See the adjacent Software Information
links for general details regarding LUSAS Bridge software products and
Prestress and post-tensioning with LUSAS
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
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.
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.
post-tensioning analysis types are supported; Beam, Tendon,
Plane Stress and Solid.
bridge slab deck
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
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.
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.
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.
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.
Time stage construction
All types of time staged
construction methods can
be used in conjunction with the post-tensioning facility. See
construction analysis information page for more details.
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