Request for Preliminary Bridge Girder Comparisons

Preliminary Bridge Girder Comparisons (continued)

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).