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

Materials

Use Class S concrete ( fc'
= 4.0 ksi). Refer to district-specific corrosion protection requirements for regions where bridge decks are exposed to de-icing agents and/or saltwater spray with regularity. If thus required, use Class S (HPC) concrete.
Use Grade 60 reinforcing steel or deformed welded wire reinforcement (WWR) meeting the requirements of ASTM A1064. Refer to district-specific corrosion protection requirements for regions where bridge decks are exposed to de-icing agents and/or saltwater spray with regularity. If thus required, use one of the following types of corrosion resistant reinforcement (refer also to Item 440):
  • Epoxy-Coated Reinforcing Steel meeting the requirements of ASTM A775 or A934
  • Epoxy-Coated WWR meeting the requirements of ASTM A884 Class A or B
  • Hot-Dip Galvanized Reinforcing Steel
  • Glass Fiber Reinforced Polymer (GFRP) Bars; 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.
     Specify a minimum modulus of elasticity for GFRP of 7,500 ksi in the plans.
  • Low Carbon/Chromium Reinforcing Steel meeting the requirements of ASTM A1035 Gr 100 Ty CS
  • Stainless Reinforcing Steel meeting the requirements of ASTM A955 Ty 316LN, XM28, 2205, or 2304; Use only for extreme chloride exposure in coastal areas.

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 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 spread box beams, which have a 0 ft. minimum overhang.

Design Criteria

Where applicable, use the Empirical Design of Article 9.7.2 with the following requirements:
  • For I girders and steel I beam/girders maximum beam spacing is 10 feet. For spread box beams, U beams, and steel tub girders maximum of 10 feet spacing from exterior web.
  • Top mat reinforcement is No. 4 bars at 9 in. maximum spacing (0.27 sq. in./ft.) in both transverse and longitudinal direction. Place
    transverse
     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.
  • For continuous beams (ie. steel plate girders and concrete spliced girders), where the longitudinal tensile stress in the concrete deck due to either the factored construction loads or Load Combination Service I in Table 3.4.1-1 exceeds 0.9fr:
    • Provide longitudinal reinforcement with a total cross-sectional area of at least one percent of the total cross-sectional area of the cast-in-place portion of the concrete deck
    • Design and detail for the worst-case between the full depth cast in place deck or patrial depth cast in place deck over panels when both options are allowed on the span sheet.
    • Extend longitudinal reinforcing steel at least one development length Ld
      past the point of contraflexure.
  • 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°, is needed in these cases. The Thickened Slab End Details 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 the Prestressed Concrete Panels (PCP) standard drawing.
  • The overhang need not extend past the exterior girder more than 6 in. beyond the flange edge (0 in. for spread slab or spread 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 Traditional Design of Article 9.7.3 where the provisions listed above for empirical deck use are not met. Use the Traditional deck design of Article 9.7.3 for steel twin tub girder spans designed for redundancy per Chapter 3 – Superstructure Design, Section 17 - System Redundancy Evaluation for Steel Twin Tub Girders.
  • The minimum amount of longitudinal reinforcement in the top mat is No. 4 bars at 9 in. maximum spacing for these deck designs.
  • For continuous beams (ie. steel plate girders and concrete spliced girders), where the longitudinal tensile stress in the concrete deck due to either the factored construction loads or Load Combination Service I in Table 3.4.1-1 exceeds 09fr
    :
    • Provide longitudinal reinforcement with a total cross-sectional area of at least one percent of the total cross-sectional area of the cast-in-place portion of the concrete deck.
    • Design and detail for the worst-case between the full depth cast in place deck or patrial depth cast in place deck over panels when both options are allowed on the span sheet.
    • Extend longitudinal reinforcing steel at least one development length Ld
      past the point of contraflexure.
Overhang strength for extreme events, per Article 9.5.5, is satisfied through TxDOT’s rail crash testing.

Detailing

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