Ssf en projektblatt composite construction

Composite Construction for Railway Bridges

Introduction Composite constructions consist of the material steel and reinforced concrete whereas the use of each material in the cross section is to be favourably combined in terms of material characteristics and production costs. This combination is possible in the main, the secondary and transverse load-bearing direction.

It is reasonable to utilize beam frameworks in main load-bearing direction as composite construction. On bridges with the main load-bearing structure above the deck, such as trusses, tied-arch or through constructions, the bond is primarily in the area of the carriageway in transverse direction. The completion of load-bearing

steel constructions assembled beforehand is in general implemented shear-resistant with in-situ concrete by shear studs. To increase construction efficiency on site, the use of prefabricated reinforced concrete panels as formwork support becomes more frequent.

Example of bridge over the Teltow Canal in Berlin. Single-span frame in VFT® construction method for a 2-tracked railway bridge over water ‘ Teltow Canal’, 4-web open composite cross section, steel girders S355J2+N as solid web welded girders with variable web height, prefabricated VFT® upper chord C45/55, upper chord width 2.50 m, span width 42.50 m; slenderness at span centre 1/21.8; slenderness at framing corner 1/14.4; thickness of cast in-situ concrete 0.40 m; crossing angle 79 gon, abutments founded each on 5 bored piles ∅ 1.50 m; assembly weight per VFT®-girder around 75 tons

Area of application Composite construction distinguishes itself by use of steel and concrete in line with material and stress conditions and by a high degree of prefabrication improving construction efficiency.

One area of composite construction is the economic efficient bridging of large span widths with low weight and easily manageable mounting sections, justifiable construction heights and at the same time the absence of falseworks.

Example of 2-web T-beam superstructure, putting in evidence the advantages of span wiadth and slenderness; in the background the old one for comparison

Advantages and disadvantages of composite construction In general, composite constructions are very suitable for railway bridges, as composite bridges can be implemented with low deformation, have a long life cycle and are easy to inspect.

The composite construction disposes of numerous other advantages in addition to optimum exploitation of specific characteristics of the two materials steel and concrete.

Advantages - The high degree of prefabrication of composite construction allows fast construction, short close-off periods, and thus high operational availability in the area of the construction site. Little restrictions because of the short construction time lead to a high acceptance with persons affected by the construction.

- The use of steel for load-bearing cross-sections permits to prefabricate large construction elements off-site as the weight per assembly unit is much lower than in case of concrete constructions.

- The fabrication of essential construction elements at the plant under consistent, weather-protected conditions contributes to the high quality of the composite constructions.

- When concrete is used above the bearings of continuous girders, too, additionally to the construction of the carriageway (double composite construction), even lighter and larger mounting units are achieved by at the same time saving expensive structural steel.

This applies also to hybrid load-bearing structures (e.g. combination of composite with prestressed concrete construction) in the area of spans and supports.

- Supplements to the cross-section in in-situ concrete simplify the construction of geometrically difficult structures as the geometric adaptation of construction elements to the steel structure, which deforms slightly during construction stages, is unproblematic.

- The erection of composite constructions is easy and effective, also with large span widths and under topographically difficult boundary conditions. Ground-supported falseworks or launching trusses are dispensable, temporary piles as supports for launching of superstructures are not needed or their number can be reduced. Mounting devices and temporary constructions for longitudinal and transversal launching can be dimensioned significantly smaller because of the lower weights to be launched.

- Bridges with box section in solid construction method present in some cases problems when concreting high, (too) slender webs with dense reinforcement and corresponding number of prestressing tendons. In the concept of steel composite crosssections with boxes, this problem does no longer exist.

- The use of in-situ concrete for the carriageway of deck bridges with the load-bearing structure underneath the deck entails the reduction or even absence of damage-susceptible joints and connections. The underneath lying steel construction is generally fully covered by the composite carriageway slab.

- Steel constructions are, contrary to solid constructions, feasible throughout the whole winter.

- Compared to an orthotropic steel slab, a carriageway slab made of in-situ concrete diminishes the airborne sound level produced by passing trains.

- Other advantages in the case of a load-bearing structure above the carriageway slab in composite method are the following: - Compared to a pure steel bridge with orthotropic carriageway slab, the relatively high fabrication effort (penetration plates, alignment works) and anti-corrosion works on cross girders and secondary longitudinal girders or longitudinal stiffeners are expendable.

- Compared to pure steel bridges, composite bridges are much stiffer with almost the same or fewer use of steel so that high demands to admissible deformations – especially on high-speed lines – can be satisfied with habitual material quantities.

- The construction of railway bridges with large spans, having a significantly higher dead weight portion compared to external traffic loads, is much more advantageous even on unfavourable ground for reason of the low superstructure’s weight in comparison with solid bridges.

Example of a 2-web T-beam superstructure, the first railway overpass with prefabricated composite elements (VFT-girders)

- When steel cross girders of superstructures with on top loadbearing structure become part of the composite slab, the result is a closed bottom view of the bridge without edges and corners susceptible to accumulate dirt. Especially for trough bridges with composite carriageway slab this principle is applied.

- Composite steel cross-sections distinguish themselves by simple maintenance (welding) similar to full steel cross-sections.

Increase of load-bearing capacities is feasible by fishplate reinforcement.

- Composite steel cross-sections excel also by their advance warning at the end of their life cycle similar to full steel cross-sections.

Disadvantages - The dynamic loading of composite bridges due to train traffic has the tendency to be higher with regard to the low dead weight than in case of solid bridges.

- The initial investment is higher than compared to soli constructions.

Indications for design and execution Because of the high and concentrated railway loads, railway bridges have to be designed very stiff to assure wheel-rail contact in case of high speed. Particularly for steel and steel composite bridges, static as well as dynamic calculations are signification during structural design to assure excellent, durable use. This comprises a careful formation of structural details which require a cross-section design orientated at force flow, with few notches and thus low susceptibility to fatigue.

These requirements, important for durability and serviceability, have to be applied unceasingly during implementation, fabrication at the plant and mounting on the construction site.

- Calculation and dimensioning of composite constructions of railway bridges is especially difficult and complex because of the interaction of concrete and steel and with regard to the high requirements to sufficient fatigue strength and the respect of deformation criteria of the whole structure.

- Steel cross-sections of composite construction are in general thin construction elements. Therefore, the structures are always to be examined for stability failure.

- To analyze stresses, deformation and stability behaviour, the production history of the load-bearing structure is at the basis of verifications. The fabrication of the steel structure, the sectional production of the composite cross-section and the application of design loads essentially influence verifications of serviceability.

