Chandoga M., Jaroševič A., Sedlák J., Sedlák E. 3rd fib International Congress

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1 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress EXPERIMENTAL AND IN SITU STUDY OF BRIDGE BEAMS SUPPORTED BY BOTTOM EXTERNAL TENDONS Doc. Ing. Miln Chndog, PhD., Projstr PK, Brtislv, Slovki Doc. RNDr. Andrej Jroševič, PhD., Projstr PK, Brtislv, Slovki Ing. Ján Sedlák, Fculty of Civil Engineering, STU, Brtislv, Slovki Ing. Edurd Sedlák, Inžinierske stvby.s., Košice, Slovki ABSTRACT The primry subject of this pper is 10-spn bridge construction built in Slovki. The superstructure consists of 2 girders in cross-section with spn lengths m nd totl length 347 m. The pir of externl tendons is devited in the middle of ech spn through V-shped steel sddle. The stndrd cpcity of the externl tendons is nd t butment spns. The bridge ws monitored during the construction period. Some cross-sections over the supporting pillrs nd in the middle of spns were chosen nd equipped with vibrting strin guges for strin monitoring of the concrete. Elstomgnetic force sensors were instlled both on the selected internl tendons nd on the most significnt externl tendons. The test model ws constructed ccording to the cross-section shpe of the bridge construction, but considering only 2-spn continuous bem with steel sddles in longitudinl direction. Results of mesurements re compred with ech other. Chnges of strin in the concrete during the prestressing of ech stge, incresing of force in the tendons during prestressing, decreses due to losses nd stress rnge in the externl tendons during loding, were monitored, nd they were lso verified on non-liner computing model. Keywords: Monitoring, Assessment, Mintennce, Post-Tensioning

2 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress INTRODUCTION Viduct (Fig. 1 nd Fig. 2) is locted on the highwy D1 Fričovce Prešov west (Slovki) nd is designed s continuous post-tensioned slb with 2 bems, supported in the middle of the spns by tendon ties. The spn lengths re m, nd the totl bridge length 347 m (Fig. 8). A similr bridge construction viduct Osomort in Giron (Spin) ws implemented in the 1990s, nd this bridge is considered to be highly successful technicl nd rchitecturl construction. Structurl systems of bridges with high eccentricity externl cbles re still very populr in present times. Externl tendons locted under the bridge slb in the form of ties re plced outside the bridge contour becuse of the higher effectivity of prestressing. These structurl systems re clssified in the sme bridge ctegory s extrdosed bridges. Bridge is the first of its type of structurl bridge in Slovki nd lso from this point of view it ws necessry to monitor in detil the stress stte nd deformtion of the bering structure during the construction period. Fig. 1 Pnormtic perspective of the whole bridge structure during the construction period Fig. 2 Prt of viduct during the construction period DESCRIPTION OF THE BRIDGE MONITORING FOCUS OF MONITORING The bering structure ws built in 5 stges with spns number 5 nd number 6 first due to more rpid construction. Ech following stge consists of one spn from both sides (direction 2

3 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress to city Prešov spns number 1, 2, 3, 4 nd direction to city Poprd spns numbers 7, 8, 9, 10 on other side). Besides the stndrd test on concrete specimens cubes, prisms nd cylinders, nd prestressing steel, the structure stress stte of the 2 middle spns number 5 nd number 6 within the rnge ws exmined: - stress mesurement in bonded tendons with EM (elstic-mgnetic) trnsducers PSS90 (see [1] for more informtion on EM method), - stress mesurement in the externl tendons with EM trnsducers PSS140, - stress mesurement in the concrete with vibrting wire strin guges in selected cross sections. Fig. 3 EM trnsducer embedded on corrugted steel sheth (left) Fig. 4 Vibrting wire strin guge embedded on steel reinforcement (right) STRESS MEASUREMENT IN BONDED TENDONS Mesurement of stress in selected bonded strnds tendons ws crried out with EM trnsducers PSS90 (Fig. 3). Globlly were embedded 14 pieces of EM trnsducers PSS 90, of which one s compenstory (Fig. 5). Fig. 5 Lyout of tendons geometry nd position of trnsducers on bonded tendons EM trnsducers PSS90 for mesuring of force (Fig. 3) were embedded on tendons K1b (12 strnds, tendon length 85,3 m), K2 (13 strnds, tendon length 84,6 m), K2bc (13 strnds, tendon length 72,7 m), K3 (12 strnds, tendon length 47,2 m) nd K4 (19 strnds, tendon length 84,0 m) in such positions for monitoring of initil prestressing force nd its trnsmission over the length of the tendon (Fig. 5). 3

