Status of Segmental BridgeConstruction in Europe

Peter MattLosinger/VSI

Berne, Switzerland

S egmental bridge construction is amethod in which concrete seg-ments, either cast in place or precast,are post-tensioned together to form thesuperstructure of a bridge. Segmentalconstruction methods can also be ap-plied to beam or arch bridges in pre-stressed or reinforced concrete.

Although many variations are cur-rently in use, only the three main con-

Note: This paper is based on a presentationgiven at the Segmental Concrete Bridge Confer-ence in Kansas City, Missouri, March 9-10, 1982.The Conference was sponsored by the AssociatedReinforcing Bar Producers CRSI, FederalHighway Administration, Portland Cement Associ-ation, Post-Tensioning Institute, and PrestressedConcrete Institute.

struction methods will be discussedhere: the span-by-span method (since1960); the free cantilever method (castin place since 1950; precast since1962); and the incremental launchingmethod (since 1962). Cable-stayedbridges will not be discussed here.

This paper is intended to be a de-scription of the actual situation inEurope (see Fig. 1). The survey isbased upon a study of available litera-ture and contacts with several key indi-viduals in the European bridge indus-try. Where objective statistics are un-available, the author's subjective obser-vations and comments are offered.

This review covers the situation in 18

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Fig. 1. Map of Europe showing location of countries whose bridges are included in thesurvey described in article.

Western European (OECD,) countries,where more than 18 different languagesare spoken. Information (gathered in1980) comparing the size of Europe inrelation to the United States is providedin Table 1. It can be noted that Europe,which is densely populated, achieveswith 50 percent more people only 10percent more in gross national productthan the United States. Within Europe,the differences in GNP per capita areenormous, varying from $9244 down to$1901 (in U.S. dollars).

Clearly, Europe is far from being asingle entity. A gap in technology be-tween certain countries parallels theeconomic disparity. Wealthier coun-

tries, due to their higher labor costs,generally prefer labor-saving methodswith high mechanization. Segmentalconstruction was consequently devel-oped in these countries and is appliedto a much lesser extent in the lesswealthy regions of Europe.

Right .now, Europe does not have aunified standard in civil engineering,nor is it likely that such a standard willbe established in the near future. Al-though a "Eurocode" is in the planningstages, the concept faces so many ob-stacles that the prospects for adoptiondo not appear very promising.

The Model Code published jointly bythe CEB and FIP in 1978 certainly rep-

PCI JOURNAL/May-June 1983 105

Table 1. Statistical comparison of Europe and the United States.

Area.(sq km)

Population(millions)

GNP(billion U.S. $)

GNP/Capita(billion U.S. $)

Europe (OECD) 3,594,320 350 2018 5766

United States 9,363,386 228 1832 8035

resents an excellent achievement.However, as indicated by the title, thisis a model rather than a code for regulardesign work. The situation today issuch that each country has its ownstandards.

It is only logical that differences innational character, economy, and stan-dards have led to differences in con-struction practices as well. The largenumber of bridges needed and builtduring a relatively short period follow-ing World War II spurred the develop-ment of the wide variety of constructionmethods known today.

Statistical figures from the FederalRepublic of Germany are indicative ofEuropean construction trends. Between1965 and 1975, the total number ofbridges in Germany increased by 7710,of which 4174 were prestressed con-crete, 3262 were reinforced concrete,77 were steel, and 197 were compositestructures of steel and concrete. Per-haps even more revealing is a compari-son of percentages of the areas ofbridge decks built during this period:

Prestressed concrete 75.0 percent Reinforced concrete 14.2 percent Structural steel ...... 6.7 percent Composite

steel-concrete ....... 4.1 percent

The above figures, which show theimportance of prestressed concrete inbridge construction, are applicable notonly to West Germany but also to otherEuropean countries.

Although similar statistics from theUnited States were not available, acomparison of the consumed tonnage ofprestressing steel in bridges during thedecade from 1965 to 1975 appears sig-nificant. This comparison is presentedin Table 2. Note that the production ofprestressed concrete bridges in Europewas more than four times the produc-tion in the United States. This is per-haps one of the major reasons whyEurope has been so innovative in thisfield.

WHY SEGMENTALCONSTRUCTION?

