# 751.35 Concrete Pile Cap Integral End Bents

## 751.35.1 General

### 751.35.1.1 Material Properties

Concrete
Class B Concrete (Substructure) $\, f'_c$ = 3.0 ksi
$\, n$ = 10

Class B-1 Concrete (Substructure) may also be used in special cases (See Project Manager). The following equations shall apply to both concrete classes:

 Concrete modulus of elasticity, $\, E_c = 33000 K_1 w_c \sqrt [1.5]{f'_c}$
 Where: $\, w_c$ = unit weight of non-reinforced concrete = 0.145 kcf $\, K_1$ = correction factor for source of aggregate = 1.0
 Modulus of rupture: For minimum reinforcement, $\, f_r = 0.37 \sqrt{f'_c}$ For all other calculations, $\, f_r = 0.24 \sqrt{f'_c}$ $\, \sqrt{f'_c}$  is in units of ksi

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

## 751.35.2 Design

### 751.35.2.1 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 $\, \eta_i$ = 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 abutment design:

STRENGTH – I
STRENGTH – III
STRENGTH – IV
STRENGTH – V
SERVICE – I
FATIGUE
EXTREME EVENT - II

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 and LRFD 6.5.4.2
For all other limit states, $\, \phi$ = 1.00

Loads from stringers, girders, etc. shall be applied as concentrated loads applied at the centerline of bearing. Loads from concrete slab spans shall be applied as uniformly distributed loads.

Loads from stringers, girders, etc. shall be applied as concentrated loads applied at the centerline of bearing. Dynamic load allowance (impact) should be included for the design of the beam. No dynamic load allowance should be included for foundation design.

For wings with detached wing walls, no portion of the bridge live load shall be distributed to the detached wall. The detached wing wall shall be designed as a retaining wall. The weight of the safety barrier curb on top of the wall shall be included in the dead load.

Collision

Collision shall be designed if abutments are located within a distance of 30.0 feet to the edge of roadway, or within a distance of 50.0 feet to the centerline of a railway track and conditions do not qualify for exemptions given in EPG 751.2.2.5.

### 751.35.2.3 General Design Assumptions

Beam

The beam shall be assumed continuous over supports at centerline of piles.

One half of the dead load of the approach slab shall be included in the beam design.

Wing

The standard horizontal reinforcement shown below was designed for soil pressure, EH, live load surcharge, LS and a railing collision force, CT for Extreme Limit State II Load Combination.

The minimum steel placed horizontally in wings shall be as shown in the figure below.

Part Section Thru Beam

### 751.35.2.4 End Bent Analysis

Step 1 – Obtain loads from superstructure

The live load reactions (LL), dead load of structural components (DC), and dead load of future wearing surface (DW) will be needed to design the end bents. Strength I Load Combination will be used to design the reinforcement.

Step 2 – Design bearing pads or girder chairs

From the loads obtained in Step 1, design the bearing pads or girder chairs according to EPG 751.11.

Step 3 – Find beam cap width

The standard beam cap width will be 3’-0”. However, if the bearing pad size required exceeds the allowable edge distance, the beam cap width may be widened. The bearing pads shall be centered over the centerline of pile location, which is 15” away from the stream or crossing face of the cap.

Step 4 – Design longitudinal steel in beam cap

If the centerline of bearing is 12” or less on the centerline of piles, use 4 - #6 bars at the top and bottom of the beam cap. Otherwise, the ultimate moment used for designing the longitudinal steel shall be approximated by the following equation and figure. The loads shall be factored according to the Strength I Load Combination.

$\, M_u = 0.2 R_u L + 0.13 WL^2$

Where:

 $\, R_u$ = maximum interior girder reaction of factored superstructure loads, kips. $\, L$ = pile spacing, ft. $\, W$ = factored substructure loads equally distributed across the beam, k/ft.

Basic Assumption for Beam Analysis

A minimum of 4 - #6 Bars shall be used for the longitudinal steel in the beam cap. If more steel is required, increase bar size and keep the number of bars to 4. For example, use 4 - #7 bars instead of 5 - #6 bars.

The minimum reinforcement and bar spacing shall also be checked against the appropriate limits.

