Distribution Tab
When you click Analysis Factorsbutton, the Analysis Factors dialog box displays with the Distribution tab displaying.
Distribution Factor Computation Options
Precast/Prestressed Girder allows you to specify how dead loads are to be distributed to different beams. You can either choose to distribute the dead load equally to all beams or distribute them based on tributary fraction (more accurate in cases where beams are not spaced uniformly).
The program calculated distribution factors appear in the text boxes on the screen. You can select the Computed option to allow the program to calculate the factors or select the Manual option to have the program use customized or user-defined factors. For customized or user-defined factors, you must select the specific span # and beam #, and check the Manual option and overwrite the calculated values in the text boxes.
Check the option to Use Composite DC Distribution as per FDOT to compute the dead load Comp. DC factors as per Florida SDG 2.8 (Barrier/Railing Distribution for Beam-Slab Bridges). All DC comp loads will be distributed using the alternative distribution factors when this check box is checked.
For impact factors, if the Computed option is selected, then the impact factor will be calculated according to IRC6-2000, clause 211.
Live Loads
Precast/Prestressed Girder allows users to manually enter the live load distributions factors or to allow the program to calculate them based on one of the following options:
- Use Code Equations
This option calculates the reaction factors based on the Courbon’s Method for estimating transverse distribution of live load between girders in a beam and slab type bridge. In this method, the reaction of the transverse truck placement on deck on any girder of a deck slab type bridge with parallel girders can be computed by assuming a linear variation of the deflection in the transverse direction. Detailed samples of calculations, assumptions and theoretical references for this can be found in Reference 1 (Raina).
- Use Refined Methods of Analysis
This option allows users to compute and subsequently use more accurate live load distribution factors in the design and load rating of prestressed concrete bridge beams. For more information on this feature, refer to the section on Refined Methods of Analysis for Distribution Factor Computation.
