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 propagates in a stable way converting a large part of the absorbed energy into plastic work. Both the material characterization and the specimen failure mechanisms pointed out the need of fracture mechanics tests in order to define the fracture toughness of the base material in the elastic-plastic regime. These tests, performed according to the ASTM E 813-89 code (1989), permitted the determination of the critical value J1c, viz. the change of the elastic-plastic work per unit crack extension at the onset of stable crack extension. Moreover, the critical value of the crack tip opening displacement (CTOD), in agreement with ASTM E 1290-93 code (1993) was measured. It provides a unique estimate of localized plastic strain. The samples used to determine J1c embodied a mechanical notch that was sharpened with a fatigue pre-crack induced by a constant amplitude sinusoidal loading. The multiple- specimen technique was adopted being the specimens drawn from the end plate normal to the weld bead. After fatigue pre-cracking, the specimens were subjected to a displacement controlled three-point bending test up to the crack extension. A value of J1c equal to 115 kJ/m 2 was obtained in accordance with literature data (SAC Background Reports, 1997). In addition, the critical value of the crack tip opening displacement (CTOD) was measured. In detail, the crack mouth opening displacement was detected through a displacement gauge, by means of quasi- static bending tests on a pre-cracked specimen. A value of 0.31 mm was obtained, showing a good correlation with the corresponding J1c value. As a matter of fact, the J1c value can be converted into the CTOD index through the following relationship: J = mσ CTOD ( 3.1 ) 1c y where m is the so-called constraint factor. It is worthwhile to emphasize that CTOD values computed through the correlation in Equation (3.1) are approximate owing to the inherent variation of toughness properties of materials in building construction. 3.4.3 Testing equipment and measuring apparatus All specimens were tested in a rigid reaction frame, illustrated in Figure 3.6. In detail, ITS specimens were connected directly to the rigid counter-beam of the frame while a column stub was attached to the counter-beam in order to test CTS specimens as illustrated in Figure 3.6a. The loading arrangement relevant to CJ specimens is depicted in Figure 3.6b. The column is kept horizontal and hinged at both ends at the distance of 2000 mm while the horizontal loading is applied at the 53
3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS beam top. Displacements were applied to the free end of the specimen by means of a servo-controlled hydraulic actuator while a jack imposed an axial load of 300 kN to one column end. 54 Actuator Load Cell Reaction Frame Specimen 2970 530 a) b) 530 Hydraulic Actuator F, Specimen Jack N=300kN G G Reaction Frame 530 5060 530 Figure 3.6. Test set-up and boundary condition for: a) Isolated Tee stubs and coupled Tee stubs specimens; b) Complete Joint specimens. B B H A B B A C A A I H C I D(E) F D(E) F a) I D F E E H I H F D H I H Figure 3.7. Details of the measuring apparatus for a Complete Joint For brevity, only the instrumentation used in the CJ specimens is illustrated in Figure 3.7. It allows to detect the overall joint displacements as well as the contributions of the various components. In detail, displacement transducers (LVDTs) enabled detection of the following average quantities: 1. Connection uplift (LVDTs A); I I b)
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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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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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