Structure Project Manager

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25 Νοε 2013 (πριν από 4 χρόνια και 1 μήνα)

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ODOT

Structure Project Manager

Seminar


Concrete Decks


ODOT’s Requirements

1.
Materials

2.
Design

3.
Plan details

4.
Misc. Insights

Selection of Concrete for
Bridge Decks


The following concrete types may be specified:

A.

Class S Concrete

B.

Class HP Concrete

C.

Class S Concrete for New Bridge Decks with Warranty

D.

Class HP Concrete for New Bridge Decks with Warranty

E.

QC/QA Concrete Class QSC2

F.

QC/QA Concrete Class QSC3


District to confirm the selection of concrete to be used.

Concrete Design Allowable: Load Factor Design 4500 psi


Reinforcing Steel
Requirements

Minimum concrete cover for reinforcing

A. Top reinforcing steel ……………………....... 2½ inches

B. Bottom reinforcing steel …………………….1½ inches

C. Clearance to edge of deck ….……………… 3 inches



All reinforcing steel shall be epoxy coated, Grade 60 ksi



Suggested Minimum Lap Splices for Deck
Reinforcing
Steel:



#4 min. lap

2’
-
0”


#5 min. lap

2’
-
6”



#6 min. lap

3’
-
0”


Design Requirements


In 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 .


Design Thickness


For 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.


Design Controls


Flexure strength


Spacing, crack control


Longitudinal distribution

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


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.

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.

Highlights of NCHRP 333


Concrete mix proportions should produce
low
-
permeability, but not increase propensity
for cracking


Epoxy reinforcing steel

with minimum
practical bar size and spacing


Minimum concrete cover of 2 ½ inches


Develop performance based specification
with warranties


Adequate curing is essential


Report published in 2004


Design Insight

Deck design is known to be conservative

Conservative assumptions:


Live load moment formula, same for positive and
negative


Point load v tire contact area


Westergaard theory (1930’s)


rigid supports


Wearing surface depth neglected


Single vs double reinforced section


Effective span length


FWS weight


Haunch section effects


Rounding of spacing and coinciding of top and
bottom reinforcing steel


Higher actual material strengths

Construction tolerances, deck importance, high
wearing, history of good performance

ODOT History of deck design


1940’s top cover 1 ¾ inch, bottom cover 1 inch; 180
lbs/cy, use of bent bar


Asphalt concrete overlays


1950’s top cover 1 inch plus monolithic ws
(CF30=1/2”;CF130=3/4”;CF400=1”),
Min deck 7 ½
inches
’ #6 and #5 bars


1960’s top cover 2 inches, #6 and #7 bars, 260 lbs/cy


1976 reverse main bars to today’s practice


1977 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 mats


1990’s top cover 2 ½ inches and bottom cover 1 ½
inches,
min deck 8 ½ inches

Topics of Interest


Alternate reinforcing steel


FRP,
stainless steel, etc.


Rapid replacement with precast
concrete or prefabricated steel grids


Advanced waterproofing systems


Place approach slab with deck


Deck cracking (post
-
tensioning)

STAY IN PLACE FORMS



Galvanized 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, t
he
precast concrete panel alternative,
previously used by ODOT, has shown
cracking problems at the joints between
the panels
.


Deck forming


Deck cantilever

Shear connectors




Concrete testing

Concrete placement




Sidewalk

Deck grooving