Cold-formed Steel Storage Racks Research Articles

A review: plastic analysis in structures

Purpose Brief introduction on the importance and the need for plastic analysis methods were presented in the beginning section of this review. The plastic method for analysis was considered to be the more advanced method of analysis because of its ability to represent the true behaviour of the steel structures. Then in the following section, a literature analysis has been carried out on the previous investigations done on steel plates, steel beams and steel frames by other authors. The behaviour of them under different types of loading were presented and are under the investigation of innovative new analysis methods. Design/methodology/approach Structure member connections also have the potential for plastic failure. In this study, the authors have highlighted a few topics to be discussed. The three topics in this study are T-end plate connections to a square hollow section, semi-rigid connections and cold-formed steel storage racks with spine bracings using speed-lock connections. Connection is one of the important parts of a structure that ensures the integrity of the structure. Finally, in this technical paper, the authors introduce some topics related to seismic action. Application of the Theory of Plastic Mechanism Control in seismic design is studied in the beginning. At the end, its in-depth application for moment resisting frames-eccentrically braced frames dual systems is investigated. Findings When this study involves the design of a plastic structure, the design criteria must involve the ultimate load rather than the yield stress. As the steel behaves in the plastic range, it means the capacity of the steel has reached the ultimate load. Ultimate load design and load factor design are the methods in the range of plastic analysis. After the steel capacity has reached beyond the yield stress, it fulfills the requirement in this method. The plastic analysis method offers a consistent and logical approach to structural analysis. It provides an economical solution in terms of steel weight, as the sections designed using this method are smaller compared with elastic design methods. Originality/value The plastic method is the primary approach used in the analysis and design of statically indeterminate frame structures.

Biaxial bending design of solid steel storage rack uprights in global buckling

This study aims at investigating the biaxial bending capacity of cold-formed steel (CFS) storage rack uprights undergoing global (lateral-torsional) buckling. A previously published and validated biaxial bending numerical model for local and distortional buckling of CFS rack uprights is initially validated in this paper for global buckling and then used to evaluate and analyse the biaxial bending response of nine unperforated upright cross-sections. Nine biaxial bending configurations were considered per cross-section. Results show that a nonlinear interactive relationship typically governs the biaxial bending of the studied uprights. This relationship is discussed and analysed for different cross-sectional slenderness. The numerical capacities are compared with both the classical DSM predictions and the use of inelastic reserve capacity in the DSM. Results show that the classical DSM equations underestimate the biaxial bending capacity by up to 55% but results in better predictions when the inelastic reserve capacity is considered. Finally, an extended range of inelastic reserve strength for global buckling is proposed which results in a 14% improvement of the DSM predictions. The appropriate form of the DSM to estimate the global biaxial bending capacity of unperforated cold-formed steel storage rack uprights is discussed.

Analysis and design of cold-formed steel storage rack uprights under localised fires

A fire in a storage warehouse creates a scenario that the load bearing members, notably storage rack uprights, are exposed to localised fires, generating the temperature field whose distribution is not uniform along the member length. This non-uniformity in temperature distribution is different from the assumption implied in the current structural fire design guidelines. This paper investigates the resistance of the uprights subjected to localised fires, in particular, fires at the bottom of the uprights, by accounting for the temperature gradients along the member length. Finite Element (FE) models of cold-formed steel storage rack uprights are developed, and are validated against experimental results from aspects of both heat transfer and buckling behaviour. The validated FE models are employed in a parametric study to investigate the resistance and buckling behaviour of the uprights under localised fires. The parametric study results show that the failure modes of the uprights are very sensitive to the localised fires. Moreover, it is observed that the Direct Strength Method (DSM), in the current form, does not produce accurate predictions for the cold-formed steel storage rack uprights under localised fires. Hence, modified DSM global curves are proposed in the paper to allow for the effects of localised fires, and prove to be sufficiently accurate through reliability analysis.

Cold formed steel storage racks subjected to axial, shear and bending interactions

This research article aims to study the behaviour of expansion bolts under axial, shear and bending interaction of base plate connected cold form steel storage racks. The bilinear moment rotation relationship was adopted to identify the ultimate moment of resistance and stiffness of the base plate connected to a concrete block using M10 grade anchor bolt at different range of axial loads ranging from 25% to 100% there by the design strength of upright profile was studied. The dimension of the upright and the base plate thickness has to be changed so that the extreme stability under various ranges of axial and transverse loads had been studied. Using finite element analysis software (Abaqus), a model has been created and designed to observe moment rotation characteristics, behaviour of base plate under simultaneous axial, shear and bending interactions and compared with experimental analysis. Comparative studies reveal that there was no failure in the concrete block and when the upright thickness increases, the stiffness and moment of the base plate increases despite having a similar cross section. An interaction equation was developed to find the stiffness and ultimate moment of resistance of the base plate connection.

