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Rehabilitation and seismic upgrading of the masonry arch bridge over the Magra river in Villafranca
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Structural Integrity 00 (2018) 000–000 Available online at www.sciencedirect.com Available online atProcedia www.sciencedirect.com Structural Integrity Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
Procedia Structural Structural IntegrityIntegrity Procedia1100(2018) (2016)371–378 000–000
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XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018 XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018
Rehabilitation and seismic upgrading of the masonry arch bridge Rehabilitation and seismic upgrading of the masonry arch bridge overonthe Magra Villafranca XV Portuguese Conference Fracture, PCFriver 2016, in 10-12 February 2016, Paço de Arcos, Portugal over the Magra river in Villafranca a Nicola Croceaa, Pietro Crocebb*,Marino Pelusi , Raffaeleturbine Taccolaaablade of an Thermo-mechanical modeling of a high pressure a Nicola Croce , Pietro Croce *,Marino Pelusi , Raffaele Taccola Studio Croce Engineering, via Carducci, 47, Ghezzano (PI) 56010, Italy airplane gas turbine engine Croce Engineering, Carducci,of47, Ghezzano (PI) 56010, Italy1, Pisa 56123, Italy Department of CivilStudio and Industrial Engineering,via University Pisa, Largo Lucio Lazzarino a a
b
Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 1, Pisa 56123, Italy
b
P. Brandãoa, V. Infanteb, A.M. Deusc*
AbstractaDepartment of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, The paper deals with the rehabilitation of an historical masonry bridge crossing the Magra river and connecting the small towns Portugal TheMulazzo with the rehabilitation of an historical masonry crossing the Magra river and connecting the small towns c paper deals of and Villafranca in the northern part of Instituto Tuscany (I). bridge CeFEMA, Department of Mechanical Engineering, Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, of Mulazzo and Villafranca in the northern part of Tuscany (I). The masonry arch bridge, characterized by eight arches spanning 19 m around each and by around 12 m height intermediate Portugal The masonry bridge,foundations, characterized bybuilt eightin arches masonry piers arch on shallow was 1874. spanning 19 m around each and by around 12 m height intermediate masonry on shallow foundations, was built in 1874. to allow two lanes, in 1961 it was widened by means of two lateral Since thepiers original carriageway width was not sufficient Since the original width was notpiers, sufficient to allow two lanes, in 1961 itseverely was widened by means lateral Abstract prestressed concretecarriageway beams, supported by the so hiding the arches and modifying the original aspectofoftwo the bridge prestressed concrete beams, supported by the piers, so hiding the arches and modifying severely the original aspect of the bridge itself. itself. During their the operation, modern two aircraft engine arecollapsed subjected demanding In 2011, during Magra flooding, arches on thecomponents Mulazzo side duetotoincreasingly scour of the extreme pier.operating conditions, thethe high pressure turbine (HPT) blades. conditions cause these to undergo different types time-dependent In especially 2011, during Magra flooding, two arches on theSuch Mulazzo side dueparts toofscour of the extreme pier. The reconstruction of the collapsed arches and rehabilitation and thecollapsed strengthening the bridge, which has beenofcompleted last degradation, oneand of the which is creep.arches A using the finite element method (FEM) wasbridge, developed, order to be able toinpredict The reconstruction rehabilitation and the of the which has been completed last year, is discussed thecollapsed execution of model theand interventions, which hasstrengthening performed without erection of in temporary support the the iscreep behaviour of HPT blades. Flight data records (FDR) a specific aircraft, provided by a commercial aviation year, discussed and the execution of the interventions, which hasfor performed without erection of temporary support in the riverbed, is also illustrated. company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model riverbed, is also illustrated. Particular attention is devoted to the original solutions which have been adopted for the full seismic upgrading of the bridge needed for the FEM analysis, the a HPT blade scrap was scanned, and its chemical composition andupgrading material properties were Particular attention is devoted original have the been adopted for the fullaspect seismic of the bridge according to the Italian BuildingtoCode currentlysolutions in force,which recovering original architectural of the bridge and widening obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D according to the as Italian the carriageway well. Building Code currently in force, recovering the original architectural aspect of the bridge and widening block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The therectangular carriageway as well. overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a Copyright © 2018 Elsevier All reserved. model can be useful inB.V. theB.V. goal of rights predicting turbine blade life, given a set of FDR data. Copyright All rights reserved. Copyright©©2018 2018Elsevier Elsevier B.V. All rights reserved. Peer-review under responsibility of CINPAR the CINPAR organizers Peer-review under responsibility of the 2018 2018 organizers Peer-review under responsibility of the CINPAR 2018 organizers © 2016 The Authors. Published by Elsevier B.V. Keywords: Masonry archresponsibility bridge, Seismic Historical bridge, Strenghtening; Peer-review under ofupgrading, the Scientific Committee of PCF 2016. Keywords: Masonry arch bridge, Seismic upgrading, Historical bridge, Strenghtening;
Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.