The sections of the steel structure, mounting type and process as well as length and number of concreting sections determine pivotal effects and effects of connections and generate changes in the gravity centre line in the participating cross-sections which are to be analyzed.

- Local load concentration and stress peaks at nodes are to be avoided; supplementary stresses of individual construction elements and connections have to be subject to continuous examination because of the deformation behaviour of the load-bearing structure.

the target gradient. It is also the basis to draw up workshop plans where the stress-free workshop shape with pre-bending and pre-torsion of each sheet is determined.

- To dimension durable bridges made with steel or composite load-bearing structures, the actual deformation behaviour has to be exactly calculated in order to record supplementary stresses.

Although the ductile steel allows – like in case of cracking of reinforced concrete – to transfer local stress peaks from internal and supplementary stresses due to flow of the steel, the evaluation of fatigue behaviour necessitates the knowledge of all existing loads (see also (3)), as unexamined, local bending stresses caused by operational loads lead to fatigue cracks in the loadbearing structure.

- For fatigue analyses according to German directive Ril 804, the load-bearing structure is to be described with its stiffness as realistic as possible. Hence, the railway directive demands for railway bridges to represent truss girders as framing structures for these verifications. The fatigue strength verifications are to be carried out under consideration of all supplementary stresses.

- A particular system is box cross-sections. They can be calculated as single-beam, girder grillage with accompanying torsion girder or as folded plate structures.

- To find the adequate system, a consideration of the whole concept is recommendable. In addition to geometry of the bridge, cross-section stiffness, extent of verifications, necessary stability analyses, non-linearity, comprehensibility and output of results play a decisive role. Influences from form-stability of the crosssection and stiffenings are to be taken into account in the overall considerations.

- It is important to keep clarity in the whole system; especially in view of deformation, plausibility considerations and structure or system optimizations. Individual verifications can be carried out on separated system details (e.g. force-applying points).

- In case of structural formation of load introduction points, a fatigue-reduced structural formation has to be strived at.

- The iterative dependence between cracking of the composite slabs and the stresses in the cross-section does not have to be overlooked or neglected.

- The exact knowledge of structure deformations in the final stage as well as during construction stages is indispensable to reach

- In general, nowadays cast in-situ concrete carriageway slabs are no longer pre-stressed. The durability of reinforced concrete

Example of a double-tracked superstructure as truss construction with upper composite slab, two lattice girders as underneath-lying load-bearing structure and upper carriageway slab, 4 spans, span widths between 57 m and 66 m

slabs, subject to tensile forces, depends essentially on the corrosion protection of the assembled reinforcement. The durability is structurally assured by limiting the crack widths to be expected for the construction type and a sufficient concrete covering. The valid standard delivers calculation methods for verification of crack width limitation which describe realistically the cracking in composite slabs.

- Mounting of the steel structure on site highly influences the economic efficiency of composite structures. Requirements to the erection processes are thus a simple execution and short processes as well as cost minimization of supports to be assembled and removed. The mounting concept depends on the structures construction method, the fabrication possibilities of the steel plant, the transport routes and the local conditions on site.

- Mounting consist of the completion of the individual construction elements produced off-site. To reduce works on site and thus overall costs of the steel construction by at the same time increasing quality, the mounting of elements as large as possible, i. e. highly prefabricated, should be strived at.

- The mounting concept determines the sections of the static system at construction stage as well as the detail formation of the supports and temporary fixations of the steel structure’s bearings. Knowing exactly the whole mounting process is hence a necessary basis for the technical treatment of the composite superstructure.

- Construction execution necessitates in principle highly qualified personnel, cooperating with each other. Especially the cooperation between substructure and steel structure during mounting as well as completion of the superstructure with composite concrete poses high demands to managing as well as executing personnel. To proficiently coordinate interfaces of steel and solid construction, special technical coordinators are charged which are also in contact with clients, designers, inspecting engineers and of course finishing trades.

- The ideal personnel for construction supervision are teams of engineers which complete each other by their technical competence in view of specific characteristics of steel construction, on-site mounting as well as solid construction.

Composite constructions Representative overview of composite cross-section in railway bridge construction Cross-sections of railway bridges are intended to hold single- or double-tracked lines or multi-tracked sections in the areas of stations. Single-piece superstructures are preferred to doubletracked lines. The bearing systems used in composite bridge construction are in general to be put down to the basic structures beam, frame and arch. In few cases, there is a combination of these basic systems.

Overview For small span width, WiB-girders (rolled girders in concrete) are commonly used or, less frequently, double composite girders (“Preflex”). Both construction methods distinguish themselves by their suitability for low construction heights. Their use is preferred for bridge replacements in urban area. For single- or doubletracked (straight) lines, where the superstructure can be arranged centrically to the track, double- or four-web T-beams with open

fully welded girders are economic cross-sections and suitable for span width of 50 to 65 m and sufficient construction heights. For reason of the high percentage of the specific steel use, for large span width, double-web T-beams with torsion connections and highly load-distributing reinforced concrete slab or single-cell box sections are appropriate.

For span width of up to 80 m on double-tracked lines, superstructures with one or two box sections achieve good steel use values.

To bridge transport routes with these span widths and more, habitually load-bearing structures on top of the deck (tied arches, truss structures) are utilized. If transport routes are bridged with around 60 m, trough constructions are economically efficient solutions. In rare cases and for large span widths, such load-bearing structures are combined to increase stiffness (e.g. truss with arch stiffening or box section bridges with cable suspension).

Example of a 2-tracked superstructure as trough cross-section with lateral steel box sections

Most frequent types of composite construction load-bearing structures underneath the bridge deck rolled girders in concrete (WiB)

composite in longitudinal direction

double composite slab „Preflex“

composite in longitudinal direction

composite T-beam bridges

open fully welded girders composite in long./(transv.) direction

composite T-beam bridges

box sections composite in long./(transv.) direction

composite truss bridges

composite in long./(transv.) direction

load-bearing structures above the bridge deck composite tied-arch bridges

composite in long./(transv.) direction

composite trough bridges

composite in long. and/or transv. direction

composite truss bridges

composite in transversal direction

special construction methods

composite in transversal direction

The WiB construction method was specially develop for use in railway bridge construction. Many of these bridges were already built at the beginning of the last century and are still in use because of their simple and robust construction as well as their load-bearing reserves under changed conditions. Bridges made of rolled girders in concrete represent the classical, as long-lasting, and proven application in railway construction as single- and multi-span girder and for element combinations of steel and reinforced concrete, even though this reflects not the composite construction as it is known today. Because of the simple construction and execution, this construction type established itself mainly for span widths between 12 and 25 m.

