Innovative Retrofit Solution for ExteriorUnreinforced R.C. Beam-Column Joints

NZSEE 2023 Journal Cover — Seismic Retrofit Research

Abstract

Most reinforced concrete (RC) frame buildings in New Zealand constructed pre-1960s have no transverse reinforcement in beam-column joints. Following MBIE/NZSEE assessment guidance, the seismic performance of RC frames with unreinforced beam-column joints is often limited by the strength of the joint,
especially for exterior joints with plain longitudinal beam reinforcement terminating in 180º hooks. Previous testing has shown that for this joint type, due to bond deterioration and bar slip, a compression force develops in the concrete wedge at the back of the joint which can cause it to spall out, compromising the
gravity-load carrying capacity of the column

In this paper, an innovative retrofit approach is investigated using a bidirectional test on a corner beamcolumn joint with the aforementioned deficiencies, based on a 1930s RC frame building in Wellington, NZ. This retrofit uses drilled and epoxied reinforcement bars at the face of the joint to increase the tensile strength of the joint and prevent the concrete wedge spalling failure.

Introduction

One of the typical deficiencies in reinforced concrete structures designed pre-1970s is lack of joint transverse reinforcement and lapped splices located close to the joints. Severe damage in a joints may result in deterioration of the structure during a seismic event.

Different strengthening techniques for beam-column joints has been widely studied by a number of researchers
(Realfonzo 2014) (De Vita 2017) (Prota 2004) (Sharbatdar 2012) (Shafaei 2014) (Maddah 2020) (Pampanin 2007). Pampanin et al. (Pampanin 2007) proposed wrapping the columns, beams, and the joint with GFRP.

Their study showed the load-carrying capacity can be enhanced by about 200%; however, strength deterioration starts to happen at 2% drift. Shafaei et al. (Shafaei 2014) proposed joint enlargement using prestressed steel angles to shift the plastic hinges away from the joint panel. Their proposed method was shown to significantly enhance the seismic capacity of the joints, in terms of strength, stiffness, energy dissipation and ductility capacity.

Shaaban and Seoud (Shaaban 2018) investigate the efficiency of an added ferrocement layer (i.e. steel wire mesh embedded in cement mortar) to retrofit beam-column joint with insufficient confinement reinforcement. Their proposed technique improved the seismic performance and increased the dissipated energy. Wang et al. (Wang 2019) used externally CFRP sheet and near-surface mounted CFRP strips to shift the plastic hinge away from the joint.

Reference & DOI

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Research Details