2. types of steel-concrete...

steel-concrete bridges - 2004

Dr. A. Romeijn 4

2. Types of steel-concrete bridges

Roughly speaking, the steel-concrete bridges can be divided into three categories:- several I-shaped girders- two main girders- boxed girder

2.1 Several I-shaped girdersProbably the oldest type of steel-concrete bridge is shown in fig. 5a. In the past, a great number of thesestatically determined bridges with small spans have been built. The constructive flexibility of this typesimplifies adaptations, such as the enlargement of an existing bridge from two to four tracks.To enable larger spans and to keep meeting the deflection requirements, it was aimed at to increase the bendingstiffness of the structure. The solution was found in installing the concrete roadway on top of the steel structure,fig. 5b. Dowels are used to join the steel structure, rolled girders or welded plate girders, onto the concreteroadway. By this application of the steel girders, new mechanisms were introduced, like lateral (torsional)buckling and plate buckling. Because of these stability criteria, the possibilities on increasing the span lengthwere rather limited. Therefore, other cross-sections were developed, such as steel girders with K-frames in-between or with a (transverse) crossbeams. As the last I-shaped bridge type, the so-called preflex-girder ismentioned, fig. 5c. These girders are prefabricated and therefore have the usual advantages of prefabrication.Also, the ratio between the load-capacity and the construction height is favourable. The small constructionheight is made possible by a upward deflection of the steel girder before casting the concrete, which finallyintroduce a prestressing of the concrete. This system, developed in the fifties, is hardly applied anymore,because the rigidity is small.Some examples of cross-sections when the span in transverse direction is enlarged.

(a)

(b)

(c)

Fig. 5. Use of several I-shaped girders.

Rolled girders are often applied at a c.t.c. distance starting from 2 – 4 m.

Composite plate girders are often applied at a c.t.c. distance of about 4 – 6 m.With a view to stability (construction phase, operation phase), often a transversetruss frame is applied.


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In case of further increase of the span in transverse direction(up to about 8 m) applying an extra rolled girder often createsan in-between support.

At a span in transverse direction larger than about 8 m, the structure is provided with cross beams, placed c.t.c.about 4 m. Together with the vertical stiffeners (to avoid local web buckling) on the main girders, the crossbeams provide stability to the main girder. It is a very common construction, often applied at traffic bridges witha span up to about 100 m. The slenderness is about 1/25 for a statically determined system.

2.2 Two main girdersAt a bigger span, adaptations to the concept of several I-shaped girders are required. With a K-shaped crossframe or a cross beam (fig. 6) for instance, a connection has been achieved between the main girders (e.g. plategirders). This construction has been often applied with traffic bridges with one or more spans of 20 to 100 m.Apart from providing stability, the transverse portal frame also provides load spreading at oblique andexcentrical vertical loads and contributes to torsional stiffness of the entire structure. The latter is especiallyimportant at the bearings. The concept of using tow main girders is often applied for railway bridges. Anongoing ballast bed has been installed on the concrete roadway. By the greater self-weight and higher trafficloads the construction height of railway bridges is larger, compared to a highway bridge with the same span.

Fig. 6. Steel main girders with K-frame in transverse direction (a) or cross beams (b) and concrete deckcombined with ballastbed (right fig.).

The next type in this category is a steel-concrete railway bridge, consisting of aconcrete deck, installed on uniplanartruss girders, fig. 7. This type is suitablefor spans between 50 and 100 m.

Fig. 7. Composite railway bridge, steeltruss main girders.

a

b


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The main girder of the double track railway bridge consists of a truss, sometimes placed a little eccentrically tothe outside in relation to the centre of each track. The lowerchord members of the two truss girders are joined with eachother at several places through steel girders.For statically undetermined highway bridges, a designconsisting of two or more boxed girder with a concrete deck isoften applied, fig. 8. With this type it is possible to make bigcantilevers, e.g. for a foot- and/or cycle path. This constructionis especially attractive because of the relatively smallconstruction height in relation to the span.

Fig. 8. The use of two or more steel box girders and concrete deck.

The latter type deals with here is a type that is composed of a concrete under & upper flange and truss girdersin-between, fig. 9. This construction usually is statically undetermined and has to be prestresses in longitudinaldirection. To reduce the loss of prestressing (the truss, by its own rigidity) usually a Warren-truss is selected.This type of truss has a relatively smaller stiffness in longitudinal direction.

