: dynamic effects of railway bridges for high speed

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DYNAMIC EFFECTS OF RAILWAY BRIDGES FOR HIGH SPEED

USAGE: APPLICATION EXAMPLE STEEL-COMPOSITE TRUSS

BRIDGE

M. Heiden1, H. Bokan

2, Lus Simes da Silva

3, R. Greiner

4, M. Pircher

5e H. Pircher

6

SUMMARY

The recent expansion of the high-speed rail network in Europe and the Far East hasled to the need to reevaluate the design criteria for high-speed railway bridges. In particular,the evaluation of the dynamic effects associated with train-bridge interaction originated newsafety and passenger comfort criteria that translated into maximum limits for the accelerationfor the interacting structural system of the bridge and the moving train.

Motivated by the launch of the Portuguese high-speed railway project, it is presentedand discussed in the present paper:

(i) the organization of part 2 of Eurocode 1 and the annex A2 of Eurocode 0,with special emphasis on the design checks associated with dynamic effects

and train-bridge interaction;(ii) a discussion some additional rules recently imposed in the German

regulations;(iii) the application of these rules to a composite trussed railway bridge

currently being designed for the German rail network.

1. INTRODUCTION

The set of design rules applicable for the design against static loading must for highspeed railway bridges be expanded in order to fulfil the structural requirements for the designagainst dynamic forces. The rules for dynamic analysis in accordance with the Eurocode [1,2]

will be described in this paper as well as the corresponding proceedings in accordance withthe German regulation [3]. Currently the new ICE-train lines in Germany are being

1 Project Engineer, TDV GesmbH., Graz, Austria2 Project Engineer, TDV GesmbH., Graz, Austria3 Professor Associado com Agregao, Universidade de Coimbra, Departamento de Engenharia Civil, Coimbra4 Professor, Technical University Graz, Institute for Steel, Timber and Shell Structures, Graz, Austria5 Research Associate, Univ. Of West Sydney, Sydney, Australia6 Managing Director, TDV GesmbH., Graz, Austria


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298 IV Congresso de Construo Metlica e Mista

investigated for their suitability for travel with velocities up to 300km/h. This paper furtherreports on the outcome of the dynamic analysis of an interesting steel truss bridge withconcrete deck. Using this bridge as an example some dynamic design criteria of theabovementioned standards will be discussed.

2. ORGANIZATION OF THE EUROCODE RELATED TO HIGH SPEED RAILWAY

BRIDGE DESIGN

The principle design rules of railway bridges on a high-speed route differ from the

design of railway bridges on conventional routes. The following additional checks become

necessary:

Verification of maximum peak deck acceleration under the rail track.

Stresses according to dynamic loading must not exceed given stress limits.

Check for fatigue failure.

Verification of maximum acceleration in the coach.

Reduction of other permitted deformation criteria.

The limits for coach acceleration are influenced by concerns regarding passengercomfort. The rest of the other criteria are related to the structural integrity of bridge

structures.

The design of high-speed railway bridges is regulated in two different parts of the Eurocode:

EN1990-Annex A2 [1] containing principal bridge performance criteria and EN1991-2 [2]

containing the requirements related to loading, dynamic increment of loading, requirements

for a dynamic analysis [6].

2.1. Requirements for Dynamic Calculations in Accordance with EN1991-2

The organization of the EN1991-2 [2] can be divided into seven parts:

Verification whether dynamic analysis required;

Loading and load combination;

Velocities to be considered;

Structural bridge parameters (eg. damping, mass, stiffness);

Modeling of the excitation and the dynamic behavior;

Verification of the limit states;

Additional check against fatigue failure;

2.1.1 Verification whether dynamic analysis required

EN1991-2 [2] provides a flow chart considering speed, bridge type, span arrangement,

first bending and first torsional mode. For bridges with a behavior similar to a simplysupported beam, a dynamic analysis might not be necessary as indicated by a span and

frequency depending diagram. For all other structures and velocities greater than 200km/h a

complete dynamic analysis is deemed necessary

2.1.2Loading and load combination

So-called HSLM universal train types (eg. Figures 1 and 2) are defined to serve as

loading models for the dynamic analysis. Depending on the type of structure and span

arrangement two different sets of train types (HSLM-A and HSLM-B) are available. In


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Estudos Especiais 299

addition all real trains and train combinations using the investigated line have to be

investigated as well. Only one track has to be loaded by moving trains

D D

3.525

d D d 3 11 9

3.525

4*P(1)

3*P(2)

2*P(3)

2*P(3)

3*P(2)

4*P(1)

N x D

(1) Power Car (leading and trailing power carsidentical)

2 End coach leadin and trailin end coaches

Fig. 1 HSLM-A Load Train Types according to the EUROCODE

d

N x 170kN

d d d d d d d

Fig. 2 HSLM-B Load Train Types according to the Eurocode

2.1.3 Velocities to be considered

A certain range of train velocities must be investigated and possible resonance effects

within this range must be located. The maximum velocity of this range to be considered in the

calculation is commonly set at 1.2 times the maximum line speed. For simply supported

beams the spacing of axle groups is considered as a parameter for the determination of

possible resonance speeds. In the vicinity of such possible resonance speeds, the interval of

the investigated train speeds should be smaller.

