03.11: Experimental investigation of the creep effect on prestressed bolts used in innovative friction connections

Abstract

ABSTRACTIn the framework of a RFCS project entitled “FREEDAM ‐Free From Damage Connections”, innovative friction connections activated as dissipative zones in case of seismic actions are studied, with the objective to avoid any damage in the structures not only for frequent and occasional seismic events, but also for destructive earthquakes. These friction connections are made of stainless steel plates with specific coatings fastened with preloaded bolts placed in long slotted holes allowing significant displacement of the plates when the friction resistance is reached and so allowing significant dissipation of energy.As a partner of this project, The University of Liege is in charge of proposing analytical design procedures for these innovative joints and in particular of investigating the evolution of the prestressing in the bolts according to time, a key parameter when it is intended to dissipate energy through the activation of friction.This paper presents first preliminary results obtained through long term tests (5 months) performed on steel plates with particular coatings fastened with M20 Bolts. The main parameters registered during these tests were the relative displacements between the connected plates and the evolution of the prestressing in the bolts. The tests were performed according to EN 1090‐2, in order to assess the loss of preloading over time and the creep of the plate. The final objective of the conducted studies is to propose a methodology to predict the prestressing loss in order to ensure that a minimum level of prestressing is kept over the full life of the structures, i.e. at least 50 years.