Shaking table tests on strengthening of masonry structures against ...

Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010 www.nat-hazards-earth-syst-sci.net/10/1209/2010/ doi:10.5194/nhess-10-1209-2010 © Author(s) 2010. CC Attribution 3.0 License.

Natural Hazards and Earth System Sciences

Shaking table tests on strengthening of masonry structures against earthquake hazard F. Ersubasi1 and H. H. Korkmaz2 1 Civil

Engineer, Konya Municipality, Konya, Turkey University, Engineering and Architecture Faculty, Department of Civil Engineering, Konya, Turkey

2 Selcuk

Received: 23 March 2010 – Revised: 3 May 2010 – Accepted: 10 May 2010 – Published: 17 June 2010

Abstract. Turkey and neighborhood countries like Greece and Iran are situated on an active earthquake region. Masonry type structures are very common on these countries, especially on the rural areas. During the last earthquakes, several masonry type houses were collapsed, causing loss of life and property. Strengthening methods of masonry houses were discussed in this study. The paper summarizes the results of a experimental programme carried out on models, scaled 1/10, of one-storey masonry buildings. First specimen tested was the reference specimen and used for comparison purposes. Other specimens contained several strengthening strategies. A total of 9 specimens were tested. The results allow to assess the efficiency of the various strengthening techniques employed.

1

Introduction

Western Peloponnissos, Ionian Islands of Greece and lands of Turkey, are among the most seismically prone areas of Southern Europe (Karantoni and Bouckovalas, 1997). 90% of the land area of Turkey is situated on one of the most active seismic zones of the world and devastating earthquakes frequently occur. Bingol, Turkey, located in a region of high seismic risk, an earthquake of magnitude 6.4 occurred on 1 May 2003. In the disaster area, 308 buildings collapsed, 2566 buildings have severe and moderate and 2546 buildings have light damage. In this earthquake, 174 deaths and 520 casualties were reported by the Governor of the city (Kaplan et al., 2003). On 27 March 2004 and earthquake that struck Erzurum with a magnitude of 5.1 killed 8 people in rural areas. A moderate earthquake of 5.1 on the Richter scale was occurred on Friday, 2 July 2004, near Dogubayazit townCorrespondence to: F. Ersubasi ([email protected])

ship and 18 people were killed and 25 people were injured, 1000 building affected from the earthquake (Bayraktar et al., 2007). Recently, a 6.0 magnitude earthquake has struck the eastern province of Elazig in Turkey on 8 March 2010. This is the most seismically hazardous zone according to the seismic classification criteria adopted for Turkey (G¨ulkan et al., 1993). The area is sparsely populated, with most dwellings having one or two stories constructed from masonry without timber reinforcement or adobe and brick (Sandikkaya et al., 2010). In Fig. 1, several damaged masonry houses were illustrated in Elazig Earthquake. Structures located in the seismically active zones are far from possessing qualities that would ensure satisfactory seismic performance (Ozcebe et al., 2003). Developing countries commonly have poor and under educated population living in self-constructed masonry houses, which are at high risk if they are located on seismically active regions. The behavior of the masonry buildings during the earthquakes is poorly understood and appropriate tools to analyse them are now urgently required. On the other hand, numerical modeling of the seismic behavior of masonry structures represents a very complex problem due to the constitutive characteristics of the structural material and its highly physical and geometrical nonlinear behavior when subjected to strong ground motion (Bayraktar et al., 2007). The structural vulnerability and damage-failure patterns of unreinforced masonry (URM) were studied by many researchers (Korkmaz, 2010; Bruneau, 1994; Tornabvie, 1997; Benedetti et al., 1998; Abrams, 2001; Paquette and Bruneau, 2003; Doherty et al., 2002). Of the methods considered, injection grouting, insertation of reinforcing steel, prestressing, jacketing, use of FRP and various surface treatments were the most common (Albert et al., 2001). The difficulties in performing advanced testing of this type of structures are quite large due to the innumerable variations of masonry, the large scatter of in situ material properties and the impossibility of reproducing it all in a specimen (Zucchini and Lourenco, 2004).

Published by Copernicus Publications on behalf of the European Geosciences Union.

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F. Ersubasi and H. H. Korkmaz: Shaking table tests on strengthening of masonry structures

(a)

(b)

(c) Fig. 1 Several failure of masonry houses observed after Elazig earthquake (2010) This paper discusses the effectiveness of masonry strengthening techniques The scope includes construction of Fig. 1. Several failure of masonry houses observed after Elazig one reference and eight strengthened identical 1/10 scaled one storey masonry houses and dynamic testing of specimens on uniaxial shaking table. The performance of each strengthening technique was compared with earthquake (2010). reference specimen. 2. Material and Method In the context of this study, evaluation of different strengthening techniques for masonry houses was aimed. The testing of masonry structures under lateral loads is a very difficult task. The reinforced concrete structures can be tested under lateral point loading, since the mass of the structure is concentrated on the storey levels (Ersubasi, 2008). On the other hand, point loading of masonry walls is very difficult due to local shear failure of the bed joints. Also mass of the structure is distributed through the wall height. Computer controlled shaking table test were very popular to simulate the destructive effects of recorded or generated earthquake records. But, the equipment for a full-scale computer controlled shaking table is too costly for many institutions (Turer et al., 2007). Several more economic testing techniques were developed to evaluate the earthquake performance of the masonry structures. Tilting table test setup was first used by Zegarra et al. (2000) and Turer et al. (2004). Roorke shock table (Figure 2) was another setup in the literature (Keightley, 1986). Indian researcher Jagadish K.S (2002) used a pendulum and a free vibration table o simulate the earthquake forces on the masonry houses. Altın et al. (2005) and Kamanli and Balik (2010) used a more simplistic shaking tablet o test the different strengthening strategies on the masonry houses.

