french practices and experience past and modern...

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FRENCH PRACTICES AND EXPERIENCE

Past and modern generations

Philippe JANDIN*, Damien CHAMPENOY+, Jérome MICHEL#

* Project director in Cerema ITM

[email protected]

+ Co-head of division Civil Engineering Structures, Cerema Est

[email protected]

# Project engineer in Cerema ITM

[email protected]

Keywords: integral bridges, retrofitting

Abstract: Referring to integral bridge definition, France has a long experience with this

kind of bridges since the early 1970’s and the French road network modernization.

Standard integral bridges, in the range of spans from 5 to 25 meters, were indeed designed

and described in guidance books written by Setra (early name of Cerema ITM). In the early

2010’s, climate change and energy demand management had to be taken into account to

propose new bridges designs in order to reduce structural weight and future maintenance.

A new integral or semi-integral bridges generation has been designed and built in

roadways or railways. This paper briefly describes the past generation of integral,

standard reinforced concrete bridges. Then examples of different recent integral bridges

are given, concerning different kinds of structures: filler beam decks, composite

steel/concrete girders, pre-stressed precast concrete beams. Retrofitting has also been

experienced in two old steel bridges in Northeast of France. As a conclusion, integral and

semi-integral bridges are increasing in France, even in retrofitting field. However, some

features require further specifications (maximum length limits, soil/structure interaction,

design and calculation of frame corner in the case of composite steel/concrete bridges…).

Ph. JANDIN et al.: French practices and experience

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1 INTRODUCTION

Referring to integral bridges definition as bridges without expansion joints and without

bearings, many integral bridges were built in France from the end of the 60’s and the

beginning of the 70’s, period corresponding to the French road network modernization.

Until now, there are no national standards or recommendations dealing with integral

bridges design in France, with the exception of guidance books written by Sétra 1 for

standard bridges and presented in Chapter 2.

In the last few years, however, some new integral bridges have been designed and built on

roadways or railways. In addition, from the end of the 2000’s, Sétra had to take into

account climate change and energy demand management to propose new bridges designs

that will reduce structural weight and to re-examine actual conceptions and practices of

standard bridges toward semi-integral or integral bridges that require less expensive

maintenance. A French Working Group was set up in order to make a state of the art and to

put forward rules for designers and bridges’ owners in the field of the construction of new

bridges and the retrofitting of existing bridges.

Chapter 3 will describe a new integral bridges’ generation designed as part of new and

sustainable technologies. Some examples of already built bridges or bridges in progress are

presented.

And conclusion will give some different points or questions remaining before being able to

design technical recommendations. In order to generalize integral bridges, the aim is to give

some easy calculation rules and constructional features and not be forced to use complex

Finite Element Modeling (FEM) for global or local behavior.

2 FIRST INTEGRAL BRIDGES’ GENERATION IN FRANCE

For the implementation of the post-war roads reconstruction work and the motorways

development plan, Setra have created standard bridges; some of which are in fact integral

bridges. Three reinforced concrete standard bridges with framed abutment are concerned:

- Closed frame underpass;

- Open frame underpass;

- Double open frame.

The following sections shortly describe these three kinds of bridges. Furthermore, some

semi-integral bridges’ designs are sketched up in the guidance book named PP73 [1] (piers

and bents) devoted to bridges’ supports.

2.1 Closed frame underpass

1 Setra, Technical Department for Transport, Roads and Bridges Engineering and Road Safety, is a technical department within the Ministry of Transport and Infrastructures. Its field of activities is roads, transportations and structures. Created in 1968, it was the centerpiece of the organization set up by French government to modernize its road network and create its highway network. In the field of bridges, Setra develops knowledge and good practices through technical guides and software. In particular, at its beginning, it produced guidance books in order to standardize the design of thousands bridges in order to build new networks, which helped France to have one of the most modern highway network in Europe. In 2014, Setra became Cerema ITM with creation of Cerema.


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Closed frame underpass (PICF [2]) is an underpass designed for motorways but it can be

disposed under any other network (road or rail). PICF was subject to a first guidance book

in 1964, amended in 1967 to follow the evolution of reinforced concrete rules. A 1992

technical guide [3], called “Closed and open frames design guide”, replaces the 1967

guidance book. The PICF shape is as designed in figure 1.

