MASONRY INFILL Milad Oliaee 1(*), Paolo Morandi 2, Guido Magenes 2 1UME School, IUSS

Proceedings of the 6th International Conference on Mechanics and Materials in Design,

Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015

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PAPER REF: 5541

IN-PLANE SEISMIC BEHAVIOR OF A STRONG MASONRY INFILL

Milad Oliaee1(*)

, Paolo Morandi2, Guido Magenes

2

1UME School, IUSS Pavia, Italy

2Department of Civil Engineering & Architecture, University of Pavia, Italy and EUCENTRE, Pavia, Italy

(*)Email: [email protected]

ABSTRACT

Poor performance of reinforced concrete frame buildings with unreinforced masonry infills in

recent post-earthquake reconnaissance may underline a deficiency in our knowledge on their

seismic behavior. Particularly past experiments have lacked testing on strong masonry

typologies typically used in modern construction in Europe introduced mainly for

architectural needs. As the strong masonry typology significantly influences the global

building behavior, a comprehensive appraisal of seismic performance for full and open infill

panels will, in turn, improve our assessment of overall building behavior. From in-plane

damage to out-of-plane collapse, a comprehensive appraisal of performance goals for the non-

structural component will aid new design. A recent experimental campaign of in-plane and

out-of-plane cyclic tests on single-bay/single-story RC frames indicates differences in seismic

response in comparison to weaker, more slender infills. Significant in-plane resistance

continues beyond the drift at peak strength and shows resilience to severe damage. The

calibration of a macro model to special interpretation of the experimental data precedes a

parametric study involving several model building structures varying in infill density,

ductility class, number of stories and exposure to seismic intensity. Particular attention to the

path dependent behavior of the infill strut in comparison to the extracted hysteresis represents

the net effect the infill on the bare frame response. It provides a more accurate model in terms

of seismic energy dissipation, unloading stiffness and matching the cyclic strength envelope.

Limit state verifications using nonlinear dynamic analyses with specific drift indices selected

for the masonry typology help to convey the in-plane non-structural seismic performance.

The assessment of performance reflects current design procedures in the Italian annex and

Eurocode at the full range of seismic hazard currently mandated in Italy. Extrapolation of the

macro model parameters to other aspect ratios has been made possible by the adjustment of

existing empirical relations to determine the cracked stiffness and peak strengths. The effect

of the infill panels on the global building performance demonstrates the need to take into

account their behavior for new building design.

Keywords: Infilled frame building, seismic performance, earthquake engineering, macro

model, numeric calibration, nonlinear dynamic analysis.

INTRODUCTION

Masonry infills in southern Europe function architecturally as the building envelope and/or

internal partitioning for mid-rise buildings. The infill panels are considered nonstructural, but

since the 1950s, the interaction between infill panels and the frames of buildings have been

known (Polyakov, 1956). Since then heavy damage to modern buildings with unreinforced

clay masonry infills has occurred even during relatively moderate earthquakes, as seen in the

2009 L’Aquila and 2011 Christchurch aftermaths. However, limits on interstory drift ratios

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Seismic Behaviour Characterization and Strengthening of Constructions

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have existed in seismic provisions to mitigate damage at seismic intensity less than design

earthquake levels in Eurocode 8. Therefore the current seismic provisions in jurisdiction have

been evaluated in a numerical study following the calibration of a macro model to in-plane

cyclic tests of an RC frame infilled with the strong masonry typology.

A recent experimental campaign has characterized the mechanical properties of the masonry

typology and provided cyclic test data at the full scale level. The tests carried out at the

structural laboratory of the Department of Civil Engineering & Architecture at the University

of Pavia consist of in-plane and out-of-plane loading in sequence (Morandi et. al, 2014). An

additional bare frame test at matching target drifts has brought a direct comparison of the bare

and infilled frame hysteresis curves. More specifically, the cyclic loading paths of the bare

frame have been interpolated and subtracted from the infilled frame response to better

determine the appropriate parameters for the single strut model (Crisafulli, 1997). The

original material strength backbone has been significantly modified to capture a second post-

peak plateau found in the response of the fully infilled frame subassembly. The strut stiffness

from the equation by Stafford Smith has been reduced an order of magnitude to better match

the cyclic unloading stiffness (1966).

