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THE EFFECT OF OPENINGS ON OUT-OF-PLANE CAPACITY OF
MASONRY INFILLED REINFORCED CONCRETE FRAMES
Filip ANIĆ1, Davorin PENAVA2, Ivica GULJAŠ3, Vasilis SARHOSIS4, Lars ABRAHAMCZYK5,
Christoph BUTENWEG6
ABSTRACT
Reinforced concrete frames are usually infilled with masonry walls. However, during the seismic design of RC
buildings, the contribution of masonry walls in the overall seismic performance of the frame is mistakenly
neglected. This paper, discusses the effect of openings on out-of-plane behavior of masonry infilled reinforced
concrete frames. A series of numerical analyses were conducted on a 1/2.5 scale model structure of single-bay
single-storey infilled frame containing a door or medium sized window openings, centrically and eccentrically
positioned. Use made of the three-dimensional software ATENA 3D Eng. The numerical model was initially
calibrated against experimental tests. Then, a monotonic out-of-plane uniform load was applied in the structure
and the failure mechanisms and force against displacement relationships obtained. From the results analysis, it
was found that the presence and type of openings significantly influence the out of plane behavior of RC frames
with openings.
Keywords: masonry, infill, RC frame, opening, finite element method, nonlinear analysis, out-of-plane
1. INTRODUCTION
Structural frames, constructed by reinforced concrete (RC) are often infilled with masonry
panels/walls. However, in structural practice, the influence of masonry infill on seismic behavior is
usually ignored, i.e. is considered as a non-bearing element as laid out in Eurocode 8 provisions (CEN
2005). Research undertaken over the last few decades demonstrated that they utterly contribute to the
overall dynamical behavior of the frames (Dowrick 2009). However, most of the researches
investigate the effect of the in-plane (IP) behavior rather than the out-of-plane (OOP) one. With
respect to research in the OOP loading, the main focus was on fully infilled frames (Asteris et al.
2017), with certain exceptions to single openings such as in Akhoundi et al. (2016), i.e. there is no
classification, or analytical models on openings and their effect on OOP behavior.
The first to investigate the effect of the OOP loading on masonry infilled frames was in late 50’s with
the research of (McDowell et al. 1956). There the “arching action” was established. From that point,
nearly the entire field of OOP loading adopted the same loading method of a uniform (or rarely point)
load applied directly onto the infill (Akhoundi et al. 2016; Abrams et al. 1996; Pereira et al. 2011;
1PhD student, Faculty of Civil Engineering Osijek, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia,
[email protected] 2Dr., Faculty of Civil Engineering Osijek, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia,
[email protected] 3Professor, Faculty of Civil Engineering Osijek, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia,
[email protected] 4Dr., School of Engineering, School of Engineering, Newcastle University, Newcastle upon Tyne, United
Kingdom, [email protected] 5Dr., Earthquake Damage Analysis Centre EDAC, Bauhaus University, Weimar, Germany,
[email protected] 6Professor, Faculty of Civil Engineering, RWTH Aachen University, Aachen, Germany, [email protected]
aachen.de
2
Hak et al. 2014). Those loading methods are suitable for blast modelling as shown in (Parisi et al.
2016; Wu & Hao 2007). For the seismic analysis of infilled frames, this approach may be inaccurate
as the seismic excitement is transferred trough frames and diagraphs and not trough the infill, such as
it is used in IP loading (Nicola et al. 2015).
Consequently, this paper studies OOP response of six infilled RC frames configurations by a 3D
micro-modelling approach using the Atena3D software (Cervenka Consulting 2015). Those six
structural configurations were divided into two groups to account variation in size and location of
openings (Penava 2012) and presented in Table 1. The first group (I) consisted of four masonry
infilled RC frames containing an unconfined opening (e.g. door or window) centrically and
eccentrically positioned. The second group (II) had two reference specimens, i.e., fully infilled framed
and bare frame. Hence, the research includes: a) II/1 RC frame without infill; b) II/2 RC frame with
full infill; c) I/1 RC frame with centric door opening in the infill; d) I/2 RC frame with centric window
opening in the infill; e) I/3 RC frame with eccentric door opening in the infill; and f) I/4 RC frame
with eccentric window opening in the infill. The opening area (𝐴𝑜) was selected to be 2.0 m2 which
falls within the range (i.e., 𝐴𝑜 > 1.5 m2 and 𝐴𝑜 > 2.5 m2) defined by EN 1998-1 (CEN 1998). RC
frames were designed as medium class ductility frames (DCM) according to EN 1992-1-1 provisions
(CEN 2004). Atena 3D (Cervenka Consulting 2015) software used for the analysis. For further details
on the computational models, the reader is kindly requested to refer to (Anić et al. 2017).
