SEISMIC PERFORMANCE ASSESSMENT AND RETROFITTING OF RC STRUCTURES

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1 Aristotle University of Thessaloniki KE.DE.A. Conference Hall I Tuesday 11 Thursday 13 November, 2014 SEISMIC PERFORMANCE ASSESSMENT AND RETROFITTING OF RC STRUCTURES Luigi Di Sarno, PhD, MASCE ldisarno@unisannio.it UNIVERSITA' DEGLI Dipartimento di Ingegneria Palazzo Bosco Lucarelli, Piazza Roma, 821

2 RC Bridges INTRODUCTION LAB TESTS SIMULATIONS CONCLUSIONS

3 BACKGROUND & MOTIVATION The seismic vulnerability assessment of existing and new lifeline systems, especially transportation systems, is becoming of paramount importance in resilient social communities. Unfortunately, the transportation systems, especially in Italy, were mainly built in the late 60s and early 70s and were designed primarily for gravity loads. As a result most of the bridges do not employ seismic details. In addition, Eurocode 8 does not contain specific rules for the assessment of existing bridges. In Italy, guidelines for the assessment of existing bridges in seismic prone-areas were proposed within the Reluis Consortium. A large scale testing program was initiated within the European project RETRO, a research program of the Seismic Engineering Research Infrastructures for European Synergies (SERIES), financially supported by the Seventh Framework Programm of the European Commission. Additional projects are still working in progress on the seismic response analysis of existing RC bridge structures with and without retrofitting measures.

4 Seismic Engineering Research Infrastructures for European Synergies TRANSATIONAL ACCESS USE - JRC (RETRO ) Assessment of the seismic vulnerability of an old R.C viaduct with frame piers and study of the Effectiveness of different isolation systems through pseudodynamic Test on a large scale model Participants (F. Paolacci, R. Giannini, A. Mohamad, L. Di Sarno, R. De Risi, R. Ceravolo, M. Erdik, C. Yenidogan, A. Marioni, M. Sartori) University of Roma Tre (coordinator) University of Naples University of Sannio Polytechnic of Turin Univertsity of Bogazici ALGA Spa Milan UNIVERSITA' DEGLI STUDI DEL DI SALERNO SANNIO Dipartimento di Ingegneria Palazzo Bosco Lucarelli, Piazza Roma, Benevento

5 EXperimental &Computational Hybrid Assessment Network for Ground- Motion Excited Soil- Structure Interaction Systems (PIRSES-GA EXCHANGE-SSI)

6 RETRO PROJECT Paolacci F, Pegon P, Javier Molina F, Poljansek M, Giannini R, Di Sarno L, Abbiati G, Mohamad A, Bursi O, Taucer F, Ceravolo R, Zanotti Fragonara L, De Risi R, Sartori M, Alessandri S, Yenidogan C (2014) Assessment of the seismic vulnerability of an old RC viaduct with frame piers and study of the effectiveness of base isolation through PsD testing (RETRO). doi: /63472

7 Rio-Torto Viaduct The case study is an old R.C. viaduct (Rio Torto) placed along the Firenze-Bologna Highway between Roncobilaccio and Pian del Voglio, and was built at the end of the 50 s It is characterized by: Thirteen-span bays deck with two independent roadways sustained by 12 couples of piers Frame piers with height variable between 14 and 50 m RC members with smooth bars Gerber Saddles

8 275 INTRODUCTION LAB TESTS SIMULATIONS CONCLUSIONS spalla BO spalla FI 29, ,05 17,35 30,61 30,49 26,75 27,86 39,41 41,34 36,49 piena piena cava piena piena cava cava cava 25,74 17,19 14,37 13,8 piena piena piena cava Pier 9 Pier 11 An experimental test campaign was performed at ELSA Laboratory of JRC (Ispra, Italy). Two piers (scale 1:2.5) were built and tested using the PsD technique with sub-structuring: Pier 9: a 3 floor, 1 bay frame with columns with an hollow section Pier 11: a 2 floor, 1 bay frame with columns with a full section Pier 11 Pier 9

9 Pier 9 Pier 11

10 Isolation system installed on the strong floor

11 TEST SET-UP

12 U D P

13 U D P Opensees Model (with and w/o bond-slip and shear) Flexural Model

14 U D P The simplified model has been built using non-linear springs simulating the transversal response of each pier, whereas the deck has been considered as a linear elastic element with the geometrical characteristics of the deck. The saddles have been considered as hinges. This is the most simply model that can be adopted for the PsD test within a certain range of transversal displacements given that the influence of the overturning moment on the axial force of the columns and consequently on their flexural strength is not significant.

