The student David Santamaria Palomino obtained an EXCELLENT CUM LAUDE

The student David Santamaria Palomino obtained an EXCELLENT CUM LAUDE

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• Thesis title: Effect of Manufacturing Tolerances on the Initial Stiffness of Speed-Lock Beam-To-Upright Connections in Steel Storage Pallet Racks

Court:

• Presidency: Jordi Bonada Bo (Universitat Politècnica de Catalunya)
• Vocal:Syed Naveed Raza Shah (University of Galway)
• Vocal: Eduardo Núñez Castellanos (Universidad Católica de la Santísima Concepción)
• Vocal: Miren Larrañaga Serna (Mondragon Unibertsitatea)
• Secretary: Aurea Iñurritegi Marroquín (Mondragon Unibertsitatea)

Abstract:

The increasing demand for high-density storage solutions, driven by the expansion of e-commerce, has established industrial racking systems as an efficient solution. These systems consist of vertical upright frames, beams, floor connections, and speed-lock (boltless) beam-to-upright connections. These joints are characterised by their semi-rigid behaviour and high sensitivity to manufacturing imperfections, which increases their structural instability and consequently alters their mechanical response, particularly their initial stiffness. As these racking systems are susceptible to second-order effects, the design of speed-lock joints is crucial for overall stability.

This thesis investigates the impact of manufacturing tolerances on the initial stiffness of speed-lock connections in pallet racking systems. An experimental study was conducted using a cantilever beam test (according to EN15512) in nine different configurations. The moment-rotation curves revealed significant deviations in the linear mechanical response of theoretically identical joints, attributable to geometric imperfections. Several methods for calculating initial stiffness were compared, and a new approach based on the mechanical behaviour of the joint was proposed. It was observed that reducing the dispersion in the failure moment can increase the design moment by up to 35%, although with a 17% reduction in design stiffness. By adjusting the moment reduction factor, an optimal balance between these two parameters was achieved. Under ideal conditions without imperfections, improvements of up to 30% in the design moment and 33% in stiffness were recorded.

Subsequently, a numerical analysis of speed-lock joints was developed using a finite element model incorporating detailed geometric features. This approach enabled the independent assessment of the effects of the connector tab inclination, upright slot inclination, and 3D weld bead, identified as the most influential factors. This model improved the prediction of initial stiffness by 60% compared to previous approaches, with only an 8% error compared to experimental data. Critical interactions between the connector and the upright were analysed, highlighting the upper tab-to-slot and connector-to-upright lateral interactions as the most significant. A parametric study on the beam height, weld position, upright thickness, and rotation centre position showed that increasing these geometric variables generally enhances stiffness, although reducing the rotation centre position optimises it further. It was observed that this position changes during loading, affecting the relative contribution of interactions.

The impact of manufacturing tolerances on initial stiffness was evaluated by combining experimental measurements of imperfections with numerical predictions. Notable differences between right and left-side joints were quantified, highlighting the need for an individualised analysis. The inclusion of geometric errors in the model modified the moment-rotation curve in all cases. A parametric study on the most critical geometric tolerances of the upright and connector showed that clearances in the upper tab-perforation interaction can reduce stiffness by nearly 60%, while increasing the slot angle can enhance it by up to 20%.

These findings provide key insights for optimising manufacturing processes and design standards, enabling improvements in the mechanical properties of speed-lock joints, minimising instabilities, and enhancing the overall stability of storage installations.