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 who’s 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 | Hole Type in Outer Ply | Required Washer |
|---|---|---|
| A325 or F1852 (½" - 1½") | Oversized or Short-Slotted | ASTM F4361 |
| Long-Slotted | 5/16" thick plate washer or continuous bar2, 3 | |
| A490 (≤ 1") | Oversized or Short-Slotted | ASTM F4361 |
| Long-Slotted | 5/16" thick plate washer or continuous bar2, 3 | |
| A490 (> 1") | Oversized or Short-Slotted | 5/16" thick ASTM F4362, 4 |
| Long-Slotted | ASTM F436 with a 3/8" thick structural grade plate washer or continuous bar2 | |
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What is the difference between hardened washer, flat washer & standard washer?
@Darrel- A hardened washer is heat treated for use with high strength bolt grades. A standard or flat washer is used for general purpose, lower strength bolting.
HOW MANY WASHERS ARE PROVIDED FOR A325 and A490 BOLTS?
@Senthilkumar- It depends on the application. Sometimes there are no washers used, sometimes washers are required. You’ll need to consult the AISC/RCSC to see when washers are required.
can you tell me the disadvantages of using washer?
@Narendra- We see two immediate disadvantages. First is cost. Washers may only be a few cents per unit, but over several thousand connections that can add up. Second is thread length. A325 and A490 bolts have short thread lengths to help control threads in the shear plane, so depending on how your joint was designed, it is possible that you may not have enough thread stick out to accommodate a washer.
Please let me know
1.What’s the standard thickness of F436 washer for the A325 bolt for which 3/4″ and 1″ Dia.
2.What’s the difference between A325 and F1852 structural bolts vice Versa in A490 and F2256
@Veeramani- The thickness for a 3/4″ F436 washer is 0.122″ to 0.177″.For a 1″ washer, the thickness is 0.136″ to 0.177″. As for your second question, the difference is bolt style. A325 and F1852 are mechanically and chemically identical, but A325 covers heavy hex head bolts, whereas F1852 covers tension control/twist-off bolts. The difference is the same for A490 (heavy hex head) and F2280 (twist-off/TC).
hi I wanted to know about slotted bolted connection. Please let me know about in slotted connection the bolt nut with washer will come on the face of slotted side or on the either side. Please do your valuable advise.
@Sonu- The thick washer need to go up against the slotted hole. If there are slotted holes on both faces, then two washers would be used, one under the head, one under the nut.