* Corresponding author. Tel.: +39-050-2218-2017; fax: +39-050-2218-201. * E-mail Corresponding Tel.: +39-050-2218-2017; fax: +39-050-2218-201. address:author. [email protected] E-mail address: [email protected] 2452-3216 Copyright © 2018 Elsevier B.V. All rights reserved. 2452-3216 Copyright © 2018 Elsevier All rights Peer-review under responsibility of the B.V. CINPAR 2018 reserved. organizers. Peer-review under responsibility of the218419991. CINPAR 2018 organizers. * Corresponding author. Tel.: +351 E-mail address: [email protected] 2452-3216 © 2016 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3216 Copyright 2018 Elsevier B.V. All rights reserved. Peer-review under responsibility of the CINPAR 2018 organizers 10.1016/j.prostr.2018.11.048
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Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al./ Structural Integrity Procedia 00 (2018) 000–000
1. Introduction The paper deals with the rehabilitation of an historical masonry bridge crossing the Magra river and connecting the small towns of Mulazzo and Villafranca in the northern part of Tuscany (I) (Fig. 1). The single lane carriageway masonry arch bridge, characterized by eight arches spanning 19 m around each and by around 12 m height intermediate masonry piers on shallow foundations, was built in 1874. In Fig. 2 it is shown the bridge during the erection phase of the piers. It must be stressed, that at that time the course of the river was slightly different; the bridge was on a right bend, so that the velocity of the current was usually higher on the left bank, Villafranca side, than on the right bank, the Mulazzo, as it is evident looking at the river bed in fig. 2. This is presumably the reason why the dept of the original pier foundations diminished from Villafranca toward Mulazzo.
Fig. 1. Map of the Magra river in Villafranca - Mulazzo area
Fig. 2. The Villafranca bridge during the erection phase (1874)
Since the original carriageway width was not sufficient to allow two lanes, in 1961 it was widened by means of two lateral prestressed concrete beams, supported by the piers, so hiding the arches and modifying severely the original aspect of the bridge itself, as shown in Fig. 3. More recently, due to the modification of the river course, scour occurred at the piers on the Mulazzo side, so that in the years 2005-2010 a relevant crack pattern was detected on the last two arches, as illustrated in Figs. 4 and 5. Despite the monitoring program setup to control the structural decay, in 2011, during the Magra flooding, two arches on the Mulazzo side collapsed due to scour of the extreme pier, and a temporary Bailey bridge was placed on the deck to allow at least light car traffic (Fig. 6).
Fig. 3. Elevation of the bridge after the carriageway widening (1961)
Fig. 4. Inspection of a damaged arch - monitoring phase (2010)
In the paper, the reconstruction of the collapsed arches and the rehabilitation and the strengthening of the bridge, which has been completed in 2016, is discussed and execution of the interventions, which has performed without erection of temporary support in the riverbed, is also illustrated, devoting particular attention to the original solutions adopted for the full seismic upgrading of the bridge according to the Italian Building Code in force at that time (NTC, 2008), recovering the original architectural aspect of the bridge and widening the carriageway as well.
Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al/ Structural Integrity Procedia 00 (2018) 000–000
Fig. 5. Main crack on the arch (Mulazzo side 2010)
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Fig. 6. The temporary Bailey bridge after the collapse of the two arches (2012)
2. Rehabilitation, strengthening and seismic upgrading of the bridge The rehabilitation, strengthening and seismic upgrading interventions were defined not only considering structural aspects, but also taking into account the needs of the preservation of the historical value of the bridge, according the Guidelines of the Italian Ministry of Cultural and Historical Heritage (2011), the ISO standard 13822 (2001) and the general approached widely described by Croce and Holicky (2013, 2015). The intervention involves, inter alia, the consolidation of 6 of the 8 arches, the reconstruction of the collapsed pier and of the two arches closest to the right bank and the strengthening of the remaining parts. The two collapsed arches have been rebuilt in reinforced concrete as well as the collapsed pier (see Fig. 7.a), characterized by micro-pile foundation. For casting these new concrete parts, special non-removable lateral formworks have been used, overlaid with bricks and stones looking similar to the original ones, anyhow underlining the modern replacement (Fig. 7.b).
Fig. 7.(a) The new r.c. arches and pier
(b) The lateral formworks overlaid with stones and bricks
These two new spans are a continuous beam on three supports, with varying cross section, being the end sections prevented from lengthening, so allowing the transfer of the trust of the adjacent arch to the right embankment, whose structure has been executed with cast in-situ reinforced concrete. Finally, the foundations of the pile are realized with "tubfix" type steel micro-piles 300 mm in diameter, around 12.0 m long. The 6 spans subject to rehabilitation were strengthened through a continuous reinforced concrete deck, supported by the existing piers, duly reinforced using tubfix micropiles extending till to the extrados of the existing arch bridge (Figs. 8 and 9), supplemented also by local strengthening interventions on the piers based on 24 injected horizontal rebars (Fig. 10). In this way, at the end of the intervention the deck behaves like a new reinforced concrete bridge, of variable thickness, whose scheme is a continuous slab on seven supports, so transferring directly the traffic loads to the existing piers and through their micro-pile reinforcement to the soil, also relieving the existing masonry arch structure, without modifying its behavior (see Fig. 10), contributing to prevent also the scour of the pier. Moreover, to limit the execution time avoiding temporary works in the riverbed, the two r.c. arches were cast on temporary trusses placed above the 200 years flood return period (see Figs. 7.b and 11), so eliminating problems during flooding, that occurred several times during the works (Fig. 12)
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Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al./ Structural Integrity Procedia 00 (2018) 000–000
Fig. 8. Longitudinal cross section of the bridge
Fig. 9. Execution of micro-pile trough the existing piers
Fig. 11. Temporary trusses
Fig. 10. Detail of the strengthening interventions
Fig. 12. Flooding during temporary phase of erections
The static and seismic assessments of the bridge have been performed adopting the same actions as for new bridges, so adopting the traffic actions given in the Italian code (NTC, 2008), conforming with those given in Eurocode EN1991-2 (2003), and the seismic actions given in the aforementioned Italian code, considering a soil of category E, according to Eurocode EN1998-1 (2004) and referring, where possible, also to EN1998-2 (2005). In defining the seismic actions, it has been considered that the bridge, for its particular position, and function, is strategic for the civil protection needs, so that it belongs to Class IV structures, according to Italian Code (NTC, 2008), so resulting in a coefficient of usage Cu=2.0. Moreover, the relevance of the bridge from the historical point of view imposed to consider a notional design working life of 100 years, so that the reference period for the structure resulted 200 years, to which corresponds, according to the Italian code, a return period of 1898 years for the evaluation of the seismic design actions for the ULS for life safety assessment. Considering that the reference PGA on soil Category A for the considered site is 0.309 g and taking into account the presence of masonry arches, the behavior factors has been set to 1.0 both for vertical and horizontal component
Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al/ Structural Integrity Procedia 00 (2018) 000–000
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of the response spectra. Therefore, the dynamic linear seismic analysis has been carried out considering the horizontal and vertical elastic response spectra represented in Fig. 13. Thanks to the full integration of the functions between new parts and existing structure, static and seismic assessment where satisfactory, confirming the effectiveness of the proposed solutions. It must be highlighted that the adoption of variable thickness for the continuous reinforced concrete slab supporting the carriageway executed on arches not affected by the collapse, allowed also to reduce the effects of the temperature variations, so allowing eliminating expansion joints not only along the bridge, but also at the embankments. As already said, the concrete deck transfers the loads to the existing structure only at the piers; with this aim, the deck was executed casting in situ prefabricated reinforced concrete predalles (Fig. 14), supported by intermediate sheets of soft material, polystyrene, 30 mm thick, already shown in Fig.10, previously placed above the filling of the arches of the bridge, so limitating the interactions between the new concrete deck and the existing arches (see also Fig 15).
