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Title: Stress at Ultimate in Internally Unbonded Steel Based on Genetic Expression Programming

Author(s): Nazar Oukaili and Iqbal Peera

Publication: Structural Journal

Volume: 119

Issue: 6

Appears on pages(s): 177-191

Keywords: flexural concrete member; genetic algorithm; post-tensioning; ultimate loading; unbonded steel tendon

DOI: 10.14359/51734803

Date: 11/1/2022

This study demonstrates the development of a new genetic programming-based model to predict the increase in stress Δfps beyond effective prestress, and the total value of stress fps at ultimate loading in the internally unbonded steel tendons of post-tensioned concrete flexural members. Genetic expression programming (GEP) was employed to develop an accurate predictive model for Δfps, summarizing almost all the influencing parameters including the geometrical properties of the structural member, the mechanical properties of steel and concrete, and the loading type and pattern into one single empirical expression. Comprehensive experimental outcomes of 218 data points were compiled from published literature since 1962 and the experimental program carried out recently by authors on prestressed concrete flexural members (beams and one-way slabs) with internally unbonded steel. To inspect the potentiality of the proposed model against 22 expressions suggested by various researchers and Codes of Practice, an extensive comparative study was carried out to assess Δfps. Compared to the other predictive models, the proposed model showed the highest correlation between the estimated and the experimental stress increase Δfps in internally unbonded steel at ultimate loading with a coefficient of determination R2 of 0.78.