Table 1 Classification and description of the specimens (Penava et al. 2016)
Specimen Appearance of the
specimen
Opening
Group Mark Type and area Position
I
1
Door Centric
lo / ho = 0.35 / 0.90 m
eo = li / 2 = 0.90 m Ao = 0.32 m2
Ao / Ai = 0.14
2
Window Centric
lo / ho = 50.0 / 60.0 cm eo = li / 2 = 0.90 m
P = 0.40 m Ao = 0.30 m2
Ao / Ai = 0.13
3
Door Eccentric
lo / ho = 0.35 / 0.90 m
eo = hi / 5 + lo / 2 = 0.44 m Ao = 0.32 m2
Ao / Ai = 0.14
4
Window Eccentric
lo / ho = 50.0 / 60.0 cm eo = hi / 5 + lo / 2 = 0.44 m
P = 0.40 m Ao = 0.30 m2
Ao / Ai = 0.13
II
1
Not considered in OOP
2
- -
3
Figure 1 RC frame and masonry unit dimensions
2. DEVELOPMENT OF THE MODEL, MATERIALS AND BOUNDARY CONDITIONS
2.1 Development of the model and materials
For the numerical model, 3D solid elements for concrete, clay blocks and elastic plates were used. In
addition, 2D interface elements to represent block to block contacts and block to frame contact
implemented. Finally, 1D truss rebar elements for concrete were selected as shon in (fig.3).
Material properties used in this paper were adopted from (Penava et al. 2016) (tab.2&3). Bedjoint
interface materials take into consideration the interlocking effect (fig.2) to account for the effect of the
mortar filled between the voids in the masonry blocks. Material model CC Nonlinear cementitious 2
(Cervenka et al. 2012) for clay block in (Penava et al. 2016) incorporates the experimentally obtained
and calculated properties in direction of voids. However, for masonry walls, bending tests conducted
in accordance with EN 1052-2 provisions (CEN 1999), clay block parameters such as tension strength
ft and tension softening function had to be modified in order to simulate the tests. The tests were
carried out as a preliminary study of infills OOP behavior, i.e. to establish the governing OOP bending
parameters. Further on, the tensile strength was changed from that in direction of voids 1.80 MPa to
strength perpendicular to voids 0.38 MPa. The end displacement of tension softening function ranged
from 1∙10-4 m to 1∙10-5 m (fig.1b). Clay blocks fracture energy is depended on the blocks tensile
strength ft (eq.3). Fracture energy calculated with tension strength in direction of voids. Equations 1, 2
and 3 are adopted from (Cervenka et al. 2012). Minimum normal Knn,min and tangential stiffness Ktt,min
are normal and tangential stiffness divided by 1000 as recommended by (Cervenka et al. 2012).
Knn = E / t (1)
Ktt = G / t (2)
Where t is mortar thickness (standard thickness of 10 mm).
