TY - CONF A1 - Stengel, Dominik A1 - Thiele, K. A1 - Clobes, M. A1 - Mehdianpour, Milad T1 - Aerodynamic damping of nonlinear movement of conductor cables in laminar and turbulent wind flow T2 - ICWE14 - 14th International conference on wind engineering N2 - It is widely accepted that aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors in turbulent wind flow. But anyway, methods of how to account for the effects of aerodynamic damping differ significantly and so might do the results. In this work, the source of aerodynamic damping shall be revised leading to the well-known formulation for a linear pendulum being the result of the relative velocity between the structure and wind flow. Based on wind tunnel tests and validated by simulations, the differences to a pendulum movement of a sagging cable are shown. The reasons for that deviation are the large deflections, resulting in a movement non parallel to the acting wind flow. For some analysis, in particular those in frequency domain, it is practically not possible to incorporate aerodynamic damping implicitly by fluid structure interaction. If the dynamic movement can be linearized at a working point of the mean deflection, a modification to the linear approach is suggested. This approach is validated by simulation with a finite element model of an existing overhead transmission line, calibrated with onsite measurements for wind velocities at lower levels. Further accent is put on the different possibilities to incorporate aerodynamic damping in time step analysis, such as Rayleigh damping or modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate representation of aerodynamic damping. T2 - ICWE14 - 14th International conference on wind engineering CY - Porto Alegre, Brazil DA - 21.06.2015 KW - Aerodynamic damping KW - Conductor cables KW - Overhead transmission lines KW - Wind tunnel experiments KW - Nonlinear finite element simulation PY - 2015 SN - 978-85-66094-07-7 SP - 1 EP - 9 AN - OPUS4-33612 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stengel, Dominik A1 - Thiele, K. A1 - Clobes, M. A1 - Mehdianpour, Milad T1 - Aerodynamic damping of nonlinear movement of conductor cables in wind tunnel tests, numerical simulations and full scale measurements JF - Journal of Wind Engineering and Industrial Aerodynamics N2 - Aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors. Methods of how to account for the effects of aerodynamic damping differ significantly and so might do the results. In this work, the source of aerodynamic damping being the result of the relative velocity between the structure and wind flow will be revised. Based on wind tunnel tests and validated by simulations, the differences of linear movement compared to a pendulum movement of a sagging cable are shown. The reasons for that Deviation are the large deflections, resulting in a movement non-parallel to the acting wind flow. For analysis in frequency domain, it is not possible to incorporate aerodynamic damping implicitly by fluid structure interaction. If the dynamic movement can be linearized at a working point of the mean deflection, a modification to the linear approach is suggested. This approach is validated by simulation with a finite element model of an existing overhead transmission line, calibrated with full scale measurements. Aerodynamic damping is incorporated in time step analysis by Rayleigh damping and modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate. KW - Aerodynamic damping KW - Overhead transmission lines KW - Conductors KW - Nonlinearities PY - 2017 DO - https://doi.org/10.1016/j.jweia.2017.07.002 SN - 0167-6105 SN - 1872-8197 VL - 169 SP - 47 EP - 53 PB - Elsevier AN - OPUS4-41028 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stengel, Dominik A1 - Mehdianpour, Milad A1 - Clobes, M. A1 - Thiele, K. ED - Cunha, A. ED - Caetano, E. ED - Ribeiro, P. ED - Müller, G. T1 - Numerical simulation of an overhead power line section under wind excitation using wind tunnel test results and in-situ measured data T2 - EURODYN 2014 - 9th International conference on structural dynamics (Proceedings) N2 - Overhead transmission lines are very sensitive structures in regards to wind action. The cables, spanning over a few hundred meters contribute in particular to the overall action on the suspension towers. These slender structures incorporate both structural nonlinearities from the large deformation of the cables and aerodynamic nonlinearities which need to be accounted for when it is to estimate the system response to strong wind events. In this work, a finite element procedure is presented to model an existing power line section using nonlinear cable elements. The wind force is assumed quasi-steady with force coefficients determined in wind tunnel test on a conductor section. Further, aerodynamic damping is incorporated by considering the relative velocity between cable nodes and oncoming wind flow. The results are compared with on-site measurements of the cable’s support reaction. The results show a significant effect of damping since almost no resonant amplification is visible both in observation and simulation. In addition, wind tunnel tests approved aerodynamic damping to be large for the system of sagging cables, but nonlinear in its nature. It is concluded, that the dynamic response of overhead transmission line cables has to be modeled with care, considering all sources of nonlinearities. That is of particular interest in case of random excitation such as wind because