Using the Decanini (1993) strength equations and strength reduction factors to account for

openings (Dawe and Seah, 1988), the mechanical properties of the infill strut calibrated to the

experiment have been extrapolated to the archetype building frame geometry and applied to

the code compliant 3, 6 and 9 story RC frame structures. Performance criteria have been set

by drift indices at which irreversible damage occurs and the life safety can no longer be

guaranteed.

For each design PGA and ductility class, a theoretical building has been designed to reflect

the current European and Italian building code design requirements. Due to the stringent

drift limits adopted in the Italian National Code (NTC08), story stiffness requirements often

govern the design of the RC sections to abate excessive displacements estimated in

preliminary linear elastic analysis. To determine the highest PGA intensity level passing the

performance criteria set forth, the criteria gauge the effectiveness of current seismic

provisions to achieve seismic performance goals.

EXPERIMENTAL CAMPAIGN

The strong masonry infill typology considered represents an upper bound of the possible

strength & stiffness properties a masonry infill could exhibit. The typology represents a

single-leaf unreinforced masonry infill of 35 cm thickness, consisting of vertically hollowed

lightweight tongue and groove clay block units, having nominal dimensions of 235 x 350 x

235 mm with a nominal volumetric percentage of holes near 50%. The mortar bed-joints

consist of a general purpose mortar type M5 whereas the interlocking head-joints are without

mortar. The perimeter of the infill panel has been set in complete contact with the surrounding

frame (see Fig. 1).

A series of in-plane quasi-static cyclic tests have been carried out on full scale single-story,

single-bay RC frames with a full infill panel, open infill panel, and no infill panel shown in

Fig. 2. Like the numerical building models, the frames tested have also been designed

according to modern European (and Italian) code provisions. Prior to the cyclic tests, a

detailed characterization of all the material components (i.e., concrete, reinforcing steel,

mortar, masonry units and masonry) have been performed. The dry tongue and groove joints

dry head joints have been known to have significant strength benefits (Maheri, 2011).

Proceedings of the 6th International

Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26

(a) (b) Fig. 1 - Masonry unit (a) isometric view,

(a)

Fig. 2 - Schematic of a) the

During the cyclic tests, a single actuator applies the incremental later

along the centerline of the beam (Fig. 3). The end plate remains in contact with the beam cap

by the fastening of steel rods to the face of the opposite beam end. The post

imparted to the beam varies during each

Fig. 3 - Front & side view of the experiment apparatus on the bare frame specimen.

During the testing procedure, p

defined per in-situ observations of the panel. The drift indices for the damage and ultimate

limit states (DLS and ULS) are defined according to performance levels described in EC8 and

NT8. For the infill without an opening, a 0.5

limit state and 1.75% drift index

Conference on Mechanics and Materials in Design,


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(c) asonry unit (a) isometric view, (b) profile views (mm), and (c) course lay

(b)

the full infill panel, b) the open infill panel, and c) the

During the cyclic tests, a single actuator applies the incremental lateral load quasi


by the fastening of steel rods to the face of the opposite beam end. The post

imparted to the beam varies during each half cycle of loading due to tendon relaxation.

Front & side view of the experiment apparatus on the bare frame specimen.

During the testing procedure, performance levels for a single strong masonry infill have been

situ observations of the panel. The drift indices for the damage and ultimate


NT8. For the infill without an opening, a 0.5% drift index has been assigned

index for the ultimate limit state. For the case of

(mm), and (c) course lay-up.

(c)

the bare frame.

al load quasi-statically


by the fastening of steel rods to the face of the opposite beam end. The post-tensioning force

half cycle of loading due to tendon relaxation.