2.1.4 Structural bridge parameters

Damping characteristic, mass and stiffness govern the dynamic properties of the

bridge response to a moving train. According to EN1991-2 [2] damping has to be chosen

according to tables taking into account material and span length. For the determination of the

bridge and train mass and the stiffness of the bridge an upper and a lower estimation should

be used for the dynamic analysis. Damping has a significant influence on the response in the

event of resonance effects [7]. The variation of stiffness is often performed by varying the E-

Modulus which shifts the resonance speed.

2.1.5Modeling of the excitation and the dynamic behaviour

According to EN1991-2 [2] the dynamic effects of the moving train can be simulated bysets of moving concentrated loads. These sets are defined to include the interaction between

vehicle and structure and the effects of moving masses. The structural bridge model has to be

accurate enough to take account for all possible vibration modes. Therefore the design

engineer has to decide on the particular model characteristics to account for all existing local

and global effects. [4] provides a scheme for modeling the train-bridge interaction to be used

as a guide line where necessary.


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2.1.6Verification of the limit states

The acceleration of the bridge deck generated by high speed trains along the track axis

has to be checked at the Serviceability Limit State (SLS) to avoid the risk of ballast instability

and in extremis a reduction in wheel/rail contact forces [6]. The limitation is 0.35g for

ballasted track and 0.5g for direct fastened decks. In addition a maximum loading check has

to be carried out, which means that the maximum of the most unfavorable case of normal railbridge loading and the most unfavorable case of the high speed rail traffic loading has to be

taken for the design.

2.1.7Additional check against fatigue failure

Where the frequent operating speed of the train is close to a resonant speed additional

fatigue checking has to be performed.

2.2Principal Bridge Performance Criteria in Accordance with EN1990-Annex A2 [1]

To allow stability, track continuity and to guarantee wheel track contact the followingsafety criteria have to be kept:

Maximum vertical acceleration of the deck.

Maximum variation of cant (deck twist).

Maximum end rotation (vertical deformation of the deck).

Maximum horizontal deformation.Limits for the variation of cant, the horizontal deformations and the vertical

acceleration are given in EN1990, Annex A2 [1]. The limit criteria of the maximum end

rotation is not given explicitly but reference is made to [2] where the requirements are stated

to be the same for dynamic and static analysis. In the previous edition of this Code [13] limits

for maximum allowable end rotations were defined. It has been found in the past that end

rotation can become a governing design factor for bridges with relatively deep main girders[7].

3. RULES IMPOSED IN GERMAN REGULATIONS

The German regulations RIL 804 [3] are quite similar to the Eurocode [1,2]. In

addition to the design rules comments and explanations are also given in [3]. Nevertheless,

there are some significant differences listed in the following:

Eight normative design trains (ICE1,-2, -3, Thalys2, Eurostar,ETR-Y500, TalgoAV2, Virgin) are defined in the German regulations in addition to the HSLM-trains.

A different verification flow chart is given to decide if dynamic analysis is required. A different calculation method for finding the maximum resonance speed is used in

the German standard where the total wagon length is used as opposed to the axle

distance in the Eurocode.

The vertical acceleration has to be checked for certain discrete positions on thebridge. In comparison the Eurocode requires all points on the bridge structure below

the rail track to be checked.

In the German regulations the dynamic results (forces, deflections and accelerations)are multiplied by an additional factor to cover track irregularities.


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In contrary to the EUROCODE , which provides several limiting criteria, only themaximum vertical acceleration is limited by the German regulations.

If results from a dynamic analysis become governing then the German regulationsrequire that they must also be used for the SLS and ULS checks.

4. APPLICATION EXAMPLE: COMPOSITE TRUSSED RAILWAY BRIDGE

4.1. Outline

The bridge described in the following serves as an application example to illustrate

some of the abovementioned issues. Consider a 15 span truss bridge with a concrete deck.

