2.5.1 Live Load

AnalysisCaseLive object is an analysis/load case which contains the vehicular

live load for finite element model.

OpenBrIM is capable of running full influence surface based live load analysis given

a surface (usually represent a roadway), setting design lane patterns and

determining the location of design lane load and design truck.

Influence Surface Method

Live load analysis by influence surface method works as follows:

Equally spaced grid points (represented by IncX and IncY parameters) for influence loads are placed on the surface which is commonly represented by a roadway on which the vehicle loads are applied.
During analysis, a unit load (represented by Fz parameter), with no vehicular load yet, is placed at each grid point one at a time to measure its effect on the structure. Analysis is done once this task is completed.
Let us suppose the user wants to see the maximum reaction at a node due to vehicular live load case, OpenBrIM obtains the reaction effect of each grid point which is called the influence surface. In which the influence surface algorithm figures out how the vehicle(s) should be positioned to produce the maximum reaction at specific node. This happens in real time and the results are displayed as requested like scrolling through results spreadsheet or looking at graphical results.

OpenBrIM stores data on browser where about a gigabyte or less could be stored or less. Therefore it is important to keep the analysis parameters within its limit. Each FESurface node stores 6 numbers (3 translations and 3 rotations) in which each number is 8 bytes in size.

For instance, a 240 feet long and 30 feet wide 2-span bridge can use a minimum spacing for influence loads of 4 feet (IncY="48", in inches) along length and 3 feet (IncX="36", in inches) along width. 240 ft / 4 ft = 60 unit loads along length and 30 ft / 3 ft = 10 unit loads along width. In which OpenBrIM needs to analyze 60 * 10 = 600 unit loads which becomes an analysis case. Assuming that the FESurface which represents the roadway has 3000 nodes. The analysis will take a size of 3000 nodes * 60 unit loads * 6 numbers * 8 bytes = 8,640,000 bytes or 8.64 MB which is within the range of a what a browser is capable to store.

Syntax

</O>

Objects

Parameters

Design Lane Load

Lane object is used to apply design lane load on a surface (representing a roadway).

Syntax

</O>

Parameters

Design Truck

Vehicle object is used to apply design truck weight on a surface (representing a roadway).

Syntax

</O>

Objects

Example

<O N="Design Lane" T="Lane" VehicleMargin="1" LaneLoadWidth="10" ...

...LaneLoad="0.64" Width="12" VehicleSpacing="5">

</O>

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