Currently, the density of high-rise buildings in Korea ranks 11th in the world based on buildings that, amount to 400 in total and are more than 150m in height (under construction or completed based on (The Council on Tall Buildings and Urban Habitat (CTBUH, XXXX) statistics in 2018). In Seoul, it is expected that high-rise buildings will be continuously constructed due to the high-density and strengthening of the urban redevelopment plan in old districts. During disasters, the risk of property damage is amplified due to this increase in density in a larger scale and complexity, especially in concentrated urban areas. However, the concern of spreading the damage to the surrounding environment remains. For instance, and in the case of the 9/11 terrorist attacks in New York City, the collapse of the world trade center, surrounding buildings and explosion itself have caused damages to the surrounding environment. Loss, destruction by fire and damage of the facade and structure were caused by the collapse. In order to reduce risk and damage to high-rise buildings in urban areas, domestic studies are underway to improve the building performance against individual disasters by strengthening standards of materials and structure, equipment and evacuation procedures against fire due to recent earthquakes. However, most of these studies have focused on research and suggestions of partial improvement of evacuation-oriented buildings for individual disaster scenarios. Therefore, studies on evaluation criteria, evaluation methods, and design guidelines to reinforce buildings against various catastrophic disaster risks are insufficient. The purpose of this study is to construct a disaster risk assessment model (tentative K-IDES) for Korean high-rise buildings to reflect the domestic reality and analysis studies of the advanced cases that were conducted on Federal Emergency Management Agency (FEMA) risk assessment series in the US to manage risks and analyse it quantitatively by developing a risk assessment system against various disasters. This study aims to establish basic instructions related to risk evaluation criteria and risk assessment methods related to disasters based on comparative analysis of the domestic applicable parts of the FEMA Integrated Rapid Visual Screening (F.E.M.A., 2011). This analysis is derived from evaluation methods from case studies of the USA FEMA risk assessment series and domestic building guidelines and codes. Among various disasters, terrorism, fire, and wind, which are likely to occur in Korea, several study scenarios were selected. This study proposes a weight setting method and an integrated risk assessment method to improve the accuracy of the risk evaluation model and analyze the results through simulations of urban high-rise buildings by applying this risk evaluation method in the next step.

FEMA has published multidisciplinary guidelines related to risk management to ensure safety in the event of a disaster so that it can be applied to building design and operation by disasters. In addition, special purpose buildings such as schools, hospitals, and important facilities are subdivided according to user importance. However, this study is restricted to FEMA guides related to general commercial high-rise buildings. These are divided into risk assessment, building design guides and rehabilitation of community for the purpose of the use.

In the case of fire, FEMA classifies fire into natural disasters and social disasters. However, a fire in the building categorizes a scenario of fire due to explosive terror and arson and presents design guides and risk assessment methods that use NFPA fire standards. In case of natural disasters, FEMA subdivides risk management guidelines for earthquakes that are likely to occur by phase. In particular, it provides step by step instructions to restore crucial facilities that affect the community after the occurrence of earthquakes.

The IRVS risk assessment is calculated based on an analysis of three factors: Consequence (C), Threat (T) and Vulnerability (V). The first Consequence assesses the degree of damage to a building (property) and the loss of the building’s operating system due to the disaster. Second is Threat (T), which is the assessment of the degree of hazards to natural disaster, social disaster, potential events, signs, and behavioral threat factors that lead to the injury of an asset, individual or organizations. Finally, the Vulnerability (V) factor consists of assessments of the vulnerable elements of the building that can increase damage to the asset in the event of a disaster. FEMA IRVS caculates the risk level by multiplying the evaluated C, T, and V values and provides a sum. Weighting items are specified, but distinct values for the weight are not indicated in contrast to FEMA ‘Rapid Visual Screening’ (F.E.M.A., 2009). From a risk evaluation aspect, except for core infrastructure such as hospitals, schools, and critical facilities, it is difficult to derive differentiated results when buildings with similar uses are evaluated. Since in the case of Vulnerability, Fire, Security, and Cyber Security, evaluation items consist of qualitative analysis contents of buildings with a high error rate depending on the evaluator’s subjective choices. Most evaluation items are limited to two, unlike others that must have all five or more as these evaluations reduce the sensitivity and accuracy of the risk assessment. In addition, the evaluation items with high weights of regional characteristics and environmental indicators of C and T are different from domestic high-density characteristics in urban areas, frequency and intensity of earthquakes and typhoon in Korea, and direct application of FEMA IRVS evaluation items to domestic cases’ analysis are limited. Based on this research, the domestic risk assessment model is formulated for the differential comparison by deciding the criteria for evaluation target, deleting the items that are difficult to apply in IRVS and analyzing the domestic standards related to the evaluation target.