Fig. 9. Concrete upper and lower flange with steel truss girder in-between.

2.3 Box girderThe first type consists of an open steel box that at the topside is closed by a concrete roadway, fig. 10. The boxis composed of plates and cross frames and is suitable for spans up to 100 m or for heavily loaded (railway)bridges. Railway bridges of this type already have been constructed, for instance the railway at Baanhoek nearRotterdam and the high speed bridge over the Hollandsch Diep. If the bridge is constructed as staticallyundetermined, the concrete at the in-between supports isusually prestressed in order to limit the tensile stresses and/orsatisfy the criteria on crack width (durability).

Fig. 10. Open, steel box girder with concrete deck on the top.

The construction height of this type of steel-concrete bridge isrelatively larger than with a concrete variant.

Fig. 11. Open steel box girder with concrete deck on the top.


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By closing the open, steel profile, a new type comes into existence, fig. 12. Here, the topside of the box is closedby means of a steel upper flange, on which the concrete deck is placed. An advantage as compared to thepreceding type is the more equal load distribution between steel andconcrete. This is favourable for e.g. fatigue. Also the scaffolding is lesscomplicated, because the concrete is poured directly on the steel upperflange. In case the bridge is lying in a curvature, erection is madeconsiderably easier by the great torsion stiffness. Launching is also apossibility here. This type of bridge is suitable for greater spans and/orheavy loads.

Fig. 12. Closed box girder, constructed by steel plates and steel crossframes.

A variant on the above type, which is also very suitable for statically undetermined structures, is a box girderconsisting of concrete upper and lower flange and steel web plates, fig. 13. This type can be very well combinedwith the previous type of fig. 12. The concrete lower flange makes this type very suitable at in-betweensupports, where the lower flange is loaded by compression.

Fig. 13. Box girder, constructedby concrete flanges and steelweb plates.

Another type of bridge cross section consists of a central concrete box girderwith steel tubular members supporting the deck incl. cantilevers, see fig. 14.

Fig. 14. Example of a concrete box girder combined with steel tubularmembers supporting the deck.

An example, in which one single composite box girder has been applied as a railway bridge is the HSL-Moerdijk bridge is shown in fig. 15.

Fig. 15. HSL-Moerdijk railway bridge.


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2.4 Alternative cross section shapesApplication of a triangle shaped main girderThis construction type consists of a concrete roadway, resting on a triangle shaped steel girder, consisting ofweb plates/truss and a tubular member as a lower flange, fig. 15. In the case of a continuous girder, the steeltube, at the bearings, is loaded on compression and therefore filled with concrete. The web plates may consist ofcorrugated steel plates, welded onto the upper flanges and to the pipe. The advantage of these corrugated steelplates related to flat steel web plates is that the stiffness of the plate in longitudinal direction of the bridge isvery small (harmonica-effect), so that pretension, if any, of the concrete, can be effectively used. There is alsoan advantage with regard to limiting the sensitivity to local buckling.

Fig. 16. Triangle shaped steel main girder with tubular memberas a lower flange (filled with concrete at the in-between supports).

Application of in longitudinal direction flexible steel web plate

Fig. 17. Alternative application of in longitudinal direction flexible steel web plate (combination of web panelsand tubular members).

Examples of application of a pipe, filled with concrete.


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Fig. 18. Examples of application of a tubular member, filled with concrete.

Example of application of corrugated web plates: Hondani integral bridge, Japan.

Box girder bridge with a prestressed concreteroadway and corrugated web plates. Also the lowerflange is constructed in prestressed concrete. Thebridge has been made as a fully integral concept,meaning fully clamped at the piers and abutments.Applying perfoband strips has effected the connectionbetween concrete and steel.

Fig. 19. Hondani integral bridge, Japan.

Example of the application of high strength steel: Europe bridge, PortugalThe roadway, constructed as a box girder, is put together from a concrete upper deck C45/55, prestressed in twodirections, thickness variation between 200 – 930 mm, a concrete lower deck (300 mm thick), prestressed inlongitudinal direction, the so-called pedestrian part, and tubular steel members as diagonals (high strength steel:S460NH, EN 10210). The box girder has been prefabricated in parts near the site as a full prefab element. Theconnection between concrete and steel is established by contact pressure instead of shear.


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Fig. 20. Europabridge, Portugal.

2. types of steel-concrete...

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