4 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress STRESS MEASUREMENT IN EXTERNAL TENDONS Mesurement of the stress stte in 8 pieces of externl 19 strnd tendons ws crried out with EM trnsducers PSS140. Trnsducers on tendons VK4 VK7 (4 middle spns number 4, 5, 6, 7) re embedded on the protective HDPE duct (Fig. 7). The position of the trnsducers (Fig. 6) mkes it possible to monitor prestressing force, long with its losses. Fig. 6 Lyout of externl tendons geometry nd position of trnsducers (left) Fig. 7 EM trnsducer embedded on protective HDPE duct (right) STRESS MEASUREMENT IN CONCRETE Stress mesurement in fibers of concrete ws crried out in selected cross sections with vibrting wire strin guges. Strin guges with thermometers (ST) re embedded in 5 cross sections (Fig. 8) in ech bem t the bottom (bottom fiber) nd t the top (upper fiber) for estimte of stress behviour over the depth of the girder (Fig. 8). Fig. 8 Lyout of selected cross sections with embedded strin guges EVALUATION OF MONITORING During the construction period 4 building stges were exmined in detil, 3 of them during prestressing of bridge bems (Fig. 5). The lst stge of monitoring represented mesuring of stress chnges during the prestressing of externl tendons in the spns number 4, 5, 6, nd 7. Within the scope of monitoring totl of 23 mesurings of stress in concrete fibers nd forces in prestressing tendons were crried out, including continuous mesuring during its post-tensioning. Before putting the bridge into service 3 stges of mesuring were crried out 4

5 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress s prt of the loding test before, during nd fter the loding test. Due to the lrge scope of monitoring only selected nd interesting results re presented. FORCE MEASUREMENT IN BONDED TENDONS Tendon K2 with 3 EM trnsducers ws prestressed on in the first building stge. At first the tendon ws prestressed with the full mount of designed force from side A (Fig. 5), nd then from side B. Trnsfer of force over the tendon length (in position of EM trnsducers) nd estimtion of losses due to friction re illustrted in Fig N k 1250 / F K2_2/2 K2_2/3 K2_2/4 N k / 1500 /4 2 K, / K 500 y = x y = x K2/3 K2/4 K2/3 K2/ :10 07:15 07:20 07:25 07:30 07:35 07:40 07:45 07:50 07:55 08:00 08:05 08: K2/2 / kn Fig. 9 Trnsfer of force in tendon K2 nd estimtion of losses due to friction Mesurement of the force in bonded tendons ws lso crried out fter 3 time periods. In these time stges were registered time-dependent losses of prestress (Fig. 10) in the rnge 1,1 3,9%. Creep nd shrinkge of concrete re closely ssocited with reltive humidity. The temperture of the concrete ws mesured with vibrting wire strin guges (Fig. 10). Fig. 10 Chnge of force in time nd temperture of construction COMPARISON OF MEASUREMENT AND THEORY A comprison of theoreticl nd mesured vlues of force in tendon K2 over its length is illustrted in Fig. 11. For better results of monitoring number of EM trnsducers were used 5

