https://doi.org/10.14311/APP.2022.33.0597 Acta Polytechnica CTU Proceedings 33:597–603, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague FRACTURE BEHAVIOR OF MULTIPLE ADHESIVE POSTINSTALLED ANCHORS SUBJECTED TO SHEAR FORCE Yuji Tajimaa,∗, Kazuaki Hokib a Aichi Syukutoku University, 2-9 Katahira Nagakute-city Aichi Prefecture 480-1197 Japan b The University of Kitakyusyu, 1-1 Hibikino Wakamatu-ku Kitakyusyu-city Fukuoka Prefecture 808-0135 Japan ∗ corresponding author: yujita@asu.aasa.ac.jp Abstract. In this study, experiments were conducted on post-installed anchors subjected to shear force in order to enhance applicability when post-installed anchors were used for seismic reinforcement. Furthermore, since there were a large number of post-installed anchors when they were actually used, an experiment was conducted in which aăshear force was simultaneously applied to one to four anchors. In this study, it was focused on number and pitch of anchors. Major findings of this study were summarized as follows: in case of 22.46 (N/mm2) for concrete compressive strength, shear strength of anchors was not double, triple, and quadruple as number of those increased to 2, 3, and 4, and that gradually decreased as number of those increased, the boundary condition between anchor shear rupture and pry-out failure was found that concrete compressive strength was 25.12 (N/mm2) or less and anchor pitch was 30 to 50 mm, and anchor was tensile strength over SD390. Keywords: Adhesive post-installed anchor, anchor pitch, multiple anchors, shear strength. 1. Introduction In Japan, reinforced concrete structures built in 1960s and 1970s were reinforced for sustainable use of build- ings due to lack of earthquake resistance. Steel braces were most often used to reinforce buildings, and many anchors were installed in existing buildings to trans- mit stress to steel braces. Since the stress transmis- sion between the existing building and the steel brace had a high ratio of shear force, when using the post- installed anchor for seismic reinforcement, the anchor reinforcement should be designed with shear perfor- mance. However, for post-installed anchors, struc- tural standards in Japan [1] were determined based on tensile performance of one anchor to ensure safety. The above-mentioned problem should be considered in terms of shear performance, but had been limited in effective use due to standards for tensile perfor- mance. On the other hand, there were many ten- sile tests about one anchor, and there were shear tests about it, but in any case, experiment about it had been done according to past studies. Therefore, in this study, experiments were conducted on post- installed anchors subjected to shear force in order to enhance applicability when post-installed anchors were used for seismic reinforcement. Furthermore, experiments were conducted in which not only one anchor but also multiple anchors were subjected to shear force simultaneously. For post-installed anchors, various factors such as anchor tensile strength, concrete compressive strength, embedding depth, anchor pitch, and clear- ance distance should be considered. As mentioned above, although there were various factors, it was nec- essary to narrow down the parameters. Therefore, the embedding depth was constant, and the exper- iment was conducted focusing on differences in con- crete strengths, anchor strengths, and anchor pitches. As an additional note, the anchor bars were installed at a sufficient distance from the edge of the concrete so as not to consider the edge rupture. 