Bridges in WiB construction method are slabs with concreted, hot-rolled double T-profiles. Hence, they belong to “solid composite bridges”. The concreted rolled girders are connected to the concrete without bonding agent (shear studs) only by the profile of the girder and act together as load-bearing cross-sec-

40

Rolled girders in concrete (WiB)

a0 2

≥100 Sst≤700 a0≥150

Detail of WiB connection to slab

Typical cross-section of a single-tracked WiB superstructure

6.145

tion; in a larger sense, they can be considered as bending-stiff reinforcement. So the densely lying rolled profiles have the purpose of tendons in the final stage. At construction stage, they act as formwork.

In transversal direction, the WiB girder acts as reinforced concrete slab by assembled reinforcing bars.

Fabrication, transport and mounting The rolled girders are fabricated at the plant including drillings, convexities and corrosion protection, then transported to the construction site and laid with small mobile cranes. If in case of continuous systems the steel girders have to be cut in sections because of their length, the sections are to be arranged at positions where the loading does not reach any peak values (moment zero point). The bridge slab is fabricated, depending on the boundary conditions on site, either directly in final position or next to or behind the abutment and then launched. Between the rolled girders, fibre cement slabs are laid as formwork onto the bottom

flanges and glued to the rubber strips in-between. The cantilever arms are produced by conventional method on a scaffolding suspended between WiB girders. It has to be taken care that the double T-beams at the edges are not overloaded Guidelines for application: Spans [m] approx.12 ≤ Ls ≤ 26 (30) (Values in brackets are for continuous girders) Slenderness approx. 17 ≤ Ls/Hc ≤ 24 (28) Adequate use for: - Small span width on single or- multi-span structures - Single- and multi-tracked superstructures (normally 1 to 3 tracks) - Limited construction height above traffic routes - Limited possibility for erection of scaffoldings/no scaffoldings at all - Limited construction time/short close-off periods - Replacements, especially within urban area Lengthspan / Hightconstruction = slenderness Ls= Lengthspan / Hc = Hightconstruction Hgc /Lgs= slenderness of cross girders

WiB superstructures with different edge beams/cornices

15.42 5

65

4.00

a1

a2

Vigas de perfil metálico solidarizado em L

Vigas de perfil metálico solidarizado em L

2

3

d d

d

1

Advantages - High stiffness with low construction height for small span widths - Simple verification and dimensioning - Low lifting weights of individual elements - Simple and robust construction type - Simple modular system, offerable by many construction companies - High degree of prefabrication by at the same time high fabrication quality - Easily manageable mounting as complete construction element without falsework/temporary constructions - Short close-off periods for lifting/mounting - Monolithic construction suitable for erection by launching - Low formwork effort - Small slab thickness of WiB superstructure simplifies adaptation to existing structures - Protected steel construction, as embedded in concrete - No connecting joints between steel/concrete within directly weather-exposed areas - Low production and maintenance costs compared to pure steel bridges - Simple bridge inspection, as main load-bearing elements are easy to check - Execution as frame is possible Disadvantages: - In case of continuous structures, the rolled girders are to be welded by sections acc. to special requirements - Multi-tracked superstructures with high transverse bending moments necessitate many drillings in the rolled girders’ webs for transversal reinforcement - Construction of superstructure slab in many individual parts and threading of the reinforcement - High and specific portion of steel compared to solid construction types and modern composite constructions - Difficult post-application of anti-corrosion works at the contact surface of the reinforced concrete of the bottom steel webs

1 Arrangement of girders for variable track distances 2 Rolled girder, also suitable for curved bridges 3 Example of a bridge with WIB superstructure (rolled girders)

Double composite slab („Preflex“) This construction method, also called Preflex method, has been developed in the 1950s in Belgium and found wide application in the 1960s for bridges with small span widths and large slenderness.

This construction type is applied where, due to limited construction height, common solid solutions are unsuccessful or where steel constructions are inappropriate only because they are uneconomic or cause too much noise. The area of application of Preflex constructions is bridges with small to medium span widths with large slenderness. In the cross-section, the double composite slab resembles the WiB superstructure whereas in contrast to this regular construction method the steel girder is pre-stressed. Application of the pre-stress is achieved by pre-flexing. In addition to WiB constructions, bridges with double composite girders belong to the

so called “solid composite bridges”. The pre-stressed steel girder is completely covered with concrete and is comparable to a solid bridge regarding its characteristics of noise and corrosion protection and fire resistance. The Preflex girder is pre-stressed already at the plant under consistent conditions. A hot rolled double T-profile is pressed (superelevation) against a slight pre-bend by a pressing device.

The pre-pressing is done in direction of the later on bending. In the pre-bended state, a concrete chord is concreted to the bottom flange. When using a sufficiently high concrete quality, presses can be relived in general after five days. After setting of the quickhardening concrete and removal of constraining forces, the girder springs slightly back, the stretched steel chord tries to deform in its

Open double-tracked cross-section with pre-stressed double composite girders, above lying upper carriageway slab between Preflex upper chords with cast in-situ supplement; span widths 33.0 m, slenderness Hc/Ls= just 1/24

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4.45 2.20

93

10 20

2.20

1.46 5

2.20 5.86 5

2.20

2.20

2.20 5.86 5

1.46 5

2

1

3

4.45

4.45 2.20

25

93

1.07 5

2.20

86 5

1.00

2.00 5.85 5

2.00

2.00

2.00 5.85 5

1.0

86 5

initial position and causes favourable compressive stresses at the concreted flange. This upward bend is time-dependent so that between fabrication at the plant and installation on site a timeframe occurs.

Apart from tensile stresses due to creep and shrinkage, the loaded girder is subject to tensile stresses theoretically only when the composite girder is bent to such extent as it was during concreting of the flange. Due to the pre-stress, the girder is almost free of cracks on its tension side and stiffens thus very effectively the slender composite girder.

The girder is so light during prefabrication that not the weight for limitation of the girder length is decisive but the pre-stressing device at the plant, or in some cases the transportable length.

