Live Load Distribution Factors Dialog Box

This dialog box allows you to directly specify shear and moment live load distribution factors and a single impact factor to be used for both shear and moment impact. The left and right curb widths are specified Loads/Analysis Tab with this dialog box. To open this dialog box, click the Live Load Distribution Factors button on the Loads/Analysis tab.

When there are rows of live load distribution factors in the dialog box, CIP RC/PT Girder will uses the values instead of calculating design specification based factors. The same process is applied to impact. If you delete all rows of distribution factors, CIP RC/PT Girder will calculate live load distribution factors per the design specifications and using the values specified for left and right curb width.

If the User-Defined Impact check box is deselected, CIP RC/PT Girder will calculate separate shear and moment impact factors.

Adding Live Load Distribution Factors

Perform the following steps to add a live load distribution factor to the analysis:

Select the girder from the drop-down list in the Girder field.
In the grid, select the distribution factor you want to add to by clicking anywhere in its row. A blue arrow displays on the left side of the grid to mark the selection.
Click the Add LL Dist button. This adds a new distribution factor after the selected one.
Enter the distribution factor values in the grid. A definition for each parameter is available below.

Deleting a Live Load Distribution Factor

Perform the following steps to delete a live load distribution factor:

Select the girder from the drop-down list in the Girder field.
In the grid, select the distribution factor you want to delete by clicking anywhere in its row. A blue arrow displays on the left side of the grid to mark the selection.
Click the Delete LLDist button to remove the selected distribution factor.

Copying Live Load Distribution Factors

Perform the following steps to copy the live load distribution factors to all other girders:

Select the girder from the drop-down list in the Girder field.
In the grid, select the distribution factor load you want to delete add to by clicking anywhere in its row. A blue arrow displays on the left side of the grid to mark the selection.
Click the Copy to all Girders button. This copies the selected distribution factor to all other girders.

Defining the Impact Factor

To define the impact distribution factor, click the box next to the User-Defined Impact option and enter the distribution factor in the Impact Factor field.

Grid Definitions

Setting

Description

Gir

This read only field indicates if the live load distribution specification is for the full cross section or an individual girder.

Reference Type

CIP RC/PT Girder allows you to locate a live load distribution specification using one of three methods:

Setting	Description
Span	Live load distribution location specified with respect to spans. Spans are defined as the distance between supports (piers or abutments) except that the first span is defined as starting at the BB and the last span ends at the EB.
Support	Live load distribution location specified with respect to supports (i.e. abutments or piers).
Bridge	Live load distribution location specified with respect to the beginning of the bridge or girder.

Ref Num

Select the number of the reference item consistent with the method of locating the live load distribution specification. This will either be a span number or a support number. This field will be disabled for the Bridge method.

Ref Unit

Select either ft (or m) or percent (%) as the method to locate the live load distribution specification along the bridge or girder. The distance field, LL Dist Location, must be consistent with the location method.

LL Dist Location

Specify the distance along the bridge or girder for the live load distribution specification. This value must be consistent with the location method.

1-Lane Shear

Shear live load distribution for single lane loading.

1-Lane Moment

Moment live load distribution for single lane loading.

Multi-Lane Shear

Shear live load distribution for multi lane loading.

Multi-Lane Moment

Moment live load distribution for multi lane loading.

Technical Discussion

CIP RC/PT Girder will automatically calculate shear and moment impact factors and single and multi-lane, shear and moment live load distribution factors and use them in the formation of a live load response. There are situations when the design specification factors are not applicable or you may have more precise factors to use. The Live Load Distribution Factors dialog box allows users to direct CIP RC/PT Girder to use a specified impact factor (for both shear and moment) and specified single and multi-lane, shear and moment distribution factors.

Live load distribution factors are defined for single ad multi-lane loading. When in LFD mode, the distribution factor is the number of wheel lines, and when in LRFD mode, it is the number of lanes. The single lane factors are used in the calculation of the side-by-side live loading (normally used for permit or overload trucks). See Theory for the methodology. The multi-lane factors are used for calculation of all other live load responses.

CIP RC/PT Girder will linearly interpolate all distribution factors for points in-between distribution specifications and will use the first and last specifications for points beyond the limits of the specifications.

This dialog box is also used to specify the left and right curb widths used when CIP RC/PT Girder calculates live load distribution factors.