Temburong - IABSE 2014

8/9/2019 Temburong - IABSE 2014

1/16IABSE Madrid Symposium Report, Vol. 102

37th IABSE Symposium Madrid 20141971

Temburong Bridge, Brunei A new 30 km road link

Fig. 1: Layout Plan of Temburong Bridge

Temburong Bridge, Brunei – A new 30km road link

Steve KITE Associate DirectorArupHong Kong

[email protected]

Kok On YEEDirector of RoadsPublic Works DepartmentBrunei [email protected]

Naeem HUSSAIN Fellow & DirectorArupHong [email protected]

Kok Kong CHIN Managing PartnerOve Arup dan Rakan RakanBrunei [email protected]

Sammy YIP AssociateArupHong Kong

[email protected]

Murphy TOAssociateArupHong [email protected]

Summary The new 30km Cadangan Projek Jambatan Temburong (Temburong Bridge Project) in Brunei willconnect the relatively isolated district of Temburong with the more developed Brunei -Muaradistrict. Improved connectivity will enhance the movement of labour, goods and services to andfrom Temburong, and will facilitate the development of eco -tourism in the area.

The paper describes the objectives of the project, the project planning, the procurement strategy andthe design for the various structures. Details are provided on the overall design criteria followingEurocodes, the seismic analysis, and the construction planning.

Keywords : project planning, sea -crossing, procurement, Eurocodes

1. Introduction Temburong District is isolated from the rest

of Brunei by the Brunei Bay to the north,and Malaysian state of Sarawak to the south,east and west. Its only land - based access isthe road that passes through Limbang,Sarawak. Its isolated location and lack ofconnectivity with the main commercialdistricts of Brunei and the associated portand airport infrastructure essential for globaltrade and commerce has constrained theeconomic growth in the district.

The Cadangan Projek Jambatan Temburong(Temburong Bridge Project) in Brunei will

connect Temburong with the moredeveloped Brunei -Muara district. Improvedconnectivity will enhance the movement oflabour, goods and services to and fromTemburong, and will facilitate thedevelopment of eco -tourism in the area.

The new 30km link will comprise 14,6kmlong marine viaducts and cable stayed bridges across Brunei Bay, 12km of elevated structuresacross the Temburong peat swamp forest and a small area of mangroves, and approximately 3,6kmroad in Brunei -Muara district where 3 lengths of tunnels are required as well as at -grade roads andviaduct ramps to link with the existing road network. The construction is planned to commence in2014 with completion targeted in 2018. The key challenges include very soft ground conditions,

shallow waters, difficult access, lack of local raw materials and the required fast -track programme.




2. Objectives of the Project The new link will bring significant socio -economic benefits to Brunei. These include: Providing a road transport link for the movement of labour, goods and services to and from

Temburong, hence encouraging more business activities and development there.

Allowing direct movement of international visitors into Brunei and onwards to Temburong,which has been earmarked as Brunei’s centre for eco -tourism. Potential tourism clusters can bedeveloped that include not only Brunei but also surrounding Malaysia, by developing packagesthat provide a range of locations and sights within the one visit. This has downstream effects toBrunei tourism sector as a whole including the national airline, hotels and restaurants which

potentially could capture a wider tourism market that visits Temburong and onwards to otherareas.

Increasing mobility of the workforce so that more citizens can settle in quiet Temburong and yetwork and enjoy leisure time in the capital or other parts of Brunei. Over time, it is expected thatthe link will allow a resident population within Temburong to establish and grow with itcommercial and industrial sectors and the necessary social infrastructure such as medical andeducational facilities. This will potentially result in greater social and economic development

for Brunei as a whole. Providing easy land transport from Temburong to the port in Brunei -Muara, or to the shops and

markets in other districts of Brunei. At present, farmers in Temburong practice subsistenceagriculture rather than commercial agriculture. Temburong can be transformed into thecountry’s source of commercial agriculture to help diversify the country’s oil - based economyand help in reducing food commodity imports.

Providing a strategic link to allow Brunei emergency response teams to be dispatched toTemburong quickly, or vice versa.

