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Introduction of ASTM A490 Bolts and A325 Structural Bolts

Structural bolts are a kind of high-strength bolt with good fastening performance, which belongs to the standard fastener. Structural bolts are mainly used in large-scale engineering and machinery of steel structures, such as steel bridges and steel structure steel plate connection points on cranes. Structural bolts are also often used for the connection of railway heavy rail. The common high strength structural bolts are A325 structural bolts and ASTM A490 bolts.

Rivet connected bridge

Before structural bolts were widely used, structural parts such as bridge main beams and crane rails were mostly connected by rivets. In the field construction operations of some large-scale steel structure projects, the rivet connection is often time-consuming and has a high risk. Workers need to heat the head of the rivet and insert it into the hole, and flatten the head at the ends of the rivet. During construction, multiple workers are required to operate at the same time. Later, high strength structural bolts were gradually used in steel structure connection. Due to its simple installation and consistent strength of structural bolts, it quickly replaced rivets as the preferred method for connecting structural parts on site. Next, we will introduce the two commonly used structural bolts ASTM A490 structural bolts and A325 bolts in detail.

A325 Structural Bolts

A325 structural bolts

A325 structural bolts are heavy hex structural bolts, heat-treated structural steel bolts with a minimum tensile strength of 120 / 105ksi. According to relevant standards, bolt performance grades are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, grade 8.8 and above bolts are made of low carbon alloy steel or medium carbon steel and heat treated (quenched and tempered), which are generally called high-strength bolts, and the rest are generally called ordinary bolts. A325 structural bolts are high-strength bolts.

ASTM A490 Bolts


ASTM A490 is the standard for minimum tensile strength 150ksi alloy steel heat-treated structural bolts. ASTM A490 bolts refers to alloy steel bolts, studs and screws with a minimum tensile strength of 150ksi. ASTM A490 bolts consists of one bolt, one nut and one washer.

Installation Method of High Strength Structural Bolts for Steel Structure Engineering

The installation of structural-bolts
  1. After a construction section is completed and the steel structure forms a stable frame unit, structural bolts shall be installed. Let's take the ASTM A490 bolts as an example.
  2. Pay attention to the direction when installing the A490 bolts: the washer of the A490 bolt is installed on the side of the nut, and the chamfered side of the washer hole should contact the nut.
  3. The direction of A490 bolts penetration shall be subject to the convenience of construction, and each node shall be neat and consistent. After tightening the high-strength A490 structural bolt with a wrench, remove the temporary bolt and replace it with a high-strength bolt.
  4. The tightening of ASTM A490 bolts must be carried out twice. The first is the initial tightening: the initial tightening is to 60% - 80% of the standard axial force (i.e. design pretension) of the bolt. The second tightening is the final tightening, when the final tightening, the plum head of the ASTM A490 bolt shall be screwed off.
  5. The A490 bolts that are initially tightened should be marked for confirmation. In order to prevent missing tightening, the A490 structural bolts installed on the same day shall be finally tightened on the same day.
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