`Introduction The naturallyoccurring ground movement, which eventually goes on creating disasters such asfailure of structure and natural phenomenon is known as the Earthquake. Theenergy that is discharged from those seismic activities makes waves.
Thesewaves cause ground movement, which in turn is transmitted to the structure via thefoundation. Depending on the intensity of these vibrations, cracks andsettlement is caused to the structure. Force is induced in structure; because of thisthe resulting damage to the structure increases with the ground motion. Manyengineers introduce ductility to thebuilding (pliable but not losing itstoughness, meaning a building could be deformed during an earthquake but wouldnot collapse upon the people inside it.
Imagine an elastic band. Though able towithstand great force, it will eventually break; in the context of thebuilding, the maximum point it can deform before breaking, called the Elasticlimit. Upon reaching the Elasticity limit, cracks form in the building). However,elastic materials add much more to the overall construction price which is asignificant disadvantage.. In addition, elasticity decreases damage byincreasing the strength, giving a disadvantage to the components of thebuilding with less strength. Though the reinforcements are strong, all theforce of the earthquake is directly transferred to the building.
Baseisolation is a frequently adopted earthquake-resistant system. Isolation beingthe separation of a building from its foundations, The basic principle of baseisolation is to differentiate the building from its foundation, so during seismicaction, the building stays unaffected from the ground motion. Separating thestructure from the ground by introducing a flexible isolation system betweenthe foundation and the structure is the solution to this problem. Baseisolation reduces the displacement of the structure during seismic event.Utilizing bearing pads which is put between the foundation and the building(the substructure and the superstructure). Bearings are built to be very strongvertically (meaning when force is applied, it will not bounce) but flexiblehorizontally (therefore, in the event of an earthquake, the superstructurewould move parallel to the direction of the earthquake. Figure 1: A Conventional Fixed-BaseBuilding in Contrast to Base-Isolated BuildingNote infigure 1 the comparison between a fixed-based building and a base-isolatedbuilding in seismic activity. The ground beneath each building, therefore, ismoving towards the left (see the arrow beside Ground motion).
However, thefixed-based building is displaced towards the right. Its plane of movement isthe same as ground motion though its direction is different due to inertia. Inmost seismic actions, inertia forces are what most affects and deforms thebuildings.