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The default values for the input variables are as follows:

1) Minimum number of girders in the cross section: for Option A this is 4. In Option B and Option C, the number of girders is incremented by 1 and 2, respectively.

2) Maximum desirable concrete strengths: 6.67 Ksi at release and 7.55 Ksi at 28 days. Note that release strengths in excess of 6.67 Ksi are possible in some cases. However, the user should carefully check feasibility with producers. In many cases of adjacent box beams, the structural requirements set a limit on the maximum number of strands, which limits f'ci to less than 5.80 Ksi.

3) The Deck Overhang for spread beams is automatically set at 1/2 of the girder spacing for Options A, B and C (Beam Selections 1, 2 and 3).

4) Minimum desirable basic beam depth: the default value is set internally using complex formulas which will result in a predicted release strength near the practical maximum for the first solution (Option A, Selection1).

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INPUT MESSAGES AND WARNINGS

The program has built-in messages that will be displayed when inputs exceed certain established program limits. These warnings are:

Entered value is below industry recommended minimum concrete release strength: Whenever the predicted release strength is below 3.3 Ksi, this message ("LOW") indicating the required f'ci is low will be shown, and, therefore the section size is too big for the given span and spacing. Note that there is nothing structurally wrong with the deeper section. However, a shallower depth (or a wider spacing) would probably result in a more economical design.

Entered value is above industry recommended maximum concrete release strength: When the predicted release strength exceeds the desirable ("target") value, a message to that effect ("HIGH") will be printed out. It is suggested that a deeper section or smaller beam spacing be used. But, since the program also checks other options with smaller spacing and deeper sections, often there is no need for additional runs.

Entered span length is outside of program limits: The study is based on a database of exact solutions within a practical range of prestressed concrete bridge girder applications that vary for different girder types. This warning reflects the limit of the underlying research.

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This small girder spacing is out of the domain of this program: The study is based on exact solutions within a practical range of prestressed concrete bridge girder applications that vary for different girder types. This warning reflects the limit of the underlying research for Solution Option A.

This large girder spacing is out of the domain of this program: The study is based on exact solutions within a practical range of prestressed concrete bridge girder applications that vary for different girder types. This warning reflects the limit of the underlying research for Solution Option A.

Generally standards require a minimum of 4 girders per span: In order to allow deck replacements while in use, a practice that requires a minimum of four girder cross sections for spread beam structures.

The number of girders per span is probably too large: When the total number of girders per span of spread beam structures exceeds 8 girders this warning is given.

Total width of computed beams does NOT match out-to-out bridge width.

Suggested out-to-out bridge width ______ ft

This warning and suggestion will appear when the inputted out-to-out bridge width for adjacent box beam structures does not match to an integer multiple of the selected beam width (48 inch or 36 inch). The solutions presented will be based on the recommended bridge width.

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Preliminary Design Aids : Quik Beam AASHTO Features And Limitations