In order to establish standards, codes and design guidelines related to risk assessment for high-rise buildings against various disasters in Korea, nationals have not coordinated with private experts under the leadership of the government, yet design guidelines to ensure safety against disasters are continuously promoted through studies in diverse fields. The results of research is reflected in the improvement of building performance. The criteria is analyzed to construct items of the risk assessment of this study through the content analysis of (Public Safety & Security, 2014), (Government, 2009), (Land, 2010), & (Land, 2017). The grouping of similar items for the first classification was made by referring to items related to the architectural planning elements of buildings and the articles of IRVS. The Anti-Terrorism Building Design Guidelines in Multi-purpose facilities contains articles similar to those of FEMA RVS standards and detailed design guide contents that are not mentioned in the table below. Since the mandatory installation of the evacuation safe zone in domestic standards differs from the evacuation space design standard of the high - rise buildings in the United States according to analysed results, the developed concepts for the check list contains the criteria for the evacuation safe zone and design plan for effective evaluation but differs from the IRVS. The assessment items derived from reviewing articles are applied to the 1st sub-category and reflected on the subdivision and standardization of the assessment items for developing the K-IDES

The risk assessment method of IDES is calculated by using the concept of FEMA IRVS. In addition to it, FEMA’s risk assessment method is used for other disasters based on the same formulas and concepts. In this study, the formula of FEMA risk assessment calculation, and the conceptual definition of consequences, threats, and vulnerability necessary for the quantitative evaluation of risk are applied. The evaluation criteria, evaluation items and evaluation contents are limited to the types of buildings in the high-rise buildings of more than 150m for nonresidential buildings in the center of Seoul or Busan in Korea. Among the evaluation items of FEMA IRVS, the reviewing items that do not meet domestic standards, or have no relation to building characteristics, are deleted. Additionally, the evaluation items reflecting domestic standards and design guidelines such as the preliminary disaster impact assessment, the anti-terrorism design guidelines, domestic firefighting standards, and the Korea Building Code are revised or newly proposed to establish evaluation methods for the development of the Korean disaster evaluation model

Since K-IDES and FEMA IRVS are different from evaluation target types, this research attempts to limit the usable range of the evaluation method through comparing the FEMA with the IRVS. Among the evaluation areas of K- IDES, the vertical evacuation function is important for fire and evacuation, but IRVS cannot be applied to the evacuation analysis method of domestic high-rise buildings because it grasps the application of fire standards of NFPA CODE for general buildings. Thus, the contents of the evacuation section are divided into separate fields. In terms of recovery, it is difficult to specify the recovery concept and the quantitative evaluation system of the building after the disaster in Korea. Since the evaluation system of FEMA and IRVS is a qualitative assessment of a general building target, it is expected that there will be no distinguishable in its application to high-rise buildings. In this study, the evaluation items for recovery were excluded

The K-IDES disaster risk assessment is based on IRVS’s individual risk assessment and integrated risk assessment formula. K-IDES calculates the values of Consequence, Threats, and Vulnerability to sum up each item by disaster scenario, and the individual risk is calculated by using the following formula. The risk values of individual disasters exclude the interrelationships between disasters. It sums the integrated risks with the disaster risk by scenario. The risk value calculation formula derives the average risk value based on the concept of P-Norm in linear algebra.

