MONOTONIC AND CYCLIC CHARACTERIZATION OF … · of masonry infill panels, particularly in the...

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: 5730

MONOTONIC AND CYCLIC CHARACTERIZATION OF THE OUT-

OF-PLANE BEHAVIOUR OF INFILL MASONRY WALLS

André Furtado 1, Hugo Rodrigues

2 (*), António Arêde

1

1Faculty of Engineering, University of Porto, Porto, Portugal 2Department of Civil Engineering, Polytechnic Institute of Leiria, Leiria, Portugal (*)Email: [email protected]

ABSTRACT

During the last years, it has been observed that the contribution of the masonry infill walls

should be considered in the structural response of the existing buildings Typically infill

masonry walls are considered non-structural elements; however when subjected to

earthquakes, they tend to interact with the surrounding RC frames which can result in

different failure modes, with in-plane failure and the out-of-plan collapse.

An experimental campaign of full scale masonry infill walls was performed in order to better

understand and characterize the out-of-plane behaviour of infilled masonry panels, in

particular with and without in-plane damage. Three experimental tests were made, two out-of-

plane tests (monotonic and cyclic) in original infill masonry panels and another out-of-plane

test in a third infill panel damaged during a previous in-plane test. In the paper, the results of

the experimental tests are presented and discussed in terms of hysteretic force-displacement

curves, damage evolution, stiffness degradation, infill panels’ capacity and energy dissipation.

Keywords: masonry infill walls, static cyclic test, out-of-plane behaviour, experimental

response

INTRODUCTION

The contribution of the infill walls to the building’s seismic performance can be favourable or

not, depending on a large series of uncertain phenomena, detailing aspects, mechanical

properties, and others. Technical surveys on damaged and collapsed reinforced concrete (RC)

buildings in recent earthquakes in Europe have identified that a large number of buildings that

suffered severe damage or collapse had their poor performance associated with the influence

of masonry infill panels, particularly in the southern region of the Europe, such as L’Aquila

(Italy, 2009) [1], Lorca (Spain, 2010) [2, 3] and Emilia (Italy, 2012) [4]. Typically the infill

masonry walls are considered non-structural elements; however when subjected to

earthquakes, they tend to interact with the surrounding RC frames which can result in

different failure modes, among which are the in-plane failure and the out-of-plane (OP)

collapse.

The infills OP behaviour has been observed as one of the most important critical failures of

such type of non-structural elements (Figure 1) [5-7]. One of the major factors that cause the

OOP instability and poor performance is the deficient/insufficient support-width on the

reinforced concrete (RC) beams and/or slabs, normally adopted to minimize the thermal

bridges effect, no connection between the interior and the exterior panel and finally no

connection to the surrounding RC frames [1].

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Seismic Behaviour Characterization and Strengthening of Constructions

Fig. 1 - Masonry infill walls earthquake out

It is required a deeper knowledge of the

subjected to OP loadings proceeded

appear as a useful tool allowing

cyclic experimental tests. Thus, a

was performed at the Laboratory of Earthquake an

better understand and characterize the monotonic and cyclic infill masonry panels’ OP

behaviour of. For this, two experimental tests were made (monotonic and cyclic) in original

infill masonry panels. The geometr

statistical study about geometric characterization of the Portuguese reinforced concrete

buildings with masonry infill walls, representative of the construction in the 1950

decades [8]. Along the paper the experimental results

of hysteretic force-displacement curves, damage evolution, stiffness degradation, infill panels’

capacity and energy dissipation.

