Recalculate Bridge Section Girder Spacing Form



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Access the Recalculate Bridge Section Girder Spacing form, with the Bridge Modeler enabled, as follows:

  1. Click the Bridge menu > Bridge Deck Sections command, or on the  Bridge Wizard select the Deck Sections item and click the Define/Show Sections button, to display the Define Bridge Deck Sections form. Then do one of the following:

    • Click the Add New Section button to display the Select Bridge Deck Section Type form. Click the Precast I Girder button to display the Define Bridge Section Data - Precast Concrete I Girder form, or the Precast U Girder button to the Define Bridge Section Data - Precast Concrete U Girder form, or the Steel Girder button to display the Define Bridge Section Data - Steel Girder form.

    • Highlight a previously defined Precast Concrete I Girder, Precast Concrete U Girder, or Steel Girder bridge deck definition and click the Add Copy of Section or Modify/Show Section buttons to display the Define Bridge Section Data - Precast Concrete I Girder form, the Define Bridge Section Data - Precast Concrete U Girder form or he Define Bridge Section Data - Steel Girder form.

  2. Set the Constant Girder Spacing Item to No.

  3. Click the Recalculate Girder Spacing button to display the Recalculate Bridge Section Girder Spacing form.

 

Use the Recalculate Bridge Section Girder Spacing form to quickly and easily calculate user-specified spacing of the girders when at least one "fixed spacing" has been specified. The spacing applied depends on the user-specified fixed spacing,  the number of girders specified, and the distance over which the girders are to be distributed (i.e., the Total Width minus the Left Overhang Length and the Right Overhang Length).

  1. On the Define Bridge Section Data - Precast Concrete I Girder form or the Define Bridge Section Data - Precast Concrete U Girder form, do the following:

    1. Specify the Number of Interior Girders.

    2. Specify the Total Width of the deck section.

    3. Specify No for the Constant Girder Spacing option.

    4. Enter a desired value in one or more of the Girder Space Sn edit boxes, where n is the Number of Girders specified; spacing IDs are assigned from left to right. Note that to use the recalculate feature, at least one of the values specified should be considered a "fixed value." The remaining spacing will be calculated based on the ratio of the other values specified (see example below).

    5. Click the Recalculate Girder Spacing button to display the Recalculate Bridge Section Girder Spacing form.

  2. In the List of Spaces display list, highlight the spacing(s) that is to remain fixed.

  3. Click the Add button. This will move the selected Spacing to the Spaces to Remain Fixed display list. Repeat as necessary. Spacings in the Spaces to Remain Fixed list can be removed by first clicking on the spacing to be removed and then clicking the Remove button.

  4. Click the Calculate button. The Define Bridge Section Data - Precast Concrete I Girder form or the Define Bridge Section Data - Precast Concrete U Girder form will redisplay with the values calculated for Girder Space Sn based on the values specified in Step 1d.

Example

Assume that the Number of Interior Girders is set to 3 and that the Total Width of the section is specified as 70 feet. The Left and Right Overhangs are both specified at 3 feet. Thus, 5 girders (the left and right exterior girders, plus the 3 interior girders) will be distributed across 64 feet (70 feet minus 6 feet for the overhangs), requiring specification of spacing values for Girder Space S1, Girder Space S2, Girder Space S3 and Girder Space S4 (numbered left to right across the cross-section).

By default, the program will specify equal spacing of the girders (16 feet each). For this example, assume that the three center girders are to be closely spaced near the center of the section.

  1. Specify 6 feet for Girder Space S2 and 8 feet for Girder Space S3.

  2. Click the Recalculate Girder Spacing button to display the Recalculate Bridge Section Girder Spacing form.

  3. Highlight S2 (6 ft) in the List of Spaces display list and click the Add button to move it to the Spaces to Remain Fixed display list.

  4. Click the Calculate button. The Define Bridge Section Data - [Type] Girder form will redisplay with the values calculated for Girder Space S1 = 23.2, Space S3 = 11.6 and Space S4 = 23.2.

The total length available for the three "un-fixed" girder spaces (S1, S3 and S4) is 58 feet (64 feet minus the 6 feet specified as fixed for Space S2). This 58 feet is distributed to spaces S1, S3, and S4 in proportion to their originally specified distances (16, 8, and 16 feet respectively) as 23.2, 11.6, and 23.2 feet respectively.

If both Spacing S2 (6 feet) and S3 (8 feet) are set as fixed on the  Recalculate Bridge Section Girder Spacing form (for a total of 14 feet), the program calculates Spacing S1 at 25 feet and Spacing S4 at 25 feet because the original values were equal and their sum must equal 50 feet (the total distribution distance of 64 feet minus the fixed spacing of 14 feet).

 

 

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