4.2 Deck Slabs [5.13.1][9.7]

4.2.1 Bridge Length Definitions (07/04)  2004 July: Defined Short bridges as 100 ft or less and Long bridges as greater than 100 ft.

For establishing profilograph and deck thickness requirements, bridge structures are defined as Short Bridges or Long Bridges. The determining length is the length of the bridge structure measured along the Profile Grade Line (PGL) of the structure. This includes the lengths of exposed concrete riding surface of the approach slabs. Based upon this established length, the following definitions apply:

A. Short Bridges: Bridge structures less than or equal to 100 feet in PGL length.

B. Long Bridges: Bridge structures more than 100 feet in PGL length.

4.2.2 Deck Thickness Determination (01/07)  2007 Jan: Changed G. "milling" to "planing."  2004 July: Added requirements for thickness below railing.

A. For new construction of “Long Bridges” other than inverted T-Beam bridge superstructures, the minimum thickness of bridge decks cast-in-place (CIP) on beams or girders is 8½-inches.  The 8½-inch deck thickness includes a one-half inch sacrificial thickness to be included in the dead load of the deck slab but omitted from its section properties.

B. For new construction of “Short Bridges” other than Inverted-T Beam bridge superstructures, the minimum thickness of bridge decks cast-in-place (CIP) on beams or girders is 8-inches.

C. The cast-in-place bridge deck thickness for Inverted-T Beam bridge superstructures with Inverted-T Beams spaced on two foot centers is 6½-inches and 6-inches for bridges meeting the definition of Long and Short Bridges, respectively. The deck thickness beneath traffic railings must be increased to 8 1/2-inches for Long Bridges and 8-inches for Short Bridges. The increased deck thickness must extend to the first interior beam for edge railings, and at least one full bay each side of the traffic railing for interior railings

D. For “Major Widenings,” (see criteria in Chapter 7) the thickness of CIP bridge decks on beams or girders is 8-inches.  However, whenever a Major Widening is selected by the Department to meet profilograph requirements, a minimum deck thickness of 8½-inches to meet the requirements and design methodology for new construction of the preceding paragraph, must be used.

E. The thickness of CIP bridge decks on beams or girders for minor widenings or for deck rehabilitations will be determined on an individual basis but generally will match the thickness of the adjoining existing deck.

F. The thickness of all other CIP or precast concrete bridge decks is based upon the reinforcing cover requirements of SDG Table 1.2.

G. Establish bearing elevations by deducting the determined thickness before planing, from the Finish Grade Elevations required by the Contract Drawings.

4.2.3 Grooving Bridge Decks (07/06)  2006 July: Added new pay item 400-9.

A. For new construction utilizing C-I-P bridge deck (floors) that will not be surfaced with asphaltic concrete, include the following item in the Summary of Pay Items:

Item No. 400-7 - Bridge Floor Grooving

XX Sq. Yards

Item No. 400-9 - Bridge Floor Grooving and Planing

XX Sq. Yards

B. Quantity Determination: Determine the quantity of bridge floor grooving in accordance with the provisions of Article 400-22.3 of the “Specifications.”

4.2.4 Deck Slab Design [9.7.2][9.7.3] (01/09) 2009 Jan:Added 32-inch Corral Shape to table. Deleted "beyond the outer edge of the top flange of the exterior beam." from the last sentence of last paragraph (B). 2004 July: Paragraphs "A"& "B" - Added proviso for Staged Construction or Future Widening. Clarified deck overhang measurement criteria.

A. Empirical Design Method: For Category 1 structures meeting the criteria in LRFD [9.7.2.4] and are not subject to either staged construction or future widening, design deck slabs by the Empirical Design method of LRFD [9.7.2]. In lieu of the minimum area and maximum spacing reinforcing requirements of LRFD [9.7.2.5], use no. 5 bars at 12-inch centers in both directions in both the top and bottom layers. Place two additional No. 5 bars between the primary transverse top slab bars (4-inch nominal spacing) in the slab overhangs to meet the TL-4 loading requirements for the FDOT standard traffic railings. Extend one of the additional bars to the mid-point between the exterior beam and the first interior beam; extend the second additional bar 36-inches beyond this mid-point. The maximum deck overhang is 6 feet, measured from the centerline of the exterior beam.

