Structural Seismic Analysis of the Great Portico of Medina Azahara

Abstract

The Great Portico of Medina Azahara is a prominent remnant of the 10th-century Caliphate of Córdoba. Once the monumental entrance to the Caliph’s palace complex, it is now a partially preserved four-arched masonry structure. The site is a UNESCO World Heritage monument of major cultural significance. This study investigates the seismic response of the existing remains of the Great Portico using finite element modelling and nonlinear pushover analysis. It aims to identify its dominant vibration modes, primary failure mechanisms, and the points of concern for damage due to seismic loading. The study adopted a continuum homogeneous modelling strategy. Multiple three-dimensional finite element models were constructed in an iterative approach. Due to lack of in-situ measurements, the model geometry was approximated based on detailed drawings of the structure. Three building materials were defined: limestone masonry, brick masonry and limestone. Boundary conditions fixed the column bases, and loading consisted of the self-weight followed by a modal pushover analysis. The dominant eigenmodes were determined using an eigenmode analysis. Both the in-plane and out-of-plane responses of the structure were analysed. The in-plane response is characterized by tensile cracking in the arches’ brick masonry and at the interfaces between brick masonry and limestone blocks. The out-of-plane response had the most critical failure mechanism. Cracking in the limestone masonry initiated at the bases and mid-height of the columns, leading to tensile failure and toppling of the second arch. However, the overall capacity of the Great Portico, estimated at approximately 1.0 g, is relatively high compared to results from shake-table tests on masonry structures. Sensitivity analyses demonstrated that halving the tensile strength had minimal influence on global capacity, while reducing stiffness decreased peak base shear but did not alter failure modes. Crushing was observed only at high displacements, well after tensile cracking dominated the response, confirming that tensile failure controls the seismic vulnerability. In conclusion, this study indicates that the remaining part of the Great Portico is most vulnerable under out-of-plane loading, leading to tensile cracking in the limestone masonry of the columns. The in-plane response, while stronger, is controlled by cracking within the brick masonry in the arches and at the interfaces between the brick masonry and limestone blocks. Crushing failure is not governing for both mechanisms.