2-thome [compatibility mode](1)

8/12/2019 2-Thome [Compatibility Mode](1)

1/19

Tom Richards

BATTERED PILE MISCONCEPTIONS

INTRODUCTION

Problem s tatement Which batter is better? How to determine batter angles?

Simple Refined

Do batter piles have bending moments? NOT covering seismic stiffness / load attraction in detail


2/19


3/19

AASHTO LRFD Bridge Design Specificat ions (2010)

C10.7.1.4In some cases , i t may be desirable to use bat ter

piles. From a general viewpoint, batter piles provide a

much sti ffer resis tance to horizontal loads than would be

possible with vertical piles. They can be very effective

in resisting static horizontal loads.

Due to increased foundation stiffness, batter piles

may not be desirable in resisting horizontal dynamic

loads if the structure is located in an area where seismic

loads are potentially high.

PennDOT Design Manual Part 4 June 2009

6.15 PILES 6.15.1 General ..

Based on the parametric study conduc ted by the

Department, .a pile gro up com posed of

both vertical and battered piles which is subj ected to

lateral load shall be designed assuming th at all lateral load

is resisted by the horizontal component of th e axial

capacity of the battered piles. .

The use of the above design procedur e with

any of the following conditions requires the approval of

the Chief Bridge Engineer:

Piles with a specified steel yield strength other than 250 MPa {36 ksi} Piles with bending stiffness properties less than HP250X62 {HP10X42}

Very soft clays or very loose sands .

Unfactored vertical load to horizontal load ratio less

than 3.5 (excluding seismic forces)


4/19

PennDOT Design Manual Part 4

5.13.4 Concrete Piles5.13.4.1 GENERAL C5.13.4.1

The following shall supplement A5.13.4.1.

Piles shall b e designed as struc tural members capable

of safely supporting all impos ed loads. A pile group

compos ed of both vertical and battered piles which is

subjected to l ateral load sh all be designed assuming that all

lateral load is resisted by the horizontal compo nent of the

axial capacity o f the battered piles.

HMMMM?

6.15 PILES

6.15.1 General

The following shall r eplace A 6.15.1.

Piles shall be designed as structural members capable

of safely supporting all imposed loads.

For a pile group composed of only vertical piles

which is subjected to lateral load, the pile structural

analysis shall include explicit consideration of soilstructure

interaction effects using a COM624P analysis

(Wang and Reese, 1993) or LPILE 5.0 analysis.

Based on the parametric study co nducted by the

Department, which is described in the commentary, an

abutment or retaining wall with a pile group composed of

both vertical and battered piles which is subjected to

lateral load shall be designed assuming that all lateral load

is resisted by t he horizontal component of the axial

capacity of the battered piles. The vertical load shall be

distributed among piles in the group using a simple elastic

procedure. The use of the above design procedure with


the Chief Bridge Engineer:

Piles with a specified steel yield strength other than250 MPa {36 ksi}

Piles with bending stiffness properties less than

HP250X62 {HP10X42}

Very soft clays or very loose sands as defined in

Standard Drawing BC-795M

Piles with bending stiffness properties less than

HP310X79 {HP12X53} in soft clays or loose sands

as defined in Standard Drawing BC-795M




5/19

10.7.3.12 NOMINAL HORIZONTAL RESISTANCE OFPILE FOUNDATIONS

10.7.3.12.1 Batter Piles

The batter piles in a pile group shall resist the entire

horizontal load through th e horizontal component of their

axial capacity, unless an alternate method is appro ved by

the Chief Bridg e Engineer.

Refer to D6.15.1 for d esign pr ocedures for pile gro ups

containing b attered piles.

Cant I just take axial capacity times batter?

Resolution of Forces at Top of Pile Pile and Ground

1

xBatter 1:x

Batter angle=atan(1/x)

Ph = P*sin(batter angle)

?