This paper discusses the effectiveness of masonry strengthening techniques The scope includes construction of one reference and eight strengthened identical 1/10 scaled one storey masonry houses and dynamic testing of specimens on uniaxial shaking table. The performance of each strengthening technique was compared with reference specimen. 2

(d) Fig. 2 Different masonry testing setups

to budgedtesting constraints of the researchers, relatively more economic Fig. 2. DifferentDuemasonry setups. (a) Tilting test setup (Ze- shaking table by the authors. This setup was also used in previous study (Turer et al, 2004). garra, 2000). (b)developed Tilting setup (Turer, Roorke shockand accelerations. Th custom madetest and generates sinusoidal2004). motions at(c) increasing frequency canPendulum be move in only forward and backward The movement of the table (Keightley,a platform 1986).that(d) and vibration tabledirections. (source: an electric motor and frequency control mechanism. The illustration of the mechanical Jagadish, 2002).by Figure 3

Material and method

In the context of this study, evaluation of different strengthening techniques for masonry houses was aimed. The testing of masonry structures under lateral loads is a very difficult task. The reinforced concrete structures can be tested under lateral point loading, since the mass of the structure is concentrated on the storey levels (Ersubasi, 2008). On the other hand, point loading of masonry walls is very difficult due to local shear failure of the bed joints. Also mass of the structure is distributed through the wall height. Computer controlled shaking table test were very popular to simulate the destructive effects of recorded or generated earthquake records. But, the equipment for a full-scale computer controlled shaking table is too costly for many institutions (Turer et al., 2007). Several more economic testing techniques were developed to evaluate the earthquake performance of the masonry structures. Tilting table test setup was first used by Zegarra et al. (2000) and Turer et al. (2004). Roorke shock table (Fig. 2) was another setup in the literature (Keightley, 1986). Indian researcher Jagadish (2002) used a pendulum and a free vibration table o simulate the earthquake forces on the masonry houses. Altin et al. (2005) and Kamanli and Balik (2010) used a more simplistic shaking table to test the different strengthening strategies on the masonry houses. Due to budged constraints of the researchers, relatively more economic shaking table test equipment was developed by the authors. This setup was also used in previous study (Turer et al., 2004). The shaking table is custom made and generates sinusoidal motions at increasing frequency and acNat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

Fig. 3 Custom made shaking table test setup TheFig. frequency of the rotation and also platform motion be adjusted by an AC motor controller. The stroke 3. Custom made shaking tablecantest setup. length of the shaking platform can be modified mechanically as the long bar connection location on the rotational disk is moved close or away from the disk centroid when the platform in not in operation. The platform displacement-amplitude (X) can be adjusted by changing the radius of the rotating disc (r). Amplitude is a function of the rotational angle () of the motor disk which depends on angular velocity (w) times time (t). In order to obtain a sinusoidal wave, (L) which is the length of the arm linking the rotating disk and the sliderplatform must be long enough. The relationship between the table displacement and other parameters explained above can be written as in Equation 1 using geometric relationships as;

celerations. The setup consisted of a platform that can be move in only forward and backward directions. The movement of the was  platform  driven by an electric motor and r x  r  cos(w t )  L 1  1  sin( w t )  (1)  frequency control The illustration of the meL mechanism.  chanical system is shown in Fig. 3. The first derivative of Equation 1 yields the velocity (v) function of the platform as shown in Equation 2. The frequency of the rotation and also platform motion can r of (2) x be v adjusted r sin( w t ) w by an AC motor sin( wcontroller. t ) cos(w t ) w The stroke length r 1  sin( wcan t ) be modified mechanically as the the shaking Lplatform L long bar connection location on the rotational disk is moved The second derivative of the displacement function yields the acceleration (a) function of the platform as shown close3.or away from the disk centroid when the platform is in Equation 2

2

2

2



2

2

2

  3   r r 2 2 2 sin( w t )  cos( w t )  2 cos( w t )  1        www.nat-hazards-earth-syst-sci.net/10/1209/2010/ L L  x  a  r  w 2  cos(w t )     (3) 3 1   2 2  r2  r2 2 2   1  L2 sin( w t )  1  L2 sin( w t )         





5.

Error % shaking _ table  10 Error % shaking _ table  10

L 2.0165 1.0083log   r

(4)

L 2log  r

(5)

F. Ersubasi and H. H. Korkmaz: Shaking table tests on strengthening of masonry structures Error % shaking _ table  10

 L 2 log   r

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(6)

Shaking Table Acceleration Percent Error Graph

L/r=10

100

100

L/r=3 Maximum Acceleration Percent Error (%) with Respect to Sinusoidal Function

L/r=3

L/r=10

10

10 1

0.1 1

10

100

1000

(L/r) ratio

1

0.1 0

10

20

30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 180 190 200

(L/r) ratio

Fig. 5 Shaking table maximum acceleration error change as a function of L/r ratio.

Fig.used 5. in Shaking table maximum acceleration change as a func- waves with The shaking table this study has an L/r ratio equal to 80 whicherror generates close-to-sinusoidal of L/rThe ratio. maximum errortion of 1.25%. amplitude of the accelerations generated by the shaking table setup is a function of rotary disk radius (r) and square of rotation frequency (w2) as seen in Equation 3. The level of acceleration can only be increased by changing rotation speed or rotation frequency (w) since rotary disk radius (r) cannot be changed during testing. The natural vibration frequencies of the 1/10 scale test specimens are much higher than the testing frequency range of the shaking table; therefore, amplification errors due to resonance condition is not The shaking table acceleration versus angle graphs for difan issue. The levels of acceleration that cause failure of the test specimens are determined by using Equation 3. ferent ratios prepared et al.for (2004) and given The accelerations for theL/r failure levelare of loading shouldby alsoTurer be corrected their equivalent accelerations if the Fig. 4 Normalized shaking table acceleration comparison for different L/r ratios tests were conducted in full scale. The correction factoracceleration for a 1/N scale model can be from calculated in Fig. 4. The shaking table diverges theconsidering the stiffness, Fig. 4. Normalized shaking table acceleration comparison for dif- mass, and acceleration changes in a 1/N scale test. The lateral stiffness term of a 1/N scale model sinusoidal wave form L/rregardless ratio isofsmall indicating that would be N times smaller than the full scalewhen stiffness the stiffness type (e.g., shear or bending ferent L/r ratios. dominant stiffness). The force equivalence in a 1/N scaleatreduced model would be compatible with the stiffness the ratio should be kept large all 2times. Sensitivity analy(K) times the displacement () and should be modified by (1/N) . The dynamic equilibrium equation of (F=m*a) 3 sis onforthe maximum error shaking acceleration might be rearranged acceleration (a=F/m) andbetween would have ratios of table (1/N2)/(1/N ) which would yield (N). Therefore, equivalent accelerations causing failure 1/N scale in model would be N maxitimes larger compared not in operation. The platform displacement-amplitude (x) the and a perfect sinusoidal waveofisa plotted Fig. 5. The the full scale model. Consequently, accelerations causing failure of a full scale model must be decreased by a can be adjusted by changing the radius of the rotatingto disc mum acceleration error of the shaking table decreases as the factor of N (Turer et al., 2004). L/r=100

