Impact of the soil-foundation-structure interaction in the seismic behaviour of a heritage masonry tower: The Giralda of Seville

The seismic safety of heritage buildings may be affected by the interaction between the soil, the foundation and the structure, which is usually neglected in conventional seismic assessments. These factors are particularly important in the case of slender constructions, such as masonry towers, over soft strata. Hence, this work deals with the influence of the soil-foundation-structure interaction in the seismic behaviour of complex heritage masonry towers. The investigations have been carried out considering the case study of the Giralda tower in Seville, Spain. The region is an earthquake-prone area, characterised by far away very large earthquakes with long-return periods. The Giralda tower is a slender brick unreinforced masonry tower, 95 m high and about 13 m wide. It features a high artistic value and popularity as it has been the historical symbol of the city. It was declared a UNESCO Word Heritage Site of Outstanding Universal Value in 1987. Apart from its slenderness, the tower presents some other seismic vulnerabilities: openings irregularities, material heterogeneity and the position of a belfry on the top. Furthermore, the building is placed on soft alluvial strata and has a shallow foundation. Likewise, the tower has a considerable weight, which has caused large settlements. A thorough evaluation of the soil, the foundation and the structure has been carried out to develop a complex and detailed finite element model. Macro mechanical elements and the direct method have been used to develop the numerical model of the tower in the OpenSees framework. Free ambient vibration tests and non-destructive experiments have been used to calibrate the model. Its dynamic behaviour has been evaluated considering the seismic action suggested by the Spanish Code and those determined through a seismic response analysis, bearing in mind different return periods and considering real ground motions. Finally, the numerical results showed that the effect of the soil and the foundation have a significant impact on the seismic behaviour of the bell tower, amplifying the acceleration and its damage at the top.