Transmission & Distribution Program

Transmission Line Design Structures & Foundations

TADP 549

Steel Poles -

Pier Foundations -

Software

Presentation 6.6

Dr. Prasad Yenumula

Commercial Software

MFAD

CAISSON

LPILE

Rigid Pile Theories

Several rigid pile theories

– Broms method, 1964

– Brinch Hansen, 1961

– Parker and Reese, 1970

– Petrasovits and Award,1972

– Meyerhof et al., 1981

– Prasad and Chari, 1999

Comparison Between Rigid Pile Theories

Different theories assume different soil pressure distributions and shape factors, so these methods yield different results

MFAD (Moment Foundation Analysis and Design)

MFAD

– EPRI Software

– MFAD predict both ultimate moment capacity

and deflections/rotations

– Uses Brinch-Hanson theory to predict ultimate

moment capacity

MFAD (Moment Foundation Analysis and Design)

•MFAD software uses

“Four-spring” nonlinear

subgrade modulus model

•In the subgrade reaction

approach, continuous

nature of the soil medium

is ignored and is idealized

by four different types of

non-linear springs

Source: IEEE 691-2001

MFAD (Moment Foundation Analysis and Design)

•To characterize the

springs, deformation

modulus of soil is required

•FAD suggests to use

pressuremeter modulus

value

•Pressuremeter modulus

values shall be obtained

from empirical correlations

or through actual

pressuremeter test

Source: IEEE 691-2001

CAISSON

CAISSON

– Product of Power Line Systems

– Predict ultimate moment capacity

– Uses modified Broms’ theory

– No features to predict deflections/rotations

Illustrated Example-1

For a self-supported deadend steel pole,

design a pier foundation using the following

data:

Loadings on the pier (extreme wind load

case)

Lateral load = 171.0 kips

Moment = 11193.0 kips-ft

Axial load = 78.0 kips

Illustrated Example-1 (Cont.)

Design pier foundation for following conditions:

Part A – Factor of safety against lateral soil failure = 1.0, no limitations

on deflections/rotations

Part B – What will happen if the following limitations on rotations and

deflections are applied:

• Total ground line rotation limit: 2 deg

• Non-recoverable ground line rotation limit: 0.5 deg

• Total ground line deflection: 2 inches

• Non-recoverable ground line deflection: 1 inch

Illustrated Example-1 (Cont.)

Illustrated Example-1 (Cont.)

Solution (Part A)

– Factor of safety against lateral soil failure = 1.0

– No limitations on deflections/rotations

Illustrated Example-1 (Cont.)

Solution (Part B)

– What will happen if the limitations on rotations and

deflections are applied:(* Note: Caisson does not

have capabilities to predict deflections/rotations)

Illustrated Example-1 (Cont.)

Remarks

– In part A, FAD and CAISSON software provided

different embedment depths because they use

different theoretical models

– In part B, the deflection/rotation criteria

governed over the ultimate lateral soil failure

– Do not generalize these sample results

Illustrated Example-1 (Cont.)

Structural design of concrete Pier (Part A)-MFAD

Illustrated Example-1 (Cont.)

Structural design of concrete Pier (Part A)-MFAD

Illustrated Example-1 (Cont.)

Structural design of concrete Pier (Part A)-MFAD

Illustrated Example-1 (Cont.)

Structural design of concrete Pier (Part A) - MAD

Illustrated Example-1 (Cont.)

Structural design of concrete Pier (Part A) - MFAD