B. Traditional Design Method: For all Category 2 Structures and for Category 1 Structures that do not meet the requirements of LRFD [9.7.2.4]  and are subject to either staged construction or future widening, design deck slabs in accordance with the Traditional Design method of LRFD [9.7.3]. For the deck overhang design and median barriers, the following minimum transverse top slab reinforcing (As), may be provided (without further analysis) where the indicated minimum slab depths are provided and the total deck overhang is 6 feet or less. However, for 8-inch thick decks with eight-foot sound wall traffic railings the deck overhang is limited to 18-inches beyond the outer edge of the top flange of the exterior beam. The extra slab depth for deck grinding is not included.

 

Traffic Railing Barrier

(Test Level)

 Slab Depth

As/ft (sq in)

32-inch F-Shape (TL-4)

8-inches

0.80

32-inch Vertical Face (TL-4)

8-inches

0.80

32-inch Corral Shape (TL-4)

8-inches

0.80

32-inch F-Shape Median (TL-4)

8-inches

0.40*

8'-0" Sound Barrier (TL-4)

8-inches

0.93**

8'-0" Sound Barrier (TL-4)

10-inches

0.66**

42-inch F-Shape (TL-5)

10-inches

0.75

42-inch Vertical Face (TL-5)

8-inches

(with 6-inch sidewalk)

0.40*** (0.40)

*   Minimum reinforcing required in both top and bottom of slab. Less reinforcing may be provided in the bottom, provided the sum of the top and bottom reinforcing is not less than 0.80 square inch per foot.

** For the eight foot sound wall, the area of top slab reinforcing 6 feet each side of deck expansion joints must be increased by 30% to provide a minimum 1.21 square inches per foot for an 8-inch thick slab and 0.86 square inches per foot for a 10-inch thick slab. Evaluate the development length of this additional reinforcing and detail hooked ends for all bars when necessary.

*** Minimum reinforcing based on the 42-inch vertical face traffic railing mounted on a 6-inch thick sidewalk above an 8-inch deck with 2-inch cover to the top reinforcing in both the deck and sidewalk. Specify No. 4 Bars at 6-inch spacing placed transversely in the top of the raised sidewalk.

For traffic railings located inside the exterior beam (other than median barriers), the minimum transverse reinforcing in the top of the slab may be reduced by 40% provided the bottom reinforcing is not less than the top reinforcing.

If the above reinforcing is less than or equal to twice the nominal slab reinforcing, the extra reinforcing must be cut-off 12-inches beyond the midpoint between the two exterior beams. If the above reinforcing is greater than twice the nominal slab reinforcing, then half of the extra reinforcing or up to 1/3 the total reinforcing must be cut-off midway between the two exterior beams. The remaining extra reinforcing must be cut off at 3/4 of the two exterior beam spacing, but not closer than 2 feet from the first cut-off.

4.2.5 Traffic Railing Design Requirements (01/09) 2009 Jan: Added 32-inch corral shape. Changed Mu equation to 1.00*MDeadload.

A. In lieu of the Traditional Design Method shown above, the following design values may be used to design the top transverse slab reinforcing, for the types listed:

Traffic Railing Type  (Test Level)

Mc

Tu

Ld

32-inch Corral Shape (TL-4)

15.7

7.1

7.67

32-inch F-Shape (TL-4)

15.7

7.1

7.67

32-inch Vertical Face (TL-4)

16.9

7.1

7.67

32-inch Median (TL-4)

15.3

3.5

7.67

8-foot Sound Barrier (TL-4)

20.1 ***

***5.9

21.00

42-inch F-Shape (TL-5)

20.6

9.0

13.75

42-inch Vertical Face (TL-5)

25.8

10.6

12.50

*** For the 8-foot sound wall, increase the ultimate slab moment and tensile force by 30% for a distance of 6 feet each side of all deck expansion joints, except on approach slabs.

Where:

Mc = Ultimate slab moment at the traffic railing face (gutter line) from traffic railing impact (kip-ft/ft.

Tu = Ultimate tensile force to be resisted (kips/ft.).

Ld = Distribution length (ft.) along the base of the traffic railing at the gutter line near a traffic railing open joint (Lc + traffic railing height).