It introduces precast structures, an architectural dimension, which did not exist in former

guidance book. A chapter is dedicated to detailed design, according new materials (concrete

and reinforcement) and another chapter develops new building methods such as ripping. It

brings new design rules according to load traffic and concrete codes available at this time.

The software is also updated in 1991 to follow the last reinforced concrete design code

(BAEL 91).

Eurocodes, Europeans standards adopted by European Committee for Standardization

(CEN) members, replaced all French design codes in 2010. In order to be current with

standards, Setra developed new software called CHAMOA [3] (Modular Algorithmic Chain

for Engineering Structures). Thanks to a CHAMOA unit, every customer can get a

complete and detailed calculation note in Eurocode format for PICF.

2.2 Open frame underpass

Open frame underpass (PIPO[5]) is the prolongation of PICF for more important openings

beyond 20 meters. PIPO was subject to several guidance books (1962, 1963, 1964 and

1967), which last one, from 1974, was written to follow reinforcement concrete rules and

traffic loads on bridges developments. The PIPO shape is as designed in figure 2.

Figure 1: PICF shape

Figure 2: PIPO shape

PIPO is an open frame structure which abutments can be considered from embedded (when

founded on rock) to hinged (when founded on two converging files of small diameters

piles) going through all intermediate partial embedded degrees (footing on moveable soil).

The 1992 technical guide replaces the 1974 guidance book. A CHAMOA unit is dedicated

to open frames.

2.3 Double open frame

Double open frame (POD) is a two spans open frame with a central pier. It can favorably

replace open frame underpass as the opening exceeds 15 meters and it is possible to set up a


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central pier. POD allows bridging more important gaps in excellent economic conditions

while being easy to build.

A guidance book was written in 1976 [6]. The only difference with open frame guidance

book PIPO is the intermediate bearing, made with a Freyssinet bearing and considered as a

plastic hinge in analysis. The guidance book also goes with an automatic calculation

program.

Picture 1 – Illustration of an outstanding double open frame: 2 spans of 42m and skew

angle of 25gr

The guidance book was never updated. The 1992 technical guide briefly deals with double

open frames but does not give detailed designs. Because of the small number of this kind of

structures in France, no CHAMOA unit is dedicated to double open frames.

3 MODERN INTEGRAL BRIDGES

3.1 Introduction

At the end of the 2000s, Sétra, technical center of the French Ministry of Ecology, had to

take into account Grenelle Environment2 Acts in the field of transportation infrastructures.

In particular, in the fields of climate change and energy demand management, one action

for “Innovate: SDHQ3 structures design“ has been initiated. Several innovation approaches

have been identified in order to propose the use of new materials with high mechanical and

environmental performances, to propose new bridges designs that will reduce structural

weight and to re-examine actual conceptions and practices of standard bridges toward semi-

integral or integral bridges that require less expensive maintenance.

Before setting up a French working group into Cerema, several projects have been designed

these last years to acquire experience. Some of them have been studied by Government

2 Grenelle Environment: open multi-party debate meetings organized in France at the end of 2007, in order to make long-term decisions regard to environment and sustainable development.

3 SDHQ = Sustainable Development High Quality (in French: HQDD = Haute Qualité Développement Durable)


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offices (Cerema, IRD4), some other were designed here or there in several departments by

local authorities. Many integral bridges have been designed too in the South Europe

Atlantic high-speed railway project.

The following sections describe these different projects.

3.2 Cormontreuil bridge over A4 highway (built in 2014)

Cormontreuil Bridge is located in the east of Reims, very well known for its famous

cathedral and its champagne. The project consists of doubling an existing bridge in A34/A4

interchange. Cerema suggested an integral design of initial four spans filler beam deck.

Despite fear of innovation, the client, (Champagnes-Ardennes DREAL5) accepted this idea

provided there was no planning delay and no additional costs.

The design follows Anglo-American practices for the deep foundations and on FEDRO6

Swiss documents for transition slabs. Nord-Picardie Territorial Direction of Cerema

(formerly CETE) completed the project, with external control by Cerema ITM (formerly

Setra). Total length is 68.3 meters.

