This paper presents an experimental investigation of the concrete filled thin-walled welded steel tubes. Square and rectangular columns are tested with and without the bond between the steel profile and concrete. In order to remove the bond in the latter columns a polyethylene (PE) film is placed inside of the steel profiles. Experimental results are verified via the finite element analysis and compared to the results obtained using the analytical calculation methods. The significance of the steel–concrete bond is evaluated, referring to the differences of the critical loads, ultimate loads and effective cross-sectional areas of the columns with and without the PE film inside and the differences are found to be considerable. It is found that the columns without the film had an up to 47 % higher effective cross-sectional area to full cross-sectional area ratio. The average reduction of the effective cross-sectional area of the column having a poor bond is found to be 12 %. It is also found that the resistance is often overestimated when using the analytical formulas, especially for the columns with the PE film inside.

This paper presents experimental and numerical analysis of the composite steel-concrete columns. Three columns are tested experimentally. Overall forty-eight FE models are created. Sixteen different models for every experimental column are analysed to evaluate the influence of the different types of imperfections. It was found that the imperfections reduced the resistance of the composite columns by up to 10 %. Limiting the geometrical imperfection amplitudes to B/200, the steel profile effective cross-sectional area reduction by up to 23 % was observed, while the critical buckling stress was reduced by up to 74 %. Expressions for the calculation of the effective cross-sectional area ratio and critical buckling stress are proposed.

There are many cement replacement materials and one of them is zeolites. Zeolites are crystalline solids structures made of silicon, aluminum and oxygen that form a framework with cavities and channels inside where cations, water and/or small molecules may reside. In this study natural zeolite clinoptilolite was used. Clinoptilolite is the most popular natural zeolite mineral with the chemical formula (Na, K, Ca) 23 Al 3 (Al,Si) 2 Si 13 O36·12H 2 O. The present paper shows the results of using ultrasound treated clinoptilolite as Portland cement replacement material. The duration of ultrasound treatment was 5 min, 10 min, and 20 min. Results showed that the XRD of ultrasound-treated clinoptilolite slightly differs in comparison to conventional clinoptilolite. The cement samples with 5% and 10% clinoptilolite substitute provide the strength increase, 30% significantly reduces the strength compared to control samples. The heat measurements of Portland cement paste hydration, containing clinoptilolite, showed that the clinoptilolite slightly increases the duration of hydration, but hydration temperature is lower than in the controls samples. The experimental results suggest that ultrasound-treated clinoptilolite positively influence cement hydration processes, consolidation kinetics, CSH formation; the mechanical strength of the samples is increased. Typical content of Portland cement substituting does not exceed 20% of mass of Portland cement in samples. Reducing the consumption of Portland cement with substituting it with ultrasound treated clinoptilolite is preferred for reasons of environmental protection.

No abstract

No abstract