Pallet Racks Research Articles

Progressive collapse of beam-to-upright subassemblies of steel storage racks under a column removal scenario

This paper presents an experimental investigation into progressive collapse behaviour of steel storage pallet racks under a column removal scenario. The double-half-span substructure is applied in experimental tests. A total of eight substructures are tested, considering two types of beam-to-upright connections, i.e., boltless and bolted connections, commonly used in pallet racks. Different upright profiles and thicknesses, varied beam heights, and the number of tabs are carefully considered in the tests, and their effects on progressive collapse behaviour of pallet racks are thus evaluated. In particular, the influence of pallet loads is carefully evaluated in this paper. Detailed experimental results of all specimens are provided, including the full-range force-displacement curves and the failure modes. The dominated failure modes observed in the tests are the combination of tab crack and bolt bearing failure leading to tearing of beam-end-connector (T+B), the combination of tab crack and bolt bearing failure leading to tearing of upright wall (T+C), and tab crack (T). The test results revealed that the presence of pallet loads greatly influences structural progressive collapse behaviour and thus should be considered in further studies. Moreover, in bolted connections, smaller beam heights and thinner column thicknesses exhibit better resistance against progressive collapse. Whereas in boltless connections, increasing the number of tabs enhances the resistance against progressive collapse. Generally, the bolted connections are proven to have better resistance against progressive collapse than boltless connections and can be used in storage racks to improve structural robustness.

Predicting the thermal structural behaviour of steel pallet rack connections using machine learning

Unlike traditional bolted or welded steel connections, the beam-to-column connection in steel pallet racks is established using a unique beam end connector with punched tabs, which is welded to the end of the pallet beam. This design leads to complex structural behaviour, particularly at elevated temperatures due to reduced steel properties, thermal expansion, and fire-induced failure modes. Design standards recommend experimental testing for each connector type, as a general analytical model is lacking. However, such testing is often costly and time-consuming. Recent advancements in machine learning offer a promising alternative to traditional testing methods in civil engineering. This study explores the application of machine learning techniques to predict the moment-rotation behaviour of steel pallet rack beam-to-column connections under elevated temperatures. The methods investigated include Linear Regression, Ridge Regression, Ridge Cross-Validation Regression, Logistic Regression, Least Shrinkage Regression, Least Absolute Shrinkage and Selection Operator with Cross-Validation Regression, and Localised Linear Support Regression. The dataset comprised 63 experimental tests, varying in column thickness, beam depth, and number of tabs in the beam end connector, conducted at temperatures ranging from 25 °C to 700 °C. Model evaluation employed metrics such as mean-square error, Pearson correlation coefficient, and coefficient of determination. Results indicate that linear regression effectively predicts moment-rotation behaviour, closely aligning with experimental data. While other machine learning techniques performed well in moment prediction, their accuracy in rotation forecasting was limited. This research enhances the accuracy of structural behavior predictions and offers a cost-effective alternative to physical testing for steel pallet rack designers. Future research recommendations are provided based on these findings.

Numerical characterisation of reaction forces’ contribution to initial stiffness in speed-lock beam-to-upright connections

This article presents a detailed numerical model of speed-lock (boltless) beam-to-upright connections in steel storage pallet rack systems. The model is capable of predicting initial stiffness and characterising the reaction forces of connector-to-upright interactions. The study examines nine configurations, combining three types of uprights and three types of beams with a common connector. Initially, experimental tests were conducted using the monotonic cantilever test method according to EN 15512 standard, with initial stiffness calculated using a standardised version of the initial stiffness method. Subsequently, a numerical analysis was developed through a finite element model based on the experimental setup. The model introduces new geometric details, evaluating each impact on behaviour, particularly on initial stiffness. Results show that numerical accuracy improves with detailed components such as inclined tabs, more detailed perforations, and 3D weld modelling. The contribution of reaction forces of connector-to-upright interactions to initial stiffness was analysed, considering the impact of the rotation centre’s position. It was found that a lower rotation centre position reduces the connector-to-upright lateral contact contribution while increasing tab-to-slot interaction contributions. The impact of beam height and beam weld position on initial stiffness was also analysed, with results showing that increasing these variables consistently led to increased initial stiffness. Finally, the rotation centre’s position was shown to evolve throughout the test, redefining the contribution of interactions. It clarified that connector-to-upright lateral interaction and tab1-to-slot1 and tab2-to-slot2 interactions have the highest contributions. This information is valuable for rack manufacturers to improve, optimise, and ensure the safety of their designs.

