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. Any exceptions to these limits must be approved in writing by the TxDOT Bridge Division.
= 4.0 ksi and
= 5.0 ksi and a maximum
= 6.0 ksi and
= 8.5 ksi. Any exceptions to these limits must be approved in writing by the TxDOT Bridge Division.
Use non-shrink cementitious grout for shear keys.
Use prestressing strand with a specified tensile strength,
of 270 ksi.
of 270 ksi.
Geometric Constraints
The maximum skew angle for decked slab beam bridges is 30°.
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 Prestressed Concrete Decked Slab Beams Details (DSBD) standard drawings.
- Live load distribution factors for all beams (both moment and shear) must conform to Table 4.6.2.2.2b-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 Prestressed Decked Slab Beams Non-standard Designs (DSBND) standard drawings.
- Debond strands in 3-ft. increments at beam ends if necessary to control stresses at release. If the strand size is larger than 0.6” diameter, base section increments on Article 5.9.4.3.3.
- Debonded strands must conform to Article 5.9.4.3.3 except as noted below:
- Debond no more than 50% of the total number of strands.
- Debond no more than 50% of the number of strands in that row.
- Replace Restriction B with, not more than 50% of the debonded strands, or 10 strands, whichever is greater, shall have the debonding terminated at any section, where section is defined as an increment (e.g., 3 feet, 6 feet, 9 feet).
- Up to 75 percent of debonded strands may be used for the total number, the number of strands per row, and number terminated in a section as long as principal stress at or near the transfer length is designed for per Article 5.9.2.3.3, regardless of the concrete strength.
- Do not design for Restriction E.
- Replace Restriction G with, 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.
- For multi-web sections having bottom flanges, replace Restriction J with:
- Uniformly distribute debonded strands.
- Bond the outer-most strand in each row.
- Calculate required stirrup spacing for #4 Grade 60 bars according to the Article 5.7. 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 5.7.4 and Article 5.9.4.4.
- 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.