Figure 3 – Longitudinal section

The abutment foundations are (steel) H-Piles (HEB500 type) to give more flexibility and so

reduce the embedment moment. According to PD6694-1:2011 [7], they are from type 4h,

piles enclosed in sleeves. The 7.50m length H-Piles are sealed in bored concrete piles

(17.50m length) in the last 2.5 meters to provide enough vertical capacity (not assumed by

the H-Piles alone in the chalk of Champagne and could not be driven into the chalk). The

HEB 500 H-Piles, with a length of 25 meters, are arranged around their strong axis bending

(restraint forces doubled but elastic modulus Wel 5 times stronger than along weak axis

bending) in order not to exceed the steel yield stress.

4 IRD = Interdepartmental Road Directorate (in French: DIR = Direction Interdépartementale des Routes)

5 DREAL = regional environment, planning and housing agency (In french : Direction Régionale de l’Environnement, de l’Aménagement et du Logement

6 FEDRO = FEDeral ROads Office


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Figure 4 – Foundation proposed for works

Each abutment includes 11 HEB H-Piles covered with an Im2 painting system, set up in

lost steel pipes filled with granular material after producing drilled concrete piles (800 mm

diameter) on the five last meters.

3.3 Bosc’s rest area bridge over A75 highway (project)

As part of the creation of a rest area on A75 highway connecting Clermont-Ferrand to

Béziers cross the Massif Central and very well known for Millau viaduct, Cerema ITM has

studied an innovative integral bridge as an answer for the Client’s requirements: minimize

traffic interruptions, reduce disruptions on A75 during works, and reduce maintenance

costs. The result is a composite steel/concrete integral bridge, with 5 hot-rolled beams in

weathering steel, without any bracing, in one span of 38m50 length.

Figure 5 – Transverse section

Figure 6 - Side Elevation of bridge (project)

The bridge looks like a long open frame underpass, founded on shallow footings.

The deck is entirely built alongside the highway, then, after abutments erection, Kamags lift

it up and set it up on temporary bearings in one night. After deck installation, the upper part

of the frame corner and the slab over a length of about 4 meters are cast to embed deck into

abutments.


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Figure 7 – Concrete phasing

Frame corner was designed according to Eurocode 2 and Intab report [8]« Composite

Bridges with Integral Abutments » with a strut-and-tie (6.5 part of EN1992-1-1). In order to

reduce stresses in nodes, a steel sheet and a bracket have been designed at the end of the

bottom flange of the girder.

Figure 8 – Strut-and-tie modeling of frame

corner

Figure 9 – End steel sheet and bracket

Soil/structure interaction has been taken into account under two methods. First one is

standard method use for open frame underpasses or double open frame underpasses (Bosc

bridge span length is in double open frame range). Active earth pressure coefficient has

been taken into account with Rankine’s coefficient K in a range of 0.25 to 0.50. Second

method used is according to Swiss model [9] using increased earth pressure coefficient KeR,

similar to former BA42/96 British advice note (now replaced by PD6694-1:2011

recommendations [).

On the backfill side, moment at the end of pier is 20% higher with French method (K=0.25

to 0.50) and moment at feet is 10% higher with Swiss method (increased earth pressure

coefficient KeR 0.81). On the motorway side, maximum moment is 10% higher with Swiss

model. Although these differences, piers’ sizing can remain the same, only reinforcement

slightly differs.

3.4 Integral road bridges on the SEA high-speed line [

The South Europe Atlantic (SEA) high-speed railway is a new infrastructure with two

traffic lanes of 300 km between Tours and Bordeaux, and almost 40 km for all the

connections with the existing network. This new line has been operational since February

2017. It connects Paris to Bordeaux in only 2 hours.

1st concreting

phase, before

deck installation

2nd concreting phase, after

deck installation


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This project included the creation of 484 bridges along the line, amongst which 163 road

bridges made with pre-stressed precast concrete beams. This type of bridge is nowadays a

frequently chosen design for the construction of road bridges with spans ranging from

around 10 m to 25 m and, usually, precast beams or end diaphragm are supported on a line

of elastomeric bearings. In order to improve the construction methods of these bridges and

reduce maintenance in the future, the constructor studied an alternative that consisted in

embedding decks into abutments or piers. In the project, 123 road bridges are integral

bridges or semi-integral bridges. The great majority of them (112) have three spans ranging

from 14.90 m to 23.50 m. Among the 11 other bridges, there is 1 bridge with only one span,

4 bridges with four spans, 4 bridges with five spans and 2 bridges with six spans. For the

majority of these bridges, they are located near the existing network and must cross several

railways. The longest central span is 24.35 m for these bridges.