 

The following relationship must be satisfied:

 

(Tu / ØPn) + (Mu / ØMn) ≤ 1.0

 

for which:

 

Pn = As fy

 

Where:

 

Ø = 1.0

 

Pn   = Nominal tensile capacity of the deck (kips/ft.).

 

As  = Area of transverse reinforcing steel in the top of the deck (sq. in.)

 

fy  = The reinforcing steel yield strength (ksi).

 

Mu =  Total ultimate deck moment from traffic railing impact and factored dead load at the gutter line

(Mc + 1.00*MDead Load) (kips-ft/ft).

 

Mn - Nominal moment capacity at the gutter line determined by traditional rational methods for reinforced concrete (kips-ft/ft).

B. For locations inside the gutter line, these forces may be distributed over a longer length of Ld + 2D(tan 45º) feet.  Where "D" equals the distance from the gutter line to the critical slab section. At open transverse deck joints, use half of the increased distribution length D(tan 45º).

C. For flat slab bridges the transverse moment due to the traffic railing dead load may be neglected. The area of transverse top slab reinforcing determined by analysis, for flat slab bridges with edge traffic railings must not be less than 0.30 sq in/ft within 4 feet of the gutter line for any TL-4 traffic railing or 0.40 sq in/ft within 10 feet of the gutter line for any TL-5 railing.

D. When more than 50% of the total transverse reinforcing must be cut off, a minimum of 2 feet must separate the cut-off locations.

E. For traffic railings located inside the exterior beam, or greater than 5 feet from the edge of flat bridges, the designer may assume that only 60% of the ultimate slab moment and tensile force are transferred to the deck slab on either side of the traffic railing.

4.2.6 Reinforcing Steel over Intermediate Piers or Bents

A. When CIP slabs are made composite with simple span concrete beams, and are cast continuous over intermediate piers or bents, provide supplemental longitudinal reinforcing in the tops of slabs.

B. Size, space, and place reinforcing in accordance with the following criteria:

1.) No. 5 Bars placed between the continuous, longitudinal reinforcing bars.

2.) A minimum of 35 feet in length or 2/3 of the average span length whichever is less.

3.) Placed symmetrically about the centerline of the pier or bent, with alternating bars staggered 5 feet.

 4.2.7 Minimum Negative Flexure Slab Reinforcement [6.10.1.7]

Any location where the top of the slab is in tension under any combination of dead load and live load is considered a negative flexural region.

Commentary: See Chapter 7 for additional slab reinforcing requirements.

4.2.8 Crack Control in Decks [5.10.8] (01/09) 2009 Jan: Extensively revised to cover all deck types. 2008 Jan: Revised section to expand deck casting requirements and include continuous decks on simple spans including new paragraphs C.; D.; & E. 2007July:  A.- Changed 80’ construction joint spacing to points of contraflexure and added continuous flat slab bridges ;C.- Added commentary

A. To minimize shrinkage and deflection cracking in cast-in-place decks, develop a designated deck casting sequence for continuous flat slab and beam/girder superstructures and simple span beam/girder superstructures with continuous decks. Indicate on the plans the sequence and direction of each deck pour so as to minimize cracking in the freshly poured concrete and previously cast sections of deck. For continuous steel and concrete beam/girder superstructures, the sequence should result in construction joints spaced approximately at locations of the points of dead load moment contraflexure.  For continuous flat slab superstructures, show construction joints at most one-quarter and/or three-quarter points in the spans. Space joints at not less than 20 feet or more than 80 feet.  Provide additional construction joints as required to limit the volume of cast concrete.

B. For simple span and continuous steel beam/girder superstructures, develop camber diagrams taking into consideration the deck casting sequence and the effect on the changing cross section characteristics of the superstructure.  On continuous superstructures, check longitudinal tension stresses in previously cast sections of deck during deck casting sequence per LRFD 6.10.3.2.4.  State on the plans that a minimum of 72 hours is required between pours in a given continuous unit. See also SDG 5.2 .

C. For continuous concrete beam/girder superstructures, develop build-up diagrams taking into consideration the deck casting sequence, time dependent effects, and the effect on the changing cross section characteristics of the superstructure. State on the plans that a minimum of 72 hours is required between pours in a given continuous unit.

