Washers for Structural Bolts - Portland Bolt
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Washers for Structural Bolts
QAre washers required to be used with an A325 or A490 structural bolt?
A
It is known that the required grade of washer to be used with an A325 or A490 structural bolt is an ASTM F436 hardened
washer, however whether or not a washer is required to be used in a given application is often brought into question. The
purpose of using a flat washer with a bolt is to provide a smooth bearing surface under the head of the bolt and / or nut.
There are different grades and styles of washers, which may differ in their thickness and outside diameter, providing a
larger or smaller bearing surface. Per the ASTM A325 and A490 specification, they are specific to the grade of washer that
is recommended, however it is not stated that a washer is required.
Although the ASTM A325 and A490 specifications do not require the use of a washer, there are a few circumstances where
we know for sure that F436 hardened washers are required. When using A490 structural bolts, the strength of the material
being connected can determine whether or not a washer should be used. Specifically, if the material being connected has
specified minimum yield strength of less than 40 ksi, a washer should be used. According to the AISC 13th Edition, page
16.2-40:
When ASTM A490 bolts are pretensioned in connected material of specified minimum yield strength less than 40 ksi,
ASTM F436 washers shall be used under both the bolt head and the nut
It is worth noting that an A490 strength, round head tension control bolt whos head meets the bearing surface diameter requirements of ASTM F1852, does not require a flat washer under the head. The only other circumstance where a washer is
required is if the hole in which the bolt is being inserted is oversize or slotted. The washer requirements for this situation are
found in Table 6.1 in the AISC 13th Edition, page 16.2-41, which is summarized below.
ASTM Grade and Diameter
A325 or F1852 (" 1")
Hole Type in Outer Ply
Required Washer
Oversized or Short-Slotted
ASTM F4361
Long-Slotted
5/16" thick plate washer or continuous bar2, 3
Oversized or Short-SlotA490 ( 1")
ted
Long-Slotted
ASTM F4361
5/16" thick plate washer or continuous bar2, 3
1. This requirement does not apply to round head tension-control bolts that meet the dimensional tolerances of
F1852
2. Multiple stacked washers that add up to a thickness of 5/16" do not meet the requirement
3. The washer must be structural-grade steel, but does not need to be hardened
4. A 3/8" thick plate washer and a regular F436 washer can be used instead. The plate washer doesn't need to be
hardened
6/27/2015 10:49 AM
Washers for Structural Bolts - Portland Bolt
2 of 3
ASTM Grade and Diameter
http://www.portlandbolt.com/technical/faqs/washers-required-with-a325-...
Hole Type in Outer Ply
Oversized or Short-Slotted
Required Washer
5/16" thick ASTM F4362, 4
A490 (> 1")
Long-Slotted
ASTM F436 with a 3/8" thick structural grade plate washer or continuous bar2
1. This requirement does not apply to round head tension-control bolts that meet the dimensional tolerances of
F1852
2. Multiple stacked washers that add up to a thickness of 5/16" do not meet the requirement
3. The washer must be structural-grade steel, but does not need to be hardened
4. A 3/8" thick plate washer and a regular F436 washer can be used instead. The plate washer doesn't need to be
hardened
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Written April 19, 2011 by
Anthony Porreco
Phone: 800.599.6926
Email: anthony@portlandbolt.com
4 comments
Matthew Manning
January 19, 2015 at 7:47 am
Hi, Could you tell me what the Minimum Yield Strength for 2-1/4 F436 Washers is for use with B7 studs.
Many thanks
Dane McKinnon
January 19, 2015 at 12:30 pm
@Matthew F436 washers are not tested for tensile or yield (because the material thickness is too thin for machine
out test specimens), and are qualified on the basis of hardness only. Hardness range for plain finish washers is
38-45 HRC, and hot dip galvanized 26-45 HRC.
Ali
June 3, 2015 at 2:43 pm
if plain finish washers have 26 46 HRC ? any rejection will be , the use with A490 bolts
Dane McKinnon
6/27/2015 10:49 AM
Washers for Structural Bolts - Portland Bolt
3 of 3
http://www.portlandbolt.com/technical/faqs/washers-required-with-a325-...
June 4, 2015 at 1:46 pm
@Ali- Plain finish washers for use with A490 bolts have a HRC range of 38-45. Only hot dip galvanized washers
have the lower 26-45 HRC range, but they should not be used with A490s because of the hot dip zinc coating.
6/27/2015 10:49 AM
