Myriads of earthquakes have occurred around the world since the 2000s, and the magnitudes of the earthquakes are also growing. Moreover, earthquakes that are common around the Pacific Rim are also occurring inland on an increasingly larger scale. The earthquake that occurred in the Gyeongju region l...
Myriads of earthquakes have occurred around the world since the 2000s, and the magnitudes of the earthquakes are also growing. Moreover, earthquakes that are common around the Pacific Rim are also occurring inland on an increasingly larger scale. The earthquake that occurred in the Gyeongju region last September was 5.8 in magnitude, breaking the record for earthquakes in Korea; thus, it became evident that Korea was no longer a safe zone from earthquakes. Earthquakes of large magnitude can result in quickly rising human casualties and property damage due to the destruction and damage to structures. Structural damage from earthquakes are concentrated in the columns that carry the load to the lower floors and the ground, and reinforced concrete (RC) structures are more vulnerable to earthquakes than steel structures due to the properties of the material.
Therefore, the present study aims to develop a seismic reinforcement method for RC columns. When an earthquake occurs, temporary retrofitting must be performed quickly to minimize the secondary damage of structures, prior to full restoration of a structure, as needed. Accordingly, the study proposes the method of retrofitting the columns that are expected to be damaged, or that have been damaged, by wrapping them with seismic reinforcement, glass fiber reinforced polymer (GFRP) and Velcro, to constrain them. The proposed method is designed to minimize the damage to a structure from retrofitting, use lightweight materials, and connect parts mechanically to quickly complete the work with minimal human labor.
The seismic reinforcement made with GFRP is designed to have mechanical connectors; the connectors, made with aluminum, are designed using finite element analysis and manufactured into a shape that prevents any loss of strength, is easy to adjust the length, and is easily removable. The seismic reinforcement made with Velcro has an excellent adhesion and tensile strength, and is a factory mushroom-type product that can exert peeling and shear strength above the required strength, and is very cost-effective for the performance it delivers.
The results of the sectional analysis on the 450 ㎜ × 300 ㎜ RC columns with non-seismic sectional details showed that GFRP retrofitting with connectors gave the displacement ductility ratio of 6.0; whereas, the 200 ㎜ × 300 ㎜ column sectional details retrofitted with mushroom-type Velcro reinforcement gave the displacement ductility ratio of 7.5.
Performance of the proposed seismic reinforcement was evaluated by a quasi-static repeated loading experiment with RC column specimens developed for the experiment. The strength of the FRS specimen used in the experiment on GFRP seismic reinforcement at the end of the 450 mm-wide RC columns increased 10% compared to the un-retrofitted specimen; however, the displacement ductility ratio increased and energy dissipation capacity increased 130% and 300%, respectively. The strength of the RRS specimen that was GFRP retrofitted increased only 13% compared to the un-retrofitted specimen; however, the displacement ductility ratio and energy dissipation capacity increased by 180% and 500%, respectively. The strength of the VARC specimen in which the entire columns were retrofitted with Velcro increased only 7% compared to the un-retrofitted specimen; however, the displacement ductility ratio and energy dissipation capacity increased 60% and 270%, respectively. The strength of the VTRC specimen that was retrofitted with Velcro only at the end of the columns also increased 8% compared to the un-retrofitted specimen; hence, the displacement ductility ratio and energy dissipation capacity also increased 70% and 36%, respectively. The results suggest that the proposed retrofitting greatly improved the ductility of the RC columns.
The optimum number of and the optimal locations for the proposed seismic reinforcements to retrofit the columns of a school building in a RC structure were derived using the optimization method. The optimization method is based on the ant colony optimization (ACO), and involved 3D modeling of the school building steel structure and dynamic analysis for accurate and reliable time history analysis.
The algorithm to derive the optimal location for the retrofit was derived by combining ACO and 3D nonlinear time history analysis.
In time history analysis using natural seismic waves, it is typically more effective to apply individual dominant frequency bands separately, and it was found that, in the case of the multi-span, low-rise structure, such as the school building in Korea, natural seismic waves with dominant frequency of 5 Hz or less should be applied. Therefore, it was found that, in the case of school buildings in Korea with non-seismic RC details, it was adequate to evaluate their seismic response using the seismic waves of the Kobe Earthquake of 1995 and the San Fernando Earthquake of 1971.
The results showed that the strength of the structures varied depending on the direction of the earthquakes, and the variation was significant. When the excitation was introduced separately toward the x-axis direction with a few spans, 45°, and the y-axis with many spans, it was found that the strain was smaller when the direction of excitation was toward the y-axis, indicating larger strength.
The results also showed that, to meet the current seismic design criteria, more than 80 of the 186 columns of the school building in Korea with non-seismic details must be retrofitted; the higher the peak ground acceleration (PGA) of the seismic waves, the more reinforcement is needed in the lower floors than the higher floors. It was found that it is more efficient to arrange the reinforcement in a crisscross pattern over a wide range, rather than a narrow range.
The results of the sensitivity analysis with varying arrangements of reinforcement showed that the outer columns on the lowest floor (first floor) were the most sensitive, and the inner columns on the highest floor (third floor) were the least sensitive. Thus, it is most likely economic and effective to retrofit the first floor and outer columns first in the event of emergency seismic reinforcement. The findings on the number of reinforcements for columns and the outcomes for different arrangements are expected to greatly influence future seismic reinforcement design and construction.
