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Section 8: Pretensioned Concrete Decked Slab Beams

Materials

Use Class H concrete with a minimum= 4.0 ksi and= 5.0 ksi and a maximum = 6.0 ksi and = 8.5 ksi.�

Use non-shrink cementitious grout for shear keys.

Use prestressing strand with a specified tensile strength, fpu of 270 ksi.

Geometric Constraints

The maximum skew angle for decked slab beam bridges is 30 degrees.

Use a 2-in. minimum thickness asphaltic concrete pavement (ACP) overlay for most roadways. A two-course surface treatment, or no wearing surface, may be used for low-volume roadways at the District’s discretion.

Structural Analysis

Beam designs must meet the following requirements:

  • Distribute the weight of one railing to no more than three beams.
  • Use section properties provided on the pretensioned concrete double-tee beam standard drawings.
  • Live load distribution factors for all beams--both moment and shear--must conform to Table 4.6.2.2b-1, using cross section (j) if beams are connected only enough to prevent relative vertical displacement at their interfaces. Use K = 2.0 when determining the live load distribution factor.
  • Use S/10 as maximum limit on live load distribution.
  • Do not apply the skew correction factor for moment as suggested in Article 4.6.2.2.2e.
  • Do not take the live load distribution factor for moment or shear as less than the number of lanes divided by the number of girders, including the multiple presence factor per Article 3.6.1.1.2.

Design Criteria

Standard beam designs must meet the following requirements:

  • Add and debond strands in the order shown on the DSBND standard drawings.
  • Debond strands in 3-ft. increments at beam ends if necessary to control stresses at release.
    • Debond no more than 75 percent of the strands per row or per section.
    • The maximum debonding length is the lesser of: (a) one-half the span length minus the maximum development length; (b) 0.2 times the beam length; or (c) 15 ft.
  • Calculate required stirrup spacing for #4 Grade 60 bars according to the Article 5.8. Change stirrup spacing as shown on the DSBD standard drawing, only if analysis indicates the inadequacy of the standard design.
  • Standard decked slab beams satisfy Article 5.8.4 and Article 5.10.10.
  • Connect adjacent beams with lateral connectors, shown on standard drawing DSBD, spaced at 5 ft. maximum, with the first lateral connectors set 1 ft. from bent centerlines. See span standard drawings for completion of lateral connection details.
  • See Section 4, Pretensioned Concrete I Girders, for other design criteria.

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