Brittle materials will snap and fracture when subjected to earthquake tremors. While the materials may be structurally strong in other ways, most brittle materials are not suited for earthquake zones. Instead, the field of Earthquake Engineering exists to study the effects of tremors on building materials and find the best compromise between strength and safety. For example, while concrete creates a stable and strong base for buildings, it is subject to fracture, and can undermine a building even if the fractures are limited to the foundation. However, with ductile (flexible) steel rods laid in certain patterns, concrete fracturing can be prevented, contained, and more easily repaired if it is not severe. The difference is between the vertical and horizontal stress load on the building; most buildings are built only for vertical stress, not the side-to-side horizontal stress of earthquake tremors. Various designs exist for earthquake-resistant buildings, including interior and exterior bracing, unusual materials such as bamboo, and making sure each floor in the building is as light as possible.