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Experimental modal analysis of brick masonry arches strengthened prepreg composites
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Original article
Experimental modal analysis of brick masonry arches strengthened prepreg composites Ferit Cakir a,∗ , Habib Uysal b,1 a b
Faculty of Architecture, Amasya University, Amasya, Turkey Faculty of Engineering, Ataturk University, Yakutiye, Erzurum, Turkey
a r t i c l e
i n f o
Article history: Received 24 January 2014 Accepted 11 June 2014 Available online xxx Keywords: Polymer composites Prepreg composites Brick masonry arches Modal parameters Experimental modal analysis Finite element analysis (FEA)
a b s t r a c t Polymer composites have been significantly used for strengthening of masonry structures in order to improve their structural behavior. In this study, the modal parameters and dynamic responses of the brick masonry arches, strengthened with prepreg polymer composites, have been experimentally assessed using experimental and numerical tests. The study was carried out in four major steps. Firstly, prepreg composites and traditional Horasan mortar were produced in the laboratory. In the second step, compression and tensile tests on the materials were conducted to determine the mechanical properties. In the third step, semicircular arches were built with masonry units and the prepreg composites were applied to four different strengthening configurations on the extrados and intrados surface of the arches. Finally, modal parameters of all arches were determined through experimental modal analysis method (EMA). After that, the results of the experimental analysis were compared with the numerical analysis. The results of the analyses show that the prepreg composites play an important role in the strengthening of the brick masonry arches and the prepreg composites enhance the frequencies and damping ratios of the brick masonry arches. © 2014 Elsevier Masson SAS. All rights reserved.
1. Research aims The cultural heritage in the world and their preservation for the next generation is crucial. Many historical structures continue to offer services and historical values; and as such, it is important to understand their structural behavior and collapse mechanism when developing a plan for their preservation and retrofit. New restoration and retrofitting methods should be preferred where traditional methods are insufficient. New technologies that can be appealing to historical structures are emerging with current advancements in materials and construction techniques. The main objectives of this research are: • to show the importance of the prepreg composites and to prove a reliable approach for strengthening and retrofit of historical structures; • to evaluate the effectiveness of the prepreg composites for brick masonry arches in terms of dynamic loads;
∗ Corresponding author. Tel.: +903582421613; fax: +903582421617. E-mail addresses: [email protected] (F. Cakir), [email protected] (H. Uysal). 1 Tel.: +904422314772; fax: +904422360757.
• to examine and prove the benefits of using the prepreg composites in strengthening brick masonry arches. 2. Introduction The use of engineering materials has depended on their local availability, so far. However, the diversity of engineering materials has completely changed thanks to the innovations in material technology. Modern technologies have greatly improved the efficiency of materials and workmanship. Especially, polymeric materials have been of significant importance to the engineering community for many years, and they have been broadly used in many different areas. Today, polymer materials are used as a strengthening material for existing and new structures because of their excellent engineering properties. They are significantly used for strengthening of masonry structures in order to increase their ultimate capacity. Many masonry structures have been built in earthquake prone zones and large portions of them are seismically unsafe. Thus, they have to be strengthened with convenient restoration materials. Over the years, engineers have strengthened masonry structures to withstand static and dynamic loads. In general, and to most extent, engineers have relied on several traditional strengthening materials that could be applied for masonry structures. However,
http://dx.doi.org/10.1016/j.culher.2014.06.003 1296-2074/© 2014 Elsevier Masson SAS. All rights reserved.
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traditional retrofitting materials have been inadequate to improve structural behavior and seismic resistance of these structures. Polymer technologies that can be appealing to masonry structures are emerging with current advancements in materials and construction techniques. In the last few decades, the polymer technology has been significantly expanded because of its proven effectiveness as an attractive solution for the structural and seismic retrofitting. For these reasons, applications of polymeric composites have increased gradually for masonry structures. One of the most important products of polymer technology is prepreg composite. Prepreg, which is known as preimpregnated reinforcement fabrics, is a product obtained with polymer technology in the past decade [1]. Prepreg composites have been used as an industrial material in different areas such as aerospace, automotive, and civil engineering. In previous studies, many researchers focused on the dynamic parameters and behavior of masonry structures using modal analysis methods [2–7]. However, in almost all of the previous studies, operational modal analysis was carried out in order to determine the dynamic parameters [8–10]. In addition, several experimental studies were carried out in order to monitor the dynamic behavior of masonry structures [11–14]. Unlike operational modal analysis and monitoring technique, experimental modal analysis has been rarely performed on masonry structures [15,16]. Moreover, the dynamic parameters of composites strengthened masonry arches are not completely clarified and investigated. Therefore, this study mainly focuses on unidirectional prepreg composites and their effects on dynamic behavior of masonry brick arches. 3. Materials and methods 3.1. Preparation of prepreg composites Prepreg composites are multi-component materials, such as matrix and filler materials, and they consist of a continuous sheet of oriented fibers, which have been completely impregnated with a polymer. In this study, the matrix material was preferred as a polymer matrix, and it was two-part epoxy system manufactured by Huntsman. This system consisted of Araldite® LY 1564 SP epoxy resin and Aradur® XB 3486 hardener, and they were weightily mixed in the ratio of 100:34, respectively. Furthermore, in the production of the prepreg material, carbon fibers were used as the filler materials. The carbon fibers were obtained from DowAksa Advanced Composites Holdings BV and 12 K A-42 code fibers were used in the production of the prepregs. The prepregs were manufactured by means of a specialized prepreg machine. In the production
Fig. 1. The production of the prepreg composite.
of the prepregs, in the first step, the carbon fibers were completely applied through the epoxy mixture. In the second step, the resinous fibers were wound onto the wax paper covered wheeler drum, and finally, the wound fiber sheet was properly cut and allowed to dry [15]. In this method, the carbon fibers were successively impregnated by polymer, and they were evenly spreading a metered volume of the resin and storage. After prepreg preparation, the laminate was treated by being heated at 80 ◦ C for 30 minutes with a pressure of 0.5 MPa [17,18] (Fig. 1). All of the prepregs were produced at the laboratories of Department of Mechanical Engineering at Ege University, Izmir, Turkey. 3.2. Preparation of masonry arches A series of semicircular arches, which have the same geometrical properties, were built from masonry hollow bricks. The arches were built on timber shutters, and they were removed two days after the construction of the arch. Traditional mortar mixture was preferred as a connection material between masonry bricks. For this purpose, traditional Horasan mortar, which was used in many historical structures in Anatolia [19,20], was chosen in this study. During preparation of the mortar, Alberia® bonding material (obtained from BASF Chemical Company), fine sand, lime paste, stone powder, and brick powder were mixed in equal ratios in weight.
Fig. 2. a: the preparation of brick masonry arches; b: the stacking of masonry arches to take the cure.
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Fig. 3. a: epoxy system application; b: prepreg composites application.
