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

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6. SUMMARY, CONCLUSIONS AND FUTURE PERSPECTIVES c. connections with σy/σu = 0.9 exhibit reduced fracture driving force demands but also limited plastic regions. The yield-to-ultimate strength reduction must comply with the requirements of plastic analysis. Besides, the study is currently concentrating on the damage evolution aspect both for the components and the joint. The availability of adequate damage assessment methods is a pre-requisite to the development of reliable hysteretic models for research as well for design purposes. The confirmation of the above-mentioned conclusions to the complete joints tested deserves further studies. 6.2.2 Seismic response of partial-strength composite joints The objective of this study was the investigation of the seismic performance of a realistic size moment resisting frame structure of high ductility class according to Eurocode 8 (2002) under various levels of earthquake. Dissipative elements were conceived to be partial strength beam-to-column joints and column base joints at later stages. Some full-scale substructures, representing the interior and exterior joints, have been subjected to monotonic and cyclic tests at the Laboratory for Materials and Structures Testing of the University of Pisa in Italy. Experimental results and three-dimensional finite element analysis of composite substructures has allowed the composite joints to be calibrated; and some inelastic phenomena characterizing their behaviour, such as the distribution of longitudinal stresses in the composite slab around the composite columns and the distribution of stresses in the column web panel and flanges to be understood. Moreover, analyses have demonstrated the adequacy of three-dimensional finite element models based on the smeared crack approach. The parametric analyses conducted both on exterior and interior joints have revealed that the full activation of Mechanisms 1 and 2 in the concrete slab causes a stiffening and strengthening of joints. This represents the most favourable design situation also due to a substantial increase of the effective breadth. Nonetheless, the aforementioned mechanisms have not the same stiffness, exhibiting Mechanism 1 a greater stiffness than Mechanism 2. Therefore, it is not easy to benefit from the strength of both mechanisms. For the exterior joint the full activation of Mechanism 2 is the mot favourable design situation, while for the interior joint Mechanism 1 seems to be more effective, owing to the interaction phenomena between the two parts of the composite slab. The quantification of the stiffness corresponding to the activation of Mechanism 1 and of Mechanism 2 analysed in the parametric study performed in this work clearly imposes further study. Simulation and implementation in FE codes of the deteriorating behaviour of dissipative components of the joints, by means of robust hysteretic models, deserves further studies. 247
6. SUMMARY, CONCLUSIONS AND FUTURE PERSPECTIVES Subsequently, a new mechanical model of the partial strength beam-to-column joint has been described. The model, which still relies on experimental data, is capable of simulating the behaviour of the steel-concrete composite partial strength joints subjected to monotonic loading. In detail, the model is capable of defining yielding and failure evolution of different components. The component models of the slab have indicated clearly that the compressive strut strength of the composite slab bearing on the column flange depends on the shear stiffness of the column web panel. Moreover, the activation of diagonal compressive struts on column sides induced by transversal reinforcing bars is hindered by the direct bearing of the compressive strut. Some force-displacement relationships provided by the proposed mechanical model have been compared with analytical formulae and current European standards. The principles set forth have then been applied to the design of beam-to-column joints and columns of a full-scale frame structure that was built and subjected to pseudo-dynamic tests at the ELSA Laboratory of the Joint Research Centre in Ispra. The construction of the full-scale structure proved that the construction of steel-concrete composite structures with partial strength beam-to-column joints and partially encased columns is highly efficient. Pseudo-dynamic and cyclic test results confirmed that properly designed and constructed partial strength beam-to-column joints and partially encased columns without concrete in column web panels exhibit a favourable behaviour in terms of energy dissipation, limited strength degradation and ductility. 6.2.3 Seismic behaviour of RC columns embedding steel profiles This part of the Ph.D. thesis has been written with the intent of underlining the importance of the studies conducted on Innovative Beam-to-Column Composite Joints in order to provide the reinforced concrete structures of the necessary amount of ductility in those critical zones usually strongly affected by the occurrence of seismic events. The general recommendation is to reinforce some strategic points of the building, as the joints of the 1 st storey, allowing in this manner to save the structure from a global collapse due to localised brittle type of failures. Both the solutions studied, with long and short steel profile encased in the concrete column, as expected, revealed to be effective in order to greatly improve the performance of the concrete members in terms of strength and ductility at large deformations. In fact, it can be stated that also the short steel profile stump is able to guarantee an adequate amount in terms of resistance and ductility at the joint critical region, even if some inconveniences occurred in the column length between the joint and the inflection point. It means that, a not accurate constructive process 248
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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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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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