Performance of elliptical steel hollow section columns, subjected to hydrocarbon fire

Abstract

The elliptical hollow section (EHS) is the most recent addition to the steel hollow section (SHS) family, providing an alternative hollow section solution, for architects and structural design engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance data and design guidance is restraining applications. This experimental and numerical analysis investigation has studied, for the first time, the structural performance of steel columns with elliptical hollow section, when subjected to extreme temperatures, represented by the hydrocarbon fire curve.

A total of 12 unfilled, unprotected pin-ended elliptical hollow section steel columns were tested in a two part experimental programme. Two different sections were tested, 250 x 125 x 8.0 mm and 200 x 100 x 8.0 mm with slenderness = 40.1 and = 50.8, namely EHS-A and EHS-B respectively. The first stage tested six columns, three of each slenderness, unrestrained and under three different loading levels ( = 0.3, 0.45, 0.6). These first tests demonstrated the unique local and overall buckling failure modes of the EHS columns under compressive loads and elevated temperatures, while recording invaluable load-displacement data, paralleled with steel temperature profiles. The second stage of the experimental program applied axial restraint against the EHS columns thermal expansion. As columns are rarely used in isolation, the application of an axial restraint represents a more realistic column boundary condition found in construction. This study illustrates that the additional axial forces present when restraint is applied, will accelerate the failure rates of the EHS columns.

The recorded experimental data and the finite element method (FEM) was utilised to quantitatively express the performance of the EHS columns. The calibrated model demonstrated that a very good numerical approximation solution was obtained, on careful consideration to the thermal expansion coefficient and geometric imperfection of the column. Using the FEM model, a comprehensive parametric analysis was performed, which provided a platform to aid in the development of the critical buckling stress equation and validation of design guidance. A proposed theoretical formula for stub columns in compression under elevated temperatures is also presented. The thesis concludes that the current Eurocode method for determining the critical temperature of steel hollow sections is deemed safe for unprotected elliptical hollow section steel columns under uniform compression.

Date of Award	Jan 2013
Original language	English
Sponsors	Department for Employment and Learning, Northern Ireland
Supervisor	Faris Ali (Supervisor) & Ali Nadjai (Supervisor)