Ανάπτυξη των γραμμών διαρροής σε εφελκυόμενες κοχλιωτές συνδέσεις αλουμινίου. Αριθμητική και πειραματική προσέγγιση

Abstract

As the development of technology of modern materials is leading to a plethora of alternative structural applications, the option of the use of structural aluminium becomes a very attractive choice. In order to exploit all the advantages of aluminium in the civil engineering projects and in particular in the field of structural joints, the thorough investigation of the structural capabilities of aluminium connections by means of the T-stub idealization is imperative as long as it represents an efficient modeling tool for the resistance of the components of bolted joints. In the present work, both a numerical simulation and an experimental analysis program concerning the investigation of the response of aluminium T-stub joints in tension are presented. The scope of the present research effort was to analyze all the phenomena developed in the elastic and the post-elastic range taking into account especially the development of yield-like lines. The configuration of the specimens was based on the dictations of Eurocode 9 [prEN 1999-1-1: 2004], whereas the experiments were performed by using a device manufactured by professor M. Zygomalas for displacement measurements on several points distributed along the T-stub flanges. In addition, the purpose of the present effort was to study all those factors that dominate the realistic structural behaviour of aluminium bolted connections and to contribute to the broadening of the knowledge concerning their tensile response and the developed yield lines. In this framework, both the codified failure mechanisms and the theoretical yield patterns provided by Eurocode 3 [prEN 1993-1-8: 2003] have been verified in the case of aluminium T-stub joints, whereas in the mean time, useful conclusions have been reached concerning the post-elastic behaviour of aluminium. The step-by-step observation of the behaviour of the specimen up to collapse and the registration of all the resultant values of deformation are also included in the present work; the latter were used as a calibration basis for the respective numerical investigation carried out by means of a finite element analysis scheme. The dissertation consists of eight chapters. In the first chapter, the framework of the research effort is described and the basic target of the thesis is presented. A general presentation of aluminium as a structural material is described in the next chapter where both physical and mechanical properties of the material are presented. The third chapter includes the provisions of Eurocode 9 [prEN 1999-1-1: 2004] with emphasis on the proposed analytical models of stress-strain relationship (σ ?ε ) and the ultimate and serviceability limit states, along with the heat affected zones (HAZ) theory. In Chapter 4 the theoretical background concerning structural aluminium connections and especially bolted joints is presented, while a detailed presentation of yield-line theory and the collapse mechanisms of the T-stub model of steel and aluminium plates is done in Chapter 5. The experiments carried out at the Laboratory of Aristoteles University of Thessaloniki regarding the response of aluminium T-stub specimen under tension are in details presented in Chapter 6. The whole experimental procedure is being presented step by step and the sum of the results are included in Appendix A. The numerical approach of the problem have been presented in Chapter 7, where all special features of the material, e.g. strain-hardening and limited ductility have been incorporated in the model. The numerical results have been calibrated on the basis of the experimental ones with specific interest in the theoretical verification of collapse mechanisms of Eurocode 9 and the post-elastic phenomena of the mechanical behaviour. Finally, all conclusive remarks regarding the developed yield lines on the surface of aluminium T-stub flange, along with the comparative diagrams of laboratory and numerical results are concluded in Chapter 8. In particular, a critical examination of the resultant values on the basis of the theoretical elements provided in Eurocodes 3 & 9 is presented, while a deeper insight concerning yield lines in aluminium T-stub joints is attempted.