• Steel and Composite Structures
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• 제32권1호
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• pp.1-19
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• 2019

The aim of the paper is the prediction of the seismic collapse mode of steel storage pallet racks under seismic loads. The attention paid by the researchers on the behaviour of the industrial steel storage pallets racks is increased over the years thanks to their high dead-to-live load ratio. In fact, these structures, generally made by cold-formed thin-walled profiles, present very low structural costs but can support large and expensive loads. The paper presents a prediction of the seismic collapse modes of multi-storey racks. The analysis of the possible collapse modes has been made by an approach based on the kinematic theorem of plastic collapse extended to the second order effects by means of the concept of collapse mechanism equilibrium curve. In this way, the dissipative behaviour of racks is determined with a simpler method than the pushover analysis. Parametric analyses have been performed on 24 racks, differing for the geometric layout and cross-section of the components, designed in according to the EN16618 and EN15512 requirements. The obtained results have highlighted that, in all the considered cases, the global collapse mechanism, that is the safest one, never develops, leading to a dangerous situation that must be avoided to preserve the structure during a seismic event. Although the studied racks follow all the codes prescriptions, the development of a dissipative collapse mechanism is not achieved. In addition, also the variability of load distribution has been considered, reflecting the different pallet positions assumed during the in-service life of the racks, to point out its influence on the collapse mechanism. The information carried out from the paper can be very useful for designers and manufacturers because it allows to better understand the racks behaviour in seismic load condition.

• Earthquakes and Structures
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• 제7권6호
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• pp.955-967
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• 2014

Storage racks are used worldwide in industries and commercial outlets due to the advantage of lighter, faster erection and easy alteration of pallet level as required. The studies to understand the behaviour of cold formed steel pallet racks, under seismic action is one of the emerging area of research. The rack consists of perforated uprights and beams with hook-in end connector, which enables the floor height adjustments. The dynamic characteristics of these racks are not well established. This paper presents the dynamic characteristics of 3-D single bay two storey pallet rack system with hook-in end connectors, which is tested on shake table. The sweep sine test and El Centro earthquake acceleration is used to evaluate the seismic performance of the cold formed steel pallet racks. Also an attempt is made to evaluate the realistic dynamic characteristics by using STAAD Pro software. Modal analysis is performed by incorporating the effective moment of inertia of the upright, which considers the effect of presence of perforations and rotational stiffness of the beam-to-upright connection to determine the realistic fundamental frequency of pallet racks, which is required for carrying out the seismic design. Finite element model of the perforated upright section has been developed as a cantilever beam through which effective moment of inertia is evaluated. The stiffness of the hook-in connector is taken from the previous study by Prabha et al. (2010). The results from modal analysis are in good agreement with the respective experimental results.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2023년도 춘계학술대회
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• pp.250-251
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• 2023

팔레트는 낱개의 여러 화물을 동시에 묶어 운송할 수 있게 하는 하역 장비로써 원자재 조달에서부터 소비자에게 전달되기까지의 흐름을 통합적으로 연결하는 중요한 요소이다. 더불어 일관수송을 통한 비용 절감, 거래단위의 표준화, 운송수단의 효율적인 운영, 하역작업 개선을 목적으로 팔레트 표준화가 활발히 진행됨에 따라 T-11형, T-12형 등의 표준 팔레트가 우리나라 물류 산업 전반에 걸쳐 사용되고 있다. 그러나 대형·중량화물을 비롯한 특수화물의 경우, 크기 및 중량 등의 이유로 표준 팔레트에 적재하는 것이 불가능하기에 대부분 자체 팔레트를 개발하여 사용하고 있다. 본 연구는 다양한 특수화물을 취급하는 팔레트의 크기를 결정하는 문제로써, 특수화물의 종류, 크기 및 중량, 보관 수량 등을 고려하여 최적 팔레트 크기를 산출하고자 한다. 이를 위해, 이웃해 탐색 알고리즘을 변형하여 전역 최적해를 찾을 수 있는 최적화 기법을 제안하였으며, 입력 데이터로서는 특수화물의 종류별 제원 및 보관 수량 정보, 제약조건 관련 정보가 사용되었다. 또한, 특정한 특수화물을 대상으로 최적화 시뮬레이션을 수행하여 최적해 도출 여부를 확인함으로써 본 최적화 기법의 최적성을 검증하였다.

