Preliminary Bridge Girder Comparisons - page 1
Results of the Analysis:
All information generated from the computer program is summarized and placed in a report for presentation to the engineer. Relative cost indices are included for all schemes (Figure 2).
FIG. 2
Cost and Weight Index Summary
| Scheme | Design Method | Spans | Material | Stiff. | Web | Girder Spacing | No. of Girders | Wt. Each Girder (lbs) | WT. all Girders (tons) | WT. Index | Cost Index |
| A | LFD | 3@127' | A572 | T | 63 X V | 12.00' | 7 | 97080 | 340 | 1.35 | 1.21 |
| B | LFD | [email protected]' | A572 | T | 60 X V | 12.00' | 7 | 71816 | 251 | 1.00 | 1.00 |
| C | WSD | [email protected]' | A572 | T | 60 x V | 12.00' | 7 | 75754 | 265 | 1.05 | 1.03 |
| D | LFD | [email protected]' | A36 | T | 63 x V | 12.00' | 7 | 85757 | 300 | 1.19 | 1.05 |
| E | LFD | [email protected]' | A572 | T | 42 x V | 10.50' | 8 | 72713 | 291 | 1.16 | 1.11 |
From this information, designers can make economic comparisons between their numerous options. Some typical comparisons include the following:
- Unpainted A588 versus painted A572
- Load Factor Design versus Allowable Stress Design
- Number of girders in cross-section
- Span arrangement
- Effects of depth restrictions
The optimum scheme is shown with complete detail and material listings (Figure 3).