Guidelines for application: Spans [m] approx. 20 ≤ Ls ≤ 35 Slenderness approx. 20 ≤ Ls/Hc ≤ 30 Adequate use: - Small span width of single- and multi-span structures (usually single-span structures) - Single- and multi-tracked superstructures - Limited construction height above traffic routes - Limited possibility for erection of scaffoldings/no scaffoldings at all - Limited construction time/short close-off periods

4

Stirrup put through the web drilling

Advantages: - High stiffness with low construction height for small span widths - Simple verification and dimensioning - Simple and robust construction type - Reduction of number of girders per track compared to WiB girders (thus, reduction of necessary reinforcement in transversal direction) - By sufficient pre-stress of the concrete tension chord, no cracking at the underside under permanent load - Low lifting weights of individual elements - Simple superstructure construction with high degree of prefabrication and at the same time high construction quality - Easily manageable mounting as complete construction element without falsework/temporary constructions (short close-off periods for mounting/assembly/launching) - L ow formwork effort (fibre cement slabs as joint covering on the concrete flanges); lateral formwork of edge areas and cantilever arms suspended at the lower concrete flanges - P rotected steel construction, as embedded in concrete - No connecting joints steel/concrete within directly weatherexposed areas -N o later anticorrosion works - Low production and maintenance costs compare to pure steel bridges Disadvantage: - F ew suppliers, no developed market of fabrication companies - Multi-tracked superstructures with high transverse bending moments necessitate many drillings in the rolled girders’ webs for transversal reinforcement, especially for reinforcement splices with large overlap - Keeping the timeframe between fabrication at the plant and assembly on site

Longitudinal reinforcement

55

15-40

Stirrup

50-160 AG Shear stud

AFI

1 Preflex girder on middle supports at construction stage 2 Coupling of Preflex girder by screws/welding to a multi-span structure 3 Closed double-tracked cross-section with pre-stressed with double composite girders and cast in-situ supplement to form one complete slab 4 Cross-section of a pre-stressed composite girder

Multi-web T-beam with open profiles Two longitudinal girders made of open profiles on a single-tracked line or four longitudinal girders on a double-tracked line normally allow a sufficient transversal distribution of traffic loads in case of a at minimum 35 cm to 45 cm thick cast in-situ slab and can be implemented without additional cross girders. The slenderness of these cross-sections including cast in-situ slab is at Hc/Ls = 1/13 - 1/15 for multi-span girders. In some cases a larger slenderness is possible.

The cast in-situ slab of such cross-section types can be concreted to prefabricated elements as formwork elements, or prefabricated composite elements (VFT) with wide reinforced concrete flanges are used to avoid formwork for the slabs. The mounting of webs made of complete welded girders is in general accomplished by crane. Longitudinal launching above the piers with slides is also possible in case of large span widths and steep terrain.

- Relatively low lifting weights of individual elements - Low maintenance costs - Suitable for implementation as integral structure - Protected as steel construction underneath the carriageway slab; no problematic connecting joints steel/concrete within directly weather-exposed areas Disadvantages: - Not suitable for limited construction heights (large construction height required) - Divided bottom view with flanges susceptible to accumulate dirt - Very simple design approach, especially for continuous construction heights.

- Large ramp height necessary because of the underneath lying load-bearing structure

Guidelines for application: Spans [m] 30 ≤ Ls ≤ 80 Slenderness 13 ≤ Ls/Hc ≤ 18 (depending on single-span girder or continuous girder) Adequate use: - S ingle-span girder/continuous girder -M edium span widths - S ufficient construction height - L imited possibility for erection of scaffoldings/no scaffoldings at all - S hort construction time/construction during close-off periods -M ulti-tracked superstructures -O blique bridges Advantages: - Simple construction processes on site as there is no scaffolding and the amount of formworks is low (e. g prefabricated slabs on the upper chords; cantilever arms – pre-mounted formwork at welded girders); no formwork travellers - Use of prefabricated composite elements (welded girders with upper concrete flanges assembled at the plant) increases efficiency on site, simplifies formwork works and entails structural advantages (material savings of steel by dead weight connection, high position and tilting stability, high initial stiffness) -H igh to very high degree of prefabrication - S imple construction method -H igh economic efficiency - L arge stiffness in case of sufficient construction height

1 Example of 4-web T-beam superstructure with prefabricated composite elements (VFT-girders) 2 Double-tracked superstructure as conventional steel bridge with box ­sections (span widths around 45 m); slenderness Hc/Ls = just 1/17 or alternatively in composite construction as: 3 2-web T-beam cross-section, span width around 50 m, slenderness Hc/Ls = just 1/19; 4 4-web T-beam cross-section with open welded girders and prefabricated slabs as formwork; 5 4-web T-beam cross-section with prefabricated composite elements ­(VFT-girders); lowest use of steel

1

2

2.70

4.00

11.62

3 4.00

2.28

2.67

50

2.25 – 2.32

5.20

4

2.28 – 2.35

4.00

2.67

2.32

2.76

2.60

2.30 – 2.59

5

4.00

2.28 – 2.35

2.67

38

2.32

2.76

2.60

2.30 – 2.59

Double-web T-beam with open profiles (double-tracked line) 1

2

The individual girders can be delivered at span lengths of up to max. 60 m and mounted by crane. Connections at the level of the bottom chords are not only meant to absorb wind loads but also to improve the transversal distribution of torsion flow in the cross-section as it is obtainable in a single-cell box section. Traffic loads make up a high portion of the total loads so that a good transversal distribution of loads increases the economic efficiency and durability of the structure.

To increase economic efficiency it is conceivable to produce the connections at the bottom chord level with reinforced concrete prefabricated elements which do not participate at the distribution of longitudinal forces because of their joints.

On this connection at the bottom chord level, a grillage to walk on and to close the gap can be installed.

The cast in-situ slab is concreted with a formwork traveller or as formwork element on two prefabricated slabs. For multi-span structure, supporting cross girders can be made of concrete to avoid welding and weld inspection on site.

1+2 Examples of implemented T-beam cross-section with two welded girders, double-tracked superstructure, spans: left about 50 m, right about 40 m; slenderness Hc/Ls = approx. 1/15 3 Cross-section with continuous height as continuous girder, spans of up to 50 m, torsion connection at the bottom chord level, slenderness Hc/Ls = 1/14 4 Double-tracked cross-section as double-web T-beam with open welded girders of variable construction height, span width 83 m, slenderness in the span Hc/Ls = just 1/25, torsion connection at the bottom chord level

On straight double-tracked lines with large span widths and large construction heights, the need of steel for the webs has a great influence on the economic efficient of the construction method so that double-web cross-sections are preferred. They can also be implemented with open profiles when at the level of the bottom chords a connection is installed. The girders are fabricated as welded girders made of sheets. When producing multi-span structures, the webs of the welded girders can be designed with variable construction heights, so that a construction advantageous in design and reasonable in structural aspects is the result.

When using haunched T-beams for railway bridge construction slenderness in the span of Ls/Hc = 1/25 and more is achievable in case of sufficient construction heights above the piers.