3. Project PlanningThe Government of Brunei Darussalam hasrecognised the geographical separation and lackof connections to and within Temburong whichhave constrained development and growthwithin the district and development of its fullsocio -economic potential. In 2010, Arup wascommissioned to carry out the feasibility studyto provide a road and bridge link between thedistricts of Brunei -Muara and Temburong.

A route selection exercise was carried out todetermine the most favourable route acrossBrunei Bay as well as the optimum connection

points in both Brunei -Muara and Temburongdistricts. The route selection study took intoaccount a comprehensive range of criteria,including transport planning, engineering, landmatters, environmental issues, impact on localcommunity, programme and cost. During thisexercise, land use [1] and environmentalinformation were collected in GeographicalInformation System (GIS, see Fig. 2 forscreenshots) to better understand therelationship between alignment options andvarious constraints. Stakeholders were alsoconsulted to understand their opinions and other

constraints. After the route selection exercise, more in -depth engineering assessment, cost estimation and cost -

Fig. 2: Alignment options and environmentalconstraints from GIS model




benefit analyses were carried out. The conclusion of the feasibility study was that the Project istechnically feasible, economically viable and that the environmental impacts can be managed ormitigated and hence acceptable.

Following the feasibility study, the Government decided to proceed with the construction of thelink. In early 2013, the Government engaged Arup to carry out detailed design and support services

for the procurement of the Project, including the prequalification and tendering processes,management of the construction contracts and other associated engineering support.

4. Procurement Strategy In order to achieve the target opening date of 2018 for the project, a fast track approach is essential.Delivering the project on a fast track basis requires innovative contract packaging and phasing ofworks. Activities which might traditionally be carried out sequentially are carried out in parallel andthe schedule is managed to focus on critical path activities and give priority to constructionactivities that take the longest time.

4.1 Procurement Arrangement The Project is being procured as a traditional engineer -design, contractor -construct arrangementunder various contract packages. It is intended that all these construction contracts will be procured

by selective tendering method. Prequalification will be adopted, and the subsequent tender for thecontracts will be invited from prequalified tenderers only. The prequalification and tendering

process will be separately carried out for each construction contract.

4.2 Contract Packaging The civil works for the project is divided into six construction packages in order to enhancecompetition and permit an early start to the construction works. This also gives more opportunityfor local contractors to be involved in contracts suitable for their skills and experience.

The current division of the work is outlined in Fig. 3 below:

Fig. 3: Layout plan of Contract Packages

The main features of the packaging are: Contract CC2 is exclusively 50m span typical viaducts. This is relatively more straightforward

to design than other components, and can therefore be tendered on a fast track basis. This isimportant because it will take considerable time to construct the large numbers of spans.

Contract CC3 brings together both of the navigation bridges. These will take longer to design but because the total quantity of construction work is less than Package CC2 it can be built in ashorter time.

Contract CC4 involves the construction of structure across peat swamp forest of highecological value. The findings of environmental impact assessment and ground investigationare crucial for design. These started in 2013 and hence CC4 is procured at a later date.




Table 1 below summarises the key contract scope in more details:

4.3 Tender and Construction Programme In order to achieve the target date, the programmed construction period is 45 months. This isgoverned by Contract CC2 Marine Viaducts. Therefore this package was tendered first. It wasestimated that Contract CC3 and CC4 would each take 36 months to construct. These packages aretherefore tendered in a second wave. By staggering the various contracts, the project procurementteam and bidding contractors can focus on each tender one at a time.

Fig. 4: Tender and Construction Programme (as of February 2014)

Table 1: Summary of Contract Packages

Contract Key Contract Scope Length

CC1A – Mentiri Interchange

Grade-separated connection to Jalan Utama Mentiri. Interchange

CC1B – Mentiri Tunnels

Tunnels across Mentiri Ridge; At-grade roads and viaducts between tunnels.

about 3,6km

CC2 – Marine Viaducts

Marine viaducts in Brunei Bay Turnaround facility at Pulau Baru-Baru; Provision for future connection to Pulau Berambang.

about13,4km

CC3 – Navigation Bridges

Navigation bridges across the Brunei Channel andEastern Channel;

Viaducts between tunnel portal and Brunei Channelnavigation bridge;

Connecting ramps to Jalan Kota Batu; Administration building at Jalan Kota Batu.

about 1,1km(and sliproads)

CC4 – Temburong Road

Land viaducts and river crossing bridge; Turnaround facility; Reconfiguration of Jalan Labu at connection point.

about11,8km

CC5 –

Traffic Control andSurveillance System Route -wide traffic control and surveillance systems. Route -wide




Fig. 7: Rendering of Brunei Channel Bridge

minimises the amount of in -situ concreting and more importantly, the narrow gap would facilitatethe delivery of material such as precast segments on the erected deck.