A Mechanical Model to Predict the Initial Stiffness of The Beam-to-Upright Connection in A Steel Pallet Racking System

A Mechanical Model to Predict the Initial Stiffness of The Beam-to-Upright Connection in A Steel Pallet Racking System

Seismic fragility of unbraced industrial steel pallet racks

Past Italian earthquakes revealed the high seismic vulnerability of steel pallet racks designed for gravity loads only, which are still the most widespread industrial storage system. This study aims to derive the seismic fragility of these structures to enable more refined estimates of enterprise risk and the definition of effective retrofit solutions. For this purpose, 3D non-linear models of 27 unbraced pallet racks, representative of the Italian context, were analysed in Time-History under 268 bidirectional events, representative of Italian seismicity. Multiple fragility models were then derived, based on various engineering demand parameters and seismic intensity measures, through a cloud approach.

Optimization of cold-formed steel beam cross-sections for pallet rack storage systems

This paper aims to obtain optimized cold-formed beam cross-sections for industrial pallet rack storage systems. The optimal sections were obtained by applying fitness functions aimed at reducing cross-sectional area and/or displacement and solving them using the Genetic Algorithm. These functions imposed a behavioral constraint so that all optimized solutions had the same resistant bending moment. The calculation of the characteristic resistant bending moment was carried out according to the direct strength method, with load factors defined by the elastic stability analysis with CUFSM, in an analysis routine implemented on the MATLAB platform. Four parameterized sections were studied, verifying the optimum set of height, width and stiffening elements that met the objectives defined by functions, assuming reference values of a rectangular hollow section. Manufacturing constraints were also taken into account. The results show that it is possible to manufacture cold-formed beams that consume less material and/or have a better moment of inertia in relation to the reference section, without compromising the strength of the structural element.

Seismic design-assisted-by-testing approach for racks with dissipative baseplates in the cross-aisle direction

A design-assisted-by-testing strategy is proposed for the upright frames of adjustable pallet racks. This methodology defines a procedure that aims to locate marked post-elastic behavior at the floor-to-upright connections of lateral resisting frames in the cross-aisle direction. Such connections are intended to enhance the performance of the cross-aisle frames when subjected to dynamic forces in their plane. The chosen baseplate connection is experimentally tested using monotonic and cyclic protocols at the Steel Structures Laboratory of the National Technical University of Athens (Greece). Then, a numerical model of the baseplate is calibrated using literature parameter definitions and hence validated using physical data. Additionally, the dynamic response of two upright frames is numerically investigated: one with traditional hinge connections and another with dissipative ones. This study indicates that the proposed procedure successfully enhances ductility, resulting in a significant reduction (up to 50%) in upright axial forces compared to the conventional configuration. Finally, the open-source code for ground motion selection, together with its database, is released.

Dynamic analysis with point-masses of perforated pallet rack structural members by means of the Generalized Beam Theory

This paper presents two different formulations for introducing point-masses into a dynamic problem using the Generalized Beam Theory (GBT) method. The first one implies placing a point-mass at a beam-node (with or without eccentricities) while the other implies placing a point-mass at a cross-section node. In order to evaluate the accuracy of such formulations, different modal analyses of members have been performed using GBT beam elements, shell elements and classical beam elements. The values of natural modal frequencies obtained through different models have been successfully compared. The results of various harmonic analyses are also presented. Some of the studied structural members include perforations. Finally, the influence of GBT modes and perforations when using point-masses is discussed.

Automated Pallet Racking Examination in Edge Platform Based on MobileNetV2: Towards Smart Manufacturing

Automated Pallet Racking Examination in Edge Platform Based on MobileNetV2: Towards Smart Manufacturing

Optimalisasi Perencanaan Dan Pengendalian Produksi Rak Palet Menggunakan Metode Cutting Plane

PT Atlantic Anugrah Metalindo is a manufacturing company that produces costumize products, steel door systems and fireproof doors. Currently PT Atlantic Anugrah Metalindo is producing 100 units of pallet rack manufacturing with customers from PT X so that proper material requirements planning is needed. The purpose of this research is to determine the material requirements of pallet racks optimally and efficiently. This research requires calculating the Bill of Materials (BOM) using the Cutting plane method and controlling the production process to run effectively and efficiently. Based on the calculations that have been carried out, the results show that for 2 mm thick mild steel material requirements, 6 sheets of plate are needed, 3 mm thick mild steel requires 173 sheets of plate, 3.6 mm thick mild steel requires 12 sheets of plate and 5 mm thick mild steel requires 12 sheets of plate. So that from these calculations PT Atlantic Anugrah Metalindo is expected to minimize the material requirements of pallet rack products.

