The development of nature-inspired gripping system of a flat CFRP strip for stress-ribbon structural layout

Viktor Gribniak,Aleksandr K. Arnautov,Arvydas Rimkus 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.2

The elegant stress-ribbon systems are efficient in pedestrian bridges and long-span roofs. Numerous studies defined corrosion of the steel ribbons as the main drawback of these structures. Unidirectional carbon fiber-reinforced polymer (CFRP) is a promising alternative to steel because of lightweight, high strength, and excellent corrosion and fatigue resistance. However, the application of CFRP materials faced severe problems due to the construction of the anchorage joints, which must resist tremendous axial forces acting in the stress-ribbons. Conventional techniques, suitable for the typical design of the strips made from anisotropic material such as steel, are not useful for СFRP strips. The anisotropy of СFRP makes it vulnerable to loading in a direction perpendicular to the fibers, shear failure of the matrix, and local stress concentrations. This manuscript proposes a new design methodology of the gripping system suitable for the anchorage of flat strips made from fiber-reinforced polymers. The natural shape of a logarithmic spiral Nautilus shell describes the geometry of the contact surface. The continuous smoothly increasing bond stresses due to friction between the anchorage block and the CFRP strip surface enable the gripping system to avoid stress concentrations. The 3D-printed polymeric prototype mechanical tests proved the proposed frictional anchorage system efficiency and validated the developed analytical model.

Application of FE approach to deformation analysis of RC elements under direct tension

Ronaldas Jakubovskis,Rimantas Kupliauskas,Arvydas Rimkus,Viktor Gribniak 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.3

Heterogeneous structure and, particularly, low resistance to tension stresses leads to different mechanical properties of the concrete in different loading situations. To solve this problem, the tension zone of concrete elements is reinforced. Development of the cracks, however, becomes even more complicated in the presence of bar reinforcement. Direct tension test is the common layout for analyzing mechanical properties of reinforced concrete. This study investigates scatter of the test results related with arrangement of bar reinforcement. It employs results of six elements with square 60×60 mm cross-section reinforced with one or four 5 mm bars. Differently to the common research practice (limited to the average deformation response), this study presents recordings of numerous strain gauges, which allows to monitor/assess evolution of the deformations during the test. A simple procedure for variation assessment of elasticity modulus of the concrete is proposed. The variation analysis reveals different deformation behavior of the concrete in the prisms with different distribution of the reinforcement bars. Application of finite element approach to carefully collected experimental data has revealed the effects, which were neglected during the test results interpretation stage.

On the parametric instability of multilayered conical shells using the FOSDT

John Lair,David Hui,Abdullah H. Sofiyev,Viktor Gribniak,Ferruh Turan 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.31 No.3

This paper investigates the parametric instability (PI) of multilayered composite conical shells (MLCCSs) under axial load periodically varying the time, using the first order shear deformation theory (FOSDT). The basic equations for the MLCCSs are derived and then the Galerkin method is used to obtain the ordinary differential equation of the motion. The equation of motion converted to the Mathieu-Hill type differential equation, in which the DI is examined employing the Bolotin’s method. The expressions for left and right limits of dimensionless parametric instability regions (PIRs) of MLCCSs based on the FOSDT are obtained. Finally, the influence of various parameters; lay-up, shear deformations (SDs), aspect ratio, as well as loading factors on the borders of the PIRs are examined.

Application of FE approach to deformation analysis of RC elements under direct tension

Jakubovskis, Ronaldas,Kupliauskas, Rimantas,Rimkus, Arvydas,Gribniak, Viktor Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.3

Heterogeneous structure and, particularly, low resistance to tension stresses leads to different mechanical properties of the concrete in different loading situations. To solve this problem, the tension zone of concrete elements is reinforced. Development of the cracks, however, becomes even more complicated in the presence of bar reinforcement. Direct tension test is the common layout for analyzing mechanical properties of reinforced concrete. This study investigates scatter of the test results related with arrangement of bar reinforcement. It employs results of six elements with square $60{\times}60mm$ cross-section reinforced with one or four 5 mm bars. Differently to the common research practice (limited to the average deformation response), this study presents recordings of numerous strain gauges, which allows to monitor/assess evolution of the deformations during the test. A simple procedure for variation assessment of elasticity modulus of the concrete is proposed. The variation analysis reveals different deformation behavior of the concrete in the prisms with different distribution of the reinforcement bars. Application of finite element approach to carefully collected experimental data has revealed the effects, which were neglected during the test results interpretation stage.

