ORIGINAL RESEARCH PAPER

In-plane cyclic tests of seismic retrofits of rubble-stonemasonry walls

Ming Wang1,2 • Kai Liu1,2 • Hongfei Lu2 • Hima Shrestha3 •

Ramesh Guragain3 • Wen Pan4 • Xiaodong Yang4

Received: 12 May 2017 / Accepted: 5 November 2017� Springer Science+Business Media B.V., part of Springer Nature 2017

Abstract The recent catastrophic Gorkha Mw7.8 earthquake in Nepal showed that rubble-

stone masonry houses can be extremely vulnerable and responsible for a large number of

casualties. Seismic retrofitting techniques were experimentally studied for rubble-stone

masonry walls widely used in the Himalayan belt. Four seismic retrofitting techniques were

designed using locally available and affordable materials (e.g., wood, gabion wires, and

tarpaulin). Full-scale walls with and without retrofitting were tested under lateral in-plane

cyclic loads. The failure modes, hysteresis characteristics, and load–displacement

responses were recorded and analyzed. The experiment results show that, with properly

designed inexpensive retrofitting techniques, improvements in structural stiffness, ductility,

and integrity can be achieved to effectively reduce damage during an earthquake.

Keywords Stone masonry � Seismic retrofit � Gabion wire � Wooden bandages � In-planecyclic testing

& Kai Liuliukai@bnu.edu.cn

1 Key Laboratory of Environmental Change and Natural Disaster, Ministry of Education, BeijingNormal University, Beijing 100875, China

2 Academy of Disaster Reduction and Emergency Management, Ministry of Civil Affairs andMinistry of Education, 100875 Beijing, China

3 National Society for Earthquake Technology-Nepal, Kathmandu, Nepal

4 School of Civil Engineering, Kunming University of Science and Technology, Kunming 650500,China

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Bull Earthquake EngDOI 10.1007/s10518-017-0262-z

1 Introduction

Stone masonry buildings are widely used in the Himalayan belt, including Nepal, Ban-

gladesh, and India. These buildings are constructed with stones placed in a random manner

and are therefore susceptible to earthquake damage. The recent catastrophic Gorkha

Mw7.8 earthquake in Nepal showed that non-engineered construction in the regions of the

Himalayan belt, especially rubble-stone masonry houses built from mud mortar, can be

extremely vulnerable and responsible for a large number of casualties during an earth-

quake. Figure 1 shows that houses made of rubble stone and mud mortar suffered severe

damage during the Gorkha earthquake in the mountainous area of Nepal.

Most stone masonry buildings in the Himalaya belt have one or two stories and have

double-leaf walls built with loose rubble stones of variable shape and dimensions. Voids

are filled with mud mortar and small stones. The double-leaf walls typically have poor

seismic performance owing to inadequate connections between leaves causing bulging/

separation (delamination) of walls in the two distinct wythes during an earthquake (Fig. 1).

Moreover, floors and the roof sit directly on the stone walls with a limited number of wood

columns supporting the vertical loads. There is a lack of connection between walls in two

orthogonal directions at L and T junctions and also between walls and roofs. No earth-

quake-resisting elements, such as horizontal bands, sufficient through stones, and vertical

reinforcements, are used. Because construction materials such as brick, cement, and steel

are expensive in regions of the Himalayan belt, particularly mountainous rural areas with

limited road access, non-engineered stone buildings will continue to be used in those

regions, which poses a great future risk. There is an urgent need to build/retrofit these

buildings employing practical, inexpensive, and effective construction/retrofitting tech-

niques to improve their seismic performance and thus reduce casualties and increase

resilience in low-income communities during earthquakes.

Numerical and experimental studies have been conducted to investigate the seismic

performance of stone masonry structures. Theoretical prediction and experimental verifi-

cation have been conducted to investigate the mechanical properties and performance of

natural stone masonry under compressive and shear loadings (Cominelli et al. 2017; David

et al. 2012) that have provided some basic values of parameters affecting masonry strength.

The methodology of the seismic strengthening of masonry structures varies greatly.

