Mechanical Properties of Partially Damaged Steel, Concrete, and Concrete Filled Steel Tube Materials Induced by High Strain Rate Loading at Elevated Temperatures
Creators: name: Mirmomeni, Mahsa
Publisher: name: Monash University
Year: 2017
Subjects: subject: 90506 Structural Engineering
subject: FOS: Civil engineering
subject: FOS: Civil engineering

description: In today’s world, designing structures to withstand normal lading conditions is not safe enough and engineers aspire to design protective structures that can withstand extreme loading scenarios. With the unfortunate rise of terrorist attacks and road side accidents causing explosions or high speed collisions, survivability of structures under large dynamic loads and potential subsequent fire initiating from them have become a major design concern for structural engineers. The post-impact/blast fire combined effect is profoundly different from when the structure is exposed to either loading. That is, the subsequent fire is imposed on a structure which is now in an altered and potentially weaker state to what had been assumed during the original fire-resistance design. Finite element method based software packages currently used in engineering practice for structural analysis rely on constitutive models to predict material response and simulate deformations. Accurate material models that can predict the behaviour of structural materials under such extreme loading conditions are essential for analysis and design of structural systems. <br> This thesis aims to develop a fundamental understanding of the behaviour of conventional construction materials namely steel, concrete and steel-concrete composites under the combined actions of post-impact-fire and to present material models which can accurately reflect such complex behaviours. <br> For this purpose, series of benchmark experimental tests have been conducted on mild steel, unconfined self-compacting concrete and concrete filled steel tubes (CFST) to identify the mechanical characteristics of these materials under the fully coupled effect of high strain rate and subsequent elevated temperatures. The results have indicated that the strength and ductility of these materials at elevate temperatures are significantly dependent on the rate of loading and the pre-deformation history. The reduction factors currently available in design codes for fire considerations have shown to fall short of reflecting the loading history and inadequate for such combined effects. This has necessitated the development of a relation which not only reflects the mechanical characteristics as a function of temperature but also the level of rate dependant pre-deformation for a rational fire analysis and design of structures. <br> Based on the extensive experimental data, a unified, versatile and generic empirical material relation which reflects the initial impact damage on the temperature behaviour of steel, concrete and CFSTs has been developed. The proposed expression is calibrated and validated on the basis of test data for each material and has proven to be capable of successfully reproducing material strength and ductility. The empirical model resulted from this research can easily be incorporated in commercial packages such as ABAQUS and LS DYNA with the potential for inclusion in prospective codes of practice for rational engineering for extremes based designs.