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Overview|
In LARSA 4D, influence line and surface results are an extension of the moving
load analysis. By running a unit load over the deck of a bridge, the effects
of any set of vehicles, even with variable axle spacing, can be computed
without needing to re-run an analysis.
Using this method, the engineer need not decide ahead of time which points on the
structure he wants influence results for. Once the fast Influence Analysis is run,
results for any point on the structure are computed in real-time as they are needed.
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Vehicle Variation-
Influence line and surface analysis reports the most extreme effects generated by
any permutation of vehicle parameters.
LARSA 4D supports varying wheel positions, multiple vehicle applications with varying distance between the vehicles, minimum vehicle spacing longitudinally and transversely, and varying axle distances.
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Lane Load Variation-
UDL/patch lane loading is applied only where it contributes to the extreme force effects.
UDL magnitude can be constant or variable based on the loaded length according to
UK BS5400 or a custom length-load curve. For variable magnitude loading, the smallest
loaded length that produces the most extreme effect is used.
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Influence Lines-
Influence lines are used when the bridge is modeled as line girders. Vehicle and
lane loads are applied directly to the girder. Distribution of load across lanes is
accomplished using lane loading factors. Lanes can be offset transversely from
the girder to which the loads are applied.
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Influence Surfaces-
Influence surfaces are used for plate-deck models, using standard and new
two-dimensional vehicle definitions that model both the length and width of the vehicle
and tire contact area.
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Supported Codes|
AASHTO LFD and LRFD and the Indian Roads Congress codes for lane loading are among the codes that can be strictly followed using LARSA 4D.
The vehicle load patterns for these codes are provided with LARSA 4D, and other load patterns can be entered by the user as needed.
In combination with Linear Result Combinations and Extreme Effect Groups, influence-based result cases can be put together to derive any loading scenario required by a design code.
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Live Load Wizard|
The Live Load Wizard automates code requirements, creating the required load combination scenarios that will show the most extreme effects for design. In a multi-lane bridge, for which dozens of scenario permuations are required, the Live Load Wizard saves many hours of engineering time. The wizard supports AASHTO LRFD and IRC 2000.
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