Optimal Schemes of Tall Pinned Masts

Rimantas Belevičius,Donatas Jatulis,Dainius Rusakevičius 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.2

A procedure for simultaneous topology, shape, and sizing optimization of tall pinned guyed masts is presented in the paper, seeking the minimal total mass of the mast structure including guys. The typical schemes of tall telecommunication masts of four different heights with different antenna areas distributed in the top 15% of the mast height that is triangular in plan and supported by two to four guys’ clusters are examined. The mast structure is optimized for self-weight and wind loading evaluated according to Eurocodes. Since the non-gradient stochastic optimization algorithm requiring thousands of problem solutions is used, the non-linear behaviour of the guyed mast is mimicked by a suggested approximate linear analysis procedure. The optimization constraints involve all strength, local, and global stability requirements. Analysis of the optimization results leads to the following most important findings: at equal conditions of the mast scheme, a higher number of guys’ clusters always reduces the mast mass; in case of four guys’ clusters levels the anchoring points of the top and the next-to-last level guys should be superposed. Also, the optimal ranges of pre-stresses in guys of different levels, their inclination angles, and the ratios of spans between guys’ levels are provided.

Physical and mechanical changes on titanium base of three different types of hybrid abutment after cyclic loading

Rimantas Ožiūnas,Jurgina Sakalauskienė,Laurynas Staišiūnas,Gediminas Žekonis,Juozas Žilinskas,Gintaras Janužis 대한치과보철학회 2023 The Journal of Advanced Prosthodontics Vol.15 No.1

Purpose. This study investigated the physical and mechanical changes in the titanium base of three different hybrid abutment materials after cyclic loading by estimating the post-load reverse torque value (RTV), compressive side fulcrum wear pattern of titanium base, and surface roughness. Materials and methods. A total of 24 dental implants were divided into three groups (n = 8 each): Group Z, LD, and P used zirconia, lithium disilicate, and polyetheretherketone, respectively, for hybrid abutment fabrication. RTV was evaluated after cyclic loading with 50 N for 1.2 × 106 chewing cycles. The compressive sides of the titanium bases were analyzed using a scanning electron microscope, and the roughness of the affected areas was measured using an optical profilometer after loading. Datasets were analyzed using Kruskal–Wallis test followed by Mann-Whitney tests with the Bonferroni correction (α = .05). Results. Twenty-three samples passed the test; one LD sample fractured after 770,474 cycles. Post-load RTV varied significantly depending on the hybrid-abutment material (P = .020). Group P had a significantly higher median of post-load RTVs than group Z (16.5 and 14.3 Ncm, respectively). Groups LD and P showed minor signs of wear, and group Z showed a more pronounced wear pattern. While evaluating compressive side affected area roughness of titanium bases, lower medians were shown in group LD (Ra 0.16 and Rq 0.22 µm) and group P (Ra 0.16 and Rq 0.23 µm) than in group Z (Ra 0.26 and Rq 0.34 µm); significant differences were found only among the unaffected surface and group Z. Conclusion. The hybrid abutment material influences the post-load RTV. Group Z had a more pronounced wear pattern on the compressive side of titanium base; however, the surface roughness was not statistically different among the hybrid-abutment groups.

A comparative biomechanical study of original and compatible titanium bases: evaluation of screw loosening and 3D-crown displacement following cyclic loading analysis

Rimantas Ožiūnas,Jurgina Sakalauskienė,Darius Jegelevičius,Gintaras Janužis 대한치과보철학회 2022 The Journal of Advanced Prosthodontics Vol.14 No.2