Existing technologies mainly include confinement, stitching and grout/epoxy injection, and

surface treatment. The confinement technique uses reinforced/steel columns at the corners

Fig. 1 Typical stone masonry damaged during the 2015 Gorkha earthquake in Nepal

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and intersections to confine the walls (Bhattacharya et al. 2014). Stitching and grout/epoxy

injection involves injecting grout or epoxy into the masonry walls. Comparative experi-

mental and numerical studies (Milosevic et al. 2013; Miranda et al. 2017; Isfeld et al. 2016;

Silva et al. 2014, 2017) confirmed the effectiveness of grout injection as a reinforcement

technique. For example, the injection of lime-based mortar into stone masonry walls has

been found to increase the strength of walls by a factor of 3 (Almeida et al. 2012). Surface

treatment usually applies steel mesh, bars, wire mesh or polymer strips/mesh to the

building exterior (Bhattacharya et al. 2014). Kadam et al. (2014) applied welded wire mesh

and micro-concrete to reinforce masonry buildings and it is experimentally verified that the

shear strength and ductility of masonry wall is greatly enhanced. Experiments also show

that fiber-reinforced polymers (FRP) is an effective reinforcement material though costly,

such as placing glass fiber nets/grids into masonry during construction (Sisti et al. 2016),

using externally bonded glass fiber strips (Fayala et al. 2016) or carbon fiber reinforced

polymer laminates (Rinaldin et al. 2017). The selection and implementation of these

methods depend on the types of local structural systems and customs of construction

practice, and are often affected by the social and economic conditions of local commu-

nities. The applications of many well-tested techniques may be restricted in rural areas

because of the relatively high cost and complicated procedures.

The present study performs comparative experiments to explore practical, inexpensive,

and effective retrofitting techniques for rubble-stone masonry buildings that are largely

used in the Himalayan belt. A series of wall cyclic tests is conducted to evaluate the

effectiveness and applicability of different techniques. The overall behavior, failure mode,

load capacity, ductility, and hysteretic behavior of the walls are presented for different

building/retrofitting techniques. The remainder of the paper is organized as follows. Sec-

tion 2 gives details of the schemes to be tested while the Sect. 3 presents the experimental

setup. Experimental results are presented in Sect. 4 and discussed in Sect. 5. Conclusions

are given in Sect. 6.

2 Retrofitting schemes and test specimens

Retrofitting schemes are designed according to three principles: (1) the use of locally

available and affordable materials, (2) improvement of the structural integrity, ductility or

stiffness, and (3) cost efficiency and easy implementation. Strengthening approaches that

include the use of cement and steel are not appropriate considering their high cost or

difficult delivery to rural mountainous areas. As an alternative, wood and gabion wire are

relatively easy to obtain and considered inexpensive in the mountainous areas of Nepal.

Four building/retrofitting techniques are therefore designed on the basis of these materials,

aiming to improve the integrity and load-carrying capacity of rubble-stone masonry

structures. Five wall specimens, one as a reference specimen without a retrofit and four

retrofitted with different approaches, were prepared in the laboratory for in-plane cyclic

testing. Figure 2 shows the five specimens to be tested in the laboratory.

2.1 Stone masonry wall without a retrofit (NR)

A stone masonry wall with dimensions of 2400 mm 9 2100 mm 9 400 mm

(width 9 height 9 thickness) was constructed as a reference specimen without retrofitting

(W1), as shown in Fig. 2a. This wall contains natural rubble stones that are widely used in

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Nepali mountainous areas. The construction of the wall followed the practice often used by

local masons in such areas. Thin layers of mud were applied between stones as mortar. Ten

through/corner stones were used during the construction according to the traditional rules

of local construction. Wall specimens with various retrofitting techniques were constructed

following the same practice used for the reference specimen (W1), in terms of stone

selection and construction procedures.

2.2 Horizontal wooden bandages and posts combined with gabion-wirejacketing (WB 1 GWJ)

The first retrofitting technique combines wooden bandages and posts and gabion-wire

jacketing. Figure 2b shows that wooden bandages are provided in four different layers: the

first band at the bottom (plinth level), second at a height of 825 mm (sill level), third at a

height of 2025 mm (lintel level), and fourth at the top (floor level) as per the Nepal

National Building Code NBC 203. The wooden bandages are made from two connected

wooden sticks with a cross-section of 75 mm 9 38 mm. Four equally spaced wooden

NR: W1 WB+GWJ: W2

GWM:W3 GWK: W4

TS: W5

Gabion wire

Wooden post

Wooden bandage

Gabion wire mesh

Wooden post

Gabion wire

Tarpaulinstrips

(a) (b)

(c) (d)

(e)