Seismic pushover analysis of unbraced adjustable pallet racks in the down-aisle direction. Need for multimode analysis

Modal Pushover Analysis has been proposed to account for the higher modes contribution in seismic analysis of slender structures, such as unbraced racks in the down-aisle direction. In these structures, only single-mode pushover analyses have been used so far. This paper investigates a suite of 96 unbraced representative prototype racks, and six of them are selected to be analyzed through modal pushover analysis. Results show that global damage significantly exceeds that derived from considering the first mode alone, thus proving that higher modes contribution is relevant for racks with low mass participation in the first mode (<90 %).

Low-cost very narrow aisle pallet racking vehicle utilisation monitoring solution

Low-cost very narrow aisle pallet racking vehicle utilisation monitoring solution

Full‐scale tests of industrial steel storage pallet racks

Industrial steel storage pallet racks are framed structures typically made of cold‐formed steel profiles. The characteristics and the variability of the racking systems in terms of components and configurations make their behaviour quite complex to be predicted and the “design by testing” approach is commonly adopted. As part of an extensive research on the racks’ static and seismic behaviour carried out at the University of Trento, a total of eight full‐scale tests on four‐level two‐bay commercial pallet racks were performed, taking advantage of an innovative full‐scale testing set‐up. The experimental plan comprised of two preliminary tests in which racks with an initial out‐of‐plumb were vertically loaded up to their collapse and of six monotonic push‐over tests with three different levels of vertical loads and an inverse triangular pattern of horizontal forces in the down-aisle (longitudinal) direction. Tests’ results enabled investigation of the failure modes and evaluation of the racks’ behaviour factor q. The main features and findings of this experimental study are presented and discussed in the paper.

Structural analysis of rack upright frames under a pure compression load by means of a nonlinear Generalized Beam Theory analysis

AbstractRack upright frames of conventional pallet racking systems are obtained by the assembly of uprights and braces or diagonals. Rack uprights are commonly mono‐symmetric open thin‐walled members with regular perforations along their length. These perforations are used to enable the connection with braces and beams by means of bolts or hooks. The structural behaviour of a rack upright frame under a pure compression load, in which the buckling phenomenon has a relevant influence, depends on several geometrical parameters, such as the column cross‐sectional dimensions, perforations characteristics, frame length, distance between braces, etc. Therefore, these particular issues should be considered to perform a proper structural analysis.In this paper, the structural behaviour of a pallet rack frame under a pure compression load is analysed by means of eigenbuckling and geometrically nonlinear Generalized Beam Theory (GBT) analyses. The influence of GBT deformation modes involved in the analysis is discussed. Moreover, different approaches to reproduce the connection between uprights and braces are presented and discussed. Finally, GBT results are compared with beam, shell finite element analysis and experimental values.

Comparison between numerical models for unbraced multiple bay pallet racks

AbstractUnbraced pallet racks are cold‐formed steel structures intended for the storage of products. They are subjected to severe lateral actions, and are particularly instability prone in the down aisle direction. Therefore, their design is compromised and needs of an accurate modelling. In current design practice, models using simplified beam formulations are regularly considered (such as Euler‐Bernoulli or Timoshenko), being them not able to reproduce torsional warping, or cross‐sectional distortion; these phenomena are accounted for indirectly via reduced sectional properties, and in the post‐process. This paper presents a comparison between three single column models, intended for the modelling of racks with a significant number of bays. Three models are presented: –Two 2D beam models using gross and equivalent section properties –A 3D beam model using equivalent section properties. Additionally, the results of these analyses are compared with those of a 3D model using shells and beams, presented in a previous research paper. Two rack configurations with different level heights are considered. The aim of this study is to capture the influence perforations of the uprights, warping, eccentricities and cross‐sectional distortion in the nonlinear response of racks subject to severe lateral actions.

Influence of design parameters on beam-to-column connections of steel storage rack systems

Storage rack systems are the products of cold-formed steel material. Increase in the volume of distant sale in recent years has also increased the importance of logistics and storage industry. In steel storage racks, plug-in beam-end connectors are used to produce boltless and semi-rigid beam-to-column connections. Variability of tab designs for beam-end connector makes it heavily difficult to develop a generalized analytical model. For some typical connectors, several analytical models are available to evaluate the performance of connections. In this study, sixteen beam-to-column connection tests were conducted on a commercially available pallet rack assembly by varying the most effective parameters such as the wall-thickness of the column section, height of the beam, vertical beam position on the connector, and installation of the bolts at connector level among the opening of the column. Being the main goals of this study, failure mechanisms and moment-rotation effects of changing vertical position of the beam on the connector and placing bolts among the opening of the column at the horizontal alignments of the connector, were investigated. These experimental results have shed light on how the ultimate moment capacity, rotational stiffness and rotational ductility values ​​vary by changing these design parameters. In the light of these results, an analytical model has been proposed in order to predict the structural behavior of beam-to-column connections with an acceptable accuracy.

