Steel-concrete composite deck design for the Piano delle Rose viaduct

• Modelling of a 4-span viaduct with a curved deck

• Steel and composite deck design to the Eurocodes

• Fast and excellent optimisation of steel and reinforcement quantities

Overview

LUSAS bridge analysis software and PontiEC4 was used by Alhambra srl to design a bridge deck for the Piano delle Rose viaduct in Sicily on behalf of its client Sintagma srl. The deck comprises two longitudinal beams curved in plan, four spans of 75m, 87.5m, 87.5m and 75m, with K-shaped reticular transverse beams supporting an intermediate beam, and torsion bracing members. By using LUSAS with PontiEC4 a fast and excellent optimisation of structural steel and of reinforcement steel was obtained.

Modelling in LUSAS

The structure was modelled by discretising the slab and the beams' webs with shell elements and the flanges with beam elements. This allowed for modelling the real position of the reticular transverse trusses and of the torsion braces. The intermediate beam was also included in the model. The portion of the slab straddling the supports, for an extension equal to 15% of the span of the respective spans, was assumed to be cracked.

Traffic loading – vehicle load optimisation

The identification of the traffic load positions that give the maximum / minimum design actions on the various elements of interest was carried out through an automated procedure involving the processing of the surfaces of influence of the various stress characteristics, at the points of interest using a “Direct Method Influence” (DMI) analysis. Once done, a Vehicle Load Optimisation analysis found the most unfavourable traffic load positions.

Axial force, shear force and bending moment at the points of interest in a beam-shell model are obtained by integrating the results on “slices” through the model that are placed independently of the mesh. From these, influence surfaces, defined in order to evaluate the maximum / minimum bending and shear stress on the most stressed longitudinal beam can be calculated.

Results visualisation

The “slices” allow the forces and moments in sections to be obtained at chosen locations according to needs and make the visualisation phase of the results fast and concise even if only a small number of “slices” are used.

Diagam of My for the external and intermediate girder for the fundamental ULS.

Definition of verification sections in PontiEC4 

The definition of the slices in LUSAS allows for automatic creation of the verification sections in PontiEC4, which nests them in the corresponding segment of the steel beam, and loads in the corresponding design forces and moments. If not used, the sections and segments must be defined directly in PontiEC4 and the design forces and moments imported from an Excel file.

PontiEC4 geometry window - Section definition

Import data from LUSAS and geometry definition 

The most straightforward use of PontiEC4 is for checking of all sections of a single longitudinal beam. Using the x coordinate of the section in a longitudinal beam, PontiEC4 associates with the section the width of the slab that is collaborating and is to be considered in the checks due to the shear lag effect.

Classification and plastic check of the section on pile support axis P1

Shear lag data dialog in PontiEC4

ULS, SLS & fatigue calculations in PontiEC4

• Section properties

• Primary (isostatic) effects of shrinkage and temperature change

• Creep & shrinkage coefficients (EN1992-1-1, App B)

• Classification of sections (EN1993-1-1, Table 5.2)

• Ultimate bending check for Class 1 & 2 sections (EN1993-1-1, 6.2.5) 

• Stress checks for Class 3 & Class 4 sections (EN1993-1-5, Section 4) 

• Ultimate shear & web buckling (EN1993-1-5, Section 5) 

• Bending-shear interaction (EN1993-1-5, Section 7) 

• SLS stress checks (EN1994-2, 7.2.2 (5) & EN1993-2, 7.3) 

• SLS web-breathing check (EN1993-2, 7.4) 

• RC crack checks (EN1994-2, 7.4.3) 

• ULS, SLS and fatigue checks for connectors (EN1994-2, 6.6 & 6.8) 

• ULS, SLS and fatigue checks for bolted connections (EN 1993-1-8) 

• Fatigue checks for both structural steel and reinforcement components (EN 1993-1-9, EN 1994-2, EN 1993-2) 

• Longitudinal and transversal stiffeners check (EN 1993-1-5, 9.2.1, (4), (8), (9), 9.3.3 (3))

“The possibility of obtaining force and moment diagrams from a series of sections of a beam-shell model, coupled with the availability of generating influencing surfaces for the same sections, allowed us to model the bridge with transverse beams and torsion braces in their real position, fully considering the effects of the curved plan. The use of LUSAS with PontiEC4 allowed a fast and excellent optimisation of structural steel and of reinforcement steel.”

Federico Durastanti – Technical Manager Sintagma srl (Perugia - I)

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Modelling approaches possible

Finite element modelling of steel-concrete bridge decks typically involves the use of one of the following methods :

• Grillage of steel-concrete beams.

• Concrete slab modelled with shells and steel members with eccentric beams.

• Concrete slab and steel web with shells, flanges and bracings with beams.

Methods 2 or 3 are easily achieved by finite element software. They also permit dealing with curved girder structures (where significant torsional stresses arise) and when design stresses in any bracing are to be obtained directly from the model.

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