Fig. 13. Design (elastic) response spectra for bridge
Fig. 14. Preparation of the new r.c. cast in situ deck
The intervention has been carried out according to the following phases: • Phase 1: strengthening of the external body of existing piers by means of steel bars 24, spaced 0.8 m vertically and 1.0 m horizontally, duly injected, strengthening of the foundations of the existing piers with external micropiles connected to the existing foundations and protected from scour by means of stone barrier (Fig. 16) (in this phase light traffic was permitted); • Phase 2: erection of foundation and body of the new concrete pier (light traffic permitted on the bridge); • Phase 3: setup of alternative routes to mitigate the effects of the closure of the bridge; • Phase 4: dismantling of prefabricated beams in c.a.p. put in place in 1961 to widen the carriageway (fig. 17) and restoration of the external surfaces (Fig. 18); • Phase 5: disassembly of the Bailey bridge; • Phase 6: erection of the two new spans in c.a. cast in place (Fig. 19); • Phase 7: strengthening of the remaining part of the bridge (6 arches); • Phase 8: erection of the new r.c. concrete deck slab (Fig. 19); • Phase 9: finishes. The total cost of the intervention, including the execution of the temporary pedestrian bypass, was about 1.1 M€, for a unit cost, referred to the total deck surface, of around 800 €/m2.
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Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al./ Structural Integrity Procedia 00 (2018) 000–000
Fig. 15. Cross section of the deck
Fig. 16. Strengthening of the existing piers and foundations
Fig. 17. The bridge after the dismantling of the prefabricated r.c. beams
Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al/ Structural Integrity Procedia 00 (2018) 000–000
Fig. 18. Restoration of the external surface
Fig. 19. Preparatory works for execution of the continuous r.c. slab
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3. Conclusions In the paper, the reconstruction of the collapsed arches and the rehabilitation, strengthening and seismic upgrading of the Villafranca bridge on Magra river, has been shortly discussed. The design of interventions aimed not only to repair the collapsed arches, but also to widen the carriageway, fulfilling at the same time severe requirements in terms of static and seismic performances. In fact the bridge is now able to withstand traffic loads and seismic actions foreseen for new bridges. In particular, due to strategic needs, seismic actions with return period of 1898 years have been adopted, considering a soil Category E and a refence PGA on soil Category A of 0.309 g. Nonetheless, the assessment was very satisfactory confirming the effectiveness of the proposed solutions. It must be also highlighted that the interventions have been conceived in order to preserve as much as possible the historical and cultural value of the bridge, adopting were possible reversible solutions, like for the new concrete deck, and recovering the original aspect of the bridge, anyhow not hiding the unavoidable additions, linked with the reconstruction of the collapsed parts (Fig. 20).
Fig. 20. A fisheye photo of the Villafranca bridge at the end of works
Acknowledgements The design has been carried out by the staff of the Studio Croce srl, composed, beside the authors, by Vladimiro Croce, Matteo Di Prete, Claudia Imbrenda, Stefania Morino and Davide Petrozzino. The Authors acknowledge Stefano Michela, Manager of the technical office of Massa Carrara province, Filippo Bellesi, Major of Villafranca Lunigiana, Claudio Novoa, Major of Mulazzo and the enterprise F.lli Gliori srl. References Croce, P. and Holicky, M., 2013 Operational methods for the assessment and management of existing structures. TEP, Pisa. Croce, P. and Holicky, M., 2015. Operational methods for the assessment of aging infrastructures. CTU, Prague. EN1991-2. Eurocode 1, 2003. Actions on structures – Part 2: Traffic loads on bridges. CEN, Brussels. EN1998-1. Eurocode 8, 2004. Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings. CEN, Brussels. EN1998-2. Eurocode 8, 2005. Design of structures for earthquake resistance – Part 2: Bridges. CEN, Brussels. ISO 13822, 2001. Basis for design of structures -Assessment of existing structures. ISO, Geneva. Italian Ministry of Historical and Cultural Heritage, 2011. Guidelines for seismic assessment and seismic risk reduction of the historical and cultural heritage according to NTC 2008. Italian Ministry of Infrastructure and Transport, 2008. NTC 2008 Italian Building Code. D.M. 14/01/2008 (in Italian).
