PROCEEDINGS OF THE 10TH INTERNATIONAL SYMPOSIUM ON TUBULAR STRUCTURES, 18 – 20 SEPTEMBER 2003, MADRID, SPAIN

Tubular Structures X Jaurrieta, M.A., Alonso, A., Chica, J.A. (Eds.)

Welded circular hollow section (CHS) joints in bridges Ulrike Kuhlmann Hans-Peter Günther Reiner Saul Marc-Ulrich Häderle

A.A. BALKEMA PUBLISHERS LISSE / ABINGDON / EXTON (PA) / TOKYO

1 INTRODUCTION

Spatial truss girders built up with tubular membersare more and more used in modern bridge design dueto their architectural transparent appearance. Mostimportant for the design and durability of suchstructures is the design and the construction of thejoints.

The recently in Germany completed highwaybridge “Korntal-Münchingen” design by Leon-hardt, Andrä und Partner was constructed using caststeel joints at the intersection of the tubular mem-bers. However, during the design process of thisbridge, several proposals suggested the use of cost-effective welded joints. Due to some lack of infor-mation, mainly concerning the durability and fatiguebehaviour of this kind of joint and due to some posi-tive experience with cast steel in former CHSbridges, the relevant highway authority finally de-cided to use cast steel joints.

This was the starting point for intensive numeri-cal investigations in order to clarify whether for thisspecific type of bridge welded joints would havebeen a possible alternative, see also Kuhlmann et. al.(2002).

2 CHS IN BRIDGE DESIGN

2.1 General

The use of circular hollow section members as partof the main load-carrying structure of bridge girdersis a relatively new constructional concept. Duringthe last couple years several steel-concrete compo-site bridges had been constructed, see Table 1. Thetypical cross-section of this type of bridge generallyconsists of a tubular spatial truss girder carrying theconcrete deck slab (Figure 1). The deck slab is con-nected directly to the steel structure by either shearstuds, concrete dowels or in some cases where notop chord exist, as e.g. at the “Nesenbachtal” bridgeby saw-tooth connections, see Schlaich et. al. (2000).

Figure 1. Cross-section of the bridge “Korntal-Münchingen”

Welded circular hollow section (CHS) joints in bridges

U. Kuhlmann & H.-P. GüntherInstitute of Structural Design, University of Stuttgart, Germany

R. Saul & M.-U. HäderleLeonhardt, Andrä und Partner, Consulting Office, Stuttgart, Germany

ABSTRACT: The use of circular hollow section members in bridge design is a relatively new concept. Theapplication of such constructions is strongly influenced by the design and manufacturing of the joints. In gen-eral, there are two possibilities: either to use cast steel joints or welded joints.This contribution tries to give an overview about the advantages and disadvantages of both possibilities con-cerning the aspects of resistance, fatigue, manufacturing and economy in order to help practical engineers intheir decisions and to allow for a further application of circular hollow sections in bridge design.As a crucial question, special considerations are given to the fatigue assessment of welded circular hollowsection joints. For an example of a recently completed bridge with a typical spatial CHS truss and cast steeljoints it has been shown that also welded connections would have been a possible alternative. This conclusionis drawn from numerical studies based on FE calculations applying the hot-spot stress approach for the fatigueassessment of the welded joints.

At the bottom chord of the tubular space trussfour brace members have to be connected to thecontinuous bottom chord. This type of joint is usu-ally named KK-joint (Figure 2).

Table 1 summarizes the dimensions of five CHShighway bridges recently built in Switzerland (CH)and Germany (D), as well as their joint characteris-tics. The table clearly indicates that all five bridgesresemble each other concerning their overall globaland local dimensions.

Figure 2. Typical multiplanar KK-joint with notations

3 JOINT CONSTRUCTION

3.1 Cast Steel Joints

3.1.1 Material Properties

Through the ongoing development within themanufacturing of cast steel products it is possiblenowadays to gain almost the same mechanical andchemical qualities in terms of strength, toughness,weldability and corrosion resistance as for ordinaryrolled steel products, see e.g. Schober (2001) orMang & Herion (2001).

