# Thermal Stability of Concrete and Concrete-Filled Steel Tubular Arches

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Bouras, Yanni (2020) Thermal Stability of Concrete and Concrete-Filled Steel Tubular Arches. PhD thesis, Victoria University.

## Abstract

The stability of arches is a classical mechanics and pragmatic engineering problem that has been extensively studied by many researchers over the years. Despite the comprehensive construction and research of arches throughout history, their complex behaviour still presents a challenge to engineers and ensures they are the subject of continual investigation. The problem of arch stability is of contemporary relevance due to the surging popularity of concrete-filled steel tubular (CFST) arch bridges. Hence, due to the inherent complex structural function of arches when coupled with the increasing construction of CFST arches, research into the response and stability of CFST arches under all possible environmental conditions is necessitated. However, investigations into the effects of extreme temperatures on concrete and CFST arches have not been conducted. This thesis presents a comprehensive analytical and numerical investigation into the stability of circular concrete and CFST arches subjected to combined mechanical and thermal loading. Original models are derived for the non-linear prebuckling and buckling analysis including closed-form solutions for the in-plane elastic buckling loads of concrete and CFST arches, and non-discretisation mechanically-based numerical models for their elastic and inelastic analysis prebuckling analysis. Additionally, a numerical methodology to determine the elastic flexural-torsional buckling loads of CFST arches is proposed. Furthermore, a novel fractional viscoelastic creep law is developed for concrete at elevated temperatures in order to analyse the significance of basic creep strain on thermal response and stability boundaries. The fractional-derivative creep law proves to be a robust and compact method of modelling basic creep strain under stress and temperature varying conditions. Finite difference schemes are employed to numerically approximate the fractional derivative and incorporate basic creep into the prebuckling and stability analyses. Finite Element (FE) models are developed to verify the derived models and to also investigate the inelastic buckling strength and fire performance of concrete and CFST arches. The findings of this study provide a detailed understanding of the fundamental thermomechanical behaviour and failure modes of concrete and CFST arches. Consequently, engineers may utilise the results detailed herein to assess and improve the fire resistance of concrete and CFST arch structures. Additionally, the developed creep law has widespread application in the analysis of concrete structures under elevated temperatures. The proposed inelastic numerical models also provide efficient tools for the analysis of other structures such as steel arches and beams.