In this work, the seismic capacity of single and multi-span masonry arch bridges was assessed by limit analysis. A preliminary statistical survey was carried out on a stock of about 750 railway bridges in Italy, classified according to characteristics and expected collapse mechanisms under seismic excitation. A comprehensive parametric study was carried out on identified homogeneous classes, to calculate limit horizontal accelerations triggering the collapse mechanism in longitudinal and transverse directions. Iso-acceleration envelope curves, representing limit horizontal acceleration\ud of the bridge as a function of geometric parameters, were then derived. These graphs can be used for preliminary seismic safety checking of existing masonry bridges, once the main geometric parameters are available by simple visual inspections and geometric surveys, and can easily be implemented in a Bridge Management System to prioritise seismic retrofitting interventions
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
Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the limit analysis method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic analysis. The process involves determination of the collapse mechanism, calculation of the limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05-1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity
The Rolling-Ball Rubber-Layer (RBRL) system was developed to enable seismic isolation of lightweight structures, such as special equipment or works of art, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through choice of the system parameters.The necessity to have a simple and effective design procedure has led to a new parametric experimentation at Tun Abdul Razak Research Centre (TARRC) on the rolling behaviour of the RBRL system and load-deflection behaviour of the recentering springs. The experimental results, together with theories for the rolling resistance of a loaded steel ball on a thin rubber layer and the lateral load-deflection behaviour of cylindrical rubber springs, are used to develop a general design method for the RBRL system, which allows the system to be tailored to the specific application.Sinusoidal test results are presented for the small-deflection behaviour of the system, influenced by the presence of a viscoelastic depression on the rubber tracks beneath each ball, and an amplitude-dependent time-domain model is proposed, based on these results and on the steady-state behaviour of the system. The model is validated through comparison with previously performed shaking-table tests. Attention is here restricted to uniaxial behaviour.
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