P

Ph


6/19


6.15 PILES 6.15.1 General ..Based on the parametric study conduct ed by the

Department, .a pile group co mposed of





The use of the above design proc edure with


the Chief Bridge Engin eer:

Piles with a specified steel yield strength other than 250 MPa {36 ksi}

Piles with bending stiffness properties less than HP250X62 {HP10X42}

Very soft clays or very loose sands . Unfactored vertical load to horizontal load ratio less


Which batter is better?


7/19


8/19

Which batter is better? What do actual tests say?Reese & VanImpe (2001)

1.0

2.0

1.5

0.5

3.13 EFFECT OF BATTER. The lateral soil-resistance curvesfor a vertical pile in a horizontal groundsurface were modified by a constant toaccount for the effect of the inclinationof the pile. The values of themodifying co nstant as a function ofthe batter angle were deduced fromthe results in the test tank(Awosh ika & Reese 1971) and alsofrom the results from full-scale tests(Kubo 1964). .

As shown in Figure 3.34, theagreement between the empirical curveand the experiments for the out-batterpiles (q is positive) agrees somewhatbetter than for the in-batter piles. Thedata indicate that the use of themodifier will yield results that aresomewhat questionable ; .( OPTOMISTIC )

Which batter is better? Consider failure wedges

What does LPILE say? Cohesive


9/19

Which batter is better? Consider failure wedges

What does LPILE say? Granular

Which batter is better? Consider failure wedges and

vertical load


10/19

Cant I just take axial capacity times batter? MAYBE

Resolution of Forces at Top of Pile Pile and Ground

1

xBatter 1:x

Batter angle=atan(1/x)

Ph = P*sin(batter angle)

Pv Can we just wish this load here?

PhP


6.15 PILES 6.15.1 General ..

Based on the parametric study conduct ed by the

Department, .a pile group co mposed of





The use of the above design proc edure with


the Chief Bridge Engin eer:

Piles with a specified steel yield strength other than 250 MPa {36 ksi} Piles with bending stiffness properties less than HP250X62 {HP10X42}

Very soft clays or very loose sands .




11/19

Which batter is better? Consider failure wedges andvertical load

What does LPILE say? Granular

Note 70 kips * tan(20 deg) = 25.5 kips

How to determine batter angles

A s imple graph ical procedure for es timat ing th e compressive andtensile forces in micropile groups c ontaining not mo re than threerows of micropil es is described in Tomlinson (1987) and Teng (1962).

For analysis of t hree-dimensional pile groups that considersnonlin ear soil response and pile-soil-pile interaction, the GROUP 7program can be used.


12/19

How to determine batter angles SIMPLE STATICS

How to determine batter angles - TENG


13/19

How to determine batter angles - TENG

How to determine batter

angles - TENGCenter of Gravity of Group

Pile Group Moment of Inertia

Transformed Moment to CG

Vertical Force/pile = P/A+M/S


14/19


15/19

How to determine batter angles GROUP modeling

Do batter piles have bending moments?


16/19

An interest ing outcomefrom working with theGROUP program is therealization that evenbattered pile gro ups havebending moments in thepiles.

Battered p iles cansubstantially reduce andbalance, but not eliminate,the bending moments inthe piles.

Piles shou ld have pipe orcages at the top200 kip vertical load per pile 7x0.5 casing14 deg batter



200 kip vertical load per pile 7x0.5 casingMoment = 5% of allowable stress


17/19

Pinned Fixed




18/19

Problem Statement - Revisi ted

To deal with lateral load just batter the piles ???Maybe depends on vertical loads and hitting the sweet spot in ratio

between lateral and vertical load Example questions from Engineers

Is 60 ton allowable lateral capacity reasonably achievable for 12 inpressure grouted micropiles up to a 20 (1 : 2.75) batter?

depends on vertical loads What lateral capacities are reasonable and at what batter angles, for

post grout installation methods at this site?

depends on vertical loads Cant I just take axial capacity times batter?

NOT and satisfy basic equilibrium = NO

CONCLUSIONS

Battered piles are only efficient wi th vertical load Batter angles can be determined by

Determinant statics Graphic Numerical modeling - GROUP

Battered piles have bending moment even

without horizontal load and need bendingductility and strength


19/19

2-thome [compatibility mode](1)

Documents