Picture 2 – General view of one integral road bridge on SEA project (© Pacal Le Doaré)

Among the 123 road bridges that are concerned by the constructor’s alternative, only 13 are

semi-integral bridges, embedded into piers only. Of the 13 bridges, it corresponds first to

the 10 bridges which have more than three spans: in fact, the total length of these bridges is

relatively important (113.10 m for the longest bridge) so it was decided to free the two

deck’s extremities, because of the displacements due to thermal loads, or creep and

shrinkage (expansion, shortening). Moreover, it was not possible to embed the deck into

abutments for three bridges with three spans, because their abutments did not permit to

bring enough flexibility to the structure.

All the other bridges are integral bridges and the deck is embedded into abutments and

piers.

Figure 10: Typical transversal cross section


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Picture 3 – Deck embedded into piers

Picture 4 – End steel sheet and bracket

Two other main adaptations were adopted too: widening of the top of the piers in order to

permit a direct laying of beams without any temporary supports and modifying the beams’

formwork using T beams instead of rectangular beams.

These adaptations are advantages for the construction, especially as the number of bridges

is relatively large:

- improvement of the security on the construction methods: absence of temporary

supports for beams, bottom shuttering of the slab made with T beams directly,

- simplification of deck works because formwork of end diaphragms or deck

extremities are simplified, no operation is necessary to put the deck on the

definitive bearings (directly on the definitive supports).

- time saving: the constructor in comparison with the classic elastomeric bearings

design estimated a gain ranging from 30% to 50%.

After the civil works’ completion, maintenance operations are reduced: no replacement of

elastomeric bearings during the bridge’s lifetime and easier maintenance of expansion joint.

The software ST1[10], developed by Cerema ITM was used. It enables calculation stress in

a bar model. For these bridges, a 2D model has been developed, in which all the geometry

and loads are defined with parameters, aiming to automate calculations of the 123 different

bridges.

Figure 11: Extract of 2D calculation models with ST1 software


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The interest of these models lies in modeling all bridge’s structure: abutments and piers

(including foundations, piles or footings), the deck (slab and beams). In fact, as it deals with

integral bridges, it creates a structural interaction between the different parts of the bridge,

as well as a more complicated interaction soil/structure on abutments. That is why, it is

necessary to have a unique model for all the structure.

A specific study of the connection between piers (or abutments) with beams and slabs was

necessary to establish an easy reinforcement principle for the building site and renewable

on the 123 integral bridges. It was decided to position with a good precision the waiting

bars from the head of piers or end bents. This position was a sensitive and critical point on

the construction site, in order to avoid any conflict of bars between reinforcement from

piers/abutments, beams and slab, but also to permit to correctly pour the concrete in this

zone densely reinforced.

Figure 12: Reinforcement principle at embedment in piers

3.5 Other examples and retrofitting

3.5.1 Berthelot crossroads bridge in New Caledonia

Composite steel/concrete bridge: the deck is built with 6 box girder bolted to concrete slab,

35,40 meters’ length, with full height frame abutments founded on shallow footings.

The bridge is an open frame underpass. We can notice 3 particularities:

- non symmetric bridge, 3.70m gap between each shallow footing elevation,

Figure 13 – Longitudinal section

- Frame abutment with hinge at connection with footing


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Picture 5: Hinge reinforcement (stainless steel rebars)

- PreCo-Beam box-girders, with CL shape continuous shear connection

Picture 6: Box-girders with CL shape shear connection positioning

3.5.2 Retrofitting of two old steel bridges

The bridge, located in Northeast of France, is made up of the different decks, the older built

in 1906 and the second in 1976. Heavy maintenance works were scheduled and Cerema

suggested modifying these bridges into semi-integral bridges by eliminating expansion

joints that caused a large part of the disorders. On the more recent bridge, there was heavy

corrosion at the ends of the main girders and on the abutment cross-beams. On the older

one, besides the same desorders, the leak defect of expansion caused a severe corrosion of

steel bearings.