L/r=100

(r). Amplitude is a function of the rotational angle (θ) of L/r ratio is increased. Log-log plot of the error versus L/r rathe context of the experimental part, test specimens were designed such that they were 10 times scaled down the motor disk which depends on angular velocity (w) Intimes tio shows a linear relationship which is given in Eq. (4). The models. Only one room and one storey of a typical masonry house was considered. Turer et al. (2004) tested a time (t). In order to obtain a sinusoidal wave, (L) which relationship can be with further show Eq.was (5).very small comparing typicalisone storey one room rural house 12m2 simplified base area. Theas scale of theinstudy the 1/1 tests. Korkmaz (2007) used same model ratio and compared the length of the arm linking the rotating disk and the slider the 1/1 test conducted in METU as a with L pattern in reference and strengthened part of World Bank DM-2003 project. She 2.0165−1.0083·log found the same failure r specimens can be compared with each platform must be long enough. The relationship between the andError% specimens concludedshaking that thetable major (4) =failure 10 characteristics of the other. table displacement and other parameters explained above can L be written as in Equation 1 using geometric relationships as; prototype has 3m x 4m in plan and 3m2−log Current in height. r Consequently, the test model had 30 cm height and it Error% = 10 (5)Clayey soil was shaking table   s was constructed as 30cmx40cm in plan. Masonry units were also scaled down with 1/10 scale. x = r · cos(wt) + L 1 − 1 −

r2 sin(wt)2  L2

The first derivative of Eq. (1) yields the velocity (v) of the platform as shown in Eq. (2).

used as mortar and material properties were not modeled. Generally brick, stone or briquette masonry houses has L houses were not modeled, instead thick marble plate RC slabs masonry (1) and a roof on it. The heavy roof of the 2−log r was used to represent RC slab of = the10 structure. Additional weight was included on the Error%the (6)roof of the test shaking table specimen. In order to see crack propagation on the masonry walls, a thin clay plaster was applied and painted. White plaster is quite welcome to observe the cracking pattern of the walls. In Figure 6 dimensions and general The shakingwere table used in this study has an L/r ratio equal function configuration of the test specimens depicted.

·

x = v = r sin(wt) w +

r2 q sin(wt) cos(wt) w 2 L 1 − Lr 2 sin(wt)2

(2)

The second derivative of the displacement function yields the acceleration (a) function of the platform as shown in Eq. (3).  r 3 2 2  ·· 2 L sin(wt) · cos(wt) x = a = r · w cos(wt) − 3 2 2 1 − Lr 2 sin(wt)2  · 2cos(wt) − 1   − 1  r2 2 2 1 − L2 sin(wt) r L

2

www.nat-hazards-earth-syst-sci.net/10/1209/2010/

(3)

to 80 which generates close-to-sinusoidal waves with maximum error of 1.25%. The amplitude of the accelerations generated by the shaking table setup is a function of rotary disk radius (r) and square of rotation frequency (w2 ) as seen in Eq. (3). The level of acceleration can only be increased by changing rotation speed or rotation frequency (w) since rotary disk radius (r) cannot be changed during testing. The natural vibration frequencies of the 1/10 scale test specimens are much higher than the testing frequency range of the shaking table; therefore, amplification errors due to resonance condition is not an issue. The levels of acceleration that cause failure of the test specimens are determined by using Eq. (3). The accelerations for the failure level of loading should also be corrected for their equivalent accelerations if the tests were conducted in full scale. The correction factor for a 1/N scale model can be calculated considering the stiffness, mass, and acceleration changes in a 1/N scale test. The lateral stiffness term of a 1/N scale model would Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

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F. Ersubasi and

and increased with time. As the frequency of the motion was increased, also acceleration of the table wa increased remembering the amplitude of the motion was constant during the testing. The failure instant an frequency of the failure was noted. The rate of increase is tried to be kept constant for all tests. The frequencie causing failure are noted for each test. The failure modes of the specimens were captured by three camera located at the three corners of the laboratory. The acceleration versus time graphs of the platform was given i H.Figure H. Korkmaz: 7 for differentShaking L/r ratios.table tests on strengthening of masonry structures Frequency=14 Herz

80

L=40cm-r=0,5cm L=20cm-r=0,5cm L=10cm-r=0,5cm L=5cm-r=0,5cm L=2cm-r=0,5cm L=1cm-r=0,5cm

Loading direction

N

Acceleration (m/sec2)

60 40 20 0 0

0,05

0,1

0,15

0,2

-20 -40 -60

Tim e (s ec)

Fig. 7 Acceleration versus time graph of the platform for frequency 14 Hz

Fig. 7. Acceleration versus time graph of the platform for frequency 14 Hz.

3. Experimental study

In this section summary of the experiments were given with photos of the specimens to represent the damag conditions. Since type of the experiment was dynamic, it was not possible to stop the testing and mark the crack the three roofcameras of thewere testused specimen. In failure ordersequence to see in crack on the walls. Instead, to capture the video propaformat and a commerci gation masonry thin clay views plaster was applied software converted video on filesthe to bitmap files. walls, Differenta perspective of the specimen at the same insta were given in a row. followingWhite row corresponds next instant of theto damage. andThe painted. plaster toisthe quite welcome observe the

cracking pattern of the walls. In Fig. 6 dimensions gen-no strengthenin Fig. 6 Geometry of model house First specimen was the reference specimen tested to observe reference capacity andand contained Fig. 6. Geometry of model house. Other specimens eral were configuration strengthened withofdifferent The performances of specimens were compare the testproposals. specimens were depicted. the testing a constant amplitude sinusoidal displacement was applied. Maximum velocity andtesting against each other using acceleration levels causing collapse or heavy damage to the structure. During the a constant amplitude sinusoidal dis-The comparison ation were linear functions of w and w2. The frequency of the motion was started from low frequencies placement creased with time. the smaller frequency of the wasstiffness increased,regardless also acceleration of the table was was applied. Maximum 2velocity and acceleration be N As times than the motion full scale of were instant linear and functions of w and w . The frequency of the ed remembering the amplitude of the motion was constant during the testing. The failure the stiffness type (e.g., shear or bending dominant stiffness). was started from low frequencies and increased with cy of the failure was noted. The rate of increase is tried to be kept constant for all tests.motion The frequencies The force equivalence in a 1/N scale reduced model would g failure are noted for each test. The failure modes of the specimens were captured by threeAs cameras time. the frequency of the motion was increased, also be compatible with the stiffness (K) times the displacement at the three corners of the laboratory. The acceleration versus time graphs of the platform was givenof in the table was increased remembering the amacceleration 7 for different(δ) L/r and ratios. should be modified by (1/N)2 . The dynamic equilib-