Guidelines for application: Spans [m] 30 ≤ Ls ≤ 60 Slenderness 11 ≤ Ls/Hc ≤ 16 (depending on single-span girder or continuous girder‚ cross-section double- or multi-web) Adequate use: - S ingle-span structure/continuous girder - S mall to medium span widths - S ufficient construction height -M ulti-tracked superstructures - Limited possibility for erection of scaffoldings/no scaffoldings at all - S hort construction time/construction during close-off periods Advantages: - S ee point 4.2.3 Disadvantages: - Not suitable for limited construction heights (large construction height required) -D ivided bottom view with flanges susceptible to accumulate dirt -G enerally use of formwork traveller for cast in-situ concreting - Very simple design approach, especially for continuous construction heights.

- Large ramp height because of the underneath lying load-bearing structure

3

3.07

40

4.60

6.13 5 12.37

4

2.95

40

1.06

2.20

4.60

2.20

1.06

1

1.14

40

6.41

80

1.42 5

1.42 5

80

4.45

4.50

3.90

3.90

2.80

35

2

2.25

1.10

1.10

2.25

3

4.80

4.23

1.88

40

4.23

5.23

Double-web T-beam with box sections (double-tracked line) The double-web T-beam with box sections as webs is a very appropriate cross-section because of its torsional stiffness (and low tilting danger in the construction stage), especially for curved bridges with medium spans.

The box sections can be implemented as open U cross-sections forming the carriageway, or as closed-cell, tightly welded boxes suitable for longitudinal launching. The double-web box T-beam is an economically efficient alternative to the single-cell box sections, as a high degree of prefabrication can be achieved and welding works on site are only necessary between the steel sections. The composite carriageway deck is commonly produced with formwork travellers. Alternatively, the box section can be completed to composite prefabricated elements with concrete flanges so as to achieve an early bond and to do without a formwork of the cast in-situ slab. Multi-web cross-sections with steel box sections are used for shorter spans with large slenderness when the bridge axis is curved or when box sections are necessary for design reasons.

The maintenance-low boxes, which are difficult to walk in, are advantageous in areas which are difficult to access, such as above rivers or above very frequented routes. Mounting of the box sections is done by crane, but launching is also feasible.

Guidelines for application: Spans [m] 40 ≤ Ls ≤ 80 Slenderness 15 ≤ Ls/Hc ≤ 18 (depending on single-span girder or continuous girder) Adequate use: - Sing-span structure/continuous girder (special measures to limit crack widths are required) -M edium and large spans

- Sufficient construction height - Multi-tracked superstructures - Oblique bridges - Curved bridges - Limited possibility for erection of scaffoldings/no scaffoldings at all Advantages: - High degree of prefabrication - Low weights - Suitable for curved bridges - Large steel pieces in transportable and mountable dimensions - Large span widths - High stiffness - Haunching of multi-span structures leads to attractive constructions - Low production and maintenance costs - Use of prefabricated slabs as auxiliary formwork - Limited use of composite prefabricated elements - Protected as steel construction underneath the carriageway slab; no problematic connecting joints steel/concrete within directly weather-exposed areas - Closed bottom view without edges/flanges susceptible to accumulate dirt - Minimum surface divisioning, minimum corrosion protection because of minimum surface portion of the load-bearing structure Disadvantages: - Not suitable for limited construction heights (larger construction heights required) - Usually, use of formwork travellers required for in-situ concreting - Large ramp height necessary because of the underneath lying load-bearing structure

4 1 Cross-section with two double-cell, tightly welded box sections for small and medium spans (approx. 20 to 50 m), cross-section with supporting cross girders, slenderness Hc/Ls = just 1/17 2 Cross-section with closed-cell, walkable box sections for large span widths (approx. 52 m), slenderness Hc/Ls = just 1/17, prefabricated ­elements between the boxes as formwork supports 3 Double-tracked cross section as double-web T-beam cross-section with ­U-shaped boxes (difficult to walk in), medium spans approx. 34 m, slenderness Hc/Ls = approx. 1/18 4 Example of a double-tracked superstructure with two steel boxes and composite slab, spans approx. 57 to 74 m, slenderness Hc/Ls = 1/15 – 1/17

Trough bridges with open profiles (double-tracked line) 1

1.00

1.00

45 25

70

4.00

4.00

5.31

5.31 10.62

Trough bridges are used as single- or multi-span bridges, whereas the main girders are implemented as open steel girders or as steel composite girders with compression chord made of concrete at a constant height or adapted to the moment variations.

The slenderness of a single-span girder should be at Ls/Hc ≥ 1/12 and the slenderness at an interior span of a continuous girder at Ls/Hc ≥ 1/14. The webs are stiffened with sheets and T-profiles as well as vertical bulkheads to assure stiffness of the compression chord.

The base (carriageway) slab is executable as reinforced concrete slab or, in general, as composite girder grillage with a slenderness of Ls/Hc approx. 1/11 – 1/15. Oblique systems are statically feasible and structurally manageable. In principal, trough bridges, as well as other bridges with their main load-bearing

system above the deck, require special attention to structurally balanced, fatigue-appropriate and weather-protected transitions to the transversal structure. Crane mounting of trough bridges is easy and fast. Firstly, the main girders are lifted into place and secured against tilting; then the cross girders are screwed to the main girders. When using prefabricated concrete elements in transversal direction, the cast in-situ slab can be reinforced without formwork and then concreted. Generally, trough bridges can be fabricated completely at the mounting place (with or without concrete slab) and launched transversally or longitudinally.

Guidelines for application: Spans [m] 30 ≤ Ls ≤ 60 Slenderness 10 ≤ Ls/Hc ≤ 12 (depending on single-span girder or continuous girder)

2

58

22

2.83

4.80

13.55

1  Example of a double-tracked superstructure as trough cross-section with composite slabs and partially concreted main girder webs, spans 42 m, cross girder made of rolled profiles, cross girder distance 0.75 m, slenderness Hc/Ls = 1/10,5, slenderness of cross girders Hgc/Lgs = 1/15 2  Trough cross-section, main girder completely concreted, spans 42 m, cross girder made of rolled profiles, cross girder distance 0.75 m, slenderness Hc/Ls = 1/10, slenderness of cross girders Hgc/Lgs = 1/17

Adequate use: - Single-span structures/continuous girders - Medium span widths - Limited construction height - Multi-tracked superstructures - Oblique bridges - Limited possibility for erection of scaffoldings/no scaffoldings at all - Limited construction period/construction during close-off periods Advantages: - High to very high degree of prefabrication - Low construction height - Large steel pieces in transportable and mountable dimensions - Low mounting weights - Large span widths