Step 5 – Design for number and size of pile

### 751.35.2.5 Beam Reinforcement Special Cases

SPECIAL CASE I

If centerline bearing is 12" or less on either side of centerline piles, for all piles (as shown below), use 4-#6 top and bottom and #4 at 12" cts. (stirrups), regardless of pile size.

SPECIAL CASE II

When beam reinforcement is to be designed assuming piles to take equal force, design for negative moment in the beam over the interior piles.

(*) Dimensions are for illustration purposes only.

## 751.35.3 Dimensions

### 751.35.3.1 Front Sheet

 Notes: The following are details and dimensions for the Plan view on the Front Sheets. Details for unsymmetrical roadways will require dimensions tying Centerline Lane to Centerline Structure.

### 751.35.3.2 Wing Brace

The wing brace dimensions will only vary on the wing with obtuse angle. Wing brace dimensions shown are minimum dimensions. The wing brace with the acute angle will always be 18" minimum.

### 751.35.3.3 Prestressed Girder End Bent

 12" Minimum at gutter line top of concrete. All concrete in the end bent above top of beam and below top of slab shall be class B-2. Provide a minimum of 8" cl. from outside edge of pile to face of beam. For pile greater than 14” wide (dia.), shifting pile centerline towards fill face is preferred based on structural considerations (eccentric load to pile). Otherwise, increase abutment beam width (1” increments) towards front face in order to meet 8” min. cl. Example: Pile size = 16” Option I (preferred): Shift pile centerline 1” towards fill face and consider eccentric load to the pile. Min. abutment width = 20”+16”=3’-0” Option II: Increase beam width 1” towards front face. Min. abutment width = 21”+16”=3’-1” See Design Layout for maximum slope of spill fill. (*) Keep 1 1/2" Min. clear cover for a #6 bar reinforcement between approach notch and girder. Increase abutment beam width (1" increments) to get the 1 1/2" clear cover if necessary. (**) See Protective Barricades

 Note: Neoprene bearing pads are to be used on integral bents (steel or prestressed structures) if pad size and beam clearance permit; otherwise, use girder chairs. (*) 18" (Min.) 2'-0" (Max.); provide a minimum of 8" cl. from outside edge of pile to outside face of beam.

### 751.35.3.4 Steel Girder or Beam End Bent

 12" Minimum at gutter line top of concrete. All concrete in the end bent above top of beam and below top of slab shall be class B-2. Provide a minimum of 8" cl. from outside edge of pile to face of beam. For pile greater than 14” wide (dia.), shifting pile centerline towards fill face is preferred based on structural considerations (eccentric load to pile). Otherwise, increase abutment beam width (1” increments) towards front face in order to meet 8” min. cl. Example: Pile size = 16” Option I (preferred): Shift pile centerline 1” towards fill face and consider eccentric load to the pile. Min. abutment width = 20”+16”=3’-0” Option II: Increase beam width 1” towards front face. Min. abutment width = 21”+16”=3’-1” See Design Layout for maximum slope of spill fill. (*) Use 3" Min. when girder chairs are used and use 1" past the end of the bearing pad when bearing pads are used. (**) Keep 1 1/2" min. clear cover for a #6 bar reinf. between approach notch and girder. Increase abutment beam width (1" increments) to get the 1 1/2" clear cover if necessary. (***) See Protective Barricades

 Note: Neoprene bearing pads are to be used on integral bents (steel or prestressed structures) if pad size and beam clearance permit; otherwise, use girder chairs. (*) 18" (Min.) 2'-0" (Max.); provide a minimum of 9" cl. from outside edge of pile to face of beam. (*) 3" cl. between sole plate and keyed const. joint (Typ.)

### 751.35.3.5 Wing & Detached Wing Walls

 (*) Detached wing wall shown is for illustration purpose only. Design detached wing wall as a LFD retaining wall (EPG 751.24). (**) See EPG 751.24 LFD Retaining Walls.