OVERVIEW OF THE EXPERIMENTAL CAMPAIGN

Test programme and specimen’s description

Within the scope of the present experimental campaign, two out

infilled RC frames were performed

be 4.80x3.30 m, with the RC columns and beams cross section of 0.30x0.30m and0

receptively. In Figure 2, is illustrated the infilled RC frame geometry and the corresponding

columns and beams dimensions and reinforcement detailing. The dimensions of the specimen

is representative of the Portuguese building stock, and particul

infill panels that were observed to collect a complete geometric characterization.

collected data was utilized to derive probabilistic distributions, whose goodness

partially verified with a statistical test.

modelling development of nonlinear models for masonry infill panels, or computation of


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Masonry infill walls earthquake out-of-plane collapses examples

deeper knowledge of the behavior of these non-structural elements

proceeded or not of in-plane damage. Thus the

allowing characterizing their behavior such through

experimental tests. Thus, an experimental campaign of full scale masonry infill walls

was performed at the Laboratory of Earthquake and Structural Engineering (LESE) in order to



infill masonry panels. The geometry of the infill panels were defined taking into account a


buildings with masonry infill walls, representative of the construction in the 1950

the experimental results will be presented and

displacement curves, damage evolution, stiffness degradation, infill panels’

capacity and energy dissipation.

OVERVIEW OF THE EXPERIMENTAL CAMPAIGN

Test programme and specimen’s description

the scope of the present experimental campaign, two out-of-plane tests of full

infilled RC frames were performed. The general dimensions of the specimens were selected to

be 4.80x3.30 m, with the RC columns and beams cross section of 0.30x0.30m and0

, is illustrated the infilled RC frame geometry and the corresponding


is representative of the Portuguese building stock, and particularly of a data of 1500 masonry

infill panels that were observed to collect a complete geometric characterization.

collected data was utilized to derive probabilistic distributions, whose goodness

partially verified with a statistical test. The results from the study can be used in structural


plane collapses examples.

structural elements when

e experimental tests

their behavior such through static or dynamic

n experimental campaign of full scale masonry infill walls

d Structural Engineering (LESE) in order to



y of the infill panels were defined taking into account a


buildings with masonry infill walls, representative of the construction in the 1950-1990

ll be presented and discussed in terms

displacement curves, damage evolution, stiffness degradation, infill panels’

plane tests of full-scale

. The general dimensions of the specimens were selected to

be 4.80x3.30 m, with the RC columns and beams cross section of 0.30x0.30m and0.30x0.50

, is illustrated the infilled RC frame geometry and the corresponding


arly of a data of 1500 masonry

infill panels that were observed to collect a complete geometric characterization. The

collected data was utilized to derive probabilistic distributions, whose goodness-of-fit were

The results from the study can be used in structural



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

fragility models. In addition, the statistical parameters such as mean values, standard

deviations, probability density functions and their goodness

for all the entire parameters [8]

Fig. 2 - Infilled RC frame specimen dimensions

The two infill panels had equal geometry with the overall dimensions of 2.30x4.20x0.15m,

and a hollow horizontal clay brick type was used, such this is one of the most common

masonry type in Portugal. No reinforcement was used to connect the infill

surrounding RC frame. The infill panel was constructed as an external leaf and placed in the

external side of the RC beam.

Experimental test setup

The out-of-plane test consisted on the application of

through a system composed by seven nylon airbags

steel structure, as illustrated in Figure 3 and 4.

composed by five vertical and four horizontal alignments of steel bars that

connected. Twelve reinforcement bars cross the RC elements were used to transmit the

reaction from the pressure applied by the airbags in the infill panel. The reinforcement bars

were placed strategically to capture the load distribution throu

frame. In order to avoid the load concentration on the RC elements crossed by the

reinforcement bars, it was used distribute plates

Additionally, it was addicted to the experimental setup twelv

transmission by the reinforcement bars for the reaction steel structure. A wood platform were

placed in the front of the steel structure to support the airbags.

After the realization of the experimental tests it was conclud

equilibrated test setup allows to perform out

any structure to restraint the RC bare frame such it wasn’t verified any out

displacement in the top and bottom beams or e

applied through a hydraulic jack that was placed between a head steel profile in the top of

each column and was connected to the steel profile foundation through two dywidag bars. The

connection between dywidag

Thus this axial load application allows to perform also in



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ity functions and their goodness-of-fit have also been investigated

[8].

