# Post-Fire Axial Compressive Behavior of Circular GFRP Tube-Confined Concrete Short Columns

## TL;DR

This study examines how circular GFRP tube-confined concrete columns behave after fire exposure, finding that peak temperature is the main factor affecting their strength.

## Contribution

The study introduces a new reduction-factor model to predict post-fire axial capacity based on temperature and wall thickness.

## Key findings

- Peak temperature primarily affects residual axial capacity and stiffness of CFGFT columns.
- Thicker GFRP tubes offer better confinement but only at high temperatures.
- A binary quadratic regression model with R2 of 0.901 predicts post-fire axial capacity reduction.

## Abstract

What are the main findings?
Peak temperature governs residual axial capacity and stiffness of CFGFT columns.Wall thickness affects confinement efficiency and failure mode after fire exposure.Constant temperature duration (60–120 min) shows no systematic strength effect.

Peak temperature governs residual axial capacity and stiffness of CFGFT columns.

Wall thickness affects confinement efficiency and failure mode after fire exposure.

Constant temperature duration (60–120 min) shows no systematic strength effect.

What are the implications of the main findings?
Post-fire performance should be assessed based on peak temperature rather than duration.Thick GFRP tubes provide only relative confinement advantages at high temperatures.A reduction-factor model enables rapid post-fire capacity evaluation of CFGFT members.

Post-fire performance should be assessed based on peak temperature rather than duration.

Thick GFRP tubes provide only relative confinement advantages at high temperatures.

A reduction-factor model enables rapid post-fire capacity evaluation of CFGFT members.

This study experimentally investigates the residual axial compression behavior of circular glass fiber-reinforced polymer (GFRP) tube-confined concrete short columns (CFGFT) after exposure to elevated temperatures. A total of 27 specimens were fabricated and tested under axial compression, with key parameters including GFRP tube wall thickness (5, 8, and 10 mm), exposure temperature (100, 150, 200, and 300 °C), and constant temperature duration (60 and 120 min). The results show that the load–displacement responses of CFGFT short columns after elevated temperature exposure exhibit distinct two-stage characteristics, culminating in brittle failure at the ultimate axial capacity. Wall thickness significantly influences the failure modes of the specimens, while elevated temperatures increase the occurrence of unfavorable failure modes. Temperature is identified as the primary factor governing the degradation of residual axial capacity and initial stiffness, with performance deterioration becoming more pronounced at temperatures exceeding 200 °C. In contrast, the effect of constant temperature duration within the range of 60–120 min is relatively limited. Based on the experimental results, a simplified binary quadratic regression model incorporating the coupled effects of temperature and wall thickness is proposed to predict the post-fire axial capacity reduction factor (Kr), with a coefficient of determination (R2) of 0.901. These findings provide experimental evidence and a practical predictive approach for the fire-resistant design and post-fire safety assessment of CFGFT members.