5.2.2 SubstructureDue to the shallow water, dredging or temporary access bridge will be required to gain access to

carry out piling works. A number of foundation options were studied. Bored piles were initiallyconsidered but to achieve the required programme and to minimise cost, it was decided that driven piles would be adopted instead. Three types of piles are used:

(1). Majority of the piles will be 1m diameter concrete spun piles, which are precast circularhollow sections with high density concrete achieved by spinning during the manufacturing

process.

(2). Steel tubular piles of 1m diameter are adopted for locations where hard materials are shallow.(3). Steel tubular piles of 1,6m diameters are adopted at piers subject to higher ship impact forces

near the navigation channels

To construct the piles rapidly, it is envisaged that contractors would drive the full length of 30 to70m long piles in one piece on site. This will require the use of large piling rigs on barges.

The soffit of pile cap will be above the Mean High High Water level for ease of construction. The pier columns are solid for short piers and hollow for piers taller than 5,5m. To simplifyconstruction, there is no pier crosshead and the deck will sit on the pier columns.

5.2.3 ArticulationOne of the key drawbacks of the use of concrete spun piles is that they have limited capacity toresist bending and can behave in a brittle manner. Compound with the fact that the groundinvestigation information would not be available until a late stage during detailed design, the designteam decided to use high damping rubber bearings for all the bearings of marine viaducts. Not onlythis reduces the seismic force on the foundations, it also reduces the sensitivity of the design to theground conditions.

5.3 CC3 Navigation Bridges There are two navigation channels in Brunei Bay, namely Brunei Channel and Eastern Channel.Each channel will be crossed by a cable stayed bridge. The Brunei Channel Bridge will be agateway between the Brunei -Muara and the Temburong districts and hence designed as an iconic

bridge. The Eastern Channel Bridge will follow a similar form.

To cater for future navigation needs of trade andnavy vessels, Brunei Channel Bridge will have amain span of 145m with the soffit level at about23m. The Eastern Channel Bridge will cross aninternational waterway with a main span of 260mand the soffit level at about 34m. Both bridgeshave a concrete ladder beam deck whichcomprises two edge girders and cross beams

between the edge girders, with concrete slabspanning between the cross beams. Foundationswill be 2,2m diameter concrete bored piles.

The concrete pylons are designed to be uniqueand instantly recognisable with gateway qualitiesand incorporating Islamic architectural features.

The design of the two cable stayed bridges are discussed in further details in another paper [2].

6. Design Criteria In Brunei, bridges used to be designed to British Standards. In this project, it was decided thatEurocodes, with UK National Annex where relevant, would be adopted. A project -wide Master




Design Criteria has been established to clarify how the Eurocode rules shall be applied in thedesign, and supplemented with additional project specific criteria where necessary to cover issuessuch as seismic action, wind climate and ship impact.

The main loading considered are briefly described below:

1) General actions – Dead loads and superimposed dead loads are implemented in accordance withthe relevant parts of Eurocodes and the UK National Annex.

2) Traffic action – The UK National Annex traffic action is adopted as other bridges in Brunei have been designed for UK Highways Agency BD37 loading previously. This ensures that the bridgesin the transport network are designed for similar loading.

3) Wind action – A site -specific wind climate assessment was carried out based on historic data.Considering the thunderstorm phenomenon which could lead to sudden burst of high windspeed, the 10 -minute wind speed with mean return period of 50 years is conservatively taken as26m/s at 10m above mean sea level.

4) Thermal action – A statistical analysis of historical data was carried out and the maximum andminimum air shade temperatures are 40

°

C and 15°

C respectively.