Front & side view of the experiment apparatus on the bare frame specimen.

ngle strong masonry infill have been

situ observations of the panel. The drift indices for the damage and ultimate


has been assigned for the damage

case of the infill with the

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opening, drift values of 0.35% and 1.0% indicate the damage and ultimate limit states,

respectively. In both the cases, an operational limit state, equal to 2/3 the damage drift index

has been selected in accordance with seismic design provisions but not indicated in Fig. 4.

ULS -1.75%

DLS -0.50%

DLS 0.50%ULS 1.75%

ULS -1.0% DLS -0.30%

DLS0.30%

ULS1.0%

-3.3% -2.2% -1.1% 0.0% 1.1% 2.2% 3.3%

-400

-300

-200

-100

0

100

200

300

400

-100 -80 -60 -40 -20 0 20 40 60 80 100Force (kN)

Disp (mm)

Drift

Bare

Full

Open

Fig 4 - The envelope curves averaging the cyclic peaks of net infill’s effect on story shear.

The curves in Fig. 4 represent the difference between the cyclic backbones of the bare frame

and the infilled frames. The backbones are defined by the average of the maximum force for

each of the three cycles at repeated target drifts. Note the additional story shear resistance due

to the full infill panel approaches the maximum shear strength of the bare frame. The initial

stiffness provided by the infills cause the in-plane resistance of the frame to be controlled

mainly by the masonry at smaller drifts; however, at larger drifts the concrete frame

eventually surpasses the residual strength of the infilled frame. At this point the infill panel

begins to spall outer shells of the masonry unit cavities triggering the ultimate limit state

condition due to falling debris.

Defining the ultimate state of the infill intends to protect the life safety of building inhabits

and the public, particularly for those in egress or in the path of the falling debris during the

earthquake. The damage limit state for the infill panels happen to occur near the peak

resistance of the infill shear contribution for both the full and open infill panels. It represents

the point of irreversible, but reparable damage. The two performance levels help to

distinguish the specific objectives of the building behavior at different levels of seismic

intensity.

MACRO MODEL CALIBRATION

Macro models can capture the global response of masonry infills while reducing the number

(and complexity) of finite elements required to obtain accurate numerical results, especially

for nonlinear dynamic modeling (Fig. 5). The infill strut calibration serves as an opportunity

to best match the experiment and extrapolate the results to other geometries in a complete

building model. Because the strong masonry infill overwhelmingly participates in the overall

building response, special interpretation of the net effect of the infill in comparison to the bare

frame response allows circumvention of local effects altering the response of the RC members

due to strut action of the infill. Thus the calibration of the infill strut serves two purposes: 1)

to account for the additional strength and stiffness of the infill panel and 2) to capture the

reduced response of the bare frame at low drift.

Proceedings of the 6th International

Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26

Fig 5

Other macro models have been proposed in the past and implemented for different purposes.

Multiple strut models with offset st

elements. Other single strut models have been proposed to allow damage in the panel to

influence both directions of the response (Rodrigues, 2008). Because the building models in

the parametric study are perfectly symmetric and not subject to near

single strut model can satisfy the specific needs for this numerical study.

In general, the strength, energy

criteria for modeling decisions. Due to the complexity of the hysteresis rules, the parameters

cannot be independently calibrated, and the optimization problem is rendered multivariate and

nonlinear. A preliminary trial and error approach did not satisfy all

calibration, so instead an enumerative search strategy results in a better solution found by

locating the global minimum error on an array of surfaces generated by an optimization

algorithm.

For the building models subject to design

the post-peak region of the cyclic tests. The lowest relative error for the specific strength,

energy dissipation and stiffness criteria identify the best parameters for the full and open infill

implemented in the numerical study (Oliaee, 2015). Fig. 6 and 7 convey the sequence of the

calibration procedure that starts with the bare frame model and then modifies the strut to

match the net effect of the infill on the global response. The end result, show

most plots show good agreement with the infilled frame tests.

Fig. 6 - The bare frame, infilled frame and infill hysteresis for the full infill configuration.

During the calibration procedure, the story shear contribution of the RC elements in the

numerical model of the infilled subassembly change with respect to the numerical model of

the bare subassembly. That is, both the strength envelope and energy dissipa

elements during the input load history decrease due the axial forces induced to the frame

Conference on Mechanics and Materials in Design,


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5 - The equivalent diagonal single-strut model.


