Structural health monitoring of a ravine bridge of Egnatia Motorway during. construction.

Transcription

1 Loughboough Univesity Institutional Repositoy Stuctual health monitoing of a avine bidge of Egnatia Motoway duing constuction. This item was submitted to Loughboough Univesity's Institutional Repositoy by the/an autho. Citation: PANETSOS, P., NTOTSIOS, E. and PAPADIMITRIOU, C., Stuctual health monitoing of a avine bidge of Egnatia Motoway duing constuction. IN: Uhl, T., Ostachowicz, W. and Holnicki-Szulc, J. (eds). Stuctual Health Monitoing 2008 Poceedings of the Fouth Euopean Wokshop, 2nd-4th July 2008, Cacow, Poland, pp Additional Infomation: This confeence pape is epinted fom the Fouth Euopean Wokshop on Stuctual Health Monitoing, Lancaste, PA: DEStech Publications, Inc. Metadata Recod: Vesion: Accepted fo publication Publishe: c DEStech Publications Please cite the published vesion.

2 This item was submitted to Loughboough s Institutional Repositoy ( by the autho and is made available unde the following Ceative Commons Licence conditions. Fo the full text of this licence, please go to:

3 Repinted fom Fouth Euopean Wokshop on Stuctual Health Monitoing, Lancaste, PA: DEStech Publications, Inc.

4 Title: Stuctual health monitoing of a avine bidge of Egnatia Motoway duing constuction. Authos : Panagiotis Panetsos Evangelos Ntotsios Costas Papadimitiou

5 ABSTRACT The instumental apid monitoing of the dynamic (ambient) esponse of a balanced cantileveed avine bidge of Egnatia Motoway duing its constuction phases, when subjected to wind and othe constuction loads, was implemented. The aim is to veify the confomity both of the sequential constuction phases and of the final completed stuctue of the avine bidge of Metsovo to the design pedictions. In this pape the modal fequencies, damping atios and modeshape components of the completed balanced cantileve of pie M3 wee identified fom ambient acceleation ecods, and its analytical dynamic model was updated to detemine the actual stiffness and mass popeties of the stuctue. INTRODUCTION In Nothen Geece the lagest and most challenging Geek poject of design, supevision, constuction, opeation, maintenance and exploitation of 680 km of the motoway, linking Euope with Tukish bodes, has been almost constucted. This is the Egnatia Motoway (E.M.) poject. EGNATIA ODOS S.A. (E.O), the company esponsible fo the design, constuction, maintenance and exploitation of E.M. developed an integated Bidge Management System fo optimizing the maintenance and epai policies fo bidges of the motoway. In the last yeas, the initial visual inspection of all the newly established bidges was done, in combination with the instumental monitoing of some of the majo bidges of the motoway, to give initial stuctual and functional Panagiotis Panetsos, Depatment of Capital Maintenance, Egnatia Odos S.A., Thessaloniki , Geece Evangelos Ntotsios, Costas Papadimitiou, Depatment of Mechanical and Industial Engineeing, Univesity of Thessaly, Volos 38334, Geece condition data.

6 Some majo bidges ove steep and deep avines, in the west secto of the E.M., cossing paticulaly difficult geological teain and obstacles, will be the last to be constucted, fo completing the poject. In this pape the fist esults fom the apid instumental monitoing of the ambient vibation of one of these majo avine bidges of the west secto of E.M., duing its constuction phases ae pesented. INSTRUMENTAL MONITORING OF METSOVO RAVINE BRIDGE The new unde constuction avine bidge of Metsovo (Figue 1), in section 3.2 (Anthohoi tunnel-anilio tunnel) of E.M., is cossing the deep avine of Metsovitikos ive, 150m ove the ivebed. This is the highe bidge of E.M., with the height of the talle pie M2 equal to 110m. The total length of the bidge is 357m. As a consequence of the stong inequality of the heights of the two basic pies of the bidge, Μ2 and M3 (110m to 35m), the vey long cental span of 235m, is even longe duing constuction, as the pie M2 balanced cantlileve is 250m long, due to the eccentical position of the key segment. The key of the cental span is not in midspan due to the diffeent heights of the supestuctue at its suppots to the adjacent pies (13,0m in pie Μ2 and 11,50 in pie M3) fo edistibuting mass and load in favo of the shot pie M3 and thus elaxing stong stuctual abnomality. The last was the main eason of this bidge to be designed to esist eathquakes fully elastic (q facto equal to 1). The bidge has 4 spans, of length 44,78m /117,87m /235,00m/140,00m and thee pies of which Μ1, 45m high, suppots the boxbeam supestuctue though pot Figue 1. Longitudinal section of Metsovo avine bidge of Egnatia Motoway. Figue 2. Views of unde constuction Metsovo avine bidge a) Geneal view b) key of cental span.

