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Overview-
The LARSA Section Composer is a graphical companion tool for modeling
arbitrary sections for use in LARSA 4D. The Section Composer supports
nonprismatic and composite sections based on standard, parametric,
and custom shapes, and it is able to compute section properties in real-time.
The Section Composer is fully integrated with LARSA 4D. Sections created in the Section
Composer are used directly in LARSA 4D like any other section. When graphical rendering
is turned on, the true shapes of member sections are shown in the LARSA 4D
graphics windows.
Accurate modeling of bridges requires the use of nonprismatic sections, sections whose
dimensions vary along the length of the member. The LARSA Section Composer makes
it easy to define nonprismatic variation in sections by applying a formula to a parametric section
definition.
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Parametric Sections Library-
LARSA 4D and the Section Composer feature a parametric section library comprised
of the most common cross-sectional definitions. Both basic shapes, like I, C, and
angles, and complex shapes including many types of box girders can be added to a
project simply by specifying the values of the dimensions, like width, depth,
and thickness.
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Automatic Computation of Properties-
The Section Composer can be used to model cross sections with holes, composite parts,
and built-up parts with any arbitrary shape. Properties including area, moment of inertia,
radius of gyration, and the torsion constant J are all computed by the Section Composer
for any shape.
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Parametric Definitions-
Sections in the Section Composer are defined parametrically, meaning points are normally entered
as equations of a few parameters, such as depth (d), width (b), and thickness (t). The benefit
of a parametric definition is twofold. First, sections defined this way can be reused and
resized as needed without recomputing the coordinates of control points. By simply changing
a parameter, coordiantes are immediately updated. Secondly, parametric definitions make it simple to
add nonprimsatic variation.
There is no limit to the number of parameters that a user may enter for a section, and equations
defining coordinate points can be as simple or as complex as needed for the project.
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Types of Nonprismatic Variation-
Formulas give the vale of a parameter as a function of the position on the span. Linear, parabolic,
sinusoidal, and other types of functions can be attached to parameters, to control nonprismatic variation.
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Computation of Properties-
LARSA 4D and the Section Composer automatically compute the section properties at stations along the
length of the span. These calculated properties are shown in easy-to-read graphs so that variation
can be visually verified.
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Reference Axis-
LARSA 4D uses a member reference axis to align parametric sections to the members to which
they are assigned. By placing the reference axis at the top of a box girder section, the
user can easily keep the tops of the members aligned by just drawing a straight line
of members in LARSA 4D. The members will automatically be offsetted internally to match
the offsets of their centroids from the reference axis.
Post-tensioning tendons follow the reference axis as well, rather than the member centroids,
so that the user can specify their positions relative to a fixed edge.
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