Content sliding investigations for pallet racking systems (ERIES-RACKSLIDE)

The ERIES-RACKSLIDE project is an experimental program on industrial racks. Specifically, two racking systems (of different height, period, and stiffness) have been tested against multi-component earthquake motion. The program was carefully designed in order to comprehensively test the seismic response of racking systems including: (i) testing different loading levels (“story levels” in conventional building parlance), (ii) testing pallet sliding, (iii) testing the effect of CSSI (Content-Structure-Sliding Interaction), (iv) testing of the POS (plastic ovalization strategy), which refers to a concept to introduce some ductility to otherwise non-ductile racking systems (in cross-aisle direction), as well as additional low-cost mitigation measures.

The project has the following main objectives:

− 1. To assess sliding displacements on racks with different structural characteristics (finishing of contact surface, stiffness, height) and at different loading levels.

− 2. To assess the accuracy of the ED1 modification factor employed in EN16681 to account for the reduced effective mass of pallets due to sliding.

− 3. To calibrate simplified and detailed mechanical models to correctly account for CSSI.

− 4. To verify the efficiency of the POS design in providing ductility to racks and confining damage to diagonals.

− 5. To calibrate empirical relationships to assess pallet sliding for future code applications.

These objectives have been fulfilled by performing a combination of material characterization tests (with ample support from the participating manufacturers), static friction tests and shake table tests under inputs with increasing intensity. Moreover, numerical and analytical models have been realized to support testing, analysis, and design of the rack specimens and to develop reliable methodologies to account for CSSI during design and assessment.

The specimens are 1:1 scale replica of two pallet loading levels that characterize typical ARSW (Automated Rack Supported Warehouse) and APR (adjustable pallet racking) configurations. It comprises two upright frames, with bracing elements “hooked” on the uprights. The uprights are bolted via end-plates at their bottom and top to the Eucentre 9D System base table and top platform, respectively. All members are made of cold-formed steel sections. Up to three pallets of 600 kg are placed on each of the two loading levels, plus the minimal weight of the rack (<300 kg).

Standard pallets for European facilities have been employed, e.g., EUR-pallets (https://en.wikipedia.org/wiki/EUR-pallet) 80×120 cm in plan, while their contents was represented by cast concrete blocks. The height is 4.02 m while the plan dimensions are 2.94 m × 1.10 m. For safety, and to prevent excessive pallet sliding, each pallet was equipped with a timber stopper, strategically positioned so that, in the event of significant displacement, it would come into contact with the rack beam and thereby arrest further sliding. Leg buckling was not allowed, because preventing it is the main goal of the POS strategy promoted (among others) by ERIES-RACKSLIDE.

ERIES-RACKSLIDE brings together seven universities, one association of manufacturers, and two supporting industrial partners with active interest in pallet sliding research, and proposing the usage of the Eucentre 9D System facility to conduct innovative investigations that will form the state-of-art in content- structure-sliding interaction and inform the future of EN16681, the seismic rack-design standard.

The experimental campaign of the ERIES-RACKSLIDE project was carried out at the EUCENTRE-IUSS Research infrastructure, within the framework of ERIES project (Engineering Research Infrastructures for European Synergies). ERIES is funded by the European Commission's Horizon Europe program, it is coordinated by the Scuola Universitaria Superiore IUSS in Pavia, has a budget of €11.6 million and has a four-year duration, from 2022 to 2026. ERIES aims to provide transnational access to advanced research infrastructures in structural, seismic, wind, and geotechnical engineering. The project seeks to enhance resilience against natural hazards such as earthquakes and extreme winds by fostering innovative and sustainable solutions to mitigate economic losses and social disruptions. Additionally, it develops new technical standards and methodologies to improve infrastructure safety and supports frontier research through international collaboration.