"acoustic emission location" and "cable" and "bridge"
119555547
Time domain modeling of self excited aerodynamic forces for cable supported bridges: A comparative study
Prediction of the wind induced dynamic response of suspension bridges, emphasizing self excited forces, is discussed in this paper. The self excited forces have been modeled by two commonly applied unsteady models and an unsteady model introduced and explained in this article. A novel frequency independent approximation of the self excited forces, which for the suspension bridge considered provides results as accurate as those from the unsteady models, is also presented. An integration method that may reduce the number of time steps necessary to avoid amplitude and phase distortion of the self excited forces has been introduced and applied successfully in a comprehensive case study.
Ole Oiseth Anders Ronnquist Ragnar Sigbjornsson
119689985
Effects of co spectral densities of atmospheric turbulence on the dynamic response of cable supported bridges: A case study
Abstract This study deals with the importance of the co spectral density of the horizontal and vertical turbulence components when predicting the wind induced dynamic response of long span bridges. The simultaneous measurements of turbulence and response accelerations of the Sotra Bridge are investigated. A turbulence model including the cross spectral density of the horizontal and vertical components is fitted to the turbulence measurements. This turbulence model is used to predict the standard deviations of the wind induced accelerations of the Sotra Bridge. The predicted response is compared to the measurements, and it is concluded that the predicted horizontal response is closer to the measured response values if the co spectral density of the turbulence components are included. The vertical response was not affected by the co spectral density of the horizontal and vertical turbulence components. It is concluded that the influence on the predicted response is observable, but the contribution is low compared to the overall uncertainty in the modelling of the wind field.
Ole Oiseth Anders Ronnquist Ragnar Sigbjornsson
116040583
Short term monitoring of a cable stayed timber footbridge
Alvsbacka cable stayed timber bridge was built in 2010, over Skelleftea River in Sweden. Sensors were integrated at strategic locations of the bridge during the construction process. This paper explores the bridges' synchronized structural health monitoring system that consists of GNNS, force transducers, a weather station and wireless accelerometers. The initial results from short term monitoring are reported and correlation between deformation of the bridge and effect of temperature changes is emphasized. It is planned to perform long term monitoring for complete understanding of structural behaviour of the bridge.
Erhan Saracoglu Anders Gustafsson P Fjellstrom
111041128
Health monitoring of a cable stayed timber footbridge
This paper presents a structural health monitoring system to a timber bridge that will be built in Skelleftea during 2011. The bridge is a cable stayed timber footbridge spanning 130 meters. The main objectives of using the health monitoring system are to verify the structural design and the long term behavior of the bridge. The structural health monitoring system consists of GNSS receivers, MEMS accelerometers, laser positioning systems, wireless moisture content sensors, strain gauges and weather stations. The number of timber bridges has increased a lot in Sweden during the past 20 years. In general today the health of the bridges is assessed at regular intervals by visual inspections and if necessary some minor local tests. Continuous measurements could complement the inspections and provide a better basis for planning maintenance activities and evaluating the remaining service life. The overall objective of this project is to develop monitoring tools for timber structures to guide the planning of maintenance and to signal any urgent problems that should be addressed immediately. A timber footbridge will be built over the Skelleftea River in Sweden 2011. It is a cable stayed bridge with span 130 m. The building of this advanced timber structure gives an exclusive opportunity for testing and developing monitoring methods for timber structures. The monitoring of the bridge will contribute to wood research on specific areas such as durability of timber bridges and vibrations of wooden deck plates, but also to research on measurement and data transmitting techniques. This research project takes advantage in that the bridge is being built during the project period and that the measurements are planned in cooperation with manufacturers, builders and the owner. This gives the opportunity to install equipment during the construction of the bridge. In this way, the measurements will deliver
Niclas Bjorngrim Anders Gustafsson Anne Pousette Olle Hagman
122561094
Erratum to "Simplified prediction of wind induced response and stability limit of slender long span suspension bridges, based on modified quasi steady theory: A case study" [J. Wind Eng. Ind. Aerodyn. 98 (2010) 730 741]