7 beaings (movable in both hoizontal diections), while Μ2, Μ3 pies connect monolithically to the supestuctue. The bidge is being constucted by the balanced cantileve method of constuction and accoding to the constuctional phases shown in Figue 2. The total width of the deck is 13,95m, fo each caiageway. The supestuctue is limited pestessed of single boxbeam section, of height vaying fom the maximum 13,5m in its suppot to pie M2 to the minimum 4,00m in key section. The pie M3 balanced cantileve has been instumented afte the constuction of all its segments and befoe the constuction of the key segment that will join with the balanced cantileve of pie M2 (Figue 3). The total length of M3 cantileve was at the time of its instumentation 215m while its total height is 35m. Pies Μ2, Μ3 ae founded on huge cicula Ø12,0m ock sockets in the steep slopes of the avine of the Metsovitikos ive, in a depth of 25m and 15m, espectively. Six uniaxial acceleometes wee installed inside the box beam cantileve M3 of the left caiageway of Metsovo avine bidge. The acceleomete aays, ae shown in Figue 3. Due to the symmety of the constuction method (balanced cavtileveing) and as the same numbe of segments wee completed on both sides of pie M3, the instumentation was limited to the ight cantileve of pie M3, following two basic aangements: a) accoding to the 1 st aangement two (2) sensos wee suppoted on the head of pie M3, one measuing longitudinal and the othe tansvese acceleations (Μ3L, Μ3T), while the emaining fou (4) acceleometes wee suppoted on the ight and the left intenal sides of the box beam s webs, two (2) distant 46m and two (2) distant 68m fom M3 axis, espectively (LV3, RV4, LV5, RV6). All fou wee measuing vetical acceleation. b) accoding to the 2 nd aangement the last two sensos of the 1 st aangement wee fixed in a section nea the cantileve edge, distant 93m fom M3 axis, while the othe fou emain in the same positions. In both aangements the sixth senso was adjusted to altenatively measue both in vetical and in tansvese hoizontal diection (RV6 o RT6). IDENTIFICATION OF THE MODAL CHARACTERISTICS OF THE METSOVO BRIDGE The esponse of the cantileve stuctue subjected to ambient loads as the wind, and loads induced by constuction activities as the cossing of light vehicles placing the pestessing cables inside the tendon tubes, was as expected of vey low intensity (0,6% of the acceleation of gavity). The acceleation esponse time histoies,

8 Μ3Τ Μ3L RV6_1 RΤ6-1 LV5_1 RΤ6 RV6 LV5 RV4 LV3 25ος Figue 3. Acceleomete installation aangements. measued fom σπόνδυλ the 6 channel σπόνδυλ aays, wee analyzed σπόνδυλ using the use fiendly modal ος ος ος identification 6softwae, developed 6 6 by the System 4 Dynamics Laboatoy of the Univesity of Thessaly in coopeation ' with Egnatia Odos. All the basic modal RV6_1 fequencies, modeshapes and RΤ6 RV6 RV4 damping atios of the bidge wee identified. 1 Μ3L In the so developed modal identification methodologies based on ambient vibations, pocessing output only data, the excitation is consideed as white noise LV5_1 ' LV5 LV3 Μ3Τ m stochastic pocess. The estimation of modal chaacteistics is 2achieved using the RΤ6_1 method of least squaes. Specifically the identification is achieved by minimizing 2. a 46 3 weighted measue of fit N * T ˆ m E( ψ) t S( k ; ψ) S( k ) w S( k ; ψ ) Sˆ( k ) (1) k l N0 N0 between the coss powe spectal density functions (CPSD) S ˆ( k ) C that ae computed fom measued esponse time histoies and the CPSD functions N0 N0 19ος 93 S( k ; ψ ) C pedicted by a modal model, whee N 0 is the numbe of the measued degees of feedom (DOF), is the step in the discetized fequency aay, k l,..., N ae the indices especting to fequencies k, N is the N0 N0 numbe of discete points in the fequency ange, w R the matix including all the weight coefficients and ψ is the vecto of the paametes to be identified. Fo the solution of the minimization poblem a thee steps algoithm is being used, which is analytically descibed in [1]. The identified values of the modal fequencies and the coesponding values of the damping atios ae shown in Table I. Due to space limitations only ten of the identified modal fequencies and thee of the modeshapes ae pesented in Table I and Figue 4. The aows ae placed in measuing points and thei length is popotional to the espective value of the nomalized modal component. The accuacy in the estimation of the modal chaacteistics is shown in Figue 5 compaing the measued with the modal model pedicted CPSD. 14ος 68 m m m TABLE I. IDENTIFIED MODES OF THE METSOVO RAVINE BRIDGE Measued Measued Measued Design Model No Identified fequencies Hz Damping ζ% Model fequencies 1 1 st ot, z axis st longitudinal