Fig. 2 Five specimens to be tested

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battens with a cross-section of 50 mm 9 30 mm are used to connect the two wooden

sticks. The wooden bandages have a dimension of 2100 mm 9 400 mm so as to fit the size

of the wall. The four wooden posts with a cross-section of 75 mm 9 75 mm are placed on

both sides of the wall and connected to the four wooden bandages using steel strips nailed

to bandages. The purpose of using four layers of wooden bandages is to horizontally

restrict the wall at different heights and to hold the two leafs of the wall together. The

overall flexural capacity and integrity are expected to be improved with the mutual support

of the wooden bandage and post. Additionally, gabion wires with a diameter of 2.94 mm,

which are commonly used in Nepal, were placed on the wall as a jacketing spaced at

75 mm both vertically and horizontally. Through wires, with a diameter of 2.94 mm, were

used to tighten the gabion wires at the back and front of the wall with a spacing of 300 mm.

The gabion-wire jacketing restricts the wall both horizontally and vertically so that the

overall flexural capacity can be increased. Moreover, the gabion-wire jacketing can help

prevent the out-of-plane falling of stones under extreme in-plane loading. Therefore, the

combination of the wooden bandage and post and gabion-wire jacketing (WB ? GWJ) is

expected to appreciably improve the seismic resistance of rubble-stone masonry walls.

2.3 Horizontally layered gabion-wire meshing with wooden posts (GWM)

In the second retrofitting technique, horizontally layered gabion-wire mesh is proposed to

substitute the wooden bandage considering that it is lighter and more affordable in rural

regions. Figure 2c shows that wire mesh was placed at the plinth, sill, lintel, and floor

levels. Short wooden stitches were used at the edge of each layer to provide a connection

with the wooden posts via nailed steel connecters. The horizontally layered gabion-wire

mesh is expected to resist a shear force under lateral loading.

2.4 Gabion-wire knitting (GWK)

The two aforementioned reinforced techniques are designed for newly built buildings.

Herein a gabion-wire knitting technique is proposed for retrofitting existing stone masonry

structures. It involves drilling holes in the walls and placing wires through the holes to knit

the stones. Wires with diameter of 2.94 mm were placed horizontally with an approximate

spacing of 75 mm all the way around the wall. For vertical knitting, the wires were tied

through the wall once every three or four layers of stone with a horizontal spacing of

75 mm, as shown in Fig. 2d. The purpose of using gabion-wire knitting is to restrict the

wall both horizontally and vertically so that the overall stiffness increases. Moreover, wire

knitting at a certain density can help prevent the out-of-plane falling of stones under

extreme in-plane loading.

2.5 Horizontally wrapped tarpaulin strips (TS)

The fourth technique is designed for both newly built and existing buildings with exter-

nally bonded fibers and has previously been investigated for rural rammed earth con-

struction (Liu et al. 2015; Wang et al. 2016). The tarpaulin strips used in this study has a

mass density of 680 g/m2 and a thickness of 0.83 mm, with a tensile strength of

49.03 MPa. Figure 2e shows that tarpaulin strips were wrapped horizontally around the

wall using NF compound as adhesive. More details on the adhesive and implementation of

the technique can be found in the literature (Liu et al. 2015; Wang et al. 2016). The bonded

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tarpaulin strips on one hand increase the overall stiffness of the wall and on the other hand

prevent local out-of-plane failure.

3 Experimental setup

The experimental verification of the retrofitting techniques involved in-plane cyclic tests of

the five wall specimens. The tests were performed in a laboratory of Kunming University

of Science and Technology in Yunnan Province, China. The test groups are listed in

Table 1. All tested walls were cast on a concrete footing beam with dimensions of

2400 mm 9 400 mm 9 502 mm (length 9 width 9 depth). The footing beam was bolted

to the ground to ensure a fixed boundary condition. Figure 3 shows that a fixed steel frame

(yellow frame) was built for the vertical loading and a hinged steel frame for horizontal

loading of the walls. A constant vertical pressure of 0.068 MPa was applied to the top of

the wall throughout the test to represent the gravity loads transmitted from the upper story

of a typical two-story building. The vertical hydraulic jack was connected to the fixed steel

frame, and the vertical loading was applied to the wall via the concrete loading beam

positioned at top. A steel loading beam was placed between the concrete beam and the

vertical hydraulic jack to ensure that the load can be applied uniformly to the wall. Since

the vertical hydraulic jack did not move with the wall, rollers were placed on the steel

beam to ensure a constant vertical loading when wall deforms. The hinged steel beam on

top was connected to the two steel columns by bolts. The columns were seated on rolling

supports to allow free rotation of the frame and to ensure the steel beam was always

horizontal during movement. The steel beam also prevented the overall rotation of the

tested walls under extreme loads. Cyclic lateral loads were applied by controlling the

horizontal displacement measured by linear variable differential transformers at two ends

of the walls with an increment of 2 mm for each full cycle. The testing stopped when

severe structural failure or damage was observed.