2. Test Program 2.1. Specimens Properties of specimens were summarized in Table 1. There were 23 specimens in total. Most of the test results were based on reference [2]. The added spec- imens were marked with * in the Table 1. The an- chor was used deformed bar of nominal diameter of 10mm(D10). The post-installed anchor arrangement was made such that only one anchor is arranged, two anchors are arranged along loading direction (Dp = 100mm, Dp/da = 10, da: nominal diameter), three anchors are arranged (Dp = 50mm, Dp/da = 5), and four anchors are arranged (Dp = 30mm, Dp/da = 3). In other words, pitches of two, three and four an- chors were arranged along loading direction at 100, 50 and 30mm, respectively. The compressive strengths of concrete were 3 types of 23.12, 25.12 and 29.34 (N/mm2). Materials of anchors were used SD390 and SD295. The embedded depth was constant 70mm (7 da). An epoxy resin was used as a fixing agent for the post-installed anchor. 597 https://doi.org/10.14311/APP.2022.33.0597 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en Yuji Tajima, Kazuaki Hoki Acta Polytechnica CTU Proceedings Serial number Material of Anchor σy σu Es n Dp σB Ec Quantity MPa MPa GPa (mm) MPa GPa 1 SD390 D10 428 590 209 1 − 29.34 26.9 12 2 100 3 3 50 4 4 30 5 1 − 25.12 23.1 16 2 100 7 3 50 8 4 30 9 1 − 23.12 24.6 1 10 - 1,2 2 100 2* 11 3 50 1 12 - 1,2 4 30 2* 13 SD295 D10 345 479 183 1 − 29.34 26.9 114 2 100 15 3 50 16 4 30 17 1 − 22.46 31.4 1 18 2 100 1 19 - 1,2 3 50 2* 20 4 30 1 Table 1. Properties of Specimens. 2.2. Loading Method and Instrumentation A loading apparatus was shown in Figure 1. The loading method was monotonous loading. Shear force was simultaneously applied to a plurality of arranged anchors using a loading frame. Shear force was mea- sured by a load-cell installed outside a loading frame. The displacement between tensile tool and concrete was measured by two displacement transducers. The average value of these outputs was taken as the shear displacement. This value was evaluated as a shear displacement, although the flexural deformation of the anchor bar was included. 3. Test Results 3.1. Shear Force - Shear Displacement Relations Shear force-shear displacement relations were shown in Figure 2 for each concrete compressive strength and anchor tensile strength. In Figure 2, the experi- mental values of four anchors, three anchors, two an- chors and one anchor were shown by a solid line, a two-dot chain line, a one-dot chain line and a dotted line, respectively. Although some specimens showed experimental values with different initial stiffness due to construction accuracy, they roughly showed the same initial stiffness even when the number and pitches of anchors were different. As the shear force increased, the local concrete gradually failed in com- pression and the flexural moment of anchors grad- ually increased. These states could be clearly seen from the history in Figure 2(c) and (e). 3.2. Crack Pattern and Failure Mode Examples for crack patterns of concrete and shear ruptures of anchors were shown in Figure 3 and 4. Ex- cept for specimens numbered 12-1 and 2, the anchors of the other specimens failed in shear rupture. Spec- imens numbered 12-1 and 2 using four D10(SD390) anchors and a concrete compressive strength of 23.12 (MPa) failed in pry-out. The above mentioned pry- out failure was a type of concrete failure that was scraped as shown in Figure 4(a). As a result, two of the four anchors did not rupture in shear. For a specimen numbered 8 using four D10(SD390) anchors and a concrete compressive strength of 25.12 (MPa), although the anchors eventually failed in shear rup- ture, as shown in Figure 4(b), diagonal cracks oc- curred on the back in the loading direction. This could be judged as a sign of a pry-out failure. The cracks for specimens of one and two anchors were iso- lated as shown in Figure 3(a) and (b). On the other hand, cracks for specimens of three and four anchors were connected as shown in 3(c) and (d). In the next chapter, the maximum shear force and the shear dis- placement at the maximum shear force were discussed based on the hysteresis, crack and anchor fracture properties. 