Span Length
60′ 80′ 100′ 120′ 140′ BI51 BI63 BI75 70′ 80′ 90′ 100′ 110′ 120′ 130′ 140′ BI51 BI63 BI75
Section Properties (gross)
Product Name Depth (in) Area (in2) Yb (in4) Ixx (in4) Iyy (in4) PLF @ 165
BI51 51" 566 25.2 191444 16303 650
BI63 63" 638 31.1 327551 16519 733
BI75 75" 710 37.1 509572 16735 815

Product Information


The Bulb I (BI) girder is a standard variation of the Bulb-T girder. Use the BI shape only when it has benefits over a Bulb-T girder. Since the BI girder have a narrower top flange, it requires less concrete build-up than a Bulb-T. Therefore bridges with high super elevations (generally, greater than 7%) may want to consider the BI girder.

Standard Design Options


  • Forming and Diaphragm Inserts.
  • Adjust web thickness to accommodate post-tensioning (for spliced girders). For such cases increase the web thickness from 6″ to 7.5″
  • Cast in inserts or hole for diagraph reinforcing
  • Cast in inserts for mounting utility brackets
  • Top flange/web holes for mounting deck forming brackets

3D Viewer

3D Viewer Tools


  • 3D Viewer Functions:
  • Move, Span, Zoom Assemblies
  • Isolate Single Components in View
  • Explode Assembly Single Components
  • Use Markup to Sketch Details
  • General Measurements for Concept
  • Print Views

Need More Info?

We Are Here to Help


Have a question, need a budget or detailed schedule?  Knife River sales team is ready to discuss precast solutions for your project.  Reach out to our staff below :

Sam Jewell

Outside Sales Representative