Curved Girder Analysis

Selected Applications

Curved Girder Analysis

Composite deck modelling options
Viewing results in deck, girders or cross frame bracing
Slice sectioning facility highlighted

In the USA the use of curved girder bridges has steadily increased year by year and is now estimated to represent 25 percent or more of the entire steel bridge market. With curved girder structures significant torsional stresses must be accounted for at the design stage and careful consideration is also required to ensure their safe erection. To arrive at meaningful results for curved girder bridges grillage-based analyses are not sufficient. Full 3D modeling and analysis is required to accurately model the beams and, in particular, to derive the tension and compression forces in the ‘K’ or ‘X’ frame bracing members.

LUSAS Bridge is ideal for curved girder analysis and has many useful modelling and results processing features to help you optimise your design.

Composite deck modelling

Unlike some analysis systems LUSAS Bridge allows you to idealise your composite deck/curved girder structure in a number of ways:

The choice of which modelling idealisation to use depends upon what is required from the results of the analysis. For instance, if a curved girder analysis is being performed and the lateral forces in the top and bottom flanges are required then the shell element modelling and beam element modelling of flange idealisations would be suitable but the beam element modelling of the whole girder would not. Complete 3D modelling of a curved girder structure including cross frame bracing allows the tension and compression in these members to be obtained. This cannot be achieved using 2D grillage models.

Shell element modelling of the whole deck.	Beam element modelling of flanges.	Beam element modelling of the whole girder.

With this modelling method discrete features are defined for the top flange and slab because their materials are not identical. The slab has an eccentricity to define a bending plane that is not coincident with the top flange and these two components are combined using an equivalence attribute.	With this, the shell elements representing the top and bottom flanges of the girder are replaced by beam elements running along the top and bottom of the girder with the appropriate properties for the flange members.	With this, the girder is replaced with a single beam element having appropriate geometric properties and an eccentricity to offset the bending plane of the beam from the deck.

Some common questions...
Can LUSAS accommodate varying widths and thicknesses of flanges?

YES - Geometric dimensions and properties can be varied to exactly match your proposed design.

Can slab and girder connections be modelled as rigid connections; or with an interference mesh between the slab and the girder; or can individual shear studs even be modelled if thought necessary?

YES - Unlike some analysis systems LUSAS Bridge allows you to idealise your composite deck/curved girder structure in any way you wish.

Can LUSAS model areas of cracked concrete - such as may occur in regions of slabs around and over supports?

YES - The cross-sectional properties of your structure can be varied along the bridge deck.

Can LUSAS handle staged erection analysis?

YES - Elements in your model can be deactivated and re-activated to mimic the erection process and show stresses and forces induced during the construction process.

Can I load LUSAS models with arbitrary truck loading?

YES - Vehicle loading can be manually assessed or the Autoloader vehicle optimisation facility will assess worst case loading patterns for any point on your structure. LUSAS deals with this as standard.

3 span curved girder bridge with HS20 loading on span 1

Circumferential bending moment contours in deck

Can I isolate parts of my model for more detailed results processing?

YES - The useful group facility allows you to break down your model into named components and this allows selective display of model features or for isolated viewing of particular results.

Girders isolated for results viewing

Can I slice through my model to get results at selected points?

YES - A slice section facility allows forces and moments to be obtained at any chosen location on 3D beam and shell models and is of particular use for curved girder analysis. It allows slice sections to be defined at user-specified distances along the deck or along individual girders. Slice sections are visualised, labelled on the model, and results are written to a results window for creation of force and moment diagrams if required.

Slice sectioning at cross frame positions along an edge beam

Can I see the tension and compression forces in the cross frame bracing members?

YES - Diagrams of axial force in beam elements can be easily plotted to assist you with the design of your bracing.

Axial forces in cross frame bracing members

Any modelling and analysis capabilities described on this page are dependent upon the LUSAS software product and version in use.