Multiple strut models with offset struts aim to capture local effects on the surrounding frame



tudy are perfectly symmetric and not subject to near-field ground motions, the

single strut model can satisfy the specific needs for this numerical study.

trength, energy dissipation and stiffness of the response represent important

eria for modeling decisions. Due to the complexity of the hysteresis rules, the parameters


nonlinear. A preliminary trial and error approach did not satisfy all the objectives of the



For the building models subject to design earthquake intensity, the error criteria focuses on

peak region of the cyclic tests. The lowest relative error for the specific strength,


nted in the numerical study (Oliaee, 2015). Fig. 6 and 7 convey the sequence of the


match the net effect of the infill on the global response. The end result, show

most plots show good agreement with the infilled frame tests.

The bare frame, infilled frame and infill hysteresis for the full infill configuration.



the bare subassembly. That is, both the strength envelope and energy dissipa



ruts aim to capture local effects on the surrounding frame



field ground motions, the

of the response represent important

eria for modeling decisions. Due to the complexity of the hysteresis rules, the parameters


the objectives of the



earthquake intensity, the error criteria focuses on

peak region of the cyclic tests. The lowest relative error for the specific strength,


nted in the numerical study (Oliaee, 2015). Fig. 6 and 7 convey the sequence of the


match the net effect of the infill on the global response. The end result, shown in the right

The bare frame, infilled frame and infill hysteresis for the full infill configuration.



the bare subassembly. That is, both the strength envelope and energy dissipated by the RC


Symposium_10


elements by the infill strut axial forces. For the strong infill typology, the present calibration

method is preferred because the

numerical model cannot be superimposed due to nonlinear effects.

Fig. 7 - The bare frame, infilled frame, and infill hysteresis for the first cycles of the open infill configuration.

PARAMETRIC STUDY

For the input ground motions t

elastic response spectrum adopted for design at the ultimate limit state

ground acceleration (0.15gS),

damage limit state. For each of the two target spectra

by the minimum error for a period range

deviation of the average of ten e

spectral value at zero period anchors

Only earthquakes recorded on ground type

for the damage limit state and magnitudes 5.5

the spectrum compatible records have been scaled to the remaining PGAs adopted for design

0.023gS, 0.040gS, 0.097gS and 0.142

0.10gS, 0.25gS and 0.35gS for

ground motion selection below.

Table

DLS Earthquake

EQ1 Irpinia 24/11/1980

EQ2 L'Aquila 07/04/2009

EQ3 Gran Sasso 09/04/2009

EQ4 Friuli (3rd) 15/09/1976

EQ5 Friuli 18/05/1976

EQ6 L'Aquila 13/04/2009

EQ7 Gran Sasso 09/04/2009

EQ8 East Sicily 13/12/1990

EQ9 Italia Meridionale 16/01/1981

EQ10 Friuli 11/06/1976

An extensive analysis parameterizing the building configurations and design categories

evaluate the overall performance of the strong masonry infill typology for


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because the combination of the infill strut and the frame elements in the

cannot be superimposed due to nonlinear effects.

The bare frame, infilled frame, and infill hysteresis for the first cycles of the open infill configuration.

For the input ground motions two sets of records were selected, one compatible with the

elastic response spectrum adopted for design at the ultimate limit state at an

and one corresponding to the elastic response spectrum at the

For each of the two target spectra, the ground motions have been selected

by the minimum error for a period range between 0.05 s and 3.0. The log normal standard

deviation of the average of ten earthquake spectra has been reduced below 10%, and the

anchors to the PGA.

Only earthquakes recorded on ground type B have been considered, with ma

for the damage limit state and magnitudes 5.5 - 6.0 for the ultimate limit state

compatible records have been scaled to the remaining PGAs adopted for design

and 0.142gS for the damage limit state verifications

for the ultimate limit state verifications. Table 1 lists the final

ground motion selection below.

