Giovanni Tecchio

Simplified seismic assessment of railway masonry arch bridges by limit analysis

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 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.

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.

Limit analysis of transverse seismic capacity of multi-span masonry arch bridges

Thousands of road and railway masonry arch bridges are still in service in the Italian and European transportation network, and many of them are located in highly seismic areas. In this work, a kinematic analysis procedure is developed to assess the transverse seismic capacity of multi-span masonry bridges with slender piers, as they may be vulnerable to transverse seismic action. The procedure can calculate the limit horizontal load multiplier of overall collapse mechanisms involving transverse deformation of deck and piers. The procedure is then adopted in a parametric study describing the typical ranges of the main parameters influencing bridge transverse capacity. Parametric analysis yielded a set of iso-acceleration envelope curves which supply the resistant seismic acceleration of a bridge as a function of simple geometric parameters. The resulting graphs can thus be used for preliminary seismic assessments.

Static and seismic retrofit of masonry arch bridges: case studies

Thousands of road and railway masonry arch bridges are still in operati on in the Italian tran sportation network: most of them need being improved in their carrying capacity and to be upgraded to the standards of the current seismic code. In this paper three case-studies of the static and seismic retrofit of historical masonry arch bridges are presented, outlining some methodological approaches to the renewal intervention according to the different typological characteristics of the bridges and their state of maintenance. The main phases of work, combining both traditional and innovative strengthening techniques, are described. In the S.Gallo Bridge the load bearing capacity of the existing structure has been preserved and increased through a thickening of the old arch with a new layer of brick masonry and the application of CFRP laminates. Many refurbishment techniques, derived from the historical heritage restoration field, have been used for the Rio Moline Bridge, where new longitudinal internal brick spandrel walls connected to the extrados of the vaults have been built to share some of the load and enhance the seismic resistance. In the case of the Gresal Bridge the seismic vulnerability has been reduced by creating a new structural arrangement through a new rc slab anchored to the piers with vertical ties and restrained at the abutments, collaborating with the existing structure in carrying horizontal loads. Appropriate analytical models comparing the load bearing capacity before and after the repair intervention have been implemented to prove the effectiveness of the strengthening techniques. Bridge Maintenance, Safety, Management, Resilience and Sustainability – Biondini & Frangopol (Eds)

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.

Dynamic Modal Assessment of Old Reticular Steel Railway Bridges Undergoing Fatigue Deterioration

To reduce traffic disruption due to a live-cycle and seismic damage it is necessary to study the causes in infrastructures and bridges. When we talk about steel structures and in particular steel bridges, we know that they are very flexible and consequently easy to identify by ambient vibration methods. In a collaborative project between the University of Padua and the Italian Railway Authority, two old reticular steel bridges (1920) were subject to in-situ structural identification, demolition and consequent laboratory fatigue tests. On account to their similarity it was possible to acquire dynamic data for several days by using the same acquisition logger and 12 acceleration sensors After the data of the two analyzed reticular bridges have been filtered, accurate vibrating modes were identified by using both time and frequency domain techniques and the results were outstanding. In order to use best-fitted material characteristics in the elements of the structures, destructive and non-destructive tests were executed. The results permitted to realize very accurate finite element models and calibrate them for successive fatigue scenarios by comparing laboratory and numeric tests.

Seismic Intervention and Dynamic Testing of an Arch Bridge

This work presents the dynamic tests on a retrofitted masonry arch bridge. The Gresal Bridge, located in the North-East of Italy, was highly exposed to seismic hazard, due to the slenderness of its high piers. A retrofit intervention has been carried out, and a new rc slab has been built under the pavement, anchored to the piers with high strength vertical ties and restrained at the abutments, to create a new resistance arrangement withstanding inertial forces. The dynamic behaviour has been initially assessed with numerical models comparing the response of the bridge before and after the repair, and has subsequently been tested by the Output-Only technique to detect the variation of the modal response induced by the strengthening intervention. The dynamic tests have shown the structure to be more rigid than expected and, after calibration, a good agreement to exist between the numerical frequencies and the experimental records captured on the retrofitted bridge.