Engineering analysis + design software

Additional Information

See the adjacent Software Information links for general details regarding LUSAS Bridge software products and options.

Prestress / Post-tensioning

Prestress / Post-tensioning in LUSAS is suitable for beams, slabs and volumes, and incorporates time-stage with creep and shrinkage. Span-by-span, progressive placement (segmental), balanced cantilever and incremental launching time staged construction methods are supported. 

Use the post-tensioned bridge wizard to generate a box girder as constructed by the "Free Cantilever Method"

  • LUSAS calculates equivalent nodal loading due to any tendon prestressing or post-tensioning and assigns these forces automatically to beam, shell, or solid elements of a model for a chosen loadcase or set of loadcases. 
  • Computation of tendon forces can be carried out in accordance with supported design codes.

Beam (line), shell (surface) and solid (volume) modelling of concrete is supported.

Tendon definition and modelling

Define tendon profiles and view the developing tendon shape in real-time as it is being defined, or copy and paste data from a spreadsheet. Tendons can also be generated by selecting lines, arcs or splines that are defined or imported into LUSAS Modeller. Manual definition by coordinates in 3D space or by defining coordinates in two 2D planes is supported. Locally defined tendon profiles can be used anywhere in the model and any number of times. 

Define tendon properties and values/settings relating to instantaneous and time-dependent losses. All other values required in order to carry out calculations of prestress losses in accordance with the design code are obtained directly from the model. Elastic shortening due to stressing of other tendons according to the selected design code or user-defined percentage losses is taken into effect. Time dependent effects can also be considered.

Supported design codes which include time dependent effects for any stage of construction are:

  • AASHTO LRFD 5th to 9th Edition
  • CEB-FIP Model Code 1990
  • EN 1992-1-1:2004 / 2014 Eurocode 
  • fib Model Code 2010
  • IRC:112-2011
  • JTG 3362-2018

Supported design codes which exclude time dependent effects, only producing results for short term and long term losses are:

  • AASHTO LRFD 2nd Edition
  • AASHTO LRFD 5th to 7th Edition
  • BS5400-4:1990
  • DD EN1992-1-1:1992 Eurocode 2
  • EN 1992-1-1:2004 /2014 Eurocode 2
  • JTG D62-2004

LUSAS calculates losses appropriate to the age of the concrete and the magnitude and duration of prestress and other loading at any selected time typically at each stage, and at the end of the service life of the structure. Depending upon the design code these loss calculations may be:

  • Based on time inputs and calculated stresses, which allow for producing details and results of losses at any time and for any stage of construction.

  • Approximate, requiring input of estimated stresses, which allow for producing details and results of short term and long term losses only.

For design codes that support time-dependent loss calculations, adjustment of losses to account for prior losses are also calculated.

Simply assign the tendon loading (which associates a tendon profile and a tendon property with a specified prestress force and associated jacking and loss details) by dragging and dropping it onto selected line, surface or volume features in a model for a single or a range of loadcases. When solving a model, LUSAS calculates equivalent nodal loading from the assigned prestress tendon loads and assigns these forces automatically to those features (and hence nodes and elements) of the model for a specified loadcase. Discrete loads and the applied forces / moments calculated can be viewed for checking purposes.


Produce graphs of tendon prestress force after time-dependent losses. Add tendon properties, profile, loading, losses and setting-out data for all tendons assigned to a model to a model report.

Typical graph showing reduction in prestress force after time-dependent losses

Produce reports of tendon properties, profile, loading, losses and setting-out data for all or selected tendons.

Post-tensioned bridge slab deck

External tendon modelling

For modelling external tendons as, for example, where external tendons are included between deflector plates in a structure, the tendons can be incorporated into the model as bar/ beam elements with applied forces, and typically requires shell or solid elements to be used to model the structure. 

Modelled in this way, the true behaviour of tendons due to the compression of the concrete is obtained. 

Alternatively, equivalent load methods could also be used.

Box girder model with external tendons

Time stage construction

All types of time staged construction methods can be used in conjunction with the post-tensioning facility. See the staged construction analysis information page for more details.

