The cultural heritage of fortresses is often exposed to external elements, leading to significant damage from stone weathering and natural disasters. However, due to the nature of cultural heritage, dismantling and restoration are often impractical. Therefore, the stability of fortress cultural heritage was evaluated through non-destructive testing. The durability of masonry cultural heritages is greatly influenced by the physical characteristics of the back-fille material. Dynamic characteristics were assessed, and endoscopy was used to inspect internal fillings. Additionally, a finite element analysis model was developed considering the surrounding ground through elastic wave exploration. The analysis showed that the loss of internal fillings in the target cultural heritage site could lead to further deformation in the future, emphasizing the need for careful observation.

This study investigated the rocking behavior of unreinforced masonry walls and wall piers under cyclic loading. Based on the benchmark tests, the characteristics of load-deformation relations in masonry walls with rocking failure were captured, focusing on observed deformation modes. The rocking strengths of masonry walls (i.e., peak and residual strengths) were evaluated, and the effects of opening configurations on the masonry wall strength were examined. The deformation capacity of the rocking behavior and the hysteresis shape of the load-deformation relations were also identified. Based on the results, modeling approaches for the rocking behavior of masonry walls were discussed.

As earthquakes have increased in Korea recently, people are paying attention to the seismic performance of buildings built in the past. Many school buildings in Korea were built based on standard drawings before the seismic design was applied. However, since school buildings are often designated as emergency evacuation facilities in case of disasters such as earthquakes, seismic evaluation and retrofit must be done quickly. This study investigated the failure modes among structural components (beams, columns, and joints), focusing on 1980s standard drawings for school buildings. The effects of column axial force, partial masonry infills, and different material strengths for concrete and rebar were considered for detailed evaluation. As a result, most of the joints were found to be the weakest among structural components. Column axial forces tended to make the joints more vulnerable, and partial masonry infills increased the possibility of joint failure and shear failure in columns.

This study investigated the seismic performance of reinforced concrete (RC) wall-slab frames with masonry infills. Four RC wall-slab frames with or without masonry infill were tested under cyclic loading. The RC frames were composed of in-plane and out-of-plane walls and top and bottom slabs. For masonry infill walls, cement bricks were stacked applying mortar paste only at the bed joints, and, at the top, a gap of 50 mm was intentionally left between the masonry wall and top RC slab. Both sides of the masonry walls were finished by applying ordinary or fiber-reinforced mortars. The tests showed that despite the gap on top of the masonry walls, the strength and stiffness of the infilled frames were significantly increased and were different depending on the direction of loading and the finishing mortars. During repeated loading, the masonry walls underwent horizontal and diagonal cracking and corner crushing/spalling, showing a rocking mode inside the RC wall-slab frame. Interestingly, this rocking mode delayed loss of strength, and as a result, the ductility of the infilled frames increased to the same level as the bare frame. The interaction of masonry infill and adjacent RC walls, depending on the direction of loading, was further investigated based on test observations.

Based on the nonlinear static analysis and the approximate seismic evaluation method adopted in “Guidelines for seismic performance evaluation for existing buildings, two methods to calculate strength demand for retrofitting individual structural walls in unreinforced masonry buildings are proposed.” The displacement coefficient method to determine displacement demand from nonlinear static analysis results is used for the inverse calculation of overall strength demand required to reduce the displacement demand to a target value meeting the performance objective of the unreinforced masonry building to retrofit. A preliminary seismic evaluation method to screen out vulnerable buildings, of which detailed evaluation is necessary, is utilized to calculate overall strength demand without structural analysis based on the difference between the seismic demand and capacity. A system modification factor is introduced to the preliminary seismic evaluation method to reduce the strength demand considering inelastic deformation. The overall strength demand is distributed to the structural walls to retrofit based on the wall stiffness, including the remaining walls or otherwise. Four detached residential houses are modeled and analyzed using the nonlinear static and preliminary evaluation procedures to examine the proposed method.

