Section 3: Concrete Deck Slabs on U Beams (U40 and U54)
Anchor: #i1383358Materials
Use Class S concrete (ƒ'c= 4.0 ksi). If the deck will be subjected regularly to de-icing chemicals based on district policy, add the following plan note: For Class S concrete in slab, use one of the mix design options 1 through 5 required by Item 421.
Use Grade 60 reinforcing steel. Use uncoated reinforcing steel unless the deck will be subjected regularly to de-icing chemicals based on district policy, in which case use epoxy-coated reinforcing steel.
Waterproof deck slabs with one of the two classes of treatment specified in Item 428, “Concrete Surface Treatment,” of the TxDOT Standard Specifications.
Anchor: #i1383384Geometric Constraints
TxDOT standard deck slabs are 8 in. and 8.5 in. with top clear cover of 2 in. and 2.5 in. respectively. Use the 8.5-in deck slab for bridges where regular use of de-icing salts is anticipated. Both deck slabs use 1.25-in. bottom clear cover.
Reinforce the cast-in-place portion of the slab with #5 bars spaced at 6 in. in the transverse direction and #4 bars spaced at 9 in. in the longitudinal direction
Anchor: #i1383968Design Criteria
With standard deck slabs, use the following beam spacing and overhang width limits:
- Maximum clear span is 8.583 ft. If permitting use of prestressed concrete panels, ensure clear span is acceptable based on limits shown on standard drawing PCP.
- Typical overhang is 6 ft. 9 in. measured from the center line of the bottom of the exterior beam to the edge of the slab.
- Maximum overhang is 3.917 ft. measured from slab edge to beam flange edge. At span ends, reduce the 3.917-ft. limit to 3.083 ft. to account for reduced wheel load distribution.
- Minimum overhang is 0.5 ft. measured from face of rail to beam flange edge to allow sufficient room for the slab drip bead.
- For overhangs (measured from the centerline of the outside beam to the edge of the slab) in excess of 7 ft. 3 in., check the outside web-to-bottom flange joint of the exterior beam for adequacy under construction loads.
An empirical design method must meet criteria specified in Article 9.7.2 of the AASHTO LRFD Bridge Design Specifications except the deck slab must be at least 8 in. thick or 8.5 in. thick when deicing chemicals are used. Do not use an empirical design method for conventional staged construction because it does not provide the minimum overhang. Do not use an empirical design method if permitting use of prestressed concrete panels.
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.
Overhang strength for extreme events, described in Article 9.5.5 of the AASHTO LRFD Bridge Design Specifications, is satisfied through TxDOT’s rail crash testing.
Anchor: #i1384158Detailing
In overhangs, use a 3-in. space between outermost Bars D to minimize slab damage from rail impacts. Space Bars T at 9 in. to provide better crack control at construction joints, precast panel ends, and control joints placed at interior bent locations with continuous slab/simple span construction.