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.

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.

In this study, material tests were performed on the masonry specimens constructed with bricks and mortar used in Korea. The specimens included two types of thickness(0.5B and 1.0B) and physical conditions (good and poor). It was shown that 1.0B specimens have 3.2~1.8 times larger shear strength than 0.5B specimens and shear strength of specimens in poor condition was 66%~38% of those in good condition. Average shear stress of masonry-infills was calculated from previous experimental studies, and relationships with failure mode, material strength of masonry, aspect ratio, and frame-to-infill strength ratio were investigated. In addition, the effects of masonry strength on the seismic performance of a masonry-infilled frame was studied using a simple example building. It can be seen that the obtained average shear stress were considerably higher than the default masonry shear strength recommended by the ASCE 41, and low values the strength of masonry does not guarantee conservative evaluation results due to the early shear failure of frame members.

The seismic performance of school buildings has been a matter of common interest socially and academically. The structural system of the school buildings is representative of the domestic low-rise reinforced concrete moment resisting frames, which apply extensively infills in their masonry walls. The masonry infilled walls are divided into full masonry infill in the transverse direction and partial masonry infill in the longitudinal direction. The masonry infilled walls are usually not included in structural analysis during the design process, but affect significantly the seismic performance because they behave with surrounding frames simultaneously during earthquakes. Many researchers have studied the effect of the masonry infilled walls, but several issues have been missed such as the increase of asymmetry by adding the full masonry infill, the size of the mean strength of the full masonry infill, and short column effect by the partial masonry infill. The issues were analytically investigated and the results showed that they should be checked at least by nonlinear pushover analysis in the seismic performance evaluation process. The results also confirm the weakness of the guideline of Korean Educational Development Institute where the seismic performance is basically assessed without structural analysis.

조적 끼움벽은 건축물의 건설에 있어서 공간을 나누고 구획하는데 사용되는 가장 흔한 시스템 중의 하나이다. 조적 끼움벽의 많은 장점에도 불구하고, 대상 시스템은 지진하중에 대하여 주의를 가지고 사용되어야 한다. 지진이 작용하는 동안 끼움벽에는 대각 방향의 압축 스트럿이 형성되면서 주변의 RC 골조에 작용하는 요구 하중을 크게 한다. 특히 개구부가 있는 조적 끼움벽의 경우, 하중 전달과정이 매우 복잡하기 때문에 시스템의 설계에 있어서 엔지니어의 주관적인 판단이 필요하게 된다. 본 연구에서는 개구부를 갖는 조적 끼움벽에 대하여 유한요소 해석(FEA)를 실시하여 거동을 조사하였고, 그 결과를 현행 설계기준인 ASCE 41을 적용한 경우와 비교하였다. ASCE 41의 기준을 적용할 때, 압축 스트럿의 등가폭이 FEA를 통한 결과에 비하여 32%까지 작게 나타났다. 또한 하중저항 능력은 ASCE 41을 적용한 경우 FEA에 의한 결과에 비하여 28% 작게 나타났다. 따라서 상당한 노력이 필요한 FEA를 대신하여, 조적 끼움벽의 해석과 설계에 ASCE 41을 적용하면 약 25% 수준의 보수적이며 적절한 결과를 얻을 수다고 할 수 있다.