The role of masonry infill walls in strong earthquakes.

This text was originally published in Spanish in Factor FEMCIC Magazine in Mexico, where I provided my professional insight into this topic, following the Venezuela 2026 earthquake. I have used ChatGPT to translate the text to English. Although the text is of my full authorship, the image was sourced from public domain online.

Modern seismic structural design is based on the capacity design philosophy, whereby the structure is conceived so that certain “fuse” elements can undergo plastic deformations to dissipate energy during a strong earthquake, while the remaining elements remain within their elastic range, preserving global stability and reducing the probability of collapse.

Among the most widely used structural systems are moment-resisting frames, which are extensively adopted because of the architectural advantages they offer, their ability to lengthen the fundamental period of the structure toward more favorable regions of the design spectrum, and their high levels of ductility, which allow them to dissipate significant amounts of energy during a seismic event.

The issue of combining flexible with brittle

These systems are designed and checked to limit interstory drift and prevent damage that could compromise the stability or reparability of the structure. However, they are frequently combined with nonstructural elements that are incompatible with such deformations, such as masonry infill walls. Although regulations exist for the seismic design of nonstructural elements, these walls are rarely designed by a structural engineer. Their detailing is often absent from the structural drawings and, consequently, they end up being constructed according to the contractor’s judgment, who generally prioritizes construction and finishing considerations over seismic performance.

There is extensive research on the interaction between masonry infill walls and steel or reinforced-concrete frames, as well as simplified models to represent this behavior in structural analyses. Nevertheless, modeling this interaction remains a challenge due to the high degree of uncertainty associated with masonry behavior. Its properties depend on numerous factors, including the nonlinear characteristics of the materials, the dimensions of the masonry units and mortar joints, the wall slenderness and aspect ratio, and the relative stiffness of beams and columns. These variables can lead to different failure mechanisms, such as shear failure through the mortar joints, diagonal tension, corner crushing, or out-of-plane instability.

An infill wall that remains in contact with all edges of the surrounding frame provides initial stiffness and strength that are rarely considered explicitly in design, even though they can be significantly greater than those provided by the bare frame. Although this might initially appear to be a conservative condition, the increase in stiffness reduces the fundamental period of the structure and may shift its response toward less favorable regions of the seismic spectrum, different from those considered during design.

Furthermore, this additional stiffness and strength degrade rapidly during the first loading cycles of a strong earthquake due to the progressive deterioration of the masonry. As a consequence, the structure experiences abrupt changes in its dynamic response that may promote phenomena such as the formation of soft or weak stories when damage becomes concentrated at certain levels, typically at the ground floor.

Recent earthquakes, such as those that occurred in June 2026 in northern Venezuela and in February 2023 in southern Türkiye, have once again highlighted the role these elements can play during the emergency phase. Even in buildings where structural damage was limited or that were subjected to moderate seismic intensities, masonry panels failed out of plane and posed a direct risk to occupants through detachment or crushing. They also blocked exits and evacuation routes, while those located on façades became detached, endangering people attempting to leave the building.

Beyond the immediate risk to life, damage to nonstructural elements limits the reoccupation of buildings and forces occupants to seek temporary or permanent shelter, amplifying the social and economic impact of the disaster and reducing the resilience of the affected community. In many cases, the cost of repairing this damage is so high that it ultimately compromises the economic feasibility of rehabilitation and leads to the demolition of the building, even when its primary structure remains essentially intact.

What can be done?

The most common solution I have observed in practice is to leave a gap between the masonry wall and the upper beam. Although this measure partially reduces the interaction between the two elements, simple contact with the columns remains sufficient to develop significant additional forces and stiffness. Consequently, this is an incomplete solution that could even prove counterproductive by inducing unanticipated failure mechanisms. On the other hand, separating the wall from the columns may compromise its out-of-plane stability and require additional stabilizing elements, increasing construction costs.

Although there is not a single answer, some options that the designer has to look into include:

1. Explicitly incorporate the contribution of infill walls into the structural analysis.

This approach requires considering not only the structure with the walls intact, but also scenarios in which they have partially or completely lost their stiffness and strength, evaluating unfavorable configurations such as the formation of soft or weak stories. Although conceptually rigorous, this solution requires accepting lower building resilience and working with models characterized by high levels of uncertainty.

2. Decouple nonstructural elements from the seismic response of the structure.

In this case, the stability of the walls must be ensured through an independent design that guarantees both their out-of-plane behavior (due to floor accelerations) and their ability to accommodate interstory deformations without developing significant interaction with the primary structure. From a resilience perspective, this represents a much more attractive alternative, since limited, easily repairable damage compatible with almost immediate reoccupation of the building would be expected. Nevertheless, it also involves significant technical and economic challenges.

3. Replace masonry with enclosure systems compatible with large deformations.

This problem is particularly common in low- and mid-rise buildings designed using conventional procedures. In contrast, high-rise buildings often incorporate more sophisticated façade systems, such as lightweight panels, metal or prefabricated façades, and glazing systems with connections specifically designed to accommodate significant relative displacements without compromising their integrity. Although these solutions increase the building’s initial cost, they also significantly improve its performance and resilience during strong earthquakes.

The next challenge

For decades, seismic design has focused on preventing structural collapse. However, the next challenge is to achieve buildings that, in addition to protecting the lives of their occupants, remain safe, functional, and occupiable after a severe earthquake. To achieve this, the design of nonstructural elements must no longer be regarded as a secondary consideration and must instead become an integral part of the structural design process.

There is significant scope for innovation, both in the development of new construction solutions and in the evolution of design philosophies applied to nonstructural elements. In this process, research, industry, and, above all, the leadership of the structural engineer will play a fundamental role in transforming current paradigms and advancing toward truly resilient buildings.

me@fernandogu.com