Table 1 Description of tested specimens

Wallspecimenno.

Retrofitting technique Retrofitting materialsused

W1 Non-retrofitted (NR) as a reference specimen –

W2 Retrofitted with built-in wooden bandages with wooden postscombined with gabion wire jacketing (WB ? GWJ)

Wood and gabionwires

W3 Retrofitted with built-in horizontally layered gabion wire meshingand wooden posts (GWM)

Wood and gabionwires

W4 Retrofitted with gabion wires knitting (GWK) Gabion wire only

W5 Retrofitted with horizontally wrapped tarpaulin strips (TS) Tarpaulin strips andNF compound

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4 Experimental results

The experimental results of the five cyclic tests are summarized in terms of (1) the

structural behavior and failure mode, (2) the hysteresis behavior, and (3) the load–dis-

placement response. The failure mode describes the overall seismic behavior, particularly

at the failure stage, including the cracking patterns and damage states. The load–dis-

placement response quantifies the relationship between the horizontal displacement and the

corresponding maximum force in each cycle. The hysteresis behavior reflects the energy

dissipated under the cyclic loading, which is the seismic capacity of a structure.

4.1 Overall behavior and failure modes

4.1.1 Non-retrofitted specimen (NR: W1)

Specimen W1 was the reference specimen without retrofitting. The rubble stones used

varied greatly in terms of size and shape. The thin layers of mud mortar used to fill the

voids did not contribute to the shear capacity. The lateral loading was mainly resisted by

inertial friction between stones. The failure mode of W1 was typical shear failure with

diagonal cracking patterns. Figure 4a shows that the cracks originated in the top center

section at a horizontal displacement of 8 mm. The cracks further extended to the center and

lower center area at 14 mm and small crushed stones started to fall. As the displacement

continued to increase to 22 mm, vertical cracks started to form at two corners. At 28 mm,

the diagonal cracks extended to lower left and right corners. The testing terminated at

32 mm when the center of the wall was squeezed outward and the wall underwent severe

out-of-plane deformation. A similar diagonal cracking pattern was observed on the back of

the tested wall.

Horizontal Hydraulic JackHinged Steel Frame

Concrete Foo�ng Beam

Tested Specimen Ver�cal Hydraulic Jack

Fixed Steel Frame

Fig. 3 Schematic drawing of the experimental setup

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Specimen W1Green 8mmYellow 14mmOrange 22mmRed 28mm

Specimen W2Green 12mmYellow 20mmOrange 30mm

Specimen W3Green 14mmYellow 28mmOrange 30mm

Specimen W4Green 62mmYellow 76mmOrange 100mmRed 112mm

Specimen W5Green 22mmYellow 24mmOrange 38mmRed 56mm

(b)

(a)

(c)

(d)

(e)

Fig. 4 Structural damage and cracking patterns at failure (left: front view, right: back view)

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4.1.2 Retrofitted specimen with wooden bandages and gabion-wire jacketing(WB ? GWJ: W2)

Specimen W2 used wooden bandages to increase flexural strength and gabion-wire jack-

eting to increase overall integrity and to prevent possible out-of-plane failure. Figure 4b

shows that cracks started to appear near the center of the wall at 12 mm. More diagonal

cracks were observed at 20 mm and a few horizontal cracks at 30 mm. In contrast to the

case for W1, the cracks in W2 were mainly confined in the center area and did not extend

to corners at the top and bottom. After the horizontal cracks formed at 30 mm, the upper

half of the wall started to slide along the horizontal cracks with an increase in deformation,

which allowed the wall to deform further. However, stones at the center area started to be

squeezed outward during the cyclic pushover. The testing terminated at 66 mm when the

stone at the center fell out. In the final stage, the center areas at both front and back sides of

the wall appeared to be pushed outward and the maximum out-of-plane deformation

reached 150 mm (front) and 130 mm (back). The stones at the left and right sides of the

wall were also squeezed outward in the plane. In contrast to the case for W1, vertical

cracks did not form at either the left or right corner in W2.

