Advanced Seismic Design of Innovative Precast Systems for Structural Response Control

Abstract

Emerging Design Philosophy. In current design philosophy a key concept is ductility, a parameter that reflect intrinsic energy dissipation capacity of structural elements. The key concept is the reduction of the structural cost, from the point of view of the initial cost, for design under moderate or important earthquake levels assuming possible damages at structural and non structural elements but ensuring the Life Safety. However, when the ductility of the elements is activated damage is introduced. Since, the described philosophy has been introduced, a lot of buildings have been designed and constructed. They have been subjected to various earthquakes and the obtained performances make evident the limits of this design philosophy. The considered arguments require the development of structural systems able to realize higher structural performances under level of the earthquakes moderate or severe. The most serious obstruction is the increase in cost. If substantial increase in cost is not required, compared with those required in ordinary buildings then, it is rational to design buildings characterized by absence of damage even for very rare earthquakes and a such design will be accepted by the society. Therefore, we should changeover the direction of technology development from cost reduction keeping same performance level to higher performance level without cost increase. Advanced Seismic Design Methodologies and Procedures. The characterization of systems with higher structural performances calls for the introduction of design methodologies able to defie the structural response in a more efficient and detailed. In the cost analysis, costs related to Non Structural component and contents (NCs) are usually dominant, especially for buildings with relevant impact for society. The response of NCs must be carefully characterized, and must be taken into account. In particular, the interaction between structural and non structural components must be properly investigated. Evidently, Performance based seismic Design Methodologies largely developed in the research field, are necessary and should be apply, even by practitioners engineers. In the comparison with Strength Based Seismic Design Procedures, Displacement Based Seismic Design Procedures appear to be more appropriate to better achieved the performance objectives. A displacement Based Seismic Design Procedure via Inelastic Displacement Ratio is highlighted and an analysis of Inelastic Displacement Ratio-key aspect in the mentioned procedure-is developed. Innovative Systems applied to Precast Concrete Structures. The introduction of innovative structural systems for seismic response control is particularly effective for precast prestressed concrete structures. Precast structural elements, produced in the factory and trucked in the construction site, must be appropriately connected. The necessity to realize appropriate connections and to introduce a dissipation capacity not involving damage to structural elements make attractive the introduction of new systems, not based on the cast in place emulation, where connections are designed to develop a specific deformation pattern, independent from the large seismic action variability. The displacement capacity is basically related to the deformability in post-tensioned partially unbounded steel strands that, provided the elastic behavior, guarantee re-centering capacity, removing any residual deformation. The well-defined deformation pattern and the dissipation capacity concentration in external metallic energy dissipators give to the structure a reliable dissipation capacity, easily replaceable without relevant additional costs. Thanks to the introduced characteristics the conceived structural system improves performances of traditional precast concrete buildings without a sensible variation in the cost production.