Ductility improvement of adjustable pallet rack speed-lock connections: Experimental study

Abstract

This paper presents seismic cantilever monotonic and cyclic tests of speed-lock (boltless) beam-to-upright connections of adjustable pallet rack systems; the objective of the monotonic tests is to obtain the bounds that are employed to define the loading protocol of the subsequent cyclic tests. The beam-to-upright connections consist of welding the beam to an intermediate end-plate (L-shaped) that, in its turn, is linked to the upright through a hooked assembly. The performed experiments investigate the connections hysteretic behavior, as it contributes to the rack lateral strength, stiffness, and ductility. More precisely, the main objective of this research is to propose a new strengthened design of the weld beads geometric configuration. This design is oriented for the connection failure not to arise in the weld, but the hooked assembly. This shift is expected to increase the connection ductility; in this sense, specimens with traditional and novel weld geometric designs are tested. In most of the tests performed, the results confirm that the new weld design leads to more ductile failure modes; preliminary evaluations state that the ductility increase might be sufficient to absorb most of the input seismic energy. On the other hand, tests are conducted according to two loading protocols: the traditional one by following European regulations and a new strategy proposed by Prof. Castiglioni accounting for the influence of gravity loads. Comparison between their results shows that the Castiglioni approach is more demanding and seems to reproduce the actual seismic behavior of racks better.

Comparison between numerical models for unbraced multiple bay pallet racks

“…One upright and one beam are considered in this study; their main dimensions are displayed in Figure 3 The weld between beam and end-plate (Figure 4.c) is performed all around the section of the beam; small trims are made to the external flanges to allow the weld of the internal ones (Figure 4). Papers [9][10] study the mechanical behavior of such a welding pattern. The beam-to-upright and floor rotational characteristics are obtained by of means of monotonic tests.…”

“…With regard to the beam-to-upright connections, they have been tested under hogging (downward) and sagging (upward) motions, since they present a non-symmetric behavior. More details on the testing campaign can be found in [9][10]. The constitutive law of the upright is linear elastic in 2D models (subsection 3.2), and based on a bilinear model with isotropic strain hardening in 3D models (subsection 3.3); beams are considered to be in the linear elastic range.…”

“…The Young Modulus is E = 210 GPa for all the structural members. The yield point of the upright is fy = 407 MPa [9]. The tangent stiffness after yielding is taken 1/100 th of the initial one; the upcoming Eurocode EN-1993-1-14, dedicated to the finite element modelling [16], recommends this value for cold-formed structures.…”

State-of-the-art review on adjustable pallet racks testing for seismic design

“…Within this context, monotonic and cyclic bending tests on beam-to-upright connections are presented. As discussed in Section 4.3, the cyclic experiments are carried out according to an innovative imposed displacement protocol that differs from [27] in the sense that the effect of the weight of the stored products is explicitly considered; both testing procedures are compared in [29,30,42]. • Giordano et al [43].…”

“…The influence of these parameters on the connection stiffness is discussed. • Bové et al [29,30]. This study covers seismic cantilever monotonic and cyclic tests of speed-lock (boltless) beam-to-upright connections of adjustable pallet rack systems (Figs.…”