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Unit loads consisting of a pallet, packages, and a product securement system are the dominant way of shipping products across the United States. The most common packaging types used in unit loads are corrugated boxes. Due to the great stresses created during unit load stacking, accurately predicting the compression strength of corrugated boxes is critical to preventing unit load failure. Although many variables affect the compression strength of corrugated boxes, recently, it was found that changing the pallet’s top deck stiffness can significantly affect compression strength. However, there is still a lack of understanding of how these different factors influence this phenomenon. This study investigated the effect of pallet’s top-deck stiffness on corrugated box compression strength as a function of initial top deck thickness, pallet wood species, box size, and board grade. The amount of increase in top deck thickness needed to lower the board grade of corrugated boxes by one level from the initial unit load scenario was determined using PDS™. The benefits of increasing top deck thickness diminish as the initial top deck thickness increases due to less severe pallet deflection from the start. The benefits were more pronounced as higher board grade boxes were initially used, and as smaller-sized boxes were used due to the heavier weights of these unit loads. Therefore, supposing that a company uses lower stiffness pallets or heavy corrugated boxes for their unit loads, this study suggests that they will find more opportunities to optimize their unit loads by increasing their pallet’s top deck thickness.

This work investigates the contact between abrasive particles and workpieces in microfinishing processes with special consideration given to the determination of unit force, unit pressure, and grain, the forces exerted by individual abrasive grains. A detailed methodology was established for measuring the contact area, penetration depth, and circumferences of grain imprints at depths corresponding to multiples of the total height of the abrasive film, represented by the parameter Sz. The following depths were analyzed: 0.05 Sz, 0.15 Sz, 0.25 Sz, and 0.35 Sz. Results show that the areas closer to the central microfinishing zone bear the highest unit pressures and forces and, thus, contribute dominantly to material removal. It was further found that near the edges of the contact zone, the pressure and force have been reduced to lower material removal efficiency. The non-uniform geometry of abrasive particles was found to significantly affect contact mechanics, more at shallow depths of penetration, whereas the shape of the apex defines the nature of the interaction. A parabolic force and pressure distribution were evident for the irregular load distribution of the microfinishing area. The result brings out the need for further refinement in the design of the abrasive film and pressure distribution in order to achieve improvement in uniformity and efficiency during microfinishing. It would bring out valuable insights on how to improve the effectiveness of an abrasive film and ways of optimizing the process conditions. The results provide a founding stone for further advancement of knowledge in the grain–workpiece interaction, enabling better surface quality and more reliable microfinishing processes.

Existing studies usually evaluate reinforced-concrete (RC) beam strengthening schemes using different specimens and structural indicators, while embodied-carbon emissions are assessed separately. Consequently, a consistent metric for quantifying the environmental cost of each unit of flexural-capacity gain, together with a reproducible procedure for scheme selection, remains lacking. This study develops a member-level framework that uses one representative deficient RC beam as a unified functional unit and integrates nonlinear finite-element analysis, process-based A1–A5 embodied-carbon accounting, and AHP–entropy multicriteria evaluation. UHPC thin-layer, externally bonded Q235 steel-plate, and externally bonded CFRP sheet strengthening were compared under identical geometry, loading, strengthening length, and accounting boundaries. The calculated peak-load increases were 64.4%, 75.1%, and 54.7%, respectively, and the peak-load secant-stiffness increases were 82.6%, 52.4%, and 29.6%. Total A1–A5 emissions were 21.97, 18.83, and 7.59 kg CO2e, while carbon intensities per unit load-capacity increment were 0.89, 0.66, and 0.36 kg CO2e/kN. CFRP also achieved the best normalized unit-cost and construction-duration scores (0.920 and 0.950) and the highest conditional overall score (0.890). A bond-efficiency check increased its carbon-efficiency index to 0.48 kg CO2e/kN without reversing the ranking. The framework provides a transparent screening tool; however, project-specific bond, anchorage, fire, durability, and code-based verification remain mandatory.

This paper presents stochastic models for multi-tier warehouse systems that handle unit load transactions using autonomous vehicle-based technology. In this system, self-powered autonomous vehicles carry out unit-load transactions by moving along rails within a tier and using lifts or conveyors for vertical movement between tiers. We develop semi-open queuing network models to evaluate congestion effects in processing storage and retrieval transactions in this system. The queuing network is evaluated using a decomposition-based approach. The queuing model provides design insights on the effect of vehicle interference and vertical transfer mechanism on various system performance measures of interest. Insights from such studies can be especially useful during the conceptualization stage of warehouses that use autonomous vehicle technology.

Packaging could and should be considered one of the key elements that promote supply chain performance in terms of efficiency and sustainability. Although, packaging should be considered as a system comprising three different levels (primary, secondary and tertiary), in the industrial sphere design problems are usually centered exclusively on two levels: the primary packaging (the “box”) and the tertiary packaging (the “unit load”). Thus, the main object of this paper is to propose a methodology that facilitates, in a comprehensive way, decision making in packaging system design in order to reduce total costs. To do so, the methodology makes a qualitative and quantitative exploration (including a proposal of a heuristic method) to establish strategies that enable the definition, comparison and selection of an efficient range of package designs (with their associated dimensions) that is efficient and sustainable in an overall way in terms of purchasing costs, logistics costs and environmental costs. Likewise, the authors develop the successful case of a Spanish company implementing successfully the proposed methodology. To develop this case, the authors have adopted an “Action Research” approach. The empirical validation process was developed over almost 10 years.

