Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS Component (1) (2) (3) End plate and column flange in bending (1) Concrete slab in compression (2) Web panel in shear (3) --- FRd .2 ≥ 1.3F Rd.1 ( + ) Rd.1 = Rd.3 F F FRd .2 ≥ 1.3F Rd.1 --- FRd .2 ≥ 1.3F Rd.3 F ≥ 1.3F --- ( + ) FRd .3 = F Rd.1 Rd.2 Rd.3 Table 4.2. Joint capacity design for sagging bending moment Component (1) (2) (3) Reinforcing bars and I bolt-row in tension (1) Beam flange in compression (2) Web panel in shear (3) ( + ) --- FRd .2 ≥ 1.3F Rd.1 FRd .1 = F Rd.3 FRd .2 ≥ 1.3F Rd.1 --- FRd .2 ≥ 1.3F Rd.3 ( + ) FRd .3 = F Rd.1 Rd.2 ≥ 1.3 Rd.3 Table 4.3. Joint capacity design for hogging bending moment F F --- As far as resistance is concerned, particular attention must be paid for the definition and calculation of the strength of the concrete slab in compression (component 2 in the Table 2) and of the column web panel in shear (component 3) 4.5.1 Concrete slab resistance Eurocode 8 Annex C (2002) contains some formulas that refer to the design of the slab and of its connection to the steel frame in moment resisting frames in which beams are composite T-beams comprising a steel section with a slab. The Annex has been developed and validated experimentally in the context of composite moment frames with rigid connections and plastic hinges forming in the beams; it is clearly stated that the expressions in the Annex have not been validated for cases with partial strength connections in which deformations are more localised in the joints. According to this Annex two conditions have to be fulfilled to ensure that a high ductility in bending is obtained: • early buckling of the steel part shall be avoided; • early crushing of the concrete of the slab shall be avoided. The first condition imposes an upper limit on the cross-sectional area AS of the longitudinal reinforcement in the effective width of the slab. The second condition imposes a lower limit on the cross-sectional area AT of the transverse reinforcement in front of the column. 111
4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS Under sagging bending moments, composite T sections can be ductile if the crushing of the concrete is avoided. The buckling failure of the steel walls normally does not control the ultimate limit state of composite beams under sagging bending moments, because of the connections between the upper flange and the concrete. To avoid concrete failure under sagging bending moment, the proportions of a composite steel-concrete section must be such that the steel on the bottom side yields before the concrete strain εc at the top of the section are too high; for reinforced concrete elements submitted to cycling loading, this is deemed to be satisfied when εc < 2·10 -3 , when the strains εs in steel are high enough to obtain the required local ductility µ. Under earthquake loading at the connection of beam to column, a sagging bending moment on one side, and a hogging bending moment on the other side, are transmitted to the column. This implies one transfer of forces from the steel part of the composite section, which takes place through steel connecting elements and for which a design practice does exist, and another transfer of two forces Fsc and Fst from the slab. Fsc is the resulting compression force in the slab, on the sagging moment side, while Fst is the resulting tension force of the re-bars, on the hogging moment side (Plumier et al, 1998). The transfer of the compression force Fsc from the slab to the column can be realised through two mechanisms, as illustrated in Figure 4.9. b c 112 F Rd1 h c F Rd1 (1−β)/2 F Rd2 (1−β)/2 F Rd2 A T A /2 S θ = 45° A /2 S F Rd2 Figure 4.9. Two basic mechanisms of force transfer from the slab to the column β/2 F Rd2 β/2 F Rd2 Mechanism 1 is the direct compression of concrete on the flange of the column. Mechanism 2 is a truss with two compressed struts and one steel tie in tension. This mechanism can be developed only when the column cross-section has some concave zones or special connecting devices on the sides. The design resistance of these two mechanisms can be estimated in a way similar to the one used in the design of reinforced concrete structure. The design resistance FRd1 of Mechanism 1 is simply:
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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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3. SEISMIC BEHAVIOUR OF BOLTED END
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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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