The authors developed two types of block systems consisting only of main block and key block without joint mortar in consideration of seismic performance and workability. Two types of block systems have different key block shapes: One is the peanuts shape and the other is the dumbbell shape. In this study, the proposed two types of block walls as well as a typical block wall were experimentally investigated to evaluate the seismic performance. In the tests, full-scale, single-story specimens were tested under static cyclic in-plane loading, and failure patterns and cracks were carefully observed. In this paper, the loading bearing capacity, energy dissipation capacity and reuse ratio of block walls are discussed in detail. As a result, the deformability, energy absorption capacity and reuse ratio of the proposed block systems were considerably higher than those of typical block system

Choi, Ho

Hwang, Eonju

Jeong, Jaecheon

Jin, Kiwoong

Kim, Bongseok

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

https://doi.org/10.14311/APP.2022.33.0085Acta Polytechnica CTU Proceedings 33:85–91, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licencePublished by the Czech Technical University in PragueFEASIBILITY EXPERIMENTS OF SEISMIC CONCRETE BLOCKWALLS WITHOUT JOINT MORTARHo Choia,∗, Kiwoong Jinb, Jaecheon Jeongc, Bongseok Kimc,Eonju Hwangca Shizuoka Institute of Science and Technology, 2200-2, Toyosawa, Fukuroi, Shizuoka 437-8555, Japanb Meiji University, 1-1-1, Higashimita, Tama, Kawasaki, Kanagawa 214-8571, Japanc Nara & Tech Co. Ltd, 37-34, Nokbaegil, Juksan, Anseong, Kyonggi 17521, Korea∗ corresponding author: choi.ho@sist.ac.jpAbstract. The authors developed two types of block systems consisting only of main block and keyblock without joint mortar in consideration of seismic performance and workability. Two types of blocksystems have different key block shapes: One is the peanuts shape and the other is the dumbbell shape.In this study, the proposed two types of block walls as well as a typical block wall were experimentallyinvestigated to evaluate the seismic performance. In the tests, full-scale, single-story specimens weretested under static cyclic in-plane loading, and failure patterns and cracks were carefully observed. Inthis paper, the loading bearing capacity, energy dissipation capacity and reuse ratio of block walls arediscussed in detail. As a result, the deformability, energy absorption capacity and reuse ratio of theproposed block systems were considerably higher than those of typical block system.Keywords: In-plane, key block, main block, out-of-plane, unreinforced masonry.1. IntroductionIn some regions of Asia, Europe, and Latin Americawhere earthquakes frequently occur, serious earth-quake damage is commonly found resulting fromcatastrophic building collapse. Such damaged build-ings often have unreinforced masonry (URM) walls,as shown in Figure 1(a). Since the seismic perfor-mance of the URM wall buildings and infill wallsare relatively poor compared to the other struc-tural types, these buildings and walls always dam-aged when an earthquake occurs. Furthermore, inJapan which is an earthquake-prone country, the useof URM walls is prohibited by the Building Stan-dards, but concrete block fences with reinforcing barsare often used. However, the damage of the fences al-ways occurred when the earthquake occurs, as shownin Figure 1(b).Under these backgrounds, the authors developedtwo types of block systems consisting only of mainblock and key block without joint mortar in con-sideration of seismic performance and workability.Two types of block systems have different key blockshapes: One is the peanuts shape and the other is thedumbbell shape.In this study, the proposed two types of concreteblock walls as well as a typical concrete block wallwere experimentally investigated to evaluate the seis-mic performance. In the tests, full-scale, single-storyspecimens were tested under static cyclic in-planeloading, and failure patterns and cracks were care-fully observed.In this paper, the loading bearing capacity, energydissipation capacity and reuse ratio of block walls arediscussed in detail.2. Experimental program2.1. Developed block systemsThe authors developed two types of concrete blocksto improve the seismic performance of both in- andout-of-plane directions and to enhance the workabil-ity without the joint mortar [1]. The two types ofconcrete blocks only consist of main blocks and keyblocks, and they have different key block shapes: Oneis the peanuts shape and the other is the dumbbellshape, as shown in Figure 2.As shown Figures 2, the gap between the mainblock and the key block was designed to be 1.5 mm onall sides in consideration of workability and manufac-turing accuracy. As can be found in Figure 3, the pro-posed block systems have half-height difference be-tween the main block and the key block. Therefore,the seismic performances in the out-of-plane directionas well as the in-plane direction of the proposed blocksystems are expected to be much