Tavio, Tavio and Pudjisuryadi, Pamuda and Suprobo, Priyo L-Shaped Steel Collars: An Alternative External Confining Retrofit for Improving Ductility and Strength of Rectangular Concrete Columns. In: Advancing Eco-Concrete Technology for a Lifetime Sustainability.
Abstract
Confinement in concrete column has been well known to improve its strength and ductility. Such enhancement is primarily essential when needed to improve the behavior of concrete columns particularly in terms of ductility during the earthquake strike. This advantage is in line with the modern concept of moment-resisting frame which requires ductile structural framing members. Up to present, traditional transverse steel is still used as internal confinement in concrete column. Several researches have been conducted extensively to study the behavior of confined column, both analytically and experimentally. All these studies confirmed that internal confining method significantly improves the strength and ductility of the columns. However, sometimes the existing columns in a building do not satisfy the building code requirements either unintentionally or due to the unawareness of seismic hazards in terms of confinement. Once the column is built and cast, there is no way to revise the lack of transverse steel internally. The only way possible is to retrofit the columns by using external means. High demand of strengthening on existing RC buildings has made external confinement becoming increasingly popular as an alternative external confining retrofit for RC columns. Various types of external confinement have been introduced to increase the strength and ductility of the columns, such as FRP wrap or even the use of steel jacketing. These external confining techniques have been proven to be successful in retrofitting circular concrete columns. Experimental programs as well as confining models for externally confined circular columns have been well developed. It is, however, still uneasy to provide an effective confining stress by external retrofit on square or rectangular concrete column. The non-uniform confining stress on column is due to high stress concentration at column corners. Only a few experimental and analytical studies addressed these issues. The most recent proposed external confinement method is by using the steel collars with hollow square section. This kind of confinement method has been proven to work well as confining system for concrete columns. The strength and particularly the ductility of the columns have been improved significantly. However, it is still too heavy and uneconomical for use as column retrofit. The need of light and economic types of external confining retrofit is urgently required in the country like Indonesia. Thus, an external confining method that is utilizing light L-shape steel section is studied for its capability as an alternative retrofit for rectangular or square concrete columns. This paper is a part of the first phase of a multiyear research project carried out by the authors. In this paper, a proposed alternative external retrofit for improving the ductility and strength of square concrete columns is presented. Eight columns specimens were cast and tested under monotonic compressive loading. A set of L-shaped steel collars have been introduced externally on square concrete columns prior to testing. The results have confirmed that the proposed external confining techniques considerably enhanced the compressive strength and ductility of the column specimens.
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