The challenge

Out-of-plane failure in unreinforced masonry

Unreinforced masonry (URM) buildings have historically performed poorly during seismic events. A common failure mode is out-of-plane collapse, where walls and gables fall outwards or topple due to bulging. This type of failure often happens because of poor connections between walls and floors, incorrect wall geometry (walls that are too long, high, or thin), and substandard construction quality. The lack of seismic reinforcements is a key reason why URM buildings are prohibited in seismic zones worldwide.

To prevent this, walls need to be tied together to create a "box action". While this can be achieved with a stiff concrete slab, roofs in remote and rural areas are often made of timber, which acts as a flexible diaphragm. Incorporating horizontal bands (either from concrete or timber) at various heights can enhance this box behavior and has been shown to prevent collapse during earthquakes. Our rubble stone masonry schools in Nepal, which have flexible timber diaphragms and horizontal bands at five levels, successfully withstood the 2015 earthquakes without any significant damage.

What we need to do

Scientific evidence proving the benefits of horizontal bands for preventing out-of-plane failure is very sparse in the existing literature. To our knowledge, full assessments and optimization of the number of bands for rubble stone masonry buildings do not exist. Our research will bridge this knowledge gap by definitively showing that out-of-plane failure is not a primary risk for horizontally reinforced masonry (HRM).

Our research approach

We are assessing the out-of-plane behavior and the influence of horizontal bands on two case study buildings: a one-story, three-classroom school and a two-story house, both common designs in the Himalayan region. Horizontal reinforcements are included at various heights within the walls.

We will assess the designs using both hand calculations and spreadsheets, as well as with state-of-the-art software. The goal is to prove our hypothesis that out-of-plane failure is not a critical risk for horizontally reinforced masonry buildings. This is an important step toward reintroducing this technique into seismic codes in countries where stone masonry is still widely practiced.

Get involved

We are looking for experts in out-of-plane collapse of masonry and in modeling masonry with state-of-the-art software packages. If you are interested in exchanging knowledge or joining our research team, please get in touch.