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Section 2: Concrete Deck Slabs on I-Girders, U-Beams, Spread Box Beams, Spread Slab Beams, Steel Plate Girders and Steel Tub Girders

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Materials

Use Class S concrete (= 4.0 ksi). If the deck will be subjected regularly to de-icing agents based on district policy, use Class S (HPC) concrete.

Use Grade 60 reinforcing steel. Use uncoated reinforcing steel unless the deck will be subjected regularly to de-icing agents based on district policy, in which case use epoxy-coated reinforcing steel.

Optional reinforcements allowed:

  • Glass Fiber Reinforced Polymer (GFRP) bars are allowed as a substitute for epoxy coated Grade 60 reinforcing steel. The design for GFRP reinforcement in bridge decks must adhere to the AASHTO LRFD Guide Specifications for GFRP-Reinforced Concrete Bridge Decks and Traffic Railings.
  • Deformed welded wire reinforcement (WWR) meeting the requirements of ASTM A1064 is allowed as a substitute for uncoated Grade 60 reinforcing steel.
  • Dual coated reinforcing steel meeting the requirements of ASTM A1055 is allowed as a substitute for epoxy coated reinforcing steel.
  • Low carbon/chromium reinforcing steel meeting the requirements of ASTM A1035 Gr 100 is allowed as a substitute for epoxy coated reinforcing steel.
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Geometric Constraints

TxDOT standard deck slab is 8.5 in. deep. Use of thinner concrete decks is not permitted.

Cover to reinforcing bars is 2.5 in. clear to the top mat and 1.25 in. clear to the bottom mat. Cover to bar ends is 2 in.

Maximum overhang is 3.33 ft. beyond the design section for negative moment specified in AASHTO LRFD Article 4.6.2.1.6, but not more than 1.3 times the girder depth.

Minimum overhang is 0.5 ft. from top beam or flange edge except for spread slab and box beams, which have a 0 ft. minimum overhang.

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Design Criteria

Where applicable, use the Empirical Design of AASHTO LRFD Article 9.7.2 with the following exceptions:

  • Top mat reinforcement is No. 4 bars at 9 in. maximum spacing (0.27 sq in/ft) in both transverse and longitudinal direction. Place longitudinal bars closest to the top slab surface. In the overhangs, place No. 5 bars extending 2 ft. minimum past fascia girder web centerline between each transverse No. 4 bar.
  • Bottom mat reinforcement is No. 4 bars at 9 in. maximum spacing (0.27 sq in/ft) in both transverse and longitudinal directions. Place transverse bars closest to the bottom slab surface.
  • Slab regions adjacent to expansion joints are reinforced as shown on the standard drawings depicting thickened slab end details. No additional reinforcement in end regions, including those skewed over 25 degrees, is needed in these cases. These standard drawings are:
    • IGTS for Tx Girders
    • UBTS for U-beams
    • SGTS for Steel I-beams and Plate Girders
    • XBTS for Spread Box Beams
  • Cross-frames or diaphragms are not needed at supports for any prestressed concrete beam or girder.
  • Do not provide supplemental reinforcement over the webs of U-beams or steel tub girders.
  • The deck does not need to be fully cast-in-place and can utilize stay-in-place concrete formwork such as prestressed deck panels shown on standard drawing PCP.
  • The overhang need not extend past the exterior girder more than 6 in. beyond the flange edge (0 in. for spread slab or box beams). An overhang is not required for girders and beams for the temporary condition of having a stage or phase construction joint located on top of their flange.

Use the provisions of Article 9.7.3 where the provisions listed above for empirical deck use are not met. The minimum amount of longitudinal reinforcement in the top mat is No. 4 bars at 9 in. maximum spacing for these deck designs.

Overhang strength for extreme events, Article 9.5.5, is satisfied through TxDOT’s rail crash testing.

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Detailing

Place main reinforcing steel parallel to the skew up to 15 degree skews. Place reinforcing steel perpendicular to beams for skews more than 15 degrees, and use corner breaks.


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