4. Discussions 4.1. Maximum Shear Force - Number of Anchors Relations Maximum shear force-number of anchors relations used with SD295 were shown in Figure 5. In Fig- ure 5, maximum shear forces with the compressive 598 vol. 33/2022 Fracture Behavior of Multiple Adhesive PostInstalled Anchors /RDGLQJ�'LUHFWLRQ� $QFKRUV� 2LO�-DFN� 'LVSODFHPHQW� 7UDQVGXFHUV /RDGLQJ�'LUHFWLRQ� $QFKRUV /RDG�FHOO� 'LVSODFHPHQW� 7UDQVGXFHUV $QFKRUV� Figure 1. (a) Framing Plan of Loading Apparatus, Loading Apparatus. (b) Elevation of Loading Apparatus, Loading Apparatus. concrete strengths of 22.46 and 29.34 (N/mm2) were shown by triangles and circles respectively. When the average of the maximum shear force for one an- chor was calculated without considering the concrete strength, it was 28.04 (kN). The value obtained by multiplying that by the number of anchors was shown by a dotted line in Figure 5. Maximum shear forces with a concrete strength of 22.46 (N/mm2) tended to be lower than the dotted line. On the other hand, Maximum shear forces with a concrete strength of 29.34ă(N/mm2) tended to be larger than the dotted line. Maximum shear force-number of anchors relations used with SD390 were shown in Figure 6. In Figure 6, maximum shear forces with the compressive concrete strengths of 23.12, 25.12 and 29.34 (N/mm2) were shown by squares, diamonds and circles respectively. The maximum shear forces with the compressive con- crete strengths of 23.12 and 25.12 (N/mm2) for spec- imens failed in pry-out were shown by asterisks and a cross respectively. When the average of the maximum shear force for one anchor was calculated without con- sidering the concrete strength, it was 35.96 (kN). The value obtained by multiplying that by the number of anchors was shown by a dotted line in Figureă4. Maximum shear forces with a concrete strength of 23.12 (N/mm2) tended to be lower than the dotted line. Maximum shear forces with a concrete strength of 29.34 (N/mm2) were almost on the dotted line. Considering these results and the above-mentioned crack patterns, the boundary condition between an- chor shear rupture and pry-out failure was found that concrete compressive strength was 25.12 (N/mm2) or less and anchor pitch was 30 to 50mm, and an- chor was tensile strength over SD390. In this study, since the embedded depth of the anchor was constant 70mm (7da), the embedded depth was not consid- ered. When the hysteresis of the four anchors and that of the three anchors in Figure 2 were compared again from the above viewpoint, signs could be con- firmed that the second stiffness was almost the same. Furthermore, by examining the boundary conditions precisely hereafter, it would be possible to install the anchor at a shorter pitch than the current standards [1] in Japan when using the anchor for seismic rein- forcement. 4.2. Displacement at Maximum Shear Force - Pitches of Anchors Relations Displacement at maximum shear force-pitches of an- chors relations used with SD295 were shown in Fig- ure 7. In Figure 7, displacements at maximum shear force with the compressive concrete strengths of 22.46 and 29.34 (N/mm2) were shown by triangles and cir- cles respectively. Linea approximation lines with the compressive concrete strengths of 22.46 and 29.34 (N/mm2) were shown by a dotted and one-dot chain 599 Yuji Tajima, Kazuaki Hoki Acta Polytechnica CTU Proceedings � � �� ��� ��� � � �� �� �� 6K HD U�) RU FH �N 1 � 'LVSODFHPHQW�PP� ı%������6'��� � �� ��� ��� � � �� �� �� 6K HD U�) RU FH �N 1 � 