9 PSD z-axis z-axis z-axis 3 1 st tansvese nd longitudinal st bending (deck) nd tansvese nd bending (deck) nd ot,z axis d bending (deck) d tansvese Mode #1 ( Hz) Mode #2 ( Hz) Mode #1 ( Hz) x-axis x-axis x-axis y-axis y-axis y-axis Figue 4. The thee fist identified modeshapes of Metsovo bidge Channel 1 Channel 2 Modal Fit Fequency (Hz) Figue 5.Compaison between measued and modal model pedicted CPSD. UPDATING OF THE DYNAMIC MODEL OF METSOVO BRIDGE FOR EXPERIMENTALLY DETERMINED MODAL CHARACTERISTICS Thee diffeent analytical dynamic models of the bidge cantileve M3 wee constucted, epesenting mateial and geomety of the stuctue, as consideed by the design. Fo bidge modeling the softwae packages COMSOL Multiphysics, SAP2000NL and STATIK wee used. Thee dimension Eule beam finite elements wee used fo the constuction of these models, coincided with the axis connecting the centoids of the deck and pie sections. Fo bette gaphical epesentation of the highe modeshapes, on the measued points of the bidge cantileve (positions of sensos), additional igid tansvese extensions of no mass wee added to both sides of its centoid axis. Fo epesenting igid connection of the supestuctue to the pie, igid elements of no mass wee used. Analytical models shown in Figue 6 have 594, 264 and 448 degees of feedom, espectively. Pie tansvese webs wee simulated by beam elements accoding to design dawings. Fo pies foundation, lateal and otational spings at the basement of the pies wee consideed, such as to epesent fixing conditions of pies to the huge cicula ock sockets, in both

10 hoizontal diections. The aim was to examine the contibution of soil conditions on the dynamic esponse of the bidge pie cantileve as well. Figue 6. Dynamic models of cantileve Μ3 of Metsovo bidge with eule beam finite elements. a) FEMLAB, b) SAP2000NL, c) STATIK A methodology fo updating the design dynamic model of the bidge, descibed befoe, was used, based on the expeimentally identified modal data [2-3]. Accoding to this methodology, the initial finite element model is paameteized by a paamete set which epesent mass and stiffness popeties at an element o substuctue level. Such finite element popeties to be paameteized could be the elasticity modulus multiplied by the moment of inetia fo the supestuctue and pies (Ε*Ι), sping constants simulating elastomeic beaings (GA/h), and othes. The objective in a modal-based model updating methodology is to estimate the values of the paamete set so that the modal popeties geneated by the finite element model best matches the expeimentally obtained modal popeties. The used method fo model updating, seaches fo the optimal model paametes that minimize a measue of fit between the modal fequencies o/and modeshapes pedicted by the finite element model at the measued degees of feedom and the measued modal fequencies and modeshape components. Paamete estimation poblems based on measued modal data ae thus fomulated as weighted leastsquaes poblems in which objective functions [ ( ) ˆ ] J( ; ) w w ( ) m [ ˆ ] ˆ w (2) ˆ 2 measuing the fit between measued ˆ, ˆ and model pedicted ( ), ( ) modal data, ae build up into a single objective using weighting factos w [4]. Standad optimization techniques ae then used to find the optimal values of the paametes that minimize the oveall measue of fit J( ; w ) [5]. Vaious weighted least-squaes methods ae integated into the softwae. The 1 st modeshape (otation of the deck ound the pies M3) ( Hz) and the 5 th modeshape (bending of the deck) ( Hz), computed by the analytical finite element models, ae pesented in Figue 7. The obsevation of the gaphical epesentation of these modeshapes, leads to the conclusion that the stiffness of the pies govens the vibation of the bidge unde the 1 st mode, while the stiffness of the deck govens the vibation of th bidge unde the 2 nd mode.

