• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.3
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• pp.85-92
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• 2015

Response spectra of a building are made with a SDOF system taking into account a first mode shape, even though higher modes may affect on the dynamic responses of a high-rise building. A soft soil layer under a building also affects on the responses of a building. In this study, seismic responses of a MDOF system were investigated to examine the effects of higher modes on the response of a tall building by comparing them with those of a SDOF system including the kinematic interaction effect. Study was performed using a pseudo 3D finite element program with seven bedrock earthquake records downloaded from the PEER database. Effects of higher modes on the seismic responses of a tall building were investigated for base shear force and base moment of a MDOF system including story shear forces and story moments. Study results show that higher modes of a MDOF system contribute to a reduction of base shear force up to 1/4-1/5 of KBC and base moment. The effect of higher modes is more significant on the base shear force than on the base moment. Maximum story shear force and moment occurred at the top part of a building rather than at a base in the cases of tall buildings differently from short buildings, and higher modes of a tall building affected on the base forces making them almost constant at the base. A soft soil layer also affects some on the base shear force of a high-rise building independently on the soft soil type, but a soft soil effect is prominent on the base moment.

• Journal of Korean Association for Spatial Structures
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• v.20 no.3
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• pp.107-116
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• 2020

In this paper, the displacement response to seismic loads was analyzed after installing TMD in spatial structures and high-rise buildings. In the case of a spatial structures, since it exhibits complex dynamic behavior under the influence of various vibration modes, it is not possible to effectively control the seismic response by installing only one TMD, unlike ordinary structures. Therefore, after installing eight TMDs in the structure, the correlation between displacement response and mass ratio was examined while changing the mass. The TMD must be designed to have the same frequency as the structure frequency so that the maximum response reduction effect can be exhibited. It can be confirmed that the most important variable is to select the optimal TMD mass in order to install the TMD on the structure and secure excellent control performance against the earthquake load. As a result of analyzing the TMD mass ratio, in the case of high-rise buildings, a mass ratio of 0.4% to 0.6% is preferable. In spatial structures, it is desirable to select a mass ratio of 0.1% to 0.2%. Because this study is based on the theoretical study based on numerical analysis, in order to design a TMD for a real structure, it is necessary to select within a range that does not affect the safety of the structure.

• Journal of Korean Association for Spatial Structures
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• v.8 no.5
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• pp.75-82
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• 2008

In this study, the possibility of vibration control of high-rise building structures by applying top-story isolation has been investigated. To this end, El Centro NS (1940) earthquake load is applied to 20- and 50-story building structures for numerical analysis. Artificial wind loads are used to evaluate the serviceability of example structures against wind vibration. As the number of isolated stories of example buildings is changed, structural responses has been evaluated to investigate optimal isolated building mass. And the natural period of isolation systems for top-story isolation is varied to investigate the improvement of control performance compared with the fixed base structure. Based on the analytical results, the top-story isolation system can be used as a hued mass damper and effectively reduce the structural responses of high-rise buildings against wind and seismic loads.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.119-129
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• 2022

It is essential to control the lateral displacement and differential axial shortening of the vertical elements in high-rise buildings. The differential axial shortening can cause challenges in the serviceability and safety of non-structural and structural elements, respectively. Hence, in this study, the differential axial shortening of the vertical elements and effects of long term behaviors of concrete are analyzed in 120-story high-rise buildings via the construction sequence analysis. Consequently, the axial shortening of the vertical elements is classified into elastic, creep, and shrinkage shortening, and dominant factors to the maximum axial shortening are analyzed. In addition, the serviceability of the non -structural elements is checked with a differential axial shortening at 30 years after completion of construction, and member forces at design and construction stages in girders and outrigger walls are compared.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.313-316
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• 2008

As high rise buildings with 100 or more stories are being constructed, it is inevitable to use high performance materials including high performance concrete. What is most important in high performance concrete is extremely high strength in order to reduce the section of members in high rise buildings. During the last several years, there have been active researches on Ultra high strength concrete. While these researches have been mostly focused on strength development, however, other accompanying physical properties have not been studied sufficiently. Thus, the present study purposed to obtain and analyze data on the physical mechanical properties of Ultra high strength concrete through experiments and to use the results as basic information on required performance of concrete used in high rise buildings.

