Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
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<br />
3.7 Numerical analysis<br />
In this section, <strong>the</strong> inelastic finite element (FE) analyses carried out by means <strong>of</strong><br />
<strong>the</strong> ABAQUS 5.8 code (Hibbitt, Karlsson & Sorensen Inc., 2001) both on isolated<br />
Tee Stub (ITS) connections <strong>and</strong> on Complete Joints (CJ) are discussed. Therefore,<br />
both FE models were calibrated <strong>and</strong> <strong>the</strong> stress <strong>and</strong> strain state <strong>of</strong> <strong>the</strong><br />
aforementioned connections was simulated both in <strong>the</strong> monotonic <strong>and</strong> in <strong>the</strong> cyclic<br />
displacement regime. Finally, some design parameters which influence <strong>the</strong> fracture<br />
resistance <strong>of</strong> steel bolted extended plate connections are commented upon. In<br />
detail, <strong>the</strong> effects <strong>of</strong> <strong>the</strong> weld-to-base metal yield strength ratio, <strong>the</strong> end plate yield-<br />
to-ultimate strength ratio, <strong>and</strong> <strong>the</strong> residual stress influence have been determined.<br />
3.7.1 FE Models <strong>of</strong> <strong>the</strong> ITS connections<br />
Non-linear FE analyses <strong>of</strong> <strong>the</strong> tested Isolated Tee-Stubs were carried out both in a<br />
monotonic <strong>and</strong> in a cyclic loading regime. As a matter <strong>of</strong> fact, 3D finite element<br />
analyses <strong>of</strong> bolted connections are very dem<strong>and</strong>ing from a computational<br />
st<strong>and</strong>point because contact problems as well as low-cycle fatigue phenomena<br />
need to be simulated. Hence, 2D models endowed with eight-node CPS8 plane<br />
stress elements were adopted to reduce <strong>the</strong> computational expense. Specimen<br />
symmetry permitted <strong>the</strong> <strong>modelling</strong> <strong>of</strong> only one half <strong>of</strong> <strong>the</strong> specimen.<br />
2D models exploited FE layers to reproduce <strong>the</strong> end plate <strong>and</strong> additional FE layers<br />
to simulate <strong>the</strong> bolt shank. The pre-stressing condition was introduced in <strong>the</strong> model<br />
imposing a stretching <strong>of</strong> <strong>the</strong> bolt shank, in order to entail a final average shank<br />
stretch equal to 0.065 mm, similar to <strong>the</strong> one detected during testing.<br />
Welding-induced residual stresses develop unavoidably in <strong>the</strong> welds <strong>and</strong> in <strong>the</strong><br />
base metal owing to <strong>the</strong>rmo elasto-plastic deformation. Therefore, an idealised<br />
stress magnitude/distribution as <strong>the</strong> one <strong>high</strong>lighted in Figure 3.28 has been<br />
introduced. Such distribution <strong>of</strong> residual stresses, which takes into account <strong>the</strong><br />
presence <strong>of</strong> <strong>the</strong> crack, was proposed by Monahan on <strong>the</strong> basis <strong>of</strong> experimental<br />
tests performed by Porter G<strong>of</strong>f <strong>and</strong> Payne (1985). More specifically, such<br />
distribution assumes that part <strong>of</strong> <strong>the</strong> residual stresses is released as <strong>the</strong> low-cycle<br />
fatigue crack penetrates <strong>the</strong> end plate, <strong>and</strong> that <strong>the</strong> remaining residual stress is<br />
somehow redistributed throughout <strong>the</strong> uncracked ligaments. Clearly, tensile<br />
stresses at <strong>the</strong> top <strong>and</strong> bottom end plate thickness are balanced by compression<br />
stresses. Such distribution has been imposed to <strong>the</strong> mesh through several trials in<br />
order to achieve equilibrium, compatibility <strong>and</strong> <strong>the</strong> proper stress magnitude<br />
required.<br />
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