higher than that oftypical masonry walls.Each concrete block material test results are shownin Table 1 (the average values of three samples areshown in the table). The typical concrete block andpeanut shape concrete block were made by the normalcement-to-sand ratio of 1 : 3.5 used in Korea. Sincethe dumbbell shape concrete block was, however,used higher cement ratio, the compressive strengthis the highest value among three concrete blocks, asshown in Table 1. The compressive strength of thepeanut shape concrete block is higher than that ofthe typical concrete block, because the peanut shape85H. Choi, K. W. Jin, J.C. Jeong et al. Acta Polytechnica CTU ProceedingsD/¶$TXLODHDUWKTXDNH,WDO\  E1RUWKHUQ2VDNDHDUWKTXDNH-DSDQFigure 1. Masonry wall damage.Figure 2. Two types of concrete block systems (unit: mm).Compressive strength [N/mm2]1Typical concrete block Peanut shape concrete block Dumbbell shape concrete block2Block unit 8.8 14.9 22.0Block prism3 5.8 7.7 18.11 to whole area 2 with key blocks 3 a layered specimenTable 1. Mechanical properties of each concrete block.86vol. 33/2022 Seismic Concrete Block Wallsconcrete block has the key blocks in hollow parts ofthe main block.2.2. Test specimensIn this study, three full-scale, single-story specimenswere designed and fabricated supposing the single-story storage building, as shown in Figure 4(a) typ-ical concrete block wall specimen with joint mortar(Specimen CB); (b) seismic block wall with peanutsshape key block without joint mortar (Specimen PS);(c) seismic block wall with dumbbell shape key blockwithout joint mortar (Specimen DS). The specimensize is 2.0 m by 1.4 m, as shown in Figure 4.The typical concrete block wall can resist only fric-tion force to the horizontal load after losing the ad-hesive force between concrete block and joint mortar.On the other hand, the proposed concrete block wallsystems are expected higher deformability due to theshear key mechanism between the main block and thekey block.2.3. Test methodsA loading system for the static cyclic in-plane tests isshown in Figure 5. Lateral loads in the positive andnegative directions were applied to the left end of theupper beam with hydraulic actuators. As mentionedabove, since the reference building of this study is asingle-story storage building, the axial load was con-sidered as the weight of the upper beam (13.7 kN,axial stress, σ0 = 0.04N/mm2). Figure 6 shows a lat-eral loading protocol that was controlled by a driftangle R, defined as a lateral drift ∆ at the top-centerof specimen divided by the height from the bottomof the specimen, H, as shown in Figure 5.The measurement system is shown in Figure 7. Therelative lateral displacement, the lateral displacementat each layer of wall, the vertical displacement of bothends of specimen, and diagonal deformation of wallwere measured, respectively. Furthermore, the max-imum crack widths at peak loads and residual crackwidths at unloaded stages were carefully measured.3. Experimental results3.1. Failure patterns and lateralforce-drift angle relationshipsFigure 8 and 9 show the damage patterns after finalloading and the lateral force-drift angle relationshipsof all specimens, respectively. The behavior of eachspecimen to failure is summarized below.3.1.1. Specimen CBDuring the first loading drift, R, of 0.05 % rad., thecracks were observed in the entire bed joint (horizon-tal joint) causing slippage between second and thirdjoint interface. Since the shear crack in the bottomof compression side was occurred during R = 0.67 %rad., the test was terminated at R = 1.0 % rad. Untilthe final loading, this specimen showed the rockingbehavior between second and third layers. The maxi-mum strength of 14.7 kN was recorded at R = 0.67 %rad. and no remarkable strength deterioration isfound until R = 1.0 % rad.3.1.2. Specimen PSThe small width crack was occurred on the mainblock of the right-bottom end at R = 0.25 % rad.This specimen also showed the rocking behavior un-til final loading because of low axial force accord-ing to the single-story storage building. Since thecrushing and spalling off of the main block where isthe rightmost side of the second layer was occurredat R = 5.0 %, the experiment was terminated afterR = 5.0 %. The maximum strength of − 17.5 kN wasrecorded at R = −2.0 % rad. and no remarkablestrength deterioration is found until the final load-ing.3.2. Comparison of in-plane seismicperformance of each specimen3.2.1. Lateral force-drift anglerelationshipsFigure 10 shows the skeleton curves of each speci-men. As shown in the figure, the in-plane seismicperformances of Specimens PS and DS were muchhigher than that of Specimen CB. In particular, thedeformability of the proposed system has improvedremarkably due to the shear key mechanism betweenthe main blocks and the key blocks. Since all speci-mens show the rocking behavior, as mentioned above,the lateral loads of each specimen were calculatedconsidering the simple rocking mechanism, as shownin Figure 11. As shown in the figure, the axial loadswere considered as