PURPOSE. This study evaluated screw loosening and 3D crown displacement after cyclic loading of implant-supported incisor crowns cemented with original titanium bases or with three compatible, nonoriginal components. MATERIALS AND METHODS. A total of 32 dental implants were divided into four groups (n = 8 each): Group 1 used original titanium bases, while Groups 2-4 used compatible components. The reverse torque value (RTV) was evaluated prior to and after cyclic loading (1,200,000 cycles). Samples (prior to and after cyclic loading) were scanned with a microcomputed tomography (micro-CT). Preload and postload files were superimposed by 3D inspection software, and 3D crown displacement analysis was performed using root-mean-square (RMS) values. All datasets were analyzed using one-way ANOVA and Tukey’s post hoc analysis. RESULTS. Significant variations were observed in the postload RTV, depending on the titanium base brand (P < .001). The mean postload RTVs were significantly higher in Groups 1 and 2 than in the other study groups. While evaluating 3D crown displacement, the lowest mean RMS value was shown in the original Group 1, with the highest RMS value occurring in Group 4. CONCLUSION. Within the limitations of this in vitro study and under the implemented conditions, it was concluded that the manufacturer brand of the titanium base significantly influenced screw loosening following the fatigue test and influenced 3D crown displacement after cyclic loading.

IS in Public Sector ; Lithuania`s e-government gateway development

Rimantas Gatautis,Jurgita Stravinskiene 한국경영정보학회 2005 한국경영정보학회 학술대회논문집 Vol.2005 No.-

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.

Duplex positioning method for increasing the fatigue life of threaded connections under eccentric loading

Algimantas Krenevičius,Rimantas Kačianauskas,Jelena Selivonec,Stanislav Stupak 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

A new method, duplex positioning method DPM, to increase the fatigue lifetime of the threaded connection under eccentric loading is presented. When DPM is applied, the most damaged stud regions periodically are removed from risky positions by a change of the stud’s and nut’s mutual position in the axial direction alongside with a change of the stud’s position in respect to bending plane. The mathematical model for DPM enables us to predict its efficiency. To simulate the fatigue strength of the stud the following was used: Patterson’s and Kenny’s thread deflection factors, solutions for the distributions of the axial load and bending moment along the threads, Neuber’s method for the stress concentration factors in multiplier notches, Heywood’s formulas for the stress due to the thread flank loading and for the combined stresses, as well as the results of the photoelastic analysis of the araldite models under eccentric loading.

Experimental investigation of local damage in high strength concrete columns using a shaking table

Romualdas Kliukas,Rogerio Bairrao,Rimantas Kaianauskas 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.19 No.5

Experimental investigation of local damage in high strength concrete columns using a shaking table

Bairrao, Rogerio,Kacianauskas, Rimantas,Kliukas, Romualdas Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.19 No.5

In this paper the accumulation of local damage during the cyclic loading in reinforced high-strength concrete columns is experimentally investigated. Two identical column specimens with annular cross-section and spiral reinforcement were designed and two tests, up to failure, under the action of a constant vertical concentrated force and a time-dependent concentrated horizontal force, were carried out at the LNEC shaking tables facility. Sine type signals, controlled in amplitude, frequency and time duration were used for these experiments. The concept of local damage based on local stiffness degradation is considered in detail and illustrated by experimental results. The specimens were designed and reinforced in such a way that the accumulation of damage was predicted by dominating deformations (cracking and crushing of the concrete) while the increasing of the loading values was a dominating factor of damage. It was observed that the local damage of HSC columns has exposed their anisotropic local behaviour. The damage accumulation was slightly different from the expected in accordance with the continuum damage concept, and a partial random character was observed.

Time reversal invariance violating and parity conserving effects in proton-deuteron scattering

Song, Young-Ho,Lazauskas, Rimantas,Gudkov, Vladimir American Physical Society 2016 Physical Review C Vol.93 No.6

<P>Time reversal invariance violating parity conserving (TVPC) effects are calculated for elastic proton-deuteron scattering with proton energies up to 2 MeV. The distorted-wave Born approximation is employed to estimate TVPC matrix elements, based on hadronic wave functions, obtained by solving three-body Faddeev-Merkuriev equations in configuration space with realistic potentials.</P>

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.