DFI Magazine March/April 2020 - 103

FEATURE

ARTICLE

Improving Helical Pile-to-Foundation Connections
Lattice Towers

Wind Turbine Towers

Light-Frame Steel Buildings

While geotechnical studies typically
focus on the behavior of isolated or grouped
piles without considering the influence of
the connection zones, structural studies
exclusively focus on the concrete foundation response without considering the
influence of piles. The connection design is
also typically left unaddressed and is
commonly dealt with as an afterthought,
using general code equations not intended
for application to pile-to-foundation
connections nor tensile loads.
DFI's Helical Piles and Tiebacks Committee funded a research study from May
2018 to September 2019 to advance
knowledge on the influence of the connection zones of helical piles, to understand
the effectiveness of current connection
designs, and to publish recommendations
for improving robust connection design.
Conducting large-scale experimental tests
was neither practical nor cost-effective due
to the large foundation dimensions and
numerous design configurations that would

have been involved, and due to complex
loading protocols that would need to be
tested. To overcome these challenges, the
research team from The University of
Toledo, Ohio, used state-of-the-art highfidelity computational modeling along with
experimental verification studies as a first
step in developing design recommendations for helical pile connection zones
subjected to tensile loads.
This article describes the use of this
approach to create 162 full-scale foundation systems and to digitally examine the
influences of connection bracket types and
embedment depths, reinforcement percentages, shear span-to-depth ratios and
loading conditions. The copious simulation
data generated allowed the team to quantify
the influences of each variable, identify
undesirable design configurations and make
design recommendations. While this study
addresses helical piles, the research findings
are also applicable to micropiles because
they use the same termination brackets.

Tall, light structures impacted by tension forces

Many structures are subjected to cyclic
loads, which involve sequential applications of compression and tension loads
due to events such as windstorms, earthquakes or heavy vehicular traffic. Tall and
light structures - such as telecommunication or transmission towers, wind
turbines, and light-frame steel buildings -
are particularly vulnerable to the tensile
components of cyclic loads. Owing to their
high-tension capacities, helical piles
present a significant potential to create
cost-effective, practical and robust foundation systems for resisting significant
tension forces. To realize their full
potential, helical pile-to-foundation
connections must be properly designed.
Even a well-designed pile group and a
concrete foundation may fail if their
connection cannot resist the applied forces.
However, there is a lack of research,
knowledge and specific code provisions on
creating robust connections for resisting
tensile loads.

AUTHORS

Serhan Guner, Ph.D., P.Eng., and Sundar Chiluwal, The University of Toledo

DEEP FOUNDATIONS * MAR/APR 2020 * 103
DFI Magazine March/April 2020

Table of Contents for the Digital Edition of DFI Magazine March/April 2020
