The quantitative seismic damage assessment play an important role in repair cost estimation and retrofit decision making of the damaged structures. There are many damage indices for damage assessment that make use of the ductility, change in stiffness, inter-storey drift etc. to define the degree of damage quantitatively. However, as the finite element method is widely used and regarded as more precise method of analysis, there exist a need to develop a Damage Index that make use of the local strain values of Finite Element analysis output, to define degree of damage quantitatively.
In the current research, a Damage Index is proposed that make use of the local strain values, integrated over the loaded area to define the degree of damage of the reinforced concrete members quantitatively. The proposed damage index is then applied to the bridge system whose response is determined using precise structure idealization.
The investigations were carried out on reinforced concrete members, considering the variation in loading type and failure modes, specimens were tested in the laboratory for their force-displacement relationship and damage response. The two dimensional (2D) finite element models are developed in WCOMD ver.7.7 that computes the response from the widely used material models of reinforced concrete proposed by Maekawa & Okamura. The analysis response is then compared with the tested values.
The strain parameters ε x (normal strain in X-direction), ε y (normal strain in Y-direction), γ xy (shear strain)and J 2 ’ (second invariant of deviatric strain tensor) are integrated over the loaded area (shear span times dimension parallel to loading line), and investigated for their relationship with the particular damage state of the member. The investigations suggest that (ε x ) integration is the most suitable parameter to define the degree of damage especially for
the members in which the failure initiate with the yield of shear stirrup, the critical value of this Damage Index is found by dividing the yield strain of the shear stirrup with the effective steel ratio.
A single pier bridge system, designed according to specifications for highway bridge, Japan, is analyzed, as a two dimensional (2D) integrated model with soil, using the same computational tool. Two main cases of analysis are presented here one with Kobe earthquake acceleration history and the other with JSCE acceleration history, transferred at engineering base, is used as input excitation for the bridge model. As the sub-cases the amount of shear reinforcement is reduced to 1/3rd for comparison in each case. The damage index (ε x ) is determined and damage is reported as a fraction of the critical values obtained for the given bridge pier.