ScienceDirect ScienceDirect
Structural Integrity 00 (2018) 000–000 Available online at www.sciencedirect.com Available online atProcedia www.sciencedirect.com Structural Integrity Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
Procedia Structural Structural IntegrityIntegrity Procedia1100(2018) (2016)371–378 000–000
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
www.elsevier.com/locate/procedia
XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018 XIV International Conference on Building Pathology and Constructions Repair – CINPAR 2018
Rehabilitation and seismic upgrading of the masonry arch bridge Rehabilitation and seismic upgrading of the masonry arch bridge overonthe Magra Villafranca XV Portuguese Conference Fracture, PCFriver 2016, in 10-12 February 2016, Paço de Arcos, Portugal over the Magra river in Villafranca a Nicola Croceaa, Pietro Crocebb*,Marino Pelusi , Raffaeleturbine Taccolaaablade of an Thermo-mechanical modeling of a high pressure a Nicola Croce , Pietro Croce *,Marino Pelusi , Raffaele Taccola Studio Croce Engineering, via Carducci, 47, Ghezzano (PI) 56010, Italy airplane gas turbine engine Croce Engineering, Carducci,of47, Ghezzano (PI) 56010, Italy1, Pisa 56123, Italy Department of CivilStudio and Industrial Engineering,via University Pisa, Largo Lucio Lazzarino a a
b
Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 1, Pisa 56123, Italy
b
P. Brandãoa, V. Infanteb, A.M. Deusc*
AbstractaDepartment of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, The paper deals with the rehabilitation of an historical masonry bridge crossing the Magra river and connecting the small towns Portugal TheMulazzo with the rehabilitation of an historical masonry crossing the Magra river and connecting the small towns c paper deals of and Villafranca in the northern part of Instituto Tuscany (I). bridge CeFEMA, Department of Mechanical Engineering, Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, of Mulazzo and Villafranca in the northern part of Tuscany (I). The masonry arch bridge, characterized by eight arches spanning 19 m around each and by around 12 m height intermediate Portugal The masonry bridge,foundations, characterized bybuilt eightin arches masonry piers arch on shallow was 1874. spanning 19 m around each and by around 12 m height intermediate masonry on shallow foundations, was built in 1874. to allow two lanes, in 1961 it was widened by means of two lateral Since thepiers original carriageway width was not sufficient Since the original width was notpiers, sufficient to allow two lanes, in 1961 itseverely was widened by means lateral Abstract prestressed concretecarriageway beams, supported by the so hiding the arches and modifying the original aspectofoftwo the bridge prestressed concrete beams, supported by the piers, so hiding the arches and modifying severely the original aspect of the bridge itself. itself. During their the operation, modern two aircraft engine arecollapsed subjected demanding In 2011, during Magra flooding, arches on thecomponents Mulazzo side duetotoincreasingly scour of the extreme pier.operating conditions, thethe high pressure turbine (HPT) blades. conditions cause these to undergo different types time-dependent In especially 2011, during Magra flooding, two arches on theSuch Mulazzo side dueparts toofscour of the extreme pier. The reconstruction of the collapsed arches and rehabilitation and thecollapsed strengthening the bridge, which has beenofcompleted last degradation, oneand of the which is creep.arches A using the finite element method (FEM) wasbridge, developed, order to be able toinpredict The reconstruction rehabilitation and the of the which has been completed last year, is discussed thecollapsed execution of model theand interventions, which hasstrengthening performed without erection of in temporary support the the iscreep behaviour of HPT blades. Flight data records (FDR) a specific aircraft, provided by a commercial aviation year, discussed and the execution of the interventions, which hasfor performed without erection of temporary support in the riverbed, is also illustrated. company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model riverbed, is also illustrated. Particular attention is devoted to the original solutions which have been adopted for the full seismic upgrading of the bridge needed for the FEM analysis, the a HPT blade scrap was scanned, and its chemical composition andupgrading material properties were Particular attention is devoted original have the been adopted for the fullaspect seismic of the bridge according to the Italian BuildingtoCode currentlysolutions in force,which recovering original architectural of the bridge and widening obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D according to the as Italian the carriageway well. Building Code currently in force, recovering the original architectural aspect of the bridge and widening block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The therectangular carriageway as well. overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a Copyright © 2018 Elsevier All reserved. model can be useful inB.V. theB.V. goal of rights predicting turbine blade life, given a set of FDR data. Copyright All rights reserved. Copyright©©2018 2018Elsevier Elsevier B.V. All rights reserved. Peer-review under responsibility of CINPAR the CINPAR organizers Peer-review under responsibility of the 2018 2018 organizers Peer-review under responsibility of the CINPAR 2018 organizers © 2016 The Authors. Published by Elsevier B.V. Keywords: Masonry archresponsibility bridge, Seismic Historical bridge, Strenghtening; Peer-review under ofupgrading, the Scientific Committee of PCF 2016. Keywords: Masonry arch bridge, Seismic upgrading, Historical bridge, Strenghtening;
Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.
