Building materials with high ductility — the ability to undergo large deformations and tension without breaking or failing — help structures better resist seismic waves. This includes structural steel, which is strong and lightweight yet allows buildings to bend.
Concrete is also highly resistant to tornadoes, hurricanes and wind. Its strength comes from rebar inserted in concrete walls and poured concrete foundations.
Steel
Steel is a highly versatile building material, and it’s used in everything from shipbuilding to car manufacturing. Its ductility is particularly important during earthquakes. When a building is damaged, ductility allows it to change shape rather than breaking or collapsing. In countries like Chile, which sits on the Pacific Ring of Fire and is prone to earthquakes, rules have been put in place to ensure buildings can withstand disasters with as little loss of life as possible.
Steel has a high tensile strength and fracture resistance. It is also very cost-effective, and it can be fabricated into many different shapes and sizes for a wide range of applications. It is usually made from iron and carbon, but other elements can be added to improve its properties. For example, stainless steels contain at least 11% chromium to resist oxidation.
The process of making steel involves melting iron in an open or closed furnace and adding other elements to it, such as fluxing agents, carbon (typically in the form of anthracite coal pellets), alloying metals, and mill scale, which is a black layer of iron oxide that forms on hot steel and can be removed. The resulting mixture is cast into ingot molds or hot rolled to produce sheets for further processing.
Earthquake resistant construction is often built on pliable pads, such as rubber, lead, or steel, which are placed under the footings of the building. This is to prevent the building from damaging itself when the ground moves during an earthquake. It is also important that the base of the building be built on firm soil to avoid liquefaction and maintain a uniform settlement pressure.
Wood
Wood offers a wide range of benefits for disaster-resistant construction. It is versatile, aesthetically pleasing and, when treated properly, incredibly resilient. It also provides superior insulation, which can cut energy costs significantly. Furthermore, it doesn’t attract pests and is easy to work with. It can be cut and shaped with hand tools, a big advantage when it comes to speedy construction.
Wood is particularly good at resisting the damaging forces of earthquakes. Its lighter weight and multiple load paths give it the ability to flex during seismic events, mitigating damage and resistance to collapse. This ductility is enhanced by the fact that wood buildings often have numerous nails or other connections, which add more pathways to dissipate force.
The fire-resistant capabilities of wood are well documented as well. Dimensional lumber, which is used in light-frame home construction, can be clad with gypsum wallboard or other fireproof materials to meet building codes. Mass timber, such as CLT, offers even greater fire-resistant characteristics. It burns in a predictable manner, creating a char zone that protects the rest of the structure and increases its structural capacity.
Buildings made with wood are often referred to as “resilient,” and they perform well during both seismic and wind events. In fact, wooden structures are often used in safe rooms, which must withstand high wind and seismic forces.
Ductility
In disasters like flood and earthquake, buildings need to withstand the extreme forces of the environment. These events can be very destructive and cause damage to structures that is irreparable. The structures must be designed and built with ductility to ensure that they can bend considerably without breaking. In addition, they must be able to absorb the energy of these extreme events and dissipate it in a controlled manner. Ductile construction is particularly important for buildings that will be exposed to extreme seismic events. Buildings with high ductility are able to flex and deflect in a way that prevents premature collapse of the structure, which can save lives.
It is important to note that ductility is a physical property of materials and not a chemical property. Physical properties are observable in a material’s form and can be measured with simple tests. Ductility can be compared to malleability, which is the ability of a metal to be stretched into a wire and still retain its shape.
The ductility of a material is determined by its crystalline structure, which affects its performance under stress. For instance, materials with a face-centered cubic (FCC) crystal structure are more ductile than those with body-centered cubic (BCC) or hexagonal close-packed (HCP) crystal structures. Additionally, the size of the grain also influences a metal’s ductility. Smaller grains allow for more dislocations and a lower ductile-brittle transition temperature, but at the cost of strength and hardness.
Ductile cementitious composite
As natural disasters have leveled towns and stalled economies, construction professionals are looking for smarter building materials. A new concrete developed by researchers at the University of British Columbia has the potential to dramatically improve existing buildings’ earthquake resistance. The new material, called eco-friendly ductile cementitious composite (EDCC), is designed to strengthen and flex instead of crumble during an earthquake. It uses polymer-based fibres that give it a strong, malleable quality like steel. The researchers put a 10 mm layer of the new concrete on walls and subjected them to simulated tremors of 9.0 – 9.1 magnitude, similar to the earthquake that hit Tohoku, Japan in 2011.
The results showed that the EDCC can be used to reinforce existing structures without any loss of structural performance. The ductility of the new concrete can also be enhanced with the addition of microencapsulated phase change materials. These can reduce the temperature fluctuations in the concrete, which will help to increase its tensile strength and deflection capacity.
Engineered cementitious composites are a promising material for the future of civil engineering construction. They can achieve high tensile strain capacities, compensate for significant deformations and prevent early-age cracks. However, they have not yet been widely used due to their high cost and brittleness. A ductile cementitious composite with silica sand and PVA fiber has been developed, and its axial compression test, elastic modulus test and four point bending tests show that it can withstand the same structural performance as conventional concrete.