6 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress on one tendon, locted in specified positions. The theoreticl trnsmission of force is computed using recommended vlues 0,19 of μ for strnds (coefficient of friction between the tendon nd its duct) nd 0,005 m -1 of k (unintentionl ngulr displcement for internl tendons). However, for the verifiction of the rel vlues of prestressing losses in tensioning, it is recommended to mesure the trnsmission of force over the tendon length. Mesurement proved tht rel vlues of losses re lower, pproximtely 0,15 of μ nd 0,003 m -1 of k. Fig. 11 Trnsmission of force in tendon K2 nd comprison with theoreticl vlues FORCE MEASUREMENT IN EXTERNAL TENDONS Externl tendons (Fig. 12) hve simple geometry in the form of V nd they re ssembled from Monostrnds, which re pulled to the HDPE duct with n outer dimeter of 140 mm (Fig. 12). The position of end nchoring nd the direction of the tendon in the cross bem do not llow the use of 19-strnd stressing jck. Tht is why single stressing jck ws used for the externl tendons. After the completion of tendon prestressing, the HDPE duct ws filled with grouting. Fig. 12 Externl tendons on the bridge nd lyout of Monostrnds in tendon One of the tsks of the monitoring ws to ensure sufficient force trnsmission from one end of the tendon to the other, besides other tsks. Following the results of this mesurement, stressing of externl tendon from the second side ws omitted. Results of force mesurement on the tendon VK6P re illustrted in Fig

7 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress Totl force / kn F_PO F_PP Totl force t pssive side / kn y = x :30 8:40 8:50 9:00 9:10 9:20 9:30 Time / hh:mm Totl force t ctive side / kn Fig. 13 Trnsmission of force t the beginning nd t the end of tendon VK6P nd estimtion of losses due to friction EM trnsducers were locted t the beginning nd t the end of the tendon. Post-tensioning ws crried out with single stressing jck in 2 working stges. In the first stge ech strnd from the totl 19 strnds ws prestressed nd nchored with n initil stress of 100 br, nd the bundle of strnds ws strightened. Therefter with one lift of the stressing jck without intermedite nchoring the finl tendon stress ws chieved. During the second lift elongtion of the strnd to the prestressing protocol t stress vlues br ws registered. By this mens prestressing of the 8 externl tendons ws mesured. The finl grph of the dependency between the force on the ctive side nd tht on the pssive side of the tendon is shown in the Fig. 13. Prestressing losses re in the rnge 4 5% of the overll force. This is very low vlue. From prctice it is known tht stressing of the strnds from the second side cn hve more unfvourble thn positive effect. Furthermore in the stressing of strnds from the second side there cn occur nchor of wedges t the sme position nd tht is undesirble for unbonded tendons. For the stted resons given it ws decided not to stress the strnds from the second side. STRESS MEASUREMENT IN CONCRETE Stress mesurement in the concrete ws crried out with vibrting wire strin guges. For computtion of stress vlues from mesured strins, the modulus of elsticity from concrete specimens cubes, prisms nd cylinders (strength clss for concrete C35/45) from ech building stge ws evluted. The modulus of elsticity ws controlled by 3 independent lbortories in situ, supervisor nd technicl institute, seprtely for specimens from concrete csting of bems nd concrete csting of the bridge slb. For theoreticl nlysis of the first building stge vlues 33 GP for bems nd 32 GP for the bridge slb were then used. The ge of the specimens represents the time from concrete csting till prestressing of the tendons. In Fig. 14 re shown comprisons of the stress vrition between theoreticl computing nd mesurement for 3 building stges (prestressing of bonded tendons in stge 1 E1, stge 2 in the direction to city Prešov E2-PO nd stge 2 in the direction to city Poprd E2-PP). The only difference is in the stress vrition for stge 1 E1, when the 7

