LARSA 4D Introductory Training Manual for Bridge ... - LARSA, Inc.

LARSA 4D Introductory Training Manual for Bridge Projects
Combining the Left and Right Lanes
In order to compute the effects on the structure for AASHTO LRFD, we need to combine the effects
of the left and right lane.
Because of multiple presence factors, there are three cases to consider. The right lane may be loaded
individually with a multiple presenence factor of 1.2. Similarly for the left lane. Or the two lanes may
be loaded simultaneously with a multiple presence factor of 1.0.
We will create the simultaneous loading condition first. A Linear Result Combination simply sums the
numerical results of two or more cases.
Start the Results → Linear Combination tool.
Add the two influence line cases (Left Lane, Right Lane) into the right list. Either double-click
the influence cases or click a case and then click the big right arrow.
Click OK .
Linear Combination of Two Lanes
Click the new linear combination case in the Analysis Results Explorer, and then open a results
spreadsheet to view the combined effect from the two lanes.
Enveloping the three conditions (left, right, together) can be accomplished using Extreme Effect Groups
which are like saved envelopes.
Start the Results → Group for Extreme Effect tool.
Find the three cases for the right lane, the left lane, and the new linear result combination and
add them into the list on the right using the big right-arrow in the middle.
Set the factors on each as appropriate. Then click OK .
Extreme Effect Group for Right Lane
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