Section 11: Cast-in-Place Concrete Slab Spans
Anchor: #i1359024Materials
Use Class S concrete (ƒ'c = 4.0 ksi). If the slab 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 slab will be subjected regularly to de-icing chemicals based on district policy, in which case use epoxy-coated reinforcing steel.
Waterproof slabs with one of the two classes of treatment specified in Item 428, “Concrete Surface Treatment.”
Anchor: #i1359083Geometric Constraints
The maximum skew angle for slab span bridges is 30 degrees. Use shear keys 2 in. deep by 6 in. wide, parallel to traffic, with skewed spans. Shear keys should be formed into the top of substructure caps in the middle of the caps. See standard drawings for shear key details.
Break slab corners 1.5 ft. with skews more than 15 degrees.
Minimum slab depths from AASHTO LRFD Bridge Design Specifications, Table 2.5.2.6.3-1 are guidelines but are not required.
Use a top clear cover of 2 in. Use 2.5-in. top clear cover where regular use of de-icing salts is anticipated. Use 1.25-in. bottom clear cover.
Limit span lengths to approximately 25 ft. for simple spans and end spans of continuous units. Limit interior spans of continuous units to approximately 30 ft.
Anchor: #i1359193Structural Analysis
Distribute the weight of all railing and sidewalks over the entire slab width if the slab is no wider than 32 ft. Otherwise, distribute railing load over 16 ft.
Design using 1-ft. wide strips. Take bearing centerline at cap quarter points. For interior supports of continuous spans, assume bearing centerline coincides with cap centerline.
Apply both the axle loads and lane loads of the HL-93 live load in accordance with AASHTO LRFD Bridge Design Specifications, Article 3.6.1.3.3 for spans more than 15 ft.
Distribute live load in accordance with AASHTO LRFD Bridge Design Specifications, Article 4.6.2.3 using Equation 4.6.2.3-2. Use Equation 4.6.2.3-3 to reduce force effects with skewed bridges.
For longitudinal edge beams, required by AASHTO LRFD Bridge Design Specifications, Articles 5.14.4.1 and 9.7.1.4, apply one line of wheels plus the tributary portion of the lane load to the reduced strip width specified in Article 4.6.2.1.4b.
Anchor: #i1359399Design Criteria
Shear design is not required when spans are designed in accordance with AASHTO LRFD Bridge Design Specifications, Article 4.6.2.3.
The longitudinal edge beam cannot have less flexural reinforcement than interior slab regions. Do not consider concrete barrier rails, parapets, or sidewalks in longitudinal edge beam design.
Provide bottom transverse distribution reinforcement. Use AASHTO LRFD Bridge Design Specifications, Equation 5.14.4.1-1 to determine the required amount.
Provide #4 reinforcing bars at 12-in. maximum spacing for shrinkage and temperature reinforcement required to satisfy AASHTO LRFD Bridge Design Specifications, Article 5.10.8.
Assume Class 1 exposure condition when checking distribution of reinforcement for crack control except for top flexural reinforcement in continuous spans, in which case assume Class 2 exposure condition.
When calculating the cracking moment of a member
in accordance with Article 5.7.3.3.2, take the modulus of rupture, ƒr,
as 0.24
, for all normal weight concrete.