Differences Between Structural Steel Bolts And Ordinary Bolts

The core differences between structural steel bolts and ordinary bolts lie in four key dimensions: force transmission mode, material strength, construction process, and application scenarios. The design logic of the two is entirely centered around different load-bearing requirements.

Structural steel bolts are mainly used in structural steel engineering (such as workshops, bridges, and towers), with the core function of ensuring the overall stability and safety of the structure, and they need to withstand long-term dynamic or static loads. Ordinary bolts, on the other hand, have a wide range of uses and are suitable for general connection scenarios such as furniture, equipment casings, and simple brackets, only needing to meet basic fastening needs. In terms of force transmission mode, structural steel bolts transmit loads through friction force generated by preload, relying on the friction between the bolt and the connected components to resist external forces. Ordinary bolts, however, transmit force through the shear force of the bolt shank and the extrusion force between the bolt and the hole wall-essentially "resisting" external forces directly, with a load-bearing efficiency far lower than that of structural steel bolts.

Specifically, the differences between structural steel bolts and ordinary bolts can be detailed into the following five points:

1. Material and Strength

Structural steel bolts (specifically high-strength structural steel bolts) must be made of high-strength alloy structural steel, with common materials including 20MnTiB, 40Cr, and 35VB. Their strength grades are mostly Grade 8.8 and above (mainstream grades are Grade 10.9 and Grade 12.9), which can withstand large loads without easily producing plastic deformation. Ordinary bolts are usually made of carbon structural steel such as Q235 and Q355, with relatively low strength grades (mostly Grade 4.8 and Grade 5.6), only meeting basic fastening needs for low loads. They are prone to bending or breaking when bearing excessive loads.

2. Shape and Dimensions

The shape design of structural steel bolts focuses on "enhancing the stability of force transmission", with mainstream types being high-strength hexagon head bolts and high-strength torsional shear bolts: Hexagon head bolts have larger across-flat dimensions and thicker heads, which can be adapted to installation tools with higher torque to ensure the preload meets requirements; torsional shear bolts are equipped with a "torsional shear tail", and the preload is controlled by shearing off the tail during installation, avoiding human operation errors. Ordinary bolts have relatively small heads (such as hexagon heads, cross recessed heads) and thread dimensions, with generalized designs. They only need to be adapted to conventional wrenches for installation, without considering high-strength preload requirements.

3. Construction Process

The installation of structural steel bolts has strict procedural requirements: it is necessary to first perform "initial tightening" (pre-tightening to 50%-70% of the design torque), then "final tightening" (tightening to the design torque), and in some scenarios, "retightening" inspection is also required. Professional tools such as torque wrenches and torsional shear wrenches must be used to control the preload. After final tightening, it is necessary to check whether the torque value is up to standard or whether the torsional shear tail is completely sheared off. The installation of ordinary bolts is relatively simple: there is no need to control precise torque, and they can be tightened with ordinary wrenches (such as adjustable wrenches and socket wrenches) without professional construction skills.

4. Application Scenarios

Structural steel bolts are widely used in scenarios with high requirements for connection strength and safety, such as building steel structures (e.g., connection of steel columns and steel beams in workshops), bridge steel structures (e.g., splicing of steel box girders), and large towers (e.g., communication towers and power transmission towers). They need to withstand long-term external influences such as wind, rain, vibration, and temperature changes. Ordinary bolts are suitable for scenarios with no high load-bearing requirements, such as furniture assembly, equipment casing fixing, and simple shelf construction. If used in high-load scenarios, they are prone to connection failure due to insufficient strength.

5. Reusability

Structural steel bolts are usually not reusable: during installation, they need to be tightened to a preload close to the material's yield strength, which may cause microscopic plastic deformation. Reuse will lead to failure to meet the required preload, affecting connection safety. Ordinary bolts have low preload and do not reach the material's plastic deformation threshold, so they have good detachability and can be reinstalled and reused as needed (it is necessary to check whether the threads are intact and whether the shank is bent).