5)

Action during execution – This is specified for each type of structure. In particular, parts of themarine viaduct substructures and the cable stayed bridges are governed by the execution stageloading.

6) Accidental action –The cable stayed bridges are designed for sudden rupture of stay cables and50MW gasoline spill fire on bridge carriageway. Ship impact is discussed further in section 6.1.

7) Seismic action – A site specific probabilistic seismic hazard assessment was carried out forBrunei to establish the bedrock seismic response spectra. Seismic analysis and design arediscussed further in section 6.2.

6.1 Ship impact Apart from the two navigation channels described in section 5.3, the rest of Brunei Bay is very

shallow. Current vessel movements are very scarce in the Bay, with the largest vessel recorded being 36m long. Despite that there is no known plan for future port development, a larger 80m longrivertrade vessel was selected as the design vessel to safeguard future development opportunities.

The bridges are designed for ship impact in accordance with BS EN1991 -7 [3]. As there isgenerally no specific rule on the probability based analysis in this standard, the methodology inAASHTO (American Association of State Highway and Transportation Officials) GuideSpecification and Commentary for Vessel Collision Design of Highway Bridges [4] was adopted tocarry out the probability based risk assessment. A large number of vessels was assumedconservatively such that the design ship impact forces are essentially established in a deterministicway. For piers further away from the navigation channels, vessel collision associated with driftingvessels at the speed of water current has been considered for robustness.

6.2 Seismic analysis and design Based on the probabilistic seismic hazard assessment, it can be established that Brunei is a lowseismicity region based on the definition in BS EN1998 -1 [5]. Despite this fact, considering theimportance and scale of this project, seismic design is essential.

Seismic analysis and verification have been carried out in accordance with BS EN1998 -1 and BSEN1998 -2 [6]. The ground comprises thick layer of soft material and is hence classified as Type S,which means that site specific response analyses are mandatory to establish the grounddisplacement and design seismic response spectra (see Fig. 8).

The bridges are designed for two performance levels - Ultimate Limit State with 975 -year return period earthquake and Structural Integrity Limit State with 2475 -year return period earthquake. Inorder to achieve this, the analysis and verification rules in Eurocode 8 are followed for the 975 -yearearthquake. Additional checks are then carried out for the 2475 -year earthquake to ensure that thereis no brittle failure of non -ductile structural elements and no unseating of superstructure.




Fig. 8: Bedrock and design response spectra

7. Conclusion The new 30km Cadangan Projek Jambatan Temburong will facilitate the development ofTemburong and Brunei as a whole. During the project planning stage, a comprehensive feasibilitystudy was carried out. Several route options were studied and an optimal solution was chosenconsidering a wide range of criteria. The conclusion was that the Project is technically feasible,economically viable and that the environmental impacts can be managed or mitigated.

To achieve the opening target date, an innovative procurement strategy and contract packaging has been adopted to achieve a fast track programme. The marine viaduct construction is critical to thedelivery programme and has been designed in such a way that maximise the use of precast elementsto minimise the construction time. The solution is precast concrete box girder erected by span - by -span launching method with the use of driven concrete spun piles or steel tubular piles. To make the

bridge an iconic structure in Brunei, the two navigation channels will be crossed by two cable -stayed bridges with unique concrete pylons that incorporate Islamic architectural features.

The Project is one of the first major projects in East Asia that is designed to Eurocodes.

8. Acknowledgements This paper has been published with the permission of the Public Works Department, Ministry ofDevelopment, the Government of Brunei Darussalam.