* Corresponding author. Tel.: +39-050-2218-2017; fax: +39-050-2218-201. * E-mail Corresponding Tel.: +39-050-2218-2017; fax: +39-050-2218-201. address:author. [email protected] E-mail address: [email protected] 2452-3216 Copyright © 2018 Elsevier B.V. All rights reserved. 2452-3216 Copyright © 2018 Elsevier All rights Peer-review under responsibility of the B.V. CINPAR 2018 reserved. organizers. Peer-review under responsibility of the218419991. CINPAR 2018 organizers. * Corresponding author. Tel.: +351 E-mail address: [email protected] 2452-3216 © 2016 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3216 Copyright 2018 Elsevier B.V. All rights reserved. Peer-review under responsibility of the CINPAR 2018 organizers 10.1016/j.prostr.2018.11.048
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Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al./ Structural Integrity Procedia 00 (2018) 000–000
1. Introduction The paper deals with the rehabilitation of an historical masonry bridge crossing the Magra river and connecting the small towns of Mulazzo and Villafranca in the northern part of Tuscany (I) (Fig. 1). The single lane carriageway masonry arch bridge, characterized by eight arches spanning 19 m around each and by around 12 m height intermediate masonry piers on shallow foundations, was built in 1874. In Fig. 2 it is shown the bridge during the erection phase of the piers. It must be stressed, that at that time the course of the river was slightly different; the bridge was on a right bend, so that the velocity of the current was usually higher on the left bank, Villafranca side, than on the right bank, the Mulazzo, as it is evident looking at the river bed in fig. 2. This is presumably the reason why the dept of the original pier foundations diminished from Villafranca toward Mulazzo.
Fig. 1. Map of the Magra river in Villafranca - Mulazzo area
Fig. 2. The Villafranca bridge during the erection phase (1874)
Since the original carriageway width was not sufficient to allow two lanes, in 1961 it was widened by means of two lateral prestressed concrete beams, supported by the piers, so hiding the arches and modifying severely the original aspect of the bridge itself, as shown in Fig. 3. More recently, due to the modification of the river course, scour occurred at the piers on the Mulazzo side, so that in the years 2005-2010 a relevant crack pattern was detected on the last two arches, as illustrated in Figs. 4 and 5. Despite the monitoring program setup to control the structural decay, in 2011, during the Magra flooding, two arches on the Mulazzo side collapsed due to scour of the extreme pier, and a temporary Bailey bridge was placed on the deck to allow at least light car traffic (Fig. 6).
Fig. 3. Elevation of the bridge after the carriageway widening (1961)
Fig. 4. Inspection of a damaged arch - monitoring phase (2010)
In the paper, the reconstruction of the collapsed arches and the rehabilitation and the strengthening of the bridge, which has been completed in 2016, is discussed and execution of the interventions, which has performed without erection of temporary support in the riverbed, is also illustrated, devoting particular attention to the original solutions adopted for the full seismic upgrading of the bridge according to the Italian Building Code in force at that time (NTC, 2008), recovering the original architectural aspect of the bridge and widening the carriageway as well.