Figure 3 shows the first 4 of the 15 spans with a total length of 868m. The bridge consists of 6

double span girders and one three span girder in the middle of the bridge. The structure is part

of the new railway line for the ICE (German High-Speed Train) between Ebensfeld and Erfurt

in Germany. The design of this innovative structural system was completed by the design

office M. Cerin in Salzburg. Design checks according to the German regulations [3] were

required by the owner.

Fig. 3 First 4 spans of the 15 span application example

The dynamic analysis was restricted to a representative two span system as shown in

Figure 4. The small effects of interacting adjacent double spans were ignored. Cracked

concrete above the mid-pier was taken into account as shown in Figure 5. For the dynamicanalysis the mathematical model was refined in comparison to the static analysis. The

concrete deck was split into 11 longitudinal girders (Figure 6) which were connected with

cross-girders. The two main girders above the truss web are composite beams, all others are

pure concrete beams. The dynamic computer analysis for this project was carried out with the

software system RM2000 [8] including features described in [9,10]. Features for modal

analysis as well as time integration [11] are implemented in this software system and have

been used for this project.

The results for the lowest five eigenmode are summarized in Table 1. Modes 1 to 3 are

longitudinal and horizontal modes which have negligible influence on the maximum vertical

acceleration of the bridge deck. Modes 4 and 5 determine the dynamic behavior due to

vertical train loading. It can be seen from the results of the maximum vertical acceleration ofthe wings of the cross-section which will be demonstrated below that the lateral vibration

interfering with the vertical vibration (mode 5) play an important role. The German loading

specifications [3] give axle loads and axle layouts of the 8 different norm-trains which are

applied as a moving load (see also Figure 6). This results in a time dependent response, which

allows the check of the design criteria, especially the vertical acceleration.

The dynamic analysis was checked along all nodes of the structure. In accordance with

[3], the maximum vertical acceleration has to be checked just in a number of specified points.

These points of the application example are the points 141,741 at the middle of span 1 and the

points 161,761 at the middle of span 2 (right & left rail) (Figure 5)).


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wings of cross-section

6.5

0m 6.20m

13.50m

Fig. 4 Typical cross-section and structural system

Span 57.0 m

Cracked Concrete

Span 57.0 m

735

135

730

130

330

746

141

756

156

76a

167

741

141

341

751

151

351

761

161

361

771, 772

171, 172

372

Fig. 5 Representative two span system for the dynamic analysis and special investigated

nodes

Fig. 6 Loading scheme of the moving load analysis


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Table 1: Results of the Eigenmode calculation for the original design and the additional three

alternatives

4th

eigenmode 5th

eigenmode

Fig. 7 First bending and torsional mode

4.2. General Results

For the dynamic analysis of the given train speeds between 150km/h and 360km/h

were investigated. For the given structure modal damping of 0.5% can be assumed accordingto Eurocode [2] what is identical to the requirement of the German Standard [3]. The

dynamic effects due to load trains HSLM-A1 to HSLM-A10 [2] (Figure 1) as well as the load

trains given in [3] were investigated for the purpose of this paper. According to [3] the

governing results of the dynamic analysis are the maximum vertical accelerations in a set of

given points as shown in Figure 5. For the points labeled NODE 141 and NODE 161 the

accelerations are shown in Figure 8 for the German load trains. The limit of 0.5g is exceeded

slightly at NODE 141 for a train speed of 330km/h. However, longitudinal load distribution

Results node 141 Results node 161

Fig. 8 Maximum vertical accelerations at NODE 141 and NODE 161

EM ND UC SC BB Description of Eigenmode

1st 0.71 0.71 0.71 0.71 1st

long. mode, no vert.bending components

2nd 0.98 1.00 1.00 1.02 1st horiz. mode, no vert. bending

3rd 1.34 1.36 1.36 1.41 1st

horizontal bending mode

4th 1.75 1.75 1.75 1.76 1st

vertical eigenmode, only vertical bending

5th 1.97 2.01 1.98 2.33 1st

torsional mode

Legend: EM.eigenmode, ND....normal design, UC.... uncracked concrete, SC...supportedcantilever, BB...bottom bracing


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due to indirect load introduction was not taken into account for this particular analysis run.

Taking into account this effect smoothes out the peak at this velocity and reduces the

maximum vertical acceleration to an acceptable level. Figure 8 also illustrates that there are

two ranges of train velocities for most load train constellations where resonance effects can be

observed, namely at 240km/h and 330km/h. Detailed results of these analyses can be found in

[12].

4.3. Wings of Cross-Section

Figure 9 shows the maximum vertical acceleration of the deck of all structural nodes

in the bridge. From these results it could be seen that these maximum vertical accelerations

occurred at the wings of the cross-section at mid span (Figure 4) around NODE 351 as

shown in Figure 5. The high vertical acceleration in this particular area is caused by the

lateral vibration interacting with the torsional vibration. The questions arises whether this

high acceleration of the wings of the cross-section area is covered with the design criteria?