Table 1 - Spectrum compatible earthquake records.

Date Mw ULS Earthquake

24/11/1980 5.0 EQ1 Irpinia

07/04/2009 5.6 EQ2 L'Aquila

09/04/2009 5.4 EQ3 Gran Sasso

15/09/1976 5.9 EQ4 Friuli (3rd)

18/05/1976 4.1 EQ5 Friuli

13/04/2009 5.1 EQ6 L'Aquila

09/04/2009 5.4 EQ7 Gran Sasso

13/12/1990 5.6 EQ8 East Sicily

16/01/1981 5.2 EQ9 Italia Meridionale

11/06/1976 4.5 EQ10 Friuli


evaluate the overall performance of the strong masonry infill typology for


nfill strut and the frame elements in the

The bare frame, infilled frame, and infill hysteresis for the first cycles of the open infill configuration.

wo sets of records were selected, one compatible with the

at an intermediate peak

elastic response spectrum at the

, the ground motions have been selected

and 3.0. The log normal standard

has been reduced below 10%, and the

have been considered, with magnitudes 4.0 - 6.0

ultimate limit state. Subsequently,

compatible records have been scaled to the remaining PGAs adopted for design:

verifications and 0.05gS,

Table 1 lists the final

Date Mw

24/11/1980 5.0

07/04/2009 5.6

09/04/2009 5.4

15/09/1976 5.9

18/05/1976 4.1

13/04/2009 5.1

09/04/2009 5.4

13/12/1990 5.6

16/01/1981 5.2

11/06/1976 4.5


evaluate the overall performance of the strong masonry infill typology for design. The case



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study frames considered for extensive parametric analyses are assumed to represent typical

5.0 m spaced internal plane frames consisting of three bays (5.0 m, 2.0 m, and 5.0 m), in order

as part of a moment frame structure with varying numbers of stories (3-story, 6-story & 9-

story), each with a constant 3.0 m story height, as shown in Fig. 8.

Fig. 8 - Plan & elevations of the 3, 6 & 9-story bare frame buildings.

The placement of infills has feasibility for both exterior & interior frame lines. The

configuration termed all bays denotes that every bay along a single shear line has frames fully

infilled with the strong masonry typology. The partial configuration refers to a single infill in

the center bay with the adjacent bays left bare. The configurations having frames with open

infills adopt a similar nomenclature, indicated in the caption of Fig. 9 below.

(a) (b) (c) (d)

Fig. 9 - All bays (a), partial open (b), bare open (c), and partial (d) infill configurations.

Extrapolation of the calibrated parameters to the archetype buildings considers that the strut

properties change with the confining member sections and frame aspect ratio. The interval of

strength degradation is triggered by axial displacement in the strut to account for differences

in bay lengths. The drop in strut area matches the experiment for each respective open or

infill panel that has been kept proportional to the initial strut area.

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The strut widths obtained from the Decanini equations have been increased to better match

the experimental results. The additional strength most probably arises due to the dry tongue-

and-groove head joints influencing the strut behavior. The analyses with the DLS scaled

ground motions use the original elastic modulus and initial stiffness from Stafford Smith. The

analyses at the ULS intensity have a reduction in the elastic modulus to better capture the

unloading stiffness and hysteretic damping of the infills at large drift. Because the cyclic tests

were not continued until failure, the uncertainty beyond the extents of the cyclic tests will

increase. For that reason, the performance criteria have been evaluated within limits of the

tests to ensure modeling accuracy as opposed to implementing other probabilistic methods to

evaluate overall performance.

PERFORMANCE CRITERIA

If the maximum strain for the respective seismic intensity exceeds the limit for the respective

limit state, the run does not pass. Equation 1 serves to transform story drift into axial strain

respecting the inner dimensions of the panel, where L is the length of the panel, h is the height

of the panel, and δ is the story drift ratio.

ε δ( ) 1

1L

hδ−

2

+

1L

h

2

+

−=

(1)

If the majority of earthquake runs do not pass the criteria for any particular bay in any story,

the building configuration fails the criteria for that particular design PGA. The maximum

axial strain in the time history for each earthquake are compared to the drift index limits that

are listed in Table 2 below.

