Seismic Analysis of Historic Masonry Structures

Piranesi 2

The study of historic masonry structures has been a field of increasing relevance over the past few decades, with a growing interest in society on the conservation of the built heritage. This has motivated extensive work on the performance of masonry vaulted structures, including the study of their stability, their material properties, or suitable retrofitting techniques. Most of this work, however, has been devoted to the static behaviour of these constructions, with fewer works exploring the effect of dynamic loading. Seismic loading, nonetheless, can be a particularly harmful type of loading on masonry structures, as we are reminded at every seismic event that hits an inhabited region around the world and deserves attention. 

Based on the principles of limit analysis corroborated for their application on masonry structures by Heyman in the 1960s, an interesting research path for dynamic analysis has been built considering arches as idealised mechanisms (Oppenheim, 1992: “The masonry arch as a four-ling mechanism under base motion”) under the effect of horizontal inertial forces from the ground motion. Under the effect of large enough inertial forces, a number of hinges will open in the arch and its behaviour can be idealised as that of a mechanism with rigid elements.

Basilica photo 1This interesting approach has been developed mainly for the idealised, constant thickness and constant density arch, but not enough work has been done on its application to real structures of more complex geometries, and more complex failure mechanism. 

Our work aims to explore these ideas further by applying them to a real structure. This will serve two purposes: developing new studies for more complex, realistic structures, while at the same time deepening our knowledge on the chosen structure.

The case study we have selected is the Basilica of Maxentius in Rome. Built between 307 and 313 AD, this building features the largest opus caementicium vaults known to have been constructed during the Roman Empire. With barrel vaults of over 23 m span, and groin vaults of outstanding 23 x 25 m span, the structural design of this building is challenging, pushing the boundaries of roman concrete vault construction the same way the Pantheon pushed the boundaries for the case of domes.

Maxentius engravingOne of the three original naves of the building is preserved, the other two having collapsed allegedly due to an earthquake sometime in the early Middle Ages. We are hoping that our work can help us know more about this collapse, as well as about the future behaviour of the remains under a probable earthquake in the Roma area. Some of the questions we want to answer are:

  • What was the likely collapse mechanism developed in the original structure?
  • What magnitude earthquake could the remains withstand in their current configuration?
  • Is any reinforcement necessary, or at all advisable? What would be the best reinforcement technique?