PSI - Issue 22

V.M.G. Gomes et al. / Procedia Structural Integrity 22 (2019) 401–406

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V.M.G. Gomes et al. / Structural Integrity Procedia 00 (2018) 000 – 000

Nomenclature σ Y

Yield strength [MPa]

Ultimate tensile strength [MPa]

σ U ε R

Total elongation [%]

R Stress R-ratio Fu Ultimate Strength of Bolt [N] Independent Variable of the rectilinear curve Dependent Variable of the rectilinear curve Standard Deviation of the linear statistical model Slope of the rectilinear curve Intercept of the rectilinear curve Multiplicative Factor 1. Introduction

Over the years, the advances in research and development of manufacturing processes of cold-formed steel profiles made possible the use of light cold-formed profiles in racking systems. Racking systems are often used in logistic warehouses for supporting and guiding storage and retrieval (S/R) machines, which carry weighty goods at high speed over these profiles. High loads coupled with high travel speeds associated to the need of reducing the steel thickness lead these machines to induce severe dynamic loadings, raising fatigue issues. Nowadays, Eurocode 3 (CEN, 2005) has no reference about the fatigue design of thin-walled cold-formed steel profiles, and because of that FASTCOLD EU project aims at providing new fatigue rules for this kind of steel members. In addition, these members are often supplied with zinc coating manufactured by hot-dip galvanization process and are assembled by several processes including bolted joints. The zinc coating reduces significantly the friction coefficient and bolted joints are hardly performed using preloaded bolting joints techniques. In this field, it is frequent the production concept of snug tight joints, which means a bolted joint performed without preload control and by hand. Therefore, the low friction coefficient associated to low preload on bolts and the low thickness of the plates, makes the bolted joints on racking systems peculiar. This paper presents an experimental work about the fatigue performance of double-covered bolted butt joints (double shear splices), which are the most used joining method for racking systems. Moreover, previous work was carried out, where the static and friction behaviours were investigated (Gomes et al . 2019). At the present fatigue investigation work, different connection geometries (single (1+1) and multiple (4+4)), section areas (80×2 mm 2 and 70×2 mm 2 ), preload levels (standard snug tight and preloaded bolts), hole manufacturing processes (standard punching and drilling processes), and fatigue stress ratio ( R =0.1, R =0.3, R =0.5) were considered.

2. Material and Methods 2.1. Material

One steel grade called S350GD steel was investigated. S350GD is a zinc coated mild steel, which is obtained by hot-dip galvanization processes, providing good corrosion resistance. Table 1 shows the chemical composition and the typical mechanical properties for S350GD steel in accordance with EN 10346 standard.