15 U D P To evaluate the characteristics of the single pier special non-linear elements as implemented in Opensees have been used. Such elements include: Hysteretic element Pinching4 element Both elements are able to reproduce the pinching phenomena even if pinching4 model is more versatile when significant pinching is expected. Hysteretic Pinching4

16 U D P (SLC Record1) COMPLETE MODEL SYMPLIFIED MODEL BASE SHEAR (kn) displacement (cm) DISPLACEMENT (cm) time (sec)

17 U D P Base isolated configuration of the bridge deck V FPS f N N R iso

18 U D P Displacement Demand Force Demand S a f 10% f 1% T

19 U D P From a classical probabilistic seismic hazard anaysis it follows that the expected PGA ranges between 0.23g and 0.25g, whereas for the collapse prevention condition (probability of 2% in 50 years) PGA ranges between 0.30g and 0.35g. Probability of occurence X: Y: SLV SLC PGA (g) Earthquake swarms occurred in the region (i.e. the earthquake records of the 20th and 29th May 2012) were used as seismic input

20 U D P Name Description Parameters Type of test Physical Part Experimental Test Program d03 Test on Isolator_P9 V = 450 kn D = 50,40,30,20,10 mmm f03 f04 k06 k07 Preliminary test for the stiffness of pier 11 Preliminary test for the stiffness of pier 9 Not Isolated Bridge 10% SLS Not Isolated Bridge 100% SLS V = 450 kn D=1.5 mm V = 450 kn D=2 mm m01 Only physical isolators V = 450, 225, 175 kn, H = 30 mm, 1.88 mm/s, l01 Isolated Piers case 100% SLS p02 Isolated Piers case 70% ULS k09 r01 r02 r03 k10 k12 Not Isolated Bridge 100% ULS Pier 9 - Isolator case 65% ULS Pier 9 - Isolator case 80% ULS Pier 9 - Isolator case 90% ULS Aftershock - Not Isolated 100% ULS Aftershock - Not Isolated 200% ULS Cyclic displacements Cyclic displacements Cyclic displacements Isolator_P9 Pier 11 Pier 9 PGA=10% SLS PsD test Pier 9 & 11 PGA=100% SLS PsD test Pier 9 & 11 PGA=100% SLS, μ=4% (design value) PGA=70% ULS, μ=4% (design value) Cyclic Isolator_P9 & P11 displacements PsD test Pier 9 & 11 + Isolator_P9 PsD test Pier 9 & 11 + Isolator_P9 PGA=100% ULS PsD test Pier9&11 PGA=65% ULS μ=7% (actual value) PGA=80% ULS μ=7% (actual value) PGA=90% ULS μ=7% (actual value) PGA=100% ULS after a first sequence of 100% ULS (k09) PGA=200% ULS after the second sequence of 100% ULS (k10) PsD test PsD test PsD test Pier9 + Isolator_P9 Pier9 + Isolator_P9 Pier9 + Isolator_P9 PsD test Pier 9 & 11 PsD test Pier 9 & 11

21 U D P

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23 U D P Name Description Parameters Type of test Physical Part Experimental Test Program d03 Test on Isolator_P9 V = 450 kn D = 50,40,30,20,10 mmm f03 f04 k06 k07 Preliminary test for the stiffness of pier 11 Preliminary test for the stiffness of pier 9 Not Isolated Bridge 10% SLS Not Isolated Bridge 100% SLS V = 450 kn D=1.5 mm V = 450 kn D=2 mm m01 Only physical isolators V = 450, 225, 175 kn, H = 30 mm, 1.88 mm/s, l01 Isolated Piers case 100% SLS p02 Isolated Piers case 70% ULS k09 r01 r02 r03 k10 k12 Not Isolated Bridge 100% ULS Pier 9 - Isolator case 65% ULS Pier 9 - Isolator case 80% ULS Pier 9 - Isolator case 90% ULS Aftershock - Not Isolated 100% ULS Aftershock - Not Isolated 200% ULS Cyclic displacements Cyclic displacements Cyclic displacements Isolator_P9 Pier 11 Pier 9 PGA=10% SLS PsD test Pier 9 & 11 PGA=100% SLS PsD test Pier 9 & 11 PGA=100% SLS, μ=4% (design value) PGA=70% ULS, μ=4% (design value) Cyclic Isolator_P9 & P11 displacements PsD test Pier 9 & 11 + Isolator_P9 PsD test Pier 9 & 11 + Isolator_P9 PGA=100% ULS PsD test Pier9&11 PGA=65% ULS μ=7% (actual value) PGA=80% ULS μ=7% (actual value) PGA=90% ULS μ=7% (actual value) PGA=100% ULS after a first sequence of 100% ULS (k09) PGA=200% ULS after the second sequence of 100% ULS (k10) PsD test PsD test PsD test Pier9 + Isolator_P9 Pier9 + Isolator_P9 Pier9 + Isolator_P9 PsD test Pier 9 & 11 PsD test Pier 9 & 11

