Experimental Study on In-Plane Seismic Performance of Reinforced Brick Walls Bonded with Mud

Low-cyclic loading tests were carried on brick walls bonded with mud reinforced by three methods: packing belts, one-side steelmeshed cement mortar, and double-side steel-meshed cement mortar. +e failure modes, hysteresis curves of the loaddisplacement, skeleton curves, and ductility were obtained. +e results showed that the bearing capacity of the brick walls bonded withmud reinforced by the abovementioned threemethods had been increased to 1.4, 1.7, and 2.2 times as much as that of the unreinforced brick walls, respectively, and the ductility of the reinforced brick walls had been increased to 4.7, 2.1 and 2.2 times, respectively. +e integrity and ductility of the reinforced brick walls were effectively improved in different degrees. +e experimental results provided specific seismic strengthening techniques for the farmhouses built with brick walls bonded with mud.


Introduction
Masonry structure is one of the main structural styles in China [1][2][3].In the vast rural areas, there are many masonry structure houses with brick walls bonded with mud.ey are dangerous in the earthquake prone areas.e brick building cannot satisfy the requirements of seismic performance.ey need to be reinforced immediately.e seismic performance of full-scale single-room masonry buildings of different typologies under cyclic loading in quasi-static manner had been studied in India [4].Saleem [5] focused on the seismic performance of fiber-reinforced polymer (FRP) retrofitted buildings with openings at different FRP reinforcement levels.e behaviors of seven onehalf scale masonry specimens before and after retrofitting using fiber-reinforced polymer (FRP) were also investigated [6].A technically feasible and economically affordable PPband (polypropylene band) retrofitting for low earthquakeresistant masonry structures in developing countries was studied by Sathiparan [7].e in-plane seismic behavior of ordinary and the retrofitted brick flat arch diaphragms were experimentally investigated by Shakib [8].e performance of a full-scale single-story confined masonry building was investigated by subjecting it to quasi-static cyclic loading.It was found that the lateral stiffness, lateral load, and deformation capacity of the retrofitted building were improved, whereas the ductility decreased slightly [9,10].At present, only one research on the seismic performance of brick wall bonded with mud was carried out, and the method of improving the lateral stiffness of the front vertical wall was put forward [11].
In this paper, three seismic strengthening techniques have been applied to the brick walls bonded with mud.e seismic performance, such as the bearing capacity, ductility, and energy dissipation, was obtained by low-cyclic loading tests carried out on brick walls bonded with mud reinforced by packing belts, one-side steel-meshed cement mortar, and double-side steel-meshed cement mortar, respectively.e results could provide an instructive advice in the project of seismic strengthening of farmhouses in rural areas in China.

Design and Manufacture of Specimen.
e sizes and forms of the test specimens are shown in Table 1 and Figure 1.In order to ensure no slipping occurs between the brick walls and the foundations during the tests, the surfaces of the foundations were roughened and the cement mortar was used to cohere the first layer of bricks and the foundations.en, the walls were built with bricks bonded with mud (10 mm thick).e mud was mixed with clay and fine sand with a mass ratio of 4 : 1.
Considering the convenience and economy of the construction in rural areas, three methods were proposed to reinforce the brick walls [12,13].In the first method, the angle steels and packing belts were adopted.In the second and third method, the steel-meshed cement mortar was used to reinforce the walls [14,15].e test scheme was shown in Table 1.
e specimen #1 was the unreinforced prototype.After it was damaged, the first reinforced method was used to retrofit the specimen #1, the new one was named specimen #2.In this method, cement mortar was used to fill the cracks of the damaged part of the wall, and four angle steels of L45 × 5 were stuck on the four vertical corners of the wall by cement mortar.en, the wall was hooped by the packing

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Advances in Civil Engineering belts which were 16 mm in width, and the vertical spacing between the belts was 200 mm.e specimen #3 and specimen #4 were reinforced using the steel-meshed cement mortar.For the specimen #3, the wall was reinforced by the steel-meshed cement mortar (30 mm thick) on one side, the diameter of the steel bar was 4 mm, the spacing distance was 300 mm, and the steel mesh was connected with the wall by L-type tensile bar.For the specimen #4, the wall was reinforced by the steel-meshed cement mortar on both sides, and the S-type tensile bar was used to fasten the steel mesh.e parameters of the steel mesh were as same as the specimen #3. e strength of materials is shown in Table 2.