After preparation of traditional Horasan mortar, the construction of masonry arches took place. The values listed in Table 1 have been used in the construction of the arches. In this study, standard masonry hollow bricks, which had dimensions of 90 × 190 × 50 mm3 , were used (Fig. 2a). Masonry bricks have been cleaned with water in order to remove unwanted dust and foreign matter on the bricks. Iron separators have been used between the bricks in order to ensure uniformity of mortar thickness. All completed arches have been cured at least two times a day to gain high strength (Fig. 2b).
five samples and all tests were performed on a ELE - Autotest 3000 hydraulic test machine (Table 3). 3.6. Horasan mortar The compression and three-point bending tests of mortar samples at 7 and 28 days were used in order to grade the strength of the mortar (Fig. 6). The compressive strength of the mortar was obtained from compression tests on five cubes (50 × 50 × 50 mm3 ) according to TS 699, Turkish Building Code (Table 4). The tensile strength of the material samples was obtained from three-point
3.3. Mechanical properties of the materials In this study, several experimental tests were conducted to determine the mechanical properties of the materials. The mechanical properties of the prepreg composites, bricks, and mortar were obtained by testing the samples at the laboratories of Department of Civil Engineering and Department of Mechanical Engineering at Ataturk University, Erzurum, Turkey. 3.4. Prepreg composites Since tensile strength of unidirectional fiber composites is the most important property, the tensile strength was only measured in this study. The tensile strength was determined by means of standardized tests carried out with 25 × 250 mm2 dimensioned rectangular specimens. ASTM D 3039 rule [21] was based on tensile strength of the prepregs and all tests were carried out in a universal testing machine (Schimadzu Corporation) while recording load and deformation data on a computer. Table 2 summarizes the tensile strengths of the prepreg composite samples. 3.5. Masonry bricks The masonry bricks were subjected to compression and threepoint bending tests in order to determine mechanical properties of the bricks. Turkish codes were based on the compression and tensile tests of the masonry bricks. The tests were conducted on
Table 2 The tensile strengths of the prepreg composites. Samples
Tensile strength (kg/cm2 )
Density (kg/m3 )
1
775.45
1421
2
774.12
1426
3
775.25
1415
4
774.98
1420
5
776.02
1419
Table 3 The mechanical properties of the masonry bricks. Specimens
Compressive strength (kg/cm2 )
Tensile strength (kg/cm2 )
Density (kg/m3 )
1
163.15
20.1
2861
2
163.25
20.3
2859
3
164.01
21.0
2872
4
162.99
19.9
2866
5
163.86
21.9
2862
Compressive strength 28 days (kg/cm2 )
Density (kg/m3 )
Table 4 The compressive strength of Horasan mortar. Specimens
Compressive strength 7 days (kg/cm2 )
Table 1 Geometrical characteristics of the brick masonry arches. Span (mm)
1000
1
75.90
106.5
2125
Rise (mm)
500
2
73.59
116.2
2141
Arch thickness (mm)
90
3
70.10
115.4
2112
Number of the bricks
29
4
72.93
114.9
2110
Rise/span ratio
1/2
5
74.95
119.3
2166
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Table 5 The tensile strength of Horasan mortar.
5. Experimental modal analysis (EMA)
Specimens
Tensile strength 7 days (kg/cm2 )
Tensile strength 28 days (kg/cm2 )
Density (kg/m3 )
1
11.30
15.93
2120
2
10.13
15.16
2119
3
10.03
15.52
2165
4
10.12
15.63
2141
5
10.17
15.69
2124
The determination of the modal parameters, such as natural frequency and mode shapes, has always been an important issue for the design of a structure in terms of dynamic loading conditions. EMA, which is also known as frequency response function testing, has been generally preferred for the dynamic identification of the structures [25]. Therefore, in this study, EMA has been applied to assess the dynamic parameters. 5.1. Test setup and instrumentation
Table 6 Strengthening configurations. 1
Continuous strengthening at the intrados surface (CSI)
2
Continuous strengthening at the extrados surface (CSE)
3
Continuous strengthening at the intrados and extrados surfaces (CSIE)
4
Localized strengthening at the intrados and extrados surfaces (LSIE)
bending tests on five prisms (70 × 70 × 280 mm3 ) according to TS EN 1467 and 1469, Turkish Building Codes (Table 5) [22–24]. 4. Strengthening of brick masonry arches with the prepreg composites In the application phases, the arch surfaces used for reinforcement were suitably cleaned in order to remove unwanted contamination. Subsequently, the epoxy system composed of Araldite AV 138 M-1 epoxy and HV 998 hardener was applied on the arch surface as a putty layer using a spatula (Fig. 3a). Finally, the prepreg composites were carefully applied to the cleaned surface and the arches were successfully strengthened by the prepregs (Fig. 3b). Four main strengthening configurations were tested in this study. In the first stage, the composite was continuously applied at the intrados surface; in the second stage, the composite was continuously applied at the extrados surface. In the third stage, the composite was continuously applied at the intrados and extrados surfaces; in the last stage, the composite was locally applied at the critical zones, which were determined using numerical model (Table 6, Fig. 4). Subsequently, all arches were allowed for curing the composites around three days.
In experimental modal analysis, the laboratory was isolated from environmental vibration in order to obtain the most accurate results. Furthermore, all devices were closed during experimental studies in the laboratory, and people were prevented from entering the laboratory. All masonry arches were primarily fixed in the floor in order to have the desired boundary conditions. After fixing, the arches were hit from a certain point with an impact hammer. The responses of the arches against these impacts were obtained with the help of the transfer function. Applied impact force was measured with the force sensor on the impact hammer (Brüel&Kjaer 8206-002) and the responses of the arches were measured using a Laser Vibrometer (Ometron VH300+) (Fig. 5). A multi-channel data logger (Brüel&Kjaer 3050-B-040) recorded all modal analysis tests and all tests carried out at Department of Civil Engineering of Ataturk University, Erzurum, Turkey. 5.2. Determination of the frequency Following the experimental setup, all masonry arches were tested by means of EMA. Primarily, calibration tests were performed and pre-measured frequency response functions were investigated to determine the frequency resolution and the upper limits. After that, actual tests were started and all data were recorded by the data logger (Fig. 6). The rubber heading was preferred in this study. The arches were vibrated at least five times on the same point, and the linear averaging was used for this study. The peak picking (PP) technique was used to identify the frequencies and damping ratios. The natural frequencies and damping ratios were identified from the peaks in the frequency response functions (FRF). The selected peaks in the frequency response function were used to define the modes [25,26]. While the impact hammer was caused to vibrate of the arches, it was weighted at a
Fig. 4. Strengthening configurations on the arches.
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Fig. 5. Experimental setup of the modal analysis.
certain time between two impact forces for stabilization. After each impact force, the monitoring system was used, and the all response functions were controlled in order to better understand the vibration. In the all tests, four different impact points were chosen at the quarter span and middle span of the arches in- and out-of-plane. Although the frequencies and damping ratios were obtained with PULSE software, the mode shapes were not obtained due to absence of appropriate computer software. 5.3. Determination of the damping ratio In engineering terminology, the damping is to reduce the magnitude of vibration of a system. If a structure is made to vibrate, the amplitude of the vibration will reduce in the course of time due to the internal friction and absorbed energy [27]. The damping ratio directly relates to architectural properties and engineering materials of a structure. Thus, the determination of the damping ratio is crucial for structural behaviour. In the second step of experimental modal analysis tests, the damping ratio of the arches was investigated, and the effects of the strengthening member and strengthening configurations on the damping were observed. In this study, the damping ratios were determined with the halfpower bandwidth method using PULSE analysis software (Fig. 7a).
The frequency values (n ) are determined for each resonance value at the first stage of the study. The second step consists of the determination of Xmax that is the amplitude √ value for the peak point. The√ frequency bandwidth (X max / 2) is signed at below of the 1/ 2 of the amplitude value belonging to the appropriate resonance. Then, the beginning and end frequency points (2 − 1 ) of the bandwidth is determined and those points are called as half-power points. After determining all those points, the modal damping ratio () is calculated according to below formula [28]. 2 − 1 = 2 n
(1)
All the experimental tests conducted on the vibration of masonry arches are based on the determination of natural frequency and damping rations from software screenshot shown below (Fig. 7b) and some of them are calculated by using eq. (1) (Table 7). 6. Numerical analysis Three-dimensional finite element model that has been conducted for the masonry arches has been used in the context of this
Fig. 6. Five different response functions obtained from different impacts.
