Recently, the occurrence frequency of earthquake has increased in Korea, and the interests for seismic reinforcement of existing school buildings have been raised. To this end, the seismic performance evaluations for school buildings that did not accomplish the seismic design are required. In particular, this study checks the eigenvalue analysis, pushover curves, maximum base shears, performance points and story drift ratios, and then analyzes the seismic performance characteristics according to bracing configuration of steel frame system reinforcement. Also, this study presents the practical field application methods through the comparison of analysis results for the seismic performance characteristics.

2016 Gyeongju and 2017 Pohang earthquakes led Koreans to acknowledge that the Korean peninsula is not an earthquake-free zone anymore. Among various buildings crucial to after-shock recovery, general hospital buildings, especially existing old ones, are very significant so seismic retrofitting of those must be an important issue. Self-centering energy dissipative(SCED) brace is one of retrofitting methods, which consists of tendon with restoring force and friction device capable of dissipating seismic energy. The strength of the SCED brace is that the tendon forces a structure to go back to the original position, which means residual drift can be negligible. The residual drift is a very important parameter to determine usableness of general hospitals after shock. To the contrary, buckling-restrained braces(BRB) are also a very effective way to retrofit because they can resist both compressive and tensile, but residual drift may exist when the steel core yields. On this background, the seismic retrofitting effect of general hospitals reinforced with SCED braces was investigated and compared to that of the BRD in this study. As a result, although the floor acceleration cannot be reduced, the story drift and residual drift, and the shear demand of walls significantly decreased. Consequently, seismic retrofitting by SCED braces are very effective for domestic low-rise general hospitals.

The friction damper can be used for improving the seismic resistance of existing buildings. The damper is often installed in bracing members. The energy dissipation capacity of the damping systems depends on the type of the structure, the configuration of the bracing members, and the property of dampers. In Korea, there are numerous low- to mid-rise reinforced concrete moment frames that were constructed considering only gravity loads. Those frames may be vulnerable for future earthquakes. To resolve the problem, this study developed a toggle bracing system with a high density friction damper. To investigate the improvement of reinforced concrete frames after retrofit using the developed damped system, experimental tests were conducted on frame specimens with and without the damped system. The results showed that the maximum strength, initial stiffness and energy dissipation capacity of the framed with the damped system were much larger than those of the frame without the damped system.

This study mainly treats a new type of the bracing friction damper system, which is able to minimize structural damage under earthquake loads. The slotted bolt holes are placed on the shear faying surfaces with an intention to dissipate considerable amount of friction energy. The superelastic shape memory alloy (SMA) wire strands are installed crossly between two plates for the purpose of enhancing recentering force that are able to reduce permanent deformation occurring at the friction damper system. The smart recentering friction damper system proposed in this study can be expected to reduce repair cost as compared to the conventional damper system because the proposed system mitigates the inter-story drift of the entire frame structure. The response mechanism of the proposed damper system is firstly investigated in this study, and then numerical analyses are performed on the component spring models calibrated to the experimental results. Based on the numerical analysis results, the seismic performance of the recentering friction damper system with respect to recentering capability and energy dissipation are investigated before suggesting optimal design methodology. Finally, nonlinear dynamic analyses are conducted by using the frame models designed with the proposed damper systems so as to verify superior performance to the existing damper systems.

The researches related to active control systems utilizing superelastic shape memory alloys (SMA) have been recently conducted to reduce critical damage due to lateral deformation after severe earthquakes. Although Superelastic SMAs undergo considerable inelastic deformation, they can return to original conditions without heat treatment only after stress removal. We can expect the mitigation of residual deformation owing to inherent recentering characteristics when these smart materials are installed at the part where large deformation is likely to occur. Therefore, the primary purpose of this research is to develop concentrically braced frames (CBFs) with superelastic SMA bracing systems and to evaluate the seismic performance of such frame structures. In order to investigate the inter-story drift response of CBF structures, 3- and 6-story buildings were design according to current design specifications, and then nonlinear time-history analyses were performed on numerical 2D frame models. Based on the numerical analysis results, it can be comparatively verified that the CBFs with superelastic SMA bracing systems have more structural advantages in terms of energy dissipation and recentering behavior than those with conventional steel bracing systems.