The evaluation items of K-IDES comply with the evaluation classification system of FEMA IRVS, but the evaluation items are newly established in consideration of the importance of the evacuation safety zone plan derived from the high-rise building design and evaluation standards related to disasters in Korea. The purpose of evaluation between sub - items was grouped considering the correlation of similar items. K-IDES extracts the second detailed subdivision items from IRVS and the proposed items through domestic structural standards, domestic disaster related evaluation standards and guides. And then by expert’s consultation on the related fields such as structure, fire, and architectural design, it specifies the detailed selection criteria of the items and contents. It carries out the evaluation process by pre-evaluation and on-site evaluation. Pre-evaluation is the process of basic information collection on the building and surrounding environment. The field evaluation consists of 113 items grouped into 9 categories in an order of Consequences, Threat and Vulnerability and 29 weighted items that are selected through IRVS and expert’s consultation based on empirical knowledge. The evaluation items for the evacuation area are classified as the abatement items as they are important for securing the safety of high rise buildings. Since evaluation items are constructed while considering the impact on the buildings according to the disaster characteristics, the distribution and the number of items is different according to the disaster. In the case of a typhoon disaster, except for site, building, elevation, and evacuation plan, the correlation between it and other evaluation fields in the high-rise buildings is weak, and so it is expected to have little influence on the disaster evaluation and the final integrated disaster risk assessment.

Since the scoring for the quantification section of the risk assessment model developed in this study differs in the number of items among C, T, and V, the maximum value of the detail item is specified according to the ratio adjustment. The ratio is determined through the simulation together with the weighted item. K-IDES sets The minimum value at 0.1 level of the maximum value and the selection value of the detail item is determined by the isometric ratio between the intervals. According to the architectural elements affected by the disaster’s specific characteristics, item distribution is interlinked and the number of questions is 2.5 times the maximum for each disaster. It is necessary to review the distribution ratio when calculating the final risk. In this study, the risk assessment by items is a process of selecting the baseline value for the final integrated risk assessment and will be used as a criterion to refine the evaluation model by analyzing the effects of individual disasters and C, T, V items through a simulation of high-rise buildings and application of the K-IDES risk assessment.

K-IDES’ maximum and minimum values are used to proportionally divide intervals to rate the risk as a percentage (%) which are then divided into four stages of IRVS to classify the risks. IRVS graded risk intervals are at equal intervals while the K-IDES is classified as safe for values less than 40% for risk and divided the risk into 3 intervals for values greater than 40%. Calculated scores are divided into 25%, 20% and 15% according to the risk level. This study establishes a criteria for grading based on the quantitative analysis of the degree of damage to an environmental threat and disasters level and vulnerability to the physical protection function of buildings. In the next study, the risk values derived from building simulations using K-IDES will be analyzed to verify the accuracy of the model and to examine the applicability of the settled criteria.

It is necessary to apply the risk evaluation model to high-rise buildings to examine the weighted items and the weight distribution of it. K-IDES sets the selection criterion for the simulation based on the items that can analyze the influence by items in the vulnerability part of the building with minimizing the group deviation on the environmental factors. In order to verify the distribution of building vulnerability with similar conditions as the regional characteristic related indicators of the risk assessment model, the selection of a domestic high-rise building is selected a non-residential high-rise building with a heighted of 150m or more in a commercial district with a floor area of 500% or more in Seoul and Busan as a standard. K-IDES classifies the selected targets so that they could be used as a control group by an evaluation factor for the comparison to identify moving plan of vehicles and pedestrians, applicable buildings and non-applicable buildings subject to evacuation safe zone regulations and facade composition and materials to endure the external attack. It is possible to analyze the precision of the checklist by first evaluating the characteristics of items related to the architectural planning elements such as site plan, space plan, elevation plan, and structural plan and applying them to the weight and evaluation values. For other evaluation items, due to the similarity of use of non-resident high-rise buildings, the results of the review of security plans, facilities, fire prevention plans and security plan are expected to be similar.

The following table describes the characteristics of the main items selected for the simulation.