![[request information]](../../images/click_info.gif) Selected
Applications
Curved
girder analysis | Linear
and nonlinear buckling | Integral
abutment bridges | Staged
construction analysis | Concrete
modelling | Post-tensioning
Post-tensioning with LUSAS
 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.
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 all
supported by the prestress / post-tensioning facility.
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Post-tensioning:
External
tendons or internal tendons?
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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.
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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
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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.
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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.
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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.
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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.
Results plot for
incrementally launched time staged construction box girder bridge
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