No abstract

The recent development in technology of production and transport of the steel fibre-reinforced concrete enables its utilization in composite steel-concrete structures. This work is focused on development of mechanical behaviour and design model of circular hollow section (CHS) composite steel and fibre-concrete (SFRC) column at elevated temperature. Research includes two levels accuracy/complexity, allowing simplified or advanced approach to design following the coming changes in European standard for composite member design in fire (EN1994-1-2:2005) [1]. Experimental studies of the project include mechanical tests of heated fibre-concrete samples in tension and compression, thermal behaviour under uniform and nonuniform loading of stubs of CHS and tests of full scale SFRC CHS columns in steady-state and transient-state regimes. Developing advanced finite element method (FEM) simulation of global mechanical behaviour of SFRC CHS columns is a multi-levelled composite mechanical and thermo-model and provide numerous numerical experiments. Together with standard steel material model in fire, FEM model of mechanical behaviour of fibre-reinforce concrete at elevated temperature is prepared. Validated simplified and advanced thermal model of SFRC CHS at elevated temperature gives temperature fields and moisture distribution inside section which depends on direction, heat flux, sizes and gives possibility to model different fire cases of full-scale columns in bending and buckling at elevated temperature. Prepared analytical and simplified FEM mechanical model of column is taking in account degradation of mechanical properties, analytical models of transfer of heat inside column section and provides simplified solutions for designers.

This study proposes an analytical model for the evaluation of the mechanical behaviour of circular hollow section columns infilled with steel fibre-reinforced concrete when exposed to elevated temperatures in a fire situation. This work includes the discussion of the results from a sensitivity analysis conducted through numerical simulation and the development of an analytical model based on the prEN1994-1-2:2021 European standard for the design of reinforced concrete structures exposed to fire. The sensitivity analysis aims to compare the fire resistance of centrally and eccentrically loaded circular hollow section columns infilled with plain and steel fibre-reinforced concrete. The proposed analytical model for determining the design buckling load of composite steel fibre-reinforced concrete-filled tube columns in a ?re situation is ready to serve as an annexe or supplementary technical document to the EN1994-1-2:202x standard.

Briquetting is a process in which fine materials unsuitable for use as such are agglomerated to achieve a larger particle size. Auger pressing is a novel briquetting method to efficiently improve the recycling of by-products from iron and steelmaking. The high-temperature properties of auger pressing briquettes mainly consisting of blast furnace sludge and mill scale were evaluated. The aim was to determine the suitability of the briquettes for blast furnace (BF) ironmaking by studying the reduction, swelling, and cracking behavior using a laboratory-scale furnace. The blast furnace simulator (BFS) capable of performing non-isothermal reduction experiments with changing gas compositions was used to simulate the different stages of reduction up to 1100 °C in an atmosphere with N2, CO, and CO2 gases. A commercial olivine pellet and a conventional industrial BF briquette were used as reference samples. The sample weight losses were monitored by thermogravimetry, swelling as a change in the volume, and cracking by visual inspection. The samples were analyzed using microscopes and an elemental analyzer. Based on the BFS experiments, the briquettes proved to be a promising raw material for BF use. They were of a self-reducing quality due to their carbon content and showed reduction to metallic iron faster compared to the reference samples. The swelling was slight, and despite the minor cracking the structure of the briquettes did not degrade.