Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS RESIDUAL STRESS (MPa) 300 200 100 0 -100 -200 -300 Figure 3.37. 3D substructure of the JB1-3 joint used for the single- pass weld 0 2 4 6 8 10 12 14 16 18 FLANGE THICKNESS (mm) Figure 3.38. Transverse residual stress distribution 3.7.3 Parametric analyses 2D Model 3D Simulation (x = 0,16L) 3D Simulation (x = 0,50L) 3D Simulation (x = 0,83L) The parametric analyses presented in the foregoing investigate the influence of some design parameters on the fracture resistance of bolted steel component parts. In detail, the effects of the weld-to-base metal yield strength ratio, of the residual stress influence and of the end plate yield-to-ultimate strength ratio are determined through 2D and 3D non-linear finite element analyses of ITS and CJ connections, respectively. Furthermore, as noted above, the parametric study is 85
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS conducted for monotonic loading conditions only. As in prior analytical studies on welded moment connections performed by El-Tawil et al. (1998), it is assumed that the conclusions drawn from this study are qualitatively applicable to cyclic conditions. In order to reduce the computational effort, the onset of cracking method is considered in the models. Hence, the J-integral is adopted to characterize the energy release associated with the crack growth. As sharp cracks are considered, see Figure 3.29b, an accurate evaluation of the contour integral is obtained. Toughness demands are quantified in the analyses by means of the CTOD index, that represents the tearing at the crack tip. In detail, the CTOD is determined in the analyses evaluating the J-integral and converting it into the CTOD value by means of Eq. (3.1). To evaluate and compare the different analyzed connection configurations for ductile fracture potential, a rupture index is computed at different locations of the connection. Others [6] have used the same approach in analytical connection studies. The rupture index (RI) is defined as: 86 εp εy RI = σ exp −1.5 σ m eff ( 3.16 ) where εp, εy σm and σeff are, respectively, the equivalent plastic strain, yield strain, hydrostatic stress, and equivalent stress (also known as von Mises stress). The rupture index was motivated by the research of Hancock and MacKenzie (1976) on the equivalent plastic rupture strain of steel for different conditions of stress triaxiality. The process of ductile fracture initiation is caused by high tensile triaxial stresses (i.e., high tensile hydrostatic stress) that result in damage accumulation through microvoid nucleation and coalescence. The ratio of hydrostatic stress-to- von Mises stress ( m/ eff) that appears in the denominator of (16) is called the triaxiality ratio (TR). High triaxiality can cause a large reduction in the rupture strain of a material, thereby limiting its ductility (Lemaitre, 1996). For instance, a value of triaxiality ratio in the range 0.75 < σm/σeff < 1.5 may cause a large reduction of the ultimate strength in metals, whereas a triaxiality ratio σm/σeff > 1.5 entails fragile behaviour Thus, locations in a connection with higher values for RI have a greater potential for fracture. The ratio of equivalent plastic strain-to-yield strain that appears in the numerator of (1) is called the plastic equivalent strain (PEEQ) index. This index is a measure of the local inelastic strain demand, and is also useful in comparing the different analyzed configurations. The PEEQ index is computed by:
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Dipartimento di Ingegneria Meccanic
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UNIVERSITÀ DEGLI STUDI DI TRENTO D
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Ai miei genitori
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INDEX 1 INTRODUCTION...............
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INDEX iii 4.10.3 Results of the PsD
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1.1 Introduction 1 1 INTRODUCTION I
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1. INTRODUCTION imposes precise con
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1. INTRODUCTION joints whilst 2D mo
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7 2 DUCTILITY AND SEISMIC RESPONSE
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2. DUCTILITY AND SEISMIC RESPONSE O
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4. SEISMIC RESPONSE OF PARTIAL-STRE
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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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6. SUMMARY, CONCLUSIONS AND FUTURE
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