Michal Tomko

Time-dependent analysis and simulation-based reliability assessment of suspended cables with rheological properties

The intention of the paper is to illustrate the ability of the probabilistic time-dependent reliability assessment procedure applied to non-linear suspended cable structure with rheological properties, when a rope made from the high strength synthetic fibres is used in order to demonstrate the new qualitatively different concept. Attention is turned to the individual main steps in the assessment procedure, i.e. to the selection of an appropriate method of structural analysis and to derivation of an appropriate closed-form and discrete analytical models, analysis of random variables representing individual actions (four basic random variables, such as structural geometry, cables modulus of elasticity and creep strain increments and loading, are considered), evaluation of the structural response with respect to the interaction of the random variables considering a history of the time-dependent action effects and to the definition of the limiting values considering serviceability of cable structure. The potential of the method using direct Monte Carlo technique as one of the possible alternatives for simulation-based time-dependent reliability assessment as a powerful tool is emphasized. The influence of an excessive deflection of suspended cable (caused by creep of cable and rheologic changes) on its serviceability in required time is investigated and illustrative examples are performed.

Vibrations of an aramid anchor cable subjected to turbulent wind

Abstract The vibration response of an initially pre-stressed anchor cable made of parallel-lay aramid fibres excited by a measured and artificially simulated spatial turbulent wind field is presented in the paper. Results of the analyses of in situ measured wind records are described. For selected data set statistical characteristics and power spectral density functions of the measured wind velocity components are calculated. The wind stochastic velocity fluctuation is modelled as a one-variate bi-dimensional random field. Cross-power spectral density functions, at different point locations are introduced. The combination of the weighted amplitude wave superposition method (WAWS) with the Shinozuka–Deodatis method is used for the analyzed problem. A time-dependent behaviour of the synthetic cable is investigated which is subjected to turbulent wind with large expected oscillations that arise as a result of slackening due to the relaxation effects. A nonlinear transient dynamic analysis is used in conjunction with the finite element method to determine the dynamic response of the cable subjected to turbulent wind at its initially prestressed state and in the selected times after the relaxation effect. The constitutive equation of the relaxation of the aramid cable follows an experimentally obtained law of the logarithmic type. To monitor the dependences of the individual quantities of cable vibration in the phase space, attractors and Poincare maps are created by sampling the cable’s displacement and velocity at periods of relevant frequencies. Interesting findings based on the response of the cable with rheological properties to turbulent wind are presented.

Analysis of the resistance of thin-walled cold-formed compressed steel members with closed cross-sections. Part 1

From the material and geometric point of view, the thin-walled cold-formed profiles have specific specialties, which their design must responsibly take into account. In the terms of their resistance, an important issue is the effectiveness of mutual interaction between several webs. The local stability requirements related to unfavourable buckling effects of their compressed parts are very significant. Favourable effects, related to membrane stresses and post-critical behaviour are also important. Different calculation procedures with different results in the relevant standards and their confrontation with experimental results indicated the need for further investigation of post-critical behaviour of these members. The paper is divided into two parts. Part 1 presents fundamental information about experimentaltheoretical research oriented to determinate the resistance of thin-walled compressed steel members. The investigated members had closed cross-sections made from homogeneous materials. The theoretical analysis in this research is oriented to determinate the resistance of mentioned members according to European and Slovak standards, while the experimental investigation is to verify the theoretical results and to investigate the behaviour of mentioned members during the loading process. Part 2 will be focused on the numerical analysis of the results, as well as on the 3D-modelling and simulation of experimental tests. References 1. Mamalis A.G., Manolakos D.E., Ioannidis M.B., Kostazos P.K., Dimitriou C. Finite element simulation of the axial collapse of metallic thin-walled tubes with octagonal cross-section. Thin-Walled Structures. 2003. Vol. 41. Issue 10. Pp. 891–900. 2. Rasmussen J.R. Kim. Bifurcation of locally buckled point symmetric columns – Experimental investigations. Thin-Walled Structures. 2006. Vol. 44. Issue 11. Pp. 1175–1184. 3. Chen Ju, Young Ben. Cold-formed steel lipped channel columns at elevated temperatures. Engineering Structures. 2007. Vol. 29. Issue 10. Pp. 2445–2456. 4. Nuno Silvestre, Young Ben, Camotima Dinar. Non-linear behaviour and load-carrying capacity of CFRPstrengthene lipped channel steel columns. Engineering Structures. 2008. Vol. 30. Issue 10. Pp. 2613–2630. 5. Kwon Young Bong, Kim Bong Sun, Hancock Gregory J. Compression tests of high strength cold-formed steel channels with buckling interaction. Journal of Constructional Steel Research. 2009. Vol. 65. Issue 2. Pp. 278–289. 6. Rogers C.A., Yang D., Hancock G.J. Stability and ductility of thin high strength G550 steel members and connections. Thin-Walled Structures. 2003. Vol. 41. Issues 2–3. Pp. 149–166. 7. DiPaolo B.P., Tom J.G. A study on an axial crush configuration response of thin-wall, steel box components: The quasi-static experiments. International Journal of Solids and Structures. 2006. Vol. 43. Issues 25–26. Pp. 7752–7775. 8. Yuan-Qi Li, Zu-Yan Shen, Lei Wang, Yan-Min Wang, Hong-Wei Xu. Analysis and design reliability of axially compressed members with high-strength cold-formed thin-walled steel. Thin-Walled Structures. 2007. Vol. 45. Issue 4. Pp. 473–492. 9. Gardner L., Saari N., Wang F. Comparative experimental study of hot-rolled and cold-formed rectangular hollow sections. Thin-Walled Structures. 2010. Vol. 48. Issue 7. Pp. 495–507.