11 Fo updating of the initial dynamic model of the bidge, the methodology descibed above, was fist applied only fo the expeimental modal data of the fist Figue 7: Modeshapes pedicted by the finite element model of Metsovo bidge (a) 1 st (otational) (ω = Hz), (β) 5 th (bending of the cantileveed deck ω = Hz). and the fifth modal fequencies, tageting to update with accuacy the stiffness of pies and of the deck. The paameteized finite element model has two paametes and. The fist paamete descibes the stiffness of the pies, while the second paamete 2 descibes the stiffness of the deck. These paametes multiply the values of the selected model popeties that descibe, such as the values 1 2 1coespond to the initial model of the as designed bidge. In Table II the optimal values ˆ of the stiffness paametes of the pies and the deck, based on modal data of 1 st and 5 th modes, ae given. Accoding to the esults, the actual stiffness of the pies is 1.2 times the initial stiffness of the design model, while the actual stiffness of the deck is 1.57 times the initial stiffness of the design model. The finite element model that coesponds to the optimal values of paametes και 1 2 is consideed now as the nominal model of the bidge. In Table II the values of the modal fequencies pedicted by the nominal updated finite element model ae given in compaison with the espective values of the expeimentally identified modal fequencies, using data fom the fist and the fifth modes. The pecentage eos ( ( ˆ) ˆ ), between measued and model pedicted fequency values, ae hee zeo, which means that the updated model pedicts the bidge vibation identical to the measued one. Next, the updating of the nominal model of the bidge with thee paametes is pesented. The model updating is now caied out fo the fist 5 modal fequencies that have been expeimentally identified. The nominal model is paameteized by thee paametes, and. The fist paamete descibes the stiffness of the pies, the second paamete 2 descibes the stiffness of the deck, while the thid paamete 3 descibes the stiffness of the soil spings of the pie foundation. These paametes multiply the values of the selected model popeties that descibe, such as the values coespond to the nominal model of the bidge. TABLE II. OPTIMAL VALUES OF PARAMETERS FREQUENCIES, MEASURED VERS PREDICTED

12 Paamete Value Mode Measued Updated % E column st % E deck th % In Table III the optimal values ˆ of the stiffness paametes of the pies, the deck and the soil spings, based on the modal data of the fist 5 modes ae given. Accoding to the esults of Table III, the actual stiffness of the pies and the deck ae vey close to the initial. It also means that fo the excitation level of the bidge duing monitoing the pies wee pefomed as fixed to thei foundations. In Table III the values of the modal fequencies pedicted by the updated finite element model ae given in compaison with the espective values of the expeimentally identified fequencies, using data fom the fist five modes. The pecentage eos ( ( ˆ) ˆ ), between measued and model pedicted fequency values, that ae given as well in Table III, vay in the ange of 0.2% to 1.8%, which means that the finally updated model is adequate to pedict the bidge vibation accoding to the fist five measued modes. TABLE III OPTIMAL VALUES OF, MEASURED VERSUS PREDICTED FREQUENCIES Paamete Value Mode Measue Nominal Updated d % E deck st E columns nd E spings d th th CONCLUSIONS In the pesent pape the fist esults of the apid ambient vibation monitoing of a avine bidge of E.M., duing constuction, ae pesented. The successful identification of all the basic fequencies and the modeshapes of the cantileveed stuctue, enabled the updating of the model design values of the pie, the deck and the soil spings stiffness. The excellent fit to the measued modal fequencies leads to the conclusion that the poposed methodology can be vey useful fo veifying the as built condition of majo bidges duing thei constuction phases. REFERENCES 1. Ntotsios E Expeimental modal analysis using ambient and eathquake vibations: Theoy, Softwae and Applications. MS Thesis Repot No. SDL-08-1, Depatment of Mechanical and Industial Engineeing, Univesity of Thessaly. 2. Fitzen, C.P., D. Jennewein, and T. Kiefe Damage detection based on model updating methods, Mechanical Systems and Signal Pocessing, 12(1), Teughels, A. and G. De Roeck Damage detection and paamete identification by finite element model updating, Achives of Computational Methods in Engineeing, 12(2), Chistodoulou K, C. Papadimitiou Stuctual identification based on optimally weighted modal esiduals. Mechanical Systems and Signal Pocessing, 21: 4-23.

13 5. Haalampidis Y., C. Papadimitiou and M. Pavlidou. 2005, Multi-objective famewok fo stuctual model identification, Eath. Engin. and Stuct. Dynamics, 34 (6):