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Table 7 The values of frequency and damping ratio. Mode Shape
Measurement
Unstrengthened Arch
CSI
CSE
CSIE
LSIE
1
Frequency (Hz) Damping (%)
5.00 5.10
5.00 5.70
7.00 6.76
8.60 7.60
7.00 5.51
2
Frequency (Hz) Damping (%)
7.00 1.50
10.00 1.71
11.00 2.91
13.0 3.15
8.00 1.63
3
Frequency (Hz) Damping (%)
16.00 1.45
23.45 3.07
19.20 3.24
22.50 4.18
17.10 1.95
4
Frequency (Hz) Damping (%)
19.20 1.60
23.54 5.05
24.60 4.73
27.20 6.58
19.20 2.14
5
Frequency (Hz) Damping (%)
26.00 1.12
30.80 2.39
37.00 2.85
42.40 3.97
23.00 1.91
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
study. In this scope, FEA program, ANSYS Workbench [29], has been used to analyze the arches with SOLID186 elements, which has 20 nodes and three degrees of freedom per node. The arches were discretized with 4450, 6390, 6090, 8050 and 5606 solid elements with corresponding 22164, 36767, 34517, 49270 and 31171 nodes for the unstrengthened arch, CSE, CSI, CSIE and LSIE, respectively (Fig. 8a). According to the Turkish Earthquake Code [30], the modulus of elasticity (E) for masonry units used in masonry construction can be calculated by E = 200.f, where f is the compressive strength of masonry unit in MPa. Masonry arches were made of bricks and mortar. According to [31], the modulus of elasticity for new composite
material (brick + mortar) might be obtained from homogenization procedures such as: E=
tm tm Em
+ tu +
tu Eu
(2)
where tm represents the thickness of the mortar, tu represents the height of the brick, states an efficiency factor regarding the deficient bond between the two materials, Em and Eu represent the modulus of elasticity of mortar and brick, respectively. Therefore, the modulus of elasticity for brick + mortar can be calculated with the formula above. To get the most appropriate results in the numerical analyses, a reference masonry arch has been taken into consideration first that have the boundary conditions previously determined and the obtained frequency values are compared with the frequency values obtained through the numeric analyses. It is detected that the experimental data is different from the analytical data. To remove those differences, a calibration study on the numerical models recommended in the literature is intended to be conducted [8,9,25,26]. The comparisons made allowed modifications in material properties at the optimum level without changing boundary conditions and that amendment also allowed ensuring consistency between numerical analyses and experimental studies. The elasticity modulus of the masonry arches on the models was considered as 1500 MPa, Poisson ratio was 0.20 and unit volume of weight was 2800 kg/m3 . The elasticity modulus of prepreg composites was 76 GPa, Poission ratio was 0.30 and unit volume of weight was 1420 kg/m3 . The modes shapes of the arches were observed right before and after strengthening with the prepreg composites. It was observed that the strengthening configurations did not change the mode shapes while it was only affected the frequency and damping
Table 8 The frequencies obtained from finite element method. Mode Shapes
Fig. 7. a: the half-power bandwidth method [28]; b: the damping ratio screen view.
Unstrengthened Arch
CSI
CSE
CSIE
LSIE
1
4.81
5.73
6.87
8.33
5.59
2
7.95
11.40
10.63
11.06
8.53
3
16.08
19.06
23.03
22.74
17.62
4
18.46
23.61
23.24
28.28
20.40
5
26.11
30.53
37.72
43.95
22.48
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
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Fig. 8. a: finite element model of the arches; b: mode shapes obtained from finite element method.
values. The mode shapes of the masonry arches were shown on Fig. 8b and the frequency values obtained through the modal analyses was summarized in Table 8. Finally, it was observed that the experimental data were in great accordance with the numerical analyses’ results. 7. Results and discussion In the scope of this research, the semicircular arches were built with masonry units and the prepreg composites were applied to four different strengthening configurations on the extrados and intrados surface of the arches. In this study, experimental modal analysis method was carried out for dynamic evaluations. The
modal parameters of all arches were determined through EMA, and FEM. It has been seen that, in the mode shapes, the first mode of the arches has motion in the out-of-plane (Y direction) while the second mode has in plane (X direction). The third mode of vibration is torsion. The fourth and fifth modes of the arches have primarily in the Z and X directions and there is no motion in the Y directions. Therefore, the mode shapes of vibration have predominant in plane direction. In the other words, the out-ofplane mode shape has developed in the first natural frequencies of the vibration and the first five modes being different from the first mode occurred as in plane behavior. Similar to the findings of this study, several studies have reported that the first mode
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Table 9 The comparison of experimental modal analysis and numeric analysis results. Frequency
1. Mode
3. Mode
4. Mode
5. Mode
Unstrengthened Arch
Numerical (Hz) Experimental (Hz)
4.81 5.00
2. Mode 7.95 7.00
16.08 16.00
18.46 19.20
26.11 26.00
CSI
Numerical (Hz) Experimental (Hz)
5.73 5.00
11.40 10.00
19.06 19.20
23.61 23.54
30.53 30.80
CSE
Numerical (Hz) Experimental (Hz)
6.87 7.00
10.63 11.00
23.03 23.45
23.24 24.60
37.72 37.00
CSIE
Numerical (Hz) Experimental (Hz)
8.33 8.60
11.06 13.00
22.74 22.50
28.28 27.20
43.95 42.40
PSEI
Numerical (Hz) Experimental (Hz)
5.59 7.00
8.53 8.00
17.62 17.10
20.40 19.20
22.48 23.00
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
occurred out-of-plane direction, the other modes occurred in plane directions [32–34]. Similarly, some researchers have also indicated that the first five frequencies of masonry structures are lower than 5 Hz and the frequencies tended to increase with the application of the composite materials [2,32,34,35]. The analyses results prove that the prepreg composites increased frequency and damping ratio values of the arches. Moreover, it was also determined that most of the increase in the frequency values occurred due to CSIE and the lowest effect occurred due to LSIE by the consideration of the dynamic effects of composites. Besides, it was detected that the LSIE increased the frequency values by 10%, CSI increased 16%, CSE increased 45% and CSIE increased 65% for the first five modes by the consideration of effects of prepreg composites on frequencies. Furthermore, it was also observed that the frequency values, which were determined through numeric analyses, were sufficiently matched to the ones, which were determined by the experimental analysis. Finally, it was shown that the contribution of the reinforcement elements was higher for the cases where the reinforcement elements were applied onto the arch surfaces and CSE increased frequencies more rather than CSI does. Therefore, it is thought that the prepregs increased the stiffness of the arches. 8. Conclusions and recommendations In this study, “experimental modal analysis (EMA)” method was applied for determining the dynamic characteristics of masonry arches before and after strengthening with prepreg composites. Four different strengthening configurations were developed, and dynamic behavior of the arches was investigated through experimental tests. In this study, only the first five modes were evaluated and the effects of prepreg composites on the first five modes were investigated in the scope of the study. Additionally, all the experimental studies were supported with the numerical models and the effect of prepreg composites on the arches was observed with the finite element models. Moreover, the experimental and numerical studies were merged together and the consistency between data was observed. The examination of the results proved that prepreg composites have a considerable effect on the dynamic behavior of the masonry arches, and those composites generally enhanced the frequencies and damping ratios of masonry arches. Moreover, the experimental and analytical studies have shown that prepreg composite based retrofits improve stiffness of the brick masonry arches. Results of the analyses show that continuous strengthening at the intrados and extrados surfaces (CSIE) is the best strengthening way of the arch. In addition, localized strengthening at the intrados and extrados surfaces (LSIE) is lowly affected to the arch. Consequently, it is thought that prepreg composites have the potential to replace
