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 3.7 Numerical analysis In this section, the inelastic finite element (FE) analyses carried out by means of the ABAQUS 5.8 code (Hibbitt, Karlsson & Sorensen Inc., 2001) both on isolated Tee Stub (ITS) connections and on Complete Joints (CJ) are discussed. Therefore, both FE models were calibrated and the stress and strain state of the aforementioned connections was simulated both in the monotonic and in the cyclic displacement regime. Finally, some design parameters which influence the fracture resistance of steel bolted extended plate connections are commented upon. In detail, the effects of the weld-to-base metal yield strength ratio, the end plate yield- to-ultimate strength ratio, and the residual stress influence have been determined. 3.7.1 FE Models of the ITS connections Non-linear FE analyses of the tested Isolated Tee-Stubs were carried out both in a monotonic and in a cyclic loading regime. As a matter of fact, 3D finite element analyses of bolted connections are very demanding from a computational standpoint because contact problems as well as low-cycle fatigue phenomena need to be simulated. Hence, 2D models endowed with eight-node CPS8 plane stress elements were adopted to reduce the computational expense. Specimen symmetry permitted the modelling of only one half of the specimen. 2D models exploited FE layers to reproduce the end plate and additional FE layers to simulate the bolt shank. The pre-stressing condition was introduced in the model imposing a stretching of the bolt shank, in order to entail a final average shank stretch equal to 0.065 mm, similar to the one detected during testing. Welding-induced residual stresses develop unavoidably in the welds and in the base metal owing to thermo elasto-plastic deformation. Therefore, an idealised stress magnitude/distribution as the one highlighted in Figure 3.28 has been introduced. Such distribution of residual stresses, which takes into account the presence of the crack, was proposed by Monahan on the basis of experimental tests performed by Porter Goff and Payne (1985). More specifically, such distribution assumes that part of the residual stresses is released as the low-cycle fatigue crack penetrates the end plate, and that the remaining residual stress is somehow redistributed throughout the uncracked ligaments. Clearly, tensile stresses at the top and bottom end plate thickness are balanced by compression stresses. Such distribution has been imposed to the mesh through several trials in order to achieve equilibrium, compatibility and the proper stress magnitude required. 75
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS 76 0 1/4 1/2 3/4 1 a/tp =0.13 -fy - 0 + + σ 11 +fy 0 1/4 1/2 3/4 1 y/tp Figure 3.28. Transverse residual stress distribution in a cracked plate Moreover, different mechanical properties are assigned to the base metal, the weld metal and the HAZ. Two-node gap contact elements are located below the end plate surface to cater for the unilateral contact condition imposed by the rigid counterbeam. In the finite element model, the gap between the bolt shank and the hole, about 1 mm, was modelled too. Hence, the contact between the shank and the end plate is modelled by using contact surfaces whilst the contact between the end plate and the nut is reproduced through gap elements. Moreover, the friction between the end plate and the column flange is neglected because its effects on the force-displacement response of this connection type are not significant (Bursi and Jaspart, 1998). At the weld toe where stress concentrations are expected, a refined FE mesh is adopted. A crack endowed with a length of 0.26 mm (small-to-moderate root 2 tp 1
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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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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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