ORCID

Abstract

This thesis investigates the coupled thermal, flexural and steel–concrete bond response of steel-reinforced geopolymer concrete (GPC) and ordinary Portland cement concrete (OPCC) beam cross-sections subjected to one-sided standard fire exposure. A sequential analytical framework is developed to link transient heat-transfer analysis, temperature-dependent sectional flexural analysis, and temperature-dependent bond and flexural–bond coupling assessment.The thermal analysis is performed using a one-dimensional transient heat-conduction model implemented in MATLAB PDEPE. Separate temperature-dependent density, specific-heat and thermal-conductivity relationships are adopted for OPCC and GPC. A dedicated OPCC model of the B1 validation specimen is assessed against 13 matched experimental reinforcement-temperature measurements, giving R^2=0.9542 and an RMSE of 39.87 °C. Independent three-dimensional ANSYS transient thermal analysis provides a numerical-consistency assessment of the MATLAB implementation, giving R^2=0.9998 and an RMSE of 2.24 °C.The calculated concrete-temperature fields and tensile-reinforcement temperature histories are transferred to a temperature-dependent sectional model based on strain compatibility, force equilibrium and equivalent rectangular concrete stress-block relationships. The model determines the dynamic compression-zone depth, the temperature-dependent ultimate moment capacity M_T, and the flexural strength-retention ratio η=M_T/M_0, while explicitly checking the under-reinforced condition. The same reinforcement-temperature histories and the tensile-force demands obtained from the sectional analysis are subsequently introduced into a temperature-dependent plain-bar bond model. The available bond-transfer capacity is compared with the required tensile-reinforcement force to distinguish flexural yielding from bond-controlled failure and to calculate the coupled resistance.The OPCC and GPC reference sections are compared using matched geometry, reinforcement arrangement, ambient reference strength and fire exposure, while retaining their respective temperature-dependent thermal and mechanical material models. Parametric analyses examine reinforcing-steel thermal strain, tensile-reinforcement ratio, concrete cover, and reinforcing-bar size and number. Under the adopted models and boundary conditions, the GPC reference section develops lower tensile-reinforcement temperatures after heating commences and consequently retains greater flexural and bond resistance during the three-hour analysis. The early reduction in flexural resistance is governed principally by degradation of the tensile reinforcement and the accompanying reduction in compression-zone depth. Increasing concrete cover delays reinforcement heating and slows the loss of both flexural and bond resistance. Within the ranges investigated, the tensile-reinforcement ratio has a comparatively limited influence on the normalised flexural-retention history, whereas reinforcing-bar size and number affect the absolute bond-transfer capacity through the total bonded perimeter.The study establishes a consistent quantitative framework for tracing the effects of transient thermal exposure from the concrete temperature field to reinforcement degradation, sectional flexural resistance, bond-transfer capacity and the governing coupled failure mode. The conclusions apply to the theoretical sections, material relationships and modelling assumptions adopted in this thesis and should not be interpreted as universal design recommendations for all OPCC and GPC mixtures.

Awarding Institution(s)

University of Plymouth

Supervisor

Long-yuan Li, Shanshan Cheng

Keywords

Geopolymer concrete, Ordinary Portland cement concrete, Reinforced concrete beams, Fire resistance, Transient heat transfer, Elevated-temperature flexural capacity, Steel–concrete bond, Thermo-structural coupling

Document Type

Thesis

Publication Date

2026

Embargo Period

2026-09-18

Deposit Date

September 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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