Seismic strengthening of RC columns using external steel cage

Abstract

SUMMARYSteel caging technique is commonly used for the seismic strengthening of reinforced concrete (RC) columns of rectangular cross-section. The steel cage consists of angle sections placed at corners and held together by battens at intervals along the height. In the present study, a rational design method is developed to proportion the steel cage considering its confinement effect on the column concrete. An experimental study was carried out to verify the effectiveness of the proposed design method and detailing of steel cage battens within potential plastic hinge regions. One ordinary RC column and two strengthened columns were investigated experimentally under constant axial compressive load and gradually increasing reversed cyclic lateral displacements. Both strengthened columns showed excellent behavior in terms of flexural strength, lateral stiffness, energy dissipation and ductility due to the external confinement of the column concrete. The proposed model for confinement effect due to steel cage reasonably predicted moment capacities of the strengthened sections, which matched with the observed experimental values.

The Retrofitting Of Reinforced Concrete Columns

“…Experimental tests had let to the conclusion that both variants have as results the increasing of axial load capacity but also of ductility, as effect of a better concrete confinement [2], [3]. The metal addition also increases the bending capacity and the shear force capacity.…”

Numerical Investigation on Load-carrying Capacity of High-strength Concrete-encased Steel Angle Columns

“…Since the distribution of confining pressure in CES-A sections is similar to that of rectangular tied RC sections, existing concrete confinement models can be used, regarding steel angles and transverse reinforcement as longitudinal bars and transverse bars, respectively (Montuori and Piluso 2009;Nagaprasad et al 2009). In the present study, the compressive stress-strain relationship of concrete was characterized by the confinement model of Saatcioglu and Razvi (Saatcioglu and Razvi 1992;Razvi and Saatcioglu 1999) (Fig.…”

“…(2) Steel angles provide good confinement to concrete core (Calderon et al 2009;Montuori and Piluso 2009;Nagaprasad et al 2009;Badalamenti et al 2010;Kim et al 2014Kim et al , 2017Eom et al 2014;Hwang et al 2015Hwang et al , 2016, but the effect of local buckling on the confinement should be also considered. Thus, unlike the existing models (Calderon et al 2009;Montuori and Piluso 2009;Nagaprasad et al 2009;Badalamenti et al 2010), in which the full leg b s of steel angles was assumed to exert the confining pressure in whole analysis steps, the proposed model assumed that only the effective leg b s;eff exerts the confining pressure after local buckling of steel angles (Fig.…”

“…Structural steel angles for columns have been widely studied and used in various ways: (1) to externally strengthen existing RC columns with batten plates (i.e., steel jacketing for reconstruction or seismic retrofitting) (Critek 2001;Zheng and Ji 2008a, b;Montuori and Piluso 2009;Nagaprasad et al 2009;Calderon et al 2009;Badalamenti et al 2010;Garzon-Roca et al 2011a, b, 2012Campione 2012a, b;Khalifa and Al-Tersawy 2014;Tarabia and Albakry 2014;Cavaleri et al 2016); (2) to replace wideflange members with the built-up members connected by battens (Hashemi and Jafari 2004); (3) to reduce laborious fieldwork of composite columns by prefabrication (Kim et al 2011;Eom et al 2014;Hwang et al 2015Hwang et al , 2016; and/ or (4) to improve structural capacity and cost efficiency of composite columns by maximizing the contribution of highstrength steel (Kim et al , 2017. According to the primary purpose, steel angles could be either encased in concrete or exposed, and could transmit column loads or not (providing confinement only).…”

Pushover Analysis of Retrofitted Reinforced Concrete Buildings

“…Furthermore, steel jacketing is not only less interruptive, less time consuming and less expensive, but also results in minimum loss of floor area. Practically, steel jacketing (or caging) consists of steel angles at corners of RC columns and steel straps at few places along the height which provide composite action at the interface of steel and concrete element [2].…”