Commentary: Generally for continuous beam/girder superstructures, all of the positive moment sections of the deck are cast first, followed by the negative moment sections.

D. For simple span concrete beam/girders with continuous decks, locate construction joints at the ends of the spans and at intermediate locations as required. Include the alternate detail showing the deck continuously cast over intermediate supports with tooled joints in lieu of construction joints.  After placement of the first unit, begin succeeding placements at the end away from and proceed toward the previously placed unit. State on the plans that a minimum of 72 hours is required between adjacent pours in a given continuous unit.

E. For simple and continuous flat slab superstructures, develop camber diagrams indicating the deflection of the spans due to self weight of the deck and railings. For continuous flat slab superstructures, show construction joints at most one-quarter and/or three-quarter points in the spans. Space joints at not less than 20 feet or more than 80 feet.  After placement of the first unit, begin succeeding placements at the end away from and proceed toward the previously placed unit. State on the plans that a minimum of 72 hours is required between adjacent pours in a given continuous unit.

Commentary:  For flat slab superstructures, the Contractor is responsible for determining the deflection of the formwork due to the weight of the wet deck concrete, screed and other construction loads.

F. For all superstructure types listed above, state on the plans that the casting sequence may not be changed unless the Contractor’s Specialty Engineer performs a new structural analysis, and new camber diagrams are calculated.

G. Units composed of simple span steel girders with continuous decks are not allowed due to the flexibility of the girders.

Commentary: Casting sequences and the location of the construction joints should be sized so that the concrete can be placed and finished while the concrete is in a plastic state and within an 8 hour work shift. A reasonable limit on the size of a superstructure casting is 200 cy to 400 cy. Plan the location of construction joints so the concrete can be placed using a pumping rate of 60 cy/hr for each concrete pumping machine. Site specific constraints (i.e. lane closure restrictions, etc.) should be taken into account when determining the size of a deck casting and/or location of construction joints.

4.2.9 Structures Continuous for Live Load (01/09) 2009 Jan: The information in this section has been removed.

Removed information.

4.2.10 Concrete Decks on Continuous Steel Girders (01/09) 2009 Jan: Deleted additional design requirements for the remainder of the deck.

For longitudinal reinforcing steel within the negative moment regions of continuous, composite steel girder superstructures, comply with the requirements of LRFD [6.10.1.7].

4.2.11 Skewed Decks [9.7.1.3] (01/05)  2005 Jan: Clarifies that longitudinal reinforcement be placed along full width of deck.

A. Reinforcing Placement when the Slab Skew is 15 Degrees or less:

Place the transverse reinforcement parallel to the skew for the entire length of the slab.

B. Reinforcing Placement when the Slab Skew is more than 15 Degrees:

Place the required transverse reinforcement perpendicular to the centerline of span. Since the typical required transverse reinforcement cannot be placed full-width in the triangular shaped portions of the ends of the slab at open joints, the required amount of longitudinal reinforcing must be doubled for a distance along the span equal to the beam spacing for the full width of the deck. In addition, three No. 5 Bars at 6” spacing, full-width, must be placed parallel to the end skew in the top mat of each end of the slab.

C. Regardless of the angle of skew, the traffic railing reinforcement cast into the slab need not be skewed.

4.2.12 Temperature and Shrinkage Reinforcement

For all cast in place decks, design temperature and shrinkage reinforcement per LRFD [5.10.8] except do not exceed 12-inch spacing and the minimum bar size is No 4.

4.2.13 Stay-in-Place Forms (01/09) 2009 Jan: Revised per TDB C08-05.

A. Clearly state in the “General Notes” for each bridge project, whether or not stay-in-place forms are permitted for the project and how the design was modified for their use; e.g., dead load allowance.

B. Design and detail for the use of stay-in-place metal forms, where permitted, for all beam and girder superstructures (except segmental box girder superstructures) in all environments.

Commentary:  Effective with the January 2009 Workbook, per Specification Section 400-5.7, polymer laminated non-cellular SIP metal forms will be permitted for forming bridge decks of superstructures with moderately or extremely aggressive environmental classifications.

C. Precast, reinforced concrete, stay-in-place forms may be used for all environmental classifications; however, the bridge plans must be specifically designed, detailed and prepared for their use.

D. Composite stay-in-place forms are not permitted.