Seismic behaviour of the first modern high-rise buildings in Mexico City: lessons for future design

The seismic resilience of early reinforced concrete (RC) high-rise buildings in Mexico City presents a compelling engineering paradox: many 75-year-old legacy structures remain functional despite being designed under outdated codes and lacking ductile detailing. The construction of tall buildings in Mexico City has faced significant challenges because of complex regional conditions, including soil subsidence, variations in groundwater levels, and seismic activity. The earliest tall buildings, constructed in the early 1930s, featured skeletal metal structures. From the 1940s onwards, reinforced concrete became the primary structural material, mirroring the development of the Modern Movement in Mexican architecture. Buildings within the new University Campus of Mexico were constructed during this period, with two of them being the tallest reinforced concrete high-rises in Mexico City at the time. This study investigates the seismic behaviour of two high-rise buildings designated UNESCO World Heritage Sites, which have sustained only minor damage despite repeated exposure to major earthquakes. Nonlinear three-dimensional finite element models were developed under fixed-base conditions. A total of 52 bidirectional ground motion records, comprising eight motions representative of rocky soil, eight of transitional soil, and ten of soft soil in Mexico City, were employed for linear and nonlinear time-history analyses. Key seismic response parameters, including elastic and inelastic interstorey drifts, global damage indices, and code-defined damage states, were evaluated under fixed-base conditions. To validate the analytical results, a qualitative evaluation based on a physical condition assessment was conducted. The results show that, even though both buildings were designed under an incipient Mexican seismic code with low acceleration values, vulnerability increases significantly in transitional and soft soils. They exhibit adequate seismic behaviour, a low global damage index, and a low vulnerability level, given the rocky soil on which they are settled. Both buildings were analysed in accordance with their original structural design. The numerical results are consistent with the rapid visual damage assessment of the buildings conducted in this study following the 2017 Puebla earthquake. These results also offer lessons for future building design: a critical ‘drift-damage paradox’ was identified; when reinforced concrete frame buildings were relocated over transition or soft soils, their damage index increased significantly, leading to severe damage and drift values below the code limits. Building codes should be reviewed for these systems. Even though both buildings have an acceptable level of seismic damage, some structural elements do not meet the code requirements. Assessment of whether it is appropriate to reinforce these buildings is needed.