EVALUATION OF STRUCTURAL PERFORMANCEFOR CONFINED MASONRY WALLS RETROFITTED
WITH WIRE MESH AND WITH DISPOSABLE FIBER
MATS
Lourdes Ana Maria Cardenas Paredes *MEE08171

Supervisor: Tomohisa MUKAI**ABSTRACTThis study presents a prediction method on structural performance for confined masonry walls and for
retrofitting of confined masonry walls by comparison with results of structural test performed atstructural laboratory in CISMID UNI-Lima-Peru. The cyclic loading tests on walls were carried out
two different kinds of the retrofitted schemes of confined masonry walls: the one is a wire meshwrapping alternative and the other is the combined materials such as adhesive and disposal mats withdifferent arrangements. On the other hand, the methodology to evaluate structural performance forretrofitted confined masonry wall is suggested. And the accuracy of the prediction method could beverified, and the applicability of this model in analysis is confirmed using pushover analysis.
Keywords: Confined masonry wall, retrofit method, structural performance evaluation, analyticalmodel.

1. INTRODUCTION
The masonry is one of the materials commonly used around the world. At the time of colonization bySpain, it was the main material used to build the first cities in South America, including Peru. The
evolution in construction started with adobe housing, quincha or baharenque, adobe with quincha andactually with clay bricks. Reasons such as low cost, material availability ease of fabrication anddurability make this material remains still common throughout years.
In the last decades approximately 70% of housings in Peru were built using masonry walls.
Among these 40% has been constructed without reinforcement elements or without structural design.
This problem mainly occurs in rural areas or small cities, because those local people build houses
valuing only an economical problem and/or are also lack of technical knowledge. This is the reason
why many houses in Peru are not following the construction requirements given by the codes. There isalways the possibility of severe earthquake occurrence in this area, and such non-engineeringbuildings without reinforcement are very vulnerable.
Based on the above screen of damages, it is necessary to develop new alternatives aiming at
improvement of seismic structural performance. Such systems which improve the safety of thehousing and avoid loss of lives should be resistant, durable and with low cost. Started many years ago
the development of different techniques that allow the existing masonry buildings to be retrofitted;
however in Peru there are only a few comparisons of experimental and analytical simulation studies.
For this reason a further development of retrofit technique of masonry buildings is required as apriority issue.
* Center for Earthquake Engineering Research and Disaster Mitigation (CISMID) of Peru.
** International Institute of Seismology and Earthquake Engineering, Building Research Institute,Japan12. SUGGESTION OF EMPIRICAL FORMULAS TO PREDICT THE STRUCTURALPERFORMANCE FOR ORIGINAL CONFINED MASONRY WALLS AND RETROFITONE
For the modeling confined masonry wall in the analysis, it is necessary to understand some concepts
for the evaluation of walls. The originals confined masonry walls are divided by two components: themasonry wall and RC frame, in order to find individually equations that could evaluate unique points,
and then the idealization curve for the originals confined masonry walls is suggested.
2.1 Idealization Curve of Original Confined Masonry
For idealization curve, we must know and analyze the process of structural damages on confined
masonry walls. Through this investigation, it is possible to understand the behavior of the wall andidentify the damage for each structural element.
Actuador

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382

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6228
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248 205

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822278

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374309130

180018276

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110 228289314382309

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130248First cracks

231

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35218248 205
248

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278231

206
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182

4260

260

382

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31182

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Stiffness degradations
Stiffness and strength degradations.
Figure 1: Process of structural damagesa) Elastic behavior: The wall keeps elastic behavior until the first cracks are observed on confined
masonry walls. When the small displacement is given by the cyclic lateral loading test, the horizontal
cracks appears in columns, and the small cracks appear on the wall.
b) Stiffness degradations: After the first cracks, there are an increment of the cracking until the initial
diagonal cracks appears. Then the confined masonry wall shows a slope post–elastic stiffness. This
stiffness has less value than the initial; and then the specimen reaches at maximum strength.
c) Stiffness and strength degradations: After the confined masonry walls reach the maximum strength,
it keeps constant value until the diagonal cracks penetrate through the RC Frame and the wall fails inshear wall. Then the stiffness decreases with a negative slope with a drastic reduction of the strength.
2.1.1 Idealization Curve of Masonry Wall using Peruvian Codea) Cracking State: Peruvian masonry design code for walls defines an elastic shear limit (Ve) toprevent the cracks and establish a cracking control. The intention is to avoid the cracks of masonrywall due to moderate earthquake, where Ve is given by the following equation:

