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

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4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS by means of a macro-level approach for concrete fracture, in which plain concrete is assumed to be an equivalent isotropic continuum. The material model for concrete is developed within the framework of the theory of plasticity. Though it does not predict explicitly crack initiation and evolution, as the companion model based on the coaxial rotating crack formulation does, it is more doubtless robust from a computational standpoint. In particular, the pressure-dependent Drucker- Prager yield criterion formulated in stress space is adopted. Figure 4.38. General view and details for the 3D Finite Element (FE) model of the CJ-EXT specimen 143
4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS The two material constants are linked to the Mohr-Coulomb constants, viz. the cohesion and the angle of internal friction, by matching the fictitious tensile strength ft and the biaxial compressive strength f’bc of concrete according to transformation formulae in Chen (1982). Moreover, a non-associated flow rule is exploited. The strain-hardening behaviour of concrete is governed by means of the stress-strain law of concrete in uniaxial compression or uniaxial tension, complemented with appropriate post-peak softening rules. In detail, the tension-softening behaviour of concrete related to its progressive fracturing or tension-stiffening behaviour owing to the presence of reinforcements is reproduced with exponential decay curves (Stevens et al, 1991). Confining effects owing to transversal reinforcements and profiled-steel sheeting are considered in the compression regime by means of the model of Mander et al. (1988). The concrete model does not embody the specific fracture energy Gf, to overcome mesh-dependent results (Hilleborg et al, 1976). However, as the concrete slab is moderately reinforced both in the longitudinal and transversal direction, the mesh-dependency is small. Moreover, the FE analyses account for steel 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. Longitudinal rebars in the slab are assumed to be made with a hardening elasto- plastic material and modelled using discrete two-noded beam elements for 3D models. The discrete representation of the reinforcements is adopted because the influence of bond-slip is of interest. Thereby, dimensionless bond-link elements are adopted to connect concrete and steel nodes. In detail, the bond stress-slip relation is modulated according to the law proposed in Stevens et al. (1991). Friction between the structural steel and the concrete slab is not modelled because it has little influence on the substructure responses. Elastic and inelastic convergence studies have been conducted to evaluate and arrive at the final mesh for the finite element models. The reaction force vs. the controlled displacement is illustrated in Figure 4.39, where the numerical simulations are compared to the envelope curve of the cyclic experimental response. One may observe that experimental data and numerical prediction are in a good agreement. Under sagging bending moment the specimen yield strength is well captured as expected; moreover the numerical simulation captures very well the hardening branch of the experimental response, both in term of strength and stiffness; this indicates a satisfactory behaviour of the numerical model. The model clearly shows the evolution of the distribution of the principal stresses of compression in the slab for the specimen subjected both under sagging and hogging bending moment. 144
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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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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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6. SUMMARY, CONCLUSIONS AND FUTURE
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