Investigation on the monotonic behavior of the steel rack upright-beam column connection

The cold-formed steel storage racks are extensively employed in various industries applications such as storing products in reliable places and storehouses before distribution to the market. Racking systems lose their stability under lateral loads, such as seismic actions due to the slenderness of elements and low ductility. This justifies a need for more investigation on methods to improve their behavior and increase their capacity to survive medium to severe loads. A standardized connection could be obtained through investigation on the moment resistance, value of original rotational stiffness, ductility, and failure mode of the connection. A total of six monotonic tests were carried out to determine the behavior of the connection of straight 2.0 mm, and 2.6 mm thickness connects to 5 lug end connectors. Then, the obtained results are benched mark as the original data. Furthermore, an extreme learning machine (ELM) technique has been employed to verify and predict both moment and rotation results. Out of 4 connections, increase the ultimate moment resistance of connection by 13% and 18% for 2.0 mm and 2.6 mm upright connection, respectively.

Parametric Studies and Design Rules for Local and Distortional Biaxial-Bending Capacity of Cold-Formed Steel Storage-Rack Uprights

AbstractThis paper first describes a finite element model using advanced analysis to determine the biaxial bending capacity of cold-formed steel storage rack upright sections. The model is found to...

Investigation of a Method for Strengthening Perforated Cold-Formed Steel Profiles under Compression Loads

Cold-formed steel (CFS) storage rack structures are extensively used in various industries to store products in safe and secure warehouses before distribution to the market. Thin-walled open profiles that are typically used in storage rack structures are prone to loss of stability due to different buckling modes such as local, distortional, torsional and flexural, or any interaction between these modes. In this paper, an efficient way of increasing ultimate capacity of upright frames under compression load is proposed using bolts and spacers which are added externally to the section with certain pitches along the height. Hereinto, experimental tests on 81 upright frames with different thicknesses and different heights were conducted, and the effect of employing reinforcement strategies was examined through the failure mode and ultimate load results. Non-linear finite element analyses were also performed to investigate the effect of different reinforcement spacing on the upright performance. The results showed that the reinforcement method could restrain upright flange and consequently increase the distortional strength of the upright profiles. This method can also be effective for any other light gauged steel open section with perforation. It was also observed that the reinforcement approach is much more useful for short length upright frames compared to the taller frames.

Factors contributing to the transverse shear stiffness of bolted cold-formed steel storage rack upright frames with channel bracing members

Accurately determining the transverse shear stiffness of steel storage rack upright frames is essential in calculating the elastic buckling load, performing earthquake design and serviceability checks. International racking design specifications recommend different approaches to evaluate this stiffness. The Rack Manufacturers Institute (RMI) specification conservatively uses an analytical solution based on Timoshenko and Gere's theory while the European (EN15512) and Australian (AS4084) specifications recommend experimental testing to be conducted. Previous studies have shown that Finite Element Analyses (FEA), solely using beam elements, fail to reproduce experimental test results and may overestimate the transverse shear stiffness by a factor up to 25. This discrepancy is likely attributed to the local deformations occurring at the bolted joints. In this paper, a model to capture the transverse shear stiffness of upright frames is developed using shell elements and advanced FEA. Its accuracy is verified against published experimental test results performed on three commercially used upright frame configurations with lip-to-lip bracing pattern. The model accurately reproduces the experimental stiffness, with differences ranging from 2% to 17%. Based on the FE model, the factors contributing to the transverse shear deformation of the frames are quantified and discussed for both lip-to-lip and back-to-back bracing patterns. For lip-to-lip upright frames, results show that the local deformations at the end of bracing members contributes the most to the shear deformation of the frames. For back-to-back upright frames, bolt bending and axial deformation of braces contribute the most to the shear deformation of the frames. Results from this paper would assist the racking industry in improving their products by focusing on the factors influencing the most the behaviour of the frames.

Local and Distortional Biaxial Bending Capacities of Cold-Formed Steel Storage Rack Uprights

AbstractCold-formed steel storage rack-supported buildings, also referred to as clad racks, support both the building enclosure and the stored goods. Because of combined actions of wind loading and...