Looking at the costs of concretestructures, the following average per-centages stand out:

Labor ................38 percent Material ..............46 percent Equipment ........... 9 percent Transportation ........ 7 percentLabor and material costs amount to

more than 80 percent of the total cost ofa project. The ratio of labor to material,

Table 2. Comparison of prestressed concrete bridge construction in Europe and theUnited States, based on consumption of prestressing steel.

Total prestressingsteel consumption

Prestressing steelper capita Percent

United States approx. 75,000 t 0.35 kg 100

Europe approx. 500,000 t 1.46 kg 417

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Fig. 2. Beckenried Viaduct, Switzerland.

approximately 45:55, has remainedfairly constant for decades. Between1950 and 1970, however, salaries in-creased approximately 500 percent andsocial welfare costs increased to aneven greater degree; yet material costsfor concrete or reinforcing steel in-creased only about 200 percent.*

A drastic reduction in man-hours overthe years explains why the labor tomaterials cost ratio has remained con-stant. Reasons for the reduction includeincreased mechanization of construc-tion sites, rationalization of single oper-ations, and, last but not least, the de-velopment of efficient segmental con-struction techniques.

A highly repetitive, standardizedconstruction cycle with a minimum ofalterations throughout a particular jobbrings the number of man-hours to a

*Internal documentation, Losinger Ltd., Berne,Switzerland.

minimum, due to the advantages of thelearning curve. It is obvious, therefore,that the segmental construction methodis competitive only if a bridge has acertain minimum length and astraightforward layout. Unusual topog-raphy or other conditions may also leadto the requirement of a segmentalmethod.

One might question the need for sev-eral types of segmental constructionmethods and the reasons why one seg-mental method is not sufficient to coverall needs. It might also be argued thatthese methods have been developed in"old" Europe, therefore reflecting thein-grained customs of different regionsor countries. However, examples showthat, if correctly applied, all the differ-ent construction methods have theirjustification. Furthermore, it should benoted that the development of the vari-ous methods was made possible by theparallel development of the post-ten-sioning technique.

PCI JOURNAL/May-June 1983 107

j Fig. 3. Beckenried Viaduct, Switzerland.

SPAN-BY-SPAN METHODThe span-by-span method, which

uses a movable scaffold system, datesback to 1960. In the past 22 years, thisconstruction technique has been usedextensively in Europe, mainly in WestGermany, Austria, and Switzerland. Avariety of launching trusses have beendeveloped, but basically two types canbe distinguished, namely, the under-lying type and the overlying type.

Figs. 2 and 3 show an underlyingtype of truss, which was used for themore than 10,000 ft (3048 m) long Beck-enried Viaduct in Switzerland.' Theviaduct has two parallel superstruc-

*This and subsequentcost indications are takeneither from available literature or the best es-timates of the author.

tures, each 35.4 ft (10.8 m) wide andhaving typical spans of 180 ft (55 m). Ittook two weeks to assemble one span.The total cost per launching truss (totalweight about 750 tons each), includinginitial erection and dismantling, wasabout $1.7 million or $4.55 per sq ft ofbridge deck ($50 per m2).*

Note that the movable scaffold sys-tems were reused for a prestressed seg-mental bridge crossing the Tigris Riverin Iraq.

Fig. 4 shows an overlying type oftruss which was used for the Ahrtal-bridge in West Germany. It was de-signed for a maximum span of 348 ft(106 m). The truss, without formwork,weighed about 2100 tons. The bridge,completed in 1976, has a total length of5000 ft (1500 m) and consists of twoparallel structures with a width of 49.5

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Fig. 4. Ahrtalbridge, Federal Republic of Germany.

ft (15.1 m) each. To the author's knowl-edge, the truss was never reused. Thismeans that the cost, at least $4.5 millionor $9.30 per sq ft ($100 per m 2), had tobe depreciated on this job.

A compromise was found for the con-struction of the more than 6700 ft (2000m) long Gruyere Viaduct in Switzer-land, which was built from 1975 to1979. The typical span is 198 ft (60.5 m)and the superstructure consists of asingle box with a deck slab 78 ft (23.7m) wide (see Figs. 5, 6, and 7).

For this project, the segmental prin-ciple was amplified in that the super-structure was subdivided not only lon-gitudinally, but also transversally. Acomparatively light movable scaffoldsystem with a total weight of about 660tons was used to cast the box onlywithin a 3-week cycle. Note that of thesystem's total tonnage, about 505 tonswere structural steel and the rest werefor formwork, wor