Strengthening Sequence Based on the Relative Weightage of Members in Global Damage Using Energy Dissipation Model

Abstract

Damage caused by an earthquake depends not just on the intensity of an earthquake but on the engineering and construction practices of the region. Past earthquakes in Asian countries have highlighted inadequate construction practices and caused huge property and life loss, indicating the severe need to retrofit existing structures. For this, an understanding and quantification of damage are required to assess the amount of damage. Many researchers have proposed many indices; out of those, energy-based indices are chosen for this study. In literature, energy-based damage indices have progressed well but with a gap in mapping of local-to-global indices though they can be computed at local and global levels. This study bridges the gap between global and local energy-based indices using weighting factors, which further proposes sequence of strengthening. Strengthening activities shall be done first at the higher weighted members to increase the capacity of the building immediately and then to the other members. The proposed strengthening sequence is proposed to make it more economical and efficient. This study is conducted on existing buildings, mainly on gravity load-designed buildings (Type G) and precode buildings of IS 1893 designed as per the 2002 version (Type P). These buildings represent a significant stock of RCC MRF buildings on site that should be strengthened. The members contributing significant damage are identified in existing buildings, different weights are allotted to members as per their contribution to global energy dissipation. Nonlinear static analysis is conducted to quantify the damage. The methodology adopted to compute the contribution of local damage to the exterior and interior columns is verified with nonlinear time history analysis with eleven earthquakes. In gravity, load-designed buildings, higher weight for exterior columns is observed in the energy dissipation capacity of the building than interior columns. However, in precode buildings of IS1893, the significance of exterior and interior columns is similar. Storey-wise weights are computed using energy dissipated by each hinge in that storey. Therefore, the highest weighted stories are identified for each type of building. Damage is distributed within stories as a parabolic curve. In type G buildings, as the height of the building increases, parabolic distribution changes from convex to concave, and the maxima location of the parabola shifts from bottom to middle stories. In type P buildings, parabolic damage distribution remains convex or like a straight line. As the height of the building increases, damage shifts to upper stories in a convex parabolic shape. An increase in the storey height of a building does not change the damage distribution pattern and the quantity of damage. The sequence for strengthening activities is proposed as per the computed weighting factors. Strengthening activities shall be done first at the higher-weighted members to increase the capacity of the building immediately. Further, a strengthening sequence is proposed as per the weighting factor in descending order for regular RCC buildings. Therefore, proposals made in the study would increase the efficacy of strengthening activities.