Acceleration (m/sec2)

plitude of the motion was constant during the testing. The rium equation of (F = m∗ a) might be rearranged for accelfailure instant and frequency of the failure was noted. The 2 )/(1/N3 ) Herz Frequency=14 eration (a = F /m) and would have ratios of (1/N 80 rate of increase is tried to be kept constant for all tests. The L=40cm-r=0,5cm which would yield (N). Therefore, the equivalent acceleraL=20cm-r=0,5cm 60 L=10cm-r=0,5cm frequencies causing failure are noted for each test. The failtions causing failure of a 1/N scale model would be NL=5cm-r=0,5cm times L=2cm-r=0,5cm ure modes of the specimens were captured by three cameras L=1cm-r=0,5cm larger compared to the full scale model. Consequently, ac40 located at the three corners of the laboratory. The acceleracelerations causing failure of a full scale model must be detion versus time graphs of the platform was given in Fig. 7 20 creased by a factor of N (Turer et al., 2004). for different L/r ratios. 0 In the context of the experimental part, test specimens 0 designed such 0,05 that they were 0,1 were 10 times0,15 scaled down 0,2 -20 models. Only one room and one storey of a typical masonry 3 Experimental study house was considered. Turer et al. (2004) tested a typical -40 one storey one room rural house with 12 m2 base area. The In this section summary of the experiments were given with e (s ec) -60 scale of the study was very Tim small comparing the 1/1 tests. photos of the specimens to represent the damage condiFig. 7 Acceleration of the platform for frequency 14 Hz tions. Since type of the experiment was dynamic, it was Korkmaz (2007)versus used time samegraph model ratio and compared with the 1/1 test conducted in METU as a part of World Bank not possible to stop the testing and mark the cracks on the DM-2003 project. She found the same failure pattern in refwalls. Instead, three cameras were used to capture the failerimental study erence and strengthened specimens and concluded that the ure sequence in video format and a commercial software major failure characteristics of with the specimens be comsection summary of the experiments were given photos of thecan specimens to represent the damage converted video files to bitmap files. Different perspective ons. Since typepared of thewith experiment was dynamic, it was not possible to stop the testing andviews mark the each other. of cracks the specimen at the same instant were given in a walls. Instead, three cameras were used theinfailure format and row.a commercial The following row corresponds to the next instant of Current prototype hasto 3capture m×4 m plan sequence and 3 m in in video height. e converted video files to bitmap files. Different perspective views of the specimen at the same instant the damage. Consequently, the test model had 30 cm height and it was ven in a row. The following row corresponds to the next instant of the damage. constructed as 30 cm×40 cm in plan. Masonry units were First specimen was the reference specimen tested to obecimen was the reference tested to observe capacity contained no strengthening. also scaled specimen down with 1/10 scale. reference Clayey soil was and used as serve reference capacity and contained no strengthening. specimens were strengthened with different proposals. Themodeled. performances of specimensOther were specimens compared were strengthened with different proposals. mortar and material properties were not Generally each other using acceleration causing collapsehouses or heavy to the structure. The comparisons brick, stone or levels briquette masonry hasdamage RC slabs and a The performances of specimens were compared against each roof on it. The heavy roof of the masonry houses were not other using acceleration levels causing collapse or heavy modeled, instead thick marble plate was used to represent the damage to the structure. The comparisons of cracking and RC slab of the structure. Additional weight was included on heavy damage accelerations are made in reference to the Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010



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Fig. 8 Failure sequence of specimen Ref

South side

North side

West and north side

Fig. 9 Wire mesh strip application

Fig. 9. Wire mesh strip application.

3.2

Fig. 8 Failure sequence of specimen Ref

Fig. 8. Failure sequence of specimen Ref.

reference specimen as a ratio of aS /aR . Here, aS and aR are strengthened specimens and reference specimens failure accelerations, respectively. 3.1

Reference specimen (Ref)

Fig. 9 Wire mesh strip application

The first specimen tested was reference specimen (Ref) with original construction details. The capacity oft this specimen was used for comparison purposes. The dynamic excitation to specimen Ref was applied in East-West direction. The first cracks were initiated diagonally above the North window and also above the door of the model. New diagonal cracks were formed perpendicular to the previous ones as the direction of the movements was reversed. This diagonal cracks extended up to the bottom of the structure. As the frequency of the motion was increased, similar X type cracks were observed on the West window and previous cracks were widened. After that, a portion of the wall above the North window and door was separated and fell down. A horizontal shear crack was propagated above the door. After so much damage, stability of the structure was disturbed and a sudden and total collapse of the roof took place. Total collapse of the model was observed at the end of the test and classified as a brittle and sudden failure. The failure acceleration of this reference specimen was taken as 1. The failure sequence of the specimen was depicted in Fig. 8. www.nat-hazards-earth-syst-sci.net/10/1209/2010/

Strengthened specimen CF1

The first method of strengthening was based on the use of CFRP type material. Application CFRP on the masonry walls is a well known technique and several researches are available in the literature. CFRP was applied on the walls with epoxy. The benefit of CFRP on the wall is; it delays the disintegration of walls units and can withstand axial tension forces on the wall. On the other hand CFRP material is very expensive. To cover all the wall surfaces with this material is not economical. Rather, several critical stress concentration points can be covered. As observed from the reference specimen test, corners of the structure and openings are the most critical points. To model the CFRP material on this study, several material alternatives were tried. Plaster mesh wire made of plastic based material was quite welcome fort his purpose. Silicone based glue was used to represent the epoxy. Plaster wire mesh was cut in strips with 3 cm wide and corners of the specimen were covered with these strips (Fig. 9). Vertical strips on the corners were connected with three horizontal strips to delay the disintegration of the corners. In the reference specimen test, wall portions above the openings were failed. Consequently, strips were also applied above the openings horizontally (Fig. 9). After strengthening procedure, walls were plastered and painted. Strengthening of masonry walls are not included in the current Turkish Earthquake Code (2007). The CFRP application on the masonry walls within the RC frames is given in the code only. In the regulations, there is no restrictions about the width of the CFRP strips. In the code only anchorage details of the CFRP strips on the masonry infill is given. In this study the width of the CFRP strips were not considered as a parameter. Instead, the width of the CFRP strips were taken as 3 cm constant. The anchorage of the CFRP strips were also not modeled since the model ratio of the study is small. 3 cm strip width corresponds to 30 cm width in real dimensions. The larger dimensions will increase the cost of the application. Testing of specimen CF1 was recorded with three cameras. Strips, simulating the CFRP, changed the damage and cracking modes of the specimen. First cracks were observed below the window openings (Fig. 10). These initial cracks could not propagate further and X type cracks could not form Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

