ABSTRACT

In load and resistance factor design (LRFD), bridges are designed for specific limit states that consider various loads and resistance. These limit states include strength, extreme event, service, and fatigue, and are defined in the first section of this chapter. Subsequent sections cover the following load and resistance factors in more detail:

• Load combinations and load factors

• Strength limit states for superstructure design

• Resistance factors for strength limits

• Design live loads

• Number of design lanes

• Multiple presence of live loads

• Dynamic load allowances

• Live load distribution factors

• Load combinations for the Strength I Limit State

• Simple beam moments and shears carrying moving concentrated loads

The following load combinations are defined in AASHTO. Bridges are designed for these limit states with consideration for the load and resistance factors detailed in later sections of this chapter.