Seismic Performance Enhancement of RC Columns Using Thin High-Strength RC Jackets and CFRP Jackets

George Kalogeropoulos,Alexander-Dimitrios Tsonos

doi:10.3390/fib9050029

Abstract

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of the inadequately lap-spliced reinforcement. In the present study, the effectiveness of two different strengthening systems (including either the wrapping of the columns by carbon-fiber-reinforced polymer textile or the use of thin high-strength reinforced concrete jackets), was experimentally and analytically investigated. The main variables examined were the strengthening material, the length of the lap splices and the amount of confinement provided by the jackets. Three cantilever column specimens were constructed without incorporating modern design code requirements for preserving seismic safety and structural integrity. Subsequently, the specimens were strengthened and subjected to earthquake-type loading. Their hysteresis performances were compared, while also evaluated with respect to the response of two similar original specimens and the behavior of a control one with continuous reinforcement, tested in a previous study. The predictions of the proposed analytical formulation for the hysteresis behavior of the strengthened specimens were satisfactorily verified by the experimental results.

Highlights

The poor overall hysteresis performance of existing RC structures built in the 1960–1970s or earlier is invariably highlighted in the aftermath of every moderate-to-strong seismic event worldwide [1,2,3]
They concluded that the seismic performance of old framed RC structures was significantly improved when retrofitted, showing increased dissipating energy and lateral capacity
Test results showed that retrofitting with CFRP sheets was effective for columns with continuous rebars, while only a slight improvement in the seismic behavior was achieved for the columns with lap splices

Summary

Introduction

The poor overall hysteresis performance of existing RC structures built in the 1960–1970s or earlier is invariably highlighted in the aftermath of every moderate-to-strong seismic event worldwide [1,2,3]. The catastrophic partial or/and general collapse of these structures, which form the majority of the building stoke in most countries, is extremely common, with immense social and economic impact This has triggered the continuous reformation of modern codes for the design of RC structures over recent decades, to incorporate parameters related to the controllable and hierarchically developed damage control philosophy (capacity design approach). Seifi et al [20] studied the effectiveness of the NSM technique for the flexural strengthening of columns, as well as the effectiveness of FRP jackets for the seismic retrofitting of beam-column joints. They concluded that the seismic performance of old framed RC structures was significantly improved when retrofitted, showing increased dissipating energy and lateral capacity. Test results showed that retrofitting with CFRP sheets was effective for columns with continuous rebars, while only a slight improvement in the seismic behavior was achieved for the columns with lap splices

Methods

Results

Conclusion