Loading operation efficiency at airports plays an indispensable role in international air express service performance. The authors comprehensively examined the priorities of factors that affect loading operation efficiency for air express services at Taoyuan International Airport in Taiwan. The reviewed results from surveying practical experts using a rank pair-wise comparison (RPC) revealed that load factor and load planning consistently ranked higher and more crucial among 15 elements regardless of flight properties. Long-haul services to the North American hub were most concerned with inventory control of unit load devices (ULDs). Regional feeder services attached importance to the ground operations workforce as well. Feeder services for cross-continental deliveries additionally focused on the arrangement of apron bays. The authors used the TOPSIS, i.e., technique for order preference by similarity to ideal solutions, to evaluate flights by three freighter types. Considering that the studied company performed more consistently on the top crucial factors, the sub-criteria that belong to the negative subset and are affected by the external units played a dominant role in these evaluated flights.

The precise calculation and effective control of the horizontal displacement of deep foundation pit retaining structures are critical for foundation pit support design and construction. Based on stress–strain linear elastomer theory and considering the deformation coordination between an enclosure wall and its internal support member, a formula for the redundant restraint force acting on the retaining wall was derived through the unit load method and the principle of elastic superposition. Moreover, a method for calculating the horizontal displacement of the retaining structure of a deep foundation pit was formulated, which is convenient for engineering applications. The method can also be used to calculate the horizontal displacement of cantilevered and anchored retaining structures when the loading conditions of the deep foundation pit and the relevant parameters of the enclosure structure are known. A case study was conducted on a standard section with an excavation width H of 19.3 m and an excavation depth h of 17.8 m. The structural parameters of the enclosure wall, along with the elastic support stiffness coefficient and soil layer parameters of the pit, were inputted into a MATLAB calculation code. Then, four internal support constraint forces Fi and the calculated values for the horizontal displacement of the enclosure wall were obtained after running the code. The calculated curve closely matched the curve of values measured in the field. The horizontal displacements of the top of the wall of several cement–soil gravity enclosure structures mentioned in the literature were also calculated. The results of these calculations were then compared with the measured data and corresponding data from the literature. The examples provided clear evidence demonstrating that the proposed method is highly reliable for calculating the horizontal displacement of deep foundation pit enclosure structures.

Due to the complexity of the landing gear’s (LG) structural integrity and its loads under various static or dynamic working conditions, the fatigue life assessment for LG is a highly challenging task. On the basis of the whole geometric model of a large passenger aircraft’s main landing gear (MLG), the quasi-static finite element model (FEM) of the whole MLG is established, and the high-cycle fatigue issue of the Main Fitting (MF) is studied by considering the variation in shock absorber travel (SAT). Firstly, the ground loads under actual fatigue conditions are equivalently converted into the forces acting on the center of the left and right axles of the MLG, and based on these spatial force decompositions, the magnitude and direction of the load for 12 different basic unit load cases (ULC) are obtained. That is, the stress of the MLG under actual fatigue conditions can be obtained by superimposing these ULCs. Then, considering that the SAT of the MLG varies under different fatigue conditions, and to reduce the number of finite element (FE) simulations, this article simplifies all the SAT experienced by the MLG into seven specific values, so as to establish seven quasi-static FEMs of the MLG with the specified stroke of the shock absorber. In this way, the fatigue stress of the MLG with any actual SAT can be obtained by interpolating the stress components of the seven FEMs. Only 84 FE simulations are needed to efficiently obtain the fatigue stress spectra from the ground load spectra. Finally, according to the material S-N curve and Miner’s damage accumulation criterion, evaluate the fatigue life of the Main Fitting. The results of the stress component interpolation and superposition method show that at least five different SATs of the whole MLG’s FEM are needed to effectively convert the fatigue loads into a stress spectrum. The fatigue life prediction results indicate that the minimum lifespan of the MF is 53164 landings, which means that the fatigue life meets the requirement design.

Short-term hydro-unit load dispatching (SHULD) refers to the determination of the power output of each unit within a hydropower station over a planning horizon to minimize the operational cost or maximize the power-generation profit while satisfying hydraulic and electrical constraints. In China, huge hydropower stations, such as the Three Gorges (TG) and Xiluodu (XLD) stations, are composed of a large number of hydro units, which feature a high installed capacity and a high water head. SHULD models of these stations are more complex and difficult to solve compared with those of traditional stations, especially when the stations serve multiple power grids. This study develops a practical method for optimizing SHULD models by considering the XLD hydropower station as a case study. First, a SHULD model for huge hydropower stations with multiple vibration zones and multiple receiving power grids is presented. Second, classical and sophisticated dynamic programming (DP) is applied to the SHULD model, and a practical strategy is proposed to balance the available water in a reservoir’s left and right banks to satisfy their load demands. Finally, the Fork/Join framework is used to parallelize DP to reduce the computation time and fully utilize the computer resources. The wet and dry season results demonstrate that the approach is efficient and suitable for huge hydropower stations with a high water head and multiple receiving power grids, thereby demonstrating its potential practicability and validity for solving the SHULD problem.

This study presents an extended unit load method in which the displacement of a chosen degree of freedom (DOF) in a nonlinear structure under arbitrary dynamic loading is expressed as an integration of mutual strain energy density over a continuum domain. This new integral formulation for the displacement of a chosen DOF is developed by using the virtual work principle and can be used for linear or nonlinear structural behaviours. The integral form of the displacement is then used to develop new formulations for structural topology optimization involving arbitrary dynamic loading using the moving iso-surface threshold (MIST) method. Presented are two specific topology optimization problems with two objective functions: (a) to minimize the peak of a chosen displacement; or (b) to minimize the average power spectral density (PSD) of the chosen displacement over a finite time interval. New MIST formulations and algorithms are developed for solving two damping topology optimization problems of a structure under arbitrary dynamic loading, with or without large displacements, and having cellular damping materials with multi-volume fractions. Several numerical examples are presented to demonstrate the validity and efficiency of the presented unit load method and the MIST formulations and algorithms.