Cross-sectional optimization of perforated pallet rack columns against distortional and global buckling

This paper presents a cross-sectional optimization procedure to increase the load carrying capacity of a perforated rack column under a compression load. The optimization method is based on a Genetic Algorithm (GA) combined with the Generalized Beam Theory (GBT), which allows to take perforations as well as sectional deformations into account. The results indicate that the optimal cross-section geometry depends on the dominant buckling mode. Therefore, a combined optimization criterion to consider distortional and global buckling is defined. Finally, nonlinear shell finite elements analyses are done in order to assess the structural behaviour of optimized cross-sections.

Bamboo Hitchhiking Point Project for the Federal University of Lavras - Minas Gerais, Brazil

The NEMATENC-UFLA began studies on bamboo during the pandemic to disseminate the use of this millennial material in construction. For this purpose, a prototype was developed for the shelter of a hitchhiking point, located on the university campus. The planning was developed in several stages. Initially, live transmissions were organized with professionals and researchers of the bamboo species existing in the university. The projects were developed for the species Dendrocalamus asper and Bambusa tuldoides. After the cuts, the treatment adopted was immersion in a solution of borax, boric acid, and copper sulfate. The pieces were stored on pallet racks designed for this purpose. After the execution of the foundation, it was assembled on site. The entire executive process had the theoretical and practical training of MSc. CE Frederico Rosalino: reduced model; cutting of plug-in connections; use of the “Vellez System” in the pillar bases; and covering with a sandwich of esterillas and waterproofing blanket. Students, engineering professionals, and others, participated in the construction. The whole process had the support of PROINFRA and collaborators. The result reached the proposed goal: promote the aesthetics and physical-mechanical properties of bamboo, besides offering comfort to the users of the university campus.

Optimal design method of the load-level isolation system for industrial steel racking

This paper focuses on an innovative system for mitigating seismic actions on industrial steel racking, called Load-Level Isolation System (LLIS). It consists of placing isolators directly between the pallet masses and the load level, thus exploiting the pallet masses (much greater than the structural mass) as tuned mass dampers. Specifically, the paper aims to derive a general design procedure for the LLIS, based on the amount of mass isolated, the position of the LLIS within the rack, and the main dynamic characteristics of the structural system. To this end, an analytical optimization method is proposed, based on the minimization of the displacement variance of a reduced structural model, representative of the rack dynamics with the LLIS. This method is applied parametrically to derive the optimal damping and frequency values of the LLIS in various design situations, and a sensitivity analysis is subsequently conducted to propose cost-effective LLIS design solutions. Prediction models of the LLIS parameters are therefore provided, as well as a simple step-by-step procedure for designing the control system. Finally, a case study is presented, with the dual objectives of showing the application of the design procedure and the effectiveness of the LLIS in mitigating seismic effects in a standard pallet rack. The results of the Time-History analysis demonstrate the validity of the proposed design method and the possibility of achieving large reductions in the seismic response of the rack using this control system, and up to 60% for both maximum displacements and axial forces of the uprights.

YOLO-v5 Variant Selection Algorithm Coupled with Representative Augmentations for Modelling Production-Based Variance in Automated Lightweight Pallet Racking Inspection

The aim of this research is to develop an automated pallet inspection architecture with two key objectives: high performance with respect to defect classification and computational efficacy, i.e., lightweight footprint. As automated pallet racking via machine vision is a developing field, the procurement of racking datasets can be a difficult task. Therefore, the first contribution of this study was the proposal of several tailored augmentations that were generated based on modelling production floor conditions/variances within warehouses. Secondly, the variant selection algorithm was proposed, starting with extreme-end analysis and providing a protocol for selecting the optimal architecture with respect to accuracy and computational efficiency. The proposed YOLO-v5n architecture generated the highest MAP@0.5 of 96.8% compared to previous works in the racking domain, with a computational footprint in terms of the number of parameters at its lowest, i.e., 1.9 M compared to YOLO-v5x at 86.7 M.