Key Engineering Materials Vol. 832

Abstract: Low carbon steel is one of the most common steels used in industry because of its low cost. If more strength is required, it can be strengthened by induction heating which is also a low-cost method. In order to investigate the effect of induction heating on large diameter shafts, we performed rolling bending fatigue tests using 10 mm diameter specimens. We found that TRO cracks originating from the boundary between the soft and hard layers governed the fatigue fracture of the shafts.

Abstract: This study investigates computation and distribution of the diffusion coefficient using fundamentals of electrochemistry for various concrete mixtures. The instrument utilized is a bulk conductivity meter which provides the bulk conductivity data for computation of the diffusion coefficient. Thirty three mixtures are investigated, where majority of them are ternary mixtures along with Ordinary Portland Cement (OPC) and binary mixtures. They are categorized in several groups based on the supplementary cementitious material (SCM) as a second component in ternary and binary based concrete mixtures. The variation and distribution of the diffusion coefficient in individual group is investigated from 7 days to 161 days. In addition, a new methodology is proposed to determine the aging factor of the diffusion coefficient of each concrete mixture. Aging of concrete is related to chloride ingress which leads to significant decrease of the diffusion coefficient with time. If this effect is not taken into account, considerable questions can be raised while predicting reliable and accurate service life of reinforced concrete structures. Further, aging factor is validated using a statistical analysis method based on published literature of Fisher Test permutation approach. Results show that diffusion coefficient in each group varies significantly and the addition of SCM and its varying replacement level influences the reduction of the diffusion coefficient remarkably over extended time period. Overall, this study could provide promising options for computation of the diffusion coefficient and its aging factor in light to its ease of measurement and shorter amount of time than conventional RCPT and other long term migration tests.

Abstract: The paper presents results of tests conducted on self-compacting mixes with the addition of engineered steel fibres. There were used four types of fibres. The fibres were added at 5 levels of the volume ratio. Firstly, fresh mixes were tested (slump flow, class of viscosity and rheological characteristics). Secondly, properties of hardened concretes were tested (compressive strength and flexural strength). Hardened concretes were also tested using non-destructive method, namely X-ray computed tomography. The tests confirmed the possibility of using steel fibres for reinforcing self-compacting concrete. The workability of mixes was maintaining and the assumed technological parameters for hardened concretes were kept. It was found that longer fibres are more likely to be oriented parallel to the direction of the mix flow. Thus, they can operate efficiently under flexural loading of the cast beam.

Abstract: The paper deals with the research on the properties of secondary raw materials resulting from the recycling of used tyres and their potential utilization for the production of construction insulations. Evaluation of the possibilities of utilization and a complex analysis has been executed on the basis of the defined basic physical, thermal-insulating and fire properties of the raw textile fibres examined. The results of the research on the material examined indicate possible exploitation of this potential material for the construction of environmentally-friendly objects. Thermal insulating parameters have been determined by the value of thermal conductivity coefficient λ. For measuring of thermal conductivity coefficient of fibres has been used the special laboratory device – the Cooling Box. Physical properties have been determined by microscopic examination and by laboratory measuring of fibres length, diameter, pour bulk and compressed bulk densities. Fire characteristics were determined during several fire tests of textile fibres. On the basis of performed fire test has been determined the combustion heat, flash point (FIT) and ignition temperature (SIT).

Abstract: Subject of this paper is numerical modelling of steel assembling bolt connections of CHS (circular hollow sections) or L-profiles respectively in the FEM software ANSYS 12.0 and their subsequent comparison with performed laboratory experiments. Non-linear calculations with both plastic behavior of materials and influence of large deformations were taken into account. Comparison of results, in the form of load-deformation curves, showed that numerical models describe the basic behavior of those joints. The direct numerical model outputs were modified. This modification was made with respect to real laboratory conditions taking into account the effect of the trial press machine slip stiffness and the initial slip.

Abstract: The paper describes experimental measurement of volume changes of cement concrete. Volume changes include swelling and shrinkage of cement concrete specimens measured by string strain gauges both internal and external. Parallel to this measurement, the volume changes will be measured by means of shrinkage drains. The measurement of volume changes by the shrinkage drains is allowing continuous volume changes to be measured from the beginning of the setting of the concrete. It is possible to capture the entire process of hydration of concrete. The specimens are in the laboratory and in the outdoor environment, so it’s possible to compare values from different environments. The measured results are compared with the calculation models of shrinkage (Model B4 from Bažant [4]; Model Code 2010 [16] and ČSN EN 1992-1-1 [9]).

Abstract: Modern fasteners offer new options for the design of timber load-bearing structures. In the design, the traditional hinged connections are increasingly being replaced with semi-rigid connections. Nevertheless, there is no feedback from the actual structures with this kind of connection regarding the accuracy of static calculations. The authors therefore decided to test one connection and compare the results with those obtained from calculation models. The paper presents the experimental verification of the frame connection in which the semi-rigid action was achieved by combining the aluminium Sherpa connector and total thread Rothoblaas screws. The timber samples were provided by Latti Extra.

Abstract: Bolting and anchoring products are mostly pre-tensioned after their putting into the construction. Pre-tensioning force is a force with clearly defined size and direction and helps the construction to transfer loads. After pre-tensioning a cable bolt some pre-tension losses occur immediately after releasing the jack and other losses progress during their working time. These losses may occur due to the mechanical properties of the cable bolt and its structure itself, but also due to the properties of the surrounding rock mass.The article deals with the enumeration and description of individual losses in accordance with applicable legislation and their measurements both in the laboratory and in actual mining conditions. The comparison of calculated and measured losses and a brief overview of pre-tensionable bolting technology within OKD coal deep mines is a part of the content as well. The result of the tests is quantification of these types of pre-tension losses including proposals for their reduction.

Abstract: This paper deals with prestressed foundation - soil interaction. For interaction task is used FEM model of thick slab with shear influence which is supported by structural strength modified elastic half-space. The calculation of deformations, internal forces and contact stresses in subsoil is performed iteratively by means of isoparametric element and numerical integration. The results of settlement and stress of non-prestressed/prestressed slab - subsoil interaction are compared on example.