Table 2 - Performance levels for the strong masonry infill panel

Limit State Operational DLS ULS Out-of-Plane

Collapse

Color

Infill Configuration Drift [%]

Full Infill Panel ≤ 0.30 ≤ 0.50 ≤ 1.75 > 1.75

Open Infill Panel ≤ 0.20 ≤ 0.35 ≤ 1.00 > 1.00

NUMERICAL RESULTS

For each story, the maximum interstory drift for the ten time histories are averaged and

plotted in Fig. 10 to compare the response in comparison to the bare frame structures. As the

seismic intensity increases, the reduced story drift continues linearly below the bare structure

reference line at low seismic intensity in which linear behavior prevails. These results concur

with a conclusion from a previous numerical study on a wide range of infill typologies that

hypothesized a thicker, stronger & stiffer masonry unit could control damage at lower ground

motion intensity (Hak, 2012). Fig. 10 also shows that at higher seismic intensity for the ULS,

the maximum drift begins to return to the bare structure reference line, especially for stories

with bays less frequently infilled. This would indicate the story strength of the infill also

needs to be considered to estimate drifts at higher seismic intensity. At large displacements

the infills soften and the seismic response of the frame structure returns to its original flexural



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frame behavior, but the open infill panels with smaller drift limits cause the panels to fail the

ULS performance criteria for some of the 6 story buildings at high seismic intensity.

All Bays Partial and Open Bare and Open Partial

0.0

0.2

0.4

0.6

0.0 0.2 0.4 0.6 0.8

Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

DLS

0.0

0.2

0.4

0.6

0.0 0.2 0.4 0.6 0.8

Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

DLS

0.0

0.2

0.4

0.6

0.0 0.2 0.4 0.6 0.8

Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

DLS

0.0

0.2

0.4

0.6

0.0 0.2 0.4 0.6 0.8Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

DLS

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5 2.0

Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

ULS

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5 2.0

Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

ULS

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5 2.0In

fill

ed F

ram

e D

rift

Bare Frame Drift

ULS

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5 2.0Infi

lled

Fra

me

Dri

ft

Bare Frame Drift

ULS

Fig. 10 - Average story drifts for the medium ductility class buildings.

For the buildings subject to the ULS scaled ground motions, the highest story drift at the base

of the buildings concentrating damage in that region, as shown in Fig. 11 and 12. Further

examination of the damage elevation show that apparently there is no significant influence of

infill configuration on the frequency of damage. Instead the range of effective fundamental

periods for the 6 story infilled frame buildings are the most sensitive to the scaled input

ground motions.

OK OK OK OK OK OK OK OK OK


DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK



DAMAGE OK DAMAGE OK OK OK OK OK OK


DAMAGE DAMAGE DAMAGE OK OK OK OK OK OK

PEAK PEAK P EAK DAMAGE DAMAGE DAMAGE OK OK OK








PEAK PEAK P EAK OK OK OK OK OK OK

PEAK PEAK P EAK DAMAGE DAMAGE DAMAGE OK OK OK

0.35g PGA 0.25g PGA 0.15g PGA

DAMAGE DAMAGE OK DAMAGE DAMAGE OK OK OK OK OK OK OK OK OK OK

DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE OK OK OK OK OK

PEAK PEAK PEAK PEAK PEAK PEAK PEAK DAMAGE PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE

OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK


PEAK PEAK OK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE

PEAK PEAK DAMAGE PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE


FAILURE FAILURE PEAK FAILURE FAILURE PEAK PEAK PEAK PEAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE

OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK


PEAK PEAK OK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE OK OK OK OK OK

PEAK PEAK OK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE OK OK OK OK OK

PEAK PEAK OK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE

PEAK PEAK DAMAGE PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE

PEAK PEAK PEAK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE DAMAGE DAMAGE OK DAMAGE DAMAGE

PEAK PEAK PEAK PEAK PEAK PEAK PEAK OK PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE



All Bays Infill Configuration Open and Partial Infill Configuration

Fig. 11 - Damage elevations at the ultimate limit state for the high ductility class buildings.