EUROCODE envelo e

GERMAN envelo e

Fig. 9 Comparison EC-German maximum vertical acceleration

4.4.Variant Study

For the purpose of this paper a number of design variants were investigated. Due to

the time-consuming nature of the analysis the following alternatives were limited to one

loading train, the ICE3 of the German Railway Company. The following alternatives were

analysed: analysis without cracked concrete area over the mid pier.

analysis with additional supported cantilevers at each truss node (21 additional beamelements on each side of the bridge.

analysis with additional bottom bracing to check if the increased torsional stiffness hasa significant influence on the maximum vertical accelerations.

All alternatives were then compared with the results of the original design described above

with cracked concrete over the mid pier:

Figure 10 shows the maximum results of the vertical acceleration for the cantilever

NODE 351 for the above mentioned alternatives together with the results for the original


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design. It is obvious, that the bottom bracing has no significant influence on the final

acceleration results. The analyses with the un-cracked concrete slab and the supported

cantilever elements show the significant influence of the cracked concrete above the piers.

Not only the overall maximum results are affected, but also the results of the investigated

nodes below the rail in the respective mid spans. As seen from Figure 11 where the maximum

vertical accelerations are shown for the nodes in mid span below the rail (NODE 161 and

NODE 761) the distinct ranges of resonance effects are less apparent in comparison to theoriginal design.

Fig. 10 Comparison alternatives, maximum vertical acceleration at NODE 351

Results node 161 Results node 761

Fig. 11 Comparison alternatives: maximum vertical acceleration NODE 161 & NODE 761

5. CONCLUSIONS

The design rules of the Eurocode against dynamic forces due to high-speed rail

loading are quite similar to the design rules of the German regulations. This paper gives anoverview on the main features of both codes and also points out the differences between the

two.

To illustrate the dynamic design according to the German regulation an application

example is presented. The example consists of a composite trussed railway bridge. It was

found that this type of structure complies with all requirements. The influence of the cracked

concrete above the piers was shown to be significant. Vertical accelerations at the wings of

the cross-section were found to be very high but did not necessitate design changes according

to the German regulations. Design alternatives and their influence on the dynamic behaviour

of the bridge were also presented.


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6. ACKNOWLEDGMENTS

The authors gratefully acknowledge that the work for this paper was funded by the

F.F.F. on behalf of the Austrian Government as part of the research project FEMBRIDGE.

REFERENCES

[1] prEN 1990-Draft, Annex A2: Application for bridges, August 2001.[2] prEN 1991-2 EUROCODE 1 Part 2: Traffic loads on bridges, July 2002 (Conversion

of ENV-1991-3 into 1991-2) (final draft).

[3] RIL804 (Modul 804.3301) Eisenbahnbrcken, Dynamische Effekte beiResonanzrisiko, Germany, 2003.

[4] UIC leaflet: UIC 776-2R Design requirements for rail-bridges based on interactionphenomena between train, track, bridge and in particular speed. (July 2002.).

[5] DIN-Fachbericht 101: Einwirkungen auf Brcken, 2.Auflage 2003[6] Bucknall, I., New Eurocode Requirements for the Design of High Speed Railway

Bridges, IABSE Symposium, 2003, Antwerp.[7] Heiden, M., Pircher, M., Pircher, H. and Janjic, D., Rolling Stcok Analysis of VariousRailway Bridges in Austria, Proceedings: IABSE-Symposium 2003, Antwerp, pp. 116-

117.

[8] TDV GesmbH. (2001) RM200 Technical Description, Graz, Austria.[9] Pircher, M., Janjic, D., Pircher, H., Bridge, R.Q., Towards a Holistic Approach to

Bridge Design, Proceedings: IABSE-Symposium 2002, Melbourne, pp. 236-237.

[10] Pircher, H., Janjic, D., FEMBRIDGE Technical Project Description, 2001, TDV-Austria.

[11] Zienkiewicz, O.C., Taylor, R.L. The Finite Element Method, Fifth Edition, McGraw-Hill Book Company, London, 2001.

[12] TDV-Austria, Final Report of the Rolling Stock Analysis of the Itztalbridge, August2003.

[13] ENV 1991-3 Anhang G Grundlagen fr Entwurf, Berechnung und Bemessung zustzliche Regelungen zu ENV 1991-1 fr Eisenbahnbrcken einschlielich

Gebrauchstauglichkeits-kriterien, 1995.

: dynamic effects of railway bridges for high speed

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