751.32 Concrete Pile Cap Intermediate Bents

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Contents

751.32.1 General

751.32.1.1 Material Properties

Concrete
Typically, shall consist of:
 Class B Concrete (Substructure)\, f'_c= 3.0 ksi
  \, n = 10

In addition, Class B-1 Concrete (Substructure) may also be used in special cases (See Project Manager).

Modulus of elasticity,

E_c = 33,000\ K_1 \ (w_c^{1.5}) \sqrt{f^'_c}

Where:

f'c in ksi
wc = unit weight of nonreinforced concrete = 0.145 kcf
K1 = correction factor for source of aggregate
= 1.0 unless determined by physical testing


Modulus of rupture,

 f_r \ = \ 0.24 \sqrt{f'_{c}}       LRFD 5.4.2.6

Where:

f'c is in ksi


Reinforcing Steel

Minimum yield strength,\, f_y= 60.0 ksi
Steel modulus of elasticity,\, E_s= 29000 ksi

751.32.2 Design

751.32.2.1 Limit States and Factors

In general, each component shall satisfy the following equation:

\, Q = \sum \eta_i \gamma_i Q_i \le \phi R_n = R_r

Where:

\, Q= Total factored force effect
\, Q_i= Force effect
\, \eta= Load modifier
\, \gamma_i= Load factor
\, \phi= Resistance factor
\, R_n= Nominal resistance
\, R_r= Factored resistance


Limit States

The following limit states shall be considered for bent design:

STRENGTH – I
STRENGTH – III
STRENGTH – IV
STRENGTH – V
SERVICE – I
FATIGUE

See LRFD Table 3.4.1-1 and LRFD 3.4.2 for Loads and Load Factors applied at each given limit state.


Resistance factors

STRENGTH limit states, see LRFD 5.5.4.2
For all other limit states, \, \phi = 1.00


Load Modifiers

751.32.3 Details

751.32.3.1 Front Sheet

Note:The following are details and dimensions for the plan view of a typical pile cap bent on the front sheet of the bridge plans. Details and dimensions for an encased concrete pile cap bent are similar.
 Details for unsymmetrical roadways shall require dimensions tying Centerline Lane to Centerline Structure.


Image:751.32 details-front sheet plan of int bent.gif

751.32.3.2 Typical Pile Cap Bent

Part ElevationPart Section
Applicable for both HP piles (shown) and CIP piles
Image:751.32 circled 1.gif Use 2'-6" minimum or as determined by the superstructure requirements or the minimum support length required for seismic criteria (expansion joint bents only) (3" increments) or the minimum beam width required to meet pile edge distance requirement.
Image:751.32 circled 2.gif = 3’-0” (Min.) for Wide Flange, Double-Tee Girders,
   Prestressed Girders and Plate Girders.
Image:751.32 circled 3.gif Check the clearance of the anchor bolt well to the top of pile. Increase the beam depth if needed.
Image:751.32 circled 4.gif If the depth at the end of the beam, due to the steps, exceeds 4'-6", the beam bottom should be stepped or sloped.
Image:751.32 circled 5.gif Use 3/4" drip groove where expansion device is located at bent. Continue to use 1-1/2" clear to reinforcing steel in bottom of beam. 3/4" drip groove shall be formed continuously around all piling at 3" from edge of beam.
Image:751.32 circled 6.gif Minimum of 3 piles at 10'-0" cts., maximum spacing (1" increments).
Piles shall not be battered.

751.32.3.2.1 Sway Bracing

(Use when specified on Design Layout or when required by design.)



Guidance for use of sway bracing for steel bearing pile:

(1) When angle slope of bracing becomes less than 15° to the horizontal, omit the diagonal angles and use the horizontal angles only (except on four pile bents, then use alternate shown above).

Note: In case of a large number of piles, see the Structural Project Manager.

751.32.3.3 Encased Pile Cap Bent

Consideration shall be given to EPG 751.1.2.20 Substructure Type before using this type of structure.

Part Section
Image:751.32 circled 1.gif Use 2'-6" minimum or as determined by the superstructure requirements or the minimum support length required for seismic criteria (expansion joint bents only) (3" increments) or the minimum beam width required to meet pile edge distance requirement.
Image:751.32 circled 2.gif = 3’-0” (Min.) for Wide Flange, Double-Tee Girders,
   Prestressed Girders and Plate Girders.
Image:751.32 circled 3.gif Check the clearance of the anchor bolt well to the top of pile. Increase the beam depth if needed.
Image:751.32 circled 4.gif If the depth at the end of the beam, due to the steps, exceeds 4'-6", the beam bottom should be stepped or sloped.
Image:751.32 circled 5.gif Height by design. Embed encasement 2 ft. (min.) below the top of the lowest finished groundline elevation, unless a greater embedment is required for bridge design.
Image:751.32 circled 6.gif Minimum of 3 piles at 10'-0" cts., maximum spacing (1" increments).

751.32.4 Reinforcement

751.32.4.1 Typical Pile Cap Bent

Image:751.32 reinforcement-part elevation.gif Image:751.32 reinforcement-section thru beam.gif
Part ElevationSection Thru Beam
 
Image:751.32 reinforcement-part plan.gif  
Part Plan 
Note:Locate #4 bars "Image:751.32 reinforcement--4 bar under bearing.gif" under bearings where required to maintain a 6" maximum spacing of combined stirrups. (#4 bars "Image:751.32 reinforcement--4 bar under bearing.gif" are not required for Double-Tee Structures.)
 For epoxy coated reinforcement requirements, see EPG 751.5.9.2.2 Epoxy Coated Reinforcement Requirements. Details of protective coating and sloping top of beam to drain shall be used when below an expansion device.


Image:751.32 reinforcement under bearings-part elevation.gif Image:751.32 reinforcement under bearings-part plan.gif
* #4 Bars (Image:751.32 reinforcement--4 bar under bearing.gif) not required for Double-Tee structures
Reinforcement Under Bearings
 
Image:751.32 transverse beam steps.gif
Transverse Beam Steps - Over 3"
or Steps Accumulating Over 3"


Image:751.32 reinforcement at end of beam-part plan.gif
Part Plan
 
Image:751.32 reinforcement-longitudinal beam steps.gif
Over 3" thru 12"Over 12"
Longitudinal Beam Steps

751.32.4.2 Encased Pile Cap Bent

Supplemental details for encased pile cap bents are provided.

Part Elevation
Part Section
Part Plan
Note:Locate #4 bars "Image:751.32 reinforcement--4 bar under bearing.gif" under bearings where required to maintain a 6" maximum spacing of combined stirrups. (#4 bars "Image:751.32 reinforcement--4 bar under bearing.gif" are not required for Double-Tee Structures.)
 For epoxy coated reinforcement requirements, see EPG 751.5.9.2.2 Epoxy Coated Reinforcement Requirements. Details of protective coating and sloping top of beam to drain shall be used when below an expansion device.
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