conventional materials with better performance. It appears that composites are the materials gaining more acceptances in terms of choice in many engineering applications (Table 9). Acknowledgements The research is supported by the Scientific Research Projects of Ataturk University, Turkey through Research Grant 2012/432 is great fully acknowledged. The authors would like to thank Professor Mustafa Yaman, Associate Professor Gürkan S¸akar and Research Assistant Volkan Acar and Raci Aydin for their guidance and scientific contributions. In addition, authors especially thanks the Department of Mechanical Engineering at Ege University and Osman Gülsüm Restoration Inc. Furthermore, the authors would like to thank Dave Colson from Cleveland State University for continuous support in improving the language of the paper. References [1] M. Sacak, Polymer Technology, Gazi Kitabevi, Ankara, Turkey, 2005 (in Turkish). [2] S. Atamturktur, L. Burnn, F. Hemez, Vibration characteristics of vaulted masonry monuments undergoing differential support settlement, Eng. Struct. 33 (2011) 2472–2484. [3] A. Bensalem, C.A. Fairfield, A. Sibbald, The effect of material stiffness upon the modal characteristics of arch bridges, in: Mouchel Centenary Conference on Innovation in Civil and Structural Engineering, Aug 19–21, Cambridge, England, 1997, pp. 301–309. [4] J. Snoj, M. Osterreicher, M. Dolsek, The importance of ambient and forced vibration measurements for the results of seismic performance assessment of buildings obtained by using a simplified nonlinear procedure: case study of an old masonry building, Bull. Earthquake Eng. 11 (6) (2013) 2105–2132. [5] P. Michelis, C. Papadimitriou, G.K. Karaiskos, D.C. Papadioti, C. Fuggini, Seismic and vibration tests for assessing the effectiveness of GFRP for retrofitting masonry structures, Smart Struct. Syst. 9 (3) (2012) 207–230. [6] S. Atamturktur, F.M. Hemez, J.A. Laman, Uncertainty quantification in model verification and validation as applied to large scale historic masonry monuments, Eng. Struct. 43 (2012) 221–234. [7] A.C. Altunisik, A. Bayraktar, B. Sevim, F. Birinci, Vibration-based operational modal analysis of the Mikron historic arch bridge after restoration, Civil Eng. Environ. Syst. 28 (3) (2011) 247–259. [8] A. Bayraktar, A.C. Altunıs¸ık, B. Sevim, T. Türker, Finite Element Model Updating of Kömürhan Highway Bridge, I˙ MO Teknik Dergi, Yazı 307, 2009, pp. 4675–4700 (in Turkish). [9] A. S¸ahin, Digital Signal Processing, Dynamic Characteristic Identification and Finite Element Model Updating Software for Experimental and Operational Modal Testing of Structures: SignalCAD - ModalCAD – FemUP (PhD Thesis), Graduate School of Natural And Applied Sciences, Karadeniz Teknik University, Trabzon, Turkey, 2009 (in Turkish). [10] F. Aras, L. Krstevska, G. Altay, L. Tashkov, Experimental and numerical modal analyses of a historical masonry palace, Construct. Build. Mater. 25 (2011) 81–91. [11] A. Carpinteri, G. Lacidogna, Damage monitoring of an historical masonry building by the acoustic emission technique, Mater. Struct. 39 (2006) 161–167. [12] S. Rahmatalla, K. Hudson, Y. Liu, H.C. Eun, Finite element modal analysis and vibration-waveforms in health inspection of old bridges, Finite Elem. Anal. Des. 78 (2014) 40–46. [13] A. Carpinteri, S. Invernizzi, G. Lacidogna, In situ damage assessment and nonlinear modelling of a historical masonry tower, Eng. Struct. 27 (2005) 387–395.
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[14] G. Bartoli, M. Betti, L. Facchini, M. Orlando, Non-destructive characterization of stone columns by dynamic test: application to the lower colonnade of the Dome of the Siena Cathedral, Eng. Struct. 45 (2012) 519–535. [15] A. De Sortis, E. Antonacci, F. Vestroni, Dynamic identification of a masonry building using forced vibration tests, Eng. Struct. 27 (2005) 155–165. [16] A. Carpinteri, S. Invernizzi, G. Lacidogna, Historical brick masonry subjected to double flat-jack test: acoustic emissions and scale effects on cracking density, Construct. Build. Mat. 23 (2009) 2813–2820. [17] V. Acar, Interface Studies of Carbon Fiber Reinforced Thermoset Prepreg Composites (Master’s Thesis), Graduate School of Natural And Applied Sciences, Ataturk University, Erzurum, Turkey, 2013 (in Turkish). [18] V. Acar, H. Akbulut, M. Sarikanat, M.O. Seydibeyo˘glu, Y. Seki, S. Erden, Enhancement of interface mechanics of carbon fiber reinforced prepreg composites with carbon nanostructures, Electron. J. Mach. Technol. 10 (3) (2013) 43–51 (in Turkish). [19] S. Acun, N. Arioglu, The evaluation of lime mortars and plasters with the purpose of conservation and restoration, Int. Arch. Photogramm. Remote Sensing Spat. Inf. Sci. XXXIV–5/C15 (2003) 1682–1777. [20] B.S. Seker, F. Cakir, A. Dogangun, H. Uysal, Investigation of the structural performance of a masonry domed mosque by experimental tests and numerical analysis, Earthquakes Struct. 6 (4) (2014) 335–350. [21] ASTM D 3039, Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials, ASTM International, West Conshohocken, PA, 2008, http://dx.doi.org/10.1520/D3039 D3039M-14 www.astm.org [22] TS 699, Methods of Testing for Natural Building Stones, Turkish Building Code, Turkish Standards Institution, Ankara, Turkey, 2009 (in Turkish). [23] TS EN 1467, Natural Stone - Rough Blocks - Specifications, Turkish Building Code, Turkish Standards Institution, Ankara, Turkey, 2012. [24] TS EN 1469, Natural Stone Products - Slabs for Cladding - Requirements, Turkish Building Code, Turkish Standards Institution, (2006), Ankara, Turkey.
9
[25] T. Türker, Determination of Dynamic Characteristics of Steel Frames by Experimental Modal Analysis Method (Master’s Thesis), Graduate School of Natural And Applied Sciences, Karadeniz Teknik University, Trabzon, Turkey, 2005 (in Turkish). [26] A. Bayraktar, A.C. Altunıs¸ık, B. Sevim, T. Türker, M. Akköse, N. Cos¸kun, Modal analysis, experimental validation and calibration of a historical masonry minaret, J. Test. Eval. 36 (6) (2008) 516–524. [27] C. Arnold, Designing for Earthquakes A Manual for Architects, Risk Management Series, Federal Emergency Management Agency (Fema) 454, Oakland, California, 2006, pp. 111–137. [28] M.R. Aydin, Vibration Analysis Of Foam Filled Honeycomb Composite Sandwich Structure (Master’s Thesis), Graduate School of Natural And Applied Sciences, Ataturk University, Erzurum, Turkey, 2013 (in Turkish). [29] ANSYS, Finite Element Analysis Program, 14. 0 Release, SAS IP, Inc., USA, 2012. [30] TEC, Turkish Earthquake Code, Specification for Structures to Be Built in Disaster Areas, Ministry of Environment and Urbanization of Turkey, Turkey, 2007. [31] P.B. Lourenc¸o, G. Vasconcelos, L. Ramos, Assessment of the stability conditions of a Cistercian cloister, in: Second International Congress of Studies in Ancient Structures, July 7–13, Istanbul, Turkey, 2001. [32] L. Pelà, A. Aprile, A. Benedetti, Seismic assessment of masonry arch bridges, Eng. Struct. 31 (2009) 1777–1788. [33] L.F. Ramos, G. De Roeck, P.B. Lourenc¸o, A. Campos-Costa, Damage identification on arched masonry structures using ambient and random impact vibrations, Eng. Struct. 32 (2010) 146–162. [34] L.F. Ramos, L. Marques, P.B. Lourenco, G. De Roeck, A. Campos-Costa, J. Roque, Monitoring historical masonry structures with operational modal analysis: two case studies, Mech. Syst. Signal Process. 24 (2010) 1291–1305. [35] L. Pelà, A. Aprile, A. Benedetti, Comparison of seismic assessment procedures for masonry arch bridges, Construct. Build. Mater. 38 (2013) 381–394.
