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 defect) was modelled at the weld toe in order to investigate the behaviour of cracked connections. More specifically, cracking is studied through contour integral evaluation in order to infer J values. Therefore, focused meshes are set to induce the singularity at the crack tip and the crack propagation is not traced. Sharp cracks have to embody singular strain fields at the crack tip for fracture mechanics evaluations. Therefore, three nodes of the same side of eight-node isoparametric elements (CPS8) have the same geometric location at the crack tip to produce a 1/r strain singularity field. The FE mesh used for the ITS connections is illustrated in a. A detail of the mesh with a spider web configuration is reported in b where the innermost ring of elements degenerate to triangles, as described above. As the large-strain zone is very localised, sharp cracks adopted in the onset of cracking method are modelled using small-strain assumptions, and therefore large deformations are ignored. The FE analyses account for material nonlinearities using the von Mises yield criterion. Isotropic hardening is assumed for the analyses. In the analysis the measured stress-strain properties of the materials obtained by tensile test were used. The elastic modulus and the Poisson’s ratio were assumed as E=210000 and ν=0.3, respectively. Convergence studies on elastic and inelastic models have been conducted to evaluate and arrive at the final mesh for the finite element models. The finite element model was verified by comparing the measured experimental responses with the predicted response. The ITS connections endowed with end plate thickness of 12 mm and 18 mm, subjected to monotonic and cyclic loading respectively, have been simulated. A typical deformed configuration at failure is reported in Figure 3.30. It is possible to observe two different meshes relevant to the bolt shank and to the plate around the hole, respectively. Moreover, an attentive reader may observe how the crack with a fixed length of 2.34 mm exhibits a width increase at the tip. As a matter of fact, the nodes at the crack tip are untied in order to generate the singularity by means of inelastic elements. The reaction force vs. the controlled displacement relevant to the TM-2 specimen is illustrated in Figure 3.31a, where the numerical simulations are compared to the experimental response. One may observe that experimental data and numerical prediction are in a good agreement. The numerical simulation relevant to the cyclic regime of the ITS TC-2 connection and the experimental response are reported in Figure 3.31b. Only a few significant displacement cycles are simulated in order to reduce the computational effort. The specimen yield strength is well captured as expected owing to the use of the isotropic strain-hardening model. 77
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS 78 INTERFACE BOLT (a) (b) WELD BEAD CRACK Figure 3.29. (a) 2D FE model of isolated Tee stub; (b) details of the “spider web” mesh Figure 3.30. Deformed configuration of TM-3 specimen with the onset of cracking method (magnification factor 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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