Seismic Vulnerability Assessment and Strengthening of New Market Building Damaged after January 4, 2016, Imphal, India, Earthquake

Important buildings located in high seismic zones of many developing countries are sometimes designed without paying much attention to the earthquake risk in the area. Such buildings are prone to severe damage during earthquakes and need immediate strengthening using techniques that should not only be economical but also should not interfere with the functioning of the building. The present study focuses on the assessment of the seismic vulnerability of a publicly funded reinforced concrete building (New Market building) in Imphal, India, that suffered severe damage during January 4, 2016, earthquake. It is further intended to suggest a suitable strengthening strategy for improving the lateral-load performance of the large building used by hundreds of local vendors. A detailed investigation of the damaged building was first carried out visually as well as using nondestructive tools and by collecting concrete core samples from various members of the building. Demand to capacity ratios (DCRs) were obtained using nonlinear static and dynamic analyses to determine the adequacy of the column sections of the building. Local seismic strengthening in the form of reinforced concrete jacketing was applied to the weaker columns ($\mathrm{DCR}>1$) based on several trials to achieve the required global strength and ductility. After retrofitting, yielding of most of the column members is substantially delayed. In addition, the peak story displacement and acceleration are found to be remarkably reduced for both the orthogonal directions. The seismic vulnerability assessment of the original building suggests that most of the column sections do not satisfy the allowable code-specified drift limits; however, the vulnerability reduced substantially after implementing the suggested strengthening scheme.