Gf = 0.000025 ft (3)
ho
lo
180
li = 130
20/20
4
Table 2 CC Nonlinear cementitious 2 material model
Description Symbol Frame concrete Concrete lintel Clay block Unit
Elastic modulus E 4.100 E+04 3.032 E+04 5.650 E+03 MPa
Poisson's ratio μ 0.200 0.200 0.100 /
Tensile strength ft 4.000 2.317 0.380 MPa
Compressive strength fc -5.800 E+01 -2.550 E+01 -1.750 E+01 MPa
Specific fracture energy (eq.3) Gf 1.200 E-04 5.739 E-05 4.500 E-04 MN/m
Crack spacing smax 0.125 0.125 / m
Tensile stiffening cts 0.400 0.400 / /
Critical compressive disp. Wd -5.000 E-04 -5.000 E-04 -5.000 E-04 /
Plastic strain at fc εcp -1.417 E-03 -8.411 E-04 -1.358 E-03 /
Reduction of fc due to cracks rc.lim 0.800 0.800 0.800 /
Crack shear stiffness factor SF 20.000 20.000 20.000 /
Aggregate size 1.600 E-02 2.000 E-02 / m
Fixed crack model coefficient 1.000 1.000 1.000 /
Table 3 CC 3D Interface material model
Description Symbol Mortat bedjoint Mortar headjoint Unit
Normal stiffness (eq.1) Knn 5.65 E+05 8.50 E+04 MN/m2
Tangential stiffness (eq.2) Ktt 2.57 E+05 3.86 E+04 MN/m2
Tensile strength ft 0.20
0.20
MPa
Cohesion c 0.35
0.35
MPa
Friction coefficient
0.24
0.24
/
Interlock function
see fig. 2a (where
applicable) / /
a) Interlocking function b) Tension softening function
Figure 2 Interface function
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 0.5 1.0 1.5 2.0
c/c 0
d (mm)
0.04, 3
0.0
1.0
0.0E+00 1.0E-05
σ/f
t
d (mm)
5
2.3 Boundary conditions
Infill loaded as shown in (fig.3). First, the 365 kN of vertical force applied to the column tops in five
steps, after which column supports are active in y and z direction. Then, a uniformly distributed load
equal to 0.002 MPa/step applied in y direction and at the entire area of the infill (excluding openings
where applicable); hence the monotonic load. While the OOP load is active, frames beam is supported
on the opposite face in regards to the infills load face (–y direction). Foundation support is active
through the whole calculation. Due to inability to develop interlocking between masonry unit and the
concrete elements, bedjoints on relations infill – frame has interlocking functions (fig.2) turned off.
Also, during the casting of lintel, concrete slips fully into the voids of masonry units, therefore, a
perfect connection on those parts was adopted.
Figure 3 Numerical model setup
Table 4. Crack propagation by stage
Crack
stage Full infill Openings
1st
Front: Diagonal cracks developed under
approx. 45° in the upper area;
Back: Horizontal cracks appear on beam –
infill connection
Front: Crack appeared around lintel; Back:
Horizontal cracks appear on beam – infill
connection
2nd
Front: Lower diagonal cracks start to
develop
Back: Horizontal cracks appear on
foundation – infill connection
Front: Crack around lintel propagate towards the
beam following approx. 45° angle
3rd
Front: as diagonal cracks develop,
horizontal cracks at infills mid height start
to develop. Back: Diagonal cracks on the
upper section start to developed
Back: Horizontal cracks appeared on foundation –
infill connection
4th Back: cracks developed at the infill around
the frame, heavy cracking of the beam
Front: Horizontal crack propagated in about infill
mid height appear. Beam was heavily cracked.
5th Front: fully developed diagonal cracking Front: Cracks started to fill the lower part of the
infill with angle of approx. 45°
y
z
x
73.000
kN/step
73.000
kN/step
0.002
MPa/step
3D solid elements
1D truss elements
support
monitoring point
6
3. RESULTS’ DISCCUSIONS AND CONCLUSIONS
Figure 4 shows the force - displacement relationships. In figure 4, displacements are the maximum
global displacement in the y direction. Figure 4a shows the area load – displacement relations, and
figure 4b shows force – displacement relations as the bearing can be different if the area is taken into
account by formula 1. Horizontal lines represent the value of the best fitting analytical model by
(Klingner et al. 1997), calculated as per eq.2. It is to be noted that analytical models excessively vary
among each other as showed in (Asteris et al. 2013).
W = w (A – Ao) (1)
l
hl
l
x
xMhhlM
lhw
yh
yv
yhyv2/
ln2ln82
(2)
, where: xy is out of plane deflection, My OOP resisting moment, h horizontal, v vertical direction.
Figure 5 shows the minimum principal stresses along the cross-section of the infill. Table 4 shows the
crack propagation at five different stages of applied load. Figure 6 shows the crack development at the
front and back side of the infill wall. Only cracks greater than 0.1mm are shown in the Figure 6 sine
these are visible with naked eye (ATC-43 1998). Load applied at the front side of the masonry wall.
