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Energy dissipation and base isolation

Keywords: viscous dampers, hysteretic devices, base seismic isolation, HDRB isolator, application to new and existing buildings
Energy dissipation and base isolation - Fig. 1
Fig. 1. Viscous damper and Crescent-Shaped Brace as diagonal dissipative bracing systems (left: Taylor Devices Inc., right: Silvestri).
Fig. 2. Effectiveness of damper systems in shear-type structures (Silvestri).
Energy dissipation and base isolation - Fig. 3
Fig. 3. Rubber Bearing isolator and the FEM model of the ex-barracks Zucchi in Reggio Emilia (Trombetti).

Building structures must be capable of providing a high degree of safety compatible with today's society expectations. With respect to earthquake input, innovative techniques, as added dissipative devices and base isolators, seem to represent promising and feasible solutions for the achievement of adequate safety levels both for new and existing buildings.

Energy dissipation
The introduction of a system of added dampers allows the maximization of the part of energy dissipated in dampers and the minimization of the part of elastic energy absorbed by the structural elements. The high efficiency shown by these passive protective devices avoid the damage in the structural elements even in the presence of strong earthquakes.

The researches carried out at the University of Bologna in the last years have focused upon the:

- the search for the system of added viscous dampers capable of optimizing its dissipative effectiveness taking into consideration at once all possible dampers sizing and placement;
- the development of a practical 5-step procedure for the seismic design of building structures equipped with viscous dampers, which aims at providing practical tools for an easy identification of the mechanical characteristics of the manufactured viscous dampers which allow to achieve target levels of performances (also accounting for simplified design criteria for nonlinear fluid-viscous dampers);
- the proposal of simplified formulas (in terms of reduction factors for the earthquake forces) for the seismic design of structures which exploit the combined effects of viscous and hysteretic dissipation, as provided by dampers and by post-yielding behavior of the structural members, respectively;
- the development of a hysteretic dissipative device (Crescent-Shaped Brace), characterized by a peculiar geometrical configuration which is ‘‘ad hoc’’ defined in order to independently match target stiffness and strength values;
- the conceptual design of a first-storey isolated building capable of satisfying selected seismic performance objectives, through the insertion (only at the bottom level of the building) of the special CSB hysteretic device;
- several applications of dampers for the seismic retrofit of existing RC buildings.

Base isolation
The introduction of isolators at the base allows for the minimization of the input energy and for the reduction of the accelerations in the structure by an increase of the fundamental period of the isolated structure and a concentration of seismic demand at the isolation system level.

The research works have regarded in general the different typologies of isolation devices (e.g. High Damping Rubber Bearing, friction pendulum), the modeling of the devices, the design criteria, specific aspects (the effects of nearfield earthquakes on the response of baseisolated structures) and applications of PBSD approaches for the seismic retrofit, using base isolators, of existing masonry structures, such as the ex-barracks Zucchi in Reggio Emilia, and the Teatro Galli in Rimini.

Total number of publications: 80.

Main publications

Palermo, M., Silvestri, S., Landi, L., Gasparini, G., and Trombetti, T. (2016). Peak velocities estimation for a direct five-step design procedure of inter-storey viscous dampers. Bulletin of Earthquake Engineering, 14(2), 599-619.

Landi, L., Grazi, G., Diotallevi, P.P. (2016). Comparison of different models for friction pendulum isolators in structures subjected to horizontal and vertical ground motions. Soil Dynamics and Earthquake Engineering, 81, 75-83.

Palermo, M., Silvestri, S., Gasparini, G., and Trombetti, T. (2015). Crescent shaped braces for the seismic design of building structures. Materials and Structures, 48(5), 1485-1502.

Landi, L., Conti, F., Diotallevi, P.P. (2015). Effectiveness of different distributions of viscous damping coefficients for the seismic retrofit of regular and irregular RC frames. Engineering Structures, 100, 79-93.

Landi, L., Fabbri, O., and Diotallevi, P.P. (2014). A two-step direct method for estimating the seismic response of nonlinear structures equipped with nonlinear viscous dampers. Earthquake Engineering and Structural Dynamics, 43(11), 1641-1659.

Palermo, M., Silvestri, S., Trombetti, T., and Landi, L. (2013). Force reduction factor for building structures equipped with added viscous dampers. Bulletin of Earthquake Engineering, 11(5), 1661-1681.

Palermo, M., Muscio, S., Silvestri, S., Landi, L., and Trombetti, T. (2013). On the dimensioning of viscous dampers for the mitigation of the earthquake- induced effects in moment-resisting frame structures. Bulletin of Earthquake Engineering, 11(6), 2429-2446.

Silvestri S., Gasparini G., and Trombetti T. (2011). Seismic design of a precast r.c. structure equipped with viscous dampers. Earthquake and Structures, 2(3), 297-321.

Silvestri S., Gasparini G., and Trombetti T. (2010) A Five-Step Procedure for the Dimensioning of Viscous Dampers to Be Inserted in Building Structures. Journal of Earthquake Engineering, 14(3), 417-447.

Silvestri, S., and Trombetti, T. (2007) Physical and numerical approaches for the optimal insertion of seismic viscous dampers in shear-type structures, Journal of Earthquake Engineering, 11(5), 787 – 828.

Trombetti, T., and Silvestri, S. (2006) On the modal damping ratios of shear-type structures equipped with Rayleigh damping systems, Journal of Sound and Vibration, 292(2), 21-58.

Research projects

2014-2016: Progetto DPC-RELUIS, Linea di Ricerca 6: “Isolamento e Dissipazione”. Coordinatori Nazionali: Prof. F. Ponzo e Prof. G. Serino; Responsabile UNIBO: Prof. T. Trombetti.

2010-2013: Progetto RELUIS2, Area Tematica 2, Linea di Ricerca 3, Task 2: “Sviluppo ed analisi di nuove tecnologie per l’adeguamento sismico”; Coordinatori: Prof. L. Ascione e Prof. G. Serino; Responsabile UNIBO: Prof. T. Trombetti.

2005-2008: Progetto RELUIS, Linea 7: “Tecnologie per l’isolamento ed il controllo di strutture ed infrastrutture”; Coord. Naz.: Prof. M. Dolce e Prof. G. Serino; Responsabile UNIBO: Prof. M. Savoia.

2000-2002: Progetto di Ricerca di Interesse Nazionale 2000 (PRIN 2000, ex 40%): “Adeguamento sismico di edifici monumentali tramite isolamento sismico e materiali innovativi”; Coordinatore Scientifico: Prof. A. De Luca, Università “Federico II” di Napoli; Responsabile Scientifico Unità di Bologna: Prof. C. Ceccoli.