Myriads of earthquakes have occurred around the world since the 2000s, and the magnitudes of the earthquakes are also growing. Moreover, earthquakes that are common around the Pacific Rim are also occurring inland on an increasingly larger scale. The earthquake that occurred in the Gyeongju region last September was 5.8 in magnitude, breaking the record for earthquakes in Korea; thus, it became evident that Korea was no longer a safe zone from earthquakes. Earthquakes of large magnitude can result in quickly rising human casualties and property damage due to the destruction and damage to structures. Structural damage from earthquakes are concentrated in the columns that carry the load to the lower floors and the ground, and reinforced concrete (RC) structures are more vulnerable to earthquakes than steel structures due to the properties of the material.
Therefore, the present study aims to develop a seismic reinforcement method for RC columns. When an earthquake occurs, temporary retrofitting must be performed quickly to minimize the secondary damage of structures, prior to full restoration of a structure, as needed. Accordingly, the study proposes the method of retrofitting the columns that are expected to be damaged, or that have been damaged, by wrapping them with seismic reinforcement, glass fiber reinforced polymer (GFRP) and Velcro, to constrain them. The proposed method is designed to minimize the damage to a structure from retrofitting, use lightweight materials, and connect parts mechanically to quickly complete the work with minimal human labor.
The seismic reinforcement made with GFRP is designed to have mechanical connectors; the connectors, made with aluminum, are designed using finite element analysis and manufactured into a shape that prevents any loss of strength, is easy to adjust the length, and is easily removable. The seismic reinforcement made with Velcro has an excellent adhesion and tensile strength, and is a factory mushroom-type product that can exert peeling and shear strength above the required strength, and is very cost-effective for the performance it delivers.
The results of the sectional analysis on the 450 ㎜ × 300 ㎜ RC columns with non-seismic sectional details showed that GFRP retrofitting with connectors gave the displacement ductility ratio of 6.0; whereas, the 200 ㎜ × 300 ㎜ column sectional details retrofitted with mushroom-type Velcro reinforcement gave the displacement ductility ratio of 7.5.
Performance of the proposed seismic reinforcement was evaluated by a quasi-static repeated loading experiment with RC column specimens developed for the experiment. The strength of the FRS specimen used in the experiment on GFRP seismic reinforcement at the end of the 450 mm-wide RC columns increased 10% compared to the un-retrofitted specimen; however, the displacement ductility ratio increased and energy dissipation capacity increased 130% and 300%, respectively. The strength of the RRS specimen that was GFRP retrofitted increased only 13% compared to the un-retrofitted specimen; however, the displacement ductility ratio and energy dissipation capacity increased by 180% and 500%, respectively. The strength of the VARC specimen in which the entire columns were retrofitted with Velcro increased only 7% compared to the un-retrofitted specimen; however, the displacement ductility ratio and energy dissipation capacity increased 60% and 270%, respectively. The strength of the VTRC specimen that was retrofitted with Velcro only at the end of the columns also increased 8% compared to the un-retrofitted specimen; hence, the displacement ductility ratio and energy dissipation capacity also increased 70% and 36%, respectively. The results suggest that the proposed retrofitting greatly improved the ductility of the RC columns.
The optimum number of and the optimal locations for the proposed seismic reinforcements to retrofit the columns of a school building in a RC structure were derived using the optimization method. The optimization method is based on the ant colony optimization (ACO), and involved 3D modeling of the school building steel structure and dynamic analysis for accurate and reliable time history analysis.
The algorithm to derive the optimal location for the retrofit was derived by combining ACO and 3D nonlinear time history analysis.
In time history analysis using natural seismic waves, it is typically more effective to apply individual dominant frequency bands separately, and it was found that, in the case of the multi-span, low-rise structure, such as the school building in Korea, natural seismic waves with dominant frequency of 5 Hz or less should be applied. Therefore, it was found that, in the case of school buildings in Korea with non-seismic RC details, it was adequate to evaluate their seismic response using the seismic waves of the Kobe Earthquake of 1995 and the San Fernando Earthquake of 1971.
The results showed that the strength of the structures varied depending on the direction of the earthquakes, and the variation was significant. When the excitation was introduced separately toward the x-axis direction with a few spans, 45°, and the y-axis with many spans, it was found that the strain was smaller when the direction of excitation was toward the y-axis, indicating larger strength.
The results also showed that, to meet the current seismic design criteria, more than 80 of the 186 columns of the school building in Korea with non-seismic details must be retrofitted; the higher the peak ground acceleration (PGA) of the seismic waves, the more reinforcement is needed in the lower floors than the higher floors. It was found that it is more efficient to arrange the reinforcement in a crisscross pattern over a wide range, rather than a narrow range.
The results of the sensitivity analysis with varying arrangements of reinforcement showed that the outer columns on the lowest floor (first floor) were the most sensitive, and the inner columns on the highest floor (third floor) were the least sensitive. Thus, it is most likely economic and effective to retrofit the first floor and outer columns first in the event of emergency seismic reinforcement. The findings on the number of reinforcements for columns and the outcomes for different arrangements are expected to greatly influence future seismic reinforcement design and construction.
주제어
#RC 기둥 내진보강 최적화 GFRP 벨크로 보강재 배치
※ AI-Helper는 부적절한 답변을 할 수 있습니다.