Research on Initial Behavior of Screwed Lap Connections of Thin Plates – Experimental Tests and FEM Analysis

Abstract

The paper continues the past research on the screwed thin-plate single-lap connections undertaken by the author. This re-search was focused on stressed skin diaphragm action, where it is essential to know values of connections behavior. Until now, initial stiffness is used for common engineering estimations. The main aim of this paper is to compare the experimental results of the shear tests conducted on the connections with the theoretical predictions of their initial behavior obtained from the FEM models. The experiments followed the Eurocode rules for design aided by testing and the European Convention for Constructional Steelwork (ECCS) recommendations. FEM parametric models are introduced as a consideration to use, taking into account screw threads and EPDM washers. In the technical literature, various techniques are described for the modelling of threaded connections. A modification to a known solution is applied in this analysis where a spiral thread is substituted by simple horizontal rings; this simplification allows use of symmetry in a static system, which is particularly desirable for large models such as those prepared in this paper. In contrast to the mentioned known solutions, the thread mod-el presented here has a triangular cross-section related to the geometry used in real screws. The numerical results correspond reasonably well to the test’s early stage measurements from the lab experiments and can be useful for initial stiffness examination (e.g. where no data is provided for a particular connector by a producer) or as a base to further research on the model.