Steel pallet racks

Why storage steel pallets racks are important?

Earthquakes are a vivid example of low-probability/high-consequence events, in terms of damage to structures and losses, and storage rack systems are not exempt from such issues, as repeatedly shown by past seismic events in Italy and abroad [1-3].

The European logistics industry, including warehousing, transshipment, and transport, is of vital importance to the European economy. The total European market for racking and storage equipment was yearly ca. € 4 billion in 2014 and has significantly increased since. Downtime is not an option for the supply chain, as these infrastructures, during a pandemic or following natural-hazard extreme events (such as wind, earthquakes, fires or explosions), assume a role of fundamental importance for society and must continue to function without interruption even under unfavorable conditions. For instance, in the Italian context, recent major seismic events, such as the 2012 Emilia-Romagna earthquake [1] or the 2016 Central Italy earthquake [2], caused the collapse of several racks and warehouses (Figure 1), underlining their inherently high seismic vulnerability. Italy is statistically hit by medium-high intensity earthquakes about every five years, therefore urgent actions are necessary to reduce the occurrence of disruptions and downtimes in such vital infrastructures. An interruption of deliveries or a loss of basic supplies during a catastrophic event could indeed have extremely serious consequences both from a social point of view and in managing the emergency as well.

Steel storage pallet racks (or simply racks) are composed of specially designed cold-formed steel elements that enable an easy and quick installation and reconfiguration, consistent with the merchandising needs of warehouse retail stores and storage goods in production facilities. Moment-connection frames are typically used as structural systems in the longitudinal direction [4-8], whereas braced frames are typical for the transverse direction [9]. In the case the rack is located in areas of high seismicity, the designer often adopts bracing systems also in the down-aisle (or longitudinal) direction, although its installation obstructs the material handling and movement. The prediction of the structural performance of racks is cumbersome because it is affected by uncommon geometries of their structural components [10,11] or content-structure interaction [12], whereas beam-to-upright and base-plate joints exhibit a strongly nonlinear behavior [8,13]. For these reasons, the only way to design racks is to be assisted by testing procedures, i.e. the numerical models used for the structural analyses must be based on ad-hoc tests of components [14]. There are different reports of full-scale experimental activities in the literature for the response of racks under seismic excitation [15-18], yet, currently, no practical indications on seismic retrofitting methodologies are available [19], nor seismic qualification procedures for entire rack portions are available to producers.

Currently, the last version of the European seismic code for rack-type structures, EN16681 [20], provides just a few recommendations to increase the seismic safety of existing racks. In addition, for these structures, it is not possible to estimate the seismic performance of the connections, rendering the seismic response assessment of such structures even more complex. Presently, there are only three available strategy interventions for the safety improvement of racks in seismic zones: rack netting, structural strengthening, and installation of base isolation systems. Unfortunately, all of them are very impractical for several logistic reasons: 

• They can lead to difficulties in material handling.

• Introduce higher accelerations throughout the system without preventing adequate product shedding; or, for base isolation systems [15, 17].

• Their installation is very expensive and, mainly for existing racks, time-demanding.

As described, the racks environment has a lack of economic and effective options for increasing safety against seismic actions. Albeit, from a structural point of view, the existing racks can be simply replaced by new ones, the consideration of huge indirect losses of interrupting activities, as well as the environmental pollution due to the production of new steels, tends to avoid such an approach biassing for not intervening at all.

Consequently, the development of adequate seismic prevention strategies, such as the useful and effective solution proposed in DESRACK, is of paramount importance, as highlighted by the lack of effective solutions [19] and the common need to undertake sustainable actions in compliance with the European Green Deal.

References

1. A. Franco, S. Massimiani, G. Royer Carfagni. 2015. Passive control of steel storage racks for Parmigiano Reggiano Cheese under seismic accelerations. J. Earthq. Eng. 19.

2. D. Perrone, P.M. Calvi, E.C. Fischer, G. Magliulo. 2019. Seismic Performance of Non-Structural Elements during the 2016 Central Italy Earthquake. Bull Earthq Eng 17:10.

3. FEMA-460. 2005. Seismic Considerations for Steel Storage Racks Located in Areas Accessible to the Public. Washington, DC 20472.

4. D. Tsarpalis, D. Vamvatsikos, F. Delladonna, M. Fabini, J. Hermanek, P.D. Margotan, S. Sesana, E. Vantusso, I. Vayas. 2022. Macro-characteristics and taxonomy of steel racking systems for seismic vulnerability assessment. Bull Earthq Eng.

5.  O. Bové, M. Casafont, M. Ferrer, F. López-Almansa, F. Roure. 2020. Systemized Structural Predesign Method for Selective Racks, J Struct Eng (US), 146:12, 2849.

6. F.S. Cardoso, K.J.R. Rasmussen, H. Zhang. 2019. System reliability-based criteria for the design of steel storage rack frames by advanced analysis: Part I – Statistical characterisation of system strength, TW Struct. 

7. K.K. Sangle, K.M. Bajora, R.S. Talicotti. 2012. Elastic stability analysis of cold formed pallet rack structures with semi-rigid connections, J Constr Steel Res 71. 

8. G. Gabbianelli, F. Cavalieri, R. Nascimbene. 2020. Seismic vulnerability assessment of steel storage racks, Ing Sism, 37:2.

9. N. Talebian, B.P. Gilbert, N. Baldassino, H. Karampour. 2019. Factors contributing to the transverse shear stiffness of bolted cold-formed steel storage rack upright frames with channel bracing members, TW Struct, 136.

10. C. Bernuzzi, A. Gobetti, G. Gabbianelli, M. Simoncelli. 2014. Warping influence on the resistance of uprights in steel storage pallet racks, J Constr Steel Res 101.

11. G. Zagari, G. Zucco, A. Madeo, V. Ungureanu, R. Zinno, D. Dubina. 2016. Evaluation of the erosion of critical buckling load of cold-formed steel members in compression based on Koiter asymptotic analysis. TW Struct, 108.

12. D. Tsarpalis, D. Vamvatsikos, I. Vayas. 2022. Seismic assessment approaches for mass-dominant sliding contents: the case of storage racks. Earthq Eng Struct Dyn, 51:4.

13. L. Dai, X. Zhao, K.J.R. Rasmussen. 2018. Cyclic performance of steel storage rack beam-to-upright bolted connections, J Constr Steel Res, 148.

14. N. Baldassino, R. Zandonini. 2011. Design by testing of industrial racks, Adv Steel Constr 4, 141-149.

15. B. Tagliafierro, R. Montuori, M.G. Castellano. 2021. Shake table testing and numerical modelling of a steel pallet racking structure with a seismic isolation system, TW Struct, 164, 107924.

16. A. Kanyilmaz, C.A. Castiglioni, G. Brambilla, G.P. Chiarelli. 2016. Experimental assessment of the seismic behaviour of unbraced steel storage pallet racks, TW Struct 108.

17. A. Filiatrault, P.S. Higgins, A. Wanitkorkul, J.A. Courtwright, R. Michael. 2008. Experimental Seismic Response of Base Isolated Pallet-Type Steel Storage Racks. Earthq Spectra 24:3.

18. Z. Tang, J.B.P. Lim, J. Maguire, L. Teh. 2017. Increasing seismic resilience of pallet racking systems using sliding friction baseplates, NZSEE Conf, NZ.

19. M. Simoncelli, B. Tagliafierro, R. Montuori. 2020. Recent development on the seismic devices for steel storage structures, TW Struct, 155, 106827.

20. EN16681. 2016. Steel Static Storage Systems - Adjustable Pallet Racking Systems - Principles for Seismic Design. CEN, Belgium.