"It's not a question of if there would be
an earthquake or not; it's a question of when.”
-Joel Conte, Ph.D., Professor at UC San Diego
Source:
http://cerato.ou.edu/category/blog/
The largest earthquake simulator in the United
States officially made its debut on February 23, 2016 in Englekirk Center for Structural Engineering,
University of California, San Diego.
Researchers from the University of Oklahoma and University of California, San
Diego used this outdoor shake table to test a magnitude 8.9 earthquake. The
experiment was to determine the behaviour and resistance of helical piles to
major earthquakes and their effects on superstructures.
Helical Piles! Source:
http://cerato.ou.edu/category/blog/
To test the seismic effect of helical piles,
researchers modeled the soil by having
a 50 foot tall metal box with sand on the
shake table. The vertical elements of the superstructure were modeled using two heavy cubes attached on top of the
metal sand box. The helical piles foundation was modeled using
7 to 12 foot long thick metal pilings. Sensors were used to
measure and analyze the behaviour and results.
The researchers wanted to experiment these
helical piles, since these worked really well with structures in New Zealand
and Japan that withstand large earthquakes. However, only qualitative
studies were observed for the seismic
structural behaviour of the structures in New Zealand and Japan. Experimental
data and quantities studies are needed to
prove the effectiveness of the helical pile seismic resistance, such that
engineers can design with them and build safer and sustainable structural
systems.
Source: https://www.macleandixie.com/
Helical Piles
Helical piles, also called screwpiles, are like large steel screws. They are made out of
slender steel shafts that anchor the superstructure into its foundation.
These deep foundation piles can be
various sizes of tubular hollow sections.
The helices consist of flat and round steel
plates welded at different pitches along the long shaft. These do most of the
resistance of axial loads, providing both tensile and compressive bearing
resistance. Normally, the helices should be spaced 3 diameters
apart along the shaft to account for uniform stress distribution between
helices. The standardized spacing can make the helices act as individual
bearing elements, so there is no need for the helices to depend on helices that
are above or below to support the loads.
Here’s how you install helical piles.
1. Attach a torque motor, drilling
equipment, hydraulic equipment or other rotary equipment to an excavator
2. Install the helical piles to the rotary
equipment
3. Mechanically rotate and penetrate
helical piles using hydraulic pressure into the ground
4. Torque capacities can range from 5kNm to
500kNm.
5. Screw the piles into the ground until
the bearing capacity is achieved.
6. Provide resistance by soil bearing on
plates and along shaft
Source: http://acsrva.com/
The Uses and Advantages of Helical Piles
Helical piles can be
used to retrofit existing structures since the piles have high
anchoring capacity, damping ratio, slenderness, ductility and good resistance
to uplift forces. They provide good support for both tensile and compressive
vertical structures.
The ease of installation and removal of helical
piles also makes it a good choice for construction. They can be used in urban
areas, since they only take up a small area and produce low noise and
vibration. Screwing helical piles does not
produce a lot of soil displacement; therefore its
application saves costs and is environmentally sustainable. Moreover,
installation of helical piles reduces time, since no concrete is required for
this process, which means there is no need to wait for curing.
Helical Piles can Prevent This
from Happening! Source: http://prophecy.landmarkbiblebaptist.net/
The Future
The tests for the seismic effect of helical
piles are now completed. Now, analysis will have to be
done. Researchers from the University of Oklahoma and University of
California, San Diego are looking to analyze the following topics:
1. Behaviour of different helical piles
with varying characteristics and installation methods
2. Quantifying the strength of helical
piles by measuring their moments, shear, axial loads
3. Behaviour of helical piles due to
different end support conditions
4. Differences between helical piles and
other types of piles
5. Relationship between slenderness and
pile behaviour
Their Contributions
The earthquake simulator can help us
understand the seismic effect of different earthquakes on different structures.
Understanding more of the uses and behaviour of helical piles will make their
use more common. Both the earthquake simulator and the helical piles can
ultimately have big impacts on building regulations. Both can lead
designers to design safer buildings in initial stages of planning for the
safety of the public.