Ultra High Performance Concrete Reinforced with Short Steel and Carbon Fibers

Fibers are usually used in High Performance Concrete with a purpose to increase bending strength and ductility. Important properties are the peak value of bearing stress (strength) and post-cracking behavior of bended element. In the framework of an experimental part, Ultra High Performance mix compositions were prepared using intensive mixer. Short steel fibers and carbon micro fibers in amount of 1% by volume, as well as its combination were used for cement matrix reinforcing. Results of compressive and bending tests proved an increase of strength value in the case of use both steel and carbon fibers. Carbon fibers were decreased the effect of explosive collapse of the UHPC cement matrix, at the same time still brittle bending behavior was take place. Steel fibers considerably improved bending ductility thanks to a pull-out mechanism of steel fibers. The best results were achieved in the case of combined application of both carbon and steel fibers

Cauruļvada ar virsmas tilpuma defektu kompozītmateriālu labošanas izpēte

Darbā definēts caurules virsmas tilpuma defekts un aprakstīta ekvivalentā (Mizes) sprieguma izmaiņa caurulē atkarībā no virsmas tilpuma defekta lieluma. Virsmas tilpuma defekta izmaiņu trijās koordinātēs raksturo izveidotais eksperimentālais plāns. Katram caurules virsmas tilpuma defekta lielumam modelētas dažāda biezuma kompozītmateriālu bandāžas. Izskaitļots ekvivalentais spriegums pie darba spiediena caurulē, izmantojot galīgo elementu metodi ANSYS programmatūrā: caurulei bez defekta, caurulēm ar dažāda izmēra virsmas tilpuma defektiem un caurulēm ar dažāda izmēra virsmas tilpuma defektiem, kas laboti ar dažāda biezuma kompozītmateriālu bandāžām. Visi iegūtie rezultāti ir aproksimēti un analizēti ar mērķi iegūt optimālo bandāžas biezumu dažādiem defekta izmēriem

Fiber Concrete Viscous Flow Numerical Simulation

Viens no efektīviem paņēmieniem, kā palielināt betona mehāniskās īpašības, ir armēt to ar dispersi izkaisītām īsām šķiedrām. Šāda paņēmiena galvenā tehnoloģiskā priekšrocība ir iespēja ievadīt īsās šķiedras betona sastāvā tā izgatavošanas stadijā, ieberot šķiedras maisītājā kopā ar citiem ingredientiem. Tai paša laikā īso šķiedru pielikšana betonam izsauc betona sastāva maisīšanas un transportēšanas pasliktināšanos. Pasliktināšanās pieaug, palielinot pielikto šķiedru garumu un to koncentrāciju betonā. Šķidrais fibrobetons ir viskozs (vai pat ļoti viskozs) šķidrums, kura ieplūšanas process veidnē, formā vai zemē izraktā tranšejā prasa papildus izpēti. Šajā darbā šķidra betona plūsma tiek skaitliski modelēta, pieņemot, ka tā veido homogēnu viskozu šķidrumu. Literatūrā var sastapt dažādus reoloģiskus modeļus, veltītus cementu saturošu materiālu plūsmas modelēšanai. Divi no tiem- Ņutona un Bingama viskoza šķidruma tecēšanas modeļi - tiek izmantoti šajā darbā. Modelēšanas rezultātā veikta plaša parametriskā izpēte lokālo ātrumu un spiediena atkarībai no izraktās tranšejas ģeometrijas, rakšanas kombaina kustības ātruma un fibrobetona padošanas spiediena

Dažādu risinājumu salīdzināšana sijas trīspunktu liecei

47. RTU Studentu zinātniskās un tehniskās konferences materiāl

Energy Extraction from Air or Water by Vibrations

The paper considers the possibility to derive energy from air or water in a non-traditional way (without using rotating equipment). For this purpose, the authors studied variations in the additional area of a vibrating object in a definite sequence found as the solution of an optimisation problem. In the work, stably moving mechatronic systems were synthesised and modelled, whose control is very simple (not requiring calibration), being a function of the changing sign of phase coordinates

Development of Experimental Optimization Methodology for the Pipelines Repairing by Using Advanced Composite Materials

Metamodelling is scientific current in the theoretical and experimental engineering science and mechanics. Metamodelling, or meta-modelling in software engineering and systems engineering among other disciplines, is the analysis, construction and development of the frames, rules, constraints, models and theories applicable and useful for modelling a predefined class of problems. This method allows obtaining information about the structure of the investigated object by analysing solely the registered output measurements of this object (machine, mechanism, technological process), and identifying both the mathematical model of the object and its input parameter values, using both natural experiments and computer experiments with different mathematical modelling software (ANSYS, LSDYNA, ADAMS, etc.). Creation of metamodels for the dependence of the response surface data to the input factors is facilitating to formulate the multiobjective optimization goal functions and constraints, conducting optimization. Verification and validation of results provides the best optimization data

Using Penalty Function Method for Analysis of Dynamic Behaviour of Viscoelastic Materials

The present article investigates the application of the penalty function method in the analysis of behaviour of viscoelastic materials, particularly silicon rubbers, under dynamic loading. To perform the analysis, the mathematical model of the object was chosen, and the Matlab code for the mathematical model was developed. The dynamic force was applied to the given model. To find the most precise element describing the behaviour of elastic material from some set of available alternatives, the penalty method, which replaces a constrained optimization problem by a series of unconstrained problems, was used

Fiber Concrete for Construction Member Subjected to Bending Load

Fiber Concrete for Construction Member Subjected to Bending Load were elaborated. Detailed mix design was performed

Non-Traditional Reinforcement for Concrete Composites – State of the Art = Netradicionālais betona stiegrojums – mūsdienu problēmas stāvoklis

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Stability of Multilayered Rubber-Metal Shock Absorbers

Stability of shock absorbers with thin-multilayered rubber-metal elements (TRME) of flat, circular shape is considered in this work. TRME packages that are used as vibration isolators usually work under heavy compressive loads, which may lead to buckling failure. Next, formulas for package design are derived: the dependence of the critical force on geometryof layer, on mechanical properties of material of elastomeric layers, on packages end-fixity conditions. The dependence of mechanical modules of elastomeric on the compressive load level is taken into account. The obtained solutions are compared to experimental data of other authors