Axial compressive behavior of square concrete columns externally collared by light structural steel angle sections

The buildings which were designed and built in the past according to the old seismic code or no seismic code at all urgently require a retrofitting effort to satisfy the current seismic and building codes. To demolish and rebuild them would be very costly than to retrofit. Some of the available seismic retrofitting techniques are the concrete jacketing, steel jacketing, external strand pre-stressing, Fiber Reinforced Polymer (FRP) jacketing, and steel collar jacketing. In this study, a new steel collar is proposed as an alternative of seismic retrofitting techniques of existing buildings. The primary objective of the study is to propose an economical, efficient, effective, and practical method for retrofitting the square or even rectangular RC columns. Light structural steel angle sections have been introduced for collar elements. These collars will be installed externally at the perimeter of RC column sections to enhance their strengths and ductilities. To achieve this objective, a set of experimental work was carried out to investigate the effectiveness of the proposed technique in retrofitting the existing RC column specimens. Eight column specimens were casted and tested under monotonic compressive load with or without the collars in order to investigate the performance of the proposed retrofitting method. The volumetric ratio of steel collar elements is set as a main parameter in the study. Three control specimens were only confined with conventional stirrups for comparison. The remaining specimens were just confined with the external steel collars. The test results indicate that the proposed external retrofitting technique works well for confinement method. Significant strength and ductility gains are observed in the study. The proposed external steel collars as an alternative of retrofitting techniques for existing columns can be concluded to be very promising.