the peak response depends on the probability distribution of the system's response. T2 - EURODYN 2014 - 9th International conference on structural dynamics CY - Porto, Portugal DA - 2014-06-30 KW - Overhead transmission lines KW - Cable dynamics KW - Aerodynamic damping KW - Wind tunnel KW - In-situ measurements PY - 2014 SN - 978-972-752-165-4 SN - 2311-9020 SP - Paper MS07, 1 EP - 6 AN - OPUS4-30993 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stengel, Dominik A1 - Mehdianpour, Milad ED - Gomes, J.F.S. ED - Meguid, S.A. T1 - Wind measurements along a high-voltage overhead transmission line in northern Germany T2 - IRF 2013 - 4th International conference on integrity, reliability and failure (Proceedings) N2 - The paper focuses on a recently launched project of wind measurements along a high voltage overhead transmission line. For reliable information on the actual horizontal distribution of the wind flow, 13 positions along two spans of an overhead electrical line of about 400 m length each are selected for wind measurements. Simultaneously, the structural response is measured at the towers. Preliminary analyses aim at the system identification of long span transmission lines exposed to gusty wind by derivation of a so called joint acceptance function which describes the admittance from wind velocity to the system's response. It can be shown that measured structural response can accurately be described using a statistical model which accounts for the irregularity of the wind as well as the structure’s behaviour. T2 - IRF 2013 - 4th International conference on integrity, reliability and failure CY - Funchal, Portugal DA - 23.06.2013 KW - Overhead transmission lines KW - Wind loading KW - Field measurements KW - Monitoring PY - 2013 SN - 978-972-8826-28-4 IS - Paper 3920 SP - 1 EP - 9 AN - OPUS4-28846 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stengel, Dominik A1 - Mehdianpour, Milad T1 - Finite element modelling of electrical overhead line cables under turbulent wind load JF - Journal of structures N2 - This paper presents a finite element model of an overhead transmission line using so called cable elements which allow reproducing the cable's nonlinear characteristics accurately employing only a few elements. Aerodynamic damping is considered in the equation of motion by taking into account the relative velocity between the flow of the wind and the moving structure. The wind flow itself is simulated by wave superposition making necessary assumptions on the lateral correlation between the wind velocities along the cable length. As result from the simulation, the following conclusions can be drawn. The first natural frequency of generally used wide spanning cables lies well below 1 Hz where also most of the energy content of the wind excitation is to be expected. Aerodynamic damping is significant for the moving cables holding very low structural damping which leads to a suppression of resonant amplification. This is particularly of interest regarding the support reaction which is dominated by the mean value and the so called background response. The latter is mostly influenced by the randomness of the wind flow, especially lateral to the main wind direction. KW - Nonlinear Finite Element Formulations KW - Nonlinear Equation of Motion KW - Turbulent Wind Excitation PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-304567 DO - https://doi.org/10.1155/2014/421587 SN - 2314-6494 SN - 2356-766X VL - 2014 IS - Article ID 421587 SP - 1 EP - 8 PB - Hindawi Publ. CY - New York, NY ; Cairo AN - OPUS4-30456 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stengel, Dominik A1 - Clobes, M. A1 - Mehdianpour, Milad ED - Schlünzen, K.H. T1 - Overhead transmission line cables under wind gust loading - measurements and numerical simulations T2 - CWE 2014 - 6th International symposium on computational wind engineering N2 - Overhead transmission lines with conductor cables spanning over a few hundred meters are highly sensitive to the action of wind. Particularly wind acting on the cables signifies a major load on the suspension towers. In order to identify critical loading parameters and the load-response mechanism of those structures, measurements are carried out along a high voltage overhead transmission line capturing the acting wind field as well as the structural response of the cables. A finite element model of the structure is built and used to simulate the system's response. A method is presented which allows generating a complete wind field for all the model’s nodes incorporating measured wind velocities and estimated parameters of the acting wind. The full scale measurements of both action and reaction will be compared to the numerical results. T2 - CWE 2014 - 6th International symposium on computational wind engineering CY - Hamburg, Germany DA - 2014-06-08 PY - 2014 SP - Article 0158_0016, 1 EP - 8 AN - OPUS4-30860 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mehdianpour, Milad A1 - Stengel, Dominik T1 - Wind measurements along a high-voltage overhead transmission line in Northern Germany - Appraisal of results T2 - EACWE 2013 - 6th European and African conference on wind engineering N2 - The paper focuses on a unique project of wind measurements along a high voltage Overhead transmission line. For reliable information on the horizontal distribution of the wind flow, 13 positions along two spans of an overhead electrical line of about 400 m length each are selected for wind velocity measurements. Simultaneously, the