1,721,053 research outputs found
An advanced design procedure for the safe use of steel storage pallet racks in seismic zones
Get PDFIndustrial steel storage pallets racks represent one of the most economical solutions for storing goods and products when space is limited. This well-recognized convenience is however counter-balanced by a structural response that is generally complex to predict, especially under earthquakes. The design procedures adopted worldwide do not seem to take adequately into account for the key features associated with these structures. From the engineering point of view, racks are designed as moment-resisting steel frames but of an unconventional type because they are characterized by an extensive use of thin-walled cold-formed members. Furthermore, the overall dynamic response is often greatly affected by a non-negligible deterioration of the joint behavior due to large excursions in the plastic range, with the direct consequence that the load carrying capacity is reduced. In this paper, the well-established non-linear time-history (NLTH) method of analysis is combined with the low-cycle fatigue (LCF) damage approach in order to (1) investigate the damage distribution, (2) assess the residual fatigue life and (3) estimate the effective load-carrying capacity after an earthquake. In particular, key open problems related to the seismic design of racks are identified and the NLTH-LCF procedure is introduced and discussed. Finally, attention is focused on a practical case study related to a medium-rise doubly-entry pallet rack. Reference is made to two recent Italian earthquakes and two models have been adopted to reproduce the cyclic joint behavior of beam-to-column joints allowing for a direct appraisal of its influence on the overall rack response
European design approaches for isolated cold-formed thin-walled beam-columns with mono-symmetric cross-section
Get PDFIn this paper attention is focused on the uprights, i.e. on the vertical elements of the steel storage pallet and drive-in racks. Their response is quite difficult to predict because of the significant influence of the interaction between local, distortional and overall buckling phenomena, owing to the presence of open mono-symmetric thin-walled cold-formed cross-sections. As a consequence, very high engineering competences are necessarily required to guarantee relevant load carrying capacities with structural systems of extremely limited weight and of very modest costs. Design provisions admit few alternatives, leading to different sizes and weight of the racks and, a consequence, to different degrees of economical competitiveness on the market.
In the framework of a more general research project on steel storage rack structures, three options to design in Europe uprights (beam-column members) have been investigated in the present paper. Several cases from practice have been selected, which comprise of uprights differing for cross-section geometry, slenderness and load conditions. A suitable finite element program for academic use characterized by a refined beam formulation capable of capturing key features of uprights has been used to model the elastic buckling interaction between the axial load and the bending moment. Non negligible differences have been observed related to the admitted approaches in terms of beam-column load carrying capacity and the direct comparison of the research outcomes offers practical indications for an optimal use of the material in accordance with the required safety standards
Analisi statiche e di buckling con profili non bisimmetrici
No full textGli elementi in acciaio impiegati nelle strutture presentano
sezioni trasversali di svariate forme. I profili senza assi di
simmetria sono largamente impiegati nella realizzazione
di scaffalature metalliche per lo stoccaggio delle merci. Dal
punto di vista della modellazione per l’analisi strutturale,
è necessario l’uso di un elemento finito beam più ‘evoluto’
rispetto a quello ‘classico’ fornito dai più comuni software
in commercio, in grado di considerare l’ingobbamento della
sezione trasversale e cioè avente 7 gradi di libertà (GDL) per
ogni nodo. Sebbene molti software commerciali abbiano
inserito al loro interno questo particolare elemento finito,
molte imprecisioni si sono riscontrate nei risultati forniti dagli
stessi. L’articolo, oltre a esporre le differenze progettuali
tra l’uso dell’elemento a 6 e 7 GDL, fornisce al progettista
una guida utile per effettuare una preliminare validazione
di un qualsiasi software commercial
EU and US design approaches for steel storage pallet racks with mono-symmetric cross-section uprights
Get PDFDesign, fabrication and erection of industrial steel storage rack systems can nowadays take place at different locations, potentially separated by thousands of kilometers. Consequently, manufacturing engineers need to understand the main code provisions adopted in the country where the rack will be in-service. Frequently, design is carried out in accordance with the European (EU) or United States (US) rack codes, which are the most commonly adopted standards for industrial storage systems. As appraisal of the key differences on structural performance associated with the different code provisions in term of storage performance, a previous study of the Authors was focused on storage pallet racks comprised of bi-symmetric cross-section uprights (vertical members). Now, attention is paid to racks with mono-symmetric uprights, typically influenced by relevant warping effects, which are traditionally neglected by rack provisions and, as a consequence, by manufacturing engineers. The design approaches already considered and compared for bi-symmetric uprights now appear to be inadequate and have been necessarily improved, as suggested by the Authors, including at