| The
earliest patent anchor was a screw foundation
designed in 1833 by a blind English brick
maker, Alexander Mitchell. Mitchell's screw
foundations were used in the construction
of lighthouses and beacons throughout the
world. There were few improvements in patent
anchoring until February 1876 when the Picket
Stake was assigned patent number 172915. While
these were the earliest of the patent screw
anchors, it was not until the late 1950s when
the A. B. Chance Company introduced the Power-Installed
Screw Anchor (PISA®) that screw anchoring
found favorable, wide-spread acceptance.
These PISA®
anchors, as they are popularly called, were
originally restricted to plastic soils.
With improvements in anchors, wrenches and
power equipment, successful installations
in packed sand and gravel can be in minutes
as compared to hours for other anchors and
methods. The addition of multiple-helix
designs results in holding capacities of
60,000 pounds in swamp country – a
load unheard of even in firm soils years
ago.
The Chance
Helical Pier® System offers a technically
superior and extremely cost effective alternative
to other remedial pier systems. It is backed
by almost ninety (90) years of structural
engineering experience.
This concept
focuses upon screwing steel piers with single
and multiple helixes into stable subsoil
until the torque applied indicates that
the necessary load capacity has been achieved.
Once the
necessary load capacity has been accomplished,
adjustable brackets are attached to the
base of foundation walls where the problem
exists. They are then hydraulically jacked
and locked into position with the weight
of the wall now shifted to the installed
piers.
The Chance
Helical Pier System®, barely disturbs
the landscape. The average residential structure
problems usually are completed in less than
two working days. The Chance Helical Pier®
System is listed with major building codes
including I.C.B.O and SBCCI.
Grout-Tech
uses only A. B. Chance helical anchoring
systems for your underpinning and foundation
support need
|
| Ground
Anchors are used to address
a number of situations with retaining walls,
dry docks, coffer dams, water tanks, concrete
gravity dams, tall buildings, Suspension bridges,
towers, ski lifts, cliff or vertical cut stabilization,
mine, pits, shafts, tunnels, underground caverns,
pipeline and oil platforms. Some of these
situations include direct tension, sliding,
overturning, dynamic-loading, and ground pre-stressing.
Anchors are used to resist uplift or overturning.
Permanent ground
anchors are pre-stressed cement-grouted
tendons used in soils or rock to restrain
and control the displacements of structural
elements such as walls or slabs. A ground
anchor is essentially a vertical or lateral
load-carrying element, developing a resisting
force by stressing the soil around the anchorage
length.
The screw anchor is
a deep foundation member consisting of a
steel shaft with helical plates welded to
the shaft. They can be used to resist compression
loads and are used as piles too. The use
of anchors is widespread for both temporary
and permanent work.
Typical anchor applications
are to hold down slabs subjected to hydrostatic
uplift, to increase the stability of a dam,
or connected with guy wire to resist overturning
of towers. Anchors are used because they
are an economical way to provide resistance
to vertical loads and are frequently far
less expensive to install than the corresponding
weight of concrete or to replace or rebuild
the structure.
Screw anchors are installed
into the soil using mechanical rotational
force, and extensions are added to advance
the assembly to achieve the desired tension
or compressive force desired . Once installed,
the anchor has bearing capacity in both
tension and compression. For over 70 years,
screw anchors have been used by the utility
industry for power pole guying, transmission
tower foundation underpinning and pipeline
supports. Today, the general construction
industry is discovering and using screw
anchors for a much wider variety of applications
including screw pile foundations |
