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Autoloader facility in LUSAS
Autoloader is a
software product option for particular LUSAS software products. It
makes use of influence surfaces to identify the most onerous vehicle loading patterns on bridges for a chosen design code and to apply these loading patterns to LUSAS models. It reduces the amount of time spent generating loadcases to replicate traffic and lane loading on models and leads to more efficient and economic design, assessment or load rating of bridge structures.
Note that LUSAS
Traffic Load Optimisation (LUSAS TLO) software exists for traffic loading to Eurocode
EN-1991-2 and provides more functionality and has fewer
limitations on use.
Worked example
The "Bridge
Slab Load Optimisation"
example is available from the Windows Start menu
Start > Programs >
LUSAS14.x for Windows > LUSAS Help > Application
Examples Manual (Bridge, Civil & Structural) > Bridge Slab Load Optimisation
You can find further information on
Autoloader in LUSAS Modeller Help:
Help >
Help Topics > Contents > Autoloader Reference Manual
You may also find the following notes
of assistance, which detail some of the issues raised by
Autoloader users.
Bridge modelling issues
-
Autoloader
cannot be used with line beam models, however grillage
modelling method is acceptable.. The model must
have a plan area for carriageway loading.
-
Grillage
models should use GRIL elements (BMS3 for upstand/downstand
grillages). Grillages assembled with 2D beam elements
will not work.
-
If
quadratic plate or shell elements are used,
Autoloader gives results which must be used with
caution. More
information on mesh refinement issues
-
If
any part of the model lies in the negative XY plane
Autoloader cannot generate loading.
-
For
a 2D deck only models search areas should be avoided
during Autoloader analysis.
It is preferable that they are deleted totally -
even from the attribute list.
When using Autoloader on a 3D structure, it is
necessary to use a search area to define the deck, but
only 1 search area should be used.
Multiple search areas will result in Autoloader
failing to produce results. More
on point/ patch loading and search areas
Carriageways & Kerbline issues
-
Carriageways
must be defined in the XY plane (i.e. Z=0) and kerbs must
run from a low X-coordinate to a higher X-coordinate (i.e.
they run broadly "left to right" rather than
"up and down")
-
The
first X-coordinate of kerb must be before first X-coordinate
of deck (important in skew decks).
-
Autoloader is not able to deal with
splayed carriageways (i.e. kerblines not parallel to each
other). This is
because it is a rigid implementation of the codes:
To analyse a splayed carriageway will require input
from an engineer since it is outside the code.
Some engineers deal with this by using several
Autoloader runs to cover several possibilities.
-
Carriageways
should have parallel kerblines (see 2 above). In addition, the points that define the kerblines should also be
orthogonally opposite to one another on the carriageway.
If they are not, this can force a slew into the shape
of your HB vehicle. This
problem is produced by the Autoloader scripting rather than
LUSAS and has been raised with the developers. To avoid the problem, slanting carriageway alignments
are readily produced by a rotation of two parallel lines.
-
Kerblines
must be within the plan area of a grillage model although
kerbs may begin and end
"off the deck" (necessary for point 3 above). If kerblines lie outside of the grillage (e.g. outside
main beams) in the actual bridge, it will be necessary to
use dummy grillage members with low stiffnesses to extend
the grillage to catch the loads.
-
When specifying multiple carriageways,
"Autoloader" needs a carriageway direction ("CWDIR
parameter") for each carriageway.
CWDIR specifies the angle of the carriageway in
degrees. Currently
the Autoloader wizard only specifies one angle (one
carriageway). The
wizard will be amended to include this extra parameter in a
subsequent release. In
the meantime, the CWDIR parameter may be entered directly
into the wizard using the menu item:
Bridge
> Vehicle Load Optimisation > Define Carriageways...
Angle of carriageway =
[angle of each carriageway in
turn in degrees separated by commas]
Proceed with the other Vehicle load optimisation
parameters as normal. If
you are using line features to define kerblines, you should
select them as usual, but pick "Kerbs from tabular
input". When
you click the Apply button, the kerb positions grid should be
filled-in automatically.
Other issues
-
In
the option: Bridge > Vehicle Load Optimisation > Results
filename (text box), the filename specified should have no
spaces.
-
By
default BD37/88 settings, (a)
no allowance for HB vehicle being scaled down or
removed for SLS cases has been made (b)
gamma_f3 has not been included.
The partial safety factors used for default are SLS:
1.2, 1.0, 1.1, 1.0; ULS:
1.5, 1.25, 1.3, 1.1.
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