- High stiffness - Low ramp height because of the load-bearing structure on top Disadvantages: - Load-bearing structure on top susceptible to collisions (installations of guiding rails) - Only restrictedly suitable for integral bridges - Connection joints of concrete and steel in weather-exposed areas - Rather difficult design - Densely arranged cross girders with many HT-connections - High reinforcement in the carriageway slab - Maintenance costs are higher than for load-bearing structures underneath the deck - No direct distribution of traffic loads (through cross girders/composite slab into the main structure)

1

17.21 11.91

2.65

1.12

2.40

2.65

1 Example of a 4-tracked superstructure as trough cross-section with closed-cell steel boxes as longitudinal load-bearing structure, composite carriageway slab on prefabricated reinforced concrete elements above open steel cross-sections, span widths approx. 40 m, slenderness Hc/Ls = just 1/17, slenderness of cross girders Hgc/Lgs = just 1/12

2

2 E xample of a trough bridge for high-speed rail traffic, composite in transverse direction, construction stage 3 Example of a 2-track superstructure as trough cross-section, composite in transverse direction, construction with prefabricated slabs, bottom view 4 Assembly of the closed-cell steel boxes as longitudinal load-bearing structure 5 Detail how on prefabricated reinforced concrete elements engage to open steel cross-sections

3

Trough bridges with closed profiles (double-tracked/multi-tracked line) Trough cross-sections are very adequate for superstructures which span widely because of multiple tracks or bridges which are slightly curved. These trough cross-sections are formed as torsion and wind-rigid box sections. The longitudinal girders can be implemented with constant or variable construction height.

In transverse direction, analogously to trough bridges with open profiles, composite girder grillages with open or closed steel cross girders can be utilized. Ideally, prefabricated slabs are used inbetween the cross girders as lost formwork when fabricating the composite slab.

Guidelines for application: Span widts [m] 35 ≤ Ls ≤ 65 Slenderness 10 ≤ Ls/Hc ≤ 13 (depending on single-span girder or continuous girder) Adequate use: - S ingle-span structures/continuous girders -M edium to large spans - L imited construction height -M ulti-tracked superstructures -O blique bridges

4

- Limited possibility for erection of scaffoldings/no scaffoldings at all - Limited construction time/short close-off periods Advantages: - High to very high degree of prefabrication - Suitable for oblique and curved bridges - Large steel pieces in transportable and mountable dimensions - Low mounting weights - Large span widths - High stiffness - Low ramp height because of the load-bearing structure on top - Minimum surface divisioning, minimum corrosion protection because of minimum surface portion of the load-bearing structure Disadvantages: - Not suitable for limited construction heights (large construction height required) - Above lying load-bearing structure susceptible to collisions (installations of guiding rails) - Not suitable for integral bridges - Connection joints of concrete and steel in weather-exposed areas - No direct distribution of traffic loads (through cross girders/composite slab into the main structure)

5

Single-web T-beam/deck bridge with single-cell box sections Upper carriageway (double-tracked line) Box sections are, compared to open profiles, torsion free and are used preferably for curved or bended bridges. In case of eccentric loads, they show a very favourable bearing behaviour because of their torsion stiffness. Box sections are strengthened with smooth outer surfaces and are also preferred to open profiles for design and maintenance reasons. Corrosion protection surfaces can be reduced and pollution by pigeons or seagulls can easily be removed.

In practice, closed air-tightly welded steel boxes with small dimensions, closed walkable box sections with large dimensions and open U cross-sections forming the carriageway are known. Closed box sections with large dimensions can be utilized when launching over large span widths is planned and the closed box section is needed for launching purposes. The webs are often inclined to compensate span widths of the composite carriageway slab in transversal direction of the bridge, so that a box with trapezoidal profile is the result. This results in design and structure advantages as the cross-section appears more harmonious and the lower chord participates over a larger width.

Guidlines for application: Spans [m] 50 ≤ Ls ≤ 120 Slenderness 12 ≤ Ls/Hc ≤ 16 (dependign on single-span girder or continuous girder) Adequate use: - Single-span structure/continuous girders (require special measures to limit cracking) - L arge span widths - S ufficient construction height -M ulti-tracked superstructures - L imited possibility for erection of scaffoldings/no scaffoldings at all

1

Advantages: - High degree of prefabrication - Suitable for oblique and bended bridges - Large steel parts in transportable and mountable dimensions - Relatively low mounting weights - Large span widths are possible - Large stiffness - Haunching of multi-span bearing structures leads to attractive designs - Closed bottom view without edges/surfaces susceptible to accumulate dirt - Minimum surface divisioning, minimum corrosion protection because of minimum surface portion of the load-bearing structure Disadvantages: - Not suitable for limited construction heights (large construction height required - Partially high production effort - Large ramp height because of the underneath lying load-bearing structure

1 Example of a double-tracked superstructure in steel composite box construction method as walkable U-shaped cross-section, 5-span continuous bearing structure with consistent construction height for large span widths up to approx. 100 m, slenderness Hc/Ls = just 1/12 up to just 1/15; 2 Example of a single-tracked superstructure, box construction as 3-span continuous bearing structure with variable construction heights (vaulted piles); span widths up to 56 m, slenderness in the pile areas Hc/Ls = 1/16, slenderness in the span areas Hc/Ls =1/30 (!)

2 14.30 4.70

2.20

5.25

3.00

45

40

2.20

6.59

1.95

1.00

5.00

1.00

Truss bridge with carriageway underneath the load-bearing structure (double-tracked line) Because of their high stiffness, truss constructions are commonly used for large span widths and when the truss is arranged as main load-bearing system above the deck to bridge traffic routes with limited construction height. Lattice girders are in general placed vertically. Composite trusses are especially implemented for railway bridges for which, despite high loads, a deformation-low steel truss superstructure and a noise-reducing concrete carriageway slab are expected. Steel truss bridges are implemented as welded profiles with some rare exceptions. Such cross-sections can ideally be adapted to loads and constructional requirements. The lower chord, acting simultaneously as bending beam for loads from transversal elements, can be designed as open or closed crosssection has however to be sufficiently stiff.

The upper chords are often conceived as closed box sections according to the high compressive stresses they are exposed to. Initial and final diagonal of the truss’ cross bars are produced with open or closed welded profiles, the inner diagonal bars are most commonly open welded girders. Orthotropic sheets for the carriageway slab are the rule for the concept of load-bearing structures in transverse direction. The implementation envisages either steel cross girders arranged very close to one another (a = approx.

