• Geomechanics and Engineering
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• 제15권3호
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• pp.833-839
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• 2018

Dynamic behaviour of a tunnel is one of the most important issues for the safety and it is generally subjected to the seismic response of the surrounding soil. Relative displacement occurred in tunnel lining during earthquake produces severe damage. Generally, it concentrates at the connecting area when two tunnels are connected in the ground. A flexible segment is a useful device for the mitigation of seismic loads on tunnel lining. In this study, 1-g shaking table tests are performed to investigate the acceleration response for the verification of the effect of flexible segment and to determine the optimum location of the flexible segment for connected tunnels. Four different seismic waves are considered; as a result, peak acceleration is reduced to 49% in case that flexible segment is implemented adjacent to connecting area. It also exhibited that the mitigation of acceleration response is verified in all seismic waves. Additionally, 3-dimensional numerical analysis is performed to compare and verify the results. And the numerical results show good agreement to those of the experimental study.

• Earthquakes and Structures
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• 제18권1호
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• pp.15-25
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• 2020

The seismic behaviour of reinforced concrete (RC) columns made from high-strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength stirrups (HSSs) and three with normal-strength stirrups (NSSs), were tested under a combination of high axial and reversed cyclic loads. The effects of stirrup strength and the ratio of transverse reinforcement on the cracking patterns, hysteretic response, strength, stiffness, ductility, energy dissipation and strain of transverse reinforcement were studied. The results indicate that good seismic behaviour of an RC column subjected to high axial compression can be obtained by using a well-shaped stirrup. Stirrup strength had little effect on the lateral bearing capacity. However, the ductility was significantly modified by improving the stirrup strength. When loaded with a large lateral displacement, the strength reduction of NSS specimens was more severe than that of those with HSSs, and increasing the stirrup strength had little effect on the stiffness reduction. The ductility and energy dissipation of specimens with HSSs were superior to those with NSSs. When the ultimate displacement was reached, the core concrete could be effectively restrained by HSSs.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.57-64
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• 1998

This paper presents the cyclic seismic performance of slip-critically designed, high-strength bolted-beam splice in steel moment frame. Before the moment connection reaching its plastic strength, unexpected premature slippage occurred at the slip-critically designed beam splice during the test. The experimentally observed frictional coefficients were as low as about 50% to 60% of nominal (code) value. Nevertheless, the bearing type behavior mobilized after the slippage transferred the increasing cyclic loads successfully, i.e., the consequence of slippage into bearing was not catastrophic to the connection behavior. The test result seems to indicate that the traditional beam splice design basing upon (bolt-hole deducted) effective flange area criterion may not be sufficient in developing the plastic strength of moment connections under severe earthquake loading. New procedure for achieving slip-critical beam splice design is proposed based on capacity design concept.

• Earthquakes and Structures
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• 제9권3호
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• pp.657-671
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• 2015

The level of ductility is determined by depending on the intended use of the building, the region's seismic characteristics and the type of structural system when buildings are planned by engineers. Major portion of seismic energy is intended to be consumed in the plastic zone in structural systems of high ductility, so the occurrence of damages in load bearing and non-load bearing structural elements is accepted in planning stage under severe earthquakes. However, these damages must be limited among specific values in order not to endanger buildings in terms of the bearing capacity. Isolators placed between the basement and upper structure make buildings behave elastically by reducing the effects of seismic loads and improving seismic performance of building significantly. Thus, damages can be limited among desired values. In this study, the effectiveness of seismic isolation is investigated on both fixed based and seismic isolated models of a hospital building with high ductility level with regard to lateral displacements, internal forces, structural periods and cost of the building. Layered rubber bearings are interposed between the base of the structure and foundation. Earthquake analysis of the building are performed using earthquake records in time domain (Kocaeli, Loma Prieta and Landers). Results obtained from three-dimensional finite element models are presented by graphs and tables in detail. That seismic isolation reduces significantly the destructive effects of earthquakes on structures is seen from the results obtained by seismic analysis.

• Structural Engineering and Mechanics
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• 제13권1호
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• pp.17-34
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• 2002

The use of local two-sided and three-sided jacketing for the repair and strengthening of reinforced concrete beam-column joints damaged by severe earthquakes is investigated experimentally and analytically. Two exterior beam-column joint specimens ($O_1$ and $O_2$) were submitted to a series of cyclic lateral loads to simulate severe earthquake damage. The specimens were typical of existing older structures built in the 1960s and 1970s. The specimens were then repaired and strengthened by local two-sided or three-sided jacketing according to UNIDO Manual guidelines. The strengthened specimens ($RO_1$ and $RO_2$) were then subjected to the same displacement history as that imposed on the original specimens. The repaired and strengthened specimens exhibited significantly higher strength, stiffness and better energy dissipation capacity than the original specimens.

