Buildings vulnerable to collapse are everywhere. A skyscraper built on a parking garage in San Francisco could have too much open space with too few structural walls. Sand mixed into concrete for a house in Mexico might contain too much mud and interfere with the chemical bond.
When a major earthquake strikes, workers with the American non-profit Build Change arrive in the affected area about two months later, once the emergency relief phase is over, to investigate damaged and destroyed buildings.
"We start out with a forensic engineering study to understand why houses collapsed in the earthquake and why they didn't," said Elizabeth Hausler, the group's founder and CEO who is also a brick, block and stone mason with a doctorate in civil engineering.
Each country has its own common problems related to construction. In Haiti, residents often prefer heavy, unreinforced concrete roofs because they stand up to hurricanes. But when those heavy roofs undergo seismic shifts in an earthquake, walls collapse, houses flatten and people get injured or killed.
In Aceh, Indonesia, which was battered by an earthquake and tsunami in 2004, a popular local building style involves framing several large windows in the front wall of a house. The windows make the wall weaker and vulnerable when exposed to shaking. Build Change moved these windows to other walls, distributing the load more efficiently.
One crucial concept is the positioning and installation of tie columns -- a tower-like structure of vertical rebar that joins horizontal, structural rebar and anchors it to the foundation. Specific attention is paid to the style of the rebar itself (ribbed steel, not smooth) and amount of overlap where the bars come together (the more the better). Both practices strengthen the tie column and the building's ability to withstand lateral shaking.
But Build Change doesn't just build and leave. Instead, they establish an expert group of local engineers that continue to continue to build earthquake-resistant homes.
"The training moves back and forth from the classroom to the building site," Hausler said. "We describe the concepts, then do practical exercises with the trainees, whether that is a configuration exercise with a shear wall-density calculation with pencil and paper, or a practical exercise laying blocks or mixing concrete."
Andre Filiatrault, director of the Multidisciplinary Center for Earthquake Engineering Research at The University at Buffalo in New York, would like to see more emphasis on training for engineers in earthquake-prone areas. Filiatrault and his university have partnered with Quisqueya University in Port-au Prince on a series of engineering seminars and plan to establish longer-term master's programs.
"No doubt the quality of construction and materials are at the root of the issue. The work they do is important, but it's not sufficient," he said. "Port-au Prince is an overpopulated capital with very little space. They really need taller buildings and trained engineers to design them."
But other hurdles -like lax building codes - often lead to spotty progress in efforts to construct safer homes. Part of Build Change's mission is to work with local officials to improve and expedite the inspection process in hopes of leading to fewer casualties next time the earth begins to shake.
