Marco Donà

Reinforced concrete and masonry arch bridges in seismic areas: typical deficiencies and retrofitting strategies

In recent years, appraisal of the condition and rehabilitation of existing bridges has become an ongoing problem for bridge owners and administrators in all developed countries. Reliable methodologies are therefore needed in the assessment and retrofit design phases, to identify the vulnerability of each bridge class. The specific problems of common arch bridge types are discussed herein, for both reinforced concrete and masonry structures, proper interventions for their static and seismic retrofitting are illustrated and several examples of applications are provided. Retrofitting is usually coupled with functional refurbishment, according to a methodological approach that takes into account bridge characteristics, state of maintenance and functional requirements, and environmental aspects connected with repair and strengthening systems.

EFFECTIVENESS OF THE RBRL ISOLATION SYSTEM: EVIDENCES FROM SEISMIC TESTS AND NUMERICAL SIMULATION

The Rolling-Ball Rubber-Layer (RBRL) system was developed to enable seismic isolation of low-mass structures, such as works of art or special equipment, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through the independent choice of the system parameters. The paper presents new results from a previous campaign of shaking-table tests (PSTRBIS ECOEST 2 Project, 1999), related to a superstructure model consisting of two concrete slabs separated by four M16 studs 500mm long, which give a first mode fixed-base response at about 2.5 Hz. In particular, attention is given not only to the global behaviour of the system, which includes the steadystate rolling, but also to its small-deflections behaviour, influenced by the creation of pits in the rubber layer due to its viscoelastic properties. These experimental results are compared to those obtained from numerical simulations, conducted in OpenSees, using a FE fixed-base model previously calibrated using other shaking-table tests performed at fixed-base. These comparisons, isolated (test) versus fixed (model) case, are presented in terms of peak values of acceleration and inter-storey drift, time-history accelerations and displacements and by means of response spectra ratios for both the slabs, and show the effectiveness of the system not only at large displacement but also for small deflections if compared with an equivalent sliding isolation system. Attention is here restricted to uniaxial behaviour. Finally, some considerations are made regarding a possible characteristic frequency of roll-out of the balls from their initial pits. 391 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 391-406

ROLLING-BALL RUBBER-LAYER ISOLATION SYSTEM: STATE OF THE ART, PERFORMANCE AND DESIGN PROCEDURE

A rolling-ball rubber-layer (RBRL) isolation system was developed at TARRC to enable isolation of lightweight structures. The system is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through the independent choice of rubber spring and rubber-layer rolling track. It is suitable for isolating light structures, and much more effective at low excitations than an equivalent sliding system would be. In this paper the state of the art and the dynamic behaviour of RBRL isolation system will be restated. Subsequently, a simple and efficient procedure will be described for the design of the system: this is aimed to get the principal value of the system parameters to meet the chosen values of isolation period and damping ratio. In particular, it will be emphasized that a certain value of rolling resistance of the device could result from different combinations of the device parameters, thus leaving the final specification to be made on the basis also of preferences regarding small-deflection behaviour and cost. Finally, a future application of the isolation system for the seismic protection of a statue is presented and discussed.