700 mm) without longitudinal stiffeners or cross girders at larger distances (a = approx. 2500 mm) with longitudinal flat steel stiffeners at a distance of a = approx. 600 mm.

The construction of the load-bearing structure in transverse direction necessitates many small sheets and laborious welding works during construction at the plant as well as for assembly on the construction site. By choosing a composite construction in transverse direction, the effort can be reduced to a minimum. A solid carriageway slab can be concreted directly to the steel cross girders which are necessary for the complete assembly. This requires formwork constructions, which however become unnecessary when arranging prefabricated element slabs on the cross girders.

It has to be paid attention to durable transitions between composite slab and main girder.

By choosing a composite construction in transverse direction, the effort can be reduced to a minimum. A solid carriageway slab can be concreted directly to the steel cross girders which are necessary for the complete assembly. This requires formwork constructions, which however become unnecessary when arranging prefabricated element slabs on the cross girders. It has to be paid attention to durable transitions between composite slab and main girder.

The implementation of composite carriageway slabs instead of an orthotropic slab results in the following advantages: - Low costs - High stiffness by low use of steel - Therefore, low deformations - Low maintenance Disadvantages: - Higher dead weight - Only taking effect at the final stage - Formworks required For mounting and launching of planned single-span girders in the final position, the girders have to be coupled to form continuous girders and to be decoupled after launching and before concreting of the carriageway slab.

Reason for choosing single-span girders or jointed continuous girders - Minimization or absence of maintenance-intensive rail fasteners

Example of orthotropic sheet with graded cross girders at a distance of 2.20 m and flat steel stiffeners in longitudinal direction at a distance of a = approx. ­600 mm

70

10.55 9.15

70

40 12 25 76

8.38

1

2

10.85 10.54

66

78 7 35 5

10.25

66

1 Double-tracked superstructure, truss cross-section, composite construction in transverse direction with open steel cross girders (a = 2.5 m); applied prefabricated element slabs and continuous cast in-situ composite slab; roadbed shoulder on the outside, span widths about 78 m, slenderness Hc/Ls = just 1/10, slenderness of cross girder Hgc/Lgs = just 1/12; 2 Double-tracked superstructure, truss cross-section, composite construction in transverse direction with open steel cross girders (a = 4.1 m); applied prefabricated element slabs and continuous cast in-situ composite slab; roadbed shoulder on the outside, span widths about 85 to 90 m as 3-span structure, slenderness Hc/Ls = 1/9, slenderness of cross girder Hgc/Lgs = just 1/9; superstructure as ballastless track 3 Example of double-tracked superstructure, truss cross-section, span widths about 60 m

Guidelines for application Spans [m] 50 ≤ Ls ≤ 100 Slenderness 9 ≤ Ls/Hc ≤ 14 (depending on single-span girder or continuous girder) Adequate use: - Single-span structures/continuous girders - Medium to large spans - Restricted construction height - Heavy traffic in the construction site area excluding the erection of scaffoldings - Multi-tracked superstructures - Limited possibility for erection of scaffoldings/no scaffoldings at all - Limited construction time/short close-off periods Advantages: - High degree of prefabrication - Oblique bridges - Steel parts in transportable and mountable dimensions - Low mounting weights - Large span widths - Large stiffness - Closed bottom view without edges/surfaces susceptible to accumulate dirt - Complete pre-mounting at the site and final erection by launching/SPMT (Self-Propelled Modular Transporter) - Low ramp height because of the load-bearing structure on top Disadvantages: - High amount of steel - Increased corrosion protection because of the high surface amount of the load-bearing structure - Maintenance costs higher than for bridges with load-bearing structures underneath the deck - Load-bearing structure on top susceptible to collisions (installations of guiding rails) - Connection joints of concrete and steel in weather-exposed areas - Not suitable for limited construction heights (large construction heights required) - Intensive production

Truss bridges with upper carriageway (double-tracked line) Analogously to truss bridges with underneath-lying carriageway slab, load-bearing structures arranged underneath the deck are an advantageous option when sufficient construction heights and especially large span widths are available.

At the plant, upper and lower chords can be prefabricated in transportable lengths. The gussets are pre-assembled. The connection to the completed truss girders is done in-situ. Truss girder bridges are completely pre-mounted and then lifted or launched. Long multispan structures are in general incrementally launched as normally there is not sufficient space for pre-mounting on-site. In the conception of carriageway slabs on top of the deck as composites crosssection in connection with the steel upper chord, attention has to be paid to a careful formation of force insertion points. Moreover, focus is to be set on an exact examination of force flow due to changes of the gravity centre line in the context of the bridge’s history. Ideally, the gravity centre lines of the upper chord and of the concrete slab are at one level. In reality, this is nearly impossible to achieve, as immense difficulties in the constructional execution would be the result.

1

42 7

50 1.96 5

1.96 5

2.50

2.50 8.93

2 2.20

2.20

6.45

39

4.00

5.45

3

7.60

39

14.30

15.60

Advantages: -H igh degree of prefabrication -O blique bridges - L arge steel parts in transportable and mountable dimensions -R elatively low mounting weights - L arge span widths - L arge stiffness - Closed bottom view without edges/surfaces susceptible to accumulate dirt -A ssembly and final mounting by longitudinal or transversal launching

24 2 22 7

2.97 1

Guidelines for application: Spans [m] 35 ≤ Ls ≤ 150 Slenderness 9 ≤ Ls/Hc ≤ 15 (depending on single-span girder or continuous girder) Slenderness of transverse bearing structure 10 ≤ Lgs/Hgc ≤ 15 Adequate use: - Single-span structures/continuous girders (requires special measures to limit crack widths) -M edium to large spans - S ufficient construction height -M ulti-tracked superstructure - Limited possibility for erection of scaffoldings/no scaffoldings at all

30

2.60

5.66

80

Disadvantages: - Not suitable for limited construction heights (large construction heights required) - Increased corrosion protection because of the high surface amount of the load-bearing structure - Due to the construction height, the low-lying pivotal point of the bridge bearing compared to the track level, an unfavourable final tangent angle can result (large deformation paths of adjoining rail fasteners) -H igh amount of steel - I ntensive production - Large ramp height due to underneath-lying load-bearing structures

1 Example of a double-tracked superstructure with two lattice girders as underneath-lying bearing structure and continuous composite carriageway slab on top, as continuous girder with medium span widths of around 36 m, Hc/Ls = just 1/10 2 Variant of a truss cross-section as series of single-span girders with m ­ edium spans (around 65 m), Hc/Ls = just 1/11 3 Variant of a truss cross-section as continuous girder for large span widths with variable construction height and double composite construction above the supports; span widths up to approx. 200 m, slenderness of piers Hc/Ls = just 1/14, slenderness of span Hc/Ls = just 1/28 4 Example of a double-tracked superstructure as truss construction with upper composite slab, two lattice girders as underneath-lying load-bearing structure and upper carriageway slab, 17 spans, total length about 600 m

Tied arch bridges (double-tracked line) Tied arch bridges with a carriageway slab underneath the loadbearing structure dispose of the advantage of a low construction height underneath the track, just as trough and truss bridges, but require the protection of the load-bearing structure above the deck consisting of arch, suspensions and stiffening girders against collision. The concrete carriageway slab acts as part of the stiffening girder. Tied arch bridges are suitable to bridge individual large spans such as rivers, channels or railway installations.