structural response is measured at the towers. Preliminary analyses aim at the appraisal of results what is important for the upcoming system identification. It is shown that system identification of long span transmission lines exposed to gusty wind is possible by derivation of a so called joint acceptance function which describes the admittance from wind velocity to the system’s response. T2 - EACWE 2013 - 6th European-African conference on wind engineering CY - Cambridge, UK DA - 07.07.2013 PY - 2013 SP - 1 EP - 8 (Paper 13) AN - OPUS4-28863 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mehdianpour, Milad A1 - Herter, Jürgen A1 - Hille, Falk T1 - Service life extension of a railway viaduct in Berlin T2 - Munich Bridge Assessment Conference - MBAC (Proceedings) N2 - Bridge retrofitting of a section of the Berlin subway which is designed as railway on steel viaduct is presented. Fatigue damage in the superstructure of the over 70-years-old viaduct made an investigation of the damage causes necessary prior to the planning of retrofitting measures. The damage specifically occurred at the inverted arched steel plates of the ballast support elements. Those plates were provided for carrying the track ballast as well as the traffic load. For the retrofitting, the inverted arched plates were unloaded. The superstructure was redesigned into a fixed track system, which is able to transfer the traffic load directly into the substructure. The new rail fastening system made it necessary to verify the structural integrity of single elements as well as of the main system of the existing viaduct. The verification was based on several experimental investigations at BAM laboratory and on-site. Based on the evaluation of all test results the operation license could be issued. T2 - Munich Bridge Assessment Conference (MBAC 2009) CY - Munich, Germany DA - 2009-05-27 KW - Life time extension KW - Fatigue KW - Load test KW - Experimental investigations KW - On-site tests PY - 2009 IS - Paper # T13 SP - 1 EP - 18 CY - Munich, Germany AN - OPUS4-19483 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mehdianpour, Milad A1 - Eisenkolb, Tino ED - Jasienko, J. T1 - Experimental investigations on sliding friction of historic bridge bearings T2 - SAHC 2012 - 8th International conference on structural analysis of historical constructions (Proceedings) T2 - SAHC 2012 - 8th International conference on structural analysis of historical constructions CY - Wroclaw, Poland DA - 2012-10-15 KW - Bridge bearings KW - Historic bearings KW - Cast steel KW - Sliding friction KW - Friction coefficient PY - 2012 SN - 978-83-7125-216-7 SN - 0860-2395 SP - 1 EP - 9(?) PB - DWE CY - Wroclaw, Poland AN - OPUS4-25793 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Klinger, Christian A1 - Mehdianpour, Milad A1 - Klingbeil, Dietmar A1 - Bettge, Dirk A1 - Häcker, Ralf A1 - Baer, Wolfram T1 - Failure analysis on collapsed towers of overhead electrical lines in the region Münsterland (Germany) 2005 JF - Engineering failure analysis N2 - End of November 2005 strong south-west wind and heavy snowfall were predominant in the region Münsterland, north-western part of Germany. This led to accretion of a considerable quantity of wet snow to overhead electrical lines in form of snow rolls on the conductors. Eighty-two transmission towers failed catastrophically, most of them by buckling, however some by brittle fracture. As a consequence nearly 250,000 people have been cut off from electrical power supply for several days with major media attention. This paper describes the forensic analysis in order to investigate the failure cause. Therefore extensive materials investigations, mechanical testing of original components and specimens thereof, estimations for the real wind and snow loads and their combinations, structural analyses as well as detailed evaluations on the basis of previous investigations, literature and regulations were conducted. It was revealed that some of the examined components were manufactured from Thomas steel which was partially in embrittled condition. The investigated towers fulfilled the design codes valid at the time of erection. However the present line loads of the wet snow rolls on the conductors exceeded by far the ones given in the design codes valid at that time. The load case leading to failure was reconstructed by the derived positions of loads mainly caused by unequal and asymmetric distribution of snow rolls on left and right electrical system. The loads and corresponding stresses acting on the structure before failure were estimated. By comparison with the fracture forces from mechanical testing of original members of the collapsed tower the component that primarily failed was localised. The primary fracture occurred on a diagonal member under tension made of Thomas steel which was weakened by embrittlement. The failure cause was a combination of heavy weather conditions (storm, approx. 0 °C and wet snowfall leading to heavy snow rolls on conductors), asymmetric loading conditions and the usage of Thomas steel which was partially embrittled. Finally, recommendations for avoiding future failures are given. KW - Transmission towers KW - Thomas steel KW - Embrittlement KW - Snow loads KW - Ice loads PY - 2011 DO - https://doi.org/10.1016/j.engfailanal.2011.07.004 SN - 1350-6307 SN - 1873-1961 VL - 18 IS - 7 SP - 1873 EP - 1883 PB - Elsevier Science Publ. CY - Oxford AN - OPUS4-24517 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -