View
215
Download
0
Category
Preview:
Citation preview
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
-1399-
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: milad.oliaee@gmail.com
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
Symposium_10
Seismic Behaviour Characterization and Strengthening of Constructions
-1400-
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,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1401-
(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
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 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
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% 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
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-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
limit states (DLS and ULS) are defined according to performance levels described in EC8 and
has been assigned for the damage
case of the infill with the
Symposium_10
Seismic Behaviour Characterization and Strengthening of Constructions
-1402-
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,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1403-
5 - The equivalent diagonal single-strut model.
Other macro models have been proposed in the past and implemented for different purposes.
Multiple strut models with offset struts aim to capture local effects on the surrounding frame
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
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
cannot be independently calibrated, and the optimization problem is rendered multivariate and
nonlinear. A preliminary trial and error approach did not satisfy all the objectives of the
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
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,
energy dissipation and stiffness criteria identify the best parameters for the full and open infill
nted 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.
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
Other macro models have been proposed in the past and implemented for different purposes.
ruts aim to capture local effects on the surrounding frame
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
field ground motions, the
of the response represent important
eria 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
the objectives of the
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
earthquake intensity, the error criteria focuses on
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
nted 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, shown in the right
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 dissipated by the RC
elements during the input load history decrease due the axial forces induced to the frame
Symposium_10
Seismic Behaviour Characterization and Strengthening of Constructions
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
Seismic Behaviour Characterization and Strengthening of Constructions
-1404-
elements by the infill strut axial forces. For the strong infill typology, the present calibration
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
An extensive analysis parameterizing the building configurations and design categories
evaluate the overall performance of the strong masonry infill typology for
elements by the infill strut axial forces. For the strong infill typology, the present calibration
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
An extensive analysis parameterizing the building configurations and design categories
evaluate the overall performance of the strong masonry infill typology for design. The case
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
-1405-
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.
Symposium_10
Seismic Behaviour Characterization and Strengthening of Constructions
-1406-
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
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
-1407-
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
OK OK OK OK OK OK OK OK OK
DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK
OK OK OK OK OK OK OK OK OK
OK OK OK OK OK OK OK OK OK
DAMAGE OK DAMAGE OK OK OK 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
OK OK OK OK OK OK OK OK OK
OK OK OK OK OK OK OK OK OK
OK OK OK OK OK OK OK OK OK
OK OK OK OK OK OK OK OK OK
DAMAGE OK DAMAGE OK OK OK OK OK OK
DAMAGE DAMAGE DAMAGE OK OK OK OK OK OK
DAMAGE DAMAGE DAMAGE OK OK OK 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
DAMAGE DAMAGE OK DAMAGE DAMAGE 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 PEAK PEAK DAMAGE PEAK PEAK 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
DAMAGE DAMAGE OK DAMAGE DAMAGE 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 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
PEAK PEAK PEAK PEAK PEAK PEAK PEAK DAMAGE PEAK PEAK DAMAGE DAMAGE OK DAMAGE DAMAGE
0.35g PGA 0.25g PGA 0.15g PGA
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.
Symposium_10
Seismic Behaviour Characterization and Strengthening of Constructions
-1408-
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
OK OK OK OK OK OK OK OK OK OK OK OK
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
PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE
FAIL URE FAILURE FAILURE FAILURE PEAK P EAK PEAK PEAK PE AK PEAK P EAK PE AK
OK OK OK OK OK OK OK OK OK OK OK OK
DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK OK
DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE DAMAGE OK OK OK OK
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 DAMAGE DAMAGE
PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE
PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE DAMAGE DAMAGE
PE AK PEAK P EAK PEAK PEAK P EAK PEAK PEAK DAMAGE DAMAGE P EAK PE AK
0.35g PGA 0.25g PGA 0.15g PGA
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
0.35g PGA 0.25g PGA 0.15g PGA
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]
6 Story 0.35g PGA SLV DCH
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 [%]
6 Story 0.35g PGA SLV DCH
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 [%]
6 Story 0.35g PGA SLV DCH
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.
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
-1409-
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
Seismic Behaviour Characterization and Strengthening of Constructions
-1410-
REFERENCES
[1]-Carr, A. J. (2007). Ruamoko Manual. University of Cantebury, Christchurch, New
Zealand.
[2]-CEN Eurocode 8 (2004) - Design of structures for earthquake resistance, Part 1: General
rules, seismic actions and rules for buildings, EN 1998-1, European Committee for
Standardisation, Brussels, Belgium.
[3]-Crisafulli, F. J. (1997). Seismic Behavior of Reinforced Concrete Structures with Masonry
Infills. PhD Thesis. University of Cantebury, Christchurch, New Zealand.
[4]-Dawe, J. L., and Seah, C. K. (1988). Lateral load resistance of masonry panels in flexible
steel frames. Proc. 8th International Brick and Block Masonry Conference. Dublin, Ireland.
[5]-Fukada, Y. (1969). Study on the restoring force characteristics of reinforced concrete [1]-
buildings (in Japanese), Proceedings, Kanto District Symposium, Architectural Institute of
Japan, Tokyo, Japan, No. 40.
[6]-Giberson, M. F. (1967). “The response of nonlinear multi-story structures subjected to
earthquake excitation,” EERL Report, California Institute of Technology, Pasadena,
California.
[7]-Hak, S., Morandi, P., Magenes, G., Sullivan, T. (2012). “Damage control for clay
masonry infills in the design of RC frame structures,” Journal of Earthquake Engineering,
Vol. 16, S1, pp. 1-35.
[8]-Morandi, P., Hak, S., and Magenes, G. (2014). In-plane experimental response of strong
masonry infills. International Masonry Conference. Guimaraes: International Masonry
Society.
[9]-Maheri, M. R., Najafgholipour, M. Q., and Rajabi, R. (2011). The influece of mortar head
joints on the in-plane and out-of-plane seismic strength of brick masonry walls. Transactions
of Civil and Environmental Engineering, 35, pp. 63-79.
[10]-Moehle, J. P., Hooper, J. D., and Lubke, C. D. (2008). "Seismic design of reinforced
concrete special moment frames: a guide for practicing engineers," NEHRP Seismic Design
Technical Brief No. 1, Gaithersburg, MD., NIST GCR 8-917-1
[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.
Recommended