4.1.3 Retrofitted specimen with horizontally layered gabion-wire meshing (GWM:W3)

Specimen W3, instead of having the wooden bandages used for W2, had four layers of

gabion-wire meshing that increased its flexural strength. Figure 4c shows that its cracking

pattern was different from the diagonal cracking patterns of W1 and W2. Vertical cracks

began forming at left and right sides of the wall at 14 mm and moved to center areas at 28

and 30 mm. The meshing layers made a limited contribution to the shear resistance and

even decreased the friction at the interface between the mesh and stone. The meshing

layers were therefore further bent under the horizontal pushing force, which allowed local

vertical deformation starting at the two sides of the wall. This explains why vertical

deformation occurred during testing. Because of the gradually extending vertical cracks,

the right side of the wall had out-of-plane failure and local delamination appeared; testing

was then terminated. The maximum deformation reached 48 mm.

4.1.4 Retrofitted specimen with gabion-wire knitting (GWK: W4)

Specimen W4 had gabion wires that knitted together the rubble stones of an existing wall,

to increase the overall structural integrity and stiffness. Figure 4d shows that the cracking

pattern was similar to that of W1, while the appearance of cracks was delayed. The top

center part of the wall started to crack at 62 mm, which already exceeded the extreme

deformation of W1. At this stage, no obvious out-of-plane deformation was observed. At

76 mm, cracks gradually extended toward the left and right corners, and the stones at the

center of the wall started to be squeezed outward at the front side and inward at the back

side. More cracks appeared in the center area and upper corners at 100 mm, and rubble

stones were observed to fall on the back side. At 112 mm, which was more than 5% of the

wall width, a horizontal crack appeared on the top of the wall and the force dropped to less

than 18 kN. The testing was terminated at 120 mm when out-of-plane deformation at the

center exceeded 12 mm and more stones started to fall.

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4.1.5 Retrofitted specimen with horizontally wrapped tarpaulin strips (TS: W5)

Specimen W5 had two-layer tarpaulin strips as a retrofitting material for bonding to an

existing wall. Figure 4e shows that the cracking pattern was similar to that of W1, while

cracking appeared at a very late stage when a larger horizontal deformation of the wall was

achieved. Because the cracking of the stone wall was covered by the strips, the cracking

pattern could only be observed as cracks appearing on the surface of the strips and areas in

between. Cracks started to appear on the strips in the center section at 22 and 24 mm.

When the deformation reached 38 mm, cracks gradually extended to the top left and right

corners, and the center area started to undergo out-of-plane deformation despite the con-

straint provided by the strips. With continuously increasing deformation, horizontal cracks

started to appear between strips in the lower part of the wall. At 56 mm, the upper part of

the wall started to slide along horizontal cracks that were already appreciable. The out-of-

plane deformation in the center part continued to increase, and the strips started to debond

from the stones. The testing terminated at 68 mm after full debonding of the strips. The

maximum out-of-plane deformation was 250 mm at the front side and 150 mm at the back

side. The strips increased the ductility to allow more in-plane and out-of-plane deformation

during the cyclic testing.

4.2 Hysteresis behavior

The hysteresis curves of lateral force versus deformation for each wall specimen are

presented in Fig. 5. The area enclosed by the hysteresis loop of a response curve is

commonly considered as a representation of the energy dissipation capacity under cyclic

loading, which is a critical index for assessing the seismic performance of a structure. For

all specimens, the hysteretic curve shows steep linear behavior at the beginning of loading.

With an increase in load, the specimen starts to crack and the stiffness of the specimen

degrades gradually, and the hysteretic loop begins to present a Z shape. W1 shows a strong

narrowing of hysteresis loop, indicating poor seismic resistant capacity. Compared with

specimen W1, strengthened specimens W2–W5 have wider hysteretic loops of greater area,

implying that the energy dissipation characteristics are improved; this is particularly the

case for W4 and W5, for which hysteretic loops are almost twice as large as that of W1.

This result is mainly due to the retrofitted specimen allowing greater dissipation owing to

(1) the increased internal friction force, (2) the deformation of retrofitting materials, (3) the

formation of cracks, and (4) the crushing of masonry materials. For specimen W4, the

knitted gabion wires do not greatly increase the wall stiffness in the early stage; however,

when the deformation of the stone increases, wires become tighter and compress the stones

more. Higher friction is therefore achieved and further dissipates energy. In the case of

W5, the presence of tarpaulin strips greatly improves the stiffness of the wall; however, the

strip debonds from the stone surface with an increase in stone deformation, which leads to

a rapid decrease in the compression force applied to the stones.