3.1.2 Structural Behaviour

The casting process allows almost perfectly mod-eling of the joint according to the flow of internalforces, avoiding large stress concentrations. The castjoints are usually designed in such a way, that theload bearing capacity of the joint is higher than thatof the attached tubular sections. This is generallydone using three-dimensional FE calculations.

During the design of the cast joints one shouldalso consider some special features regarding thecasting process. Large differences of the wall thick-ness for example, significantly influence the solidifi-cation and shrinkage process of the melt and maylead to unintentional internal blowholes and microcracks. In order to avoid this, solidification simula-tion calculations may help to get the cast free fromblowholes and to find the optimal feeder head posi-tion for fabrication.

3.1.3 Fatigue

The smooth shape of the cast joint according tothe flow of internal forces results in only small stressconcentrations, thus making cast steel joints in par-ticular advantageous for structures subjected to re-peated loading. The critical part in terms of fatigueare the welds between the cast steel joint and the tu-bular steel members. Concerning the fatigue behav-iour of this type of connection, there are only few in-vestigations documented, some associated with the“Humbolthafen” bridge in Berlin, see Seifried et. al.(1999). Based on experimental investigations onsmall and large scale test specimens, the fatigue re-sistance could be classified to detail category 71, ac-cording to Eurocode 3 Part 1.9 (2002), similar to abutt welded end-to-end connection of CHS mem-bers.

3.1.4 Manufacturing and Quality Assurance

The manufacturing of cast joints is quite expen-sive due to the high costs preparing the cast form-

Table 1. Summary of recently built CHS bridges and joint characteristics

Lully1) Dättwill2) Aarwangen2) Nesenbachtal Korntal-Münch.(CH) (CH) (CH) (D) (D)

year of completion 1997 2001 1997 1999 2002span length ≈ 43 m ≈ 38 m ≈ 48m 25 / 50 / 36 m 32 / 41 mh/L of steel truss 1 / 14 1 / 12 1 / 27 1 / 11-22 1 / 13type of joint construction welded welded welded cast steel cast steeljoint type KK KK K KK KKbrace dimensions 267 / 25 267 / 25 194 / 28 194 / 10-60 267 / 28-45chord dimensions 508 / 36 508 / 50 406 / 36 324 / 16-80 457 / 45-67joint parametersβ = d1/d0 0.53 0.53 0.48 0.60 0.58γ = d0/2t0 7.06 5.08 5.64 10.13-2.03 5.07-3.51τ = t1/t0 0.69 0.50 0.78 0.63-0.75 0.62-0.69

Θ ; cos(Θ) 60 ; 0.5 60 ; 0.5 45 ; 0.71 46 ; 0.69 60 ; 0.5

φ 69 69 -- 102 90

1) according to Dauner (1998) 2) according to Schumacher, Nussbaumer & Hirt (2001)

work. Usually, additional machining of the connec-tion device is required in order to fulfill the smalltolerances for a precise fitting of the tubular sections.

The quality assurance has to be guaranteed forboth, the welded connection between the cast jointand the tubular sections and the cast steel material it-self. In Germany, non-destructive quality controlusually is performed by ultrasonic devices in accor-dance with DIN 1690 (1991).

3.1.5 Economic Efficiency

The economic efficiency using cast steel joints isvery dependent on the manufacturing of the castformwork. If the design of the bridge allows the useof a large number of equal joints, a high cost effec-tiveness can be achieved by reducing the cost for theformwork in relation to the single joint. Dependingon the number of equal joints and the complexity ofthe joints the price varies between 3000 € and6000 € per ton cast steel.

3.2 Welded Steel Joints

3.2.1 Structural Behaviour

The forces between the members are directlytransmitted through the welds, leading to a verycomplex and multidimensional stress situation withhigh local stress concentrations.

