1 ODOT Structure Project Manager Seminar Concrete Decks Basic design, everyone has experience, go quickly to give flavor then some topics of interest
2 ODOT’s Requirements Materials Design Plan details Misc. Insights NOT MUCH TO SAYHIGHLIGHT BDM REQUIREMENTS and GO A STEP FURTHER WITH SOME TOPICS OF INTEREST
3 Selection of Concrete for Bridge Decks The following concrete types may be specified:A. Class S ConcreteB. Class HP ConcreteC. Class S Concrete for New Bridge Decks with WarrantyD. Class HP Concrete for New Bridge Decks with WarrantyE. QC/QA Concrete Class QSC2F. QC/QA Concrete Class QSC3District to confirm the selection of concrete to be used.Concrete Design Allowable: Load Factor Design 4500 psi
4 Reinforcing Steel Requirements Minimum concrete cover for reinforcingA. Top reinforcing steel …………………… ½ inchesB. Bottom reinforcing steel …………………….1½ inchesC. Clearance to edge of deck ….……………… 3 inchesAll reinforcing steel shall be epoxy coated, Grade 60 ksiSuggested Minimum Lap Splices for Deck Reinforcing Steel:#4 min. lap 2’-0”#5 min. lap 2’-6”#6 min. lap 3’-0”
5 Design RequirementsIn order to facilitate forming, deck slab overhang should not exceed 4'-0".1-inch monolithic concrete. This one-inch thickness shall not be considered in the structural design of the deck slab or as part of the composite section.The design live load shall be HS25 for decks on new superstructures and HS20 for decks on existing superstructures (optional HS25 per project scope).All bridges shall be designed for a future wearing surface (FWS) of 60 psf .
6 Design ThicknessFor reinforced concrete decks on steel or concrete stringers the deck thickness shall be computed by the following formula:Tmin (inches) = (S + 17)(12) ÷ 36 (not less than 8½ inches)Where S is the effective span length in feet.Minimum slab thickness is based on practical considerations such as adequate clearances, construction tolerances of concrete placement, deflection (serviceability), shear and bond.
13 Typical Haunch details Old reason - haunch encase top flange (compression) non-composite design Allow for beam profile differences Rehabilitation projects adjust to fit new profile Construction tolerances
14 Longitudinal Reinforcing Research has shown that secondary bars in the top mat of reinforced concrete bridge decks on stringers should be small bars at close spacing. Therefore the required secondary bar size shall be a #4. For stringer type bridges with reinforced concrete decks, the secondary bars shall be placed above the top of deck primary bars. This helps in reducing shrinkage cracking and adds additional cover over the primary bars.
15 Transverse Reinforcing To facilitate the placement of reinforcing steel and concrete in transversely reinforced deck slabs top and bottom main reinforcement shall be equally spaced and placed to coincide in a vertical plane.
17 Highlights of NCHRP 333Concrete mix proportions should produce low-permeability, but not increase propensity for crackingEpoxy reinforcing steel with minimum practical bar size and spacingMinimum concrete cover of 2 ½ inchesDevelop performance based specification with warrantiesAdequate curing is essentialReport published in 2004
18 Design Insight Deck design is known to be conservative Conservative assumptions:Live load moment formula, same for positive and negativePoint load v tire contact areaWestergaard theory (1930’s) – rigid supportsWearing surface depth neglectedSingle vs double reinforced sectionEffective span lengthFWS weightHaunch section effectsRounding of spacing and coinciding of top and bottom reinforcing steelHigher actual material strengthsConstruction tolerances, deck importance, high wearing, history of good performanceDECK DESIGN INSIGHTS, something to think about
19 ODOT History of deck design 1940’s top cover 1 ¾ inch, bottom cover 1 inch; 180 lbs/cy, use of bent barAsphalt concrete overlays1950’s top cover 1 inch plus monolithic ws (CF30=1/2”;CF130=3/4”;CF400=1”), Min deck 7 ½ inches’ #6 and #5 bars1960’s top cover 2 inches, #6 and #7 bars, 260 lbs/cy1976 reverse main bars to today’s practice1977 Deck protection; Primary epoxy coated steel top mat only; Secondary for ADTT greater than 5000 overlay (asphalt or concrete)1986 epoxy coated top and bottom mats1990’s top cover 2 ½ inches and bottom cover 1 ½ inches, min deck 8 ½ inches
20 Topics of InterestAlternate reinforcing steel – FRP, stainless steel, etc.Rapid replacement with precast concrete or prefabricated steel gridsAdvanced waterproofing systemsPlace approach slab with deckDeck cracking (post-tensioning)
21 STAY IN PLACE FORMSGalvanized steel or any other material type, stay in place forms, shall not be used.Limits visual inspection of underside of deck.For prestressed concrete beams, the precast concrete panel alternative, previously used by ODOT, has shown cracking problems at the joints between the panels.
22 Deck formingFOR THOSE THAT HAVE NOT BEEN TO CONSTRUCTION SITE Hangers support wood joist/stringers timbers that plywood sit on