Seismic damage assessment and FRP retrofit of reinforced concrete structures

Abstract

Only a small percentage of existing buildings around the world have been designed and constructed based on modern seismic codes. Majority of these buildings were designed and built based on older codes and thus are now identified as potentially hazardous due to more stringent seismic requirements of newer seismic standards. Consequently, these structures are vulnerable to earthquakes as has become evident in the recent earthquake events. Mitigating the seismic hazards for these deficient structures, instead of replacement, has been increasingly looked at by the engineering community due to obvious economic reasons.An important first step towards this mitigation is called “Damage Assessment”. Damage Assessment by definition is the evaluation of potential damage in a particular structure in a seismic event. There exist many indices such as drift based on which the extent of potential damage in a building can be described. Choosing the right index and understanding how a particular index would correlate with the seismic parameters or how sensitive it would be to a particular seismic event is quite important. Many structures, for example, are structurally sound under far fault earthquakes but may suffer from extensive damage if a near fault earthquake occurs.While many studies have been undertaken in the past towards methods of analysis that best simulate the damage and on the development of indices that better represent it, the efforts are isolated and in some instances contradictory. The current study thus attempts to address the gaps in the state of the art and presents a coherent and consistent understanding of the issue together with the introduction of a couple of damage mitigation methods.The main achievements of this thesis are as follows:✓ A simplified model for inelastic analysis of RC structures subjected to earthquakes is developed.✓ A new damage model that appropriately assesses the damage of RC structures is proposed. This new damage model is based on the single parameter of energy which naturally overrides and implicitly incorporates a number of parameters such as force, deformation and number of cycles.✓ Damage assessment in RC structures using the new damage model is performed.✓ Correlation between seismic parameters and damage indices of structures is investigated.✓ A new definition for near-fault earthquakes is developed and regions with different damage potential are established.✓ Strengthening deficient RC structures using two retrofitting techniques: plastic hinge relocation and confinement using Fibre Reinforced Polymers (FRP) is explored. The benefits of the two retrofitting techniques in terms of quantitative reduction of damage, expressed by a damage index, in RC frames subjected to different seismic intensities is addressed.