Modelling of tension-stiffening in bending RC elements based on equivalent stiffness of the rebar

Torres, Lluis,Barris, Cristina,Kaklauskas, Gintaris,Gribniak, Viktor Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.5

The contribution of tensioned concrete between cracks (tension-stiffening) cannot be ignored when analysing deformation of reinforced concrete elements. The tension-stiffening effect is crucial when it comes to adequately estimating the load-deformation response of steel reinforced concrete and the more recently appeared fibre reinforced polymer (FRP) reinforced concrete. This paper presents a unified methodology for numerical modelling of the tension-stiffening effect in steel as well as FRP reinforced flexural members using the concept of equivalent deformation modulus and the smeared crack approach to obtain a modified stress-strain relation of the reinforcement. A closed-form solution for the equivalent secant modulus of deformation of the tensioned reinforcement is proposed for rectangular sections taking the Eurocode 2 curvature prediction technique as the reference. Using equations based on general principles of structural mechanics, the main influencing parameters are obtained. It is found that the ratio between the equivalent stiffness and the initial stiffness basically depends on the product of the modular ratio and reinforcement ratio ($n{\rho}$), the effective-to-total depth ratio (d/h), and the level of loading. The proposed methodology is adequate for numerical modelling of tension-stiffening for different FRP and steel reinforcement, under both service and ultimate conditions. Comparison of the predicted and experimental data obtained by the authors indicates that the proposed methodology is capable to adequately model the tension-stiffening effect in beams reinforced with FRP or steel bars within wide range of loading.

Investigating deformations of RC beams: experimental and analytical study

Javier Ezeberry Parrotta,Hugo Corres Peiretti,Viktor Gribniak,Alejandro Pérez Caldentey 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.13 No.6

In this paper, a theoretical and experimental study of the sectional behaviour of reinforced concrete beams subjected to short-term loads is carried out. The pure bending behaviour is analysed with moment-curvature diagrams. Thus, the experimental results obtained from 24 beams tested by the authors and reported in literature are compared with theoretical results obtained from a layered model, which combines the material parameters defined in Model Code 2010 with some of the most recognized tensionstiffening models. Although the tests were carried out for short-term loads, the analysis demonstrates that rheological effects can be important and must be accounted to understand the experimental results. Another important conclusion for the beams tested in this work is that the method proposed by EC-2 tends to underestimate the tension-stiffening effects, leading to inaccuracies in the estimations of deflections. Thus, the actual formulation is analysed and a simple modification is proposed. The idea is the separation of the deflection prediction in two parts: one for short-term loads and other for rheological effects (shrinkage). The results obtained are in fairly good agreement with the experimental results, showing the feasibility of the proposed modification.

Modelling of tension-stiffening in bending RC elements based on equivalent stiffness of the rebar

Lluis Torres,Cristina Barris,Gintaris Kaklauskas,Viktor Gribniak 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.5

The contribution of tensioned concrete between cracks (tension-stiffening) cannot be ignoredwhen analysing deformation of reinforced concrete elements. The tension-stiffening effect is crucial when itcomes to adequately estimating the load-deformation response of steel reinforced concrete and the morerecently appeared fibre reinforced polymer (FRP) reinforced concrete. This paper presents a unifiedmethodology for numerical modelling of the tension-stiffening effect in steel as well as FRP reinforcedflexural members using the concept of equivalent deformation modulus and the smeared crack approach toobtain a modified stress-strain relation of the reinforcement. A closed-form solution for the equivalent secantmodulus of deformation of the tensioned reinforcement is proposed for rectangular sections taking theEurocode 2 curvature prediction technique as the reference. Using equations based on general principles ofstructural mechanics, the main influencing parameters are obtained. It is found that the ratio between theequivalent stiffness and the initial stiffness basically depends on the product of the modular ratio andreinforcement ratio (nρ), the effective-to-total depth ratio (d/h), and the level of loading. The proposedmethodology is adequate for numerical modelling of tension-stiffening for different FRP and steelreinforcement, under both service and ultimate conditions. Comparison of the predicted and experimentaldata obtained by the authors indicates that the proposed methodology is capable to adequately model thetension-stiffening effect in beams reinforced with FRP or steel bars within wide range of loading.