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Fig. 10 Failure sequence of specimen CF1 3.3 Specimen CF2 In specimen CF2, strips above the openings were removed and a horizontal strip was applied just above the Fig.12 Failure of specimen CF2 ground level of the structure. The corners strengthened like CF1 (Figure 11). The failure sequence of Fig. 10were Failurealso sequence of specimen CF1 the test was depicted in Figure 12. Initial cracks were observed above the openings like reference specimen Ref. 3.4 Specimen CF3 3.3 Specimen CF2 X type cracks were formed but limited and couldn’t reached CF1. to the foundation level. Oppositely, these cracks Fig. 10. Failure sequence of specimen were extended parallelCF2, to strips the ground. specimen was and collapsed when level theobtaining satisfactory results in specimens CF1 and CF2, in specimen CF3, only corner of the structure In specimen above the This openings were removed a horizontal strip the was acceleration applied just above the was 2 times After ground level of the structure. The corners were also strengthened like CF1 (Figure 11). The failure sequence of was covered with strengthening material. In this manner, more economic reference specimens failure acceleration. Fig.12 Failure of specimen CF2 application was maintained (Figure the test was depicted in Figure 12. Initial cracks were observed above the openings like reference specimen Ref. X type cracks were formed but limited and couldn’t reached to the foundation level. Oppositely, these cracks were extended parallel to the ground. This specimen was collapsed when the acceleration level was 2 times the reference specimens failure acceleration.

13). Initial cracks were formed in the corners of the openings and X type cracks were formed. Also horizontal

crack parallel to the ground was formed. Comparing with the reference specimen, more cracks were 3.4shear Specimen Fig. 12.CF3 Failure of specimen CF2. formed and distributed on a larger wall area. The wall, which was loaded in the out of plane direction, was failed and the test was stopped. This specimen could withstand 1.5 times acceleration according to the reference

After obtaining satisfactory results in specimens CF1 and CF2, in specimen CF3, only corner of the structure specimen. In Figure 14, failure and damage mode of the specimen was given. was covered with strengthening material. In this manner, more economic application was maintained (Figure 13). Initial cracks were formed in the corners of the openings and X type cracks were formed. Also horizontal shear crack parallel to the ground was formed. Comparing with the reference specimen, more cracks were formed and distributed on a larger wall area. The wall, which was loaded in the out of plane direction, was failed and the test was stopped. This specimen could withstand 1.5 times acceleration according to the reference specimen. In Figure 14, failure and damage mode of the specimen was given.

Fig. 1111 Specimen CF2 CF2 Fig. Specimen

Fig. 13 Preperation of specimen CF3

Fig. 11. Specimen CF2.

Fig. 13. Preperation of specimen CF3. Fig. 13 Preperation of specimen CF3

due to polymer application. Instead, wall portions under the window openings were cracked like reversed V shape. More cracks were observed comparing the reference specimen and distributed over a larger area. The testing was stopped since the width of the cracks was widened and stability of the structure was lost. At the end of the test, specimen survived 2.5 times higher acceleration than the failure acceleration of the reference specimen. 3.3

Specimen CF2

In specimen CF2, strips above the openings were removed and a horizontal strip was applied just above the ground level of the structure. The corners were also strengthened like CF1 (Fig. 11). The failure sequence of the test was depicted in Fig. 12. Initial cracks were observed above the openings like reference specimen Ref. X type cracks were formed but limited and could not reached to the foundation level. Oppositely, these cracks were extended parallel to the ground. This specimen was collapsed when the acceleration level was 2 times the reference specimens failure acceleration. Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

3.4

Specimen CF3

After obtaining satisfactory results in specimens CF1 and CF2, in specimen CF3, only corner of the structure was covered with strengthening material. In this manner, more economic application was maintained (Fig. 13). Initial cracks were formed in the corners of the openings and X type cracks were formed. Also horizontal shear crack parallel to the ground was formed. Comparing with the reference specimen, more cracks were formed and distributed on a larger wall area. The wall, which was loaded in the out of plane direction, was failed and the test was stopped. This specimen could withstand 1.5 times acceleration according to the reference specimen. In Fig. 14, failure and damage mode of the specimen was given. 3.5

Specimen SwSP

Altin et al. (2005), studied 1/1 scale ordinary masonry house on the shaking table (Fig. 15). They applied a thin (5 mm in thickness) steel strip on the inner and outer surfaces of the www.nat-hazards-earth-syst-sci.net/10/1209/2010/


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Fig. 15 Outer and inner steel strips (Altın, 2005, Altin, 2008)

Fig. 16 Steel plate application for model house After attaching the steel plates, thin application plaster was applied the wallhouse. surfaces. The first crack formed above the Fig. 16. Steel plate forover model door corner and couldn’t reached to the roof level diagonally due to steel strip (Figure 17). Rather, this crack extended horizontally and reached to the corner of the structure. Similar condition was valid for the cracks formed on the corner of the window. Damage was concentrated above and below the window openings and X type cracks couldn’t form. At the end of the test, roof was separated from the structure and experiment was stopped. The maximum acceleration applied to this specimen was 1.4 times higher than the failure acceleration of the reference specimen.

Fig. 14 Failure sequence of specimen CF3 3.5 Specimen SwSP

Fig. 14. Failure sequence of specimen CF3.

Altın et al. (2005), studied 1/1 scale ordinary masonry house on the shaking table (Figure 15). They applied a thin (5 mm in thickness) steel strip on the inner and outer surfaces of the walls. Inner and outer steel strips were connected through the wall section with several rivets. The width of the steel plates were 150 mm. At the end of the test, they obtained satisfactory results and stated that this method is effective for strengthening of masonry structures. The specimen SwSP was strengthened with this idea. In order to represent steel plates, very thin steel plates were found and cut to obtain strips. Strips were placed vertically on the walls. Four strips were placed on the long walls and three strips were placed on the short walls (Figure 16).

Fig. 15 Outer and inner steel strips (Altın, 2005, Altin, 2008)

Fig. 15. Outer and inner steel strips (Altin, 2005, 2008).