Resistance of Compressed Thin-Walled Cold-Formed Steel Members with Regard to the Influence of Initial Imperfections

Thin-walled cold-formed profiles have specific specialties, which must responsibly have their design taken into account. Local stability requirements related to unfavourable buckling effects of their compressed parts are highly significant. Favourable effects, related to membrane stresses and post-critical behaviour are also important. The paper deals with the influence of initial imperfections and presents fundamental information about experimental and theoretical-numerical research to determine the load-bearing capacity of thin-walled cold-formed compressed steel members. The investigated members consist of closed cross-sections. The theoretical-numerical analysis has been oriented towards the investigation and modelling of initial imperfection effects, caused by production processes, on the load- bearing capacities of the mentioned members. The experimental investigation has been realized to verify the theoretical results and to investigate the behaviour of these members during the loading process.

Development of Plastic Zones during the Thermal Cycle of Welding

The high temperatures induced during the welding process cause transient thermal stresses and non-continuous plastic strains around the weld. Uneven heating and cooling processes together with these plastic strains result in residual (welding) stresses, [1]. This paper deals with the development of plastic zones, related to welding stresses and their effects on the bearing capacity from a Civil-engineering perspective.

Experimental Investigation and Theoretical Analysis of Polystyrene Panels with Load Bearing Thin-Walled Cold-Formed Elements

The paper presents preliminary results of theoretical and experimental analysis of the resistance of construction panels at compressive loading. Panels, made on the base of polystyrene foam in combination with thin-walled cold-formed elements, should be used as a load-bearing wall panels for simple and small structures. Investigated panels, with dimensions 1.0x2.5x0.15 m, are formed by six thin-walled elements of U-profile with a thickness of 0.8 mm, which are stabilized by glued polystyrene board EPS 100 S, 150 mm thick. Sufficient number of strain gages and inductive sensors were used for the experimental measurement of strains and deflections. Strain gauges and inductive sensors were both-sided suitably located on each tested panel. Spatial calculation model was created within software SCIA and ANSYS. Geometrically nonlinear analysis was used for the numerical solution. Based on the numerical and experimental results, the efficiency of polystyrene boards on the stability of used thin-walled steel elements was determined.

Analysis of wind-induced vibrations of an anchor cable using a simplified fluid-structure interaction method

Wind-induced vibrations of an anchor cable using a simplified FSI method are studied.Simulations of spatially correlated in situ measured wind histories are presented.Vortex-shedding phenomena around the cross-section of the cable are obtained.The FE method is applied in the nonlinear dynamic analysis of the cable (CSD).Responses obtained by the FSI and CSD models are compared and discussed. Wind-induced vibrations of a pre-stressed aramid anchor cable using a simplified fluid-structure interaction (FSI) method are presented in the paper. Navier-Stokes equations for incompressible flow are solved in nine two-dimensional transverse planes located perpendicularly to the longitudinal axis of the cable. Based on in situ measured wind records statistical and spectral characteristics of the simulated turbulent wind fields were assigned to the investigated cable. The Shinozuka-Deodatis method is used to generate wind velocity histories. Spatially correlated wind velocity components in the longitudinal and lateral direction were considered as an inflow condition in nine created parallel plane fluid flow models. In order to generate an appropriate computational fluid dynamics model (CFD) of sufficient accuracy the verification and validation of the most critical issues were performed. The turbulent hybrid Spalart-Allmaras Detached Eddy Simulation (SA-DES) model was assumed accurate enough and applied in the plane fluid flow models of the dynamic analyses. The finite element method is applied to simulate the aeroelastic behaviour of the cable subjected to turbulent wind effects. Aeroelastic response characterised by wind velocity fields and vortex-shedding phenomena around the cross-section of the cable are presented. Results obtained from the simplified FSI analysis were used for the calculation of the Rayleigh Beta damping coefficient and applied in the nonlinear dynamic analysis of the anchor cable (CSD model). Responses obtained by FSI and CSD models are compared.

Dynamic response of reinforced concrete building from the effects of rail transport

Abstract A 3D model of a reinforced concrete building and was created in software ANSYS. The dynamic analysis was focused on the spectral response of the object represented by a random excitation experiment found in records in the form of load spectra

Numerical Estimation of Aerodynamic Characteristics of Footbridge Deck

For estimation of aerodynamic characteristics of cable-stayed footbridge deck a computational fluid dynamics (CFD) has been used. An incompressible fluid flow with Navier-Stokes equations has been applied. An adequate numerical model has been created to obtain accurate values of aerodynamic characteristics. Preliminary determination of simulation parameters have been estimated using laminar fluid flow model. Subsequently, Smagorinsky large-eddy simulation (LES) turbulent model has been applied with different simulation parameters to obtain converged values. The boundary layer separation regions and downwind vortex shedding has been observed.

Theoretical and Experimental Stress-Strain Analysis of Compressed Steel Members with Closed Cross-Sections

Abstract The paper presents fundamental information about experimental and theoretic-numerical research to determinate the load-carrying capacity of thin-walled cold-formed compressed steel members. The investigated members have closed cross-sections made from homogeneous materials. The theoretic-numerical analysis in this paper is oriented on the modeling of the initial deviations effects, caused by production process, on the load-carrying capacities of mentioned members, while the experimental investigation is to verify the theoretical results and to investigate the behavior of mentioned members during the loading process.