This study proposed a simplified finite element analysis procedure for designing the nonstructural masonry wall in the out-of-plane direction. The proposed method is a two-step elastic analysis procedure by bilinearizing the behavior of the masonry wall. The first step analysis was conducted with initial stiffness representing the behavior up to the effective-yield point, and the second step analysis was conducted with post-yield stiffness. In addition, the orthotropic material property of the masonry was considered in the FE analysis. The maximum load was estimated as the sum of the maximum loads in the first and second step analyses. The maximum load was converted into the moment coefficients and compared with those from the yield line method applied in Eurocode 6. The moment coefficients calculated through the proposed procedure showed a good match with those from the yield line method with less than 6% differences.

In this study, the seismic performance of a two-story unreinforced masonry (URM) building was assessed following the linear and nonlinear static procedures specified in the seismic evaluation guideline of existing buildings. First, the provisions to assess failure modes and shear strengths of URM walls and wall piers were reviewed. Then, a two-story URM building was assessed by the linear static procedure using m-factors. The results showed that the walls and wall piers with aspect ratios he /l (i.e., effective height-to-length ratio) > 1.5 were unsafe due to rocking or toe crushing, whereas the walls with he /l ≤1.5 and governed by bed-joint sliding mainly were safe. Axial stresses and shear forces acted upon individual masonry walls, and wall piers differed depending on whether the openings were modeled. The masonry building was reevaluated according to the nonlinear static procedure for a more refined assessment. Based on the linear and nonlinear assessment results, considerations of seismic evaluation for low-rise masonry buildings were given with a focus on the effects of openings.

최근 경주지진과 포항지진 피해사례에서 보이듯 조적벽체 구조물의 붕괴 위험이 사회적으로 큰 주목을 받고 있다. 본 연구는 수평하중에 대한 강성이 구조적으로 취약한 조적벽체 구조물에 대하여 개선된 보강재 설계 및 이를 통한 구조성능 평가를 수행하였다. 선행기술에서 제시한 FRP Plate 보강재의 경우 외부 부착 시 계면 부착파괴에 의한 보강성능 저감이 발생하는 것을 고려하여 본 연구에서는 사전제작 매립형 T-Joint BFRP 보강재를 개발하였으며, 이를 혼합 에폭시계 연성페인트와 혼합 하여 보강 구조물의 마감효과 및 에너지흡수성능을 개선하는 방법으로 제안하였다. 실험 결과, 보강 시험체의 강성은 약 1.37배, 에너지소산능력은 약 2.59배 개선됨을 확인하였다.

Seismic fragility functions for unreinforced masonry buildings were derived based on the incremental dynamic analysis of eight representative inelastic numerical models for application to Korea's earthquake damage estimation system. The effects of panel zones formed between piers and spandrels around openings were taken into account explicitly or implicitly regarding stiffness and inelastic deformation capacity. The site response of ground motion records measured at the rock site was used as input ground motion. Limit states were proposed based on the fraction of structural components that do not meet the required performance from the nonlinear static analysis of each model. In addition to the randomness of ground motion considered in the incremental dynamic analysis explicitly, supplementary standard deviation due to uncertainty that was not reflected in the fragility assessment procedure was added. The proposed seismic fragility functions were verified by applying them to the damage estimation of masonry buildings located around the epicenter of the 2017 Pohang earthquake and comparing the result with actual damage statistics.

최근 경주와 포항에서 발생한 지진피해 사례에서 보듯 조적벽체 및 필로티 구조물의 붕괴 위험이 사회적으로 큰 주목을 받고 있다. 본 연구는 명확한 내진설계지침이 없고 수평하중에 대한 내성이 구조적으로 매우 약하며 재난관리시설 중 지 진붕괴 위험이 높은 조적조 구조물에 대한 보강 설계 및 성능평가를 조사하였다. 기존 선행연구에서 발표된 FRP Plate의 외부 접착시 부착파괴의 문제점을 반영하여 부착력이 개선된 매립형 T-Joint BFRP Plate를 개발하였으며, 시공 시 에폭시 계열의 연성페인트를 활용하여 보강구조물의 연성을 개선하는 방법을 제안하였다. 최종적으로 수행된 정적 및 반복가력 실험을 통하여 보강시험체의 강성 및 에너지 소산능력이 각 1.23과 1.39배 증가함을 확인하였다.

