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Fabrication & assembly technology of Sava bridge in the city of Belgrade

Yongqiang Yang1, Chunfeng Liu1, Yunxiang Wei1, Chunlei Zheng2

(1. China Railway Shanhaiguan Bridge Group., Ltd. Qinhuangdao 066205,

China; 2. College of Materials Science and Engineering, Yanshan University,

Qinhuangdao 066004, China)

Abstract: The fabrication and assembly technology of

the Sava bridge in the city of Belgrade is introduced

in this paper. Sava bridge is a 6 span, continuous

superstructure with an overall length of 929 meters

between deck expansion joints. Safe and reliable

assembly jigs are applied in both workshop and bridge

site. Welding shrinkage and welding deformation

are considered during assembly. European standards

are strictly followed during the whole processes. This

paper can be reference for similar project as well.

Key words: fabrication; assembly; steel structure;

bridge; assembly jig

DOI: 10.7512/ j.issn.1001-2303.2017.13.14

Yongqiang YangEmail: yyqqhd@sina.com

0 IntroductionSava bridge provides the only direct connection between the New

Belgrade (Blokovi) and Čukarica (Banovo Brdo) municipalities. The

main support system is a single pylon asymmetric cable stayed structure

with a main span of 376 meters which is steel structure fabricated in

China and a back span of 200 meters. The overall deck width is 45.04

meters and planned to carry six lanes of vehicular traffic, 2 tracks of a

new light rail system (LRT) and two lanes of a pedestrian / bicycle path.

The general layout is shown in Fig.1.

This paper provides general information about fabrication and

assembly of Sava bridge.

1 Structural overview1.1 Constitution of standard segments

Main span is steel box girder and divided by 23 segments. Each

segment is consisting of deck panel, bottom panel, internal web,

external web, cross beam, bracing and struts, as shown in Fig.2.

Yongqiang Yang, senior welding engineer, principle engineer of CRSBG, Canadian welding engineer, deputy welding coordinator (ISO 3834-2 & EN 1090-2), deputy welding supervisor (DIN 18800-7), certified welding inspector (CWI), visual inspector level 2 issued by BINDT. Graduated from Yanshan University with a master degree majoring in welding. Being as a in charging welding engineer, he has involved in the fabrication of over 10 bridges in China, Germany, Serbia, Africa and America. He researches in the field of welding procedure qualification, bridge fabrication and assembly, thermal simulation of welding, properties of HSLA steel and building information modeling. He has published over 10 papers in domestic and foreign journals.

Fig.1 General layout of Sava bridge

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Fig.2 3D drawing of standard segment

1.2 Numbering system of shop panels

Due to the limitation of shop production capacity, sea transportation

and lifting capacity, each segments has to be divided by 22 parts. All

fabrication panels will be assembled in assembly yard which is near the

bridge site. Therefore, a standard segment is divided by 12 deck

panels, 2 bottom panels, 4 box parts, 2 bracings and 2 struts. Both

internal and external web panels are divided by two parts, welded

together with its adjacent deck or bottom panels, therefore, 4 box

parts are formed. Fig.3 shows the numbering system of parts in the

downstream (The part number of upstream side is the relevant part

number minus one).

Fig.3 Typical cross section with parts and numbering system (downstream)

2 Shop fabrication2.1 Fabrication requirements

Qualification for production of steel structures shall follow DIN

18800-7 class E, and welding procedure qualification shall follow EN ISO

15614-1. Welders and welding operators are qualified according to EN

287-1/EN 1418. The tolerance for welded constructions is in accordance

with EN 13920. The requirements of thermal cutting shall follow EN ISO

9013.

2.2 Panel fabrication

Take a four-rib panel as an example.

(1) Mark the transverse and longitudinal base line.

(2) Locate and weld the U-ribs

Locate U-ribs and cross beams by reference of the longitudinal

baseline and transverse baseline respectively. Add 0.5mm more to

the theoretical location when locating the cross beams to get rid of

the welding shrinkage. Typical panel drawing with baselines is shown

is Fig.4. The U-rib to deck weld is welded in flat position. Two pass

Fig.4 Typical panel drawing with baseline

Fig.5 Welding tractor applied for the U-rib to deck welds

welding process with different welding parameter is applied, the first

pass is focusing on the root penetration and the second pass focuses

on the surface appearance. Welding tractors connected with semi-auto

FCAW gun is putting into use, as shown in Fig.5.

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2.3 Fabrication of lower box

One bottom panel and two web panel comprised the lower box.

Because of weld shrinkage and the distribution of connection welds are

inside the box, the web plate will not be perpendicular to the bottom

plate after the completion of welding. A internal jig is installed during

assembly and a certain anti-welding deformation is made to compensate

for the welding shrinkage. The heat straightening and repairing work

will be minimized. The internal jig is shown in Fig.6 and Fig.7.

2.4 Fabrication of upper box

One top panel and two web panel comprised the upper box.

A internal jig is used for locating these three panels. Additional

compensation for welding shrinkage is added. The internal jig is shown

in Fig.8.

3 The assembly in bridge site3.1 Assembly of cantilever

Parts 11, 13, 15 and 17 comprised the upstream cantilever, and

parts 12, 14, 16 and 18 comprised the downstream cantilever. Those

cantilevers are welded together on the ground due to the lifting

capacity. The first 3 panel have one transversal slope valued A, the

fourth panel has a another transversal slope valued B, one steel wedge

with a slope of A+B is putting under the fourth panel to let the first

three panel putting on the horizontal position during assembly. Fig. 9

shows the assembly jig for cantilevers.

3.2 Assembly of the middle box section

2 mm, 5 mm, 8 mm and 10 mm steel shims are applied on the

top of the jig supports to slightly adjust the elevation of the parts. The

Fig.6 Assembly of lower box

(a) (b)

Fig.7 (a) Bottom panel putting on the platform,

(b) Internal jig and two web panel assembled on the bottom panel

Fig.8 Assembly of upper box

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assembly jig is shown in Fig.10. The welds connecting deck plates are

single V joint with steel backing, multi-process welding procedure is

applied. SMAW or FCAW process for the root pass and SAW process is

applied for the filling and capping passes. The welds between the lower

box and upper box shall be weld symmetrically.

3.3 Assembly of the completed segment

Cantilevers are lifted to the middle box section by portal crane. The

assembly jig is shown in Fig.11. The whole segments is delivered by

barge and lifted by derrick crane which is fixed on the bridge.

4 ConclusionIn the paper is briefly explained the fabrication and assembly

process of Sava bridge. Safe and reliable assembly jigs are applied and

European standards are strictly followed during the whole process. The

main steel structure finished erection in the end of 2011.

Fig.9 Assembly jig for cantilevers

Fig.10 Assembly jig for the middle box section

Fig.11 Assembly jig for the completed segment