The energy dissipated in each loading cycle can be estimated by calculating the area

under the hysteretic curve. The relationship between the energy dissipated and the asso-

ciated drift ratio can be obtained, as shown in Fig. 6. Results show that W2, W4, and W5

dissipate energy relatively well, which indicates a good capacity to resist seismic loading.

W1 presents a smooth curve while other walls have a sudden change upward or downward

in dissipated energy. The sudden change in dissipated energy can be related to the

occurrence of cracking, the breakage of wooden materials/gabion wires, or the rapid

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Fig. 5 Hysteretic curves for unretrofitted and retrofitted stone walls

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redistribution of loadings. W5 dissipated energy more rapidly than other specimens but its

curve drops quickly after a peak. This is different from the case for W4 in which the

dissipated energy gradually increases to a peak at a large drift ratio and moderately drops

afterward.

4.3 Load–displacement response

Envelope curves are generated for each tested wall specimen from the observed hysteresis

response curves. An envelope curve contains the maximum load in the hysteresis loop at

each cyclic loading. It provides information about the seismic behavior of a structure in

terms of initial stiffness, displacement ductility, and ultimate strength, which can be

determined by analyzing the load–displacement curve according to the standard ASCE/SEI

41-13 (ASCE/SEI 41-13 2014). The nonlinear load–displacement relationship is replaced

with an idealized bilinear relationship as shown in Fig. 7.

The first line segment begins at the origin and has a slope calculated at a base shear

force equal to 60% of the effective yield strength (Vy) of the structure. This secant stiffness

is considered the effective lateral stiffness (Ke). The yielding point of the idealized curve is

determined by balancing the areas below and above the actual curve up to the maximum

Fig. 6 Estimated dissipated energy at different drift ratios

Load

Displacement

0.6Vy

Dy

Vy

Fmax0.85Fmax

DuDe

Fig. 7 Schematic drawing ofactual and idealized load–displacement curves

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load point. The second line segment represents the positive post-yield slope (a1Ke),

determined by the point corresponding to the maximum shear and the yielding point:

Ke ¼0:6Vy

De

;

where De is the displacement corresponding to Ke.

Ductility is defined as the ratio between the ultimate displacement (Du) and the yield

displacement (Dy):

l ¼ Du

Dy

;

where Du corresponds to the point that the strength reaches 85% of the maximum lateral

force (Fmax), according to the Chinese standard for the seismic retrofitting of masonry

buildings.

Figure 8 shows envelop curves of the load–displacement relation for all specimens. The

envelope curves in the early stage remained linear for all specimens, indicating elastic

behavior. The slope at the early stage reflects the initial stiffness of the wall specimens.

The results show that W5 has greater initial stiffness of the stone masonry wall compared

with the non-retrofitted W1. The tarpaulin strips with NF compound applied on the wall

(W5) increase the stiffness by holding stones together. The initial stiffness reduces when

the wooden bandages are substituted with gabion-wire mesh (W3). Layering gabion-wire

mesh in the wall horizontally actually decreases the friction in those layers because the

mesh cannot always be placed perfectly flat, which decreases the contact area between

stones. The wall knitted with only gabion wires (W4) can also help to hold stones; how-

ever, the stiffness does not appreciably increase because the wires, especially the hori-

zontal wires, cannot be tied perfectly tight in practice. The idealized bilinear curve of each

specimen is derived based on the positive part of the envelope curves of hysteretic loops.

This is because that the wall specimen is subjected to the lateral force in the positive

direction, and then the lateral force is reversed to the negative direction. Table 2 lists the

characteristic values calculated from the idealized bilinear curves. We can see that W5 has

twice the initial stiffness of W1, while initial stiffness is largely unchanged for the other

Fig. 8 Envelope curves of hysteretic loops

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specimens. Figure 9 shows the change in stiffness with the increasing drift ratio. The

dynamic stiffness during the testing is estimated by taking the ratio of the maximum force

and the associated displacement in each loading cycle. Results show that W5 has improved

overall stiffness and W2 has a moderately reduced rate of decay of stiffness.