Loading Mode.
A low-cyclic loading mode was applied in the tests.e vertical load including the dead load and live load of the roof was kept at 40 kN during the whole tests, and the axial compression ratio was 0.1.e horizontal loading was controlled by the displacement.e increment of displacement was 0.5 mm at the beginning, and it was added to 1 mm after the crack appeared.e tests were finished when the specimens were damaged or the horizontal force dropped by 15% of the peak value.
e loading device is shown in Figure 2. e horizontal and vertical displacements of the wall, the strain of the angle steels and the packing belts in specimen #2, and the strain of the mortar layer in specimens #3 and #4 were recorded by a high-speed static sample system.

Test Phenomenon.
In order to describe the failure process of every specimen, the loading bearing surface was defined as surface A, and the other side of the wall was defined as surface B (Figure 2).e failure pattern of each specimen is shown in Figure 3.
For the specimen #1, no visible cracks appeared on the wall when the controlling displacement reached ±2 mm.When the displacement increased to ±3 mm, there were small cracks that appeared on the bottom and middle part of the wall.After the displacement reached ±4 mm, the cracks continuously extended.When the displacement increased to ±5 mm, the diagonal through cracks on the wall appeared.e maximum crack was 4 mm in width.At the same time, the specimen was seriously damaged, and the test finished.
For the specimen #2, there were no visible cracks on the wall when the controlling displacement reached ±2 mm.When the displacement increased to ±3 mm, the mended cracks cracked again.After the displacement reached ±4 mm, the diagonal cracks were widened and the vertical cracks appeared near the angle steel.When the displacement reached ±16 mm, the cracks continuously expanded and the bricks were crushed near the sides A and B. When the loading displacement reached ±24 mm, the maximum slip between the wall and the foundation was 10 mm, and the four angle steel was forced to dome outwards.e mud on the middle of the wall fell off, and the wall was damaged seriously.e test finished.

Advances in Civil Engineering
For the specimen #3, there were no visible cracks on the wall when the controlling displacement reached ±3 mm.When the displacement increased to ±4 mm, tiny cracks appeared at the root of the wall and the mortar surface.When the displacement increased from ±5 mm to ±13 mm, new cracks appeared near the root of the sides A and B, and the width of the existing cracks became larger.e brick wall began to slip on the foundation.When the displacement reached ±14 mm, the mortar surface near the root of sides A and B was separated from the wall.e load dropped by more than 15% of the peak value.e test finished.
For the specimen #4, no visible cracks appeared on the wall before the controlling displacement reached ±4 mm.When the displacement reached ±5 mm, there were slight cracks that appeared on both sides of the wall.When the displacement increased from ±6 mm to ±18 mm, new cracks appeared on the mortar surface of the sides A and B, and the existing cracks continuously expanded.When the displacement reached ±19 mm, the surface of the mortar was separated from the wall near the root of the sides A and B.
e steel bars were exposed, and the load dropped by more than 15% of the peak value.e test finished.

Analysis of the Hysteretic Curve.
e hysteresis curves of each specimen were shown in Figure 4. e crossing cracks were presented on the damaged specimen #1 and specimen #2.After the diagonal crack occurred, the hysteresis curve of the specimen #2 gradually enlarged and the stiffness of the e initial stage of the hysteresis curve had a spindle shape.With the increasing of shear force and the expanding of the crack, the curve showed the pinching e ect due to the degeneration of the sti ness.e area of the hysteretic loop curves indicated the di erent seismic energy dissipation ability of the specimens.Calculation showed that energy dissipation ability of the specimens #2, #3, and #4 was about 8, 5, and 9 times as much as that of the specimen #1, respectively.