Fig. 17 Failure sequence of specimen SwSP 3.6 Steel17. wire mesh application (SM) Fig. Failure sequence of specimen SwSP. The third method used was the mesh reinforcement and plaster application over the masonry walls. This method

is commonly used by many contractors and specialist to improve the seismic behavior of masonry structures. In walls. Inner and outer steel strips were connected through Figure 18 an application case in a school building was given. The mesh reinforcement was applied over the surface of the wall and several holes were drilled to fix the anchorages through the existing walls. Cement based the wall section with several rivets. The width of the steel plaster end was applied mesh. Same method was also used for adobe structures Aksehir Earthquake the of over thethetest, roof was separated fromafter thethe structure and on 2002 (Figure 19). plates were 150 mm. At the end of the test, they obtained experiment was stopped. The maximum acceleration applied satisfactory results and stated that this method is effective for to this specimen was 1.4 times higher than the failure accelstrengthening of masonry structures. The specimen SwSP eration of the reference specimen. was strengthened with this idea. In order to represent steel plates, veryFig. thin plates wereforfound and cut to obtain 16 steel Steel plate application model house 3.6 Steel wire mesh application (SM) strips. Strips were placed vertically on the walls. Four strips After attaching the steel plates, thin plaster was applied over the wall surfaces. The first crack formed above the were placed on the long walls and three strips were placed on The third method used was the mesh reinforcement and plasoor corner and couldn’t reached to the roof level diagonally due to steel strip (Figure 17). Rather, this crack the short wallsto(Fig. 16). of the structure. Similar condition was valid for thetercracks xtended horizontally and reached the corner application over the masonry walls. This method is comormed on the cornerAfter of the attaching window. Damage was concentrated aboveplaster and below the window and X used by many contractors and specialist to improve the steel plates, thin was appliedopeningsmonly ype cracks couldn’t form. At the end of the test, roof was separated from the structure and experiment was the seismic behavior of masonry structures. In Fig. 18 an over the wall surfaces. The first crack formed above the opped. The maximum acceleration applied to this specimen was 1.4 times higher than the failure acceleration f the reference specimen. door corner and could not reached to the roof level diagoapplication case in a school building was given. The mesh nally due to steel strip (Fig. 17). Rather, this crack extended reinforcement was applied over the surface of the wall and several holes were drilled to fix the anchorages through the horizontally and reached to the corner of the structure. Simexisting walls. Cement based plaster was applied over the ilar condition was valid for the cracks formed on the corner mesh. Same method was also used for adobe structures after of the window. Damage was concentrated above and below the Aksehir Earthquake in 2002 (Fig. 19). the window openings and X type cracks could not form. At


Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

Fig. 19 Welded wire mesh application on adobe structure

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Similar method was used to test the effectiveness of the application. In order to represent the mesh reinforcement, custom made scaled mesh reinforcement made of wires was used. Application was applied only on the corners of the structures. Mesh reinforcement was applied and gypsum was used to represent the cement based plaster. Column like gypsum-wire mesh reinforcement was given in Figure 20.


Fig. 20 Wire mesh reinforcement application on the specimen Specimen SM was tested execution starting from low frequencies and applied acceleration was increased up to the First diagonal cracks were observed on the didn’t corners of the The openings type horizontal cracks were Duefailure. to strengthening application, corner disintegration formed. cracksand areXrather at formed. the bottom and at the top of the openings. Failure acceleration of this specimen was 1.7 times higher than the reference specimen. Failure condition of the specimens was illustrated in Figure 21.

Fig. 20. Wire mesh reinforcement application on the specimen.

Fig. 18 Welded wire mesh application on a masonry school building

Fig. 18. Welded wire mesh application on a masonry school building. Fig. 18 Welded wire mesh application on a masonry school building

Fig. 19 Welded wire mesh application on adobe structure Similar method was used to test the effectiveness of the application. In order to represent the mesh reinforcement, custom made scaled mesh reinforcement made of wires was used. Application was applied only on the corners of the structures. Mesh reinforcement was applied and gypsum was used to represent the cement 19 Welded wirereinforcement mesh application on adobe structure based plaster. Column likeFig. gypsum-wire mesh was given in Figure 20.

Fig. 19. wire application adobe structure. Similar method was Welded used to test themesh effectiveness of the on application. In order to represent the mesh Fig. 21 Damage conditions of specimen SM reinforcement, custom made scaled mesh reinforcement made of wires was used. Application was applied only 3.7 Post tensioned specimen P1 Fig. 21. Damage conditions of specimen SM. on the corners of the structures. Mesh reinforcement was applied and gypsum was used to represent the cement Post tensioning of masonry walls increased the lateral load carrying and shear and bending capacities providing based plaster. Column like gypsum-wire mesh reinforcement was given in Figure 20. ductility. Several studies were exist in the literature about this idea. Vertical post tensioning increased the shear Similar method was used to test the effectiveness of the resistance of the walls and horizontal post tensioning also delays the corner separations. For this purpose, horizontal post tensioning was applied on the specimen P1. Benedetti at all. (1998) tested 2 storey model houses application. In order to represent the mesh reinforcement, on the shaking table setup (Figure 22). separations. For this purpose, horizontal post tensioning was custom made scaled mesh reinforcement made of wires was applied on the specimen P1. Benedetti at al. (1998) tested 2 used. Application was applied only on the corners of the storey model houses on the shaking table setup (Fig. 22). Fig. 20 Wire mesh reinforcement application on the specimen structures. Mesh reinforcement was applied and gypsum Specimenwas SM was tested startingthe fromcement low frequencies and plaster. applied acceleration was increased used toexecution represent based Column like up to In order to apply horizontal post tensioning and to disthe failure. First diagonal cracks were observed on the corners of the openings and X type cracks were formed. tribute the stress over the wall, wooden logs were used on the gypsum-wire mesh reinforcement was given in Fig. 20. corners of the structure. The cost of the wooden logs in real Fig. 20 Wire mesh reinforcement application on the specimen Specimen SM was tested execution starting from low freis not expensive. Steel rods were used to apply quencies applied acceleration was increased up was to increased the upapplication Specimen SM was tested and execution starting from low frequencies and applied acceleration to tension forces on the structure. The structure was wrapped the failure. First diagonal cracks were observed on the corners of the openings and X type cracks were formed. failure. First diagonal cracks were observed on the corat the roof and foundation levels. At this point door of the ners of the openings and X type cracks were formed. Due structure created problem from architectural point of view. to strengthening application, corner disintegration did not The failure condition of the specimen was given in Fig. 23. formed. The cracks are rather horizontal at the bottom and at Diagonal cracks replaced with horizontal shear cracks. Comthe top of the openings. Failure acceleration of this specimen paring with the reference specimen, more and distributed was 1.7 times higher than the reference specimen. Failure cracks can be pronounced. This specimen exposed 1.8 times condition of the specimens was illustrated in Fig. 21. higher acceleration than reference specimen. The behavior of the specimen was more ductile than the reference specimen. 3.7 Post tensioned specimen P1 Horizontal ties are very efficient in preventing collapse due to the separation of walls. Such devices were accomplished Post tensioning of masonry walls increased the lateral load carrying and shear and bending capacities providing ductilby steel ties, steel beams and RC bands. It was found that the best effects are achieved by an appropriate distribution on the ity. Several studies were exist in the literature about this idea. walls of the retaining forces due to horizontal ties (Benedetti Vertical post tensioning increased the shear resistance of the walls and horizontal post tensioning also delays the corner et al., 1998).



with shorter wooden pieces (Figure 24). The post tensioning was applied at the same pos horizontal cracks observed just above the openings. At the end of the test, rigid body motion of the capacity of the specimen. The failure of the specimen was given in Figure 25. The maxim reached at this specimen was less than the acceleration of P1 and 1.7 times higher than the t F. Ersubasi and H. H. Korkmaz: Shaking table tests on strengthening of masonry structures 1217 specimen.

