PSI - Issue 28

Lucas F.R.C. da Silva et al. / Procedia Structural Integrity 28 (2020) 1426–1430 Lucas F. R. C. da Silva et al./ Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Racking systems applied in logistics warehouses are built with thin steel sections that are joined by several processes including bolted connections. In fully automatic storage and retrieval systems, these structures are loaded 24 hours a day, 7 days a week, resulting in fatigue damage due to the cyclic nature and intensity of the resulting stresses. According to the current industrial practice, bolted joints are tightened by hand, i.e., with no torque control, leading to the concept of snug tight bolts, which behaves similarly to non-preloaded bolted joints. Previous work by de Jesus et al. showed that the average friction coefficient between zinc coated plates is μ=0.12. The low friction coefficient combined with bolts not property preloaded leads to premature fatigue failure in this kind of bolted joints. Eurocode 3 (CEN,2005) has no reference about fatigue design for snug tight bolts and thin-walled cold-formed steel profiles. The Fastcold EU project aims to provide fatigue rules for thin steel sections and bolted joints.

Nomenclature R

Stress ratio Ultimate force

Fu

∆σc Stress amplitude for R ≠ 0 ∆σc;0 Stress amplitude for R = 0 μ Average Friction coefficient

2. Overview of Experimental Program An experimental testing campaign was designed and performed in order to evaluate the influence of the connection geometry, the bolts preload, the reduction of plate width (net cross-section), the manufacturing process of holes, and the fatigue stress R-ratio in the fatigue behaviour of double shear bolted butt joints made of S350GD steel grade. The experimental setup with its dimensions in millimeters can be analyzed from figure 1. The chemical composition and mechanical properties for S350GD according to EN10025 can be found in table 1.

Fig. 1. Experimental setup (a)Single bolt; (b) Multiple Bolts; (c) Single bolt with reduced net section.