the sum of the weight of the upperbeam (N1 = 13.7 kN) and the self-weight of the spec-imen (N2 = 6.0 kN, 9.0 kN and 10.8 kN of SpecimensCB, ,PS, DS, respectively). The calculated lateralloads were shown in Figure 9. As can be found in thefigure, the calculated lateral loads agreed well withthe experimental results.3.2.2. Equivalent viscous damping ratiosIn order to compare the energy dissipation capaci-ties of all specimens, the equivalent viscous dampingratios were calculated, as shown in Figure 12. The re-sults of the proposed systems considerably had highervalues than that of Specimen CB. Furthermore, theremarkable deterioration of the ratios of the proposedsystems were not found until the final loading.3.2.3. Reuse ratios of Specimens PS and DSThe typical concrete block and brick may not com-monly reuse because of the using of the joint mortar.On the other hand, the proposed systems consistedof only main and key blocks without joint mortar canreuse. In this study, the reuse ratio is defined as theratio of no damage main blocks to all main blocks.Figure 13 shows the reuse ratio of Specimens PS and87H. Choi, K. W. Jin, J.C. Jeong et al. Acta Polytechnica CTU Proceedings.H\EORFN0DLQEORFNE'XPEEHOOVKDSHD3HDQXWVVKDSHFigure 3. Construction of the proposed block walls.D6SHFLPHQ&%  E6SHFLPHQ36Figure 4. Details of typical and proposed concrete block wall specimens (unit: mm).^ŚĞĂƌŬĞǇWƌĞǀĞŶƚŝŽŶŽĨŽƵƚͲŽĨͲƉůĂŶĞďĞŚĂǀŝŽƌ  >ĂƚĞƌĂůŚǇĚƌĂƵůŝĐĂĐƚƵĂƚŽƌ hƉƉĞƌďĞĂŵ^ƉĞĐŝŵĞŶ,'Figure 5. Loading system (unit: mm).88vol. 33/2022 Seismic Concrete Block Walls 7DUJHWGLVSODFHPHQWPP3HDNGULIWDQJOHRFigure 6. Lateral loading protocol. >5HDU@/DWHUDOGLVS9HUWLFDOGLVS9HUWLFDOGLVS'LDJRQDOGRIRUP/DWHUDOGLVSRIHDFKOD\HUFigure 7. Measurement system.D6SHFLPHQ&% E6SHFLPHQ36 F6SHFLPHQ'6Figure 8. Final crack patterns (Blue: Positive dir., Red: Negative dir., Black: Initial cracks).89H. Choi, K. W. Jin, J.C. Jeong et al. Acta Polytechnica CTU Proceedings            D6SHFLPHQ&%/DWHUDOIRUFHN1'ULIWDQJOH&DOFXODWLQUHVXOW            /DWHUDOIRUFHN1'ULIWDQJOH&DOFXODWLQUHVXOWE6SHFLPHQ36            /DWHUDOIRUFHN1'ULIWDQJOH&DOFXODWLQUHVXOWF6SHFLPHQ'6Figure 9. Lateral force-drift angle relationships of each specimen.            /DWHUDOIRUFHN1'ULIWDQJOH6SHFLPHQ&%6SHFLPHQ366SHFLPHQ'6Figure 10. Skeleton curves of each specimen.            N N18SSHUEHDPPN N1RIVHOIZHLJKWVRI6SHFLPHQV&%36'6UHVSHFWLYHO\5RFNLQJSRLQWFigure 11. Lateral load P due to rocking mechanism.        (TXLYDOHQWYLVFRXVGDPSLQJUDWLRheq'ULIWDQJOH6SHFLPHQ&%6SHFLPHQ366SHFLPHQ'6Figure 12. Equivalent viscous damping ratios.     5HXVHUDWLR'ULIWDQJOH6SHFLPHQ366SHFLPHQ'6Figure 13. Reuse ratios of the main blocks of Spec-imens PS and DS.90vol. 33/2022 Seismic Concrete Block WallsDS. As can be found in the figure, the proposed seis-mic block systems can reuse more than 70 % afterR = 5.0 % rad. This result imply that the proposedconcrete block wall systems are economical and eco-friendly.4. Concluding remarksThe current paper presented the experimental testsof the two types of new concrete block walls as wellas a typical block wall and investigated the in-planebehaviour, the loading bearing capacity, energy dissi-pation capacity and reuse ratio. The following majorfindings were obtained:1. The in-plane seismic performances of SpecimensPS and DS were much higher than that of Spec-imen CB. In particular, the deformability of theproposed system has improved remarkably due tothe shear key mechanism between the main blocksand the key blocks.2. The calculated lateral loads based on the simplerocking mechanism agreed well with the experi-mental results.3. The energy dissipation capacities of the proposedsystems considerably had higher values than thatof Specimen CB. Furthermore, the remarkable de-terioration of the ratios of the proposed systemswere not found until the final loading.4. The proposed seismic block systems can reuse morethan 70 % after final loading. This result implythat the proposed concrete block wall systems areeconomical and eco-friendly.The current paper focused only on the in-plane ex-perimental behavior. The experimental data shouldbe investigated from numerical perspectives, and theout-of-plane experimental and numerical behavioursshould be carried out, in future studies.AcknowledgementsThe project was funded by the JSPS Grant-in-Aid forScientific Research (Category (c), Grant No. 18K04425,Principal Investigator: Ho Choi) and the Joint Researchwith Nara & Tech Co. Ltd. The authors are thankful toboth agency and company for their financial support.References[1] H. Choi, K. W. Jin, J. C. Jeong, et al. FeasibilityStudy on Seismic Block without Joint Mortar, Part1Shape Determination using Finite Element Analysis,Summaries of Technical Papers of Annual Meeting,Architectural Institute of Japan 4:977-978, 2019.91

Feasibility experiments of seismic concrete block walls without joint mortar

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Feasibility experiments of seismic concrete block walls without joint mortar

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