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Original article
Experimental modal analysis of brick masonry arches strengthened prepreg composites Ferit Cakir a,∗ , Habib Uysal b,1 a b
Faculty of Architecture, Amasya University, Amasya, Turkey Faculty of Engineering, Ataturk University, Yakutiye, Erzurum, Turkey
a r t i c l e
i n f o
Article history: Received 24 January 2014 Accepted 11 June 2014 Available online xxx Keywords: Polymer composites Prepreg composites Brick masonry arches Modal parameters Experimental modal analysis Finite element analysis (FEA)
a b s t r a c t Polymer composites have been significantly used for strengthening of masonry structures in order to improve their structural behavior. In this study, the modal parameters and dynamic responses of the brick masonry arches, strengthened with prepreg polymer composites, have been experimentally assessed using experimental and numerical tests. The study was carried out in four major steps. Firstly, prepreg composites and traditional Horasan mortar were produced in the laboratory. In the second step, compression and tensile tests on the materials were conducted to determine the mechanical properties. In the third step, semicircular arches were built with masonry units and the prepreg composites were applied to four different strengthening configurations on the extrados and intrados surface of the arches. Finally, modal parameters of all arches were determined through experimental modal analysis method (EMA). After that, the results of the experimental analysis were compared with the numerical analysis. The results of the analyses show that the prepreg composites play an important role in the strengthening of the brick masonry arches and the prepreg composites enhance the frequencies and damping ratios of the brick masonry arches. © 2014 Elsevier Masson SAS. All rights reserved.
1. Research aims The cultural heritage in the world and their preservation for the next generation is crucial. Many historical structures continue to offer services and historical values; and as such, it is important to understand their structural behavior and collapse mechanism when developing a plan for their preservation and retrofit. New restoration and retrofitting methods should be preferred where traditional methods are insufficient. New technologies that can be appealing to historical structures are emerging with current advancements in materials and construction techniques. The main objectives of this research are: • to show the importance of the prepreg composites and to prove a reliable approach for strengthening and retrofit of historical structures; • to evaluate the effectiveness of the prepreg composites for brick masonry arches in terms of dynamic loads;
∗ Corresponding author. Tel.: +903582421613; fax: +903582421617. E-mail addresses: [email protected] (F. Cakir), [email protected] (H. Uysal). 1 Tel.: +904422314772; fax: +904422360757.
• to examine and prove the benefits of using the prepreg composites in strengthening brick masonry arches. 2. Introduction The use of engineering materials has depended on their local availability, so far. However, the diversity of engineering materials has completely changed thanks to the innovations in material technology. Modern technologies have greatly improved the efficiency of materials and workmanship. Especially, polymeric materials have been of significant importance to the engineering community for many years, and they have been broadly used in many different areas. Today, polymer materials are used as a strengthening material for existing and new structures because of their excellent engineering properties. They are significantly used for strengthening of masonry structures in order to increase their ultimate capacity. Many masonry structures have been built in earthquake prone zones and large portions of them are seismically unsafe. Thus, they have to be strengthened with convenient restoration materials. Over the years, engineers have strengthened masonry structures to withstand static and dynamic loads. In general, and to most extent, engineers have relied on several traditional strengthening materials that could be applied for masonry structures. However,
http://dx.doi.org/10.1016/j.culher.2014.06.003 1296-2074/© 2014 Elsevier Masson SAS. All rights reserved.
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traditional retrofitting materials have been inadequate to improve structural behavior and seismic resistance of these structures. Polymer technologies that can be appealing to masonry structures are emerging with current advancements in materials and construction techniques. In the last few decades, the polymer technology has been significantly expanded because of its proven effectiveness as an attractive solution for the structural and seismic retrofitting. For these reasons, applications of polymeric composites have increased gradually for masonry structures. One of the most important products of polymer technology is prepreg composite. Prepreg, which is known as preimpregnated reinforcement fabrics, is a product obtained with polymer technology in the past decade [1]. Prepreg composites have been used as an industrial material in different areas such as aerospace, automotive, and civil engineering. In previous studies, many researchers focused on the dynamic parameters and behavior of masonry structures using modal analysis methods [2–7]. However, in almost all of the previous studies, operational modal analysis was carried out in order to determine the dynamic parameters [8–10]. In addition, several experimental studies were carried out in order to monitor the dynamic behavior of masonry structures [11–14]. Unlike operational modal analysis and monitoring technique, experimental modal analysis has been rarely performed on masonry structures [15,16]. Moreover, the dynamic parameters of composites strengthened masonry arches are not completely clarified and investigated. Therefore, this study mainly focuses on unidirectional prepreg composites and their effects on dynamic behavior of masonry brick arches. 3. Materials and methods 3.1. Preparation of prepreg composites Prepreg composites are multi-component materials, such as matrix and filler materials, and they consist of a continuous sheet of oriented fibers, which have been completely impregnated with a polymer. In this study, the matrix material was preferred as a polymer matrix, and it was two-part epoxy system manufactured by Huntsman. This system consisted of Araldite® LY 1564 SP epoxy resin and Aradur® XB 3486 hardener, and they were weightily mixed in the ratio of 100:34, respectively. Furthermore, in the production of the prepreg material, carbon fibers were used as the filler materials. The carbon fibers were obtained from DowAksa Advanced Composites Holdings BV and 12 K A-42 code fibers were used in the production of the prepregs. The prepregs were manufactured by means of a specialized prepreg machine. In the production
Fig. 1. The production of the prepreg composite.
of the prepregs, in the first step, the carbon fibers were completely applied through the epoxy mixture. In the second step, the resinous fibers were wound onto the wax paper covered wheeler drum, and finally, the wound fiber sheet was properly cut and allowed to dry [15]. In this method, the carbon fibers were successively impregnated by polymer, and they were evenly spreading a metered volume of the resin and storage. After prepreg preparation, the laminate was treated by being heated at 80 ◦ C for 30 minutes with a pressure of 0.5 MPa [17,18] (Fig. 1). All of the prepregs were produced at the laboratories of Department of Mechanical Engineering at Ege University, Izmir, Turkey. 3.2. Preparation of masonry arches A series of semicircular arches, which have the same geometrical properties, were built from masonry hollow bricks. The arches were built on timber shutters, and they were removed two days after the construction of the arch. Traditional mortar mixture was preferred as a connection material between masonry bricks. For this purpose, traditional Horasan mortar, which was used in many historical structures in Anatolia [19,20], was chosen in this study. During preparation of the mortar, Alberia® bonding material (obtained from BASF Chemical Company), fine sand, lime paste, stone powder, and brick powder were mixed in equal ratios in weight.
Fig. 2. a: the preparation of brick masonry arches; b: the stacking of masonry arches to take the cure.
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Fig. 3. a: epoxy system application; b: prepreg composites application.
After preparation of traditional Horasan mortar, the construction of masonry arches took place. The values listed in Table 1 have been used in the construction of the arches. In this study, standard masonry hollow bricks, which had dimensions of 90 × 190 × 50 mm3 , were used (Fig. 2a). Masonry bricks have been cleaned with water in order to remove unwanted dust and foreign matter on the bricks. Iron separators have been used between the bricks in order to ensure uniformity of mortar thickness. All completed arches have been cured at least two times a day to gain high strength (Fig. 2b).
