Chapter 2: Limit States and Loads
Anchor: #BAGHFEJCSection 1: Limit States
Anchor: #i1350343Limit States
Classify all bridge designs as typical bridges when applying
the operational importance factor, 
,
to strength limit states. Use 
= 1.0
for all limit states. See AASHTO LRFD Bridge Design
Specifications, Article 1.3.5.
Provisions under Extreme Event I need not be considered except for regions near Big Bend.
Provisions under Extreme Event II must be considered only when vehicular collision or vessel collision evaluation is required.
For typical multi-column bridges, determine design loads for foundations at Service Limit State I. Foundation loads for single column bents and other non-typical substructures should be determined by Service Limit State I and Service Limit State IV. For Service Limit State IV, include the vertical wind pressure as specified in Article 3.8.2. For foundation loads on typical multi-column bents and abutments, use the multiple presence factor, m, per AASHTO LRFD Bridge Design Specifications, Article 3.6.1.1.2. Distribute the live load equally to all supporting foundations, assuming all lanes are loaded.
Follow the procedures described in the TxDOT Geotechnical Manual, which is available on the internet at ftp://ftp.dot.state.tx.us/pub/txdot-info/gsd/manuals/geo.pdf, to determine the size and length of foundations.
Check live load deflection using AASHTO LRFD Bridge Design Specifications, Articles 2.5.2.6.2 and 3.6.1.3.2. Ensure that the calculated deflection does not exceed Span/800 using a live load distribution factor equal to number of lanes divided by number of girders. If the bridge has pedestrian sidewalks, the deflection limit is Span/1000.