24 Slender piers Single-Record (MRN e/q) Short piers Multiple-Record (MRN e/q)

25 The robust fragility curves for damage limit state (left) and for the collapse limit state (right) for the as built configuration, compared with the Syner-G results

26 7th Framework Programme of UE PIRSES-GA EXCHANGE-SSI (Experimental & Computational Hybrid Assessment Network for Ground-Motion Excited Soil-Structure Interaction Systems) The main objectives of the research is to quantify the influence of advanced numerical modelling in the assessment of seismic capacity of complex structural systems At the element level (i.e. columns, piers) advanced numerical models have been proposed Numerical validation comparing analytical and experimental data for specimens with different failure modes under static cyclic load At subassembly level a numerical model validation with experimental data of a shear critical bridge bent Dynamic validation of the proposed model with numerical comparison with experimental data of a shaking table test Comparisons of available literature simplified assessment procedure with advanced nuemerical modelling

27 U D P VecTor2 model of a shear critical frame used as deck support in a typical Italian bridge with smooth reinforcement 100 V [kn] d [mm] Analytical VT2 Experimental -100

28 Bridge Pier (SD) - Flexure-critical The large errors in the displacement demand estimation for shear critical structural systems can be found in the hysteretic behavior adopted in the NLSP calibrations Base Shear [kn] Analytical VT2 FF2_ Bridge Bent (SSD) - Shear-critical Relative longitudinal displacement [mm] Base Shear [kn] Analytical VT2 FF1_1.188 CM CSM Relative longitudinal displacement [mm]

29 Maximum Displacement (m) NDA mean FEMA 440-CM FEMA 440-CSM Bridge Pier (SD) - Flexure-critical Tel = 0.47 s Both the static procedures (CM and CSM) show a reasonable accuracy, with average errors lower than 15% for the flexural critical structural systems. Maximum Displacement (m) NDA mean FEMA 440-CM FEMA 440-CSM Strength Reduction Factor, R Bridge Bent ( SSD ) - Shear-critical Tel = 0.27 s For the shear critical bridge bent, the NLSPs showed significant differences. In particular the CM presents an average error with a maximum of 40% and significant underestimation also for low ductility demands Strength Reduction Factor, R

30 U D P Frame Response Hitachi Station Tsukidate Station

31 U D P Normalized strength h = Fy / M PGA Force Reduction Factors Ductility = 2 Ductility = 4 Ductility = 6 Ductility 2 Ductility 4 Ductility 6 Normalized Strength Ratio sec Kh / K = 5% Force Reduction Factor Ratio Kh / K = 5% Safe Unsafe Period (seconds) Period (seconds) Hitachi Station Stiffening degrading model with 5% and 10% hardening

32 U D P Summarizing. Large scale PsD tests carried out on as-built non-ductile bridge systems has shown that brittle failure may occur on transverse (shear-critical) members. Base isolation is highly efficient in preventing the damage occurrence in brittle components. The results of the inelastic numerical analyses and the preliminary outcomes of the experimental tests not only confirm that multiple earthquakes deserve extensive and urgent studies, but also give indications of the levels of lack of conservatism in the safety of conventionally-designed structures when subjected to multiple earthquakes. Normalized strength spectra for seismic sequence have shown that the force demand on structures can be thrice that relative to a single event. Such demand is, however, significantly influenced by the ductility levels, especially for periods greater than 1.0 second. Consistently higher inelastic displacements have also been computed for multiple earthquakes.

33 U D P Further developments: Experimental seismic performance assessment of bridge piers with smooth bars and low-stregth concrete through shaking table; Experimental seismic performance assessment of bridge subassemblages w and w/o retrofitting. Empirical and analytical fragility analysis.