Papers by Keyword: Strengthening

Abstract: The article deals with the use of local highly dispersed unsuitable soils for the construction of foundations and pavements instead of imported expensive conditioned stone materials. A variant of solving this problem is proposed by strengthening weak (subsiding) soils with modern stabilizing additives and soil stabilizers.

Abstract: UHPC is a material which exhibits excellent mechanical properties and durability. Beside new structures it is also convenient for strengthening of existing structures. The paper investigates the possibilities of strengthening experimentally. A part of the experimental program is presented which is focused on bond of UHPC and existing concrete and on behaviour in bending. Acceptable bond may be achieved when the existing concrete is clean and reasonably rough. Structural elements are exposed to positive and negative bending moments. If UHPC overlay is applied, it works in compression and in tension. The experiments were therefore focused on verification of both alternatives (UHPC in compression and in tension). Finally, the conclusions from the experiments are drawn, which may be applied in practical design.

Abstract: In the article, the issues of using the methods of thermo-frictional and chemical-thermal treatments for surface strengthening of steel tools were disclosed. 65G steel and U8A steel were considered. A flat graver and a cylindrical root roller were considered to be tools in need of hardening. The nature of the jewellery work using such a tool has been described. Hardening techniques, experimental studies and macro photographs of the samples were presented in this article. A detailed metallographic analysis and measurement of the microhardness of the cross-sections of the prototypes after their strengthening using various methods was carried out. The metallographic nature of the reinforcement with the formation of surface "white layers" was shown. Comparison of the properties of the samples before and after strengthening was carried out. Conclusions about the strengthening effect of the thermo-frictional and chemical-thermal methods of strengthening were made.

Abstract: This article discusses the ways of intensification of the oxidation process with the formation of surface properties necessary to increase the service life of one of the parts of an internal combustion engine - a cylinder made of cast aluminum alloy. A brief overview of existing technologies for hardening the aluminum surface is presented. Environmentally friendly options are proposed for using the potential of processes that have accumulated energy within an electrolytic cell by activating the interelectrode gap and forming an oxide with desired properties. The main difference from the existing model approaches of oxide formation lies in the parallel excitation of the main participant in the process, oxygen, in order to dominate it over other, oxygen-containing donors. Ways of using the energy of cavitation phenomena due to acoustic resonance in an electrolytic solution are proposed. Redistribution of the field potential by replacing a flat cathode with a pointed one changed the conductivity conditions in the interelectrode gap as a result of the electroconvective action. The structure of the oxide layer, phase changes, and physical properties confirming the originality of oxide coatings have been investigated.

Abstract: The main aims and the objectives of the study focused on solving current problems of nanomaterial science of new materials – creating the scientific basis for competitive methods of obtaining and controlling new composite materials having improved strength properties based on carbon-containing polymer matrices with nanotubes stabilized in them. A technology for obtaining experimental samples of nanocompositional polymer material based on polymethylmethacrylate, polybutylmethacrylate, and methacrylic acid doped with carbon nanotubes has been developed, using ultrasonic action and mechanical mixing of the composite mixture to achieve the most uniform distribution of nanotubes in the matrix. To determine the possibility of implementing the mechanism of adsorption interaction of the studied polymer material with the surface of carbon nanotubes, DFT calculations of the interaction of the polymer material component and single-layer carbon nanotubes of various types have been done.

Abstract: This paper presents the experimental testing of eccentrically compressed reinforced concrete columns. There are experimental results of crack resistance of non-strengthened (control) and strengthened RC columns in the tension zone. The columns were strengthened by carbon fiber reinforced polymers (CFRP). As a result of experimental studies with the columns strengthened by CFRP, we obtain that the width of their crack decreased by an average of 33%. The eccentric compression load of the crack’s appearance increased from 40 kN to 60 kN for strengthened columns.

Abstract: A total of seven simply supported composite specimens are tested under concentrated load at the mid-span of the beam to investigate the strength of specimens to resist the applied load if web buckling take place. A novel technique of using a corrugated CFRP struts to strengthen the web of the steel girder is presented in this study. This technique provides two layers of CFRP laminate which are from biaxial fabrics to provide a knitted material that can undergo the complex state of stress in the web. The studied specimens are divided into two groups in addition to the control specimen having the same length. There are three specimens in each group, these specimens have different castellation ratios of (33.3%, 43.3% and 54.3%), the first group is identical to the second one except that the second group was strengthened with the proposed CFRP corrugated struts while the first one kept unstrengthen as a reference. Composite beams have a vertical stiffener at the action area above the supports. The reference group showed decrease in deflection of (11.11, 20 and 26.67) % for (33.3, 43.3 and 54.3) castellation ratio while strengthened girders record (13.75, 6.11 and 13.93) % for the same opening depths, compared to the control specimen. In addition, CFRP struts decrease the web buckling from (1.6, 2.9 and 83.33) to (0.8, 0.4 and 0.3) mm for beams with castellation ratio of (33.3, 43.3 and 54.3) respectively.

Abstract: Questions of thermomechanical parameters appointment under the semihot (warm) forging of metal preforms were considered. The international experience was analyzed as well. Economically effective thermomechanical conditions under semihot/warm forging, which is capable to provide a high complex of the mechanical properties of steel, are offered. The economical effect after the process integration to the industry was considered.

Abstract: Fiber reinforced polymer (FRP) is widely used in the construction industry for structural strengthening due to their outstanding mechanical properties. However, the production of synthetic fibers such as FRP is detrimental to the environment. Alternatively, natural fiber composite may be used as external strengthening material. This paper presents the potential of bamboo fiber composite plate (BFCP) to strengthen the reinforced concrete (RC) beams in flexure. The bamboo of species Dendrocalamus asper was used to produce the fiber and fiber-to-volume ratio was set at 2:5. The composite plate was fabricated by binding bamboo fibers with epoxy using a hand-lay-up method. The flexural and tensile strength of the BFCP was measured and all the beams were tested to failure under four-point bending test. It was found that BFCP exhibited a higher flexural and tensile strength compared to pure epoxy samples. Meanwhile, the RC beams strengthened using BFCP exhibited an increment of 10-12% in beam structural capacity compared to the un-strengthened beams. Bonding of BFCP in the flexure zone was able to divert the vertical cracks into diagonal at the edge of the composite plate. Findings from this work may serve as a useful guide to strengthen RC beams using a BFCP.

Abstract: The paper presents an analysis of the causes and effects of masonry vaults damage after a construction disaster in the historic church of St. George in Hajduki Nyskie (southern Poland), dated to the beginning of the XIV century. As a result of the collapse of the eastern gable wall, some parts of the vaults and a wooden roof were destroyed, as well as other structural elements and part of the church's equipment. The building combines late Romanesque, Gothic and Baroque style elements, representing high, trans-regional historical and artistic, religious and cultural values, in particular due to the valuable gothic wall paintings preserved in the nave. The paper presents the state of the building before and after the construction disaster as well as recommendations regarding the reconstruction of the vaults.