References [1] DEPARTMENT OF TOWN AND COUNTRY PLANNING, National Land Use Master

Plan 2006 -2025 , Ministry of Development, Brunei Darussalam, November 2008.[2] HOOTON M., SALIM M., CARLUCCI A., YIP S., MONEYPENNY K., KITE S.,

“Temburong Bridge, Brunei: Design of two cable stayed bridges”, IABSE Symposium Madrid 2014: Engineering for Progress, Nature and People , September 2014

[3] BS EN1991 -7:2006, “Eurocode 1: Actions on structures - Part 1 -7: General actions –Accidental actions”, 2006

[4] American Association of State Highway and Transport Officials, “Guide Specification andCommentary for Vessel Collision Design of Highway Bridges”, 2nd Edition, 2009

[5] BS EN1998 -1:2004, “Eurocode 8: Design of structures for earthquake resistance — Part 1:General rules, seismic actions and rules for buildings”, 2004

[6]

BS EN1998 -2:2005 + A2:2011, “Eurocode 8 - Design of structures for earthquake resistance- Part 2: Bridges”, 2005 Incorporating corrigenda February 2010 and February 2012

0

0.5

1

1.52

2.5

3

3.5

0 1 2 3 4 S p e c t r a

l A c c e

l e r a t i o n

( m / s 2 )

Period (s)

Bedrock response spectra

975 year

2475 year

0

2

4

6

8

10

0 1 2 3 4 S p e c t r a

l A c c e

l e r a t i o n

( m / s 2 )

Period (s)

Design response spectra (Brunei Bay)

975 year

2475 year




Temburong Bridge, Brunei Design of two cable stayed bridgesTemburong Bridge, Brunei - Design of two cable stayed bridges

Martin HOOTON Associate

ArupLondon, [email protected]

Hj Mazlan Abd SALIMSenior Executive Engineer

Public Works DepartmentBrunei [email protected]

Alberto CARLUCCISenior Engineer

ArupLondon, [email protected]

Sammy YIP Senior EngineerArupHong Kong

[email protected]

Kelvin MONEYPENNYSenior EngineerArupLondon, [email protected]

Steve KITEAssociate DirectorArupHong Kong

[email protected]

Summary The Temburong Bridge Project is a 30km long dual two -lane highway crossing over the BruneiBay. It will connect the relatively isolated Brunei district of Temburong to the other three Bruneidistricts. The main objective of the project is to stimulate economic growth in the Temburongregion by connecting it to the country’s airport and ports. The alignment crosses two navigationchannels resulting in the need for two cable stayed bridges – the Brunei Channel Bridge (145mmain span) and the Eastern Channel Bridge (260m main span).

The design of these cable stayed bridges is one of the first applications of the Eurocode to a fullyconcrete cable stayed bridge. Both cable stayed bridges draw on strong Islamic architecturalinfluences from the region to form a tower shape that is unique and instantly recognisable.

Keywords: Cable stayed bridge, concrete ladder beam deck, sea crossing, Eurocodes.

1. Introduction The Brunei district of Temburong is separated from the other three Brunei districts by the BruneiBay and Malaysian state of Sarawak. The journey time between Temburong and the rest of Bruneican take several hours by road through Sarawak, else, the journey can be made by boat across theBrunei Bay. This separation has limited the potential economic growth of Temburong compared tothe more prosperous Brunei -Muara district. The Cadangan Projek Jambatan Temburong(Temburong Bridge Project) is a proposed 30km long dual two -lane highway project to connectTemburong and Brunei -Muara, thus giving Temburong an economic boost from direct highway

access to the country’s airport and ports. Theconstruction is planned for completion in 2018.

The whole crossing comprises of a 14.6km longmarine viaduct, 12km long section of elevatedstructure over peat swamp forest, 3km of tunneland several kilometres of highway at grade.Further description of the project is given in [1].

There are two navigation channels along themarine section of the crossing – the 130m wideBrunei Channel and the 235m wide EasternChannel. To cross these channels cable stayed

bridges will be constructed, with main spans of145m and 260m respectively. These two cablestayed bridges are the subject of this paper andare here in referred to as the Brunei ChannelBridge (BCB) and the Eastern Channel Bridge(ECB). Figure 1: Site Plan of Temburong Bridge




As a result, the tendons are positioned closer to the centroid of the girder than to the bottom surface but this, rather than inconvenient, was a clear actuation of the Eurocode design strategy.