Table 3 lists the displacements at the occurrence of the first crack, maximum force, and

failure and the corresponding loads. It is seen that all retrofitted specimens achieved higher

displacements. W4 had a much larger displacement (120 mm) than other samples,

although it did not have the highest force. The gabion wires used to hold stones together

Table 2 Characteristic values of hysteretic envelopes

Specimen 0.6Vy (kN) De (mm) Ke (kN/mm) Dy (mm) Du (mm) l (–)

W1 23.53 4.93 4.77 8.20 30.26 3.69

W2 26.84 6.39 4.20 10.65 53.97 5.07

W3 16.22 3.84 4.22 6.4 40.74 6.36

W4 14.55 2.61 5.57 4.34 47.19 10.87

W5 44.27 4.28 10.34 7.13 39.02 5.47

Fig. 9 Stiffness change with increasing drift ratio

Table 3 Load and displacement at the occurrence of the first crack, maximum force, and failure

Specimen Fcrack (kN) Dcrack (mm) Fmax (kN) DFmax (mm) Ffailure (kN) Dfailure (mm)

W1 32.04 8.08 47.35 25.16 32.89 35.20

W2 42.36 11.82 68.34 29.58 24.82 65.57

W3 29.21 13.75 34.55 31.62 21.22 47.68

W4 34.41 61.61 53.36 27.64 9.70 120.01

W5 92.40 21.67 93.76 25.60 20.23 67.57

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can therefore prevent the falling of stones at large deformation and successfully maintain

structural integrity. The wires started to break at large deformation and gradually allowed

more deformation, thus improving ductility. Although W2 and W5 had different maximum

forces, they reached a similar maximum displacement. The TS in W5 thus provided and

sustained sufficient stiffness and strength before the strips failed, while the stiffness and

strength dropped rapidly when the strips started to detach from stones. In W2, the wooden

bandages increased the stiffness and the gabion-wire jacketing allowed large deformation

by preventing out-of-plane failure. W3 had moderately higher ductility as the horizontally

layered built-in gabion-wire mesh increased the flexural strength. The four layers of

horizontal mesh contributed to the dissipation of the concentrated stress in the center and

delayed the out-of-plane failure in the center area. This result is confirmed by the calcu-

lated ductility (l) in Table 2. W4 had triple the ductility of W1, while W2, W3, and W5

had moderately higher ductility.

5 Discussion

Stone masonry houses widely used in Nepal experienced severe damage that caused a large

number of casualties during the recent Gorkha Mw7.8 earthquake. Many of the houses

were made of rubble directly collected from the natural environment and mud mortar.

Without retrofitting, the rubble stone walls have low shearing and flexural strength and out-

of-plane failure can readily occur during horizontal loading, as shown in the case of W1.

Retrofitting techniques should therefore aim to (1) increase stiffness, (2) increase ductility,

and (3) improve structural integrity, so as to improve the seismic performance of rubble-

stone masonry structures. Wood and gabion wires, rather than cement and steel, are the

locally available and affordable materials for post-disaster construction in Nepal. Wooden

bandages built into stone walls can increase both shearing and flexural strength and overall

stiffness. With wooden bandages, a wall undergoes relatively small deformation when

subjected to small and moderate seismic loads. Gabion-wire jacketing can improve the

overall integrity and allow large deformation during extreme seismic loads. Retrofitting

techniques employing a combination of wooden bandages and gabion-wire jacketing can

increase the ultimate lateral load by 48.9% and maximum deformation by 106.3%. This

could delay structural failure during a major earthquake and reduce the rescue time. The

technique of using horizontally layered gabion wire mesh is shown to be ineffective and

should not be recommended in practice, although it can increase maximum deformation by

50%. Knitting stones together using gabion wires is shown to be effective, especially for

improving ductility. This retrofitting technique can be used for existing buildings. Drilling

holes through thick stone walls and tightening the wires is challenging and the effec-

tiveness of this technique is highly dependent on the construction quality. Another tech-

nique that can be used for existing buildings is wrapping tarpaulin strips horizontally.

Because of the strong constraint provided by the strips and NF compound, this technique

increases the stiffness and the maximum lateral load can increase by up to 102%. Using

this technique, the deformation can be dramatically controlled under seismic forces at a

relatively low level, before debonding occurs. As wood and gabion wires are locally

available and considered less expensive than cement and steel, they can be used inde-

pendently or in a combined manner to make stone masonry construction seismic resistant.

Both W2 and W4 have better structural performance in terms of maximum lateral loads

and displacement in pushover testing. W5 is the only design in this research with greatly

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Table 4 Summary of the performance of tested specimens

Wallspecimenno.

