1. Introduction
A substantial stock of mid-rise reinforced concrete buildings in moderate seismicity regions predates modern ductile-detailing requirements, and retrofit prioritisation requires quantitative vulnerability assessment rather than blanket assumptions of deficiency.
2. Methodology
A representative 8-storey RC office building, detailed per a pre-2002 code edition lacking capacity-design provisions, was modelled in nonlinear structural analysis software and subjected to displacement-controlled pushover analysis under a first-mode lateral load pattern, with capacity curves compared against code-prescribed demand spectra for the design basis earthquake, followed by evaluation of a column-jacketing retrofit scheme.
3. Results
The unretrofitted model exceeded the life-safety inter-storey drift limit of 2 percent at the fourth storey under the design basis earthquake demand, consistent with a soft-storey failure mechanism driven by discontinuous infill walls at that level. The column-jacketing retrofit increased base shear capacity by 34 percent and reduced peak inter-storey drift to 1.4 percent, within the life-safety limit at all storeys.
4. Conclusion
Pushover-based assessment identifies specific vulnerable storeys in pre-code mid-rise buildings and allows targeted, cost-effective retrofit rather than uniform strengthening. Future work will extend the assessment to a building population study across a representative city building stock.
References
[1] ATC-40, Seismic Evaluation and Retrofit of Concrete Buildings, Applied Technology Council, 1996. [2] FEMA 356, Prestandard for Seismic Rehabilitation of Buildings, FEMA, 2000.