• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.116-122
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• 2014

This study proposes a system reliability analysis of rack storage facilities subjected to forklift colliding events. The proposed system reliability analysis consists of two steps: the first step is to identify dominant failure modes that most contribute to the failure of the whole rack facilities, and the second step is to evaluate the system failure probability. In the first step, dominant failure modes are identified by using a simulation-based selective searching technique where the contribution of a failure mode to the system failure is roughly estimated based on the distance from the origin in the space of the random variables. In the second step, the multi-scale system reliability method is used to compute the system reliability where the first-order reliability method (FORM) is initially used to evaluate the component failure probability (failure probability of one member), and then the probabilities of the identified failure modes and their statistical dependence are evaluated, which is called as the lower-scale reliability analysis. Since the system failure probability is comprised of the probabilities of the failure modes, a higher-scale reliability analysis is performed again based on the results of the lower-scale analyses, and the system failure probability is finally evaluated. The illustrative example demonstrates the results of the system reliability analysis of the rack storage facilities subjected to forklift impact loadings. The numerical efficiency and accuracy of the approach are compared with the Monte Carlo simulations. The results show that the proposed two-step approach is able to provide accurate reliability assessment as well as significant saving of computational time. The results of the identified failure modes additionally let us know the most-critical members and their failure sequence under the complicated configuration of the member connections.

• Journal of the Korean Society of Safety
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• v.28 no.6
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• pp.49-56
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• 2013

The statistics of recent accidents in warehouses show that a heavy toll of lives were produced by various accidents, e.g. collision, overturn, fall, slip, exposure to harmful substances or environments, etc. Of significant concern amongst them is the collision, especially the collision between forklift and storage rack structure. Accordingly, this study focuses on behavioral characteristics of rack structure subjected to dynamic impact loading of a forklift. For this purpose, time-domain response analysis has been performed on a standard 2-bay six-story rack structure consisting of columns, beams and bracing members with perforated open section. In order to investigate the most critical scenario, the impact loads are applied in both down-aisle and cross-aisle directions, and the impact locations are also varied along the shelves of the palettes. In order to deal with storage distributions, three types of rack structures are further taken into account: original empty rack structure with no storage, half-loaded rack structure and fully-loaded rack structure. The numerical simulation results demonstrate that the dynamic characteristics of the rack structure are significantly dependent on the distribution of the storage goods and its natural period varies from 0.24sec to 1.06sec, approximately 4.4 times. Further, the parametric studies show that the forklift impact is most critical to the safety of the rack structure when it collides either at the base or at the top of the rack structure.

• Journal of the Korean Operations Research and Management Science Society
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• v.23 no.3
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• pp.91-108
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• 1998

Automated Storage and Retrieval Systems (AS/RSs) are an important facility for modern material management. The expected benefits of these capital-intensive facilities are gained when their control policies and their physical design parameters are determined simultaneously. In this paper we present several analytical models that capture the impact of the storage assignment policy and of the rack design on the expected storage and retrieval times. Sequential and interleaved service modes are considered for sequencing the storage and retrieval requests. We further investigate the impact of the rack structure on the relative performance of the following storage assignment policies : closest open location (random), full turnover-based policy, and class-based. Our analysis clearly indicates that significant savings in crane travel time are realized when implementing full turnover-based policy, rather than random. These savings become more and more pronounced as the profile of the storage racks approaches the square-in-time shape. Furthermore, it is shown that a class-based policy, with a small number of storage classes, will capture most of these savings and be easier to manage in practice.

• Journal of the Korea Safety Management & Science
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• v.21 no.4
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• pp.75-80
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• 2019

Sales of the Korean clothing industry grew to 16.9 percent on-year in 2010, but the growth rate dropped to 3 percent from 2011 to 2016 and the overall market began to slump to 1.1.6 percent in 2017. The competitiveness of clothing companies is also a major sector in logistics capability, and the average logistics cost of domestic clothing companies is 8.3 percent of sales in 2011, higher than the average 8 percent of domestic industries, and 36.4 percent of the total storage cost in 2011, higher than the 28.8 percent share of the total storage cost of domestic companies. As domestic production conditions such as wage hikes and labor disputes worsened in the 1990s, production facilities were rapidly moved overseas, which led many clothing companies to have no production facilities or a minimal production base in Korea and focus on marketing and design capabilities. The total storage capacity and storage efficiency of the logistics center became very important as the products were changed to the form of mass warehousing and small-volume forwarding. Research shows that building column spacing, a model of this research, can affect the amount of hanger rack storage empirically, so for sustainable growth of clothing companies, it is necessary to improve competitiveness in the logistics market by reducing costs and improving efficiency to overcome difficulties in corporate management. Because logistics costs are 8.3 percent and operating profit to sales ratio is 2 percent, it is expected that operating profit will increase by 41.5 percent if logistics costs are reduced by 10 percent. If 10% of storage cost is saved based on storage cost, operating profit is expected to increase by 15% To strengthen the competitiveness of the clothing industry, a reduction in logistics costs is essential. Therefore, the purpose of this study is to provide hints that logistics experts can have empirically small amounts in reducing storage costs through column spacing adjustment of logistics centers that have not been dealt with statistically until now, and to contribute to the continued growth of clothing companies and the development of the domestic logistics industry.

• Journal of Distribution Science
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• v.6 no.2
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• pp.5-19
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• 2008

This study aims to provide the present general state of basic data about refrigeration and freezing warehouses scold storages because basic data about refrigeration and freezing warehouses are insufficient and imperfect at the moment. Research contents include the present general state of cold storages such as sales amount, capital(money invested), storage possession state by type, keeping area, cold storage facility capacity, and facility state such as existence of rack, building structure and floor height, and possessed facility state. According to research results, it was found that 86.7% of refrigeration and freezing warehouses are located in the capital region and Busan region in terms of regional distribution, and the average keeping area was found to be bigger in these two regions than that of other regions. In addition, the research shows that more than 80% of companies possess bonded warehouses and there was no big difference in the size and capacity of refrigeration and freezing warehouses. Regarding building structure, most of them were found to be reinforced concrete. However, only 25% of companies installed racks, but there was no statistical significance between existence of rack and the amount of capital and sales. Possessed facilities were found in the order of freight elevator, information system and dock. When it comes to cargo gear, companies were found to possess 9.1 units of forklift and 2.2 units of reach stacker in average. This research is expected to lay a basis for investigating, predicting and developing the local cold storage industry, and more detailed studies will be needed in the future.