• 산업경영시스템학회지
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• 제41권4호
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• pp.59-69
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• 2018

This study deals with the case study on the pallet quantity determination problem for the flexible manufacturing system producing 32 different types of aircraft wing ribs which are major structures of an aircraft wings. A Korean company has constructed the WFMS (wing rib flexible manufacturing system) that is composed of several automated equipments such as the 5-axis machining centers, the RGV (rail guided vehicles)s, the AS/RS (automated storage and retrieval system), the loading/unloading stations, and so on. Pallets play a critical role in the WFMS to maintain high system utilization and continuous work flow between 5-axis machining machines and automated material handling devices. The discrete event simulation method is used to evaluate the performance of the WFMS under various pallet mix alternatives for wing rib manufacturing processes. Four performance measures including system utilization, throughput, lead-time and work in process inventory level are investigated to determine the best pallet mix alternative. The best pallet mix identified by the simulation study is adopted in setting up and operating a real Korean aircraft parts manufacturing shop. By comparing the real WFMS's performances with those of the simulation study, we discussed the cause of performance difference observed and the necessity of developing the CPS (cyber physical system).

• 산업식품공학
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• 제23권1호
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• pp.55-61
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• 2019

딸기에 대해 pallet 상부와 하부는 PA 필름으로, 측면은 LLDPE 필름으로 MAP 처리를 할 경우 포장 내부의 온습도 편차를 줄이며, 산소 농도 3-6%, 이산화탄소 농도 15-25%로 안정화하여 감모율이 향상되고, 곰팡이 발생률이 억제되는 것을 확인하였다. 경도향상과 이취를 고려하였을 때 적정 이산화탄소 농도는 15-20%이며, 이러한 높은 이산화탄소 농도는 경도를 21-40% 수준으로 높이는데 영향을 준것으로 판단된다. 대조구의 경우 60% 숙도 딸기의 경도가 80% 숙도에 비해 높았으나, MAP 처리구의 경우 12일차를 제외하고 60%와 80% 숙도의 경도는 통계적인 차이 없이 높은 수준으로 유지되었다. MAP 처리 시 80% 숙도는 60% 숙도에 비해 감모율, 곰팡이 및 경도 차이 없이 0.7-2.4 °Brix 높은 당도가 유지되었다. 따라서, pallet MAP를 사용할 경우 동남아시아 국가로 선박 수출하기 위한 14일 동안의 선도유지가 가능하고, 80% 이상의 높은 숙도로 딸기를 수출하여 품질 경쟁력도 향상시킬 수 있을 것으로 판단된다.

• 대한산업공학회지
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• 제21권2호
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• pp.239-254
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• 1995

Automated Storage/Retrieval (AS/R) systems have been used mostly in manufacturing or distribution industry in order to store or retrieve palletized items automatically. Since the items ore heavy or bulky, only one pallet at a time is moved by the stacker crane In this study, however, we introduce the "multi -load" AS/R system in which the items to be stored are data storage devices of equal size such as video tape or compact disc. Since the items are small and light multiple items can be stored and retrieved in each trip by using a magazine and a robot arm mounted on the crane Given the magazine capacity, and the locations of retrieval items and empty cells in the rack, the throughput of the multi-load AS/R system will depend on the selection of storage locations and the sequence of visits. We propose four heuristic algorithms for the multi-command. Computer simulation is used to evaluate the four algorithms in terms of throughput and number of back tracking of the crane.