Many Korean domestic masonry structures constructed since 1970 have been found to be vulnerable to earthquakes because they lack efficient lateral force resistance. Many studies have shown that the brick and mortar suddenly experience brittle fracture and out-of-plane collapse when they reach the inelastic range. This study evaluated the seismic retrofitting of non-reinforced masonry with Hybrid Super Coating (HSC) and Cast, manufactured using glass fiber. Four types of specimen original specimen (BR-OR), one layered HSC (BR-HS-O), two-layered HSC (BR-HS-B), one layered HSC, and Cast (BR-CT-HS-O) were constructed and analyzed using compression, flexural tensile, diagonal compression, and triplet tests. The specimen responses were presented and discussed in load-displacement curves, maximum strength, and crack propagation. The compressive strength of the retrofit specimens slightly increased, while the flexural tensile strength of the retrofit specimens increased significantly. In addition, the HSC and Cast also produced a considerable increase in the ductile response of specimens before failure. Diagonal compression test results showed that HSC delayed brittle cracks between the mortar and bricks and resulted in larger displacement before failure than the original brick. The triplet test results confirmed that the bonding strength of the retrofit specimens also increased. The application of HSC and Cast was found to restrain the occurrence of brittle failure effectively and delayed the collapse of masonry wall structures.

Concrete masonry prisms are strengthened with steel fiber-reinforced mortar (SFRM) overlay and tested for compressive and diagonal tension strength. Masonry prisms are produced in poor condition considering standard workmanship for masonry buildings in Korea. Amorphous steel fibers are adopted for SFRM, and appropriate mixing ratios of SFRM are derived considering constructability and strength. Masonry prisms are strengthened with different fiber volume ratios, while numerous strengthened faces and additional reinforcing meshes are produced for compression and diagonal tension tests. Compression and diagonal tension strength are increased by up to 122% and 856%, respectively, and the enhancement effect for diagonal tension strength was superior compared to compression strength. Finally, the test results and strength prediction equations based on existing literature and regression analysis are compared.

Nonlinear static analysis and preliminary evaluation were performed in this study to evaluate the seismic performance of unreinforced masonry buildings subjected to various soil conditions based on the revised Korean Building Code. Preliminary evaluation scores and nonlinear static analyses indicated that all buildings were susceptible to collapse and did not reach their target performance. Therefore, retrofit of those building models was carried out through a systematic procedure to determine areas to be strengthened. It was possible to make most building models satisfy performance objectives through the reinforcement alone of damaged external shear walls. However, the application of a preliminary evaluation procedure to retrofit design was found to be too conservative because all the retrofitted building models verified with nonlinear static analysis failed to satisfy performance objectives. Therefore, it is possible to economically retrofit unreinforced masonry buildings through the fortification of external walls if a simple evaluation procedure that can efficiently specify vulnerable parts is developed.

Lightly reinforced concrete (RC) moment frames may suffer significant damage during large earthquake events. Most buildings with RC moment frames were designed without considering seismic loads. The load-displacement response of gravity load designed frames could be altered by masonry infill walls. The objective of this study is to investigate the load-displacement response of gravity load designed frames with masonry infill walls. For this purpose, three-story gravity load designed frames with masonry infill walls were considered. The masonry infilled RC frames demonstrated larger lateral strength and stiffness than bare RC frames, whereas their drift capacity was less than that of bare frames. A specimen with a partial-height infill wall showed the least drift capacity and energy dissipation capacity. This specimen failed in shear, whereas other specimens experienced a relatively ductile failure mode (flexure-shear failure).

Most school buildings consist of reinforced concrete (RC) moment frames with masonry infills. The longitudinal direction frames of those school buildings are relatively weak due to the short-column effects caused by the partial masonry infills and need to be evaluated carefully. In ‘Manual for Seismic Performance Evaluation and Retrofit of School Facilities’ published in 2018, response modification factor of 2.5 is applied to non-seismic RC moment frames with partial masonry infills, but sufficient verification of the factor has not been reported yet. Therefore, this study conducted seismic performance evaluation of planar RC moment frames with partial masonry infills in accordance with both linear analysis and nonlinear static analysis procedures presented in the manual. The evaluation results from the different procedures are compared in terms of assessed performance levels and number of members not meeting target performance objectives. Finally, appropriate response modification factors are proposed with respect to a shear-controlled column ratio.

