Chapter 2: Limit States and Loads


Section 1: Limit States

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Importance Factor

Classify all bridge designs as typical bridges when applying the operational importance factor, ηI, to strength limit states. Use ηI = 1.0 for all limit states. See Article 1.3.5.

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Extreme Event Limit States

Extreme Event I and II

Provisions under Extreme Event I need not be considered except for regions near Big Bend as noted in the subsequent section on Earthquake Effects.

Provisions under Extreme Event II must be considered only when vehicular collision or vessel collision evaluation is required.

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Multi-column Bridges

For typical multi-column bridges, determine design loads for foundations at Service I Load Combination. Determine foundation loads for single column bents and other non-typical substructures using Service I and Service IV Load Combinations. For Service IV Load Combination, 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 Article Distribute the live load equally to all supporting foundations, assuming all lanes are loaded. Do not apply the Dynamic Load Allowance (IM) to the live load in determining foundation loads when the foundation elements are entirely below ground level.

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Live Load Deflection

Check live load deflection using Articles and 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.

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