Twist-shear type high-strength bolts are key fasteners commonly used in structural connections. This paper provides a detailed introduction and systematic analysis of their structure, core performance, and engineering applications: first elaborating on their basic structure and working principle, then delving into their high-strength characteristics, seismic performance, and typical applications in the engineering field, and finally proposing future development directions of such bolts to provide reference for relevant research and practice.
Keywords: Twist-shear type high-strength bolts; structural connections; mechanical properties; engineering applications; development directions
1. Introduction
As the most basic fasteners in the mechanical and construction fields, bolts are widely used in connection nodes of various structures. Twist-shear type high-strength bolts are efficient connecting components developed based on traditional bolts. With core advantages of "controllable installation torque, high connection reliability, high strength, and excellent seismic performance", they have become the mainstream connection method in fields such as steel structures and heavy machinery, and have received significant attention in engineering practice and academic research in recent years. This paper systematically sorts out the structural characteristics, core performance, and application scenarios of twist-shear type high-strength bolts, clarifies their technical advantages, and analyzes future research directions in combination with industry development needs, providing theoretical support for their wider engineering applications.
2. Structure and Working Principle of Twist-Shear Type High-Strength Bolts
The core components of twist-shear type high-strength bolts include the bolt body, nut, and washer. The essential difference between their structure and traditional high-strength bolts lies in the special twist-shear notch at the end of the bolt body-rather than "multiple twist-shear parts". This notch is a weak link connecting the bolt head and the shank, and its cross-sectional strength is precisely designed to match the pre-tightening torque of the bolt.
Its working principle is divided into two stages: "installation and tightening" and "load-bearing". During installation, a special torque wrench is used to clamp the bolt head and the hexagon socket head at the end, and pre-tightening force is generated by applying torque to the bolt. When the torque reaches the design threshold, the end twist-shear notch will be sheared off along the predetermined cross-section. At this time, the bolt pre-tightening force just meets the specification requirements, realizing precise tightening of "controlling torque through shear" and avoiding the problems of insufficient pre-tightening force or overload caused by inaccurate torque control of traditional bolts. In the load-bearing stage, the bolt makes the connected parts closely fit through the tensile pre-tightening force of the shank, transmits shear force by means of friction between the connected parts, and the shank itself can assist in bearing part of the shear load, forming a "friction-shear" collaborative bearing mechanism, which greatly improves connection reliability.
3. Performance of Twist-Shear Type High-Strength Bolts
3.1 High-Strength Performance
Twist-shear type high-strength bolts are usually made of high-quality alloy structural steel such as 42CrMoA. After quenching and tempering heat treatment (quenching + high-temperature tempering), their strength grade generally reaches Grade 10.9 or above, and products used in some special scenarios can reach Grade 12.9. Their tensile strength is not less than 1000MPa, and their shear strength is 1.5-2 times that of ordinary Grade 8.8 bolts, which can effectively meet the needs of high-load connection scenarios such as steel structure beam-column joints and bridge steel box girders. Compared with traditional high-strength bolts, their advantage lies not only in material strength but also in the bearing stability brought by "precise control of pre-tightening force"-avoiding the problem of partial bolt overload and partial bolt failure caused by discrete pre-tightening force.
3.2 Seismic Performance
The seismic advantage of twist-shear type high-strength bolts stems from the characteristics of "precise pre-tightening + flexible bearing": on the one hand, the precise pre-tightening force keeps the connected parts closely fitted. Even under the action of seismic cyclic loads, shear force can be effectively transmitted through the friction of the contact surface, reducing the shear deformation of the bolt itself; on the other hand, the quenching and tempering treatment of the bolt body gives it both high strength and good toughness. Under the impact load generated by earthquakes, it can absorb energy through slight elastic deformation to avoid brittle fracture. Relevant test data show that steel structure joints using twist-shear type high-strength bolts have no obvious damage under frequent earthquakes, and only slight plastic deformation of bolts occurs under rare earthquakes. The overall seismic performance of the joints is improved by more than 30% compared with traditional bolted connections, which can effectively reduce structural stress concentration and ensure the overall seismic safety of the structure.