Maximumforce increase(%)

Failuredeformationincrease (%)

Failure mode Retrofitting effect

W1 – – Out-of-plane failure at center areaand large diagonal cracks

–

W2 44.3 86.3 Out-of-plane failure at center areaand large horizontal cracks atcenter

Stiffness: notsignificant

Ductility:moderatelyincreased

Overall strength:significantlyimproved

Out-of-planefailure:effectivelycontrolled

Applicable toexisting building:no

W3 - 27.0 35.4 Out-of-plane failure at right-sidearea (delamination) and largevertical cracks

Stiffness: notsignificant

Ductility:moderatelyincreased

Overall strength:not significant

Out-of-planefailure: notsignificant

Applicable toexisting building:no

W4 12.7 241 Out-of-plane failure at center areaand large horizontal cracks at top

Stiffness: slightlyincreased

Ductility:significantlyincreased

Overall strength:significantlyimproved

Out-of-planefailure:effectivelycontrolled

Applicable toexisting building:yes

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increased stiffness, and the advantages (i.e., low cost and easy implementation) of this or

similar designs should be recognized. The findings of this study are summarized in

Table 4.

6 Conclusions

Stone masonry structures are widely used in the Himalayan belt. Local masons often use

rubble stones from the natural environment and apply mud as mortar to fill gaps. These

houses are extremely vulnerable to severe damaged during an earthquake. This study

designed a series of retrofitting techniques using locally available and affordable materials,

and conducted five full-scale in-plane cyclic tests to evaluate their effectiveness and

applicability. The failure mode, load–displacement response, and hysteresis characteristics

were recorded and analyzed for rubble-stone masonry walls with and without seismic

retrofitting. The following conclusions are drawn from the results of the study.

• Without retrofitting, the rubble-stone masonry wall appeared to be fragile during

testing. The capacity of energy dissipation and overall stiffness are low in the non-

retrofitted rubble-stone wall. Large diagonal cracking and local out-of-plane failure can

easily occur at relatively small lateral displacement.

• Placing horizontal wood bandages into a rubble-stone wall and applying gabion-wire

jacketing can greatly increase the shearing and flexural strength and thus prevent large

cracks and out-of-plane failure. The maximum force can be increased up to 44% and

failure deformation up to 86%. With this technique, the retrofitted stone wall can allow

large deformation both in plane and out of plane, and the ductility is increased by 38%.

This technique is recommended for newly built stone houses in regions of the

Table 4 continued

Wallspecimenno.

Maximumforce increase(%)

Failuredeformationincrease (%)

Failure mode Retrofitting effect

W5 98.0 92.0 Out-of-plane failure at center areawith TS debonding and tear-off

Stiffness:significantlyincreased

Ductility:moderatelyincreased

Overall strength:significantlyimproved

Out-of-planefailure:effectivelycontrolled

Applicable toexisting building:yes

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Himalayan belt, particularly when cement and steel are not widely available or

affordable.

• For existing rubble-stone masonry, gabion-wire knitting or tarpaulin strips with NF

compound can be used to improve structural integrity. Knitting gabion wires in existing

walls can increase in-plane deformation by up to 275% and ductility by 195%, and

provide a constraint that prevents out-of-plane failure. Horizontally applied tarpaulin

strips obvious increase the structural stiffness (by up to 117%) and ductility (by up to

48%), as well the maximum lateral force (by up to 102%). Walls retrofitted employing

the above two techniques have increased energy dissipation capacity under cyclic

loads.

• The horizontally layered gabion-wire mesh increases the failure deformation by 35%

and ductility by 72%, while it slightly decreases the maximum lateral force by 27%.

The use of a single layer of horizontal mesh decreases the friction force on the interface

of the mesh and stones while it does not increase flexural strength; this technique is

therefore not recommended in practice.

• It is evident that the seismic performance of fragile rubble-stone masonry structures can

be greatly improved using locally available inexpensive materials and proper

retrofitting techniques. The retrofitted structures allow much larger in-plane and out-

of-plane deformation and resist a much higher lateral force without structural failure

during an earthquake, which should benefit engineering practice and disaster risk

management in the least developed mountainous regions.

Funding Funding was provided by International Center for Collaborative Research on Disaster RiskReduction (ICCR-DRR) (Grant No. RETROFIT PROJECT) and Fundamental Research Funds for theCentral Universities.

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