all other spans will be cast using conventional scaffolding.Construction of the US$100 million bridge is due to begin this year, with a 2011

targeted completion date. Although working to a tight timescale, WSP engineers havebeen able to run multiple intensive analyses of the structure in every construction stageas well as its built condition.

Features of the Bentley’s RM Bridge software include linear and non-linear structuralanalysis and construction engineering. WSP Finland chose the software for its accuracyand dependability in stage-by-stage erection of concrete cable-stayed structures. Ithelped engineers address a full spectrum of structural, material, performance, andconstruction issues. The WSP team also used the specialised RM Bridge Addconapplication to optimise the stressing sequences of stay cables through linear and non-linear analysis.

The team of 25 first created a space frame model for static analysis of the bridgesystem and from there began a range of analyses to help optimise the structure. Designloading and combinations were applied in accordance with AASHTO LRFD andVietnamese 22 TCN-272-01 bridge design specifications. Permanent loads, trafficloads, wind loads, temperature changes and settlements were calculated, applied andanalysed. Tests and simulations helped the team plan for the effects of a host of possibleevents, such as ship collisions or earthquakes: the bridge is required to withstand anearthquake of magnitude six. RM Bridge was also used to determine and design forcreep and shrinkage over time.

WSP found the application of the software’s 4D modelling capabilities to be highly

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Using Bentley’s RM Bridge software to model every stage of constructionhas completely changed WSP Finland’s philosophy of analysing bridges,says head of bridge division, Sami Niemelä. The software allows theengineers to work in four dimensions, taking account of the effect of timeon structural behaviour during construction of bridges, including a new

cable-stayed crossing in Da Nang. “We can now accurately analyse the construction ofthe bridge in a realistic, beginning-to-completion sequence, stage by stage,” he says.

Da Nang city is a key commercial port on the South China Sea in central Vietnamand is one of the country’s four main municipalities. For centuries it has been host tovisitors from around the world and is a hub in an area known for its natural beauty andWorld Heritage landmarks. The city announced a design contest in 2007 for the newNguyen Van Troi – Tran Thi Ly Bridge over the River Han.

The chosen design is by WSP Finland, with Esko Leppäluoto as lead designer. It is aconcrete cable-stayed bridge with a backward-inclined tower and features striking twin-spiralled back cable arrangements that tie to an open park area on the western side.Visitors to the riverside park will pass under the bridge and from there gain access tothe main tower, where they can take an elevator running at an angled, 12° approach tothe top of the inclined tower. There, a glass-enclosed observation platform 145m overthe river will offer 360° views of the port city.

The six-lane bridge will be 731m long and 34.5m wide, with a main span of 230m.Although designed primarily for vehicular traffic, it will also accommodate pedestrianswith two 3.5m-wide footpaths. Cantilevered construction is proposed for the main span;

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A Vietnamese cable-stayed bridge has been modelled in four dimensions, taking every stage of construction into account

in the analysis

DRAMA IN DA NANG

The twin cable arrangements tie into the western abutment

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effective. This incorporates the time dimension in the construction engineering, allowingengineers to model the entire cantilevered construction sequence. The stage-by-stageanalysis enabled the team to determine long-term effects on materials including creepand shrinkage and cracking of the concrete.

“This capability has categorically changed our philosophy of how we analyse bridgesfor construction,” says Niemelä. “In the past, we concentrated on calculating the finalstage – the bridge in service – and would then work backwards, segment by segment,using rough calculations to estimate creep and shrinkage. You always question to somedegree whether the estimate is sufficient. RM Bridge has changed all that.”

The team can now carry out accurate analysis stage by stage in a sequencespanning from the beginning to completion. “The software performs intensivecalculations that would be impossible to do by hand,” he says. “Using RM Bridge, I havea high level of confidence in our design.” The model can also be used in construction.The software can perform calculations at each cross-section at any point inconstruction, stating the moments and calculating the stresses, he adds. Material andstructural conditions can be analysed in real-time at any stage.

Designers used the optimisation tool in the design of stay cable tensioning. The mainspan cables are in a single plane along the centre line of the bridge, while the backcables, twisted into a wing-like arrangement, are anchored on both sides of the bridgeoutside the deck, parallel to the river bank.

The cables penetrate the tower, giving the simplest force transfer from main spancables to back span cables and to the tower. RM Bridge was used to design strengthlimit states taking account of combined flexure and axial forces, shear and torsioneffects. Service limit states for maximum stress in the reinforcement were alsocalculated and used for crack-width checks.

Bentley Systems says that its RM Bridge software enables users to develop andanalyse a consistent bridge model in a continuous cycle, which substantially reduces thetotal engineering time required. The information is seamlessly reused, refined, andreprocessed across the design, engineering, and construction phases, avoiding the need

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© 2010 Bentley Systems, Incorporated. Bentley, the “B” Bentley logo, and LEAP are either registered or unregistered trademarks or service marks of Bentley Systems, Incorporated or one of its direct or indirect wholly-owned subsidiaries. Other brands and product names are trademarks of their respective owners.

Bridge Information Modeling – It’s everything to do with the bridge.Bridge Information Modeling (BrIM) is a compelling new methodology for project delivery that dramatically improves bridge quality and reduces risk. Using the Bentley bridge solution for BrIM, engineers develop and employ an unprecedented depth of information about the bridge as they streamline the entire bridge development process, design through construction engineering.

Join the world’s top engineering consultancies. Choose the Bentley bridge solution for BrIM – and the satisfaction of delivering safe, sustainable bridges on time and on budget.

Only Bentley can take you there. www.bentley.com/BrIM

for repeat input of information.The software system has been designed as a comprehensive tool specifically for

bridges that can streamline analytical tasks. The software has been developed by bridgeengineers directly engaged on projects including the major long-span cable-stayedcrossings such as Stonecutters Bridge and Sutong Bridge.

RM Bridge is a family of integrated software applications developed to allow usersto solve engineering or construction problems in a single engineering environment.Specialised applications offer analysis of cable sagging, wind dynamics, largedeflections, wind tunnel simulation, erection control, cantilevered construction,incremental launching and rolling stock. A new tool soon to join the family is RM BridgeCast, for segment-by-segment casting and fitting of precast bridges ■

Different stages of the construction can be modelled in RM Bridge.