Over the past 30 years a considerable amount ofresearch work on CHS joints has been driven for-ward by the petroleum industry concerning the de-sign of offshore-structures. Most of this research ispublished by CIDECT (Comité International pour leDéveloppement et l’Étude de la Construction Tubu-laire).

CIDECT Serial No. 1 (1991) includes guidelines,charts and provides parametric formulas for the designof welded CHS joints that are subjected to predomi-nately static loading. Thus, allowing a quick and easydesign of such joints, without time-consuming FEcalculations.

3.2.2 Fatigue

Welded CHS joints are very sensitive to fatiguebecause the geometric discontinuities of the weldslead to a high stress concentration. Under staticloading, these stress concentrations are less impor-tant due to local plastification. However, under re-

peated loading the high stress concentrations maylead to a premature fatigue failure. Thus, the designof welded CHS joints, particular for bridge struc-tures is very much influenced by their fatigue be-haviour.

CIDECT Serial No. 8 (2000) deals with the fatiguebehaviour of welded joints under repeated loading andincludes guidelines, charts and provides parametricformulas for the design of welded CHS joints.

3.2.3 Manufacturing and Quality Assurance

In order to ensure an optimal fitting of the diago-nal brace members onto the continuous chord at thevery complicated intersection area a precise cuttingof the tubular members is required. Nowadays com-puter-operated profile cutting machines allow for anefficient and very precise cutting process.

The welding is mainly manual. For a reliablequality inspection of the welds, especially the criticalweld root, the geometrical dimensions of the jointshould be designed in a way that enough space forinspection devices is guaranteed.

3.2.4 Economic Efficiency

As the chord member normally is continuous atthe joint and only the diagonal braces are to bewelded to the chord, the number of welded connec-tions is reduced in comparison to cast steel jointsleading to decisive savings. However, some of thesavings are compensated by the more costly weldingprocedures.

As a conclusion: for simple and standardized jointtypes such as e.g. T-, X-, K- or KK-joints with easyto reach weld positions, welded joints form the moreeconomic solution. Additionally, as the whole steelconstruction is manufactured within only one com-pany there are also logistic and organizational ad-vantages.

4 FATIGUE ASSESSMENT OF CHS JOINTS

4.1 General; S-N Concept

Fatigue assessment procedures are usually based onS-N curves which relate a nominal or geometricstress range S to the corresponding number N of loadcycles to fatigue failure.

Table 2. Construction detail and detail category of a uniplanar CHS K-joint with gap according to Eurocode 3 Part 1.9 (2002)

Detail Category Constructural detail Description

90

m = 50.2

t

t

1

0 ≥

45

m = 50.1

t

t

1

0 =

- for intermediate values of theratio t0/t1 interpolate linearlybetween detail categories

- t0 and t1 ≤ 12.5 mm

- 35°≤ Θ ≤ 50°

- d0 /t0 ≤ 25

4.2 Nominal Stress Method

In this case fatigue assessment refers to the nomi-nal stress range ∆σnom in a structural member.

The fatigue resistance is given according to aclassification catalogue in the form of standardizedS-N curves. Structural details classified in this cata-logue, see e.g. Eurocode 3 Part 1.9 (2002), corre-spond to a specific situation of stress range, direc-tion, crack position, detail dimension and weldquality which had been characteristic for the tests onwhich the classification is based.

Thus, the application of this method is limited insome extend to the geometrical dimensions or theloading conditions of the classified structural details.Table 2, for example gives the detail category ofuniplanar CHS K-joints with gap depending on therelation of the corresponding wall thickness ratiot0/t1. In this special case, the range of application islimited to a wall thickness of t0 and t1 ≤ 12.5 mmand therefore impossible to use for bridge structures.

4.3 Hot-Spot Stress Method

The hot-spot stress method also named geometricstress method has been developed for unclassifieddetails and for details where a clear definition of thenominal stress, e.g. due to geometric discontinuitiesis not possible. The hot-spot stress is defined as themaximum geometric stress occurring at the spotswhere cracks usually tend to initiate. It characterizesa fictitious measured or calculated stress at the criti-cal section (hot-spot) that is extrapolated to the weldtoe, from two or three points at certain distancesfrom the weld toe, see Figure 3.

