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Additional Information

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

Prestress and post-tensioning

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

  • Single and multiple tendon prestress wizards in LUSAS calculate equivalent nodal loading due to tendon prestressing or post-tensioning and assign these forces automatically to beam, plane stress or solid elements of a model for an active loadcase. 
  • Computation of tendon forces can be carried out in accordance with AASHTO-LRFD, BS5400, Eurocode EN1992 and JTG D62-2004. 

Internal tendon modelling

For internal tendon modelling, tendon geometry can be defined via a prestress wizard or by importing geometry data from a spreadsheet or CAD system, or by creating the geometry using LUSAS. Single or multiple tendon prestress wizards can be used to calculate forces and losses to a specified design code and these values can be applied to a beam, shell or volume model using an equivalent load method. Forces and losses from user calculations can be also be imported from a spreadsheeet for use in LUSAS. 

Four post-tensioning analysis types are supported; Beam, Tendon, Plane Stress and Solid.

Post-tensioned bridge slab deck

External tendon modelling

For external tendon modelling equivalent load methods can be used or, alternatively, true tendon modelling can be carried out. This typically requires more complex analytical models requiring, for example, 3D shell elements to be used. 

LUSAS can be used to model the full structure where the external tendons are included between deflector plates in the model. 

For true tendon modelling the tendons are incorporated in the model as bar/ beam elements with applied forces. Modelled in this way, the true behaviour of tendons due to the compression of the concrete is obtained

Box girder model with external tendons

Externally post-tensioned box girder shell model

Single and Multiple Tendon Prestress Wizards

The single and multiple tendon prestress wizards in LUSAS calculate equivalent nodal loading due to tendon prestressing or post tensioning and assign these forces automatically to beam, plane stress or solid elements of the model for the current active loadcase. Computation of tendon forces can be carried out in accordance with AASHTO-LRFD, BS5400, Eurocode EN1992 and JTG D62-2004. 

Multiple tendon prestress wizard

Single Tendon Wizard

The single tendon prestress wizard does not take into account any stressing or unstressing of any other tendons.  The single tendon prestress wizard can be used separately on each tendon in a model to derive equivalent nodal loading on the mesh for all the tendons used. Structural concrete surrounding a tendon may either be modelled as a series of beam elements, or by a set of plane stress or solid elements. Direct import of tendon forces may also be defined via an Excel spreadsheet. After load assignment the forces resulting from the tendon can be viewed. Using this simplified force approach, the effects of prestress can be defined in a separate linear loadcase that can be combined with the other loadcases to compute the overall structural behaviour.

The single tendon wizard can also be used for preliminary design, where a calculated prestressing force and centre of action is to be tested simply, rather than by entering many tendon profiles. It can be used to check if the right number of tendons and  eccentricities are being used, before coming up with a cable zone and arrangement. 

Single tendon prestress wizard

  Multiple Tendon Wizard

The multiple tendon prestress wizard does take into account elastic shortening due to stressing of other tendons according to the design code or user-defined percentage losses. As such it is more suited to staged construction analysis uses. 

Through a series of dialogs, the multiple tendon wizard simplifies the definition of tendon profiles, losses, tendon properties, loadings and their assignment to loadcases. Elastic shortening losses can be specified for multiple stressing stages useful for staged construction. Locally defined tendon profiles can be used anywhere in the model and any number of times. One very useful feature allows the tendon profile to be viewed in real-time as it is defined. Tendon material properties including short and long term losses can be specified. Definitions of tendon loading including jacking details complete the data required. The tendon can then be easily assigned to one or more line features on the model and, more importantly, to one or more loadcases at the same time saving a great deal of time.

Graphing of tendon losses

Graphs of short and long term losses in selected tendons can be plotted using LUSAS.

Graph of short and long term tendon losses

Dead, prestress and combination loading results for a prestressed beam

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.

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
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  Bridge LT
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  Choosing Software
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green_arrow.gif (94 bytes) LUSAS Bridge LT
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  Software Options
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  Case Studies
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  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
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  General information
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Any modelling and analysis capabilities described on this page are dependent upon the LUSAS software product and version in use.