Anchor: #BAGDDCIB

Section 2: Loads

Anchor: #BABCAAIE

Live Loads

Use HL93 design live load as described in Article 3.6.1.2 unless design for a special vehicle is specified or warranted.

Design widenings for existing structures using HL93. Rate existing structures using AASHTO Standard Specifications 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 3.6.1.1.2, Multiple Presence of Live Load.

For simple-span bridges, do not apply the provisions for two design trucks as described in Article 3.6.1.3.1.

Disregard recommendations to investigate negative moment and reactions at interior supports for pairs of the design tandem provided in the commentary to Article 3.6.1.3.1, Application of Design Vehicular Live Loads.

Anchor: #i1350595

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. See Article 3.6.4.

Anchor: #i1350628

Vehicular Collision Force

See Article 3.6.5.

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. If the bent or pier needs to be investigated for collision and the design choice is to redirect or absorb the collision load, the protection must meet at least one of the following requirements:

  • 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.
  • 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.

If the design choice is to provide structural resistance, design for the 600-kip equivalent static load as described in this Article. Validate that the structure provides adequate resistance for the Extreme Event Limit State. Analyze using Extreme Event II Load Combination. Use 1.25 load factor for all dead loads and 0.5 load factor for live load, considering live load only on the permanent travel lanes, not the shoulder lanes. Use of a deflection wall between the columns can be used if necessary. The Bridge Division can provide sample details for deflection walls for some bent and pier types.

Single-column bents require special consideration. Generally single-column bents have sufficient mass and will meet the requirements of Article 3.6.5. No further analysis is required for columns with a gross cross-sectional area no less than 40 sq. ft., a least dimension of no less than 5 ft. and column transverse reinforcement is composed of at least No. 4 ties at 12-in maximum spacing or a No. 4 spiral at 9-in maximum pitch.

For structures within 50 ft. of 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.

Anchor: #i1350704

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 4.7.4.4.

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.

Anchor: #i1350734

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.


Previous page  Next page   Title page