Advanced Composite Retrofit of RC Columns and Frames with Prior Damages—Pseudodynamic Finite Element Analyses and Design Approaches

Evgenia Anagnostou,Theodora Fanaradelli,Theodoros Rousakis

doi:10.3390/fib9090056

Evgenia Anagnostou, Theodora Fanaradelli + Show 1 more

Open Access

https://doi.org/10.3390/fib9090056

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Journal: Fibers	Publication Date: Sep 6, 2021
Citations: 13	License type: CC BY 4.0

Affiliation: Democritus University of Thrace

Abstract

This study develops three-dimensional (3D) finite element (FE) models of composite retrofits in deficient reinforced concrete (RC) columns and frames. The aim is to investigate critical cases of RC columns with inadequate lap splices of bars or corroded steel reinforcements and the beneficial effects of external FRP jacketing to avoid their premature failure and structural collapse. Similarly, the RC-frame FE models explore the effects of an innovative intervention that includes an orthoblock brick infill wall and an advanced seismic joint made of highly deformable polymer at the boundary interface with the RC frame. The experimental validation of the technique in RC frames is presented in earlier published papers by the authors (as well as for a four-column structure), revealing the potential to extend the contribution of the infills at high displacement ductility levels of the frames, while exhibiting limited infill damages. The analytical results of the advanced FE models of RC columns and frames compare well with the available experimental results. Therefore, this study’s research extends to critical cases of FE models of RC frames with inadequate lap splices or corroded steel reinforcements, without or with brick wall infills with seismic joints. The advanced pseudodynamic analyses reveal that for different reinforcement detailing of RC columns, the effects of inadequate lap-spliced bars may be more detrimental in isolated RC columns than in RC frames. It seems that in RC frames, additional critical regions without lap splices are engaged and redistribution of damage is observed. The detrimental effects of corroded steel bars are somewhat greater in bare RC frames than in isolated RC columns, as all reinforcements in the frame are considered corroded. Further, all critical cases of RC frames with prior damages at risk of collapse may receive the innovative composite retrofit and achieve higher base shear load than the original RC frame without corroded or lap-spliced bars, at comparable top displacement ductility. Finally, the FE analyses are utilized to propose modified design equations for the shear strength and chord rotation in cases of failure of columns with deficiencies or prior damages in RC structures.

Highlights

The dashed lines mark the 20% drop in the maximum values of the analytical and experimental base shears, considered as the lowest acceptable threshold of base shear at failure according to several seismic codes
The advanced analyses suggest that in reinforced concrete (RC) columns confined with fiber-reinforced polymers (FRPs) jackets, the maximum axial tensile force developed on the bars with inadequate lap splices of 15 dbL length is only 57% of the tensile force at yielding of the bars in columns without laps
The analyses show that for different reinforcement detailing of RC columns, the effects of inadequate lap-spliced bars may be more detrimental in isolated RC columns than in RC

Summary

Introduction

Reinforced concrete (RC) structures in seismic regions may reveal several deficiencies, such as inadequate lap splices of bottom steel bars within critical regions [1,2]. Slippage of the steel bars in critical regions may jeopardize the seismic performance of the structure and lead to premature collapse. In coastal regions, the issue of corrosion may lead to significant accumulated mass loss of steel bars and stirrups [3] and reduce the bearing capacity and displacement ductility of the structures. Suitable retrofit of deficient members can improve their strength, delay further corrosion of the reinforcement and reduce deformations in the serviceability limit state [1,13,14,15,20,21,22,23,24] Innovative advanced materials and intervention techniques such as fiber-reinforced polymers (FRPs) in the form of sheets [4,5,6,7,8,9,10,11,12], strips [13,14,15,16], composite ropes [4,17] or composite shells [18,19], among others, are widely used in deficient or damaged RC structures. 4.0/).

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