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 subject to cyclic loading, TC-2, experienced premature plate fractures at a hot spot of plastic strain concentration located at weld toes. REACTION FORCE (kN) 500 375 250 125 0 -125 -250 -375 -500 TM-2 TC-2 0 2 4 6 8 10 DISPLACEMENT (mm) Figure 3.10. Experimental response of TM-2 and TC-2 Isolated Tee stubs (a) (b) Figure 3.11. Collapse mechanism for (a) the TM-2 specimen; (b) TC-2 specimen As a result, cyclic loading reduces significantly both the ultimate strength and the displacement ductility factors. Close observation of the plate failure reveals that brittle fracture evolved in three sequential phases: i) the initiation of a ductile crack at the steel surface owing to plastic strains; ii) a stable growth of a ductile crack in 59
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS the plate thickness; iii) a sudden propagation of the crack in a brittle fracture mode. However, the test indicates that the fillet welds performed well and were able to develop the required cyclic strength. Similar considerations apply to the specimens with plate thickness equal to 18 mm. As expected, the specimen TM-3 was characterized by a Mode 2 failure according to Eurocode 3, with two yield lines located at the weld toes, whilst specimen TC-3 failed by plate fracture close to the weld toes following the same sequence described above for the TC-2 specimen. 60 REACTION FORCE (kN) 800 600 400 200 0 -200 -400 -600 -800 TM-3 TC-3 0 2 4 6 8 10 DISPLACEMENT (mm) Figure 3.12. Experimental response of TM-3 and TC-3 Isolated Tee stubs A comparative assessment of the hysteretic performances of TC-2 and TC-3 specimens can be based on the relation between the mean energy ratio (i.e., the ratio between the absorbed energy, averaged on three cycles, and the energy dissipated per complete cycle by an equivalent elastic-plastic oscillator) and the maximum ductility e/ey (ECCS, 1986). Such a comparison pointed out that: (i) owing to the Mode 1 failure pattern which involves four yield lines, the TC-2 specimen is able to absorb greater amounts of energy also at smaller ductility ratios; (ii) the ultimate displacement ductility factor e + u/e + y (see Figure 3.9) are 73 and 53 for the TC-2 and TC-3 specimen, respectively. Thereby, the TC-2 specimen performs better both in terms of absorbed energy and of ductility, as illustrated in Figure 3.13.
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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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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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