This thesis discusses wind induced dynamic response of slender cable supported bridges. The focus has been on prediction of the flutter stability limit and the buffeting response in strong winds. The thesis consists of journal papers that are either submitted or published. Multimode flutter has recently been shown to be the governing phenomenon for the aeroelastic stability limit of long span cable supported bridges. In this thesis the multimode flutter phenomenon is thoroughly studied. It is concluded that the most important indicator of possible multimode effects is the shape wise similarity of the vertical and torsional vibration modes since flutter will not occur if the still air vibration modes are shape wise dissimilar. When the stability limit of a long span bridge is assessed, the shape wise similarity of all possible mode combinations should be evaluated first. Then the system should be grouped into uncoupled subsystems. The subsystem involving the still air torsional vibration mode with the lowest natural frequency will most likely provide the lowest stability limit. If this subsystem consists of more than two vibration modes, multimode effects will occur. The reduction of the stability limit will be small if the shape wise similarities of the vibration modes are not of the same order of magnitude, or if the system consists of two torsional and one vertical mode, and the torsional modes are well separated. If these conditions are not fulfilled, the flutter stability limit should be assessed using a multimode approach. The self excited forces are particularly important when the wind induced dynamic response or the flutter stability limit is assessed for slender bridges. The self excited forces can be modelled simply using quasi steady theory. Since the quasi steady theory is frequency independent, the model may be used in both the time and frequency domains. However, it is well known that the traditional quasi steady theory may severely underestimate the flutter stability limit since no aerodynamic torsional damping is introduced into the model. In this thesis a novel modified quasi steady theory is suggested. The method takes advantage of that the self excited forces are most important at the natural frequencies of the combined structure and flow system. This implies that curves providing a frequency independent description of the self excited forces can be fitted to the experimental data in the important reduced frequency range corresponding to the natural frequencies of the system. The suggested model has been applied for the Hardanger Bridge in a comprehensive case study, and it is concluded that the model provides wind induced response and flutter stability limits of good accuracy. Simplified methods for assessment of the flutter stability limit are still considered important in preliminary designs and when designing medium span bridges where multimode effects will not reduce the flutter stability limit significantly. The most popular approach is still Selberg's formula, published almost 50 years ago. Selberg's formula provides the flutter stability limit with reasonable accuracy if the aerodynamic properties of the cross section are similar to those of a flat plate, and the vertical and torsional modes have an identical shape. In this thesis an alternative analytical approach to Selberg's formula is suggested. The formulae presented are based on the fundamental flutter equations, and the simplified solution is developed by introducing two assumptions. (i) The quasi steady model for the self excited forces outlined above is introduced in the equations of motion. (ii) The critical frequency is assumed to be on the torsional branch of the solution system and can be approximated by the uncoupled system of equations. It is demonstrated that by introducing these two approximations, the complexity of the flutter equations is significantly reduced, and if the still air damping is neglected, a closed form solution of the flutter stability limit may be obtained. The formula presented is very similar to Selberg's formula, but contains coefficients taking into account the actual aerodynamic properties of the cross section and the possible imperfect shape wise similarity of the vibration modes. The formulae presented are tested for a range of hypothetical structural configurations, in addition to the properties of a few well known bridges, considering the aerodynamic properties of two cross sections. It is concluded that the proposed formulae provide results of adequate accuracy, and that they can be regarded as engineering approximations of the critical flutter velocity. This thesis also discusses unsteady modelling of the self excited forces in the time domain. A comprehensive case study, where the wind induced dynamic response of a slender suspension bridge is assessed in the time domain, is presented. Here, the selfexcited forces have been modelled, using rational functions, indicial functions, a novel modified rational function approach explained and introduced in this thesis, and a further developed modified quasi steady theory. The quasi steady model is a further development of the model outlined above. As explained above, in the modified quasisteady theory suggested in this thesis, the experimental results of the aerodynamic derivatives are approximated with curves providing a frequency independent description of the self excited forces in the important reduced frequency range. This implies that the self excited forces may be accurately modelled at frequencies corresponding to one horizontal, one vertical, and one torsional vibration mode. The further development presented here is to uncouple the aeroelastic system utilizing the right and left hand eigenvectors. This implies that the experimental results for the aerodynamic derivatives may be accurately approximated