The rise of the arches is between 1/8 and 1/6 of the span width.

In general, two arches are arranged on both sides of the tracks (in exceptional cases, for design reasons, an individual central arch can be planned) which are arranged vertically or slightly inclined to the inside by transverse frames.

The high stiffness of the system required for railway bridges, arises in case of vertical hangers from the sum of individual stiffness of arch and stiffening girder. Crossing hangers of network arch bridges (Ls > 80 m) stiffen the system to an arch-shaped beam and lead to material savings by slender arch profiles and stiffening girders. However, mounting, adjustment, fixation and

1

construction of welded connections of the diagonal, crossing hangars entail extraordinary efforts on site. On network arch bridges, the course of the hangers’ compressive forces has to be exactly examined for half-sided traffic loads and launching procedures. A fatigue-resistant and vibration-low implementation of the hangers and connections is of utmost importance [L2].

Guidelines for application: Spans [m] 50 ≤ Ls ≤ 150, arch rise approx. Ls/Hc < 6 to 8 Slenderness of transverse bearing structure 10 ≤ Lgs/Hgc ≤ 16 Adequate use: - Single-span structures - Medium to large span widths - Limited construction height - Heavy traffic in the construction site area excluding the erection of scaffoldings - Limited construction time/short close-off periods - Multi-tracked superstructures

2

16.20 1.30

13.60

1.30

5.78

45 10 15

Disadvantages: - High production and maintenance costs compared to other underneath-lying load-bearing structures - Increased corrosion protection because of the partitioned surface of the load-bearing structure - Intensive production

3

11.10

Advantages: -H igh degree of prefabrication -O blique bridges - L arge steel parts in transportable and mountable dimensions -R elatively low mounting weights - L arge span widths - Large stiffness - Closed bottom view without edges/surfaces susceptible to accumulate dirt - Attractive design with transparent bearing structure -C omplete pre-mounting at the site and final erection by launching/SPMT (Self-Propelled Modular Transporter) - Low ramp height due to upper load-bearing structure

1 Example of a tied arch bridge superstructure underneath 2 Detail of reinforcement of the concrete decking 3 Tied-arch bridge with composite slab on cross girders, cross girders formed as box sections (0.45 x 0.25), distance of cross girders approx. 1.10 m, slenderness of cross girder in span area Hgc/Lgs = 1/19, slenderness of cross girders in connection area Hgc/Lgs = 1/16, sidewalk at the inside 4 Cross-section of tied-arch bridge (span width 62 m, arch rise 11 m) with composite slab between main and cross girders (distance of cross girders approx. 3.40 m), slenderness of cross girders Hgc/Lgs = just 1/12, concrete slab supported on four sides and with continuous haunches at the downside; roadbed shoulders on the outside

9.85

4

48 35 35 76 48

4.00

Development of new cross-sections To construct bridge replacements in urban area, in addition to slender construction heights, prefabricated superstructure solutions with high economic efficiency are demanded. For some time now, road bridges with external reinforcement, the so called VFT-WIB method (composite prefabricated elements with rolled girders in concrete) are built.

In other European countries this construction method is by now also employed for railway bridges. The external reinforcement consists of halved rolled profiles, which are connected by composite dowels to the solid cross-section. The external reinforcement on the compression side of the cross-section of single-span girders allows a large slenderness of the superstructure. The construction covers small to medium span widths from 7 to 14 meters. The external reinforcement can also be utilized as load-bearing element in transversal direction.

This combination results in a trough cross-section where the steel cross girders are for example arranged in a grid of 50 cm. The trough slab can be monolithically connected to the wall when abutments are to be newly built. This so called tangential slab distributes longitudinal and transversal forces of the superstructure directly to the abutments and reduces the rotation angle of the final tangent to nearly zero.

Guidelines for application: Spans [m] beam 7 ≤ Ls ≤ 14 m trough 10 ≤ Ls ≤ 25 m Slenderness beam Ls/Hc ≤ 18 trough cross-section Ls/Hc ≤ 16

1

Adequate use beam: - Single-span structures on existing abutments - Small span widths - Limited construction height - Heavy traffic in the construction site area excluding the erection of scaffoldings - Limited construction time/short close-off periods - Multi-tracked superstructures Adequate use trough: - Single-span structure or system of single-span girders - Extremely limited construction height - High horizontal loads simple monolithic connection to the abutment (tangential slab) Advantages beam: - Completely prefabricated, mounted in one piece or two pieces with in-situ concreting - High quality by large prefabricated elements (fabrication at the plant under consistent and weather-protected conditions) New bridge over the Simmerbach – Example of a bridge with trough crosssection with external reinforcement; superstructure with ballastless track 1 Corrosion protected girders at the prefabrication plant 2 Mounting of external reinforcement and adjustment of height position 3 Installation of reinforcement cage into formwork 4 Rail canal with pre-assembled rail fastener

2

1.00

1.00

T rough cross-section with external reinforcement; superstructure with ballastless track or ballasted track

1.15

35 2.65

1.15

5.20

66

Longitudinal section with external reinforcement

3

4

- Relatively low lifting weights - Low sound emission due to solid cross-section - No derailing protection required - Advantageous load-bearing behaviour - Small corrosion protection surface and low susceptibility to accumulate dirt - Simple sight inspection - Economically efficient in construction and maintenance

- High quality by high degree of prefabrication - Full ballast bed or ballastless track - Minimum construction height by external reinforcement in transversal direction - Small corrosion protection surface - Economically efficient in construction and maintenance - Minimized rotation angle of final tangent by tangential slab - Simple sight inspection

Disadvantages beam: - Direct rail fastening

Disadvantages trough: - Heavy lifting weights

Advantages trough: - Completely prefabricated and mounted in one piece in case of small span widths - Produced on site and laterally launched in case of large span widths

New bridge over the Simmerbach; completed VFT速-rail bridge under traffic