For design, the hot-spot stress is usually calcu-lated by multiplying the nominal stress σnom by theso-called stress concentration factor (SCF) for theappropriate structural discontinuity, see equation (1).

nomhs SCF σ⋅=σ (1)

Figure 3. Definition and extrapolation region of the hot-spotstress σhs

In general, the hot-spot stress respectively thestress concentration factor is determined by testingand/or FE analysis. For typical CHS joints CIDECTSerial No. 8 (2000) includes formulae and charts de-pending on the geometric dimensions, for theevaluation of SCF values.

Similar to the nominal stress method the hot-spotmethod uses Shs-N curves for the fatigue resistance,where Shs is the hot-spot stress range.

The advantage of the hot-spot stress method is thepossibility of predicting the fatigue lives of manydifferent types of joint configuration using only onesingle Shs-N curve.

5 STRESS CONCENTRATION FACTORS OFWELDED CHS BRIDGE JOINTS

5.1 Bridge “Korntal-Münchingen”

The bridge is located about 30 km north east ofStuttgart nearby the small city of Korntal-Münchingen and was opened for traffic in October2002.

The total length of the bridge is about 300 m. Themain middle part of the bridge consists of a tubularspace truss (Figure 1 and 4) approximately 2.9 m indepth and 4.6 m in width. Piers are typically spacedbetween 32 m and 41 m. The diameter of the hot-rolled CHS members were chosen to be 267 mm forthe braces and 457 mm for the chords. The wallthickness of the CHS members varies in order toachieve the necessary strength and stiffness. Themaximum wall thickness of the chord is 65 mm andwas needed at one of the inner-supports.

Although the joints where built in cast steel, thesetypical dimensions of the bridge structure and thejoint geometry were used as an example to clarifywhether for this bridge welded joints would havebeen a possible alternative.

Figure 4. Spatial CHS framework of the bridge Korntal-Münchingen

5.2 Finite Element Analysis

5.2.1 General

For the given CHS joint geometry it is not possi-ble to verify the fatigue resistance according to thehot-spot approach as recommended in CIDECT Se-rial No. 8 (2000). The reasons are as follows:- the parameter range of the given SCF formulas and

charts is limited to 12 ≤ γ ≤ 24 and 0,3 ≤ β ≤ cos(θ).These conditions are not fulfilled for almost everyCHS bridge according to Table 1,

- the SCF formulas are restricted to CHS KK-jointswith gap but without any eccentricity and

- the Shs-N curves are limited to a wall thicknesssmaller than t = 50 mm.

To overcome these restrictions a detailed FE analysishas been performed, determining the critical hot-spotstresses at the joint intersections, Stuba (2002). Thehot-spot stresses respectively SCF values were de-termined in accordance to CIDECT Serial No. 8(2000) and Niemi (1992) using the FE package AN-SYS. Figure 5 shows the three-dimensional FEmodel of the KK-joint. Geometrical symmetrieshave not been taken into account. 20-node solidelements with an 3x3x3 integration scheme wereused. Various mesh densities were investigated andcompared in order to ensure enough convergence ofthe stresses in the vicinity of the weld toe.

Figure 5. FE model of the multiplanar CHS KK-joint using20-node elements

5.2.2 Loading and boundary conditions

The loads were introduced as unit loads. Two dif-ferent axial loading conditions have been investi-gated:- pure axial balanced brace loading and- pure chord loading, see Figure 6.

Additional studies showed that in case of in-planebending the maximum SCF values are somewhatbelow those of the axial loading condition. Thereforeit can be concluded that the axial loading sufficientlycovers also in-plane bending.

Figure 6. Applied loading and boundary conditions

5.2.3 Stress Concentration Factors (SCF)

The stress concentrations factors (SCF) were de-termined using the quadratic extrapolations method.Studies by Romeijn (1994) have shown that for CHSjoints this method gives satisfying results.

