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

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5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES column, concrete) obtained by test were used. Moreover, the confinement of the concrete due to the presence of the stirrups in the region of the joint is implicitly taken into account. As said in Subsection 5.3.1, the confinement results in a modification of the effective stress-strain relationship: higher strength and higher critical strains are achieved. Figure 5.39. 3D numerical model of the COT9 specimen Forza (KN) 150 125 100 75 50 25 media numerica cot9 cot11+ cot11- Curva F-∆ 0 0.00 2.00 4.00 6.00 8.00 10.00 Ampiezza ciclo (e y) Figure 5.40. Predicted vs. numerical response of the specimen COT9 231
5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES Elastic and inelastic convergence studies have been conducted to evaluate and arrive at the final mesh for the finite element models. The finite element model was verified by comparing the measured cyclic response of specimen with the predicted monotonic (see Figure 5.40). As far as concerns the cyclic test, the envelope curve of the experimental tests was found and compared to the curve found using the finite element model. Even if the model is not able to capture the loss of resistance and stiffness due to the crushing of the concrete after a certain level of the imposed displacement, the experimental data are in good agreement with the numerical simulation. The elaboration of the numerical evidences has led to the modification of some geometrical and mechanical parameters related to the formulae and it has permitted to better figure out the experimental response of the joint subjected to shear loading. Also the measurements obtained from the local instrumentation by means of strain gauges helped in the understanding of the activation and evolution of the resistance mechanisms, proposed in Section 5.4, while testing. 5.7.2 Steel web panel shear mechanism verification By means of a set of elements extracted in the web panel zone of the steel profile, it was possible to monitor the evolution of the shear stress σ13 at the increasing of the imposed top displacement. As depicted in the following Table 5.16, and as expected, the stress state of web panel increases during the test until it yields uniformly for a top displacement equal to 6ey. From this point the concentration of the stresses moves in the four corners of the steel web panel, where the stiffeners are welded. In this moment the resistance of the panel zone in the steel profile is given to the contribution of four plastic hinges that have been formed. This hypothesis results confirmed analysing the experimental results obtained from the strain gauges positioned in the web and in the flange of the steel profile in correspondence of the stiffeners. The graphs below, deduced from the experimental data (strain gauges), give explanation of the shear mechanisms activated in the steel web, steel flanges and stiffeners. To obtain the shear strain by the measurement the hypothesis that the principal stress σ1 and σ3 are aligned with the axes of the steel column is made. As depicted in Figure 5.41, the measured web strain increases uniformly up to a displacement equal to 4ey÷6ey when it exceeds the steel yield strain. It is the central zone of the panel that deforms most. It can be imagined the web stresses increasing during the test until the panel zone yields uniformly for a top displacement equal to 6ey. From this point on, concentration of stresses shifts to the four corners of the steel web panel in correspondence of the stiffeners, and the resistance of the panel zone is given by the contribution of these four local plastic hinges. 232
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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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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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