Analysis of Skeleton Curves.
e skeleton curves of each specimen are shown in Figure 5.At the beginning of the tests, the skeleton curves of each specimen were in straight line before the cracking occurred.e slopes of the curves were di erent which indicated that the lateral sti ness of the walls is di erent.e maximum bearing capacity of the reinforced specimens was much larger than that of the unreinforced one by comparing the peak point of the skeleton curves.e values are given in Table 2. e positive and negative ultimate bearing capacity of specimen #2, specimen #3, and specimen #4 were increased by 43%, 41%; 70%, 40%; and 124%, 70%; respectively.At the same time, the decline part of the skeleton curve showed that the deformation capacity of the reinforced specimens was improved.
e ultimate displacement of Advances in Civil Engineering specimens #2, #3, and #4 were 4.8, 2.80, and 3.85 times that of the specimen #1 when the failure occurred.

Analysis of Sti ness Degradation.
e sti ness of the wall decreased with the increasing number of the loading cycles and the controlling horizontal displacement.e phenomenon was called the sti ness degradation, which indicated the accumulated damage in the walls.e in-plane sti ness of the wall was de ned as where P i is the peak load in the i cycle, and Δ i is the horizontal displacement in the i cycle.
Base on formula (1), the sti ness degeneration curves of each specimen were calculated.
ere were three stages during the sti ness degradation of the specimens (Figure 6).At the beginning, the initial cracks on the wall gradually formed, the sti ness curve decreased steeply, and the stiness degenerated sharply.With the extension of the cracks, the speed of the sti ness decline slowed down.After the main cracks appeared, the residual sti ness of the specimen almost remained constant.e di erences of the sti ness degeneration among the specimens are shown in Figure 6.

Ductility Analysis.
Ductility re ects the seismic performance of the structure.It is the nonlinear deformation capacity of the structure or component without signi cant reduction of the bearing capacity.Normally, the ductility coe cient is the ratio of the failure displacement and the yield displacement.However, it is di cult to determine the yield displacement for the masonry structure.
e yield displacement was replaced by the cracking displacement.
e ductility coe cient μ was calculated by formula (2), and the results are listed in Table 3.
where Δ u is the failure displacement of the specimen, and Δ cr is the crack displacement.It could be found that the cracks appeared when displacement was small, but the failure displacement of the specimens #2, #3, and #4 can reach 24 mm, 14 mm, and 19 mm, respectively, and the ductility coe cients were 4.7, 2.1, and 2.2 times that of specimen #1. e seismic behavior and bearing capacity of the reinforced specimens #2, #3, and #4 were improved in di erent degrees.e reinforced methods, packing belts, one-side steel-meshed cement mortar, and double-side steel-meshed cement mortar, proposed in this paper were practicable.

Conclusions
Low-cyclic loading tests were carried on the brick walls reinforced by packing belt, single-side steel-meshed cement mortar, and double-side steel-meshed cement mortar.e energy  (1) e bearing and deformation capacity of the reinforced specimens were improved.e bearing capacity and the ductility of the specimen #2 reinforced by packing belts increased to 1.4 and 4.7 times that of the unreinforced specimen #1. e bearing capacity and the ductility of the specimen #3 reinforced by oneside steel-meshed cement mortar increased to 1.7 and 2.1 times that of the unreinforced specimen #1. e bearing capacity and the ductility of the specimen #4 reinforced by double-side steel-meshed cement mortar increased to 2.2 and 2.2 times that of the unreinforced specimen #1.
e results indicated that the deformation capacity was greatly enhanced.
(2) After reinforced by steel-meshed cement mortar, there were no cracks that appeared in the middle part of the specimens #3 and #4.A good composite effect between the brick wall and the cement mortar layer was shown before the specimens were destroyed.Although the stiffness of the wall reinforced by the packing belts was increased slightly, it showed a good integrity due to the confined effect of the packing belts.(3) e seismic performance of the brick walls bonded with mud reinforced by packing belts, one-side steelmeshed cement mortar, and double-side steelmeshed cement mortar was improved greatly.It is noteworthy that the seismic performance depends on not only the component but also the integrity of the structure.Most of the rural houses in China are single-store structures with poor integrality.When the rural houses are strengthened, reinforcing the wall and strengthening the integrity of the structure should be considered at the same time, and the convenience and economy should also be taken into account.

Figure 6 :
Figure 6: Comparison of sti ness degradation of specimens.

Table 1 :
Sizes of specimens and reinforcement schemes.

Table 2 :
e strength of the materials.

Table 3 :
Ultimate bearing capacity and ductility coe cients of specimens.