Nicola Croce et al. / Procedia Structural Integrity 11 (2018) 371–378 Croce N. et al/ Structural Integrity Procedia 00 (2018) 000–000
Fig. 5. Main crack on the arch (Mulazzo side 2010)
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Fig. 6. The temporary Bailey bridge after the collapse of the two arches (2012)
2. Rehabilitation, strengthening and seismic upgrading of the bridge The rehabilitation, strengthening and seismic upgrading interventions were defined not only considering structural aspects, but also taking into account the needs of the preservation of the historical value of the bridge, according the Guidelines of the Italian Ministry of Cultural and Historical Heritage (2011), the ISO standard 13822 (2001) and the general approached widely described by Croce and Holicky (2013, 2015). The intervention involves, inter alia, the consolidation of 6 of the 8 arches, the reconstruction of the collapsed pier and of the two arches closest to the right bank and the strengthening of the remaining parts. The two collapsed arches have been rebuilt in reinforced concrete as well as the collapsed pier (see Fig. 7.a), characterized by micro-pile foundation. For casting these new concrete parts, special non-removable lateral formworks have been used, overlaid with bricks and stones looking similar to the original ones, anyhow underlining the modern replacement (Fig. 7.b).
Fig. 7.(a) The new r.c. arches and pier
(b) The lateral formworks overlaid with stones and bricks
These two new spans are a continuous beam on three supports, with varying cross section, being the end sections prevented from lengthening, so allowing the transfer of the trust of the adjacent arch to the right embankment, whose structure has been executed with cast in-situ reinforced concrete. Finally, the foundations of the pile are realized with "tubfix" type steel micro-piles 300 mm in diameter, around 12.0 m long. The 6 spans subject to rehabilitation were strengthened through a continuous reinforced concrete deck, supported by the existing piers, duly reinforced using tubfix micropiles extending till to the extrados of the existing arch bridge (Figs. 8 and 9), supplemented also by local strengthening interventions on the piers based on 24 injected horizontal rebars (Fig. 10). In this way, at the end of the intervention the deck behaves like a new reinforced concrete bridge, of variable thickness, whose scheme is a continuous slab on seven supports, so transferring directly the traffic loads to the existing piers and through their micro-pile reinforcement to the soil, also relieving the existing masonry arch structure, without modifying its behavior (see Fig. 10), contributing to prevent also the scour of the pier. Moreover, to limit the execution time avoiding temporary works in the riverbed, the two r.c. arches were cast on temporary trusses placed above the 200 years flood return period (see Figs. 7.b and 11), so eliminating problems during flooding, that occurred several times during the works (Fig. 12)
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Fig. 8. Longitudinal cross section of the bridge
Fig. 9. Execution of micro-pile trough the existing piers
Fig. 11. Temporary trusses
Fig. 10. Detail of the strengthening interventions
Fig. 12. Flooding during temporary phase of erections
The static and seismic assessments of the bridge have been performed adopting the same actions as for new bridges, so adopting the traffic actions given in the Italian code (NTC, 2008), conforming with those given in Eurocode EN1991-2 (2003), and the seismic actions given in the aforementioned Italian code, considering a soil of category E, according to Eurocode EN1998-1 (2004) and referring, where possible, also to EN1998-2 (2005). In defining the seismic actions, it has been considered that the bridge, for its particular position, and function, is strategic for the civil protection needs, so that it belongs to Class IV structures, according to Italian Code (NTC, 2008), so resulting in a coefficient of usage Cu=2.0. Moreover, the relevance of the bridge from the historical point of view imposed to consider a notional design working life of 100 years, so that the reference period for the structure resulted 200 years, to which corresponds, according to the Italian code, a return period of 1898 years for the evaluation of the seismic design actions for the ULS for life safety assessment. Considering that the reference PGA on soil Category A for the considered site is 0.309 g and taking into account the presence of masonry arches, the behavior factors has been set to 1.0 both for vertical and horizontal component
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of the response spectra. Therefore, the dynamic linear seismic analysis has been carried out considering the horizontal and vertical elastic response spectra represented in Fig. 13. Thanks to the full integration of the functions between new parts and existing structure, static and seismic assessment where satisfactory, confirming the effectiveness of the proposed solutions. It must be highlighted that the adoption of variable thickness for the continuous reinforced concrete slab supporting the carriageway executed on arches not affected by the collapse, allowed also to reduce the effects of the temperature variations, so allowing eliminating expansion joints not only along the bridge, but also at the embankments. As already said, the concrete deck transfers the loads to the existing structure only at the piers; with this aim, the deck was executed casting in situ prefabricated reinforced concrete predalles (Fig. 14), supported by intermediate sheets of soft material, polystyrene, 30 mm thick, already shown in Fig.10, previously placed above the filling of the arches of the bridge, so limitating the interactions between the new concrete deck and the existing arches (see also Fig 15).