본 연구는 지진에 저항하는 부재인 비보강 조적벽체로 구성된 건물의 내진성능평가에 활용되는 비선형 정적해석을 위한 비보강 조적벽체의 해석모델을 수립하고자 하였다. 본 연구의 해석모델은 비보강 조적벽체의 휨거동을 모사하기 위한 파이버 요소와 비보강 조적벽체의 전단에 대한 응답을 예측하기 위한 전단스프링 요소로 구성된다. 본 논문은 먼저 제안하고 있는 모델의 형상에 대해서 설명하고, 기존에 행해진 조적조 프리즘의 실험결과로부터 얻은 응력-변형률 곡선을 근거로 파이버와 전단스프링 요소의 물성치에 대한 결정 방법을 설명한다. 제시하고 있는 모델은 비선형 정적 해석결과와 다른 연구자들에 의해 수행된 실험결과를 비교하여 타당성을 검증한다. 해당 모델은 최대강도, 초기강성, 그리고 이들로부터 얻어지는 비보강 조적벽체의 하중-변위 곡선을 적절하게 모사하고 있다. 또한, 해석모델이 비보강 조적벽체의 파괴모드를 예측할 수 있는 것으로 나타난다.

Recent decades, maintenance and reconstruction have been paid attention to old buildings. Especially, it has been recognized that seismic retrofit measures are necessary for non-reinforced masonry buildings which are used for prevailing building constructions. However, such applications can be limited due to its excessive costs, long-period, and inherent difficulty in securing construction spaces. For this reason, different reinforcement methods have been proposed by previous researchers in the economic manner. This study carried out an adhesive retrofit material upgrading low workability and excessive costs of existing reinforcement methods and, in turn, verified the level of seismic reinforcement throughout experimental studies. In order for the objectives, masonry walls with an aspect ratio of 1.0 were designed and manufactured. Also, effective parameters which are affected by openings, adhesive material types, the number of reinforcement layers, and lateral load levels were established. Experimental results showed that MW specimens without openings were collapsed for low-seismic resistances resulting from rocking failure modes, while strength and displacement capacities were improved for reinforced openings. Also, R-MWO-3F specimens with opening which was enhanced for three layers of stiffener showed displacement, ductility capacities, and energy dissipating capacities in the stable manner, even satisfying the collapse prevention level proposed in the current seismic codes.

This report offers an economically reasonable seismic reinforcement to non-seismic mid/low reinforced concrete structures. Installed a slit in between the reinforced concrete frame and masonry infilled wall then inserted twist bar to prevent inversion and attached to the lower/upper beam. Confirmed the seismic reinforcement effect through static loading test. Total of 4 specimens were produced for the test, a masonry infilled wall without seismic reinforcement and with seismic slit or twist bar applied. As a result, applying the seismic slit and twisted bar was economically reasonable and seismic reinforcement effect was confirmed by showing stable failure, increase of maximum strength and yield displacement, increase of accumulated energy dissipation.

본 논문에서는 범용유한요소해석 프로그램인 ABAQUS를 사용하여 국내에서 사용되는 콘크리트벽돌을 조적채움벽으로 가진 철근콘크리트 골조를 대상으로 유한요소해석을 실시하였다. 해석대상은 순수골조, 채움벽의 두께가 0.5B인 골조, 두께가 1.0B인 골조의 3종류이다. 철근콘크리트 골조 및 채움벽의 재료특성은 재료시험 결과로부터 구하였으나 두께가 1.0B인 채움벽의 경우 벽돌의 쌓기방법의 차이에 의해 0.5B 두께의 실험체보다 4배 정도 증가된 인장강도를 사용하였다. 유한요소해석결과는 실험을 통해 구한 하중-변위관계 및 변위각에 따른 균열양상을 상당히 정확하게 예측하였다. 유한요소해석 결과의 분석을 통해 조적채움벽과 골조사이의 접촉응력 및 골조의 전단력과 휨모멘트를 산정하였다.