(a)

(b)

(c)

Infilled RC frame specimen dimensions (a) General dimensions (b) columns and

and reinforcement detailling.



masonry type in Portugal. No reinforcement was used to connect the infill


plane test consisted on the application of a uniformly distributed surface load

ough a system composed by seven nylon airbags, which reacts against a

steel structure, as illustrated in Figure 3 and 4. This self-equilibrated steel structure is

composed by five vertical and four horizontal alignments of steel bars that

welve reinforcement bars cross the RC elements were used to transmit the


were placed strategically to capture the load distribution throughout the entire infilled RC

In order to avoid the load concentration on the RC elements crossed by the

reinforcement bars, it was used distribute plates transmitting the loads uniformly.

Additionally, it was addicted to the experimental setup twelve load cells to control the load


placed in the front of the steel structure to support the airbags.

After the realization of the experimental tests it was concluded that this experimental self

equilibrated test setup allows to perform out-of-plane experimental tests without the need of

any structure to restraint the RC bare frame such it wasn’t verified any out

displacement in the top and bottom beams or even in both of the columns The axial load was



bars and the head and foundation steel profile are articulated.

Thus this axial load application allows to perform also in-plane experimental tests.


fit have also been investigated

b)

c)

b) columns and (c) beams dimensions



masonry type in Portugal. No reinforcement was used to connect the infill panel and the


a uniformly distributed surface load

which reacts against a self-equilibrated

equilibrated steel structure is

composed by five vertical and four horizontal alignments of steel bars that are rigidly

welve reinforcement bars cross the RC elements were used to transmit the


ghout the entire infilled RC

In order to avoid the load concentration on the RC elements crossed by the

uniformly.

e load cells to control the load


ed that this experimental self-

plane experimental tests without the need of

any structure to restraint the RC bare frame such it wasn’t verified any out-of-plane

ven in both of the columns The axial load was



bars and the head and foundation steel profile are articulated.

plane experimental tests.

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(a)

(b)

(c)

Fig. 3 - Layout of the out-of-plane experimental test setup (a) Front view (b) Lateral View (c) Plan view.

Where, 1- Foundation Steel profile; 2- Dywidag steel bar (ø30mm) used to connect the

foundation steel profile and reaction slab; 3- steel bar (ø20mm) that connect the RC frame to

the foundation steel profile; 4 – Dywidag steel bar (ø30mm) used to apply the axial load; 5 –

head steel profile; 6 - steel bar (ø20mm) that connect the RC frame and the reaction structure

7 – distributed load plate; 8 – Reaction self-equilibrated steel structure; 9 – counterweight; 10

– wood platform 11 - hydraulic jack; 12 – Wooden pallet; 13- wood platform; 14 – infill

panel; 15- RC column; 16- Distributed load plate used in the RC column

(a)

(b)

Fig. 4 - General view of the experimental test setup a) Front view b) Lateral view



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The level of pressure inside the airbags was controlled by two pressure valves that were

commanded in function of the out-of-plane displacement of the central point of the infill panel

that was used as a control node and was continuously acquired through a data acquisition

system during the tests (Figure 5a). Previously to the experimental campaign it was performed

a calibration methodology between the load cells (Figure 5b) and the airbags in order to

obtain the relationship in terms of load distribution with the increase of the distance between

the steel structure and the maximum extent of the airbags.The axial load was controlled by

two load cells with the maximum capacity of 350kN, placed in the top of each column (Figure

5c).

(a) (b) (c) Fig. 5 - General view of a) Pressure valvs b) Load cells and c) axial load cells.

Instrumentation

The instrumentation of the experimental tests was composed by a total of twenty three

variable displacement transducers (LVDTs), as illustrated in Figure 6, and were divided in 3

different groups according to the corresponding measurement objective: i) measurement of

the infill panel out-of-plane displacements (13 LVDTs) ii) measurements of the out-of-plane

rotation between the infill panel and the surrounding RC frame (8 LVDTs) and iii)

measurement of the RC frame out-of-plane displacements (4 LVDTS).

Fig. 6 - Layout of the out-of-plane experimental tests instrumentation.

