Cabling and Bracing - Purdue Agriculture

Cabling and Bracing
Harvey Holt
Purdue University
Cabling and Bracing
• Use cabling and bracing only if supports
reduce risk of failure to reasonable levels
• Periodically inspect trees and structural
supports
Cabling – Use of cables to support weak
crotches or dangerous limbs
Bracing – use of steel rods to
provide rigid support
Cabling
•
Stabilize weak or split crotch
•
Support heavy horizontal branch
Cabling Materials
• Cables
– Common
– EHS
• Anchors
– Eyebolts
– J lags
– Amon eye
• Thimbles
• Tree–Grip Dead–Ends
Eye Splice
• Common grade only
Tree–Grip Dead–Ends
• Must be used with EHS
• Use thimbles
• Match dead-end size to cable
CABLING
SYSTEMS
• Simple – Direct
• Triangular
Horizontal branch - anchor as high on
trunk as possible; angle from supported
branch is not < 45 degrees
Install
cable
2/3
distance
from
trunk
to branch
end
• Install only one cable to each anchor
• Separate anchors by stem diameter
• Don’t install anchors vertically in line
d
≥d
© 2001 International Society of Arboriculture
Install anchors
through leaders in line
with the cable path
Trees should be pruned before
hardware is installed
Cables should be taut but should not
pull limbs together
Don’t cable trees that have energized
lines passing through them
Cables must not rub against tree or
objects in tree
• Fasten eyebolts with
round washers & nuts
• Seat washers against
bark
DON’T COUNTERSINK
• Cut eyebolt shaft flush
with nut; peen end
When installing bolts in decayed
wood, use double washer
and nut configuration.
Cable Inspections
• Visual from ground – Annually
• Climbing inspection – At least once
every 5 years
BRACING
• Stabilize weak crotches
• Repair split crotches
• Hold rubbing limbs together or
apart
Bracing
• Machine Threaded Rods
– Fastened with washers and nuts
– Holes larger than rod diameter
• Wood Screw Rod
– Threaded into holes smaller than
rod diameter
BRACING LEADERS
<18” DIAMETER
• Install single rods
through crotch
• Additional rod may
be placed above
the crotch
• Offset multiple
rods
BRACING LEADERS
>18” in DIAMETER
• Install parallel
rods through
crotch
• Separate rods by
6” to 18”
• An additional rod
may be placed
above the crotch
For split crotches,
place additional
single or parallel
rods at 12–18”
spacing along
length of split
Lightning
Protection
LIGHTNING
• Potential
• Current
• Speed
10 to 100 million volts
25,000 amps
450,000 feet/second
PRIORITY LOCATIONS FOR
LIGHTNING PROTECTION
•
•
•
1. Trees where people may gather
during thunderstorms
2. Trees within 25 ft of buildings
3. High value and historic trees
LIGHTNING SUSCEPTIBILITY OF
SELECTED TREE SPECIES
High Frequency Of Strikes
Low Frequency Of Strikes
ASH
BEECH
CATALPA
BIRCH
ELM
HORSECHESTNUT
HEMLOCK
MAPLE
OAK
PINE
POPLAR
SPRUCE
SYCAMORE
TULIP POPLAR
Install air terminal in 2-3”
diameter wood
One Standard Conductor If <36” DBH
Two Standard Conductors If >36” DBH
Mini-conductors on each major leader
Fasteners
Fence Pliers – an all purpose tool
No sharp
bends in
the
conductor
In root
flare valley
Ground Rod
•
•
•
•
•
10’ copperweld rod
Multiple shorter rods if needed
At least 12’ from trunk
Prefer outside of dripline
If multiple trees in a row, one
ground every 80’ minimum
Finishing Grounding
System
• Mulch to prevent lawnmower injury
• Map system
INSTALLATION SAFETY
• Do not work if storm threatens
• Observe 10’ rule around powerlines
• Check for underground utilities
MAINTENANCE
• Overgrown conductors are acceptable
• Need to be electronically checked
using continuity test