Large-Scale Structures : Time-Dependent Behavior and Stability

Research focus

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The research focus of the group is the analysis of the complex structural problems arising in largescale structures as result of the delayed deformations due to concrete shrinkage and creep, that affect structural stability as well. In more detail, three types of structures have been studied: -Bridges. Composite bridges: the focus was the long-term sectional behavior, with rigid and flexible connections, with specific reference to: - statically-redundant composite members with flexible connectors; - prestressing effects; - simplified algebraic formulations of the viscoelastic laws. A further research topic has been the analysis of RC members subjected to the combination of axial load, bending moments in two orthogonal directions and torsion. A new approach to the analysis of composite curved bridge beams has been developed. Cable-stayed bridges have been investigated as well within the framework of homogeneous viscoelastic structures interacting with elastic restraints. Several analyses have been performed by using the Reduced Relaxation Function Method, previously developed by the research group. In particular, the very complex problem concerning the effects that the application of deck prestressing in different steps has on the time variation of the forces acting in the stays has been solved in a rather general way, by introducing concrete visco-elastic behavior, something which so far had never been done. Launched PC bridges have been studied with specific reference to the transient phases of bridge launching. In these phases, the restraint configuration evolves continuously as long as the bridge moves forward. Consequently, evaluating the state of stress and deformation becomes very demanding, since the viscoelastic problem of a non-homogeneous structure with a complex stress history has to be solved. The main results consist in the implementation of a refined analytical model capable of describing the various steps of the transient phases and numerically solving in the time domain the system of Volterra integral equations which are coupled with the differential compatibility equations in the space domain. -Precast structures. Thin-walled RC beams and precast concrete frames have been investigated. The first topic included the evaluation of the effects that closing the transverse section by means of a continuous slab extending along the beam or limited to the end regions has on the structural behavior. Refined studies have been also carried out in order to optimise slab size with reference to an actual beam, thereby defining the best configuration. For the precast frames, the transformation of pinned beam-column connections into rigid connections has been investigated by placing prestressing cables with variable eccentricity along the beams and by anchoring them to the outer surfaces of the external columns. The prestressing induced compressive stresses in the joints through controlled eccentricity,thereby avoiding any tensile stress in the service stage. The results obtained in this research project gave useful indications for a number of practical applications. -Buildings. High-rise buildings exhibiting non-regularities either in plan or in elevation were studied in regard to the shear-resistant members, which are subjected to extra forces and bending moments due to eccentricity of the vertical loads. The permanent part of these loads generates a constant horizontal force on the shear-resistant elements, causing in turn an in-time growth of the lateral displacements of the whole structure due to concrete creep. The ensuing bending coupled with torsion induces some time-dependent effects which have been extensively studied, also taking into consideration the difference in age of the various shear-resistant elements. The solution of this problem was previously limited to the elastic behavior.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Full Professors
Franco Mola
Marco Andrea Pisani
Gianpaolo Rosati
Assistant Professors
Sara Cattaneo