Papers by Keyword: Resistance

Abstract: Reinforced concrete flat slabs are frequently used structural members in building construction. One of the most dangerous form of structural failure of these system is punching of the slab by support. The best way how to verify the reliability of standard model for the assessment of punching capacity is comparison of the resistance obtained from the experiments, with the resistances calculated according to the standard. To determine the reliability of the standards a large database of test results is required, but from economical point of view, it is not possible to prepare so many tests in order to fulfill this requirement. The problem can be solved by non-linear analysis which is a tool that allows to substitute actual tests with theoretical ones. The paper deals with non-linear analysis of punching of flat slabs, where the numerical model of flat slab specimens using results taken from the experimental program carried out at the laboratory of Slovak University of Technology. The task was to find the suitable non-linear material model for concrete and reinforcement, choose the proper boundary conditions, the correct load application and choose the appropriate way of modeling. The correct adjustment of the numerical model allows to carry out parametric study of flat slabs.

Abstract: Magnesium alloys have the characteristic with high specific strength and lightweight property, it is widely used for auto mobile industry. Heat-resistant magnesium alloy is focused as a suitable material for weight reduction of the engine and power train parts in automotive field. In this study, microstructure and heat-resistant property in Mg-3mass%Al-1mass%Si (Mg-3%Al-1%Si) alloy with containing large amount of Sn (tin) were investigated. The alloys produced by permanent mold casting were investigated by optical microscope (OM), scanning electron microscopy (SEM) and measuring of bolt load retention at 423K. The heat-resistant property of Mg-3mass % Al-1mass % Si alloy with containing 6-13masss%Sn was higher compared with Sn free alloy and conventional Magnesium alloys (e.g. AZ91 and AM60 alloys).

Abstract: This paper presented the effect of DE-GMAW (Double electrode gas metal arc welding)resistance on mechanical and physical properties of aluminium alloywelded. DE-GMAWis amethodof welding process that use two electrode. A non consumable torch is added to bypass the current inorder to reduce the heat input. The variation resistance used were 15Ω, 30Ω and 45Ω. Universaltesting machine and Vickers microhardness were used to measured mechanical properties of weldmetals with respect to strength and hardness. The microstructure was investigated by microscopeoptic with 100 x magnification. The grain size of weld metals with resistance value 30Ω is finer than15Ω and 45Ω. Dye penetrant test shows DE-GMAW welding machine that made have goodperformance because it can produce welding joint without surface crack. The results show thatresistance values optimum to DE-GMAW welding on aluminium alloy 5051 with 4 mm thickness is30Ω. It can be seen from the tensile test that shows the highest tensile strength is found in the DEGMAWwelding with resistance values 30Ω.

Abstract: Ce_1.2(1-x)Mn_1-xSi_x(x=0.1,0.2.0.3,0.4) NTC thermistor materials were prepared by the traditional solid-state reaction method. The effects of SiO₂ content on the microstructure and electric properties of prepared materials are investigated through XRD, SEM, XPS and several instruments for electrical properties characterization. The results indicate that the average grain size increases with the increasing SiO₂ content. The resistivity and materials constant B value exhibit opposite change laws. The minimum room resistivity of 7.18×10⁵ Ω·cm and the maximum characteristic parameter B value of 5507K are obtained when x=0.2. And when x=0.1 the aging factor η is 0.34% and it decreases as the CeO₂ content increases.

Abstract: Flat slabs are commonly used structures in contemporary architecture. Although their common use there is still problem in design of these structures. The openings adjacent to a column are often used for plumbing and such a position of the openings increases shear stresses in the flat slab near the column. This paper deals with experimental work focused on the punching shear resistance of the flat slab specimens with openings adjacent to column compared to the flat slab specimens without openings. The opening influence is determined experimentally and by using models for the assessment of punching resistance from relevant standards and codes. The material properties of concrete and reinforcing steel were obtained from the laboratory tests.

Abstract: This article presents some results of the experimental monotonic bending tests on the behaviour of the tubular columns and the reverse channel, effected based on a parametric variation of the most significant characteristics of the tubular profiles. The parameters considered are the thicknesses and the widths of the tubular columns faces, the filling with concrete and the axial load. The experimental tests program, included in the framework of the Doctoral Program Thesis in the scientific domain of the Steel Composite Structures, were performed on a test layout, corresponds to a framed structure, in the Structural Mechanic Laboratory of the Department of Civil Engineering of the University of Coimbra. The objective is to determine the characteristics of the nonlinear cyclic behaviour of the principal components of the tubular columns and the reverse channel, in this shape of joints. These components are related to the tubular columns walls, and to the web and flanges of the reverse channel yielding, crushing or instability, when submitted to bending, shear, compression and tension. The results of this experimental tests allow correlate the parameters considered with the structural behaviour of the connection, defined by the resistance, the stiffness, and the rotation capability.

Abstract: The article deals with the current problem of determining long-term reliability of non-metallic reinforcement in concrete structures. The alkaline environment of concrete with a pH higher than 12.0 affects the glass fibres degradative, whereas this degradation presents by reduction of their mechanical characteristics, resulting in a decrease in the tensile strength of the whole composite. The article summarizes the results of the ongoing experimental program so far, which aims to quantify this influence.

Abstract: A benchmark test will insure that the equipment, procedures, and uncertainty estimates are adequate. The experiments of a well-known bulk carrier bare hull shape (the model LHI-007) has been set up and conducted at towing tank Indonesian Hydrodynamic Labotatory. The aim of the present study is to contribute data of the surface ship resistance model-scale database in calm water on one hand, and on the other – reliable Experimental Fluid Dynamics (EFD) data, as part of an internal benchmark test. Conclusions are made with regard to the available data and past uses and recommendations are provided for future uses of the available data and future data procurement.

Abstract: Two ways how to determine maximum punching resistance of flat slabs with shear reinforcement are currently used. The first way is verification of the concrete strut capacity at the column periphery defined as V_Rd,max. The second limit is defined as k_max multiple of the punching shear resistance without shear reinforcement V_Rd,c. The values of k_max are proposed usually in between 1.4 and 2.0. Results of the experimental tests are presented in the paper that were focused on above mentioned limits, whether failure of the struts can precede any other form of punching failure that is limited by k_max*V_Rd,c. Two experimental slab samples reinforced with high amount of shear reinforcement that increased punching capacity above capacity of the concrete struts were tested together with two slab samples cast without shear reinforcement. Comparison has shown that punching resistance of flat slab with shear reinforcement has been 1.7 times higher than resistance without shear reinforcement. While some standards allow for use k_max value of 1.9 in this case. This indicates that limits based only on the k_max factors may overestimate actual maximum punching shear resistance.

Abstract: Alternating current impedance has been used to study effects of hydration stages and molar ratio on the pore structure and hydration characters of basic magnesium sulfate cement. The alternating current impedance spectra of at early hydration almost appears as a straight line because none crystal hydration phases form. And it appears high frequency semicircle at late hydration stage because of decreasing of porosity and amount of 5Mg (OH)² ·MgSO₄·7H₂O gradually form with ages. Besides, alternating current impedance spectra differences among basic magnesium sulfate, magnesium oxysulfate and magnesium oxychloride cement have been studied. These differences indicate that additives such as citric acid may change the structure and charge characteristics of MgO hydration layer which make tends to form more 5Mg (OH)₂ ·MgSO₄·7H₂O phase in basic magnesium sulfate cement than that in magnesium oxysulfate cement. The higher pore solution resistance of BMS cement is the main factor of better steel-protection.