POSITIVE MOMENT CONTINUITY DIAPHRAGMS:
When simple-span precast, prestressed concrete beams and deck slabs are assumed to be
continuous over two or more spans for the computation of composite DL plus LL + Impact
moments, the closure diaphragm shall be designed in accordance with the requirements of
Article 9.7.2 of the AASHTO specifications. For such cases the following shall also apply:
•
Computation of positive moments in negative moment region due to the combined
effects of creep and shrinkage shall be in accordance with the procedures outlined in the
August 1969 PCA Engineering Bulletin “Design of Continuous Highway Bridges with
Precast, Prestressed Concrete Girders”.
•
For determining the differential shrinkage strain (εs) used in the computation of the
differential shrinkage moment, assume a minimum of 90 days between the release of
prestress and the casting of the deck slab.
•
In using this procedure, a reduction in the simple span positive moment due to composite
DL and LL + Impact may be taken for the design of the beam within the span.
•
Minimum non-prestressed positive moment reinforcement shall be 4 - #8 rebars or an
equivalent area of steel.
•
Minimum embedment length of non-prestressed positive moment reinforcement shall be
50 times the strand diameter plus the development length in tension for the deformed bar
used. In no case shall all positive moment reinforcement bars be terminated at the same
location.
•
In lieu of non-prestressed positive moment connection reinforcement, 1/2” diameter
prestressing strands may be used. When considering a service life up to two million
cycles of maximum loading, 1/2” strands may be designed at a working stress ≤ 0.15f′s.
Strands shall be embedded into the closure diaphragm a minimum of 2’- 6” from end of
beam. Pin diameter for bending 1/2” diameter strands up into the closure diaphragm
shall be 3/4”.
•
For typical positive moment closure diaphragm details, see File Nos. 12.11-3 thru -8.
ALTERNATE CONTINUITY DIAPHRAGMS:
When only the deck slab is to be continuous over two or more spans, the closure diaphragm may
be designed and detailed in accordance with the recommendations of NCHRP Report 322
“Design of Precast Prestressed Bridge Girders Made Continuous”. For such cases the following
shall also apply:
•
The reinforcing steel connecting the beams with the closure diaphragm shall be located
in the upper half of the beam only.
•
Beams shall be designed as simple span beams for both non-composite and composite
DL plus LL + Impact within the span.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
GENERAL INFORMATION
VOL. V - PART 2
DATE 01Jun2005
SHEET 1 of 12
FILE NO. 12.11-1
•
Shears due to non-composite DL for simple spans plus composite DL + LL + Impact for
continuous spans shall be used for the design of the shear reinforcing steel in the beams;
however, in no case shall this shear reinforcing steel be less than that required for simple
spans.
•
The negative moment due to composite DL and LL + Impact shall be used for the design
of negative moment reinforcement in the deck slab over the piers (see first paragraph on
page 30 of the NCHRP Report 322).
•
For typical alternate closure diaphragm details, see File Nos. 12.11-9 and 11.
CONTINUITY DIAPHRAGM THICKNESS:
The minimum continuity diaphragm thickness shown in the details of this section is 10”; however,
12” is preferred.
PIER SEAT ELEVATIONS:
Pier seats of “arriving” and “departing” beams made continuous shall be set to the same
elevation.
Where “arriving” and “departing” beams result in calculated differences in pier seat elevations, the
differences shall be applied in accordance with the following guidelines:
Difference < 1/4”: apply to the minimum computed bolster thickness.
1
/4” ≥ Difference ≤ 1/2”: apply to bearing assembly height.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
GENERAL INFORMATION
VOL. V - PART 2
DATE 01Jun2005
SHEET 2 of 12
FILE NO. 12.11-2
1.
The details shown above and in File No. 12.11-5 are for the designer’s information only.
See Introduction File No. 12.00-1.
2.
Deck slab reinforcement not shown for purposes of clarity.
3.
For Sections A - A and B - B, see File No. 12.11-5.
4.
DS04 series bars shown above shall be equally spaced between the beam top flanges.
Spacing shall not exceed 12” on centers.
5.
A three piece bar detail may be used in lieu of the one piece DS04 series bar shown above.
Minimum lap length shall be that required for a Class B tension lap splice for other than top
bars (1’- 4”). Show lap length on the plans.
6.
DL06 series bars shown above shall be equally spaced between the BC05 series bars.
Spacings of bars shall not exceed 12” on centers. Minimum lap length for DL06 series bars
shall be that required for a Class B tension lap splice for top bars (2’- 9”). Show lap length
on the plans.
7.
Minimum lap length for BC05 and BL05 series bars shall be that required for a Class B
tension lap splice for top bars (2’- 3”). Show lap length on the plans.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - FIXED
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 31Mar2006
SHEET 3 of 12
FILE NO. 12.11-3
8.
The 3/4" diameter plain steel dowels shall conform to the requirements of ASTM A36. For
number of steel dowels required, use an allowable shear stress = 0.40Fy. Minimum number
shall be four 3/4" diameter dowels between pier seats. Details of the 3/4” diameter steel
dowels and keyed construction joint shall be shown on the pier detail sheets. Dowels shall
be equally spaced between pier seats. Embed dowels 12” into pier cap.
9.
This portion of the deck slab shall be cast prior to the casting of the closure diaphragm.
