Structures Design Guidelines | July 2006
2 - Loads and Load Factors |

## 2.10 Redundancy and Operational Importance [1.3.4 and 1.3.5](07/06)
July 2006 - Per TDB C05-01, revised in entirety

A. Redundancy [1.3.4]

Delete the Redundancy factors, η R , in LRFD 1.3.4 and use η R = 1.0 unless a revised value is established in the tables below.

Redundancy Factors, ηR for Flexural and Axial Effects
Structure Type | η R Factor
Welded Members in Two Truss/Arch Bridges | 1.20
Floor beams with Spacing > 12 feet and Non-Continuous Stringers and Deck | 1.20
Floor beams with Spacing > 12 feet and Non-Continuous Stringers but with Continuous Deck | 1.10
Steel Straddle Bents or Piers | 1.20

Redundancy Factors, ηR for Steel Girder Bridges
Number of Girders in Cross Section | Span Type | # of Hinges required for Mechanism | With Diaphragms1 | Without Diaphragms
2 | Interior | 3 | 1.00 | 1.20
End | 2 | 1.00 | 1.20
Simple | 1 | 1.00 | 1.20
3 or 4 | Interior | 3 | 1.00 | 1.00
End | 2 | 1.00 | 1.05
Simple | 1 | 1.00 | 1.10
5 or more | Interior | 3 | 1.00 | 1.00
End | 2 | 1.00 | 1.00
Simple | 1 | 1.00 | 1.05
1. With at least three evenly spaced intermediate diaphragms (excluding end diaphragms) in each span.

B. Operational Importance [1.3.5]

Delete the operational importance factors, η I ,in LRFD 1.3.5 and use η I= 1.0 unless otherwise approved by the Department. For bridges considered critical to the survival of major communities, or to the security and defense of the United States, consider using η I= 1.05.