Generally the damage patterns indicated by the numerical study concur with post-earthquake

reconnaissance in that the more damage occurs at lower stories than at higher stories.

Although higher floor accelerations happen at a higher elevation, out-of-plane failures are

believed to manifest themselves only after significant in-plane damage particularly for the

strong infill typology in modern RC frame buildings.

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OK OK OK OK OK OK OK OK OK OK OK OK

DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE

PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE


DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK OK

PE AK PEAK P EAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE

PE AK PEAK P EAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE


FAIL URE FAILURE FAILURE FAILURE PEAK P EAK PEAK PEAK PE AK PEAK P EAK PE AK




PE AK PEAK P EAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK OK

PE AK PEAK P EAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK




PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE P EAK PE AK


OK OK OK

PE AK DAMAGE OK

FAILURE PEAK DAMAGE

OK OK OK

OK OK OK

PE AK DAMAGE OK

PE AK DAMAGE OK

PE AK PEAK OK

PE AK PEAK DAMAGE

OK OK OK

OK OK OK

DAMAGE OK OK

OK OK OK

OK OK OK

DAMAGE OK OK

PE AK DAMAGE OK

PE AK DAMAGE OK

PE AK PEAK OK


Open and Bare Infill Configuration Partial Infill Configuration

Fig. 12 - Damage elevations at the ultimate limit state for the high ductility class buildings.

The displacement profiles in Fig. 13 at maximum drift show the first mode dominating the

response with a shape typical for moment frame systems. The largest interstory drift occurs at

the ground floor because the base of the columns are assumed to be pinned—a conservative

assumption deemed appropriate for estimating drifts (Moehle, 2008). Fixing the column

bases increase the moment demand, stiffen the ground story and push the maximum story

drift above the ground floor but do not substantially affect maximum story drift or the

occurrence of damage.

Comparison of the drift profiles at maximum story drift for the 6 story, high ductility class

buildings subject to the 0.35g PGA scaled ground motions show higher dispersion for the

partial infill configuration than the all bays configuration, visible in Fig. 13. The standard

deviation of story drift indicated in the figure assumes a normal distribution. Thus

redundancy in infill patterns could help mitigate the dispersion especially for bays with full

infill panels. The effect of open infills on the global in-plane response has been less

influential, both in terms of drift and dispersion during the numerical study.

0

1

2

3

4

5

6

-0.10 -0.05 0.00 0.05 0.10

Sto

ry

Story Displacement [m]

6 Story 0.35g PGA SLV DCH

Disp Profile at Max Story Drift - All BaysARITHMEAN

STD DEVBELOW

STD DEVABOVE

0

1

2

3

4

5

6

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Sto

ry

Story Displacement [m]


Disp Profile at Max Story Drift - PartialARITHMEAN

STD DEVBELOW

STD DEVBELOW

0

1

2

3

4

5

6

-1.00 -0.50 0.00 0.50 1.00

Sto

ry

Story Drift [%]


Drift at Max Story Drift - All BaysARITHMEAN

STD DEVBELOW

STD DEVABOVE

0

1

2

3

4

5

6

-2.50 -1.25 0.00 1.25 2.50

Sto

ry

Story Drift [%]


Drift at Max Story Drift - PartialARITHMEAN

STD DEVBELOW

STD DEVABOVE

Fig. 13 - Relative displacement and interstory drift profiles at the point of maximum story drift.



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Interestingly, all the design PGAs pass the performance criteria at the DLS shaking intensity

for the strong masonry infill typology, most likely due to higher stiffness properties of the

strong masonry infill typology. At the ULS, the six story buildings with open infills have

difficulty passing the performance criteria at the highest design PGA. The ductility class of

buildings do not influence the performance criteria with respect to the infill panel damage.

Table 2 - Maximum PGA (g) passing each limit state.

