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

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5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES 5.7.4 Concrete compression field mechanism verification In the numerical model the stirrups in the column are not directly modelled; the confinement effect is taken into account by a modification of the effective concrete stress-strain relationship. Nevertheless, the activation of the concrete compression filed is verified by means of the strain gauges positioned in the stirrups. As evidenced in Figure 5.44, with the increase of the imposed top displacement the stirrups were mobilised to transfer the shear forces into the joint. At elevated displacements 8ey÷10ey, the transversal re-bars are subjected to high tensile stresses that should equilibrate the compression struts in the outer concrete part of the joint. The equilibrium of forces results satisfied by the tension and compression stresses in the longitudinal re-bars, which transfer the relative component of the compression strut into the column. The evolution of the tensile and compression stress in the column is reported in Figure 5.45, and was obtained through the elaboration of the numerical results. It is also possible to underline that, at elevated imposed top displacements, the deformations of the longitudinal re-bars in the panel zone increase due to the tensile and to the compressive forces transmitted by the concrete. SG-20 SG-19 SG-18 SG-17 SG-16 SG-15 500 400 300 200 100 0 -0,0005 0,0005 0,0015 0,0025 0,0035 Figure 5.44. Evolution of the measured strain in the stirrups of the column ey / 4 ey / 2 3/4 ey ey 2ey 4ey 6ey 8ey Elastic range The Bond Resistance Vjoint,bf is provided by the longitudinal reinforcing bars acting in friction with concrete and embedded in the outer joint region. The bond failure occurs in the outer elements if the compression and tension forces (due to moment equilibrium), along with the forces mobilised in the concrete compression field, are greater than the strength of the bond mechanism of a set of main longitudinal re- 237
5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES bars. In Figure 5.45, the strain values measured by means of the strain gauges stuck on the longitudinal re-bars of the column are reported. The augmentation of the strains tied to the increase of the top displacement can be noted. 238 SG-14 SG-12 500 400 300 200 100 0 0.0000 -100 -0.0003 Figure 5.45. Strains of the longitudinal re-bars of the column 5.7.5 Calibration of the mechanisms ey / 4 ey / 2 3/4 ey ey 2ey -0.0005 By means of the analysed numerical results it was possible to verify the activation of the proposed shear transfer mechanism in the joint. Moreover, by means of a detailed analysis of the stress and strain evolution obtained from the numerical model it was possible modify in the proposed analytical formulas the values of some geometrical and mechanical parameters. In detail, the most important geometrical parameter that influences the shear resistance of the joint is the depth of the joint itself, jh that is utilized both in the interior mechanisms and in the exterior mechanisms evaluation. By the analysis of the numerical results (see Figure 5.46) it was possible to determine that: • for the steel web panel mechanism, the joint depth jh can be taken equal to the distance ds of the stiffeners welded to the column; • for the concrete compression strut, the joint depth jh can be taken equal to 0.9ds the distance of the stiffeners welded to the column, due to the fact that the center line of the compression results interior to the stiffeners; • for the concrete compression filed mechanism, the joint depth jh can be taken equal to 1.1ds the distance of the stiffeners welded to the column, due to the fact that the center line of the shear force results localized at the level of the reinforcing bars in the beam.
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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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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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