Specimen P2 was identical to P1. After obtaining satisfactory results in specimen P1, wooden logs were replaced with shorter wooden pieces (Figure 24). The post tensioning was applied at the same positions. Similarly horizontal cracks observed just above the openings. At the end of the test, rigid body motion of the roof limited the capacity of the specimen. The failure of the specimen was given in Figure 25. The maximum acceleration reached at this specimen was less than the acceleration of P1 and 1.7 times higher than the that of reference specimen.

Fig. 22 Post tensioning application on masonry specimens by Benedetti et al., . (1998) In order to apply horizontal post tensioning and to distribute the stress over the wall, wooden logs were used on the corners of the structure. The cost of the wooden logs in real application is not expensive. Steel rods were used to apply tension forces on the structure. The structure was wrapped at the roof and foundation levels. At this point door of the structure created problem from architectural point of view. The failure condition of the specimen was given in Figure 23. Diagonal cracks replaced with horizontal shear cracks. Comparing with the reference specimen, more and distributed cracks can be pronounced. This specimen exposed 1.8 times higher acceleration than reference specimen. The behavior of the specimen was more ductile than the reference specimen. Horizontal ties are very efficient in preventing collapse due to the separation of walls. Such devices were accomplished by steel ties, steel beams and RC bands. It was found that the best effects are achieved by an appropriate distribution on the walls of the retaining forces due to horizontal ties (Benedetti et al., 1998).

Fig. 24 Specimen P2 and horizontal post tensioning application 24. Specimen P2 and horizontal post tensioning application. g. 22 Post tensioning application on masonry specimens by Benedetti et al.,Fig. . (1998) Fig. 22. Post tensioning application on masonry specimens by

Fig. 24 Specimen P2 and horizontal post tensioning application

et al. (1998). ly horizontalBenedetti post tensioning and to distribute the stress over the wall, wooden logs were used on the structure. The cost of the wooden logs in real application is not expensive. Steel rods were nsion forces on the structure. The structure was wrapped at the roof and foundation levels. At this the structure created problem from architectural point of view. The failure condition of the given in Figure 23. Diagonal cracks replaced with horizontal shear cracks. Comparing with the men, more and distributed cracks can be pronounced. This specimen exposed 1.8 times higher an reference specimen. The behavior of the specimen was more ductile than the reference zontal ties are very efficient in preventing collapse due to the separation of walls. Such devices hed by steel ties, steel beams and RC bands. It was found that the best effects are achieved by an ribution on the walls of the retaining forces due to horizontal ties (Benedetti et al., 1998).

Fig. 25 Failure of Specimen P2

Fig. 23 Failure of specimen P1

Fig. 25. Failure of specimen P2.

Fig. 23. Failure of specimen P1.

Specimen P2 was identical to P1. After obtaining satisfactory results in specimen P1, wooden logs were replaced with shorter wooden pieces (Fig. 24). The post tensioning was applied at the same positions. Similarly horizontal cracks observed just above the openings. At the end of the test, rigid body motion of the roof limited the capacity of the specimen. The failure of the specimen was given in Fig. 25. The maximum acceleration reached at this specimen was less than the acceleration of P1 and 1.7 times higher than the that of reference specimen. The post tensioning just above the foundation level was architecturally very difficult due to door entrance. In specimen P3, horizontal wrapping was applied only at the roof level. The structure was wrapped by steel rods and a box type behavior was obtained. The crack patters of this specimen were different than P1. Initially diagonal cracks were formed www.nat-hazards-earth-syst-sci.net/10/1209/2010/

and reached to the ground level. But corner failure was delayed due to horizontal rods and horizontal shear cracks were observed just below the window openings (Fig. 26). At the last stages of the failure, secondary horizontal cracks above the openings and corner failure near to the ground was observed. The specimen survived 1.5 times higher acceleration then reference specimen Ref.

4

Conclusions

Unreinforced masonry (URM) walls are used in a broad range of historic and modern buildings worldwide. Unfortunately unreinforced masonry construction is vulnerable to earthquake hazards. Earthquakes are considered to be the major cause of structural failure of masonry buildings in EuFig. In 25 less Failure of Specimen P2 especially in rope and Turkey. developed countries, Nat. Hazards Earth Syst. Sci., 10, 1209–1220, 2010

since they were constructed without engineering skills, based on experience of the local construction workers while scientific knowledge has been misapplied or omitted. The post tensioning just above the foundation level was architecturally very difficult due to door entrance. In specimen P3, horizontal wrapping was applied only at the roof level. The structure was wrapped by steel rods In this study, seismic performance improvement methods of masonry structures were evaluated experimentally. and a box type behavior was obtained. The crack patters of this specimen were different than P1. Initially The performance of 1/10 scale shaking table tests were compared against each other. Failure accelerations were diagonal cracks were formed and reached to the ground level. But corner failure was delayed due to horizontal given in reference to the original un-strengthened specimen Ref. The comparison of applied final accelerations in rods and horizontal shear cracks were observed just below the window openings (Figure 26). At the last stages of terms of reference specimens acceleration was presented in Figure 27. the failure, secondary horizontal cracks above the openings and corner failure near to the ground was observed. The specimen survived 1.5 times higher acceleration then reference specimen Ref.