4. Applications of Twist-Shear Type High-Strength Bolts
With their advantages of precise tightening, high strength, and seismic resistance, twist-shear type high-strength bolts have become the preferred fasteners in fields requiring high connection reliability. Typical application scenarios include:
Building steel structures: such as beam-column joints of high-rise building steel frames, crane beam connections of steel structure workshops, and node connections of large-span spatial structures, ensuring the stability of the structure under wind loads and seismic loads;
Bridge engineering: used for steel box girder splicing, connections between bridge piers and cap beams, and steel structure nodes of cable-stayed bridge towers, adapting to the complex forces of bridges under vehicle dynamic loads and temperature changes;
Heavy machinery: such as frame connections of mining machinery, tower flange connections of wind power equipment, and load-bearing structure connections of metallurgical equipment, bearing high loads and vibration loads;
Rail transit: including railway steel bridges and steel structure support connections of urban rail transit, meeting the strict requirements of the rail system for connection accuracy and durability.
It should be noted that such bolts are not suitable for long-term high-temperature (exceeding 300℃) or strong corrosion environments. If they need to be used in such scenarios, additional surface anti-corrosion treatments (such as Dacromet, zinc infiltration, etc.) and temperature-resistant alloy materials should be adopted.
5. Development Directions of Twist-Shear Type High-Strength Bolts
5.1 Material Upgrade Research
In the future, focus should be placed on developing two types of materials: one is "ultra-high strength and corrosion-resistant alloys". Combining microalloying technology and surface treatment processes, the strength is increased to Grade 14.9 on the basis of the existing Grade 12.9. At the same time, the corrosion resistance in marine atmosphere and industrial corrosion environments is enhanced by adding chromium, nickel elements or adopting chromium-free coating technology; the second is "lightweight materials", exploring the application of titanium alloys and high-strength stainless steel in twist-shear type bolts to meet the needs of lightweight and high-cleanliness scenarios such as aerospace and medical equipment.
5.2 Structural and Process Optimization
Structural optimization directions include: designing variable cross-section twist-shear notches to make the energy consumption of bolts more uniform during installation and shearing, further improving the control accuracy of pre-tightening force; developing an integrated design with "anti-loosening structure", integrating anti-loosening washers at the end of bolts to adapt to mechanical scenarios with frequent vibrations. Process optimization focuses on the combination of cold heading forming technology and heat treatment process. By precisely controlling the cold heading deformation to reduce internal material stress, combined with segmented quenching and tempering treatment, the uniformity of bolt performance is improved, and the scrap rate in the production process is reduced.
5.3 Improvement of Numerical Simulation and Test System
With the help of finite element analysis (FEA) technology, establish a full-life cycle numerical model of bolts from "installation and shearing" to "load-bearing", simulate the performance degradation law of bolts under different temperatures and corrosion environments, and provide theoretical basis for selection in special scenarios; at the same time, improve the test research system. In addition to conventional tensile and shear tests, add "fatigue life tests" and "corrosion-fatigue coupling tests", and establish a bolt life evaluation method based on reliability theory, breaking the current limitation of relying on empirical data and providing more scientific technical support for engineering applications.
6. Conclusion
Twist-shear type high-strength bolts are efficient structural connection fasteners integrating "precise tightening, high strength, and high seismic resistance". Their core advantage is to achieve precise control of pre-tightening force through a special twist-shear structure, solving the key pain points of traditional bolted connections. At present, they have been widely used in fields such as construction, bridges, and heavy machinery, becoming core components to ensure high-load and high-reliability connections.
In the future, the main development directions of twist-shear type high-strength bolts will be to achieve "higher strength + better corrosion resistance" through material upgrading, improve installation efficiency and bearing stability through structural and process optimization, and improve the performance evaluation system through numerical simulation and test research. With the breakthrough of these technologies, their application scenarios will be further expanded to more harsh fields such as marine engineering and aerospace, providing more reliable connection guarantees for high-end equipment manufacturing and major engineering construction.
