Abstract
Inadequate attention during design and construction of some of reinforced concrete (RC) buildings in Cyprus has raised questions about the performance level of these existing buildings under future earthquakes. This study aimed to assess the seismic structural response of a four story existing RC building. For this purpose, first, the weak structural elements (e.g.\ the not safety column-beam joints and weak columns) were detected using linear static procedure (LSP) analyses on the basis of Turkish earthquake code. Then, two different strengthening methods were examined. In the first method which is common in Cyprus, the existing building was strengthened based on LSP, using column jacketing to satisfy seismic code requirements to remove the weak elements. The second strengthening method was carried out using nonlinear static procedures (NSP) to achieve the basic safety objective (BSO) performance level described in FEMA 356. For existing and both strengthened structures, pushover curves were obtained and following FEMA 356, performance points were calculated and compared. The seismic responses of existing and strengthened buildings were also assessed using incremental dynamic analyses (IDA). Nonlinear dynamic time history analyses have been performed by using SDOF models of these buildings under action of different scales of 20 ground motion records. Then IDA curves for each earthquake have been constructed. Limit – states at each performance level have been defined and summarizing the multi – record IDA curves, 16%, 50% and 84% fractile curves were obtained. Since selected structure represents common existing buildings in Cyprus, probabilistic structural damage estimation fragility curves were also obtained in terms of peak ground acceleration (PGA) for each considered performance level. Results showed that the strengthening method based on the NSP to satisfy the BSO requirements is much more effective than the one based on the LSP to improve the building performance and to reduce the probability of exceeding of limit states IO, LS and CP at any seismic zone.
Highlights
Earthquake engineering is based on the fact that existing buildings show inelastic response and experience permanent deformations when are subjected to design level ground acceleration
Results showed that the strengthening method based on the nonlinear static procedures (NSP) to satisfy the basic safety objective (BSO) requirements is much more effective than the one based on the linear static procedure (LSP) to improve the building performance and to reduce the probability of exceeding of limit states immediate occupancy (IO), life safety (LS) and collapse prevention (CP) at any seismic zone
FEMA 356 [2] describes each of building performance levels as immediate occupancy that is described as building is safe to occupy but possibly not useful until repaired, life safety is described as building is safe during event but possibly not afterward and collapse prevention is described as building is on verge of collapse, probable total loss
Summary
Earthquake engineering is based on the fact that existing buildings show inelastic response and experience permanent deformations when are subjected to design level ground acceleration. FEMA 356 specifies design base earthquake (DBE) and maximum considered earthquake (MCE) hazard levels for probabilities of 10% and 2% in 50 years respectively. Both ATC 40 and FEMA 356 prescribe a basic safety objective (BSO) which comprises a dual-level performance objective. This study aimed to assess the seismic structural response of a four story existing RC building For this purpose, first, the weak structural elements (i.e. the not safety column-beam joints and weak columns) were detected using LSP analyses on the basis of Turkish earthquake code. For all existing and strengthened buildings pushover curves were obtained and following FEMA 356, performance points at two different hazard levels, DBE and MCE were calculated and compared. Probabilistic structural damage estimation fragility curves were obtained in terms of peak ground acceleration (PGA) for each considered performance level
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