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Title: Quantifying Benefits of Seismic Retrofitting Gravity Columns Using CFRP Jackets Based on Nonlinear Modeling Parameters per ACI 369.1

Author(s): Saeed Fathali, Bill Graft, Mohammad Jalalpour

Publication: Web Session

Volume: ws_F18_Fathali.pdf


Appears on pages(s):



Date: 10/15/2018

This paper presents a summary of the voluntary seismic retrofit of three parking structures in Burbank, California, and highlights how ACI 369.1 nonlinear force-displacement relationship (also known as “backbone curves”) for retrofitted columns were essential to quantify the reduction of the probable maximum loss (PML) after the retrofit. Preliminary seismic evaluations for the PML analyses had identified insufficient confinement and shear strength of gravity columns and their corbels as major seismic deficiencies of the three parking structures. The project design-build team chose wrapping the columns and their corbels with Carbon Fiber Reinforce Polymer (CFRP) material as the most efficient solution to address these deficiencies. ASCE 41-13, the standards for seismic evaluation and retrofit of existing buildings were used to calculate the demands, and to model nonlinear behavior of the existing gravity columns of the three parking structures. Then the CFRP design was carried out per ACI 440.2-17. These two references provided answers and guidelines to understand what elements were deficient, how much they were deficient, and how their retrofit could be designed and constructed. However, they did not have an answer for how much the behavior of the existing columns would improve after the retrofit, and how much that would reduce the PML. The answer to that question was provided by ACI 369.1 which includes guidelines for nonlinear force-displacement relationship of FRP-jacketed concrete columns. The information on ductility capacity and residual strength of the retrofitted columns provided by ACI 369.1 were essential to calculate the PML for the retrofitted structures, and to quantify financial benefits of the retrofit.