Fig. 13. Design (elastic) response spectra for bridge
Fig. 14. Preparation of the new r.c. cast in situ deck
The intervention has been carried out according to the following phases: • Phase 1: strengthening of the external body of existing piers by means of steel bars 24, spaced 0.8 m vertically and 1.0 m horizontally, duly injected, strengthening of the foundations of the existing piers with external micropiles connected to the existing foundations and protected from scour by means of stone barrier (Fig. 16) (in this phase light traffic was permitted); • Phase 2: erection of foundation and body of the new concrete pier (light traffic permitted on the bridge); • Phase 3: setup of alternative routes to mitigate the effects of the closure of the bridge; • Phase 4: dismantling of prefabricated beams in c.a.p. put in place in 1961 to widen the carriageway (fig. 17) and restoration of the external surfaces (Fig. 18); • Phase 5: disassembly of the Bailey bridge; • Phase 6: erection of the two new spans in c.a. cast in place (Fig. 19); • Phase 7: strengthening of the remaining part of the bridge (6 arches); • Phase 8: erection of the new r.c. concrete deck slab (Fig. 19); • Phase 9: finishes. The total cost of the intervention, including the execution of the temporary pedestrian bypass, was about 1.1 M€, for a unit cost, referred to the total deck surface, of around 800 €/m2.
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Fig. 15. Cross section of the deck
Fig. 16. Strengthening of the existing piers and foundations
Fig. 17. The bridge after the dismantling of the prefabricated r.c. beams
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Fig. 18. Restoration of the external surface
Fig. 19. Preparatory works for execution of the continuous r.c. slab
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3. Conclusions In the paper, the reconstruction of the collapsed arches and the rehabilitation, strengthening and seismic upgrading of the Villafranca bridge on Magra river, has been shortly discussed. The design of interventions aimed not only to repair the collapsed arches, but also to widen the carriageway, fulfilling at the same time severe requirements in terms of static and seismic performances. In fact the bridge is now able to withstand traffic loads and seismic actions foreseen for new bridges. In particular, due to strategic needs, seismic actions with return period of 1898 years have been adopted, considering a soil Category E and a refence PGA on soil Category A of 0.309 g. Nonetheless, the assessment was very satisfactory confirming the effectiveness of the proposed solutions. It must be also highlighted that the interventions have been conceived in order to preserve as much as possible the historical and cultural value of the bridge, adopting were possible reversible solutions, like for the new concrete deck, and recovering the original aspect of the bridge, anyhow not hiding the unavoidable additions, linked with the reconstruction of the collapsed parts (Fig. 20).
Fig. 20. A fisheye photo of the Villafranca bridge at the end of works
Acknowledgements The design has been carried out by the staff of the Studio Croce srl, composed, beside the authors, by Vladimiro Croce, Matteo Di Prete, Claudia Imbrenda, Stefania Morino and Davide Petrozzino. The Authors acknowledge Stefano Michela, Manager of the technical office of Massa Carrara province, Filippo Bellesi, Major of Villafranca Lunigiana, Claudio Novoa, Major of Mulazzo and the enterprise F.lli Gliori srl. References Croce, P. and Holicky, M., 2013 Operational methods for the assessment and management of existing structures. TEP, Pisa. Croce, P. and Holicky, M., 2015. Operational methods for the assessment of aging infrastructures. CTU, Prague. EN1991-2. Eurocode 1, 2003. Actions on structures – Part 2: Traffic loads on bridges. CEN, Brussels. EN1998-1. Eurocode 8, 2004. Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings. CEN, Brussels. EN1998-2. Eurocode 8, 2005. Design of structures for earthquake resistance – Part 2: Bridges. CEN, Brussels. ISO 13822, 2001. Basis for design of structures -Assessment of existing structures. ISO, Geneva. Italian Ministry of Historical and Cultural Heritage, 2011. Guidelines for seismic assessment and seismic risk reduction of the historical and cultural heritage according to NTC 2008. Italian Ministry of Infrastructure and Transport, 2008. NTC 2008 Italian Building Code. D.M. 14/01/2008 (in Italian).