In Eurocode 1992 -2 [3] Section 7, for post tensioned concrete structures exposed to a marineenvironment, all tendons under the Serviceability Limit State frequent combination shall remainwithin the compression zone with a margin equal to at least cmin,dur to the neutral axis, and that for

the same combination the crack width shall belimited to 0.2 mm. In conjunction with thetuning of the stay cables, positioning thetendons close to the centroid of the sectionhelped to satisfy the decompressionrequirement and it was found that theirefficiency was improved if, within the samecombinations, the maximum tensile stress atthe surfaces of the beam was kept below themean tensile strength of the concrete, f ctm. Inthis case, the code allows the designer toconsider the section uncracked for the purposeof stress calculations, which implies that byremaining uncracked, the entire section is effective and the neutral axis is kept closer to the surface.In addition, given that the section can be considered uncracked, the required crack width check isautomatically satisfied and the demand of additional passive reinforcement at the surfaces wasmainly governed by the Ultimate Limit State capacity checks both in service and, in particular,during construction.

Close to the tower, where there are not any tendons in the edge girders, the member can beconsidered in those regions as ordinary reinforced concrete element and therefore the durabilitycrack width check has to be carried out for the SLS Quasi Permanent combinations, which inaccordance to the code do not include any traffic live load. As a consequence, in those regionswhere there is a substantial axial compression due to the horizontal component of the stay cable

prestress forces, the sections are uncracked under the above combinations and so, again, thedurability crack width requirement is automatically satisfied with the passive reinforcement onlygoverned by capacity requirements. The deck has a 250mm thick slab which spans between the crossbeams and within the effectivewidth acts in composite action with the crossbeams in one direction and with the edge girders in theother.

At their ends, the bridges have solid diaphragms sitting over the bearings and thus also acting ascounterweight by eliminating undesirable bearing uplift.

In both bridges the deck is integral at the towers through a torsionally resistant hollow boxcrossbeam which becomes a solid diaphragm at the tower joint.

6. Tower Design The tower is the unique element of this pair of cable stayed bridges. It is inspired by Islamicarchitecture with the objective to be instantly recognizable.

The side legs have a curved tapering shape in the front view from the deck, while they are linearlyreducing in section when viewed from the side elevation. The side faces of the tower, perpendicularto the bridge axis, are slightly curved in a way to reduce the perception of its mass and at the sametime to be consistent with the curvilinear architectural language. The tower legs are connectedabove the deck with a recessed infill wall which terminates with an Islamic arch. The arch is framedwith a ribbed feature that originates from the pile cap kicker level and then tapers out reaching themaximum width at the crown of the arch. This element is strong with symbolism as each of the fourribs represents one of the four districts of Brunei. Above the arch there is a long window slot in theinfill wall, which allows sun -light to filter through the tower and lighten the appearance of the frontelevation. The four ribs and the slot above them signify the unification of four districts into one bythe project bridge link. The symbols of the moon and the star mounted on top of the tower are thecrowning features.

Figure 7: Deck Edge Beam Section




structure belongs. A comparative study of built structures that were clearly flexible was carried out.The conclusion was that a structure can be considered flexible when the application of the stayforce to the final stage model was within the allowable tolerance and resulted in a deflection morethan or equal to the allowable vertical deck tolerance, i.e. it can be easily measured. Both Brunei

bridges satisfied this rule and therefore the principles of EN1993 -1-11 could be applied. Inaccordance to section 5 of that code, (G+P) was taken as equal to Self Weight + Super -imposedDead Load + Creep + Shrinkage + Stay prestress, all measured and confirmed at the time of handover by reference to the actual stay loads and the actual achieved deflections. The (G+P) case wasthen factored at ULS with factors 1.35/0.95 (or better still with the weighted factors which considerthe different SDL factors in the UK NA) with the residual creep and shrinkage from handover totime infinite factored at ULS with factors 1.2/0.0.

Saddles were chosen at the tower so as to avoid the need for an inspection access route throughoutthe full height of each tower leg, which would have been necessary for an anchorage system. Thisresulted in more compact and aesthetical appealing towers. Modern cable saddles address thecorrosion protection requirements of the stay cable system and do not limit the multi -strandadvantage of individual strand replacement. Asymmetrical frictional loads transferred to the towerare taken up through the strand and the allowable magnitude of this force was checked against therather conservative Coulomb friction formula reported in the section 6 of BS EN 1993 -1-11.

fr M e

F

F

Ed

Ed ,

2

1max

(1)

Where F Ed1 and F Ed2 are the design values of the force respectively on either side of the saddle, μ isthe coefficient of friction between cable and saddle, is the angle in radians, of the cable passingover the saddle and is the partial factor for friction.

