Building Response Overview
There are two events we want to consider in relation to building response. First are earthquakes, and the second is a tsunami. Building response is based on not only the building itself but the type and strength of the tectonic earthquake and/or tsunami event. For tectonic earthquakes in Indonesia, the focus is more on normal or reverse faults where faults form when hanging walls either drop or move up due to interplate movement instead of strike-slip faults which have walls that move sideways.

Fault Movement:
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For example, in Bali, Flores, or Lombok, emphasis may be placed on the likelihood of back thrust off shore due to a seismic source zone known as the Flores Back Arc Thrust.

Back Thrust:
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A thrust fault is a break in the earth’s crust where lower levels (strata) are pushed up over higher levels as depicted in above diagram.

Earthquake Building Response

The ways in which the earth’s plates move will have a direct impact on the motion and other influences that affect the buildings. This is known as ground motion and site response. Below is an example of the way in which the earth’s movement might have an impact.

Building Motion - Earth Movement Impact:
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As the Federal Emergency Management Agency of the United States [1] summarizes, “When the ground starts to move during an earthquake, the foundation of the house moves sideways but the roof and upper stories try to remain stationary due to the inertia of the house. By the time the roof starts to move in the direction of the foundation, the foundation is already moving back towards its initial position and the roof and foundation are moving in opposite directions” (Fema, 2006). One factor that impacts building response is if it is a slow rupture or not. Another factor that could play a role is if one earthquake causes another earthquake on the opposing side of the island. Each earthquake could also be tsunamigenic, meaning it could generate tsunamis.

Tsunami Building Response

The tsunami is created by the earthquake itself and has its own set of considerations for building response. Perhaps the largest consideration is the pressure of the flowing water on the building structure. The flow occurs not only as the wave comes in, but as the water resides as well. In this case, it is recommended you have segments of the wall that are intentionally built to break away (like a curtain walls, floating walls, or freestanding wall panels) which do not carry the floor or roof loads of the building. This will give the water a pathway to flow through while lessening the stress on critical structural support, helping minimize the risk of collapse.

Water Pathway:
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Shear Strength and Shear Stress

In assessing building response, shear strength plays an important role. Shear strength is the strength of a material or component against structural failure caused by pressure when its layers are laterally (sideways direction) shifted in relation to each other. Shear forcesare pairs of equal and opposing forces acting on opposite sides of an object. Shear stress is the component of stress that is on the same plane with a material cross section (parallel). Normal stress, on the other hand, is perpendicular to the material cross section on which it acts.

Shear Crrack:
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In many cases, the strength of a given material has strength requirements or parameters described as pounds per square inch (psi) or thousands of pounds per square inch (ksi).

Learn more

References

[1] https://www.fema.gov/media-library-data/20130726-1535-20490-7368/fema232.pdf

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