10. This portion of the deck slab shall be cast monolithically with the closure diaphragm.
Minimum width of deck slab to be cast with the diaphragm shall be 4’- 0” (2’- 0” on each side
of pier centerline).
For skew angles greater than 20º, adjust width of deck slab as
necessary to ensure that this portion of the deck slab covers the entire closure diaphragm.
This dimension shall be shown on the Deck Slab Concrete Placement Schedule.
11. For plan view of closure diaphragm, see File No. 12.11-12.
12. For details of bearing assemblies, see standard BBD-8 in the Manual of the Structure and
Bridge Division, Volume V – Part 3.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - FIXED
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 31Mar2006
SHEET 4 of 12
FILE NO. 12.11-4
For location of section cuts and notes, see File Nos. 12.11-3 and -4.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - FIXED
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 5 of 12
FILE NO. 12.11-5
1.
The details shown above and in File No. 12.11-8 are for the designer’s information only.
See Introduction File No. 12.00-1.
2.
Deck slab reinforcement not shown for purposes of clarity.
3.
For Sections A - A and B - B, see File No. 12.11-8.
4.
DS04 series bars shown above shall be equally spaced between the beam top flanges.
Spacing shall not exceed 12” on centers.
5.
A three piece bar detail may be used in lieu of the one piece DS04 series bar shown above.
Minimum lap length shall be that required for a Class B tension lap splice for other than top
bars (1’- 4”). Show lap length on the plans.
6.
DL06 series bars shown above shall be equally spaced between the BC05 series bars.
Spacing of bars shall not exceed 12” on centers. Minimum lap length for DL06 series bars
shall be that required for a Class B tension lap splice for top bars (2’- 9”). Show lap length
on the plans.
7.
Minimum lap length for BC05 and BL05 series bars shall be that required for a Class B
tension lap splice for top bars (2’- 3”). Show lap length on the plans.
8.
This portion of the deck slab shall be cast prior to the casting of the closure diaphragm.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - EXPANSION
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 31Mar2006
SHEET 6 of 12
FILE NO. 12.11-6
9.
This portion of the deck slab shall be cast monolithically with the closure diaphragm.
Minimum width of deck slab to be cast with the diaphragm shall be 4’- 0” (2’- 0” on each side
of pier centerline).
For skew angles greater than 20º, adjust width of deck slab as
necessary to ensure that this portion of the deck slab covers the entire closure diaphragm.
This dimension shall be shown on the Deck Slab Concrete Placement Schedule.
10. For plan view of closure diaphragm, see File No. 12.11-12.
11. For details of bearing assemblies, see standard BBD-8 in the Manual of the Structure and
Bridge Division, Volume V – Part 3.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - EXPANSION
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 7 of 12
FILE NO. 12.11-7
For location of section cuts and notes, see File No. 12.11-6 and –7.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS - EXPANSION
POSITIVE MOMENT CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 8 of 12
FILE NO. 12.11-8
1.
The details shown above and in File No. 12.11-11 are for the designer’s information only.
See Introduction File No. 12.00-1.
2.
Deck slab reinforcement not shown for purposes of clarity.
3.
For Sections A - A and B - B, see File No. 12.11-11.
4.
DS04 series bars shown above shall be equally spaced between the beam top flanges.
Spacing shall not exceed 12” on centers.
5.
A three piece bar detail may be used in lieu of the one piece DS04 series bar shown above.
Minimum lap length shall be that required for a Class B tension lap splice for other than top
bar (1’- 4”). Show lap length on the plans.
6.
DL06 series bars shown above shall be equally spaced between the BC05 series bars.
Spacing of bars shall not exceed 12” on centers. Minimum lap length for DL06 series bars
shall be that required for a Class B tension lap splice for top bars (2’- 9”). Show lap length
on the plans.
7.
Minimum lap length for BC05 and BL05 series bars shall be that required for a Class B
tension lap splice for top bars (2’- 3”). Show lap length on the plans.
8.
This portion of the deck slab shall be cast prior to the casting of the closure diaphragm.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
ALTERNATE CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 31Mar2006
SHEET 9 of 12
FILE NO. 12.11-9
9.
This portion of the deck slab shall be cast monolithically with the closure diaphragm.
Minimum width of deck slab to be cast with the diaphragm shall be 4’- 0” (2’- 0” on each side
of pier centerline).
For skew angles greater than 20º, adjust width of deck slab as
necessary to ensure that this portion of the deck slab covers the entire closure diaphragm.
This dimension shall be shown on the Deck Slab Concrete Placement Schedule.
10. For plan view of closure diaphragm, see File No. 12.11-12.
11. For details of bearing assemblies, see standard BBD-8 in the Manual of the Structure and
Bridge Division, Volume V – Part 3.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
ALTERNATE CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 10 of 12
FILE NO. 12.11-10
For location of section cuts and notes, see File Nos. 12.11-9 and -10.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
ALTERNATE CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 11 of 12
FILE NO. 12.11-11
Dimension A shown above shall be determined by the designer and shown on the plans.
PRESTRESSED CONCRETE
CONTINUITY DIAPHRAGMS
SKEWED CLOSURE DIAPHRAGM DETAILS
VOL. V - PART 2
DATE 01Jun2005
SHEET 12 of 12
FILE NO. 12.11-12