• Computers and Concrete
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• 제12권5호
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• pp.681-695
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• 2013

In 1999 Marmara and 2011 Van earthquakes in Turkey, majority of the existing buildings either sustained severe damage or collapsed. These buildings include masonry infill walls in both the interior and exterior R/C frames. The material of the masonry infill is the main variant, ranging from natural stones to bricks and blocks. It is demanding to design these buildings for satisfactory structural behavior. In general, masonry infill walls are considered by its weights not by interaction between walls and frames. In this study, R/C buildings with infill walls are considered in terms of structural behavior. Therefore, 5 and 8-story R/C buildings are regarded as the representative models in the analyses. The R/C representative buildings, both with and without infill walls were analyzed to determine the effects of structural behavior change. The differences in earthquake behavior of these representative buildings were investigated to determine the effects of infill walls leading structural capacity. First, pushover curves of the representative buildings were sketched. Aftermath, time history analyses were carried out to define the displacement demands. Finally, fragility analyses were performed. Throughout the fragility analyses, probabilistic seismic assessment for R/C building structures both with and without infill walls were provided. In this study, besides the deterministic assessment methodology, a probabilistic approach was followed to define structural effect of infill walls under seismic loads.

• 한국지진공학회논문집
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• 제17권3호
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• pp.117-125
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• 2013

Seismic isolation has been considered and utilized in various industries as a way to prevent huge damage on to structures by large earthquakes in various industries. The laminated Laminated rubber bearings is are most frequently used in seismic isolation systems. The structural Structural safety could not be assured unless the performance of the rubber bearing is not guaranteed for the life time of the structure under the consideration that the bearing is a critical structural member to sustain vertical loads in the seismically isolated structure. However, there are few studies on the deterioration problems of rubber bearings during their service life. The long term performance of the rubber bearings was not considered in past designs of seismically isolated structures. This study evaluates the long term performance and creep characteristics of laminated natural rubber bearings that are used in seismically isolated buildings. For the this study, a set of accelerated thermal aging tests and creep tests are were performed on real specimens. The experimental results show that the natural rubber bearings would have a stable change rate of change for durability under severe environmental conditions for a long time.

• Earthquakes and Structures
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• 제13권6호
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• pp.539-549
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• 2017

Existing reinforced concrete frame buildings designed for vertical loads could only suffer severe damage during earthquakes. In recent years, many research activities were undertaken to develop a reliable and practical analysis procedure to identify the safety level of existing structures. The Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate the seismic demand and capacity of structures. However, the executions of many nonlinear response history analyses (NL_RHA) are required to describe the entire range of structural response. The research discussed in this paper deals with the proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the nonlinear response history analysis of the IDA procedure with Modal Pushover Analysis (MPA). Firstly, In this work, the MPA is examined and extended to three-dimensional asymmetric structures and then it is incorporated into the proposed procedure (IMPA) to estimate the structure's seismic response and capacity for given seismic actions. This new procedure, which accounts for higher mode effects, does not require the execution of complex NL-RHA, but only a series of nonlinear static analysis. Finally, the extended MPA and IMPA were applied to an existing irregular framed building.

• 한국산학기술학회논문지
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• 제14권7호
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• pp.3502-3507
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• 2013

스카이브릿지가 연결되는 건물에 강접합될 경우에는 비정형성이 크게 되어 지진하중에 매우 불리하게 거동할 수 있다. 따라서, 마찰진자베어링(FPS)이나 납고무베어링(LRB)와 같은 연결시스템을 사용하여 스카이브릿지와 구조물을 연결하게 된다. 이러한 연결시스템은 큰 지진하중이 발생하였을 때 스카이브릿지가 연결된 건물에서 분리되어 낙교하지 않도록 신중하게 설계되어야 한다. 본 논문에서는 수직방향 인장력에대해서 저항성이 없는 마찰진자감쇠기를 이용한 연결시스템을 설계하는 과정에서 반드시 검토해야할 사항을 분석하였다. 이를 위하여 실제 시공된 누리꿈 스퀘어를 예제구조물로 선택하였고 예상되는 지진하중이 가해졌을 때 스카이브릿지 연결시스템에서 발생하는 응답을 분석하여 낙교를 방지할 수 있는 설계 프로세스를 정립하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.569-576
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• 2003

Based on the equivalent uniform stress concept Presented by Seed and Idriss, sinusoidal cyclic loads which simplified earthquake loads have been applied in evaluating the liquefaction resistance strength experimentally. However, the liquefaction resistance strength of soil based on the equivalent uniform stress concept can not exactly reflect the dynamic characteristics of the irregular earthquake motion. The liquefaction assessment method which was invented by using the equivalent uniform stress concept is suitable for the severe earthquake region such as Japan or USA, so the proper method to Korea is needed. In this study, estimation of the resistance to liquefaction was conducted by applying real earthquake loading to the cyclic triaxial test. From the test results, the characteristics of the fine sand under moderate earthquake were analyzed and compared with the results under strong earthquakes. Typically real earthquake loads used in this study are divided into two types - impact type and vibration type. Furthermore, results of the liquefaction resistance strength based on the equivalent uniform stress concept and tile concept using real earthquake loading were compared.