Repair or Replacement of Damaged Anchor Bolts
Anchor bolts are vital components that provide
stability for structures when properly connected to their foundations. Anchor bolts for light poles and signal
structures are frequently damaged due to vehicular collision or due to forces
induced by storms when wind speeds are in excess of 90 mph. They may also sustain corrosion damage above
the foundation concrete, although the steel within the concrete may be still
intact or only sustain minor section loss.
Rather than completely abandon the damaged anchor bolt and install
replacements that may require relocation to a new foundation, repair of the damaged
anchor bolts may prove more cost effective and decrease the time the structure
is placed back in service or refurbished.
However, no actual study of equivalency of the various anchor bolt
repair methods has actually been conducted.
This includes their equivalent load-carrying capacity, their fatigue
properties if subject to varying load cycles, or their ease of repair.
The objective of this research is to
compare various anchor bolt repair methods and their structural integrity. This comparison must include actual
differences in repaired F1554 steel anchor bolts in terms of their yield and
tensile strength, strain capacity, and their fatigue strengths in tension and
rotating bending. Impact toughness
properties at different temperatures for the various anchor bolt repair methods
would also be determined. This research
would provide transportation engineers which are the most effective repair
methods for damaged or corroded bolts used to anchor light poles, bridge
bearings or various roadside hardware.
* SCOBS global
focus : *Enhance
maintenance or repair efforts; minimization of traffic disruption.
SCOBS prioritized objectives:
Determine the properties of anchor bolt repair
Provide for rapid repair of existing damaged
anchor bolts in comparison to a new foundation and relocation of anchor bolts
that would require greater costs and delay, minimizing safety hazards and
Internet searches indicate
that only a limited number of methods are used to repair damaged anchor
bolts. These include (a) welding
methods, (b) the use of various types of mechanical couplings, and (c) heating. Welding methods are recommended by AISC. The first method describes the use of a full
penetration weld whereby the damaged section is cut off flush and the
replacement bolt end is cut to a near point and then welded with shielded metal
arc electrodes. A second welding method
attaches two side plates to the damaged bolt and the new bolt is then
fillet-welded on each side. AISC does
not recommend welding F1554 Grade 105 quenched & tempered anchor bolts;
however, Grade 36 and Grade 55 bolts are weldable. Mechanical couplings are used when threads
are available or threads are cut onto the damaged anchor bolt with dies. US
Patent 5,163,775 describes a special coupling which employs both threads and
wedges for the unthreaded shanks of anchor bolts. Couplings which have “sight holes” are
purported to be most beneficial because they disclose sufficient thread
engagement. Other couplings, such as
those used for joining of rebars, can be used.
If the couplings are not threaded (called “sleeves”) but each end is
fillet-welded, there must be sufficient weld throat sectional area to carry the
intended anchor bolt loadings. Heating
to re-bend the anchor bolt is the least desirable because of metallurgical
changes, especially for quenched & tempered anchor bolts made of either SAE
4140 or 4340, the most commonly used alloys.
If excessive heat and temperatures are applied, the yield strength can
be altered and excessive grain growth can decrease impact and fracture
|Sponsoring Committee:||AKC70, Fabrication and Inspection of Metal Structures
|Research Period:||24 - 36 months|
|RNS Developer:||Christopher Hahin, MetE, CorrE, PE, Illinois DOT, Bureau of Materials|
|Index Terms:||Anchor bolts, Repairing, Bearing capacity, Fatigue (Mechanics), |
Maintenance and Preservation
Bridges and other structures