• Wind and Structures
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• v.28 no.6
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• pp.389-404
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• 2019

In coastal regions, it is common to witness significant damages on low-rise buildings caused by hurricanes and other extreme wind events. These damages start at high pressure zones or weak building components, and then cascade to other building parts. The state-of-the-art in experimental and numerical aerodynamic load evaluation is to assume buildings with intact envelopes where wind acts only on the external walls and correct for internal pressure through separate aerodynamic studies. This approach fails to explain the effect of openings on (i) the external pressure, (ii) internal partition walls; and (iii) the load sharing between internal and external walls. During extreme events, non-structural components (e.g., windows, doors or rooftiles) could fail allowing the wind flow to enter the building, which can subject the internal walls to lateral loads that potentially can exceed their load capacities. Internal walls are typically designed for lower capacities compared to external walls. In the present work, an anticipated damage development scenario is modelled for a four-story building with a stepped gable roof. LES is used to examine the change in the internal and external wind flows for different level of assumed damages (starting from an intact building up to a case with failure in most windows and doors are observed). This study demonstrates that damages in non-structural components can increase the wind risk on the structural elements due to changes in the loading patterns. It also highlights the load sharing mechanisms in low rise buildings.

• Journal of Korean Association for Spatial Structures
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• v.23 no.1
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• pp.35-43
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• 2023

Microclimate analysis was conducted through actual measurement according to land use status in urban, and CFD analysis was conducted to analyze and predict the microclimate characteristics of urban, and compared and analyzed with the actual measurement results. It was measured in high-rise areas and parks, and the temperature of the park area was 0.4 to 0.6℃ lower, and the relative humidity was 1.0 to 3.0% higher. The correlation coefficient was obtained by comparing the results of the computational fluid analysis with the results of the computational fluid analysis at the actual location located within the CFD analysis area for validation. The seasonal correlation coefficients are all higher than 0.8, so it is judged that they can be applied to microclimate analysis in urban area. The computational fluid analysis was divided into three areas (low-rise, low and high-rise, and high-rise) centered on the A2 point. On average, the low-rise area was 0.1 to 0.4% higher than the high-rise area. In the low and high-rise area and high-rise area, the pith of buildings are wide, so the airflow is smooth, so it is judged that the temperature is relatively low.

• Earthquakes and Structures
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• v.22 no.2
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• pp.169-184
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• 2022

The importance of seismicity in developing countries and the strengthening of buildings is a topic of major importance. Therefore, the study of several solutions with the development of new technologies is of great importance to investigate the damage on retrofitted structures by using probabilistic methods. The Federal Emergency Management Agency considers three types of performance levels by considering different scenarios, intensity and duration. The selection and scaling of ground motions mainly depends on the aim of the study. Intensity-based assessments are the most common and compute the response of buildings for a specified seismic intensity. Assessments based on scenarios estimate the response of buildings to different earthquake scenarios. A risk-based assessment is considered as one of the most effective. This research represents a practical method for developing countries where exists many active faults, tall buildings and lack of good implementable approaches. Therefore, to achieve the main goal, two high-rise steel buildings have been modeled and assessed. The contribution of buckling-restrained braces in the elastic design of both buildings is firstly verified. In the nonlinear static range, both buildings presented repairable damage at the central top part and some life safety hinges at the bottom. The nonlinear incremental dynamic analysis was applied by 15 representative/scaled accelerograms to obtain levels of performance and fragility curves. The results shown that by using probabilistic methods, it is possible to estimate the probability of collapse of retrofitted buildings by buckling-restrained braces and tuned mass dampers, which are practical retrofitting options to protect existing structures against earthquakes.

• International Journal of High-Rise Buildings
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• v.11 no.1
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• pp.69-74
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• 2022

- COVID -19 taught us a lot about how to protect our tall buildings from infectious diseases. This paper captures the lessons learned about airflow in indoor spaces when considering furniture and its placement. By applying them we move towards future proofing our buildings both in normal and pandemic times.

• International Journal of High-Rise Buildings
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• v.8 no.1
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• pp.29-36
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• 2019

Tall buildings are one of the most viable solutions to deal with the global phenomenon of rapid population increase and urbanization. While tall buildings are an essential building type to accommodate ever-growing urban population, as buildings become very tall they also produce many critical design challenges related to social interactions, emergency egress, structural systems, etc. While many different design solutions can be sought to resolve these challenging issues of tall buildings, this paper investigates potential of conjoined towers in producing more livable and sustainable megatall building complexes with an emphasis on their capability in efficiently providing exceedingly tall building structures.