摘要：Confining reinforcement for concrete columns have been standardized in building standards ACI 318-11 and SNI 03-2847-2013. The observation of building collapse by earthquake normally caused by malfunction of the building columns as bearing elements. The columns were failed because they did not meet the standard of confining reinforcement. In most cases, external confinement is necessary to strengthen the existing columns of old buildings. This research focused on the methods to strengthen the existing columns. Three types of pre-stressed steel rings were used to confine the concrete cylinders of 10× 20 cm and 10 × 30 cm. Several concrete strengths of 50 MPa, 70 MPa and 100 MPa were selected for constructing 18 specimens of concrete cylinders. The first type of pre-stressed is with zero pre-stressing force represented passive confinement while the second and third types were given different prestressing forces on the steel ring represented active confinement. Prestressing force on the steel ring will cause radial stress that compress the concrete cylinders. Load test were conducted on concrete cylinders to measure the strength and the relationship of stress strain concrete cylinders which was confined by varied external lateral pre-stressing. The testing results showed that the external lateral prestressing increases the ductility and strength of concrete columns. It proved the method of external lateral pre-stressing can be used effectively for retrofitting and strengthening existing columns in order to meet the requirement of ductility and strength.
