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 REACTION FORCE (kN) 800 600 400 200 0 -200 -400 -600 -800 TC-3 JB1-3 (END PLATE) 0 1.5 3 4.5 6 7.5 DISPLACEMENT (mm) Figure 3.24. Comparison of the experimental response of TC-3 and End plate of JB1-3A Complete Joint EXPERIMENTAL EUROCODE 3 Ke Ke (kN/mm) Ke,code (kN/mm) Ke,code Component TC-2 C1A1-2 JA1-2A JA1-2B JA1-2M TC-2 C1A1-2 JA1-2 TC-2 C1A1-2 JA1-2 1 - - - - - - 248 205 206 - - - - - - 685 - - - - - - 0,3 6 - - - 744 334 236 633 - - - 776 776 - - - 1,0 0,5 7 1393 795 1979 428 2539 378 378 378 3,7 2,1 4,4 Component TC-3 C1B1-3 JB1-3A JB1-3B JB1-3M TC-3 C1B1-3 JB1-3 TC-3 C1B1-3 JB1-3 1 - - - - - - 266 286 256 - - - - - - 796 - - - - - - 0,3 6 - - - 1417 869 568 1093 - - - 3790 3790 - - - 0,4 0,2 7 3003 2363 2507 345 1931 1020 1020 1020 2,9 2,3 1,6 EXPERIMENTAL EUROCODE 3 Fp Fp (kN) Fp,code (kN) Fp,code Component TC-2 C1A1-2 JA1-2A JA1-2B JA1-2M TC-2 C1A1-2 JA1-2 TC-2 C1A1-2 JA1-2 1 - - - - - - 193 235 279 - - - - - - 288 - - - - - - 0,8 6 - - - 184 226 229 228 - - - 326 326 - - - 0,6 0,7 7 234 201 264 258 257 146 146 146 1,6 1,4 1,8 Component TC-3 C1B1-3 JB1-3A JB1-3B JB1-3M TC-3 C1B1-3 JB1-3 TC-3 C1B1-3 JB1-3 1 - - - - - - 344 352 469 - - - - - - 346 - - - - - - 1,1 6 - - - 322 388 422 379 - - - 564 564 - - - 0,6 0,7 7 417 359 417 423 402 396 396 396 1,1 0,9 1,0 Components: 1. Column web panel in shear; 6. Column flange in bending; 7. end plate in bending Table 3.6. Elastic stiffness ke and plastic failure strength f p of joint components The elemental components, which give the most significant contribution, have been considered. Joints JA1-2 and JB1-3 have been selected for their satisfactory performance and as representative of joints with thin and thick extended end plates respectively. Differences among the stiffness of the same elemental components 71
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS as part of different specimen are noticeable. However, it has to be noted that the initial stiffness is very sensitive to boundary conditions and lack of fit. Table 3.6 also gathers the elastic stiffness Ke,code computed in accordance with Eurocode 3 (2001). The stiffness ratios Ke/Ke,code lie in a wide range, with the level of accuracy of the EC3 models being generally unsatisfactory. With regard to the experimental plastic failure strength Fp, defined in accordance with the tri-linear approximation of the response envelope, the differences for the same component in different specimens are more limited than the ones for the elastic stiffness. However, they are still remarkable. Such differences are a consequence of the interaction, which affects the location and evolution of plastic zones. With regard to the Eurocode 3 prediction model, the plastic strength (Fp,code) was computed using measured material properties and no resistance factors. These strength values are also collected in Table 3.6. The Eurocode underestimates significantly the strength of thin end plates, while it tends to overestimate, even remarkably, most of the other components. This seems to depend mainly on the coupling effects among different components, which is not considered in the code. Moreover, non-seismic codes do not consider the development of low cycle fatigue phenomena, which lead to initiation and propagation of cracks, and affect the yield lines sequence. A further comparison relevant to the absorbed energy was limited to the 6th elemental component column flange in bending and to the 7th elemental component end plate in bending, which dissipate most of the energy within the connection. The comparison is performed with reference to the relation between the mean energy ratio and the displacement ductility in the i-th cycle (ECCS, 1986). The elemental component column flange in bending for component parts and joints embodying a thin (12mm) extended end plate showed similar mean energy ratios approaching values of about 0.7 in the coupled Tee stubs and in the complete joints, but ultimate positive partial ductilities e + u/e + y vary between 13 and 23, with the higher value related to the coupled Tee stubs. With reference to the 7th component, the ultimate partial ductility ranges from 9 (Complete Joint) to 13 (Isolated Tee Stub), while the mean energy ratios vary between 0.6 (Isolated Tee Stub) to 0.8 (Coupled Tee stub). A similar comparison for the 6th and 7th elemental components in joints embodying thick extended end plate of t =18 mm shows even greater differences of ultimate displacement ductility factors e + 72 u/e + y and maximum values of the mean energy ratios. An evaluation of these results leads to consider the component method not sufficiently accurate for approximating the cyclic response, at least for the joint configuration considered in the study. The extension of this model in seismic analysis does not seem straightforward, when
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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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