In circumferential direction the tubular sectionshave been divided into 36 elements/nodes resultingin altogether 36 x 4 x 2 = 288 SCF values for onejoint and one loading condition.

Since no experimental results have been avail-able, the numerical FE results of test calculationswere compared to the values given in CIDECT Se-rial No. 8 (2000), leading to an acceptable differenceless than 5%.

The location of maximum stress concentration(hot-spot) always appeared in the brace near the sad-dle. Figure 8 shows the variation of the SCF valuealong the circumferential direction of the brace incase of axial balanced brace loading. Figure 7 re-flects the corresponding von Mises stress pattern atthe surface. The maximum SCF value appears in thebrace at node number 22.

Figure 7. FE-results, von Mises stress pattern in case of axiallyloaded brace

0.0

1.5

3.0

4.5

1 6 11 16 21 26 31 36node number

Figure 8. Stress concentration factor (SCF) in circumferentialdirection of the brace, brace loading

5.2.4 Influence of Weld Shape

For critical connections in terms of fatigue andwhere the wall thickness is large, full penetrationwelds should be used. However, a realistic modelingof the weld shape in circumferential direction is avery complex task, because of the ever-changing an-gle Ψ between the surface of the chord and the di-agonal braces that have to be joined, see figure 9.Especially in the “heel” zone of the connection witha small intersection angle full penetration is difficultand leads to a much higher throat thickness com-pared to the “crown” zone. Two different weldshapes have been considered:- a full penetration weld with a weld foot length

tw = 0 (butt weld) and- a full penetration butt weld with a constant weld

foot length tw, see figure 9.

Figure 10 shows the influence of the these differenttypes of weld shapes on the stress concentrationfactor. The consideration of an additional foot lengthtw leads to a reduction of the SCF of about 10 to15%.

Figure 9. Different weld shapes

0.0

1.5

3.0

4.5

1 6 11 16 21 26 31 36node number

Figure 10. Influence of the weld shape on the stress concentra-tion factor (SCF)

6 FATIGUE VERIFICATION OF THE KK-JOINT

6.1 General

In order to clarify the feasibility of welded jointsfor the bridge “Korntal-Münchingen”, the fatigueverification was performed according to Eurocode 3Part 2 –Steel bridges– (1997) and the hot-spot fa-tigue design method recommended for hollow sec-tion joints in CIDECT Serial No. 8 (2000).

Three different joints of the aforementioned tri-angular truss girder were selected. These joints differregarding their wall thickness t0 and t1 and loadingcondition because of their different positions in lon-gitudinal direction of the bridge girder. Table 3summarizes the joint dimensions and parameters.

6.2 Stress Range

Fatigue load model 3 (FLM 3) of Eurocode 3Part 2 (1997) was used to determine the nominalstress ranges in the corresponding tubular members.FLM 3 consists of a single 4-axle vehicle truck withaxle loads of 120 kN.

According to Eurocode 3 Part 2 (1997) the re-sulting stress range is transformed into the damageequivalent stress rang ∆σE,2 related to 2·106 cycles inorder to make it comparable to the fatigue strength∆σC. This is realized by the so-called damageequivalent factors λi, see equation (2). These factorsdepend on fatigue relevant parameters as e.g. thetraffic volume, the design life of the bridge or the

Table 3. Joint dimensions and parameters

joint 1 joint 2 joint 3

do 457 457 457t0 65 55 45d1 267 267 267t1 45 36 28g 79.0 65.5 52.8β = d1/d0 0.58 0.58 0.58γ = d0/2t0 3.52 4.15 5.07τ = t1/t0 0.69 0.65 0.62Θ 60 60 60φ 90 90 90

foot length tw = 0 foot length tw > 0

shape of the influence line. Table 4 summarizes thevalues applied as they are given in Eurocode 3.

nom43212,E σ∆⋅λ⋅λ⋅λ⋅λ=σ∆ (2)

6.3 Fatigue Verification

Using the hot-spot method, the fatigue limit statecan be verified using equation (3):

Mfhs.C2,EFf SCF γσ∆≤σ∆⋅⋅γ (3)

Where γFf and γMf are the partial safety factors forthe fatigue limit state, ∆σC.hs is the characteristicvalue of the fatigue strength against hot-spot stressesfor 2·106 number of cycles and SCF is the stressconcentration factor.