## 751.35.4 Reinforcement

### 751.35.4.1 Wide Flange & Plate Girders

Part Section Near End Bent
Section A-A Section B-B Section C-C
 Place U1, U2, U3, U4, and V1 bars parallel to centerline Roadway. #6 U-bar (horiz. leg placed parallel to centerline Roadway) and #6 V-bar or U-bar @ 9" cts. min. (Between barrier curbs). #5-U4 at 12" cts. - spaced with U1 and V1 bars. U1 at 12" cts. - spaced between piles and girders. #5 bars, except special cases. See tables for 1 1/16" round hole spacing for #6 reinf. bars. Same number of bars as 1 1/16" round holes in stringer or girder. By design - development length (top bars) min. Stirrups shall clear step by 1 1/2" min., if not lengthen step or skew step. #5 bars, 2'-6" long, spaced at 12" cts. along centerline bent. Bars placed parallel to centerline Rdwy.
Section D-D

Place note on plans if Girder Chairs are used:

Shift the reinforcing steel to keep 1 1/2" clearance of the angles of the girder chairs.
Keep 1 1/2" clearance between shear reinforcement and piles.
(Replace U1 bars with U3 bars at piles under girders and with V1 bars at piles between girders.)

### 751.35.4.2 Prestressed Girders

Part Section Near End Bent
Section A-A Section B-B Section C-C
 Place U1, U2, U3, U4, and V1 bars parallel to centerline Roadway. #6 U-bar (horiz. leg placed parallel to centerline Roadway) and #6 V-bar or U-bar @ 9" cts. min. (Between barrier curbs). #5-U4 at 12" cts. - spaced with U1 and V1 bars. U1 at 12" cts. - spaced between piles and girders. (Replace U1 bars with U3 bars at piles under girders and with V1 bars at piles between girders). #5 bars, except special cases. By design - development length (top bars) min. #5 bars, 2'-6" long, spaced at 12" cts. along centerline bent. Bars placed parallel to centerline Rdwy.
Section D-D

Place note on plans if girder chairs are used:

Shift the reinforcing steel to keep 1 1/2" clearance of the angles of the girder chairs.
Keep 1 1/2" clearance between shear reinforcement and piles.

### 751.35.4.3 Wide Flange, Plate Girders & Prestressed Girders

 (*) Keep a min. of 3" ctr. to ctr. spacing between #6 bars placed horizontally and #8 bars placed with grade. Use const. joint on steel structures only.
 Section A-A (Square)(K bars not shown for clarity) Part Section ThruEnd of Wing
 Use 90° standard hook in seismic areas.
 (**) Place note on plans Bend ____ F bars in field to clear girder. Note: See barrier curb details and spacing of K bars. Prestressed I-Girders shown in details, Steel Girders similar.

 Note: Sections shown above are between girders and piles. Prestressed I girders are shown in the sections above; Steel girders are similar. Use same as bottom reinforcement. Use construction joint on steel structures only.

## 751.35.5 Details

### 751.35.5.1 Reinforcing Holes

WF Beam Depth Stud Spacing "A" Reinforcing Hole Spacing
21" 2 spa, @ 4/12" 4" 2 equal spaces
24" 2 spa. @ 6" 4" 2 equal spaces
27" 2 spa. @ 7 1/2" 4 1/2" 2 equal spaces
30" 3 spa. @ 6" 4 1/2" 3 equal spaces
33" 3 spa. @ 7" 4 1/2" 3 equal spaces
36" 4 spa. @ 6" 4 1/2" 3 equal spaces

 Note: Check the dead load (DL) on angles for girders 60" or larger. Bearing stiffeners are to be designed for DL1 (no SBC or FWS) and 50 psf construction load. (No web studs are required since bearing stiffener is provided). (***) 1 1/16"ø holes for skews thru 20°. For skews > 20°, use slotted hole = 1 1/16" + 2(Web thickness)x(tan of the skew angle)

PL Girder Depth "A" Reinforcing Hole Spacing
39" 3 1/2" 4 equal spaces
42" 3 1/2" 5 equal spaces
48" 4" 5 equal spaces
54" 4 1/2" 6 equal spaces
60" 4" 8 equal spaces

### 751.35.5.2 Vertical Drains

Elevation of Wing (*) Only if rock is encountered at outside of wings.