Infill

Config

Stories DCM DCH DCM DCH DCM DCH DCM DCH

3 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.25

6 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

9 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

Config

Stories DCM DCH DCM DCH DCM DCH DCM DCH

3 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

6 0.35 0.35 0.35 0.35 0.25 0.25 0.35 0.25

9 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

Ultimate Limit StateDamage Limit State

Bare + Open Partial + Open Bare + Open Partial + Open

Full Partial Full Partial

CONCLUSION

A recent experimental campaign of in-plane and out-of-plane cyclic tests on single-

bay/single-story RC frames with a strong masonry infill indicate differences in seismic

response with respect to weaker, more slender infills. Significant resistance to in-plane

loading continues beyond the drift at peak strength and shows more resilience to severe

damage at larger drift. In-plane performance criteria for the strong masonry infill typology

have been defined and evaluated in an extensive parametric study.

The calibration of a macro model to a special interpretation of the experimental data has

preceded a parametric study involving several model building structures varying in infill

density, ductility class, number of stories and exposure to seismic intensity. Particular

attention to the path dependent behavior of the infill strut in comparison to the extracted

hysteresis representing the net effect of the infill on the bare frame response provides a more

accurate model in terms of seismic energy dissipation, unloading stiffness and the cyclic

strength envelope.

Limit state verifications using nonlinear dynamic analyses with specific drift indices selected

for the masonry typology help convey the in-plane non-structural seismic performance. The

assessment of performance reflects current design procedures in the Italian annex and

Eurocode at a range of seismic hazard in Italy. Extrapolation of the calibrated macro model to

other aspect ratios has been made possible by adjusting existing empirical relations for

determining the cracked stiffness and peak strength.

Limiting the scope to in-plane behavior of the infill walls, the study concludes that for this

particular strong masonry infill, the code compliant buildings accomplish the performance

goals in current seismic design philosophy. The effect of the infill panels on the global

building performance demonstrates the need to account their behavior in new design of

buildings. If a more realistic 3D response is to be considered in the future, the out-of-plane

behavior should be included preferably through an in-plane/out-of-plane interaction

relationship.

Symposium_10


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REFERENCES

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[3]-Crisafulli, F. J. (1997). Seismic Behavior of Reinforced Concrete Structures with Masonry

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[4]-Dawe, J. L., and Seah, C. K. (1988). Lateral load resistance of masonry panels in flexible

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[8]-Morandi, P., Hak, S., and Magenes, G. (2014). In-plane experimental response of strong

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[9]-Maheri, M. R., Najafgholipour, M. Q., and Rajabi, R. (2011). The influece of mortar head

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[10]-Moehle, J. P., Hooper, J. D., and Lubke, C. D. (2008). "Seismic design of reinforced

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[11]-Oliaee, M. A., Morandi, P., Magenes, G. (2015). “Macro-model calibration of a strong

clay masonry infill to in-plane cyclic tests,” Computational Methods in Structural Dynamics

and Earthquake Engineering, Crete Island, Greece.

[12]-NTC08. (2008). Norme tecniche per le costuzioni. Rome, Italy: Ministero delle

Infrastrutture.

[13]-Polyakov, S.V. Masonry in framed buildings, Gosudalst-Vennoe Izdatel’stvo Literature

po Straitel’stvu I Arkitecture, Moscow, 1956, Tranl. G.L. Cairns, Building Research Station,

Watford, Herts, UK, 1956.

[14]-Rodrigues, H., Varum, H., Costa, A. (2008). A non-linear masonry infill macro-model to

represent the global behavior of buildings under cyclic loading. International Journal of

Mechanics and Materials in Design, Issue 4, pg. 123-135.

[15]-Stafford Smith, B. "Behavior of square infilled frames", ASCE Proceedings, February

1966, pg. 381-403.

Documents

IN-PLANE SEISMIC BEHAVIOR OF A STRONG MASONRY INFILL … · IN-PLANE SEISMIC BEHAVIOR OF A STRONG MASONRY INFILL Milad Oliaee 1(*), Paolo Morandi 2, Guido Magenes 2 1UME School, IUSS