Ve = 0.55 ⋅ Vm
Where Ve is the shear force of a wall and Vm is ultimate shear strength associated with thediagonal cracking.
b) Maximum and Ultimate State: The maximum shear strength (Vm) of the walls is calculated by thefollowings formula for the clay bricks.
Vm = 0.5 ⋅ vm' ⋅ α ⋅ t ⋅ L + 0.23 ⋅ Pg
Where ν´m is characteristic resistance of masonry to obtained from diagonal test or parametercan consider empirical values recommended by the Peruvian code for typical kinds of blocks; α isfactor reduction (α=1), t is thickness, L is length of the wall and Pg is Axial Load.
c) Idealization Curve: Under the prior definitions based on the Peruvian code, an idealization curve is
proposed using the relations between the cracking point (55% of Vm) and the maximum shear (Vm)like figure 2.

214VmIdelization Curve from Peruvian Masonry
CodeShear Force (ton)

120.55Vm

1086420Ke01.2 ⋅ (0.55Vm ) ⋅ H
δ SHEAR =G⋅A

dmax= drift(1/800).H

24dlast=drift(1/200).H

68101214

Displacement (mm)Figure 2: Idealization curve of masonry wall
2.1.2 Idealization Curve of RC Frame using Japanese Equations
For the idealization of the RC Frame that confines the wall, the specifics points of beam and columns
were calculated. These calculations are solved by Japanese equations, where the following equations
present the flexural cracking moment (Mc) and the yielding moment (My), stiffness ratio of beam andcolumn.
Beam

Mc = 1.8 ⋅ σ B ⋅ Ze
My = 0.9 ⋅ At ⋅ σ y ⋅ dFlexural Cracking Moment (Mc):Yielding Moment (My):(1)(2)

Columns

Flexural Cracking Moment (Mc): Mc = 1.8 ⋅ σ B ⋅ Ze + N ⋅ D / 6(3)N⎛
⎞Mu = 0.8 ⋅ at ⋅ σ y ⋅ D + 0.5 ⋅ N ⋅ D ⋅ ⎜1 −Yielding Moment (My):⎟ (4)⎝ b ⋅ D ⋅ Fc ⎠In RC frame:Stiffness Degrading Ratio: α = (0.043 + 1.64( Es Ec)pt + 0.043( a D) + 0.33no) * (d/D) 2(5)S=

Initial Stiffness(S)Where:

24 EI ⎛ 1 + 6γ ⎞⎟⎜H 3 ⎜⎝ 4 + 6γ ⎟⎠IB: Inertia of Beamγ = IB I(6)CIC: Inertia of Column

QQc

Smax=S*αSdFigure 3: Idealization curve on RC frame
2.1.3 Idealization Curve by Combination of Masonry Wall and RC FrameTo obtain the idealization curve of confined masonry wall, there was some considerations as thebehavior and interaction between the RC Frame and masonry wall; at the beginning of the test, bothelements simultaneously deformed at the same time, therefore the following figures showed the RC
Frame and additionally the masonry wall for analytical model are result of combination, considering
the adaptation condition of displacement.