five samples and all tests were performed on a ELE - Autotest 3000 hydraulic test machine (Table 3). 3.6. Horasan mortar The compression and three-point bending tests of mortar samples at 7 and 28 days were used in order to grade the strength of the mortar (Fig. 6). The compressive strength of the mortar was obtained from compression tests on five cubes (50 × 50 × 50 mm3 ) according to TS 699, Turkish Building Code (Table 4). The tensile strength of the material samples was obtained from three-point
3.3. Mechanical properties of the materials In this study, several experimental tests were conducted to determine the mechanical properties of the materials. The mechanical properties of the prepreg composites, bricks, and mortar were obtained by testing the samples at the laboratories of Department of Civil Engineering and Department of Mechanical Engineering at Ataturk University, Erzurum, Turkey. 3.4. Prepreg composites Since tensile strength of unidirectional fiber composites is the most important property, the tensile strength was only measured in this study. The tensile strength was determined by means of standardized tests carried out with 25 × 250 mm2 dimensioned rectangular specimens. ASTM D 3039 rule [21] was based on tensile strength of the prepregs and all tests were carried out in a universal testing machine (Schimadzu Corporation) while recording load and deformation data on a computer. Table 2 summarizes the tensile strengths of the prepreg composite samples. 3.5. Masonry bricks The masonry bricks were subjected to compression and threepoint bending tests in order to determine mechanical properties of the bricks. Turkish codes were based on the compression and tensile tests of the masonry bricks. The tests were conducted on
Table 2 The tensile strengths of the prepreg composites. Samples
Tensile strength (kg/cm2 )
Density (kg/m3 )
1
775.45
1421
2
774.12
1426
3
775.25
1415
4
774.98
1420
5
776.02
1419
Table 3 The mechanical properties of the masonry bricks. Specimens
Compressive strength (kg/cm2 )
Tensile strength (kg/cm2 )
Density (kg/m3 )
1
163.15
20.1
2861
2
163.25
20.3
2859
3
164.01
21.0
2872
4
162.99
19.9
2866
5
163.86
21.9
2862
Compressive strength 28 days (kg/cm2 )
Density (kg/m3 )
Table 4 The compressive strength of Horasan mortar. Specimens
Compressive strength 7 days (kg/cm2 )
Table 1 Geometrical characteristics of the brick masonry arches. Span (mm)
1000
1
75.90
106.5
2125
Rise (mm)
500
2
73.59
116.2
2141
Arch thickness (mm)
90
3
70.10
115.4
2112
Number of the bricks
29
4
72.93
114.9
2110
Rise/span ratio
1/2
5
74.95
119.3
2166
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Table 5 The tensile strength of Horasan mortar.
5. Experimental modal analysis (EMA)
Specimens
Tensile strength 7 days (kg/cm2 )
Tensile strength 28 days (kg/cm2 )
Density (kg/m3 )
1
11.30
15.93
2120
2
10.13
15.16
2119
3
10.03
15.52
2165
4
10.12
15.63
2141
5
10.17
15.69
2124
The determination of the modal parameters, such as natural frequency and mode shapes, has always been an important issue for the design of a structure in terms of dynamic loading conditions. EMA, which is also known as frequency response function testing, has been generally preferred for the dynamic identification of the structures [25]. Therefore, in this study, EMA has been applied to assess the dynamic parameters. 5.1. Test setup and instrumentation
Table 6 Strengthening configurations. 1
Continuous strengthening at the intrados surface (CSI)
2
Continuous strengthening at the extrados surface (CSE)
3
Continuous strengthening at the intrados and extrados surfaces (CSIE)
4
Localized strengthening at the intrados and extrados surfaces (LSIE)
bending tests on five prisms (70 × 70 × 280 mm3 ) according to TS EN 1467 and 1469, Turkish Building Codes (Table 5) [22–24]. 4. Strengthening of brick masonry arches with the prepreg composites In the application phases, the arch surfaces used for reinforcement were suitably cleaned in order to remove unwanted contamination. Subsequently, the epoxy system composed of Araldite AV 138 M-1 epoxy and HV 998 hardener was applied on the arch surface as a putty layer using a spatula (Fig. 3a). Finally, the prepreg composites were carefully applied to the cleaned surface and the arches were successfully strengthened by the prepregs (Fig. 3b). Four main strengthening configurations were tested in this study. In the first stage, the composite was continuously applied at the intrados surface; in the second stage, the composite was continuously applied at the extrados surface. In the third stage, the composite was continuously applied at the intrados and extrados surfaces; in the last stage, the composite was locally applied at the critical zones, which were determined using numerical model (Table 6, Fig. 4). Subsequently, all arches were allowed for curing the composites around three days.
In experimental modal analysis, the laboratory was isolated from environmental vibration in order to obtain the most accurate results. Furthermore, all devices were closed during experimental studies in the laboratory, and people were prevented from entering the laboratory. All masonry arches were primarily fixed in the floor in order to have the desired boundary conditions. After fixing, the arches were hit from a certain point with an impact hammer. The responses of the arches against these impacts were obtained with the help of the transfer function. Applied impact force was measured with the force sensor on the impact hammer (Brüel&Kjaer 8206-002) and the responses of the arches were measured using a Laser Vibrometer (Ometron VH300+) (Fig. 5). A multi-channel data logger (Brüel&Kjaer 3050-B-040) recorded all modal analysis tests and all tests carried out at Department of Civil Engineering of Ataturk University, Erzurum, Turkey. 5.2. Determination of the frequency Following the experimental setup, all masonry arches were tested by means of EMA. Primarily, calibration tests were performed and pre-measured frequency response functions were investigated to determine the frequency resolution and the upper limits. After that, actual tests were started and all data were recorded by the data logger (Fig. 6). The rubber heading was preferred in this study. The arches were vibrated at least five times on the same point, and the linear averaging was used for this study. The peak picking (PP) technique was used to identify the frequencies and damping ratios. The natural frequencies and damping ratios were identified from the peaks in the frequency response functions (FRF). The selected peaks in the frequency response function were used to define the modes [25,26]. While the impact hammer was caused to vibrate of the arches, it was weighted at a
Fig. 4. Strengthening configurations on the arches.
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Fig. 5. Experimental setup of the modal analysis.
certain time between two impact forces for stabilization. After each impact force, the monitoring system was used, and the all response functions were controlled in order to better understand the vibration. In the all tests, four different impact points were chosen at the quarter span and middle span of the arches in- and out-of-plane. Although the frequencies and damping ratios were obtained with PULSE software, the mode shapes were not obtained due to absence of appropriate computer software. 5.3. Determination of the damping ratio In engineering terminology, the damping is to reduce the magnitude of vibration of a system. If a structure is made to vibrate, the amplitude of the vibration will reduce in the course of time due to the internal friction and absorbed energy [27]. The damping ratio directly relates to architectural properties and engineering materials of a structure. Thus, the determination of the damping ratio is crucial for structural behaviour. In the second step of experimental modal analysis tests, the damping ratio of the arches was investigated, and the effects of the strengthening member and strengthening configurations on the damping were observed. In this study, the damping ratios were determined with the halfpower bandwidth method using PULSE analysis software (Fig. 7a).
The frequency values (n ) are determined for each resonance value at the first stage of the study. The second step consists of the determination of Xmax that is the amplitude √ value for the peak point. The√ frequency bandwidth (X max / 2) is signed at below of the 1/ 2 of the amplitude value belonging to the appropriate resonance. Then, the beginning and end frequency points (2 − 1 ) of the bandwidth is determined and those points are called as half-power points. After determining all those points, the modal damping ratio () is calculated according to below formula [28]. 2 − 1 = 2 n
(1)
All the experimental tests conducted on the vibration of masonry arches are based on the determination of natural frequency and damping rations from software screenshot shown below (Fig. 7b) and some of them are calculated by using eq. (1) (Table 7). 6. Numerical analysis Three-dimensional finite element model that has been conducted for the masonry arches has been used in the context of this
Fig. 6. Five different response functions obtained from different impacts.