The safety factors were chosen to γFf = 1.0 andγMf = 1.15.

Values for the fatigue resistance ∆σC.hs for CHSsection joints are given in CIDECT Serial No. 8(2000) by the following formula:

( ))t/16log()Nlog(06.0

)Nlog(476.1231

f

fhs.C

⋅⋅+−⋅=σ∆

(4)

Where Nf is the number of cycles to failure and tthe wall thickness. Although the given formula islimited to a maximum thickness of t ≤ 50 mm it hasbeen applied in this case.

Based on the aforementioned FE calculations, therelevant stress concentration factors (SCF) for theobserved three joints are given in Table 5. Herein thefirst lower index describes the member (ch = chord,b = brace) and the second one the loading condition(ch = chord loading, ax = axial balanced brace load-ing).

In contrast to the given values in Table 5,CIDECT Serial No. 8 (2000) recommends a mini-mum SCF = 2.0 unless it is negligible. The follow-ing reasons are given:- a possible and uncontrollable crack initiation from

the weld root, that is not covered within the SCFvalue determined for the weld toe,

- possible deviations of the principle stress directionfrom the direction perpendicular to the weld toeand

- difficulties in FE modeling.

The recommended minimum SCF value is a rea-sonable assumption and should especially be appliedfor thin sections used for buildings or crane struc-tures. However, the authors believe, that for thicksections and high quality full penetration welds withgood accessibility SCF values in the range between1.5 and 2.0 may be acceptable as well.

With the above mentioned assumptions and basedon the SCF values given in Table 5, the fatigue limitstate has been verified for all three joints, thusclearly indicating, that for the specific type of bridgealso welded CHS joint would have been possible.

7 CONCLUSIONS

This contribution covers the application of circu-lar hollow sections in bridge design and tries to givean overview about the advantages and disadvantagesof either cast steel or welded joints in order to helppractical engineers in their decisions and to allow fora further application of circular hollow sections inbridge design.

Concerning a cost effective and robust design ofCHS joints for bridge structures the following con-clusions are drawn:- cast steel joints should be used if there are several

members to be connected at one joint resulting in acomplex joint geometry. For such cases, the castingprocess allows an optimal design of the joint ac-cording to the flow of internal forces, increasingtheir static and fatigue resistance compared towelded joints.

- for standard joint types such as e.g. K- or KK-joints that are typically used for triangular trussgirders, welded joints are the more economic solu-tion and, providing a high manufacturing standardespecially for the welds, a possible alternative.

Through detailed investigations connected to arecently completed CHS truss bridge near Stuttgart,it has been shown, that for this bridge instead of caststeel also welded joints would have been a possiblealternative. This conclusion could be drawn fromnumerical studies based on FE calculations applyingthe hot-spot stress approach for the fatigue assess-ment of the welded joints.

Table 5. Stress concentrations factors (SCF)

brace loading chord loadingSCF

chordKK

axchSCF ,

brace

KKax,bSCF

chord

KKch,chSCF

brace

KKch,bSCF

joint 1joint 2joint 3

1.992.062.08

1.681.781.85

1.401.391.37

0.300.360.41

Table 4. Assumed damage equivalent factors λi

λ description value

λ1 span length and shape of influence line; 2.25mid span, L = 40 m

λ2 traffic volume; 0.63NObs = 0,5·106 lorries per year

λ3 design life of the bridge; N = 100 years 1.0λ4 number of lanes with heavy traffic; k = 1 1.0

λ = λ1⋅λ2⋅λ3⋅λ4 1.41

Furthermore, these studies clearly indicated thatfor a wide application of cost effective and robustwelded CHS joints, the currently existing designguide CIDECT Serial No. 8 (2000) should be ad-justed to the specific situation of bridge structures,e.g. by extending the parameter range of the SCFvalues or providing values for the fatigue resistancealso for a large wall thickness.

