Section 2: Loads


Live Loads

Use HL93 design live load as described in Article unless design for a special vehicle is specified or warranted.

Design widenings for existing structures using HL93. Rate existing structures using Load Factor Rating per the current AASHTO Manual for Bridge Evaluation and HS20 loading. Show load rating and design loads on the bridge plan, for example, HS20 (Existing) HL93 (New).

Do not use the reduction in the multiple presence factor (m) based on Average Daily Truck Traffic (ADTT) on the bridge as suggested in the Article C3., Multiple Presence of Live Load.

For simple-span bridges, do not apply the provisions for two design trucks as described in Article

Disregard recommendations to investigate negative moment and reactions at interior supports for pairs of the design tandem provided in the commentary to Article, Application of Design Vehicular Live Loads.

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Braking Force

Take the braking force, BR, as 5% of the design truck plus lane load or 5% of the design tandem plus lane load.

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Vehicular Collision Force

Abutments and retaining walls—Due to the soil behind abutments and retaining walls, the collision force in Article 3.6.5 need not be considered.

Bents—Do not investigate bents and piers for collision if the annual frequency for a bridge bent or pier to be hit by a vehicle, AFHPB, is less than 0.001 using Equation C3.6.5.1-1. Design for vehicular collision force for the final condition after all construction is completed, not during construction phases with temporary traffic conditions. A bridge deck adjacent to the column is considered an adjacent roadway.

When investigating for collision, there are two design choices: redirect the collision load or provide structural resistance. When the design choice is to redirect the collision load, the protection must meet at least one of the following requirements:

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  • Protect with a structurally independent, ground-mounted 54-in. tall single slope concrete barrier (or other 54-in. tall, Test Level 5 approved barrier equivalent) if within 10 ft. from component.
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  • Protect with a 42-in. tall single slope concrete barrier (or 42-in tall, Test Level 5 approved barrier equivalent) if more than 10 ft. from component.

When the design choice is to provide structural resistance, design for the 600-kip equivalent static load as described in Article 3.6.5. See Chapter 4 - Substructure Design, Sections 6 - Columns for Multi-Column Bents and Section 7 - Columns for Single Column Bents or Piers for design information.

For structures with a clear distance of 25 ft. or less from the center line of a railway track, meet the requirements of American Railway Engineering and Maintenance-of-Way Association (AREMA), or the governing railroad company.

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Earthquake Effects

Except as noted below, bridges and structures in Texas do not require analysis for seismic loading due to the low seismic hazard as shown in Article 3.10.2.

The TxDOT Bridge Standards and conventional bridge configurations have been evaluated for seismic effects and do not require further analysis.

For conventional structures with superstructure unit lengths or interior bent "H" heights outside of the limits stated in the TxDOT Bridge Standards and which are located in Brewster, Presidio, Jeff Davis, Culberson, Hudspeth and El Paso counties, check Minimum Support Length Requirements outlined in Article

Non-conventional or exotic bridges do not require seismic evaluation, except those located in Brewster, Presidio, Jeff Davis, Culberson, Hudspeth and El Paso counties. In these locations, evaluate the structure for earthquake effects as required by Article 3.10. Contact the TxDOT Bridge Division for guidance.

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Vessel Collision

TxDOT requires that all bridges crossing waterways with documented commercial vessel traffic comply with Article 3.14. For widening of existing structures, at least maintain the current strength of the structure relative to possible vessel impact, and increase the resistance of the structure where indicated if possible. Consult the TxDOT Bridge Division for assistance interpreting and applying these design requirements.

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