Responses of cold-formed steel storage racks with spine bracings using speed-lock connections with bolts I: Static elastic-plastic pushover analysis

The objective of this paper is to investigate the seismic performance of cold-formed steel storage racks with spine bracings using a variety of speed-lock connections with bolts, where their connection behaviors were based on previous experimental studies through monotonic and cyclic loading tests. The elastic-plastic connection models were developed for five types of bolted connections previously studied, namely, a speed lock connection (JD1), a speed lock connection with an upper bolt (JD2), a speed lock connection with a lower bolt (JD3), a speed lock connection with two bolts (JD4), and a speed lock connection with two bolts and a full flange welding (JD5). Then, the connection models were introduced into the global rack structures, both single entry and double entry racks, on which pushover analyses were performed to investigate their seismic responses. The study based on pushover analyses enabled the investigations of the progress of the plastic hinge development and the distribution of the plastic hinges for all the five connection models. In addition, the results also highlighted the performance differences of the racks using the studied connections under different seismic levels and provided their response modification factors and ductility coefficients. Moreover, the results showed that the capacity curves of the five types of connections were the same in the elastic region but diverged greatly in the plastic region. The upper bolt and welds were more effective in improving the seismic performance compared to the lower bolt. Furthermore, the double entry rack exhibited a better deformability and seismic performance compared to the single entry rack and the analysis also demonstrated collapse mechanisms of the double and single entry racks were quite different. The R-factors of the single and double entry racks were approximately 3.26 and 3.63–4.34, respectively. Responses of the racks based on nonlinear dynamic response history analyses are presented in a companion paper.

Responses of cold-formed steel storage racks with spine bracings using speed-lock connections with bolts II: Nonlinear dynamic response history analysis

The objective of this paper is to investigate the seismic response of cold-formed steel storage racks with spine br acings using two types of connections: a speed-lock connection, JD1, and a speed-lock connection with two bolts and full flange welding, JD5, using the incremental dynamic analysis (IDA) as a companion paper to the pushover analysis. The racks analyzed are racks using only JD1 and JD5 connections given the insights in terms of their performances observed from the pushover analysis in the companion paper. This paper presented the structural models for the IDA analysis with the hysteretic behaviors of the connections based on the previous experimental studies. With selected ground motion records, a total of 44 IDA curves were produced for each rack model studied: a single entry unit rack (SEU) and a double entry unit rack (DEU). The impact of the ground motion records was studied based on the IDA and associated fractile curves. The response modification factor R were then calculated for each rack and compared with those from the pushover analysis. The collapse mechanisms were also studied from the IDA results and compared with those from the pushover analysis. Moreover, the seismic performances of the racks were evaluated based on nonlinear dynamic response history analysis under the ground motions that were closely matching with fractile curves.

Linear Buckling Analysis of Perforated Cold-Formed Steel Storage Rack Columns by Means of the Generalised Beam Theory

The investigation attempts to adapt a beam finite element procedure based on the Generalized Beam Theory (GBT) to the analysis of perforated columns. The presence of perforations is taken into account through the use of two beam elements with different properties for the non-perforated and perforated parts of the member. Each part is meshed with its corresponding finite element and, afterwards, they are linked by means of constraint equations. Linear buckling analyses on steel storage rack columns are carried out to demonstrate how the proposed procedure should be applied. Some practical issues are discussed, such as the GBT deformation modes to be included in the analyses, or the optimum finite element discretization. The resulting buckling loads are validated by comparison with the values obtained in analyses performed using shell finite element models. Finally, it is verified that the buckling loads produced with the proposed method are rather accurate.

A simplified method to determine shear stiffness of thin walled cold formed steel storage rack frames

The shear stiffness of braced frames of thin-walled cold-formed steel storage racks was experimentally and numerically investigated in order to establish the effect of connection flexibility on the accuracy of different analysis methods. The analyses which included a detailed 3D Finite Element model, a 2D frame analysis with beam elements and a simple hand calculation indicated significant variation of results compared with experimental values. A simplified modelling approach for 2D elastic analysis of braced frames was proposed. The approach is aimed at practical applications to account for the flexibility in bolted connections and leads to better approximation of the shear stiffness.

