Question

how we can use "mass reduction" and "external prestressing" as a "methods to retrofit" against earthquake effects the existing buildings in Civil Eng?

Answer 1

As we all know, Earthquake produces seismic waves which bounds the Earth's techtonic plates to move back and forth and causes massive destruction on the Earth surface with respect to it's intensity. We humans can't abondon nature's actions but we can prevent our losses caused by it up to some extension.

There are many methods by which we can reduce the affect of earthquake on the structures, two of them are "Mass Reduction" & "External Prestressing" which comes under the umbrella of Seismic Retrofitting.

Seismic Retrofitting is a process of modification or mitigation of the constructed existing structures to make them for flexible and stronger against the seismic waves. It is also known as structural upgradation.

Mass Reduction is a process of eliminating the multiple storey of building to reduce the dead load of the structure as well as the load distributed by the foundation to the subgrade soil. By doing this, structure will experience less movement intensity on it and the chances of developing cracks will also get eliminated upto some extent.

External Prestressing is a process of introducing the high strength steel tendons on the framed structures tightened by jacks to make the structure more flexible against the seismic waves. Prestressing helps the structure to sway back and forth with the intense movement of seismic wave tends to have less damage to the elements of the structure. Its hleps to reduce deflection, provides low fatigue & crack free members of the structure.