Multi-girder composite bridge — Initial sizing

Table 2.5.2.6.3-1 of AASHTO LRFD Bridge Design Specification 8th Edition recommends:

minimum steel girder depths of \(0.033L\) for simple spans or \(0.027L\) for continuous spans.
minimum overall depths of \(0.040L\) for simple spans or \(0.032L\) for continuous spans.

where \(L\) is the span length.

Clause 2.4.1 of WSDOT Bridge Design Manual recommends the following span/depth ratios:

Situation	Span/Depth Ratio
Simple span	22
Continuous span	25
Variable depth girder at mid-span	40
Variable depth girder at intermediate pier	20

SCI’s SteelConstruction.info recommends the following proportions:

Element	Size
Slab thickness	250mm
Girder centres	Up to 3.8m
Girder depth	Span/20 to Span/30
Top flange width	Minimum width 350 mm
Top flange thickness	Top flange width / 16 in sagging zones. Up to 50mm in hogging zones.
Bottom flange width	Girder depth / 2
Bottom flange thickness	Up to 50mm
Webs	Minimum 15 mm at mid-span. Up to 25mm at supports.
Web to flange welds	6-8mm at mid-span. 8-10mm at supports.
Shear studs	19mm diameter x 150mm high. Rows of 3 at 300 mm centres at mid span increasing to rows of 3 or 4 at 150 mm centres at supports.