Cerema proposed to replace abutment cross-beams, as initaly scheduled, and create a

backwall that could eliminate expansion joints.

Picture 7 – Replacement of the end cross-beam (on the left : recent bridge – on the right :

old bridge


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Picture 8 – Backwall reinforcement (on the left : recent bridge – on the right : old bridge)

Picture 9 – Backwall view after formwork removal (on the left : recent bridge – on the right

: old bridge)

Compared to the previous works, the retrofitting extra cost represents around 5% of the

total cost.

4 CONCLUSION

Nowadays, France does not have a national housing policy, technical rules or guidelines on

integral or semi-integral bridges. However, we have a very good knowledge in the field of

closed frame underpass, open frame underpass and double open frame, which are in fact

integral bridges with spans ranging from 10 to 45 or even 50 meters.

For some years now, we have developed specific expertise in integral bridges from 40 to 60

meters length with different structural decks: precast prestressed concrete beams (PRAD),

filler-beam decks or composite steel, concrete bridges and , since 2016 with UHPFRC

beams.

The questions still remaining concern:

- Soil/structure interaction: should an increased earth pressure be taken into account

as taken in Swiss or English rules?

- Design and calculation of the frame corner in the case of composite steel/concrete

bridges: strut-and-tie model, finite element model, simple rules?

- Maximum length limits to allow the use of integral bridges: distinction by kinds of

deck structures (concrete, composite, steel structures) and by kinds of foundations

(shallow or deep foundation)? Limitations in terms of skew, curve?

- Shall the kind of foundation be designed to seek maximum flexibility in order to

reduce stress at embedding?


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Concerning existing structures, it would be interesting to have many experiences on

different kinds of structures before extending retrofitting when important maintenance

works are scheduled.

Finally, it is necessary to ensure the good performance at the deck’s ends (cracking,

deflection) with the use of specific details. Now, the preferred solution is the design using

the Swiss transition slab, which differs with the usual practices in France.

REFERENCES

[1] PP73 guidance book, Setra 1973 (Piles et Palées in french, according to Setra

terminology).

[2] PICF guidance book, Setra 1967 (Passage Inférieur en Cadre Fermé in french,

according to Setra terminology).

[3] Closed and open frames design guide, Setra 1992.

[4] CHAMOA algorithmic modular chain for bridges, © CEREMA/ITM/CTOA/DCSL

(CHaîne Algorithmique Modulaire Ouvrages d’Art in french).

[5] PIPO guidance book, Setra 1974 (Passage Inférieur en Portique Ouvert in french,

according to Setra terminology).

[6] POD76 guidance book, Setra 1976 (Portique Ouvert Double in french, according to

Setra terminology).

[7] PD6694-1:2011, BSI 2011. Recommendations for the design of structures subject to

traffic loading to BS EN 1997-1:2004: 22-32.

[8] RFCS 2010. Design Guide - Composite Bridges with Integral Abutments (INTAB+)

[9] ASTRA 2011. Swiss directive on bridges building details “Chapter 3 – Bridges’

abutments” (Directive “Détails de construction des ponts. Chapitre 3, extrémités de

ponts” in french).

[10] ST1 software for structures using beam model, © CEREMA/ITM/CTOA/DCSL

[11]

[12] Grove, A.T. 1980. Geomorphic evolution of the Sahara and the Nile. In M.A.J.

Williams & H. Faure (eds), The Sahara and the Nile: 21-35. Rotterdam: Balkema.

[13] Jappelli, R. & Marconi, N. 1997. Recommendations and prejudices in the realm of

foundation engineering in Italy: A historical review. In Carlo Viggiani (ed.),

Geotechnical engineering for the preservation of monuments and historical sites;

Proc. intern. symp., Napoli, 3-4 October 1996. Rotterdam: Balkema.

[14] Johnson, H.L. 1965. Artistic development in autistic children. Child Development

65(1): 13-16.

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