NON LINEAR STATIC AND DYNAMIC ANALYSES OF THE AUGUSTUS BRIDGE IN NARNI, ITALY: AN INSIGHT INTO THE MECHANICAL PROPERTIES OF ROMAN CONCRETE

Abstract eng:
The present paper is devoted to the discussion of the results obtained by a series of non-linear static and dynamic analyses performed on a relevant structural Roman artwork: the Augustus bridge in Narni (Central Italy). The Roman bridge, which was in origin arranged into four arches with a maximum span of approximately 32 m, is nowadays constituted by the lateral left arch and a portion of the right part of the abutment. As a matter of fact, it ruined some centuries ago because of a combination of different causes. A recent experimental investigation pointed out the role played by a vertical foundation settlement mechanism that took place at the base of the second pier and probably led to the collapse of the two central arches. In addition, the highly prone seismic area and the great variability of the mechanical properties of the Roman concrete used to construct the bridge clearly played a crucial role. The present work is aimed at investigating the influence of such parameters on the collapse of the original structure. To this scope, a 3D model has been created starting from the geometric survey of the original four arched bridge. The double leaf masonry used by Romans has been considered in the present analyses subdividing the adopted discretization into two materials: the Travertine stone adopted for the outer leaf and the Roman concrete used as filling. Two series of non-linear static and dynamic analyses are performed respectively applying: (i) a G1 distribution of the horizontal loads along the height of the bridge and (ii) a spectrum-compatible accelerogram with two components along the vertical and transversal directions. The results are comparatively assessed with respect to the experimental observations of the ruins of the Augustus bridge. Particular attention is focused on the global force-displacement capacity curve and the damage maps obtained at the end of the analyses. The numerical results, in addition to the experimental observations, clarified the strong negative effect that a vertical settlement of the ground had on the stability of the bridge.

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