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F. Ersubasi and H. H. Korkmaz: Shaking table tests on strengthening of masonry structures 2,5

Maximum acceleration/Reference acceleration

2,5

2

2

1,7 1,5

1,5

1

1,8

1,7 1,5

1,4

1

0,5

0 RF

CF1 CF2 CF3 SwSP SM

P1

P2

P3

Specimen Name 27 Comparison Fig. 27. ComparisonFigure of test results. of test results According to the limited results of this study, the main achievements provided by the interpretation of the experimental results are as follows: Reference This specimen displayed a similar failure patterns observed after earthquakes. Diagonal X type shear application increased the failure acceleration approxicracks were observed on the walls loaded in plane direction. Separation followed by cracks near the corners was mately 150%. 2.5failure higher the and the the last stage before the collapseCF1 of thesurvived structure. The of theaccelerations reference specimenthan was sudden behavior can be classified as brittle.

reference specimen Ref. The amount of strength improve-

CFRP typement materialsremained can be appliedat overabout the masonry walls.for In specimen CF1, specimen corners and wallwith portions above 100% the test the opening were covered with a material simulating the CFRP. This application increased the failure only vertical strips at he corners and horizontal cover below acceleration approximately %150. CF1 survived 2.5 higher accelerations than the reference specimen Ref. The amount of the strength improvementRelatively remained at about %100 forstrength the test specimen with only vertical Fig. 26 Failure sequence of specimen P3 openings. inferior enhancement wasstrips at he corners and horizontal cover below the openings. Relatively inferior strength enhancement was achieved by 4. Conclusions bycoverage application of (CF3) onlywith vertical coverage at improvement the cor- of 50%. applicationachieved of only vertical at the corners a total failure acceleration Fig. 26. Failure sequence of specimen P3. Unreinforced masonry (URM) walls are used in a broad range of historic and modern buildings worldwide. The width of the CFRP strips were taken as constant. In future study, the width can be taken as a parameter of ners (CF3) with a total failure acceleration improvement of Unfortunately unreinforced masonry construction is vulnerable to earthquake hazards. Earthquakes are the study but not included in the current paper.

50%. The width of the CFRP strips were taken as constant. plate strips over the masonry changed the behavior and load carrying capacity. X type In future study, thehorizontal widthshear cancracks be taken asthe a parameter of the by a new formed and just below roof level was followed horizontal study cracks above the level. The improvement the suburbs and rural areas, houses are constructed predombut notground included inperformance the current paper. was %40 higher than the reference specimen. inantly from masonry materials. These masonry structures The fixation of thin steel plate strips over the masonry The use of welded steel mesh reinforcement and plaster application was very popular in strengthening were constructed to resist gravitational forces with no conchanged the behavior and load capacity. X type diapplications. In this specimen, strength improvement of up carrying to 70% was obtained. sideration of the lateral seismic loads. Especially rural maagonal cracks could not formed and horizontal shear cracks Post tensioning application on the masonry walls can change the shear and bending capacities. Signifcant sonry structures can be classified as non-engineered since just the roof by abe new horizontal increases of the below lateral resistance, with level respect was to the followed original one, may obtained by the application of horizontal cracks posttensioning tendons. Specimen P3, which was horizontally wrapped just below the roof level was they were constructed without engineering skills, based on above the ground level. The performance improvedisplayed rather more ductile behavior than reference specimen. The level of improvement achieved was %50 experience of the local construction workers while scientific ment was 40% higher than the reference specimen. knowledge has been misapplied or omitted. The use of welded steel mesh reinforcement and plaster In this study, seismic performance improvement methods application was very popular in strengthening applications. of masonry structures were evaluated experimentally. The In this specimen, strength improvement of up to 70% was performance of 1/10 scale shaking table tests were compared obtained. against each other. Failure accelerations were given in refPost tensioning application on the masonry walls can erence to the original un-strengthened specimen Ref. The change the shear and bending capacities. Signifcant incomparison of applied final accelerations in terms of refercreases of the lateral resistance, with respect to the original ence specimens acceleration was presented in Fig. 27. one, may be obtained by the application of horizontal postAccording to the limited results of this study, the main tensioning tendons. Specimen P3, which was horizontally achievements provided by the interpretation of the experiwrapped just below the roof level was displayed rather more mental results are as follows: ductile behavior than reference specimen. The level of imReference specimen displayed a similar failure patterns provement achieved was 50% higher than the reference one. observed after earthquakes. Diagonal X type shear cracks If the wrapping can be done at several levels like P2, the perwere observed on the walls loaded in plane direction. Sepaformance was superior to the one level application. On the ration followed by cracks near the corners was the last stage other hand, openings like windows or doors may limit the before the collapse of the structure. The failure of the referapplication. In specimen P1, wooden logs along the height ence specimen was sudden and the behavior can be classified of the structure was used. In this way, post tensioning stress as brittle. was distributed over a larger wall portion. In specimens P1, CFRP type materials can be applied over the masonry P2 and P3, cracks were distributed over a larger area and walls. In specimen CF1, corners and wall portions above the more cracks were formed. Crack pattern distribution resulted opening were covered with a material simulating the CFRP. in more ductile behavior and improved the damping ratio

considered to be the major cause of structural failure of masonry buildings in Europe and Turkey. In less developed countries, especially in the suburbs and rural areas, houses are constructed predominantly from masonry materials. These masonry structures were constructed to resist gravitational forces with no The fixation of thin steel consideration of the lateral seismic loads. Especially rural masonry structures can be classified as non-engineered diagonal cracks couldn’t



F. Ersubasi and H. H. Korkmaz: Shaking table tests on strengthening of masonry structures and energy consumption characteristics of the masonry specimens. More retarded failure was obvious. The performance improvement in specimen P1 was approximately 80%. In all of the strengthened specimens, the brittle behavior associated with sudden roof collapse had delayed or prevented. Large and clear diagonal crack formation followed by brittle collapse were less pronounced and replaced by well-distributed cracks. The failure sequences was relatively more ductile with gradual damage formation. The choice of the appropriate method depends on the availability of the material and workmanship. Application of post tensioning is rather difficult due to details of the construction. On the other hand, CFRP type materials are expensive and may be used for historic and important structures. Strengthening of historical heritage buildings require special attention from architectural point of view. The applied technique must not disturb the appearance of the structure and better to give minimum disturbance. At this point CFRP application may be the best solution considering the effectiveness. Application of steel mesh and cement based plaster can be categorized as the worst solution considering the application area surface. Post tensioning application may also create undesired appearance. Strengthening of adobe structure is a very difficult task. For the rehabilitation studies the economical cost of the existing structure and the cost of the strengthening is important. The economical value of adobe structures are low and material quality and overall structural performance is poor. The new materials applied must behave monolithically with the adobe material. CFRP application cannot be considered for rural adobe structures. Post tensioning methods may delay the disintegration of wall units and can provide time to occupant to empty the dwelling before failure. Another problem is the durability of the applied material. Steel plates can create corrosion with time. Galvanized steel plates can solve this problem for the steel plate anchored methods. Painting of the steel plates can extend the life of the plates as well. 5

Recommendations for future study

This study handled three dimensional 1/10 scaled masonry specimens. Same methods can be tested on single masonry walls loaded in plane direction. Acknowledgements. This study was supported by the Selcuk University Scientific Research Project Office (BAP). The authors also thanks to Ahmet Turer and Serra Zerrin Korkmaz for the experimental study. Edited by: M. E. Contadakis Reviewed by: two anonymous referees


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