Following the normal saddle design approach, a similar check was also introduced at theServiceability Limit State in order to prevent a sudden slippage of the saddle in service.

8. Construction For concrete deck cable stayed bridges, particularly those that adopt saddles in the tower, theconstruction sequencing of the deck is critical to achieve an economical design and stability duringconstruction. The following construction sequence has been assumed in the design as no contractorhas been appointed at the time of writing.

8.1 Tower construction The tower construction sequence is conventional, but with additional complexities due to the shapeof the towers. The tower legs can be cast in constant height lifts of approximately 4m with a jump -formwork system capable of adapting to the tapering cross section. The ribs on the inside of the legsform a constant sized feature within the leg formwork to a point above deck level where the ribsstart to grow in size. At this point the arch ribs are cast separately and the leg casting continues upthe tower. Due to the inward inclination of the tower legs, the two legs are connected withtemporary horizontal struts at regular intervals. These struts can also be used to assist the casting ofthe infill concrete wall that spans between the tower legs. Once the infill wall is cast between thetower legs the final task is to cast the growing rib feature above deck level.

8.2 Deck construction A cast in -situ deck cycle was developed to avoid additional materials to those required for the in -service condition of the bridge. For both cable stayed bridges, the first portion of the deck from thetower to the first stay is cast on falsework supported by the wide tower pile cap. For the furthersegment casting a balanced cantilever erection cycle is proposed. The sequence is that travellerforms are launched forward, simultaneously or sequentially, into position to cast the new segments,then all segment reinforcement is fixed and the cable stay anchors, stressing anchors and ducts areinstalled. The stay cable is then installed and subject to a first stage of prestressing against theformwork. Portion 1 (Figure 10) of the east and west segments are cast, and afterwards Portion 2,


16/16


and in both cases simultaneously or sequentially. Finally the second stage of stressing of the staycable from both ends is performed after having been released from the formwork system.

Figure 10: Deck casting sequence

This sequence will allow the contractor flexibility to cast the two ends of the cantileversindependently and sequentially on the condition that the cantilevers are not out of balance by morethan 50% of the deck segment weight acting with the same lever arm. 100% deck segment out of

balance was not possible as it resulted in an uneconomical deck and tower, with greater likelihoodof saddle slip during construction.

The adoption of temporary buffeting cables between the deck and the tower pile cap are assumed inthe design for the following benefits:

- reduction in wind buffeting response of the bridge during construction, in particular at themaximum extent of the balanced cantilever construction;

- reduction in the unbalanced bending moment in the tower legs due to differential weight ofcantilevers can be compensated with the prestress of the buffeting cable.

9. Conclusions When built, the Brunei Bridges will be landmark and iconic structures for Brunei.

The towers are the most recognisable elements and, whilst having an apparent complex geometry,they have been designed with conventional and well established structural solutions and means ofconstruction. The bridges show evident similarities, both in the towers and in the ladder beamdecks, and this led to an improved design efficiency by adopting a parametric procedure of analysiswhile common detailing is expected to bring benefits during the construction.

These bridges have been one of the first applications of Eurocode to the design of a fully concretecable stayed bridge.

10. Acknowledgements This paper has been published with the permission of the Public Works Department, Ministry ofDevelopment, the Government of Brunei Darussalam.

11. References [1] KITE S., YEE K.O., HUSSAIN N., CHIN K.K., YIP S., and TO M., “Temburong Bridge,

Brunei – A new 30 km road link”, IABSE Symposium Madrid 2014: Engineering for Progress, Nature and People , September 2014

[2] BS EN 1991 -2, “Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges”, 2003[3] BS EN 1992 -2, “Eurocode 2: Design of concrete structures - Part 2: Concrete bridges –

Design and detailing rules”, 2005

[4] BS EN 1993 -1-11, “Eurocode 3: Design of steel structures - Part 1 -11: Design of structureswith tension components”, 2006

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