3

As for the idealization curve of masonry wall, the stiffness in the elastic zone and horizontal
capacity cover the majority in the confined wall, comparing to RC Frame. On the other hand, when themasonry wall and RC Frame are idealized as confined masonry wall, this idealization curve has a goodaccuracy and it can predict the 80% of maximum strength obtained in the test (see Figure 4).
Idelization Curve by Masonry Wall and RC Frame
25Force (ton)2015
Masonry Wall
Test-wall 02

10RC Frame 02

5Idealization Curve on
Confined Masonry Wall

005

1015

20

25

Displacement (mm)Figure 4: Idealization curve on Masonry wall and RC frame
2.2 Idealization Curve of Confined Masonry Wall retrofits with Wire Mesh
For the retrofit of walls, two techniques were used; the first one is commonly used in Peru and isretrofit technique with wire mesh. Another is a new proposal using rice bag with adhesive; bothtechniques is showed in the below figure (below side is figures showing the specimen retrofitted walls,and above side is figures showing specimen without retrofit) where we can see their effectiveness ofretrofit, in all the cases, the specimen with better performance is the specimen retrofitted wall 02,
therefore this retrofitted wall will be focused and investigated.

Lateral Load (t)10Max.LoadEnvelope Curve -Wall 08 original

2525

Max LoadCrack

10152025-10-15-20-25
Displacement (mm)Crac

50-25 -20 -15 -10 -5-5 0

51015

2020Max.Load

15Failure

100
520

15

5-25 -20 -15 -10 -5 -5 0

Envelope Curve -Wall 06 original

2520

Lateral Load(t)15Envelope Curve Wall 03 Original

25-10

100-30 -25 -20 -15 -10 -5-5 0-10-20-15-25-20-30-25

Displacement (mm)

Crack

5-15

510 15 20 25

Crack

510Displacement(mm)152025Crack

50-25 -20 -15 -10 -5-5 0

510 15 20 25-15-20-25
Displacement(mm)Envelope Curve -Wall 06 Retrofitted

Envelope Curve -Wall 08 retrofitted

202515Max.Load

20

105Crack

0-25 -20 -15 -10 -5-5 0

15Failure510-10-15-20-25
Displacement(mm)152025Lateral Load(tf)Failure3530
25
Max Load
2015
Failure10Crack
50-25 -20 -15 -10 -5-5 0 5 10 15 20 25-10-15-20-25-30-35
Displacement(mm)Lateral Load (tf)Max

Lateral Load (tf)

Lateral Load (tf)

35
30
25
20151050-25 -20 -15 -10 -5-5 0-10-15-20-25-30
-35

10-10

Displacement(mm)Envelope Curve -Wall 03 retrofitted

Envelope Curve-Wall 02 Retrofitted

Max.Load

15
Lateral Load(t)Failure20

Lateral Load(t)Envelope Curve - Wall 02 original

Max.Loa

1050-25 -20 -15 -10 -5-5 0

K elastic

510

15

20-10-15-20-25

Displacement(mm)Figure 5: Envelopes with and without retrofits (wire mesh and disposable fiber mats)
2.2.1 Idealization Curve of retrofit portion
The face of specimen retrofitted wall 02 has arrangement as “X” shape using the wire mesh, isremoved to repair and the mortar is newly pasted on this part. Therefore the mortar and wire mesh is
focused for seismic evaluation of retrofit portion. Both materials are analyzed as bilinear curves, thesecurves was obtained from mortar and wire mesh test, and idealized using general equation, where thestrength is equal to stress of each material and multiplied by section area.

425For the retrofit wall, the influence of the portion of the masonry surface removed to replace
the retrofit portion (wire mesh and mortar) must be considered. In the case of masonry wall, newidealized curve will be the one of masonry wall (see 2.1.1) considering the difference of wall area,
therefore the limits states will be taken into account. This retrofit was only applied in masonry wallzone where had already damaged, the RC Frame has a degrading stiffness and should be considered
only the degrading stiffness (see Figure 6).
Strength & Displacement-Frame 023