8 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress whole bering structure ws still bedded in the formwork nd vlues chieved different results compred to the exct computtionl model with defined supports (pillrs nd formwork). 1,000 0,000 ] P [M 1,000 re fib r 2,000 e p u 3,000 t n tio 4,000 v ri s 5,000 S tre 6,000 7,000 Support 5 Support 6 Support 7 E1 Mesurement E1 Theoreticl vlue E2 PO Mesurement E2 PO Theoreticl vlue E2 PP Mesurement E2 PP Theoreticl vlue ] P [M re fib m to o b t n tio v ri s S tre 4,000 2,000 0,000 2,000 4,000 6,000 8,000 10,000 Support 5 Support 6 Support 7 Fig. 14 Stress vrition in stges of bonded tendons prestressing In Fig. 15 re shown comprisons of the stress vrition between theoreticl computing nd mesurement for prestressing of externl tendons VK5 in spn 5 nd VK6 in spn 6. The results show nerly equivlent vlues. 4,000 4,000 ] P [M re fib r e 3,000 2,000 p 1,000 u t n 0,000 tio v ri s 1,000 S tre 2,000 3,000 Support 5 Support 6 Support 7 VK5 Mesurement VK5 Theoreticl vlue VK6 Mesurement VK6 Theoreticl vlue ] P [M re fib m to o b t n tio v ri s S tre 2,000 0,000 2,000 4,000 6,000 8,000 10,000 Support 5 Support 6 Support 7 Fig. 15 Stress vrition in stges of externl tendons prestressing CONCLUSIONS Mesured strnd elongtions of 19-strnd tendons K4, which were prestressed in the first stge E1 with single stressing jck, show n cceptble vrince compred to theoreticl 8

9 Chndog M., Jroševič A., Sedlák J., Sedlák E. 3rd fib Interntionl Congress vlues (permitted vrince for one strnd is ±10%, the rnge of mesured vlues is -2,8% through +6,4%, verge vrince is +2,4%). Mesured vlues of force in tendon K2, K3 nd K4 over their length re higher in comprison to theoreticl ssumptions. The theoreticl trnsmission of force is computed using recommended vlues 0,19 of μ for strnds nd 0,005 m -1 of k. However for the verifiction of the rel vlues of prestressing losses in tensioning it is recommended to mesure the trnsmission of force over the tendon length. Mesurement proved tht rel vlues of losses re lower, pproximtely 0,15 of μ nd 0,003 m -1 of k, nd force in the tendons is higher thn cn be computed ccording to relevnt design codes. Mesured losses of prestressing force in the bonded tendons K2, K3 nd K4 during the time period show vlues -1,1% through -3,9% (tendon K2); -1,5% through -2,1% (K3); - 1,8% through -1,9% (K4), which represent time-dependent losses of prestress. Monitoring of prestressing losses due to friction in externl tendons shows tht the mximum vlue of losses due to friction is not more thn 5% on the pssive side of the tendons. For this reson it ws decided not to stress strnds from the second side. Mesured stress vritions in the concrete for the first building stge (E1), when the whole bering structure ws still bedded in the formwork show different results compred to the exct computtionl model with defined supports (pillrs nd formwork). Mesured stress vritions in concrete fter the prestressing of the second building stge from both sides (E2-PO, E2-PP) nd prestressing of externl tendons VK5 nd VK6 in the 2 middle spns correspond to theoreticl ssumption. REFERENCES 1. Chndog, M., Jroševič, A. nd coll.: Mesurement of force distribution long the externl tendons, Proceedings of the interntionl conference Anlyticl Models nd New Concepts in Concrete nd Msonry Structures, Technicl University of Lodz, Polnd, pp.6 Monitoring of prestressing force in externl tendons, 9-11 Jun Fbo, P., Jroševič, A., Chndog, M.: Helth Monitoring of Steel Cbles, The Elstomgnetic Method, Proceedings of Interntionl Mechnicl Engineering Congress nd Exhibition, New Orlens, USA, , pper No. IMECE Chndog, M., Jroševič, A., Sedlák, J: Stress-strin monitoring on Viduct , highwy D1 Fričovce Prešov west (Slovki), Finl report of Projstr-PK, Ltd, Brtislv, 10/2009 9