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Section 12: Cast-in-Place Concrete Slab Spans

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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):

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  • Epoxy-Coated Reinforcing Steel meeting the requirements of ASTM A775 or A934
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  • Epoxy-Coated WWR meeting the requirements of ASTM A884 Class A or B
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  • Hot-Dip Galvanized Reinforcing Steel
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  • 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.
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  • Dual Coated Reinforcing Steel meeting the requirements of ASTM A1055
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  • Low Carbon/Chromium Reinforcing Steel meeting the requirements of ASTM A1035 Gr 100 Ty CS
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  • Stainless Reinforcing Steel meeting the requirements of ASTM A955 Ty 316LN, XM-28, 2205, or 2304; Use only for extreme chloride exposure in coastal areas.
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Geometric Constraints

The maximum skew angle for slab span bridges is 30°. With skewed spans, use shear keys that are 2 in. deep by 6 ft. wide and parallel to traffic. Form shear keys into the top of substructure caps in the middle of the caps. See the Cast-In-Place Concrete Slab Spans standard drawings for shear key details.

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

Minimum slab depths from Table 2.5.2.6.3-1 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 3.6.1.3.3 for spans more than 15 ft.

Distribute live load in accordance with 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 Articles 5.12.2.1 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.

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Design Criteria

Shear design is not required when spans are designed in accordance with Article 4.6.2.3.

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 5.12.2.1-1 to determine the required amount.

Provide #4 reinforcing bars at 12-in. maximum spacing for shrinkage and temperature reinforcement required to satisfy Article 5.10.6.

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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