'LVSODFHPHQW�PP� ı%������6'��� � �� ��� ��� � � �� �� �� 6K HD U�) RU FH �N 1 � 'LVSODFHPHQW�PP� ı%������6'��� � �� ��� ��� � � �� �� �� 6K HD U�) RU FH �N 1 � 'LVSODFHPHQW�PP� ı%������6'��� 2QH�DQFKRU 7ZR�DQFKRUV �������������������7ZR�DQFKRUVჟ� 7KUHH�DQFKRUV �������������������7KUHH�DQFKRUVჟ� )RXU�DQFKRUV �������������������)RXU�DQFKRUVჟ� � �� ��� ��� � � �� �� �� 6K HD U�I RU FH �N 1 � 'LVSDOHPHQW�PP� ı%������6'��� �D�6HULDO�1XPEHU�IURP���WR������������������������������������E�6HULDO�1XPEHU�IURP���WR��� �G�6HULDO�1XPEHU�IURP����WR������������������������������H�6HULDO�1XPEHU�IURP����WR���� �F�6HULDO�1XPEHU�IURP���WR������ Figure 2. Shear Force - Shear Displacement Relations. 600 vol. 33/2022 Fracture Behavior of Multiple Adhesive PostInstalled Anchors �D���6HULDO�1XPEHU�����RQH�DQFKRU��� � �E����6HULDO�1XPEHU�����WZR�DQFKRUV��� �F����6HULDO�1XPEHU�������WKUHH�DQFKRUV��� � �G����6HULDO�1XPEHU�����IRXU�DQFKRUV��� /RDGLQJ�'LUHFWLRQ� /RDGLQJ�'LUHFWLRQ Figure 3. Examples for Crack Patterns of Concrete and Shear Ruptures of Anchors. �D���6HULDO�1XPEHU�������IRXU�DQFKRUV��� � �E����6HULDO�1XPEHU����IRXU�DQFKRUV��� 'LDJRQDO�&UDFN� Figure 4. Pry-out Failure and Diagonal Cracks (Sign of Pry-out Failure). � �� �� �� ��� ��� � � � � 0 D[ LP XP ��� ��� ��� ��� ��� � 6K HD U�) RU FH �N 1 � 1XPEHU�RI�$QFKRUV 6'��� ˜ ��ı% ������1�PP�� ʕ ��ı% ������1�PP�� ��1XPEHU�7LPHV�/LQH Figure 5. Maximum shear force-number of anchors relations. (SD295). 601 Yuji Tajima, Kazuaki Hoki Acta Polytechnica CTU Proceedings � �� �� �� ��� ��� � � � � 0 D[ LP XP ��� ��� ��� ��� ��� 6K HD U�) RU FH �N 1 � 1XPEHU�RI�$QFKRUV 6'��� ˚ � ı% ������1�PP�� ˘ � ı% ������1�PP�� ʕ ��ı% ������1�PP�� ː ��3U\�RXW�)DLOXUH�ı% ������1�PP��� ʹ ��3U\�RXW�)DLOXUH�ı% ������1�PP��� ��1XPEHU�7LPHV�/LQH Figure 6. Maximum shear force - number of anchors relations. (SD390). � � �� �� �� �� � �� �� �� �� ��� ' LVS OD FH P HQ W�� ��� ��� ��� �� DW �0 D[ LP XP �6K HD U�) RU FH �P P � 3LWFKHV�RI�$QFKRUV�PP� 6'��� VORSH����������� ı% ������1�PP�� VORSH����������� ı% ������1�PP�� ˜ ��ı% ������1�PP�� ʕ ��ı% ������1�PP�� ��/LQHDU�$SSUR[LPDWLRQ� /LQH �ı% ������1�PP��� ��/LQHDU�$SSUR[LPDWLRQ� /LQH �ı% ������1�PP��� Figure 7. Displacement at maximum shear force - pitches of anchors relations. (SD295) � � �� �� �� �� � �� �� �� �� ��� ' LVS OD FH P HQ W�� ��� ��� ��� ��� � DW �0 D[ LP XP �6K HD U�) RU FH �P P � 3LWFKHV�RI�$QFKRUV�PP� 6'��� VORSH����������� ı% ������1�PP�� VORSH����������� ı% ������1�PP�� VORSH����������� ı% ������1�PP�� ˚ � ı% ������1�PP�� ˘ � ı% ������1�PP�� ʕ ��ı% ������1�PP�� ��/LQHDU�$SSUR[LPDWLRQ� /LQH �ı% ������1�PP��� ��/LQHDU�$SSUR[LPDWLRQ� /LQH �ı% ������1�PP��� ��/LQHDU�$SSUR[LPDWLRQ� /LQH �ı% ������1�PP��� Figure 8. Displacement at maximum shear force - pitches of anchors relations. (SD390) line respectively in Figure 7. The anchor pitch was considered appropriate for the horizontal axis when evaluating shear displacement, but one anchor did not have a pitch. Therefore, the crack pattern for the two anchors was referred to in Figure 3(b). The pitch for the two anchors was 100 (mm), the cracks did not interfere each other. Consequently, the pitch of one anchor was considered as 100mm and discussed after- wards. In Figure 7, the slopes of the linear approx- imation line for each concrete strength were shown. These slopes tended to increase the displacement at maximum shear force as the pitch became shorter. Displacement at maximum shear force-pitches of anchors relations used with SD390 were shown in Figure 8. In Figure 8, displacements at maximum shear force with the compressive concrete strengths of 23.12, 25.12 and 29.34 (N/mm2) were shown by squares, diamonds and circles respectively. Linea approximation lines with the compressive concrete strengths of 23.12, 