First-Order In-Plane Seismic Response of Roman Aqueduct Bridge Structures: Numerical Modeling and Application to the Antioch-on-the-Orontes Aqueduct (Antakya, Türkiye)

Roman aqueduct bridges are widespread across the seismically active Mediterranean, but their seismic response in areas of very high seismicity remains poorly documented. Here, we present a first-order numerical investigation of the in-plane seismic response of these structures and apply the approach to plausible structural states of the Antioch-on-the-Orontes aqueduct at Harbiye (Antakya, Türkiye), in a region affected by the 6 February 2023 Mw > 7 earthquake sequence. The monument records several construction phases, repairs, and partial collapses. We use modal and linear time-history analyses of simplified 2.5D arch-and-pier finite-element models, with recorded historical ground motions applied in the longitudinal plane of the structures. We test the influence of pier height, arch width, deck thickness, reinforcement, stiffness, Poisson’s ratio, and density. The models repeatedly show stress concentrations at the arch springings and pier bases. Higher piers, wider arches, thicker decks, lower stiffness, and greater structural mass increase the calculated response, whereas buttresses, larger piers, and lower density reduce it. In the Antioch models, several zones of high calculated elastic demand coincide with observed damaged, collapsed, or repaired sectors, and the reinforced configuration shows lower stress concentrations than the comparable unrepaired one. A literature-based benchmark shows that the calculated Harbiye modal frequencies are of the same order of magnitude as experimentally identified frequencies reported for comparable masonry aqueducts and historical arch structures. However, no experimental dynamic characterization is available for Harbiye, and the monument-specific models have not been calibrated or validated. The results should therefore be interpreted as preliminary estimates of plausible first-order response patterns rather than as a quantitative seismic assessment of the existing monument.