least the contribution due to the bimoment acting along mono-symmetric uprights. Research outcomes, which are discussed in the paper, are related to a parametric analysis on several racks differing for configurations, geometry of components and degree of rotational stiffness of joints. The associated results regarding the four EU and two US considered alternatives are presented and compared directly to each other to allow for a concrete appraisal of the most relevant differences between the admitted design approaches. In order to highlight the importance of warping effects, which can be evaluated only by means of refined finite element (FE) analysis software, design has been undertaken using also the more traditional FE beam formulation implemented in the commercial analysis packages most frequently used in manufacturing offices. Finally, Appendix A presents a complete design example to be used as benchmark, where all the discussed design options are applied and compared to each other
Design rules for steel portal frames according to EC3 and AISC360 provisions
Get PDFNowadays, it frequently happens that steel constructors design and erect civil and industrial constructions all over the world, because of the complex historical and economic dynamics of the global market: as a consequence, engineers should be familiar with the use of widely accepted steel design codes. In spite of this remark, it should result attractive a direct comparison between the design rules adopted by European (EU) and American (US) design provisions on typical framed configurations of interest for routine design. This issue is the focus of the present paper: both the EU and US codes are shortly discussed with reference to the methods proposed for design analysis. Furthermore, a numerical parametric study on portal frames is presented by varying the geometry, load conditions and degree of continuity of beam-to-column joints. Research outcomes single out main differences between the methods proposed within each code and among the codes themselves
Influence of floor deflections on the performance of steel storage pallet racks
No full textOne of the most important applications of thin-walled cold-formed elements is for the fabrication of selective steel storage pallet racks used to store goods. From the structural point of view, these systems are generally unbraced in the longitudinal direction and braced in the transversal direction. Recently, pallet rack provisions have been significantly improved, especially for what concerns design assisted by testing; however, further key aspects of relevance for structural design need urgent attention. Among them, it is worth mentioning the interaction between the racks and the supporting surfaces (i.e. foundations or floor slabs), which is expected to have a non-negligible influence in routine design, owing to the high degree of redundancy of the rack skeleton frames.This paper summarizes a study on the influence of floor displacements on the performance of medium-rise steel storage pallet racks. In order to propose a wide range of data of practical interest for routine design, the effective load-carrying capacity has been evaluated by varying the position of the rack on the floor slab, the rack geometry, the ratio between the floor span and the rack length and the degree of rotational stiffness of both beam-to-column joints and base-plate connections. Moreover, a suitable equation, which is independent of the adopted design approach, is proposed to estimate the reduction of the performance with respect to the ideal case of racks supported by a rigid floor slab. Validation of the equation is carried out using design cases that are significantly different from those used for its calibration. Finally, Appendix A proposes complete design examples detailing the main calculations necessary to predict the reduction of the load carrying capacity associated with the floor slab deflection
European and United States approaches for steel storage pallet rack design. Part 2: Practical applications
No full textPerformance of mono-symmetric upright pallet racks under slab deflections
No full textGoods and products are often stored in framed systems, such as pallet racks, which are used for industrial and commercial activities. Recently, pallet rack provisions have been significantly improved but there are still relevant aspects that need urgent attention for guaranteeing safe structural design. Among them, the interaction between the rack and the supporting surface (i.e. concrete foundation or floor slab) plays a non-negligible influence in routine design, owing to the high degree of redundancy of the skeleton frames. In addition, rack design is usually carried out using analysis packages unable to capture the behaviour of mono-symmetric cross-section members and hence all the warping effects are generally ignored. This paper summarizes a study on the influence of floor displacements on the performance of medium-rise steel storage pallet racks. In order to obtain a reasonably wide range of data of practical interest for routine design, numerical analyses have been carried out by varying several key parameters such as the position of the rack on the floor slab, the rack geometry, the floor span length and the degree of rotational stiffness of both beam-to-column and base-plate connections. Moreover, attention has been focused on the influence of the accuracy of the structural model used in the design and two commercial analysis packages, differing for the degree of refinement of the implemented finite element beam formulation, have been considered. Finally, a suitable equation is presented to estimate the reduction of performance with respect to the ideal case of racks supported by rigid floor slab
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