A theoretical model for the rotational stiffness of storage rack beam-to-upright connections

Experiments are generally used to investigate connection behaviour of steel storage racks, but the procedures are expensive and time-consuming. Various connections with complicated geometrical details necessitate simple and reliable design methods. This paper presents a mechanical model based on the component method to predict the initial rotational stiffness of beam-to-upright connections in cold-formed steel storage racks. In the model, five basic deformable components contributing to the initial rotational stiffness of beam-to-upright connections, are involved, i.e. tab in bending, upright wall in bearing, and upright wall in bending, beam-end-connector in bending and shear, upright web in shear. The mechanical model is validated against experiments, and the results show that the initial rotational stiffness values obtained from the mechanical model have a satisfactory agreement with the experimental results. Finally, based on the proposed mechanical model, main components influencing the initial rotational stiffness of connections are analysed in this paper.

Finite Element Modeling of Bolted Cold-Formed Steel Storage Rack Upright Frames

Steel storage racks, commonly assembled from cold-formed steel profiles, are braced in the cross-aisle direction, where bracing members are typically bolted between two uprights forming an “upright frame”. Especially for high-bay racks and racks supporting the building enclosure, accurately determining the transverse shear stiffness of upright frames is essential in calculating the elastic buckling load, performing earthquake design and serviceability checks. International racking specifications recommend different approaches to evaluate the said transverse shear stiffness. The Rack Manufacturers Institute (RMI) Specification conservatively uses an analytical solution based on Timoshenko and Gere's theory while the European (EN15512) and Australian (AS4084) Specifications recommend testing to be conducted. Previous studies have shown that Finite Element Analyses (FEA), solely using beam elements, fail to reproduce experimental test results and may overestimate the transverse shear stiffness by a factor up to 25. This discrepancy is likely attributed to the local deformations occurring at the bolted joints. In this paper, a commercially used upright frame configuration has been modeled using shell elements in FEA and the response is verified against published experimental test results. A good correlation is found between the FEA and test results, concluding that shell elements are able to fully capture the behaviour of the upright frame. Future studies on the use of the FE model are also presented.

Monotonic and cyclic response of speed-lock connections with bolts in storage racks

The purpose of this paper is to explore the bearing capacity and energy dissipation of several variations of speed-lock connections of cold-formed steel storage racks. Commonly used speed-lock connection exists large slippage and low energy dissipation capacity, new speed-lock connections with additional bolts (and welds) are investigated in order to enhance its performance. Their monotonic behavior and hysteretic response under cyclic loading were studied experimentally using a cantilever test method. The tests were conducted using both the EN 15512 monotonic protocol and AISC seismic provisions’ cyclic-test protocol for each specimen. The failure modes, moment–rotation response, and associated stiffnesses, bearing capacities, and energy dissipation capabilities were fully investigated. Both monotonic and cyclic responses showed that the additional bolts (and welds) significantly enhanced the bearing capacities and deformability of the connections, though the initial stiffness and equivalent stiffness (i.e., according to the EN 15512 specification) showed little improvement. The hysteretic responses of all connection variations investigated demonstrated pinching behaviors. The energy dissipation capability has been greatly improved with additional bolts (and welds) except of the one with only lower bolts, which could also be corroborated through the analyses of the calculated equivalent viscous damping coefficient and the displacement ductility factor. In addition, the stiffness degradation has been observed for both positive loading and negative loading, and adding bolts and welds could effectively reduce this effect.

Determining the transverse shear stiffness of steel storage rack upright frames

The stability of steel storage racks in the cross-aisle direction is typically ensured by cold-formed steel bolted upright frames. Sensitive to second-order effects, accurately determining the shear stiffness of these frames is essential for seismic design and for ensuring the stability of the rack, especially for high-bay racks and racks supporting the building enclosure, where the outer rack frames must withstand cross-aisle horizontal actions due to wind loading. The main international racking specifications adopt different approaches to determining the shear stiffness of cold-formed steel storage rack upright frames. The Rack Manufacturers Institute (RMI) specification conservatively uses Timoshenko and Gere's theory. The European Specification EN 15512 recommends testing, however it is not clear whether the shear stiffness obtained using the recommended test procedure is correct. The newly revised Australian Standard AS 4084 adopted the European approach but also introduced an alternative test method for determining the combined bending and shear stiffness of upright frames in the transverse direction. This paper reviews and analyses the factors influencing the shear deformation of cold-formed steel bolted upright frames and introduces the alternative test set-up adopted in the revised Australian Standard. 36 upright frames have been tested using the two test methods, and experimental results are presented, discussed and compared with finite element analysis results. Recommendations on how to use the test outcomes in design are also provided. Based on these recommendations, the paper shows that the two test methods are not equivalent and yield different results for the transverse shear stiffness of upright frames.