Loading condition

As previously stated, the aim of the present experimental campaign is to better understand the

out-of-plane behaviour of the infills behaviour, in particularly when submitted to monotonic

and cyclic loading. Additionally, it was varied the axial load condition between the two

experimental infill panels such as the monotonic test was subjected to an axial load value of

Legend:

OOP masonry infill

wall displacement

OOP rotation

infill - RC frame

OOP RC frame

displacement

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300kN (Inf_01) and the other one wasn’t subjected to any axial load (Inf_02). This loading

condition was defined to better understand the axial load effect in the out-of-plane response of

the masonry infill wall.

Cyclic out-of-plane displacements were imposed at the infill panel with steadily increasing

displacement levels. The adopted load paths are summarized in Figure 7 and for each lateral

deformation demand level, three cycles were repeated. The following nominal peak

displacement levels (in mm) were considered: 2.5; 5; 7.5; 10; 15; 20; 25; 30; 35; 40; 45; 50;

50; 55; 60; 65;70 60 and 65. The control node adopted in both of the experimental tests was

defined to be the central point of the masonry infill panel where is expected to occur the

concentration of the deformation

Fig. 7 - Loading history: out-of-plane input displacement at the control node.

EXPERIMENTAL RESULTS

Aiming at characterize the monotonic and cyclic out-of-plane behaviour of the infill masonry

walls, with and without axial loading in the RC columns, the force-displacement hysteresis

are presented in Figure 8a and b respectively. The out-of-plane drift is calculated in function

of the infill panel central point.

The analysis of the force-displacement hysteretic behaviour focused on the following main

issues: i) the comparison and identification of the main differences in the shapes of the

envelopes of the monotonic and cyclic response test results; ii) evaluation of the initial

stiffness, cracking force and corresponding drift iii) characterisation of the correlation found

between the maximum strength and the cracking force iv) characterization of the strength

degradation.

The results’ analysis can be summarised as described in the following:

The initial column stiffness was slightly affected by the axial loading in the RC columns. It

was verified in the infill panel Inf_01 about 5% more initial stiffness when comparing with

the other one;



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The initial cracking was verified for lower out-of-plane drift values for the Inf_02, about 10%.

The cracking force in both experimental tests was about 50kN.

The maximum out-of-plane force was 10% higher for Inf_01 and occurred for higher out-of-

plane drift demand (about 15%). It was verified that the relationship between the maximum

out-of –plane force and the cracking force higher for the Inf_01.

Finally, it can be observed a higher strength degradation for the Inf_01 when compared with

the Inf_02.

(a) (b)

Fig. 8 - Out-of-plane force-displacement hysteresis: a) Inf_01 b) Inf_02.

Aiming at a detailed observation of the damage evolution during the experimental tests within

the present work testing campaign, each test was stopped at the end of the last cycle of each

displacement level in order to highlight and register new cracks in the last cycle and/or the

evolution of existing ones. Visual observation of the damage evolution during the tests

yielded the information described in the following paragraphs. The final damage shape of

both of the infill panels are presented in Figure 9 and 10.

It was observed for both of the experimental tests that the initial crack was in the top joint

between the RC beam and the first line of bricks, and initiated between 0.0075 and 0.01m;

At the displacement when occurs the maximum force, it was observed in the Inf_01 test a

vertical cracking in the middle of the infill panel, and in the Inf_02 it was observed a trilinear

cracking similar to the slabs with similar constrains conditions;

The final cracking shape of the Inf_01 was vertical, with detachment between the infill panel

and the surrounding RC frame in the top and bottom joints, as can be observed in Figure 9. In

the In_02 it was observed a trilinear cracking with the deformation concentrated in the middle

point of the wall, with slight cracking in the top joint, and are illustrated in Figure 10. In the

back of both of the experimental tests it was observed similar cracking, with only cracking of

the top joints and crushing of some bricks.

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Fig. 9 - Final cracking shape of Inf_01: a) Front view b) Back view.

(a) (b)

Fig. 10 - Final cracking shape of Inf_02: a) Front view b) Back view.