25.12 and 29.34 (N/mm2) were shown by a dotted, two-dot chain and one-dot chain line respectively in Figure 8. With the same idea as above, the pitch of one anchor was considered as 100mm and discussed afterwards. In Figure 8, the slopes of the linear approximation line for each con- crete strength were shown. Although the slope with SD390 was lower than the slope with SD295, the dis- placement at maximum shear force tended to increase as the anchor pitch became shorter. These meant that as the anchor pitch became shorter, the compressive failure zone for the concrete was expected deeper from the surface. 5. Conclusions The following conclusions can be drawn from the present study about multiple adhesive post-installed 602 vol. 33/2022 Fracture Behavior of Multiple Adhesive PostInstalled Anchors anchors subjected to shear force: 1. Except for two specimens, the anchors of the other specimens failed in shear rupture. The two speci- mens with four D10(SD390) anchors and a concrete compressive strength of 23.12 (MPa) failed in pry- out. For the specimen with four D10(SD390) an- chors and a concrete compressive strength of 25.12 (MPa), although the anchors eventually failed in shear rupture, diagonal cracks occurred on the back in the loading direction. This could be judged as a sign of a pry-out failure. 2. Maximum shear forces with a concrete strength of 22.46 (N/mm2) tended to be lower than the line obtained by multiplying the maximum shear force for one anchor by the number. In other words, in case of 22.46 (N/mm2) for concrete compressive strength, shear strength of anchors was not double, triple, and quadruple as number of those increased to 2, 3, and 4, and that gradually decreased as number of those increased. Considering these results, the boundary condition between anchor shear rupture and pry-out failure was found that concrete compressive strength was 25.12 (N/mm2) or less and anchor pitch was 30 to 50mm, and anchor was tensile strength over SD390. 3. Considering the pitch of one anchor as 100ămm, the slopes of the linear approximation line for each concrete strength tended to increase the displace- ment at maximum shear force as the pitch became shorter. As a result, when the anchor pitch was shortened, the compressive failure zone for the concrete was ex- pected deeper from the surface, and the displacement at the maximum shear force was increased. From the above conclusions, it was found quali- tatively that the correlation between concrete com- pressive strength, anchor pitch and anchor tensile strength at the boundary condition between anchor shear rapture and pry-out failure when the embedded depth for anchor was constant. In the future, it is necessary to conduct experiments that can quantita- tively evaluate the boundary conditions, and research the relationship between the depth of the compressive zone and the anchor pitch. And, using these results, we plan to conduct an ex- periment to investigate the sustained shear load per- formance of adhesive post-installed anchors as an aid to the sustainable use of the building. Acknowledgements This work was supported by JSPS KAKENHI Grant Number JP18K04447. Any opinions, findings, and conclusions or recommen- dations expressed in this material are those of the authors and do not necessarily reflect the views of the authors’ or- ganization, JSPS or MEXT References [1] Architectural Institute of Japan. Design Recommendations for Composite Constructions, p. 252, 2010. [2] K. Hoki, Y. Tajima. Strength Evaluation of Densely-placed Post-installed Anchors Part 2: Shear Test of Monotonic Loading for Post-installed Anchors Used SD390, Summary of Technical Papers of Annual Meeting of Kyusyu Chapter, Architectural Institute of Japan, p. 469-472, 2019. 603