Figure 7 shows the minimum principal stresses at the front and back side of the wall. Figure 5, 6 and 7
show the minimum principal stresses and crack patterns when maximum displacement in the wall is
equal to 6 cm.
From Figures 5, 6, 7 and Table 4 it can be concluded that:
a) Computational models did simulate the expected arching failure, see figure 5. The three points
of clamping that make the compression arch are clearly visible on the full infill model (III/2).
The separation of clay blocks from each other by bedjoints (developing tension) at maximum
deflection is visible at Figure 7, where gray areas denotes shear sliding and tensile failure at
the joints.
b) Compression arch has also develop in the infill outside the opening in group I (fig.5).
However, there were 4 distinct clamping points: 1. infill – beam, 2. infill – lintel, 3. infills
deflection point, 4. infill – foundation. As the consequence of 2. point of clamping, RC lintel
developed high principal stresses (fig.7).
c) Due to the development of the compression arch together with the loading a single face of the
infill, front and back side of the masonry wall have different stresses and crack patterns.
d) Cracks that developed on full infill model (fig.6a&b) replicate the arching failure when the
infill is connected by all sides to the frame as shown in (Akhoundi et al. 2016; Dawe & Seah
1989; Furtado et al. 2015).
e) The location of openings in the masonry infill wall significantly influence the bearing capacity
(fig.4), crack (fig.6) and stress (fig. 7) development. Masonry infilled wall panels containing
centric openings had higher bearing capacity than those with eccentric openings.
f) Masonry infill wall panels with centric window opening and full infill behaved in a similar
manner (fig.4b). Similar results also obtained from (Akhoundi et al. 2016). It should be
highlighted that for the model developed by (Akhoundi et al. 2016), a slightly higher capacity
observed for the infill wall with centric window than the one with the full infill (2%
difference).
g) Comparing the analytical results by (Klingner et al. 1997) to the numerical results obtained in
this study, it can be concluded that approx. 15% difference obtained for the full infill model,
3% for centric window model and 17% for centric door model.
h) As noted and calculated by (Moghaddam & Goudarzi 2010), there are two possible failure
modes: a) as a results of bending and excessive shear (slender infills)– shear failure wcr =
0.098 MPa; and b) due to crushing on clamping points wmax = 0.378 MPa. Seemingly, all
frames would fall under the category of crushing failure mode no matter the openings.
Likewise, infills cannot be considered slender.
7
i) In accordance with points b), f) & h) it can be concluded that in comparison with the full infill
model, openings did not affect the failure mode.
a) Area load versus displacement b) Force versus displacement
Figure 4. Load – displacement diagram
a) II/2 I/1 I/2 I/3 I/4
Absolute deformation ×1
Figure 5. Minimum principal stress at max. displacement cross section
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.00 2.00 4.00 6.00
w (
MP
a)
d (cm)
I/1 I/2I/3 I/4III/2 Klingner
0
100
200
300
400
500
600
0 2 4 6
W (
kN
)
d (cm)
I/1 I/2
I/3 I/4
III/2 Klingner full infill
Klingner door Klingner window
0
-1
-3
-4
-5
-6
-8
-9
-10
σmin (MPa) < −10 >0
8
a) III/2 front b) III/1 back
c) I/1 front d) I/1 back
e) I/2 front f) I/2 back
g) I/3 front h) I/3 back
i) I/4 front j) I/4 back
Min. crack width = 0.1 mm ; deformation × 1 ; crack width multiplier ×1
Figure 6 Crack patterns
9
a) III/2 front b) III/1 back
c) I/1 front d) I/1 back
e) I/2 front f) I/2 back
g) I/3 front h) I/3 back
i) I/4 front j) I/4 back
Figure 7. Minimum principal stress
0
-3
-5
-8
-10
-13
-15
-18
-20
σmin (MPa) < −20 >0
10
4. ACKNOWLEDGMENTS
The research presented in this article is a part of the research project FRAmed-MAsonry composites
for modelling and standardization (HRZZ-IP-2013-11-3013) supported by Croatian Science
Foundation and its support is gratefully acknowledged. The authors are grateful to Professor Vladimir
Sigmund (1956 – 2016) for his significant contribution and direction towards the research described in
this paper.
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