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Preliminary Bridge Girder Comparisons (pg. 2)

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).

   
 
�2003, International Steel Group Inc.