for all the natural frequencies of the aeroelastic system. It is concluded that all the unsteady models evaluated provide an adequate description of the self excited forces, but that the unsteady models may be challenging to fit to the experimental data since the same coefficients are used in the expressions for the imaginary and real part of the transfer functions, which implies that two sets of data have to be approximated using the same coefficients. It is also seen that the quasi steady model presented provides satisfying results. The results are in fact of higher accuracy than when some of the unsteady models are applied. As modern bridges become longer, slenderer and lighter, the use of nonlinear methods to evaluate the dynamic response may become necessary. This implies that time domain assessment of the wind induced dynamic response will become more important in the future. When nonlinearities are introduced into the model, it is an advantage to use the degrees of freedom of the element model directly and not use still air vibration modes as generalized degrees of freedom. This can be done modelling the self excited forces at distinct points along the girder, but this will imply that a huge amount of convolution integrals have to be evaluated at each time step. Another approach is suggested in this thesis. The starting point is a traditional beam element with twelve degrees of freedom, where the convolution integrals are added as aerodynamic degrees of freedom in each node. This implies that the convolution integrals do not need to be evaluated explicitly, since their value is calculated just like the response of the structure. Four different aeroelastic beam elements have been developed and tested. It is concluded that the elements provide wind induced dynamic response and flutter stability limits that correspond very well to results predicted by the traditional multimode approach in the frequency domain. Accurate modelling of the wind field is a crucial issue when predicting the dynamic response of long span bridges. The wind field is most commonly modelled as a multivariate Gaussian stationary and homogeneous stochastic process, where the turbulence components are assumed independent. Since the wind field is affected by the roughness at the site, the turbulence components will become correlated, since threedimensional eddies are generated by the roughness elements, but this effect is normally neglected. In this thesis the measurements of the fluctuating wind carried out at the Sotra Bride in 1975 are reinvestigated. The cross spectral densities of all the turbulence components have been determined using auto regressive (AR) models. It is concluded that the cross spectral density of the u and w components may have a significant influence on the dynamic response, in particular for structures with low natural frequencies. However for the bridge considered, reasonable estimates of the windinduced dynamic response will still be obtained if the cross spectral density of the u and w components is neglected, but the accuracy of the modelling will be improved if it is included.
Ole Oiseth Anders Ronnquist Ragnar Sigbjornsson
34068675
Infrared Spectroscopy of H Bonded Bridges Stretched across the cis Amide Group: II. Ammonia and Mixed Ammonia/Water Bridges
Clusters of two model cis amides, oxindole and 3,4 dihydro 2(1H) quinolinone, containing one and two ammonia molecules have been studied in the IR hydride stretch region using resonant ion dip IR spectroscopy. The spectra confirm that ammonia is able to form hydrogen bonded bridges across the adjacent amide N H and CO sites in a manner very similar to that of water. Such bridged structures require that ammonia assume the role of a hydrogen bond donor. Further similarities of the hydrogen bonding capabilities of ammonia and water have been revealed by investigations of ternary clusters containing an amide, one ammonia, and one water molecule. Experimentally, two species are observed having IR spectra consistent with a hydrogen bonded bridge structure. The two species differ only in the relative positions of the ammonia and water molecules within the bridge. These experimental results are well supported by optimized structures, vibrational frequencies, and IR intensities calculated using density functional
Andrei V Fedorov and John R Cable Joel R Carney and Timothy S Zwier
116144426
Wiederaufbau der Sloboda Brucke Novi Sad
Die Sloboda Brucke in Novi Sad war zum Zeitpunkt der Planung eine der weltweit grosten Schragseilbrucken mit einer freien Spannweite von 351 m zwischen den Pylonen und einer Seilebene. Anfang April 1999 wurde sie bei einem NATO Luftangriff von zwei Thomahawks jeweils am Pylonfuspunkt getroffen und dabei teilweise zerstort. Da die zerstorte Brucke eine der grosten internationalen Wasserstrasen Europas gesperrt hat, bestand die dringende Notwendigkeit, die Brucke aus der Donau zu raumen und wieder aufzubauen, um den ungehinderten Schiffsverkehr zu ermoglichen. Reconstruction of the Sloboda Bridge in Novi Sad. The Sloboda Bridge in Novi Sad with its free span of 351 m between the pylons has been one of the biggest cable stayed bridges with one cable plan in the world. Begin of April 1999 the bridge has been partly destroyed during a NATO air strike by two Thomahawks hiding the pylon bases. The destroyed bridge is an obstacle for one of the biggest European international waterways and the clearance and reconstruction are necessary in order to allow the free ship traffic.