• 산업공학
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• 제9권2호
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• pp.203-218
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• 1996

This paper deals with a Direct-Input-Output Manufacturing System (DIOMS) which has a number of machine centers placed along a built-in automated storage/retrieval system (AS/RS). During its operations, the storage/retrieval(S/R) machine picks up a pallet from the pickup/deposit port of a machine center and then moves it either to an empty rack opening of the AS/RS for temporary storage or to place it on the port of another machine center for subsequent operation. The machine layout problem in DIOMS is formulated as an integer mathematical programming whose objective is to minimize the total expected distance of the loaded S/R machine during a production period. Recognizing the limit of the exact solution procedure(the Branch and Bound method), two improvement-type heuristics are proposed. One is based on the simulated annealing method and the other the pairwise interchange method. The validity of the heuristics is examined with example problems.

• 한국경영과학회지
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• 제14권1호
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• pp.119-130
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• 1989

This paper presents average travel time models automated warehousing system where the stacker crane transports only one pallet at a time with the tchebychev travel, I/O point is located at the cornor of the rack, and items are stored by the class-based storage assignment rule. In this study, the racks are treated as the continuous rectangle in time and a statistical approach was used to develop the models. In order to test the proposed models, average travel times determined by the models are compared with the true values for various rack shapes.

• 한국포장학회지
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• 제26권2호
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• pp.61-69
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• 2020

As post-harvest processes of onions are carried by a 20 kg-net package which results in high-cost and low-efficiency, especially, the insufficient drying and physical damage of onions after harvesting leads to a huge second loss in storage, we had developed a low-cost, high-efficiency post-harvest bulk handling machinery system by collecting onions on a farm using ton-bags, drying with forced air circulation, and sorting/packaging. The post-harvest bulk handling machinery system consisted of 6 devices, and this study designed an automatic feed hopper with a feeding rate control device, an inclined belt conveyor with a two-step chute, and an automatic pallet unloading device for feeding onions into the sorting/packing line. This study also analyzed the performance and control of the total system. The device had 1-ton handling capacity, but the operational condition was set to increase the capacity. The three-step filling method of pallet by the velocity control of the inclined belt conveyor was applied in the post-harvest bulk handling machinery system for the prevention of physical damage. If one worker was set to operate the total system, the time required to complete one palletized load was approximately 5 minutes and 5 seconds. The calculated daily handling capacity was approximately 94 tons, when the daily actual working time was 8 hours. When the developed system was applied to the managerial size of 2,000 ton, the processing cost per ton of the system was decreased by 19.5%, compared with the existing 20 kg-net package-based handling. The developed post-harvest bulk handling machinery system would be a good substitute for the rapid decline and aging of rural labor.

• Steel and Composite Structures
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• 제23권2호
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• pp.143-152
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• 2017

This paper focuses on the seismic performance of pallet-type steel storage rack structures in their down aisle direction. As evidenced by experimental research, the seismic response of storage racks in the down-aisle direction is strongly affected by the nonlinear moment-rotation response of the beam-to-column connections. In their down-aisle direction, rack structures are designed to resist lateral seismic loads with typical moment frames utilizing proprietary beam-to-column moment-resisting connections. These connections are mostly boltless hooked type connections and they exhibit significantly large rotations resulting in large lateral frame displacements when subjected to strong ground motions. In this paper, typical hooked boltless beam-to-column connections are studied experimentally to obtain their non-linear reversed cyclic moment-rotation response. Additionally, a compound type connection involving the standard hooks and additional bolts were also tested under similar conditions. The simple introduction of the additional bolts within the hooked connection is considered to be a practical way of structural upgrade in the connection. The experimentally evaluated characteristics of the connections are compared in terms of some important performance indicators such as maximum moment and rotation capacity, change in stiffness and accumulated energy levels within the cyclic loading protocol. Finally, the obtained characteristics were used to carry out seismic performance assessment of rack frames incorporating the tested beam-to-column connections. The assessment involves a displacement based approach that utilizes a simple analytical model that captures the seismic behavior of racks in their down-aisle direction. The results of the study indicate that the proposed method of upgrading appears to be a very practical and effective way of increasing the seismic performance of hooked connections and hence the rack frames in their down-aisle direction.