2. Earthquake and Earthquake Resistant Buildings

Earthquake is a natural phenomenon that can be a huge threat for any building that is not designed and constructed properly to withstand it. It causes thousands of lives to be lost and huge amounst of property damages in the world every year. The most destructive earthquakes are caused by seismic waves that reach to the earth surface at areas where man-made structures are located. When seismic energy reaches the ground surface, it creates a strong ground motion, which is generally measured by maximum ground acceleration. Strong ground motion is also the primary cause of damage to the soil base upon which the community must rebuild.

Picture 2.1 - Earthquake damages on the buildings

Earthquakes are very difficult to predict today. Therefore, the only way to prevent structural damage against a seismic loading in earthquake areas is through proper design and construction. For that purpose, it is important to sufficiently understand seismic activity, dynamic effect and related building response. The dynamic response of a building against an earthquake vibration is an important structural aspect which directly affects the structural resistance and consequently the hazard level. Not only the direct member displacements and member strength must be considered in structural analysis, but also second order effects caused by large displacements due to cyclic loading.

In order to design an earthquake resistant steel building, engineers can choose different methods and structural components capable to withstand lateral loads. These structural elements can be: shear walls, concentrically or eccentrically braced frames, moment resisting frames, diaphragms, truss systems and other similar systems. The determination of an appropriate earth resisting system also is dependent upon the building design's architectural concept. Therefore, the designer responsible for making an earthquake resistant building must develop a comprehensive structural system that will address the requirements of earthquake safety, building cost, building use, and importantly the architectural design.

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