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Table 7 The values of frequency and damping ratio. Mode Shape
Measurement
Unstrengthened Arch
CSI
CSE
CSIE
LSIE
1
Frequency (Hz) Damping (%)
5.00 5.10
5.00 5.70
7.00 6.76
8.60 7.60
7.00 5.51
2
Frequency (Hz) Damping (%)
7.00 1.50
10.00 1.71
11.00 2.91
13.0 3.15
8.00 1.63
3
Frequency (Hz) Damping (%)
16.00 1.45
23.45 3.07
19.20 3.24
22.50 4.18
17.10 1.95
4
Frequency (Hz) Damping (%)
19.20 1.60
23.54 5.05
24.60 4.73
27.20 6.58
19.20 2.14
5
Frequency (Hz) Damping (%)
26.00 1.12
30.80 2.39
37.00 2.85
42.40 3.97
23.00 1.91
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
study. In this scope, FEA program, ANSYS Workbench [29], has been used to analyze the arches with SOLID186 elements, which has 20 nodes and three degrees of freedom per node. The arches were discretized with 4450, 6390, 6090, 8050 and 5606 solid elements with corresponding 22164, 36767, 34517, 49270 and 31171 nodes for the unstrengthened arch, CSE, CSI, CSIE and LSIE, respectively (Fig. 8a). According to the Turkish Earthquake Code [30], the modulus of elasticity (E) for masonry units used in masonry construction can be calculated by E = 200.f, where f is the compressive strength of masonry unit in MPa. Masonry arches were made of bricks and mortar. According to [31], the modulus of elasticity for new composite
material (brick + mortar) might be obtained from homogenization procedures such as: E=
tm tm Em
+ tu +
tu Eu
(2)
where tm represents the thickness of the mortar, tu represents the height of the brick, states an efficiency factor regarding the deficient bond between the two materials, Em and Eu represent the modulus of elasticity of mortar and brick, respectively. Therefore, the modulus of elasticity for brick + mortar can be calculated with the formula above. To get the most appropriate results in the numerical analyses, a reference masonry arch has been taken into consideration first that have the boundary conditions previously determined and the obtained frequency values are compared with the frequency values obtained through the numeric analyses. It is detected that the experimental data is different from the analytical data. To remove those differences, a calibration study on the numerical models recommended in the literature is intended to be conducted [8,9,25,26]. The comparisons made allowed modifications in material properties at the optimum level without changing boundary conditions and that amendment also allowed ensuring consistency between numerical analyses and experimental studies. The elasticity modulus of the masonry arches on the models was considered as 1500 MPa, Poisson ratio was 0.20 and unit volume of weight was 2800 kg/m3 . The elasticity modulus of prepreg composites was 76 GPa, Poission ratio was 0.30 and unit volume of weight was 1420 kg/m3 . The modes shapes of the arches were observed right before and after strengthening with the prepreg composites. It was observed that the strengthening configurations did not change the mode shapes while it was only affected the frequency and damping
Table 8 The frequencies obtained from finite element method. Mode Shapes
Fig. 7. a: the half-power bandwidth method [28]; b: the damping ratio screen view.
Unstrengthened Arch
CSI
CSE
CSIE
LSIE
1
4.81
5.73
6.87
8.33
5.59
2
7.95
11.40
10.63
11.06
8.53
3
16.08
19.06
23.03
22.74
17.62
4
18.46
23.61
23.24
28.28
20.40
5
26.11
30.53
37.72
43.95
22.48
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
Please cite this article in press as: F. Cakir, H. Uysal, Experimental modal analysis of brick masonry arches strengthened prepreg composites, Journal of Cultural Heritage (2014), http://dx.doi.org/10.1016/j.culher.2014.06.003
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Fig. 8. a: finite element model of the arches; b: mode shapes obtained from finite element method.
values. The mode shapes of the masonry arches were shown on Fig. 8b and the frequency values obtained through the modal analyses was summarized in Table 8. Finally, it was observed that the experimental data were in great accordance with the numerical analyses’ results. 7. Results and discussion In the scope of this research, the semicircular arches were built with masonry units and the prepreg composites were applied to four different strengthening configurations on the extrados and intrados surface of the arches. In this study, experimental modal analysis method was carried out for dynamic evaluations. The
modal parameters of all arches were determined through EMA, and FEM. It has been seen that, in the mode shapes, the first mode of the arches has motion in the out-of-plane (Y direction) while the second mode has in plane (X direction). The third mode of vibration is torsion. The fourth and fifth modes of the arches have primarily in the Z and X directions and there is no motion in the Y directions. Therefore, the mode shapes of vibration have predominant in plane direction. In the other words, the out-ofplane mode shape has developed in the first natural frequencies of the vibration and the first five modes being different from the first mode occurred as in plane behavior. Similar to the findings of this study, several studies have reported that the first mode
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Table 9 The comparison of experimental modal analysis and numeric analysis results. Frequency
1. Mode
3. Mode
4. Mode
5. Mode
Unstrengthened Arch
Numerical (Hz) Experimental (Hz)
4.81 5.00
2. Mode 7.95 7.00
16.08 16.00
18.46 19.20
26.11 26.00
CSI
Numerical (Hz) Experimental (Hz)
5.73 5.00
11.40 10.00
19.06 19.20
23.61 23.54
30.53 30.80
CSE
Numerical (Hz) Experimental (Hz)
6.87 7.00
10.63 11.00
23.03 23.45
23.24 24.60
37.72 37.00
CSIE
Numerical (Hz) Experimental (Hz)
8.33 8.60
11.06 13.00
22.74 22.50
28.28 27.20
43.95 42.40
PSEI
Numerical (Hz) Experimental (Hz)
5.59 7.00
8.53 8.00
17.62 17.10
20.40 19.20
22.48 23.00
CSI: continuous strengthening at the intrados surface; CSE: continuous strengthening at the extrados surface; CSIE: continuous strengthening at the intrados and extrados surfaces; LSIE: localized strengthening at the intrados and extrados surfaces.
occurred out-of-plane direction, the other modes occurred in plane directions [32–34]. Similarly, some researchers have also indicated that the first five frequencies of masonry structures are lower than 5 Hz and the frequencies tended to increase with the application of the composite materials [2,32,34,35]. The analyses results prove that the prepreg composites increased frequency and damping ratio values of the arches. Moreover, it was also determined that most of the increase in the frequency values occurred due to CSIE and the lowest effect occurred due to LSIE by the consideration of the dynamic effects of composites. Besides, it was detected that the LSIE increased the frequency values by 10%, CSI increased 16%, CSE increased 45% and CSIE increased 65% for the first five modes by the consideration of effects of prepreg composites on frequencies. Furthermore, it was also observed that the frequency values, which were determined through numeric analyses, were sufficiently matched to the ones, which were determined by the experimental analysis. Finally, it was shown that the contribution of the reinforcement elements was higher for the cases where the reinforcement elements were applied onto the arch surfaces and CSE increased frequencies more rather than CSI does. Therefore, it is thought that the prepregs increased the stiffness of the arches. 8. Conclusions and recommendations In this study, “experimental modal analysis (EMA)” method was applied for determining the dynamic characteristics of masonry arches before and after strengthening with prepreg composites. Four different strengthening configurations were developed, and dynamic behavior of the arches was investigated through experimental tests. In this study, only the first five modes were evaluated and the effects of prepreg composites on the first five modes were investigated in the scope of the study. Additionally, all the experimental studies were supported with the numerical models and the effect of prepreg composites on the arches was observed with the finite element models. Moreover, the experimental and numerical studies were merged together and the consistency between data was observed. The examination of the results proved that prepreg composites have a considerable effect on the dynamic behavior of the masonry arches, and those composites generally enhanced the frequencies and damping ratios of masonry arches. Moreover, the experimental and analytical studies have shown that prepreg composite based retrofits improve stiffness of the brick masonry arches. Results of the analyses show that continuous strengthening at the intrados and extrados surfaces (CSIE) is the best strengthening way of the arch. In addition, localized strengthening at the intrados and extrados surfaces (LSIE) is lowly affected to the arch. Consequently, it is thought that prepreg composites have the potential to replace