Post-tensioned Bridge Wizard

  • Generate a beam model of a box girder as constructed by the "Free Cantilever Method" in a fraction of the time taken by manual methods.

  • Automatically model the entire construction sequence in order for a step-by-step nonlinear analysis incorporating concrete creep and shrinkage materials (and age attributes) and tendon loading including time dependent losses to be carried out.

Easy to define

From basic setting out data, segment dimensions, construction times and concrete ages, the FCM wizard creates the necessary tendon loading attributes and assigns each to the correct segments at each stage of construction, considerably speeding-up the modelling process.

Dynamic visualisation of tendons

Dynamic visualisation of tendons in the bridge on plan, elevation and within each segment section is provided, showing the segment installation sequence for each selected construction stage, along with tendon setting out data.

Tendon profiles suitable for balanced cantilever box girder-type bridges constructed by the Free Cantilever Method are used (with FSM used at end spans adjacent to the abutments). Tendons are categorised into five types, with setting out details for each provided on the relevant prestressing tendon input pages of the FCM wizard.

Check before you build

A summary dialog shows segment length, construction times and age of segments for each selected construction stage, allowing for easy validation of inputs, and detection of errors prior to building a model.

Once complete, a model capable of modelling the entire construction sequence is built at the press of a button, and on solving a model, tendon losses are calculated to a chosen code of practice.


Bridge feature / Capability Provided by the Wizard?
Straight or curved decks of constant radius. YES
Box girder sections with vertical webs. YES
Any number of spans and supports. YES
Split piers with diaphragms. YES
Tendon types commonly used in FCM bridges  YES
User-defined tendon profiles. YES


Software Information

  Bridge / Bridge plus
green_arrow.gif (94 bytes) Software overview
green_arrow.gif (94 bytes) Modelling in general
green_arrow.gif (94 bytes) Advanced elements, materials and solvers
green_arrow.gif (94 bytes) Load types and combinations
green_arrow.gif (94 bytes) Staged construction modelling
green_arrow.gif (94 bytes) Geotechnical / Soil-structure modelling
green_arrow.gif (94 bytes) Analysis and design
green_arrow.gif (94 bytes) Design code facilities
green_arrow.gif (94 bytes) Viewing results
green_arrow.gif (94 bytes) Software customisation

  Bridge LT
green_arrow.gif (94 bytes) Software overview

  Choosing software
green_arrow.gif (94 bytes) Software products
green_arrow.gif (94 bytes) LUSAS Bridge LT
green_arrow.gif (94 bytes) LUSAS Bridge
green_arrow.gif (94 bytes) LUSAS Bridge Plus
green_arrow.gif (94 bytes) Software selection
green_arrow.gif (94 bytes) Software options

green_arrow.gif (94 bytes) Videos
green_arrow.gif (94 bytes) Case studies

  Application areas
green_arrow.gif (94 bytes) Footbridge design
green_arrow.gif (94 bytes) Movable structures
green_arrow.gif (94 bytes) Rail solutions
green_arrow.gif (94 bytes) Arch bridges
green_arrow.gif (94 bytes) Major crossings
green_arrow.gif (94 bytes) Soil-Structure Interaction Modelling

  Additional information
green_arrow.gif (94 bytes) Linear and nonlinear buckling analysis
green_arrow.gif (94 bytes) Curved girder analysis
green_arrow.gif (94 bytes) Integral or jointless bridges
green_arrow.gif (94 bytes) Post-tensioning
green_arrow.gif (94 bytes) Concrete modelling
green_arrow.gif (94 bytes) Interactive Modal Dynamics
green_arrow.gif (94 bytes) LUSAS Programmable Interface (LPI)

  General information
green_arrow.gif (94 bytes) Hardware specification
green_arrow.gif (94 bytes) Licencing and Networking options
green_arrow.gif (94 bytes) Software prices
green_arrow.gif (94 bytes) Documentation
green_arrow.gif (94 bytes) Links page

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LUSAS is a trademark and trading name of Finite Element Analysis Ltd. Copyright 1982 - 2022. Last modified: November 27, 2023 . Privacy policy. 
Any modelling, design and analysis capabilities described are dependent upon the LUSAS software product, version and option in use.