CONCLUSION

This paper reports an experimental campaign carried out at the Laboratory of Earthquake

Engineering at the Faculty of Engineering of University of Porto in order to study the out-of-

plane behaviour of masonry infill walls. For this, two full-scale infill panels were constructed

and were subjected to out-of-plane monotonic and cyclic loading, with and without axial

loading at the RC columns. The out-of-plane loading was applied by an airbags system that

reacts in a self-equilibrated structure. The experimental test setup was presented, including all

the instrumentation and loading condition



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It was observed that the infill panel subjected to monotonic loading and with axial load in the

RC columns had about 5% more initial stiffness when comparing with the other one. The

maximum out-of-plane force was 10% higher for the infill panel subjected to monotonic

loading and occurred for higher out-of-plane drift demand (about 15%). Finally, it can be

observed a higher strength degradation for the Inf_01 when compared with the Inf_02.

For both of the experimental tests was observed that the initial crack was in the top joint

between the RC beam and the first line of bricks, and initiated between 0.0075 and 0.01m.

The final cracking shape of the infill subjected to monotonic out-of-plane loading was

vertical, with detachment between the infill panel and the surrounding RC frame in the top

and bottom joints. In the other was observed a trilinear cracking with the deformation

concentrated in the middle point of the wall, with slight cracking in the top joint. In the back

of both of the experimental tests it was observed similar cracking, with only cracking of the

top joints and crushing of some bricks.

Further experimental studies will be realized in the future regarding to the characterization of

simples or double leafs infill masonry walls out-of-plane behaviour with and without

previously out-of-plane damage.

ACKNOWLEDGMENTS

The authors would like to acknowledge the technicians of the Laboratory of Earthquake and

Structural Engineering (LESE), Mr. Valdemar Luis and Mr. Nuno Pinto for their support in

the experimental activity reported in this paper, and Preceram for the provision of all the

bricks used in the experimental tests. This experimental research was developed under

financial support provided by “FCT - Fundação para a Ciência e Tecnologia”, Portugal,

namely through the research project PTDC/ECM/122347/2010 - RetroInf – Developing

Innovative Solutions for Seismic Retrofitting of Masonry Infill Walls.

REFERENCES

[1]-R. Vicente, H. Rodrigues, H. Varum, A. Costa, and J. M. Silva, "Performance of masonry

enclosure walls: lessons learned from recent earthquakes," Earthquake Engineering and

Engineering Vibration, vol. 11, 2012.

[2]-X. Romão, A.A.Costa, E. Paupério, H. Rodrigues, R. Vicente, H. Varum, et al., "Field

observations and interpretation of the structural performance of constructions after the 11

May 2011Lorca earthquake," Eng. Fail. Anal. , vol. 34, pp. 670-692, 2013.

[3]-F. Luca, G. Verderame, F. Gómez-Martinez, and A. Pérez-García, "The structural role

played by masonry infills on RC buildings performances after the 2011 Lorca, Spain,

earthquake," Bull Earthquake Eng, vol. 12, pp. 1999-2006, 2014.

[4]-A. Penna, P. Morandi, M. Rota, C. Manzini, F. Porto, and G. Magenes, "Performance of

masonry buildings during the Emilia 2012 earthquake," Bull Earthquake Eng, vol. 12, pp.

2255-2273, 2014.

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[5]-G. Calvi and D. Bolognini, "Seismic response of reinforced concrete frames infilled with

weakly reinforced masonry panels," Journal of Earthquake Engineering, vol. 5, pp. 153-185,

2001.

[6]-S. Hak, P. Morandi, and G. Magenes, "Out-of-plane experimental response of strong

masonry infills," presented at the Second European Conference on Earthquake Engineering

and Seismology, Istanbull, 2014.

[7]-H. Rodrigues, H. Varum, and A. Costa, "Simplified Macro-Model for Infill Masonry

Panels " Journal of Earthquake Engineering, Volume vol. 14, pp. 390 - 416 2010.

[8]-A. Furtado, A. Costa, H. Rodrigues, and A. Arêde, "General characteristics of the

Portuguese RC building stock with Infill Masonry walls," presented at the 9th International

Masonry Conference (9IMC), Portugal, 2014.

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