conventional materials with better performance. It appears that composites are the materials gaining more acceptances in terms of choice in many engineering applications (Table 9). Acknowledgements The research is supported by the Scientific Research Projects of Ataturk University, Turkey through Research Grant 2012/432 is great fully acknowledged. The authors would like to thank Professor Mustafa Yaman, Associate Professor Gürkan S¸akar and Research Assistant Volkan Acar and Raci Aydin for their guidance and scientific contributions. In addition, authors especially thanks the Department of Mechanical Engineering at Ege University and Osman Gülsüm Restoration Inc. Furthermore, the authors would like to thank Dave Colson from Cleveland State University for continuous support in improving the language of the paper. References [1] M. Sacak, Polymer Technology, Gazi Kitabevi, Ankara, Turkey, 2005 (in Turkish). [2] S. Atamturktur, L. Burnn, F. Hemez, Vibration characteristics of vaulted masonry monuments undergoing differential support settlement, Eng. Struct. 33 (2011) 2472–2484. [3] A. Bensalem, C.A. Fairfield, A. Sibbald, The effect of material stiffness upon the modal characteristics of arch bridges, in: Mouchel Centenary Conference on Innovation in Civil and Structural Engineering, Aug 19–21, Cambridge, England, 1997, pp. 301–309. [4] J. Snoj, M. Osterreicher, M. Dolsek, The importance of ambient and forced vibration measurements for the results of seismic performance assessment of buildings obtained by using a simplified nonlinear procedure: case study of an old masonry building, Bull. Earthquake Eng. 11 (6) (2013) 2105–2132. [5] P. Michelis, C. Papadimitriou, G.K. Karaiskos, D.C. Papadioti, C. Fuggini, Seismic and vibration tests for assessing the effectiveness of GFRP for retrofitting masonry structures, Smart Struct. Syst. 9 (3) (2012) 207–230. [6] S. Atamturktur, F.M. Hemez, J.A. Laman, Uncertainty quantification in model verification and validation as applied to large scale historic masonry monuments, Eng. Struct. 43 (2012) 221–234. [7] A.C. Altunisik, A. Bayraktar, B. Sevim, F. Birinci, Vibration-based operational modal analysis of the Mikron historic arch bridge after restoration, Civil Eng. Environ. Syst. 28 (3) (2011) 247–259. [8] A. Bayraktar, A.C. Altunıs¸ık, B. Sevim, T. Türker, Finite Element Model Updating of Kömürhan Highway Bridge, I˙ MO Teknik Dergi, Yazı 307, 2009, pp. 4675–4700 (in Turkish). [9] A. S¸ahin, Digital Signal Processing, Dynamic Characteristic Identification and Finite Element Model Updating Software for Experimental and Operational Modal Testing of Structures: SignalCAD - ModalCAD – FemUP (PhD Thesis), Graduate School of Natural And Applied Sciences, Karadeniz Teknik University, Trabzon, Turkey, 2009 (in Turkish). [10] F. Aras, L. Krstevska, G. Altay, L. Tashkov, Experimental and numerical modal analyses of a historical masonry palace, Construct. Build. Mater. 25 (2011) 81–91. [11] A. Carpinteri, G. Lacidogna, Damage monitoring of an historical masonry building by the acoustic emission technique, Mater. Struct. 39 (2006) 161–167. [12] S. Rahmatalla, K. Hudson, Y. Liu, H.C. Eun, Finite element modal analysis and vibration-waveforms in health inspection of old bridges, Finite Elem. Anal. Des. 78 (2014) 40–46. [13] A. Carpinteri, S. Invernizzi, G. Lacidogna, In situ damage assessment and nonlinear modelling of a historical masonry tower, Eng. Struct. 27 (2005) 387–395.
Please cite this article in press as: F. Cakir, H. Uysal, Experimental modal analysis of brick masonry arches strengthened prepreg composites, Journal of Cultural Heritage (2014), http://dx.doi.org/10.1016/j.culher.2014.06.003
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ARTICLE IN PRESS F. Cakir, H. Uysal / Journal of Cultural Heritage xxx (2014) xxx–xxx
[14] G. Bartoli, M. Betti, L. Facchini, M. Orlando, Non-destructive characterization of stone columns by dynamic test: application to the lower colonnade of the Dome of the Siena Cathedral, Eng. Struct. 45 (2012) 519–535. [15] A. De Sortis, E. Antonacci, F. Vestroni, Dynamic identification of a masonry building using forced vibration tests, Eng. Struct. 27 (2005) 155–165. [16] A. Carpinteri, S. Invernizzi, G. Lacidogna, Historical brick masonry subjected to double flat-jack test: acoustic emissions and scale effects on cracking density, Construct. Build. Mat. 23 (2009) 2813–2820. [17] V. Acar, Interface Studies of Carbon Fiber Reinforced Thermoset Prepreg Composites (Master’s Thesis), Graduate School of Natural And Applied Sciences, Ataturk University, Erzurum, Turkey, 2013 (in Turkish). [18] V. Acar, H. Akbulut, M. Sarikanat, M.O. Seydibeyo˘glu, Y. Seki, S. Erden, Enhancement of interface mechanics of carbon fiber reinforced prepreg composites with carbon nanostructures, Electron. J. Mach. Technol. 10 (3) (2013) 43–51 (in Turkish). [19] S. Acun, N. Arioglu, The evaluation of lime mortars and plasters with the purpose of conservation and restoration, Int. Arch. Photogramm. Remote Sensing Spat. Inf. Sci. XXXIV–5/C15 (2003) 1682–1777. [20] B.S. Seker, F. Cakir, A. Dogangun, H. Uysal, Investigation of the structural performance of a masonry domed mosque by experimental tests and numerical analysis, Earthquakes Struct. 6 (4) (2014) 335–350. [21] ASTM D 3039, Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials, ASTM International, West Conshohocken, PA, 2008, http://dx.doi.org/10.1520/D3039 D3039M-14 www.astm.org [22] TS 699, Methods of Testing for Natural Building Stones, Turkish Building Code, Turkish Standards Institution, Ankara, Turkey, 2009 (in Turkish). [23] TS EN 1467, Natural Stone - Rough Blocks - Specifications, Turkish Building Code, Turkish Standards Institution, Ankara, Turkey, 2012. [24] TS EN 1469, Natural Stone Products - Slabs for Cladding - Requirements, Turkish Building Code, Turkish Standards Institution, (2006), Ankara, Turkey.
9
[25] T. Türker, Determination of Dynamic Characteristics of Steel Frames by Experimental Modal Analysis Method (Master’s Thesis), Graduate School of Natural And Applied Sciences, Karadeniz Teknik University, Trabzon, Turkey, 2005 (in Turkish). [26] A. Bayraktar, A.C. Altunıs¸ık, B. Sevim, T. Türker, M. Akköse, N. Cos¸kun, Modal analysis, experimental validation and calibration of a historical masonry minaret, J. Test. Eval. 36 (6) (2008) 516–524. [27] C. Arnold, Designing for Earthquakes A Manual for Architects, Risk Management Series, Federal Emergency Management Agency (Fema) 454, Oakland, California, 2006, pp. 111–137. [28] M.R. Aydin, Vibration Analysis Of Foam Filled Honeycomb Composite Sandwich Structure (Master’s Thesis), Graduate School of Natural And Applied Sciences, Ataturk University, Erzurum, Turkey, 2013 (in Turkish). [29] ANSYS, Finite Element Analysis Program, 14. 0 Release, SAS IP, Inc., USA, 2012. [30] TEC, Turkish Earthquake Code, Specification for Structures to Be Built in Disaster Areas, Ministry of Environment and Urbanization of Turkey, Turkey, 2007. [31] P.B. Lourenc¸o, G. Vasconcelos, L. Ramos, Assessment of the stability conditions of a Cistercian cloister, in: Second International Congress of Studies in Ancient Structures, July 7–13, Istanbul, Turkey, 2001. [32] L. Pelà, A. Aprile, A. Benedetti, Seismic assessment of masonry arch bridges, Eng. Struct. 31 (2009) 1777–1788. [33] L.F. Ramos, G. De Roeck, P.B. Lourenc¸o, A. Campos-Costa, Damage identification on arched masonry structures using ambient and random impact vibrations, Eng. Struct. 32 (2010) 146–162. [34] L.F. Ramos, L. Marques, P.B. Lourenco, G. De Roeck, A. Campos-Costa, J. Roque, Monitoring historical masonry structures with operational modal analysis: two case studies, Mech. Syst. Signal Process. 24 (2010) 1291–1305. [35] L. Pelà, A. Aprile, A. Benedetti, Comparison of seismic assessment procedures for masonry arch bridges, Construct. Build. Mater. 38 (2013) 381–394.
Please cite this article in press as: F. Cakir, H. Uysal, Experimental modal analysis of brick masonry arches strengthened prepreg composites, Journal of Cultural Heritage (2014), http://dx.doi.org/10.1016/j.culher.2014.06.003