Section 13: Cast-in-Place Concrete Slab Spans

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Use Class S concrete ( = 4.0 ksi). If the slab will be subjected regularly to de-icing agents or could come into contact with saltwater spray, use Class S (HPC) concrete.

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

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Geometric 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. Form shear keys into the top of substructure caps in the middle of the caps. See relevant standard drawings for shear key details.

Break slab corners 1.5 ft. with skews more than 15 degrees.

Minimum slab depths from Table are guidelines but are not required.

Use a top clear cover of 2.5 in. 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.

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Structural 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 Article for spans more than 15 ft.

Distribute live load in accordance with Article using Equation Use Equation to reduce force effects with skewed bridges.

For longitudinal edge beams, required by Articles and, apply one line of wheels plus the tributary portion of the lane load to the reduced strip width specified in Article

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Design Criteria

Shear design is not required when spans are designed in accordance with Article

The longitudinal edge beam cannot have less flexural reinforcement than interior slab regions. Do not consider the additional flexural capacity of concrete barrier rails, parapets, or sidewalks in longitudinal edge beam design.

Provide bottom transverse distribution reinforcement. Use Equation to determine the required amount.

Provide #4 reinforcing bars at 12-in. maximum spacing for shrinkage and temperature reinforcement required to satisfy 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.

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