Flexural Strength(tn2.5
21.5
10.5
Klast=Kinitial for retrofit

0024
6
Displacement(mm)108Figure 6: Idealization Curve of RC Frame considering the degrading stiffness
2.3 Idealization Curve of Retrofit Confined Masonry Wall
After the computation separately for retrofit portion and new masonry wall and RC frame, then thenext step for idealization curve of retrofit wall is combination of all the elements. In the figure 7, themaximum strength of the idealization curve for retrofitted confined masonry wall is represented 80%
of test result and the accuracy of this calculation method is generally good. However, there is a roomof further investigation in terms of predictions of stiffness, because this investigation was assumed
masonry wall without damage and focused only maximum strength.
Retrofit Confined Masonry Wall 02
30.0

100%

25.0

80%

TEST

Strength (ton)

20.0
15.0
10.0
5.0

masonry+RC frame+retrofit portion

0.0
0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Displacement (mm)Figure 7: Idealization Curve of Confined Masonry Wall Retrofitted

3. INVESTIGATION OF PROPOSED MODEL USING ANALYSIS SOFTWARE
In order to show how to use this wall model in analysis, analytical model is compared to the test
results using software “Stera3D”; a nonlinear static analysis for the walls. This confined masonry wallis considered, the RC frame and masonry wall individually. As for both the confined masonry wall andretrofitted one, the accuracy of this method is high and the current analysis model could be useful toexpress behavior of the wall.

5-30

Model and Test result on Retrofit Wall-02

30

30

2525

2020

15

15

1010

50-25

-20

-15

-10-5 -5 0

51015

20

25

30

-10

Strength (ton)Strength (ton)Model and Test result on Wall-02

-30

50-25

-20

-15

-10-5-5

51015

20

25

30

-10-15-15-20-20

MonitorTest-25
Stera3D-wall 02-separation of element
-30

0-25

TestMonitor

Displacement (mm)Stera Model3D ( retrofit portion+masonry)+frame-30

Displacement (mm)Figure 8: Comparison of idealization Curve to Results(Left is the Confined Masonry Wall, right is Retrofitted one)

4. CONCLUSIONS The investigations of the test results for the specimen retrofitted shows that retrofit scheme withthe wire mesh is more effective for confined masonry wall.
 The method of idealization by the division of elements (masonry wall, RC frame, and retrofit
portion), using Peruvian masonry code and the Japanese equations is suggested
 As a result of comparison the test results to the idealization curve of confined masonry walls, theidealization curve reaches around 80% of maximum strength of the confined masonry wall test
and even the stiffness could be quite predicted accurately in the elastic range. The investigation
showed that the masonry wall contributes to most horizontal capacity in confined masonry wall.
 As a result of comparison the test results to the idealization curve for retrofitting confined masonrywalls, the results of the idealization curve shows a similarity in 80 %of maximum strength of test
result.
 Results of the simulations performed with Stera3D have a good agreement in case of the bothwalls models. The current analysis model could be useful to evaluate the seismic performance ofthe retrofitted confined masonry wall.

5. RECOMMENDATIONS
As for the evaluation of the stiffness for retrofitted confined masonry wall, there is a room of further
investigation considering actual repair method. The effect of seismic retrofit by disposable mat must
be clear, so it is necessary to carry out the structural test to fail wall part.
ACKNOWLEDGMENTS
I want to express my deepest gratitude to my adviser and supervisor Dr. Tomohisa MUKAI for hiskindly guidance and patience during his teachings and Dr. Carlos Zavala for the confidence he had onme and his support with test data.
REFERENCES
Ministerio de Vivienda y Construcción. “NTC-070- Norma Técnica E.070 Albañilería”
National Institute for Land and Infrastructure Management and Building Research Institute, 2007.08. ,“Manual on Technological Standard Related to Structure of buildings”
Saito, T., 2009,“Structural Earthquake Response Analysis 3D-Manual Building Research Institute,Japan.”
Sencico., San Bartolome., “Comments of Peruvian Masonry Code”
Zavala, C., Chang, L., Arellano, E., 2007, “Factibilidad de Uso de Mallas Electrosoldadas en
Elementos de Confinamiento de Muros de Albañileria”

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