본 연구에서는 1층 1경간 실제크기의 가력 프레임에서 내진보강에 적합한 비좌굴 knee brace을 설치하여 주기하중을 통해 가새의 지진저항능력을 실험하였다. 볼트 고정 채널이 이용된 비좌굴 knee brace는 지진력에 저항하는 코어와 두 개의 철골 플레이트로 만들어졌고 단면의 형태는 코어의 국부좌굴과 횡좌굴에 저항하도록 하였다. 비좌굴 kneebrace는 현장에서 조립이 용이하고, 시공방법 또한 간단하여 공간에 제약이 있는1층에 필로터를 가진 중저층 RC건물의 내진 보수/보강에 효과적으로 사용할 수 있다. 각 실험체에 대한 변수로 중심코어의 크기와 외부 보강재의 크기, 가이드 플레이트의 유무 등으로 정하였으며, 실험을 통해 얻어진 힘-변위 이력곡선을 통해 중심코어의 크기가 가장 큰 영향을 미치는 것으로 나타났다. 또한 가이드 플레이트의 유무에 따라 압축강도 수정계수와 파괴형태가 달라지는 것을 알 수 있었다. 각 실험체에 대한 결과는 AISC 2005 Seismic Provisions 규정에서 제시한 누적 연성도와 누적 소산에너지 측면에서도 충분한 효과를 발휘하는 것으로 나타났다.

시스템비계의 좌굴 강도는 가새재 미설치 등 현장에서 발생할 수 있는 시공적 결함에 많은 영향을 받으며, 시스템비계의 강도를 예측함에 있어 단일 수직재에 대한 축력 실험을 근거로 측정된 좌굴 강도로부터 조립된 시스템비계의 정확한 극한강도를 예측하는 것은 어렵다. 또한 국외에서 연구된 조립 시스템비계는 국내에서 사용되는 시스템비계와 연결부 형태의 차이가 발생된다. 따라서 본 연구에서는 국내에서 주로 사용되는 시스템비계를 대상으로 실물실험을 통해 가새재 설치 유무와 수평방향 단수(bay)의 변화에 따른 조립된 시스템비계의 극한하중 변화를 분석하였다.

This experimental study analyzed the reduction of the load capacity of the system support according to the uninstall bracing members by loading the ultimate load to the 3 - story system support assembly with the presence of bracing members as the key parameter. The load capacity of the 3-story specimen without bracing members is 38.4% of that of the 3-story specimen with bracing members. It is necessary to accurately reflect the installation plan of the bracing members and examine the structural safety of the system support assembly, not a single member, because there is a significant decrease in the load capacity of the system support assembly according to the uninstall of the bracing members.

본 연구에서는 역V형 강재 가새로 보강된 기존 철근콘크리트 구조물의 내진보강 설계방법 개발을 위한 실험연구를 수행하였다. 보강되지 않은 철근콘크리트 골조 기준 실험체와 강재 가새를 사용하여 강도 및 강성을 향상시킨 보강 실험체를 제작하고 내진성능을 평가하였다. 가새 보강 실험체의 경우 강성이 약 2~3배 증가를 목표로 설계하였다. 내진성능평가 결과, 무보강 실험체는 기둥에서 많은 양의 콘크리트가 박리가 되었고, 가새 보강 실험체는 초기 설계 단계에서 목표로 한 성능수준을 보여주었다. 가새를 보강한 실험체의 경우, 무보강 실험체에 비 하여 강성, 강도, 연성능력 그리고 에너지 소산 능력이 크게 향상되었다. 따라서 본 연구로부터의 실험결과를 토대로 기존 철근콘크리트 건축 물의 가새 보강공법에 관한 설계법 및 설계절차 개발을 위한 기초자료로 활용하고자 한다.

In this paper, seismic performance of RC frames reinforced by chevron braces were evaluated. The purpose of experimental study was to increase the stiffness of RC frames. As a results, if steel bracing was reinforced in RC frames, seismic performance of RC frames would be increased.

This paper presents a study of the numerical analysis of bracing connection in modular pier system using Concrete Filled Tube members. To evaluate the structural capacity of bracing connection, which have various shapes, numerical analysis is performed. For the optimal shape of bracing connection, the shape and size of gusset plate are evaluated by using analysis results.