Alfons Emge Dipl -Ing and Frank Minas Dr -Ing
106537881
NON CORRODIBLE REINFORCEMENT
This paper gives details of a project on a cable stayed footbridge in the Danish town of Herning, which uses non corrodible materials for reinforcement, cable stays, and post tensioning tendons. The research and development programme on non corrodible materials, which included this project, was conducted by the Danish Road Directorate. All 16 stay cables of the bridge are made of carbon fibre reinforced polymer (CFRP) The concrete bridge deck is reinforced with CFRP bars and stirrups in one half, and stainless steel reinforcement and traditional 'black' reinforcement in the other half. The deck is post tensioned with six unbonded CFRP tendons, in addition to the normal forces from the stay cables. The main motivation for the programme was that Danish concrete bridges are most often damaged from corrosion of reinforcement in bridge parts, such as edge beams and the lower parts of columns, that are exposed to de icing salts. The footbridge was essentially designed according to the Danish Code of Practice, using the partial safety coefficient method. The paper gives a formula for the net present value (NPV) of the life cycle costs, and presents a numerical example. Finally, it discusses the close structural monitoring, which will be applied to the bridge for several years.
Jens Christoffersen Anders Plovgaard John Bjerrum
233672445
Hybrid Electro Optical Cable Continuously Powers Downhole Coiled Tubing Telemetry and Enables Time and Carbon Footprint Reductions During Extensive Cleanout Interventions
On the Norwegian continental shelf (NCS) coiled tubing (CT) cleanout requires small bites and frequent wiper trips to the surface due to potential sand bedding in a large and deviated completion. A real time CT downhole measurement system is used to optimize the operation, following a dynamic workflow. Conventionally, the system is powered by downhole lithium battery, which limits CT downhole operating time. A continuous surface powered system was needed to promote further optimization for such operation. A new hybrid electro optical cable was introduced to enable continuous power supply from surface to the real time downhole tool sensors. The system consists of a surface power module that sends power through a layer of low DC resistance conductors and optical fibers that enable data telemetry. Conventionally, only three to four trips can be completed before replacement of the downhole battery is required. Battery replacement can take up to 8 hours due to the complexity of that offshore environment. With the continuous power supply, the CT cleanout operation can continue for days without interruption of data from the downhole tool sensors. A three well CT cleanout campaign in the NCS demonstrated the benefits of this new real time downhole measurement system by using accurate downhole weight and torque readings to control the penetration through scale and avoid motor stalls. Sections of scale bridges were identified during the cleanout by monitoring fluctuations of downhole torque of the mill. The monitoring allows CT operators to control penetration rate and bite length during the cleanout. When the milled debris are swept, downhole weight is used to detect early signs of solids plugging around the mill. Downhole pressures complement surveillance of the sweeping of solids to the surface by giving a qualitative measurement of solids loading through conversion of the real time bottomhole pressure reading into equivalent circulating density with changing CT depth. The process of optimizing bite length and sweeping speed is repeated without interruption thanks to continuous power supply from the surface, eventually leading to time reduction. In one of the wells, downhole tools uninterruptedly acquired data for 10 days straight. The CT managed to clean out a total of 40 908 kg of a mixture of scale and sand, with an estimated average time reduction of 25% when compared to CT cleanout without real time downhole data. Delivery of continuous high voltage power to downhole tools not only enables reduction in operating time, it also paves the way for extending the capabilities of CT interventions by enabling the operation of more electrically activated application tools. It allows combining multiple work scopes in a single CT run, which reduces operating cost and provides greater operational flexibility. Finally, eliminating the dependency on lithium batteries reduces the carbon footprint for a more sustainable operation.
Azwan Hadi Keong Jesus Campos Andrei Casali Anders Hansen Sindre Vingen Jordi Segura Mark E Hofacker Ted L J Brueren Inge Fossdal
117536012
Indirect monitoring of vortex induced vibration of suspension bridge hangers
Wind loading of large suspension bridges produces a variety of structural responses, including the vortex induced vibrations of the hangers. Because it is impractical to monitor each hanger, this study explores the possibility of assessing the presence of these vibrations indirectly by analyzing the responses elsewhere on the structure. To account for the time varying nature of the wind velocity, it is necessary to use appropriate time frequency analysis tools. The continuous wavelet transform and the short term Fourier transform are used here to obtain clear correlations between the vortex shedding frequency and the energy content of the Hardanger Bridge responses. The analysis of recorded signals from a permanent monitoring system installed on the deck and a temporary system installed on some of the hangers shows that it is possible to indirectly detect hanger related vortex induced vibrations from the deck response. Furthermore, this study elaborates on the detection of the two types of vortex induced vibrations (cross flow and in line) the spatial variability of the results, and a possibility to automate the detection process. The ideas reported can be implemented readily in existing structural health monitoring systems for large cable supported structures not only to identify vortex induced vibrations but also to gain a better understanding of their structural response.
Daniel Cantero Ole Oiseth Anders Ronnquist