This study investigates the impact of building insulation standards on indoor thermal environments and the risk of heat-related illnesses during heatwaves in South Korea. Indoor temperatures were measured in residential buildings located in Chuncheon and Gwangju during the 2022 heatwave, with outdoor temperature data sourced from the Korea Meteorological Administration. Probability distribution fitting was used to estimate the likelihood of indoor temperatures exceeding the critical threshold of 27 °C. Additionally, a linear regression analysis was conducted to examine the relationship between the probability of exceeding the threshold and heat-related illness data from 2017 to 2023 provided by the Korea Disease Control and Prevention Agency. The findings reveal significant variations in indoor thermal conditions during heatwaves, influenced by factors such as building type, year of construction, and climate region, which affect the thermal insulation performance. Buildings with a lower thermal insulation performance were associated with higher indoor temperatures, increasing the likelihood of exceeding the critical threshold and contributing to a higher incidence of heat-related illnesses, particularly in provincial non-metropolitan areas. These results underscore the need for region-specific building insulation standards that address both winter energy efficiency and summer heatwave resilience. Enhancing thermal insulation in vulnerable regions could significantly reduce the risk of heat-related illnesses and improve public health resilience to extreme heat events.

In this study, the vulnerability curves for masonry and concrete frame buildings are assessed based on building fragility curves for the debris-flow caused by landslides on mountain slopes. The First-Order Second-Moment (FOSM) method is used to estimate the building fragility curve (expressed as probability of damage exceedance) subjected to debris-flow. In this method, the horizontal displacement of a building impacted by debris-flow and the statistics of resistance (i.e., building displacement) following four different damage states (i.e., slight, moderate, extensive, and complete) are utilized to estimate the building fragility curve. The building vulnerability curves (expressed as mean probability of damage) were evaluated based on the estimated building fragility curve and corresponding mean damage ratio for each damage state and were verified by calculating the root mean square error with datasets obtained from post-disaster damage assessment. In this study, the effects of structural material, type, and height on the building vulnerability curves were also studied. All vulnerability curves of buildings estimated in this study were fitted and databased using parameters of the log-normal cumulative distribution function and can be used to measure the performance of buildings in debris-flow prone areas as well as to provide information for risk and loss assessment.

Investigating flow separation regions on the surfaces of three-dimensional bluff bodies in turbulent flows is important because these regions can induce significant aerodynamic loads. Separation bubbles can generate extreme pressures, making the roof components of low-rise buildings vulnerable. In this study, proper orthogonal decomposition (POD) was applied to wind-induced roof pressures to elucidate the physical significance of the dominant modes. Based on the interpretation of the first mode from the POD, the mean reattachment length of the roof separation bubbles on a low-rise building model in turbulent flow was determined. The mean reattachment length derived from the POD was then compared with the length obtained from an aerodynamic database. For the centerline of the roof, the mean reattachment length based on the POD aligned well with that from the aerodynamic database, showing a difference of less than 5%. This study highlights the efficacy of POD as a powerful tool for estimating the reattachment length of separation bubbles on bluff bodies.

In order to estimate the multi-hazards affecting the Korean peninsula, a National Risk Assessment (NRA) method is developed and applied to the regions of Incheon and Gangwon provinces using multi-hazard scenarios. National risk can be assessed on the basis of likelihood (the probability of occurrence) of a hazard and its impact (the degree of damage caused). Likelihood is assessed by statistically analyzing historical patterns of heavy rainfalls in ranges of 50-and 500-year return periods that may occur within the next five years. Impact is assessed by applying the developed fragility model based on historical damage data and expert surveys. The final national risk is assessed in the form of a 5 × 5 matrix by applying the assessment results of both likelihood and impact. The NRA method developed in this study can be utilized as a scientific basis for analyzing multi-hazards and establishing countermeasures for risk factors in the near future.

Investigations of flow separation regions on building roof surfaces in turbulent wind flows are important because of the large aerodynamic loads that the flows cause (Fig. 1). The extreme pressure occurred in separation bubbles makes roof components of buildings vulnerable (Fig. 2). Various methods have been applied to determine the mean size of roof separation bubbles by evaluating the reattachment length through wind tunnel experiments. Among them, the mean reattachment length evaluated using Particle Image Velocimetry shows high accuracy (Fang and Tachie, 2019). However, there are limits to the method of estimating the mean reattachment length only with the measured pressure data without flow measurement. Recently, a methodology for estimating mean reattachment length using a database of previously evaluated pressure coefficients and mean reattachment lengths has been proposed (Akon, 2017). However, with this method, it is difficult to evaluate the mean reattachment length for cases with different geometries of building model or flow characteristics that are not in the database. The Proper Orthogonal Decomposition (POD) can decompose physical fields according to the variables they affect. If the variables decomposed by the POD have physical meanings, separation and reattachment phenomena occurring on the roof can be identified using these variables. In this study, the eigenmode of the roof pressure measured in the wind tunnel experiment is identified using the POD, and based on this, the mean reattachment length of roof-separation bubbles is evaluated (Figs. 3 and 4). The POD results are also validated by comparing mean reattachment lengths evaluated using the POD and aerodynamic database. In the case of the roof centreline, it can be seen that the mean reattachment length based on the POD is in good agreement with that using the aerodynamic database with a difference of within 5%. It can be concluded that the application of the POD proposed in this study is useful when the mean reattachment length needs to be evaluated using pressure data.ACKNOWLEGEMENTSThis research was supported by a grant (RS-2022-00155691) of Disaster-Safety Industry Technology Commercialization R&D Program, funded by Ministry of Interior and Safety (MOIS, Korea).REFERENCES 1. Akon, F. A., 2017. Effects of turbulence on the separating-reattaching flow above surface-mounted, three-dimensional bluff bodies. Ph.D. Dissertation, Western University.2. Fang, X. and Tachie, M. F., 2019. Flows over surface-mounted bluff bodies with different spanwise widths submerged in a deep turbulent boundary layer. Journal of Fluid Mechanics 877, 717-758.3. Simiu, E., 2011. Design of Buildings for wind: a guide for ASCE 7–10 standard users and designers of special structures. Wiley.4. Stevenson, S. A., Kopp, G. A., and El Ansary, A. M., 2018. Framing failures in wood-frame hip roofs under extreme wind loads. Front. Built Environ.