8 PREFERENCES, SYMBOLS AND UNITS

ANSYS Rev. 5.7. ANSYS Inc., Southpointe, TechnnologyDrive, Canonsburg, PA 15317.

Comité International pour le Développement et l’Étude de laConstruction Tubulaire (CIDECT) 1991: Design Guide forCircular Hollow Section (CHS) Joints under PredominantlyStatic Loading. Construction With Hollow Steel Sections.Serial No. 1. Verlag TÜV Rheinland, Cologne, Germany.

Comité International pour le Développement et l’Étude de laConstruction Tubulaire (CIDECT) 2000: Design Guide forCircular and Rectangular Hollow Section Welded Jointsunder Fatigue Loading. Construction With Hollow SteelSections, Serial No. 8. Verlag TÜV Rheinland, Cologne,Germany.

Dauner, H.-G. 1998. Der Viadukt von Lully. Eine Neuheit imVerbundbrückenbau. Stahlbau 67, Vol. 1, pp. 1-14.

Eurocode 3 2002: Design of steel structures - Part 1.9: Fatigue.Draft, 7 August 2002. European Committee for Standardi-sation.

Eurocode 3 1997. Design of Steel Structures - Part 2: SteelBridges. European Committee for Standardisation.

German code (DIN 1690) 1991: Technische Lieferbedingungenfür Gußstücke aus metallischen Werkstoffen. ErgänzendeFestlegungen für Stahlguß für höher beanspruchte Arma-turen. DIN. Ausgabe: 1991-01.

Kuhlmann, U., Günther, H.-P., Saul, R., Häderle, M.-U. & Stu-ba, G. 2002. Zur Anwendung geschweißter Hohlprofilver-bindungen im Brückenbau. Stahlbau 71, Vol. 7,pp. 507-515.

Mang, F. & Herion, S. 2001. Guß im Bauwesen. Kuhlmann, U.(ed.): Stahlbaukalender 2001. Berlin: Ernst & Sohn,pp. 625-667.

Niemi, E. 1992. Recommendations concerning stress determi-nation for fatigue analysis of welded components. IIW,Document No. XIII-1458-92/XV-797-92, 1992.

Romeijn, A. 1994. Stress and Strain concentration factors ofwelded multiplanar tubular joints. PhD-Thesis, Delft,The Netherlands.

Seifried, G., Angelmaier, V., Wilhelm, G. & Beschorner, K.1999. Eisenbahnbrücke über den Humboldthafen in Berlin.Stahlbau 68, Vol. 7, pp. 511-519.

Schlaich, J., Pötzl, M., Beiche, H., Ehrke, E. & Decker, U.2000. Die Brücken über das Nesenbachtal im Zuge der Os-tumfahrung Stuttgart–Vaihingen. Beton- und Stahlbeton-bau 95, Vol. 11, pp. 678-687.

Schober, H. 2001. Rohrknoten aus Stahlguß. Der Prüfinge-nieur, Vol. 17, Bundesvereinigung der Prüfingenieure fürBautechnik e.V. (eds.), pp. 16-36.

Schumacher, A., Nussbaumer, A. & Hirt, M.A. 2001. Fatiguebehaviour of Welded Circular Hollow Section (CHS) jointsin bridges. Puthli, R. & Herion, S. (eds.): Tubular StructuresIX, Swets & Zeitlinger, Lisse, pp. 291-297.

Stuba, G. 2001. Zur Anwendung geschweißter Hohlprofilkno-ten im Brückenbau. Universität Stuttgart, Institut für Kon-struktion und Entwurf, Diploma-Thesis.

9 ACKNOWLEDGMENT

The authors would like to express their gratitudeto Mr. G. Stuba who did the FE-Analysis within hisdiploma-thesis.